β-Elimination competitions leading to CC bonds from alkylpalladium intermediates

Tetrahedron 68 (2012) 10065e10113

Contents lists available at SciVerse ScienceDirect

Tetrahedron journal homepage: www.elsevier.com/locate/tet

Tetrahedron report number 994

b-Elimination competitions leading to C]C bonds from alkylpalladium intermediates Jean Le Bras, Jacques Muzart * Institut de Chimie Mol eculaire de Reims, UMR 7312 CNRSdUniversit e de Reims Champagne-Ardenne, B.P. 1039, 51687 Reims Cedex 2, France

a r t i c l e i n f o Article history: Received 7 September 2012 Available online 20 September 2012 Keywords: Palladium Elimination Heterocyclisation Heck reaction Wacker reaction Aza-Wacker reaction Selectivity

Contents 1. 2.

3.

4.

5. 6. 7.

8. 9. 10.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10066 Competitions between hydrogen(s) and ester or carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10067 2.1. After addition to vinyl acetate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10067 2.2. After addition to an allylic ester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10068 b-OCOR or b-OCO2R elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10068 2.2.1. b-H elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10071 2.2.2. Competitions between hydrogen(s) and hydroxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10076 b-OH elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10076 3.1. b-H elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10078 3.2. Competitions between hydrogen(s) and alkoxy(s), aryloxy, silyloxy or arylsulfonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10084 4.1. After addition to a vinylic ether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10084 4.2. After addition to an allylic ether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10084 4.3. After addition to acrolein diethyl acetal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10088 4.4. After intramolecular addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10088 Competitions between hydrogen(s) and halide or arylsulfonyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10090 Competitions between hydrogen(s) and amino derivative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10090 Competitions between hydrogen(s) and silane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10092 7.1. After addition to a vinylic silane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10092 7.2. After addition to an alkene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10094 Competitions between hydrogen(s), alkoxy and ester or hydroxy or arylsulfonyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10094 Competitions between hydrogen(s), aryloxy and acetoxy or trichloroacetimidate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10094 Competitions between hydrogen(s), amino derivative or trichloroacetimidate and hydroxy or acetate or carbonate or alkoxy or carbamate or halide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10096

Abbreviations: Atm, atmosphere; Boc, t-butoxycarbonyl; cat, catalytic; COD, 1,5-cyclooctadiene; Cy, cyclohexyl; dba, dibenzylidene acetone; DMA, N,N-dimethylacetamide; dpp, 4,7-diphenyl-1,10-phenanthroline; dppb, 1,4-bis(diphenylphosphino)butane; dppe, 1,2-bis(diphenylphosphino)ethane; dppp, 1,3-bis(diphenylphosphino)propane; ee, enantiomeric excess; equiv, equivalent; Ii-Pr, 1,3-bis(2,4,6-tri-isopropyl-phenyl)imidazol-2-ylidene; L, ligand; MS, molecular sieves; Piv, 2,2-dimethyl-propanoyl; rt, room temperature; TBS, t-butyldimethylsilyl; TPS, triphenylsilyl; TEMPO, 2,2,6,6-tetramethyl-1-piperidinyloxy; THP, tetrahydropyranyl; tmeda, tetramethylethylenediamine. * Corresponding author. Tel.: þ33 3 2691 3237; fax: þ33 3 2691 3166; e-mail address: [email protected] (J. Muzart). 0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2012.09.076

10066

11. 12. 13.

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10.1. After addition to vinyl acetate or a vinyl ether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10096 10.2. After addition to an allylic alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10100 10.3. After addition to an allylic alcohol derivative or an allylic halide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10101 Competitions between hydrogen(s), acetoxy and alkyl groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10102 Competitions between hydrogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10103 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10109 References and notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10109 Biographical sketch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10113

1. Introduction

the pre-eliminated species. From their study of stoichiometric reactions,6,7 Lu and co-workers conclude that trans-elimination in acetic acid occurs with the rates in the following order: b-halide>b-OAc>b-OR>b-OHzb-H.7 The main aim of the present report is to examine, from literature examples, the selectivity of the different cleavage possibilities. The competitions are mainly between a CeH and a Cheteroatom bond or another CeH bond; examples of plausible competitions between two different heterosubstituents or between a C-heteroatom bond and a CeC bond have also been reported. The control of the elimination step is important to provide efficient and diversified selective procedures. This review, which is not comprehensive, is organized around the main b-elimination. Some procedures are, however, far from being selective, this leading to a somewhat arbitrary classification. Moreover, we will

The Pd-catalyzed C]C bond synthesis often proceeds via the reaction of a CePdII type intermediate, which involves the cleavage of the CePd bond and a CeH, C-heteroatom or CeC bond in the bposition. This reaction step is commonly named b-elimination,1 even in book courses.2 This is, in fact, an abuse of language, because this reaction is either the elimination of both elements or the transfer of the b-unit to palladium leading to a p-complex which, subsequently, release the product (Scheme 1). In the case of the CeH cleavage, a more appropriate name would be palladium-hydride elimination or dehydropalladation, as occasionally used in a review3 and a book,4 respectively, or dehydridopalladation since a hydride is usually eliminated. In this review, we will nevertheless use simplified names such as b-H elimination for the above case.

XPdZ

XPd Z

β-Z elimination

Z'

Z'

+ XPdZ

Z' Z and Z' = H, OH, OCOR, OCO2R, OSiR3, OSO2Ar, Cl, Br, NR2, SiR3, SO2Ar or CR3 Scheme 1.

Lin and co-workers have theoretically studied the concurrent

b-H and b-heteroatom eliminations from cationic complexes

[L2PdCH2CH2Z]þ where Z¼halide, OH, OMe, OAc, and L2¼H2PCH2CH2PH2.5 Their calculations indicated that the b-heteroatom elimination is thermodynamically and kinetically favoured when Z¼Cl, Br or I, whereas the b-H elimination is kinetically more favourable than the b-heteroatom elimination when Z¼F, OH, OMe or OAc. The authors pointed out that the olefinepalladium-hydride complex, which is formed as an intermediate, is, however, thermodynamically unstable relative to

not consider the hydride eliminations, which arise from h3-allylpalladium intermediates,8 and those leading to a,b-unsaturated carbonyl compounds via the dehydrogenation of carbonyl compounds9 or cascade reactions.10,11 As shown in Scheme 2, the elimination can, in some cases, arise from two positions. In order to easily differentiate between these two possibilities, the carbon having suffered the nucleophilic substitution will be named b, and the other b0 . As for the palladium species, it will be named CaePd intermediate or CaePd complex. When Z and Z0 ¼H, the H elimination selectivity will correspond to the value denoted by the b/b0 -H ratio.

XPdZ β-Z elimination Z'

Z NuPdX

Z'

PdX β' α β

Z'

β'

Nu

Z Nu

Cα-Pd intermediate Z = H, OCOR, OCO2R, OSiR3, OSO2Ar, Cl, Br, NR2, SiR3, SO2Ar or CR3 Z' = H, OH, OCOR, OCO2R, OSiR3, OSO2Ar, Cl, Br, NR2, SiR3, SO2Ar or CR3 Scheme 2.

β'-Z' elimination XPdZ' Z β

Nu

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

2. Competitions between hydrogen(s) and ester or carbonate

A more selective procedure towards stilbene was reported by Kasahara and co-workers using phenyl iodide, triethylamine and catalytic amounts of both Pd(OAc)2 and PPh3 in MeCN (Eq. 2).14 Since the reaction requires Pd0 for the insertion into the PheI bond, while the b-OAc elimination generates a PdII complex (Scheme 3), the tertiary amine is probably involved in the PdII reduction step.15,16 In the same solvent, but under Pd(dba)2 catalysis and with N-nitroso-N-phenylacetamide instead of phenyl iodide, Kikuwa et al. obtained styryl acetate as the main product (Eq. 3).17 Under these conditions, the phenylating reagent would be PhPdOAc (Scheme 4).

2.1. After addition to vinyl acetate In 1968, Heck disclosed the reaction of vinyl acetate with PhPdCl generated from phenylmercury chloride and catalytic amounts of Li2PdCl4 via a transmetalation reaction, the catalyst being regenerated with CuCl2.12 As depicted in Eq. 1, the results were highly dependent on the nature of the solvent. When the addition led to palladium attached to the terminal carbon (Scheme 3, path a), the b-elimination would only involve the acetate. When palladium is attached to the central carbon (Scheme 3, path b), both b-H and bCOMe13 eliminations occurred. Stilbene was produced via either a b-H elimination from styrene (Scheme 3, path c) or a b-OAc elimination from styryl acetate (Scheme 3, path d). This last compound was isolated only with AcOH as the solvent.

Li2PdCl4 (0.1 equiv.) CuCl2 (1 equiv.) Ph PhHgCl + OAc solvent (10 equiv.) rt, overnight AcOH: MeCN: Me2CO:

10067

isomerisation PhN(NO)COMe

PhN2OAc

Ph Ph +

+

34% 20% 31%

Ph

3% 2% 3%

Ph

PdII PhPdII

O

+ Ph

33% 8% 10%

+ Ph-Ph

OAc

Ph II

Pd

Ph

PdIIH Ph

β-H elimination

(b) PdII Ph

β-H elimination

(c)

Ph

OAc O

PdIIH

Ph

PdIIOAc OAc PhPdII (d)

Ph

Ph

β-OAc elimination OAc

β-COMe elimination

O

(2)

3%

12%

PdIIOAc

(a)

O

30%

PhPdII β-OAc elimination

Ph

OAc +

Ph

O

II

Pd

Ph O

PdIICOMe Scheme 3.

PhN(NO)COMe +

Pd(dba)2 (0.1 equiv.) OAc (2 equiv.)

PhPdOAc + N2

Scheme 4.

Pd(OAc)2 (0.01 equiv.) PPh3 (0.02 equiv.) NEt3 (1.2 equiv) Ph PhI + OAc MeCN, 100 °C, 8 h (1.2 equiv.) 52%

Ph

Pd0

Ph

OAc +

MeCN, 40 °C, 0.5 h 43%

Ph

Ph 10%

(3)

(1)

10068

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Using a supported palladium catalyst, Choudary et al. isolated stilbene in high yield from the coupling of vinyl acetate with phenyl iodide (Eq. 4).18 According to their analysis of the reaction course, at least some stilbene was produced from styryl acetate.

PdCl2 supported on montmorillonite (0.00085 equiv. Pd) PhI +

OAc (1.25 equiv.)

count by Pan and Jiao, which is mainly oriented towards the highlights of their results.20 2.2.1. b-OCOR or b-OCO2R elimination. The stereochemistry of the products shown in Schemes 5, path a and 6, path a, which were

Ph

n-Bu3N (1.25 equiv.) 100 °C, 24 h

(4)

Ph 85%

According to the above results and other literature data,19 it appears that the regioselectivity of the addition and the b-elimination selectivity depend on both the nature of the arylating agent and the experimental conditions. 2.2. After addition to an allylic ester The b-H versus the b-OAc elimination for the Pd-catalyzed arylation of allylic esters has been discussed in an interesting ac-

obtained from the syn addition to cyclic esters of organopalladium reagents generated from the Hg/Pd transmetalation, indicates an anti b-ester elimination.21 Daves considered that the antiperiplanar alignment of PdOAc and b-OAc seems to be required for the elimination of Pd(OAc)2.22 In agreement with this proposal,  et al. recently demonstrated the anti b-OAc elimination from Gagne an isolated Pd complex, through a low rate reaction, likely occurring via a boat transition state (Scheme 7).23 Lautens et al. observed selective b-OAc eliminations from the Pd0-catalyzed reaction of aryl iodides with various allylic acetates.24

Me N

MeOCH2O O MeOCH2O

MeN

+ Pd(OAc)2 O (1 equiv.) HgOAc

+ RO

NMe

R = COn-Pr (a)

NMe

O

MeCN (b)

rt, 24 h

Me N

MeOCH2O

R = CH2OMe or Si(i-Pr)3

(1 equiv.)

O

O

NMe O

RO Scheme 5.

O

Me N

NMe Ph

O

Ph

O O RO

O

MeN

R = COMe NMe

+

O

+ Pd(OAc)2 (1 equiv.)

MeCN rt, 24 h

O O

NMe O O (i-Pr)3SiO

Scheme 6.

O

Me N

(b)

Ph

(1 equiv.)

O

(a)

R = Si(i-Pr)3

HgOAc

O

O O

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Et3P OAc O

AcO AcO

PEt3

Br

Pd PEt3

AcO

C6D6 rt

OAc AcO AcO

10069

Br OAc O

Pd PEt3

AcO AcO

O

PEt3 + AcO

Pd

Br

PEt3 OAc

14 d: 40% conversion

Scheme 7.

The selective formation of isomeric coupling products from isomeric acetates, such as (E)-but-2-enyl acetate and but-3-en-2-yl acetate (Scheme 8),24 showed that these reactions occurred via a Heck-type pathway, rather than via a p-allyl intermediate. Somewhat different experimental conditions were used by Li and co-workers for the Heck-type diarylation of allylic esters or carbonates (Eq. 5), the first arylation leading to b-elimination of the heterounit.25

amine.15,16 The use of arylboronic acids, instead of aryl halides, does not require such a reduction, since the reactive arylating species can be formed from their transmetalation with PdII species.26,27 Thus, Maddaford and co-workers carried out the addition of various arylboronic acids to peracetylated glycols using only catalytic amounts of Pd(OAc)2 in MeCN (Eq. 6).28 According to the authors, syn addition of ArPdOAc from the less congested face is followed by

PdII OAc

ArI

OAc

Pd/C (0.1 equiv.) n-Bu4NCl.xH2O (3 equiv.) n-BuMe2N (4 equiv.) H2O (1 equiv.)

Ar Ar = 1-naphthyl: 51%

Ar

PdIIOAc

n-BuMe2N H2O

OAc

DMF, 180 °C, 3 h

PdII Ar

Pd0

Ar OAc Ar = 1-naphthyl: 83%

Scheme 8.

I + R

Z

Pd(OAc)2 (0.1 equiv.) n-Bu4NCl (1.5 equiv.) MeO NEt3 (8 equiv.), air

OMe (5)

MeCN, 120 °C, 12-14 h

MeO (2.5 equiv.)

R R = H, Z = OAc (89%), OCOPh (58%), OCOBn (62%), OCO2Et (58%) R = Ph, Z = OAc (30%)

The above catalytic procedures lead to the elimination of PdII species, which have to be reduced to Pd0 to close the catalytic cycle. It is usually admitted that this reduction is promoted by the tertiary

AcO PhB(OH)2 + (2 equiv.) AcO

O Pd(OAc)2 (0.1 equiv.) AcO MeCN, rt, 24 h OAc

the selective anti-elimination of Pd(OAc)2. The b-H elimination was not observed, but the authors pointed out that this elimination could be reversible29 under their conditions.

O

Ph (6)

AcO 82%

10070

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

In contrast to the above methods, the procedures developed by Sawamura and co-workers led to syn b-OAc eliminations. As catalyst, they used either a cationic PdII complex generated from Pd(OAc)2, 1,10-phenanthroline and AgSbF6 (Scheme 9),30,31 or a palladiumII dimer, which is the precursor of a monomeric PdII complex having a vacant coordination site (Scheme 10).32 For both procedures, the regioselective insertion of the PhPd species into the C]C bond would be assisted by intramolecular coordination of the carbonyl oxygen of the acetoxy group to the palladium centre. The elimination would involve a palladacycle, as shown in Scheme 11 when the active catalyst is the neutral PdII monomer.32 A similar scheme was proposed for the catalysis with the cationic complex.30,32

anions inhibit the b-H elimination, thus favouring the b-OAc elimination.36 This inhibition is probably due to the absence, under such conditions, of a vacant coordination position, which would be a prerequisite for the PdH elimination.37,38 This influence of the nitrogen ligands encouraged Lu’s team to use the association of Pd(OAc) 2 and bipyridine as catalyst to perform the acetoxypalladation-initiated cyclisation of 1,6-enynes outlined in Eq. 9.39,40 Using diastereoisomeric substrates, they disclosed that both syn and anti b-OAc elimination can apparently occur under similar experimental conditions (Scheme 12).39 Activation of the triple bond of the substrate by coordination to palladium leads to the trans-addition of acetate

Pd(OAc)2 (0.1 equiv.), AgSbF6 (0.1 equiv.) 1,10-phenanthroline (0.12 equiv.) AgOAc

N PdOAc N

SbF6 Ph

OAc PhB(OH)2 + (1.5 equiv.)

n-Bu ClCH2CH2Cl, 60 °C, 6 h 97% ee

n-Bu 65% yield, 97% ee

Scheme 9.

NO2 O2S N

Pd

O O (0.05 equiv.)

N O2S

O O

Pd

NO2

NO2 O2S N

OAc

OAc TPSO(CH2)2 97% ee

Pd

+ PhB(OH)2 (1.1 equiv.)

ClCH2CH2Cl, 60 °C, 6 h

Ph TPSO(CH2)2 76% yield, 96% ee

Scheme 10.

Recently, Li, Deng and co-workers reported Pd-catalyzed diarylations of allyl acetate with arylboronic acids in the presence of n-Bu4NCl and an inorganic base, especially KH2PO4 (Eq. 7).33e35 The study of the stoichiometric reaction depicted in Eq. 8 led Lu’s team to observe that, in AcOH, nitrogen ligands or chloride

giving 12Ac and 12At, respectively. This is followed by the cisinsertion of the CePd bond into the C]C bond. The only possible cis fusion of five- and six-membered rings leads to the formation of 12Bc and 12Bt, respectively. These intermediates evolve via elimination of AcOPdII to afford the same bicyclic compound.

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Ph

N

R1

R2

N

cinnamyl acetate and 2-phenylallyl acetate from the phenylation of allyl acetate (Scheme 13, path b).47 Under their experimental conditions (Scheme 13, path a),41 Jiao et al. did not observe traces of allylbenzene from the coupling of PhI with allyl acetate. They proposed a mechanism similar to that depicted in Scheme 15. The high regioselectivity would be due to the chelation between the carbonyl oxygen of the acetoxy group and the palladium atom; this chelation would impede the rotation about the C1eC2 bond, favouring the syn relationship between Pd and a hydrogen in C3 leading to the corresponding b-H elimination.41 There is, however, a contradiction between the Sawamura30e32 and Jiao41 proposals. Indeed, both teams have proposed the Pd/acetoxy coordination, but to explain either the b0 OAc elimination (Scheme 11) or the b-H elimination (Scheme 15), respectively. In fact, Jiao suspected that Ag2CO3 serves not only as a source of silver to scavenge the halide, but also as a base. This leads us to propose a different explanation for the absence of b-OAc eliminations in the presence of Ag2CO3 (Scheme 16). Insertion of

PhB(OH)2

Pd OAc

AcOB(OH)2 R2 R1

Ph N N

N N

O

Pd

Ph Pd

O N N

Ph Pd

OAc R2 R1

R1

R2

OAc

Scheme 11.

Pd(OAc)2 (0.1 equiv.) n-Bu4NCl (1.5 equiv.) KH2PO4 (2 equiv.) OAc Ph DMF, 120 °C, 6 h

PhB(OH)2 + (2.5 equiv.)

Pd AcO

Ph

O

OAc

+

(10 equiv.)

(7)

90%

H N

H N

10071

H N

L AcOH, rt

O

+

(8)

O OAc

2

L = pyridine (2 equiv.): 69% L = bipyridine (1 equiv.): 81% L = LiCl (10 equiv.): 75% Without L:

OAc

66%

Pd(OAc)2 (0.05 equiv.) AcO bipyridine (0.06 equiv.) (9)

Z

AcOH, 80 °C

Z

Z = O (12 h, 94%), NTs (4 h, 97%), C(CO2Me)2 (48 h, 87%) Inter- and intramolecular coupling reactions with selective elimination of ethyl carbonate are also documented (Eqs. 5,25 10 15 and 11 33e35). 2.2.2. b-H elimination. In the presence of Ag2CO3, the Pd-catalyzed reaction of linear allylic acetates with aryl iodides (Scheme 13, path a),41,42 aryliodine diacetates (Eq. 12),43 arene carboxylic acids (Scheme 14),44,45 furans and thiophenes (Eq. 13)46 selectively affords the 3-arylated allylic acetates. The selectivity can, however, depend on the reaction conditions. Indeed, Mino et al.,47 using a slightly modified version of Jiao’s procedure (Scheme 13, path a),41,42 mainly 80  C in PhMe, instead of reflux in PhH, obtained a mixture of

PhPdII into the C]C bond and partial transmetalation of Ag2CO3 would afford AgI and the bimetallic complex 16A, this latter species evolving towards the Heck product in liberating AgI, CO2 and the catalyst. We are conscious that this proposal is not fully satisfactory, since the optimum Jiao conditions utilised only 0.6 equiv of Ag2CO3. Nevertheless, subsequent researchers used 1e3 equiv of this salt or 0.5 equiv of both Ag2CO3 and CaCO3. Moreover, AgOH, which, according to Scheme 16, would be liberated, could participate in the elimination reaction. Jiao’s team retained their chelation proposal to explain the regioselective arylation and the selective b-H elimination for the

10072

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

AcO Pd

OAc a

II

OAc AcO

PdII

AcO

PdII

OAc

OAc AcO

E

E

E E = CO2Me

E

E

12Bc AcOPdII

AcO Pd

OAc a

E

E

12Ac

E

E

II

OAc AcO

E

E

E

PdII

AcO

PdII

OAc

OAc 89% from cis-substrate 88% from transsubstrate

12Bt

12At

a: Pd(OAc)2 (0.05 equiv.), bipyridine (0.06 equiv.), AcOH, 80 °C Scheme 12.

Pd2(dba)3.CHCl3 (0.05 equiv.) P(o-tolyl)3 (0.22 equiv.) n-BuNMe2 (2 equiv.)

I

OCO2Et

O

56% O

Pd(OAc)2 (0.1 equiv.) n-Bu4NCl (1.5 equiv.) MeO OCO2Et KH2PO4 (2 equiv.)

B(OH)2 + MeO

(10)

MeCN/H2O (10:1) microwaves (160 °C), 1 min

OMe (11)

DMF, 120 °C, 6 h (2.5 equiv.)

75%

reaction of alkenyl boronates and arylboronic acids with linear allylic esters or carbonates.48 For such reactions, the optimum conditions required various additives such as those depicted in Eq. 14, low yields being obtained in the absence of the fluoro additives, or, surprisingly, using Ag2CO3 instead of AgOAc. The function of the fluoro additives has not been explained, some role in the promotion of the reactivity of the boron substrates being conceivable.49 The

mechanism that we suggested above to explain the absence of the OAc elimination (Scheme 16) is inadequate for the present Hecktype reaction. The arylating species, which interacts with the substrate is, however, different, since it is generated from B/Pd transmetalation. This leads us to consider a reaction involving the acetate ligand and arising from the transition state 17A (Scheme 17). As for Scheme 16, the elimination would concern

R PhH, reflux air Pd(OAc)2 (0.05 equiv.) (a) Ag2CO3 (0.6 equiv.)

R PhI +

OAc (2 equiv.)

Ph

OAc

R = H, 10 h: 94%, E R = Me, 15 h:73%, E/Z = 80:20

(b)

R=H PhMe, 80 °C 8 h, air Ph

Ph OAc + 76%

Scheme 13.

OAc 6%

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

PhI(OAc)2 + (1.1 equiv.)

OAc

Pd(OAc)2 (0.05 equiv.) TEMPO (0.1 equiv.) Ag2CO3 (0.5 equiv.) CaCO3 (0.5 equiv.)

Ph

OAc

MeCN, 70 °C, 8 h

10073

(12)

87%

MeO

MeO

MeO

OAc

+

+ MeO

OMe

OMe OAc MeO

MeO R=H

MeO

R

CO2H

OAc

+ MeO

OMe

(2 equiv.)

Pd(OAc)2 (0.1 equiv.) Cu2O (0.01 equiv.) Ag2CO3 (3 equiv.)

95%, 10:2:1

(b)

R = Me MeO

MeO

OAc OMe

OAc

+

+ MeO

OMe

(a)

dioxane/DMSO (95:5) 110 °C, 2 h

MeO

OAc

OMe OAc MeO

MeO

OMe

62%, 5:1:4 Scheme 14.

+

Pd(OAc)2 (0.05 equiv.) OAc Ag2CO3 (1 equiv.)

OAc OAc +

DMSO/dioxane (5:95) 110 °C, 12-15 h

Z (5 equiv.)

AcO

+

Z

(13) Z

Z Z = O: 60%, 75:17:8 Z = S: 66%, 78:15:7 O

O

PhPd

H

2 3

Pd O

1

Ph

β H

Ph

O

OAc + HPd

β' Scheme 15.

a proton instead of a hydride. This proposal is more or less in agreement with other calculations, some leading to a sixmembered transition state for the accepting by an acetate coordinated to Pd of a proton from a substrate also bound to the metal,50 whereas others discarded a seven-membered transition state and also an intermediate rather similar to 17A because of their too-high energy.51 Nevertheless, these calculations were for experimental conditions and substrates different to those of Eq. 14; in particular, they did not consider a system with a second acetate, which could stabilise an intermediate such as 17A.

Under Li/Deng experimental conditions, the use of potassium aryltrifluoroborates instead of arylboronic acids with allyl acetate provided the monoarylation adduct (Eq. 15) instead of the diarylated compound (Eq. 11).33 According to the authors, the reason for this observation is the difference of stability between ArBF3K and ArB(OH)2.33 In our opinion, their mechanistic proposal is, however, unexpected34 and the corresponding scheme contains errors. Chelation generated from the coordination of both the olefin and the acetate carbonyl oxygen to cationic palladium was also

10074

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Ph

(Eq. 16)54e57 or alkenes (Eq. 17),58 and for the coupling of phenylboronic acid with undec-1-en-3-yl acetate (Eq. 18).59 The mechanism shown in Scheme 17 does not propose the formation of PdH species. Under Xiao’s conditions, which used (AcO)2Pd(dppp) as the catalyst (Eq. 19), such species would, however, be formed, the regeneration of the active PdII catalyst occurring via the reduction of acetone.60 The unusual phenylation in the C2 position could be due to steric hindrance provided by the diphosphine, which precludes the coordination of the acetate to palladium at the level of a p-complex. After the b-H elimination, some migration of the terminal double bond arises.60e62 Recently, Liu and co-workers disclosed the synthesis of 2-deoxy-Caryl glycosides via the decarboxylative Heck coupling reaction of benzoic acids with various glycols (Eq. 20).63 Due to the steric hindrance created by the C-3 substituent, the cis addition of the ArPdII intermediate proceeds on the top face of the C]C bond, this giving an intermediate with no syn relationship between the palladium unit and the hydrogen geminal to the Ar group.64 In contrast, such a relation-

OAc 0

PhI

Pd

+ AgOH + CO2 O

PhPdI O

OAc

O

AgO H

Pd

Ph

16A

O H

I Pd Ph

AgI

O O

O AgO

OAg Scheme 16.

PhB(OH)2 +

OAc

Pd(OAc)2 (0.05 equiv.) AgOAc (2 equiv.) CuF2 (1 equiv.), KHF2 (2 equiv.) OAc + Ph 91%, E/Z = 20:1

acetone, 85 °C, 5 h

(2 equiv.)

Ph

(14) 2%

Ag0 Pd(OAc)2

PhB(OH)2

2 AgOAc AcOB(OH)2

Pd0

PhPdOAc Ph

OAc

OAc

+ AcOH AcO

O O

O

Pd

Pd

Ph

H

O

O

Ph H

O

17A Scheme 17.

PhBF3K + (2.5 equiv.)

Pd(OAc)2 (0.1 equiv.) n-Bu4NCl (1.5 equiv.) KH2PO4 (2 equiv.) OAc Ph DMF, 120 °C, 12 h

OAc

(15)

55%

proposed when aryldiazonium terafluoroborates were used (Scheme 18, path a).52a Switching from allylic esters to vinyllactones precluded such a chelation; thus, more vigorous experimental conditions were required to obtain valuable yields (Scheme 18, path b).52 Chelation as proposed in Schemes 16 and 17 could also occur for the dehydrogenative Heck reactions53 of allylic esters with arenes

ship can occur with the C-3 hydrogen. Although the authors proposed the syn-elimination of HPd to afford the coupling product, a mechanism implicating Ag2CO3, as depicted in Scheme 16, could be involved. The diarylation of (S)-oct-1-en-3-yl acetate using the transmetalation of an arylstannane with a palladiumII-N-heterocyclic carbene suffered no erosion in enantiomeric excess (Scheme 19, path a), showing that the plausible reversible elimination of the hydrogen

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10075

MeO OAc N2BF4

n-Bu Pd2(dba)3 (0.04 equiv.) NaOAc (3 equiv.) PhCN

OAc

rt, 1 h

68%

(a)

n-Bu OMe

(b)

OMe

OMe (1.1 equiv.)

O O

O

O

25 °C ,12 h: 30% 80 °C, 5 h: 68%

MeO

Scheme 18.

Procedure A, B or C OAc Ph OAc PhH + (excess) Procedure A.54 Pd(OAc)2 (0.1 equiv.), AgOAc (2 equiv.), DMSO (5%/PhH), 110 °C, 12 h: 43% Procedure B.55 Pd(OAc)2 (0.05 equiv.), Ag2CO3 (0.6 equiv.), n-BuCO2H (16 equiv.), benzoquinone (2 equiv.), air, 80 °C, 48 h: 51% Procedure C.56 Pd(OAc)2 (0.05 equiv.), 3,5-dichloropyridine (0.05 equiv.), PhCO3t-Bu (1 equiv.), AcOH, 100 °C, 6 h: 57% + Ph2C=CHCH2OAc (5%)

R1

+

OCOR2

Pd(OAc)2 (0.15 equiv.) AgOAc (2.5 equiv.)

R1

(16)

OCOR2

(17)

DMSO/ClCH2CH2Cl (5:95) 110 °C

(3 equiv.)

R2 = Me, R1 = Ph (20 h, 81%), Cy (24 h, 70%) R2 = R1 = Ph (10.5 h, 70%)

O

O

Ph OAc PhB(OH)2 + (1.5 equiv.)

S Ph (0.1 equiv.) Pd(OAc)2 benzoquinone (2 equiv.) AcOH (4 equiv.)

OAc

OAc +

n-oct dioxane, 45 °C, 4 h Ph

n-oct 98%, 41:1

PhB(OH)2 +

OAc (2 equiv.)

Pd(OAc)2 (0.02 equiv.) dppp (0.03 equiv.)

Ph

Ph

Ph OAc +

acetone, 70 °C, 20 h

38%

(18)

n-oct

OAc 34%

(19)

10076

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

OMe

O CO2H +

3

DMF/DMSO (20:1) 80 °C, 4 h

OR (2 equiv.)

OMe

OMe

Pd(OAc)2 (0.1 equiv.) PPh3 (0.4 equiv.) OR Ag CO (3 equiv.) 2 3

OR

O

OR

OMe

(20)

OR

OR R = Ac (79%), t-BuCO (65%), t-BuOCO (55%), Bn (70%), t-BuMe2Si (73%)

OMe SnBu3 Pd(Ii-Pr)(OTs)2 (0.06 equiv.) MeO (3 equiv.) Cu(OTf)2 (0.25 equiv.), O2 (balloon) (a)

OAc

MS 3 Å, DMA, rt, 16 h

OAc Me(CH2)4 68%, 98% ee

Me(CH2)4

Ph2N2BF4 (1.5 equiv.) Pd2(dba)3 (0.05 equiv.)

(b)

(98% ee)

Ii-Pr:

N

N

i-Pr

i-Pr

OAc Me(CH2)4

DMA, rt, 16 h i-Pr

i-Pr

OMe

Ph 91%, 98% ee

Scheme 19.

geminal to the acetate substituent did not arise.65 In contrast, the reaction leading to the HPd species formed after the addition of the first aryl group was reversible. This afforded a p-benzyl intermediate, which yielded the diarylated product through a second transmetalation (Scheme 20). No erosion in enantiomeric excess was also noted in the

course of the Pd0-catalyzed phenylation of the same substrate with phenyldiazonium tetrafluoroborate (Scheme 19, path b).66 3. Competitions between hydrogen(s) and hydroxy 3.1. b-OH elimination

II

Cu , O2 OAc R

ArSnBu3

PdII

Ar Pd0

Ar

ArPdII OAc R

ArSnBu3 OAc

II

Pd

OAc

R

R

H R'

OAc

PdII

R

Ar H

Scheme 20.

Ar HPdII

In 1994, Hosokawa et al. assumed that the synthesis of methyl 2(methoxymethyl)acrylate from methyl 2-(hydroxymethyl)acrylate and methanol in the presence of PdCl2 involves the alkoxypalladation of the C]C bond followed by the elimination of ClPdOH (Scheme 21).67 From their study of the stoichiometric reaction depicted in Eq. 21, Lu’s team disclosed that, in AcOH, the addition of LiCl favours the b-OH elimination over the b-H elimination.7,68 The formation of both the substituted allylic alcohol and the cyclic compound shows that the hydride elimination occurs from the two possible carbon sites. The b0 -H elimination leads to an enol evolving to the corresponding aldehyde, which undergoes an intramolecular reaction with the amide unit. The dependence of the amount of the chloride anion on the elimination selectivity has also been discussed (Eq. 22).7 The trans-stereochemistry of the elimination of palladium and hydroxide in acetic acid containing an excess of LiCl has been assumed from a study of the catalytic cyclization reaction depicted in Eq. 23, but, in our opinion, the relative stereochemistries of the suspected intermediates are rather

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

PdCl2 (0.1 equiv.) MeOH (5 equiv.)

CO2Me OH

ClPd MeO

DME, 50 °C

CO2Me OH

10077

CO2Me MeO

+ HOPdCl 77%

+ HCl Scheme 21.

H N Pd AcO

O

O

H N O

+

O

β

without LiCl: with LiCl:

OH (1.1 equiv.)

H Pr

30%

64%

Ph

AcOH, rt

+ Ph

Ph

(22)

O

0 equiv.: LiCl 2 equiv.: 10 equiv.:

59% 39% 13%

18% 34% 64%

Pr

PdCl2(PhCN)2 (0.05 equiv.) Cl LiCl (4 equiv.)

Pr Cl O

+ O

OH (21)

39%

Ph LiCl (0-10 equiv.) Ph

PhPdI(tmeda) +

O

N

+

β' OH

2

HO

H N

LiCl (0 or 10 equiv.) OH + AcOH, rt (20 equiv.)

AcOH, rt, 60 h

Pr

O

Pr O 23%, E/Z = >97:3

ambiguous.6 The syn-elimination mediated by palladium requires a free coordination site on the palladium atom.5 In the presence of the large excess of LiCl, palladium is coordinatively saturated; consequently, such a syn-elimination is precluded. Moreover, this coordination of chloride anion to Pd increases the electron density of Pd, resulting in the weakening of the CePd bond.7 Therefore, the OH elimination would proceed via an E2like mechanism promoted by halide ion coordination to Pd (Scheme 22). The apparent syn-elimination will only occur under particular conditions, as observed by Hacksell and Daves.69 The addition of 1,4-

Li Cl

O

O

(23)

Pr 51%

anhydro-2-deoxy-5-O-(methoxymethyl)-D-erythro-pent-1-enitol to an acetonitrile solution of (1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-yl)mercuric acetate and palladium acetate led, at room temperature, to the adduct 23A (Scheme 23). Its exact structure has not been determined, but the cis relationship between the PdOAc and the pyrimidinyl unit was demonstrated from its reaction with NaBD4. At 70  C, the adduct evolved to (20 -S-trans)-5-[20 ,50 -dihydro50 -[(methoxymethoxy)methyl]-20 -furanyl]-1,3-dimethyl-2,4(1H,3H)pyrimidinedione. The authors proposed the formation of palladooxacyclobutane 23B as intermediate and the subsequent elimination of palladium oxide.

Cl Li

Li Cl OH

PdX

ArPdX n LiCl

Ar

Ar OH

Li Cl Scheme 22.

+ LiOH + XPdCl + (n-1) LiCl

10078

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

O R

O

MeN

R NMe

rt

O HO

NMe

MeCN + Pd(OAc)2

+

O O

HO L PdOAc 2 23A

HgOAc

N Me

AcOH R

O

NMe

NaBD4

R = CH2OCH2OMe

O

70 °C R

O O R

NMe HO

D

N Me

O

O

O

PdL2

N Me 23B

O

O L2Pd=O

O

NMe N Me

O

Scheme 23.

The Pd-catalyzed reaction of allyl alcohol with prop-1ynylbenzene and CuCl2 afforded (E)-(1-chloro-2-methylpenta-1,4dienyl)benzene as the main product (Eq. 24).70 According to Jiang’s team, trans-chloropalladation of the triple bond71 is followed by insertion of the resulting vinylpalladium species into the C]C bond of allyl alcohol. Subsequent cleavage of the CePd and CeO bonds provides the dienic compound (Scheme 24).70 Jiang and co-workers also reported the synthesis of chloro-1,3-dienes from alkynols and alkenes through reactions involving successive b-H and b-OH eliminations (Scheme 25).72 The reaction of the vinylpalladium species 25A with the alkene gives the s-alkylpalladium complex 25B, which suffers a b-H elimination, leading to 25C. The re-addition of HPdCl produces 25D. Subsequent 1,3-rearrangement affords 25E. The diene is obtained from 25E via the b-OH elimination, whereas CuCl2 mediates the regeneration of the catalyst.

(3 equiv.)

HOAc/H2O (1:1), rt, 12 h

Wang and co-workers recently reported the kinetic resolution of BayliseHillman adducts such as that depicted in Eq. 25.73 The CaePd intermediate was formed via the selective addition of the chiral arylating agent to the C]C bond of the (R)-substrate.

Cl Ph

Ph

PdCl2

+ HOCuCl CuCl2 PdCl

Cl

3.2. b-H elimination An array of reports concerns Heck reactions of allylic alcohols involving hydride eliminations as the main reactive pathways.1,75,76 For such reactions, the arylation usually occurs on the terminal carbon, leading to the internal carbon substituted by palladium. Thus, the H elimination implies a hydride geminal either to the aryl group (b-H elimination) or to the hydroxyl moiety (b0 -H elimination), leading to the arylated allylic alcohol or carbonyl compound,

PdCl2 (0.056 equiv.) . CuCl 2 2 H2O (2 equiv.) Cl OH

+

Ph

Although benzylic hydrogens were available in the b and b0 positions, the hydroxy substituent was selectively eliminated. Moreover, given the enantiomeric excess of the addition product, this intermediate was not in equilibrium with the corresponding oxo-h3-allylpalladium species.74

Cl

PdCl

OH Ph Ph OH Scheme 24.

Ph + Cl Ph

(24)

87%, 99:1

respectively (Scheme 26). For this latter derivative, the formation of an enolic species is admitted as intermediate.77,78 The carbonyl compound could be obtained from 26C via either free enol 26D (path a) or addition/elimination of HPdBr (path b) as suggested by Heck.79 Smadja et al. showed that path a is, at best, a minor reactive pathway;80 this is also demonstrated in a recent study.81 Chalk and Magennis proposed plausible equilibria between intermediates 26A, 26B, 26C, 26E and 26F, the selectivity depending on the stability of these complexes and the different rates of the HPX elimination/addition.78 We envisaged that the halide-mediated reductive elimination (path c) could compete with the usually accepted hydride elimination (path b) for the formation of the carbonyl compound from 26E.82 This proposal was inspired by a report from Goddard et al., concerning DFT calculations on mechanisms relevant to the Wacker process,83 and is based on some similarity between the Heck reaction and the Wacker oxidation, the latter involving an enolic intermediate similar to 26C.78,84 For the Wacker process, it has been shown that the elimination product never leaves the coordination sphere of the palladium at this level, the formation of the aldehyde occurring through the addition/

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Cl

R + HOCuCl

10079

HO PdCl2

CuCl2

HO

Cl

HOPdCl 25A R

ClPd R

Cl Cl

PdCl

R

ClPd HO

25E

Cl

R 25B

HO

Cl HO 25D

R PdCl

HPdCl Cl

R 25C

HO Scheme 25.

N N OH

PhB(OH)2 + (2 equiv.)

O

PdI2 N

Ph (0.15 equiv.)

O AgOTf (0.15 equiv.) NEt3 (0.5 equiv.) MeCN, rt, 24 h

O

(25) OH

O

+ Ph 38%, E/Z = 90:10 98% ee

elimination of HPdX,85 and, according to the calculations,83 via the halide-mediated reductive elimination. Under most experimental conditions, arylation and vinylation of the primary or secondary allylic alcohols with organic halides mainly provide the corresponding b-substituted carbonyl compounds.1,75,76 Such a selectivity can be also observed for the arylation with arenediazonium salts.86e89 In contrast, organic triflates90 and iodonium salts91 rather afford the substituted allylic alcohols. Nevertheless, Jeffery disclosed experimental arylation and vinylation procedures leading selectively to the substituted allylic alcohol, even from organic iodides, the key for such a selectivity being the use of silver acetate, silver carbonate or thallium acetate as additive and the absence of an ammonium salt (Scheme 27).92e94

58%, 38% ee

The role of these additives was not really rationalized by the author. Moreover, other parameters are probably involved, as exemplified in the formation of the aldehyde shown in Eq. 26,95 which was obtained under such conditions. The presence of ammonium salts often favours the formation of the carbonyl compounds (Scheme 27),93,96e99 but this nevertheless depends on the anion of the salt (Eq. 27),100 and also on the electronic properties of the aryl substituent (Scheme 28101 and Eq. 28 102). The decisive role of the experimental conditions on the selectivity has also been exemplified by the teams of Cacchi and Norrby, who observed b-H/b0 -H elimination ratios from 0.07 to 73 from the p-IC6H4CH2CH(PdX)CH2OH intermediates, depending not only on the additives but, moreover, on the solvent (Eq. 29).51

10080

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

XPdHβ

XPdHβ

Ar ArPdX OH

Ar

OH

OH β

26A

Ar

β'

OH 26D

(a) XPdHβ'

β'

tautomerisation XPdH

XPdH Ar

Ar

OH 26B

PdX

Hβ'

26C

26F

Ar (b)

Hβ'

PdX 26E

XPdH

PdX O

Ar

O

Ar

O

Ar

OH

Pd0 + HX H

(c)

Hβ'

OH Ar

Pd X O

H

Scheme 26.

Pd(OAc)2 (0.05 equiv.) Ag2CO3 (0.55 equiv.) n-Bu4NHSO4 (1.5-2.2 equiv.) MeCN, 70 °C, 4 h I

O (CH2)5Me

OH

+

54%

(CH2)5Me

OH

Pd(OAc)2 (0.03-0.05 equiv.) AgOAc (1.1 equiv.) DMF, 50-60 °C, 3-24 h

(CH2)5Me

61%

Scheme 27.

O Br

Pd2(dba)3.CHCl3 (0.025 equiv.) dppb (0.07 equiv.) Ag2PO4, CaCO3 OH

O

DMA

O H O

(26)

CHO

79%

OH Procedure A or B Ph PhBr + (1.2 equiv.)

Ph

Ph R Ph +

R +

R+

R OH O O OH R = n-C5H11 Procedure A. Pd(OAc)2 (0.012 equiv.), NaHCO3 (2 equiv.), n-Bu4NBr (3.1 equiv.), 130 °C, 3 h 85% 5% Procedure B. Pd(OAc)2 (0.012 equiv.), n-Bu4NOAc (3.3 equiv.), 70 °C, 0.5 h 85% 4% 5%

R

(27)

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10081

O HN NH2 Et

Pd

Cl

2 (0.0001 equiv.)

X +

73%

MeO

K2CO3 (2 equiv.)

OH (1.5 equiv.)

R

X=I R = OMe

n-Bu4NCl (1 equiv.) H2O, 80 °C, 12 h

X = Br R = CO2H

OH 71%

HO2C Scheme 28.

OH PhI + (1.2 equiv.)

Pd(OAc)2 (0.05 equiv.) Ph ClNBnEt3 (1 equiv.) R NaHCO3 (2 equiv.)

OH R

OH (1.5-3 equiv.)

β

R

+

(28)

82% 61% 46%

27% 24%

Pd(OAc)2 (0.03 equiv.) base, additive solvent, 90 °C

β Ar Ar = p-MeOC6H4 OH +

Ar

O

MeCN, 50 °C, 24 h R = Br: R = OMe: R = Me:

ArI +

Ph

OH + Ar

(29) Ar O+

O + Ar β

n-Bu4NOAc (2 equiv.), K2CO3 (1.5 equiv.), KCl (1 equiv.), DMF, 2 h 37% 3% 18% 9% β/β'-H ratio: 6.4 n-Bu4NOAc (2 equiv.), K2CO3 (1.5 equiv.), KCl (1 equiv.), DMA, 3 h 40% 1% 32% 1% β/β'-H ratio: 73 n-Bu4NOAc (2 equiv.), DMF, 0.3 h 48% 3% 10% 18% β/β'-H ratio: 3.4 n-Bu4NOAc (2 equiv.), PhMe, 1 h 15% 12% β/β'-H ratio: 1.2 K2CO3 (1.5 equiv.), KCl (1 equiv.), DMF, 0.3 h 4% 20% β/β'-H ratio: 0.07 a MeCHArCHO (11%) was obtained.

β'

Ar

β'

OH

+ O

Ar β'

16%

15%

20%

22%

20%

a

10082

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

29A, the b-H elimination would proceed with the same hydrogen as that for path a, but leading to the hydridopalladium alcoholate 29B, which affords the C]O unit by elimination of palladium hydride (Scheme 29).90 When aryl iodides and primary allylic alcohols were used, the oxidation of the aryl allyl alcohol was suspected as another reaction pathway for the traces of the b-arylated a,b-unsaturated aldehyde that were formed.51,109,110 The formation of cationic palladium intermediates does not, however, imply the selective formation of 3-substituted allylic alcohols. Indeed, the HeckeMatsuda reaction, which uses arenediazonium salts, involves the coordination of the C]C bond to an ArPdþ species,111,112 but mainly affords the carbonyl compounds from allylic alcohols (Eq. 31).87e89,113 Moreover, traces of the cinnamaldehyde were detected from the reaction of allyl alcohol with

The Heck intermediates formed from organic halides are fairly different from those generated from organic triflates or iodonium salts. These latter salts are more prone to form cationic palladium intermediates, this depending, however, on the species present in the coordination sphere,103e105 and the solvent.106 When triflates90 and hypervalent iodonium salts107,108 were used as reagents, this selectivity towards the substituted allylic alcohol was explained by a chelation preventing the hydrogen atom on the hydroxy-bearing carbon from the syn relationship with palladium for the palladiumhydride elimination (Scheme 29); consequently, the elimination occurs with a hydrogen geminal to the aryl or vinyl group (path a). Cacchi and co-workers, having sometimes observed the formation of a b-arylated a,b-ethylenic ketone (Eq. 30), proposed the formation of palladacycle 29A (path b) as a plausible intermediate. From

Ar2IBF4 or ArOTf

Z OH

ArPd

Ar

Pd0 + HZ

Pd0 Z

OH

(a)

Pd

Ar

O

Ar

OH (b)

Z = BF4 or OTf

PdH2 Pd

HZ

Ar

O

Ar

OPdH 29B

29A Scheme 29.

OTf

OH

Pd(OAc)2 (0.03 equiv.) K2CO3 (2 equiv.)

(30)

+ DMF, 60 °C

Et

Ph

Ph

Ph OH 60%

N2BF4 + t-Bu (1.5 equiv.)

PhN2Cl +

OH

Et

Ph

+

O traces

+

O 23%

Et

Et

O Pd(dba)2 (0.05 equiv.)

i-Pr

i-Pr MeOH, 50 °C, 2.5 h t-Bu

Li2PdCl4 (0.02 equiv.) HCO2Na, NaOAc Ph OH MeCN/H2O (85:15) rt, 1.5-2 h

(31)

83%

Ph O +

O + Ph

41%, 90:10:traces

O

(32)

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

phenyldiazonium chloride (Eq. 32).86 This uncertainty in the anticipation of the results is also exemplified with the arylations depicted in Scheme 30: oct-1-en-3-ol afforded 1-phenyloct-1-en3-ol from the reaction with diphenyliodonium tetrafluoroborate, and 1-phenyloctan-3-one with phenyl triflate,107 although the active arylating species would be a similar cationic palladium intermediate.

Pd(OAc)2 (0.02 equiv.) NaHCO3 (2 equiv.) Ph2IBF4

DMF, rt, 1.5 h

OH Ph 83%

OH

n-C5H11

n-C5H11 O

Pd(PPh3)4 (cat.) K2CO3 or NEt3

PhOTf

Ph

DMF, Δ, 6 h

n-C5H11 84-86%

Scheme 30.

The Pd-catalyzed 5-endo-trig cyclization of substituted 1-(obromophenyl)prop-2-en-1-ols led to the corresponding indanone or indenone, depending on the experimental conditions and/or the

10083

substitution of the C]C bond of the substrate (Scheme 31). The formation of 2-phenylindan-1-one was explained via an intermediate corresponding to 26E of Scheme 26,82 whereas that of 2,3-diphenylinden-1-one would involve the pathway a of this scheme.114 Indeed, Pan and co-workers proposed that this indenone is formed via the corresponding indenol and its subsequent oxidation (Scheme 32); they have effectively observed that a similar indenol was smoothly converted into the corresponding indenone under the experimental conditions,110,114 but the formation of the indenol via an apparent trans b-H elimination (Scheme 32, step a) did not attract comment from the authors.64,114 We propose that the indenone could be rather produced via the Cacchi mechanism depicted in Scheme 29, path b. From their study of the addition of phenylboronic acid to pent-1en-3-ol mediated by a stoichiometric amount of Pd(OAc)2, Lei and co-workers recently demonstrated the strong influence of additives on the selectivity of the HPd elimination.115 At 0  C in DMSO/AcOH, the b-H/b0 -H elimination selectivity was very low (Eq. 33). In contrast, the presence of a Lewis acid such as CuCl2, ZnBr2, CuCl or LiCl led to the selective formation of 1-phenylpentan-3-one. The authors suggested that, as in Scheme 29, some coordination of the hydroxy to palladium could occur at the level of the carbopalladation intermediate (Scheme 33), which would induce the b-H elimination, producing 1-phenylpent-1-en-3-ol. The Lewis acid (MX) would efficiently coordinate to the hydroxyl; this interrupts the Pd/OH interaction and favours the formation of 1-phenylpentan-3-one.

O

Pd(OAc)2 (0.05 equiv.) cinchonine (0.1 equiv.)

Ph

R=H

OH

NaHCO3 (1.1 equiv.) DMF, 120 °C, 16 h

Ph Br

R R = Ph

76% O

Pd(OAc)2 (0.05 equiv.) PPh3 (0.15 equiv.)

Ph

K2CO3 (2 equiv.) DMF, 80°C, 24 h, air

55% Ph

Scheme 31.

OH O

KHCO3 + KBr Ph

Ph PdL2 Br

K2CO3 OH

Ph HPdBrL Pd0 + 2 HOAc 0.5 O2 H2O

Ph

Ph L

OH Ph

(a)

PdBrL2 Ph

OH

Pd(OAc)2

Ph

Ph

PdBrL Ph Scheme 32.

H

10084

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

OH PhB(OH)2 + Et (1.2 equiv.)

Pd(OAc)2 (1 equiv.) additive (0-1 equiv.)

Ph

O +

β' DMSO/AcOH, 50 °C Et without additive: 25% with CuCl2 (1 equiv.): 92% with ZnBr2 (1 equiv.): 100% with LiCl (1 equiv.): 91% with CuCl (1 equiv.): 90% with CuCl (0.5 equiv.): 79%

Ph

OH β

(33)

Et 17% 0% 0% 4% 0% 8%

XPd OH β-H elimination H

Ph Et

β Ph

OH β' Et

β'-H elimination Ph

O Et

MX

XPd H

H Ph

MX

HO

Scheme 33.

The CePd intermediate stemming from the reaction of aryl halides with tertiary allylic alcohols usually evolves via the b-H elimination (Eq. 34 116).117e119 Interestingly, the coupling of 4bromobenzophenone with 2-methylbut-3-en-2-ol catalyzed by the phosphinito complex shown in Scheme 34 provided, as expected, (E)-(4-(3-hydroxy-3-methylbut-1-enyl)phenyl)(phenyl)methanone under heating (path a), whereas both b-H and OH eliminations leading to (E)-(4-(3-methylbuta-1,3-dienyl) phenyl)(phenyl)methanone arose under microwave irradiation (path b).120

Arylation and alkenylation of 2,3-dihydrofuran at the 5-position are followed by the selective elimination of a hydride in the 3-position (Eq. 37),124 but the subsequent migration of the double bond can arise leading to 2-phenyl-2,3-dihydrofuran.124,125 Such a cascade reaction also occurs with 3,4-dihydro-2H-pyran as the substrate.19

4.2. After addition to an allylic ether With an alkoxy (Scheme 5, path b21; Eq. 38 126),59,127,128 benzyloxy (Eq. 20 63),127 aryloxy (Eq. 39 129) or silyloxy (Schemes 5 and

Ph Ph I

Ph

OH Ph

N CO2t-Bu +

OH

Pd(OAc)2 (0.1 equiv.) K2CO3 (2 equiv.)

N CO2t-Bu

(34)

DMF/H2O (1:1), 90 °C, 2 h N Boc

(45 equiv.)

4. Competitions between hydrogen(s) and alkoxy(s), aryloxy, silyloxy or arylsulfonate 4.1. After addition to a vinylic ether The arylation and alkenylation pathways of acyclic vinylic ethers, which produce the CePd intermediate having the alkoxy substituent in the b-position, involve the b-H elimination (Scheme 35,121 Eqs. 35 122 and 36 60).123

N Boc

90%

6, paths b21; Eq. 40 130)59,127,131 substituent in the b0 -position, the CaePd intermediate stemming from an intramolecular reaction usually eliminates a b-hydride, giving an allylic ether as the main product. This contrasts with the elimination of the ester substituent observed by Daves and Cheng under similar conditions (Schemes 5 and 6, paths a).21 As for the arylation of allylic alcohols (Eq. 27), the teams of Cacchi and Norrby reported a strong influence of the experimental conditions on the b-H/b0 H ratio (Eq. 41), the higher selectivity being

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Ph Ph Ph Ph

OH

+

P

H

O

H PhCO

O Ph Ph

Cl Pd P

P Pd Cl

O PhCO

O

P

Ph

(0.01 equiv.)

OH

90 °C 6h

89%

(a)

Ph

AcONa (1.2 equiv.) DMF

Br (1.1 equiv.)

10085

microwave 200 °C, 20 min

(b)

PhCO

94% Scheme 34.

OMe

I + MeO

Pd(OAc)2 (0.01 equiv.) PPh3 (0.02 equiv.) NEt3 (1.1 equiv.) MeO OMe MeCN, 120 °C, 6 h

O +

aq. HCl

O

CH2Cl2 rt, 3 min MeO

(1 equiv.)

55% (overall)

MeO Scheme 35.

OEt OTf +

Pd(OAc)2 (0.03 equiv.) NEt3 (1.5 equiv.)

OEt (5 equiv.) DMSO, 60 °C, 3 h

1 PhB(OH)2 + R

(35) 82%

1) Pd(OAc)2 (0.02 equiv.) dppp (0.03 equiv.) acetone, 70 °C, 15 h OR2 (2 equiv.)

Ph 1

R 2) aq. HCl, rt, 1 h

O

R1 = H, R2 = n-Bu: 89% R1 = Me, R2 = Et: 85%

O PhI +

Pd(OAc)2 (0.05 equiv.) n-Bu4NOAc (2-2.5 equiv.) Ph MS 4 Å

O (37)

DMF, rt, overnight (10 equiv.)

78%

(36)

10086

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

OAc O

Ph(BOH)2 + AcO AcO (1.2 equiv.)

O OAc

OAc O OAc

Ph

OPh

(39)

79%

Pd(OAc)2 (0.05 equiv.) PPh3 (0.1 equiv.) OSiMe2t-Bu K2CO3 (2 equiv.)

Br + Me(CH2)4

OSiMe2t-Bu

(38)

O 71%

Pd(OAc)2 (0.05 equiv.) Cu(OAc)2 (2 equiv.) LiOAc (3 equiv.) OPh Ph DMF, 100 °C, 4 h

PhB(OH)2 + (1.2 equiv.)

OHC (2.5 equiv.)

Pd(OAc)2 (0.1 equiv.) Cu(OAc)2 (2 equiv.) LiOAc (3 equiv.) AcO AcO DMF, 100 °C, 1.5 h

(40)

DMF, 85-90 °C, 72 h OHC OSiMe2t-Bu Me(CH2)4

obtained with n-Bu4NOAc as additive (Procedure A).51 Isotopic labelling studies showed that, under these phosphine-free conditions, the styrenyl compounds are generated from b-H elimination and not from the isomerisation resulting from the b0 -H elimination and the subsequent re-addition of the HPd species.51,61 This led the authors to conclude that the corresponding product distribution is kinetic in origin.51,132 A meticulous DFT investigation performed to clarify the source of the selectivity found that acetate anions can

ArI +

OTHP

Pd(OAc)2 (cat.)

O

OSiMe2t-Bu 78%

influence the selectivity and that the product selectivity does not arise from competing b-hydride eliminations, but rather from a competition between b-elimination and hindered single-bond rotation in the initial carbopalladation product.51 According to their calculations, it seems that the carbopalladation intermediate shows a preference for a bidentate coordination mode with a single acetate ligand, even in the presence of excess acetate.51 In Scheme 36, we have summarised the proposed steps,51 which lead to the

O Pd

R

O

O Pd

n-Bu4NOAc (excess) Ar

OTHP

OTHP 36A

Ar

O

OTHP + HPdOAc

O

O

H H Scheme 36.

OTHP Ar

H

H Ar

36B

O Pd

Pd

OTHP 36C

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

formation of the allyl ether, rather than the enol ether. The hydride elimination requires that the carbopalladation product 36A loses the coordination of the aryl group. The energy for this coordination breaking and rotating to afford the agostic complex 36B is lower than the energy, which would give the agostic complex 36C. Some Pd-catalyzed syntheses of substituted allylic ethers have

OTHP

ArI +

(1.5 equiv.)

Ar = p-IC6H4

olefin at the less-hindered terminal carbon, the resulting alkylpalladium complex will evolve via the b0 -OEt elimination. Efficient exchange required the presence of CuCl2, and the author suggested that the CuCl2 only serves to regenerate PdII. Given the subsequent observations of Lu’s team summarised in Scheme 37, we suspect that the main role of the chloride salts was to favour this exchange reaction.

Procedure A, B or C

(41)

DMF, 90 °C OTHP +

β

OTHP +

Ar

10087

β

Ar Ar β'

Ar

β'

OTHP +

+ OTHP

Ar

OTHP

Procedure A. Pd(OAc)2 (0.03 equiv.), n-Bu4NOAc (2 equiv.), 0.5 h; 100% conversion 73% 6% 6% 4% 11% β/β'-H ratio: 7.9 Procedure B. Pd(OAc)2 (0.03 equiv.), Et3N (3 equiv.), 48 h; 58% conversion 27% traces 12% 17% 2% β/β'-H ratio: 0.9 Procedure C. Pd(OAc)2 (0.03 equiv.), Et3N (2 equiv.), n-Bu4NCl (1 equiv.), 1 h; 78% conversion 50% 1% 8% 17% 2% β/β'-H ratio: 2.0 been carried out in the presence of silver salts (Eqs. 20 63 and 42 54),44 but their role was to regenerate the PdII catalyst, the arylating agent being a benzoic acid,44,63,133 or an arene.54 The elimination of the ether group could be, at least in AcOH, obtained by the addition of LiCl. Indeed, Lu’s team, studying the

PhH + (excess)

Pd(OAc)2 (0.1 equiv.) OPh AgOAc (2 equiv.) Ph DMSO, 110 °C, 12 h

The CaePd intermediate formed from the intramolecular coupling of the hemiketal shown in Eq. 44 has available hydrogens and alkoxy substituents in both the b and b0 positions. Nevertheless, the elimination arose with the OTHP substituent, leading to the spirocyclic compounds with diastereoselectivities

OPh

(42)

43%

reaction of an arylpalladium complex with allyl ethyl ether (Scheme 37), observed that, in AcOH, the addition of a large excess of LiCl favours the b-OEt elimination over the b-H elimination.7,68 This elimination would proceed as assumed for the bOH elimination (Scheme 22). The promotion of the ethoxy elimination by chloride anion seems also apparent for the exchange reaction reported by Wenzel (Eq. 43).134 After Wacker-type addition of t-BuOH to the coordinated

and yields depending on the concentration of both the catalyst and the substrate. This process would involve the syn-elimination of ClPdOTHP, and this latter species could also catalyse the reaction.135 The elimination of the tosylate group in the course of the reaction of allyl tosylate with p-methoxyphenylboronic acid has allowed the formation of the 1,3-diarylated propene (Eq. 45).33e35

H N O AcOH, rt

H N Pd AcO

OEt

69% O 2

+

OEt (20 equiv.)

H N LiCl (10 equiv.) AcOH, rt

O 60%

Scheme 37.

10088

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

PdCl2 (1 equiv.) CuCl (2 equiv.), CuCl2 (4 equiv.) NaCl (2 equiv.) OEt t-BuO MeCN (4 equiv.) (40 equiv.) 7 mol/Pd t-BuOH, N2, 30°C

OH

O

OTHP

O

(43)

O

PdCl2(PhCN)2 (0.02-0.2 eq.) O

(44)

THF, rt, 15-60 min

O

O

O

51-91%

B(OH)2 + MeO

Pd(OAc)2 (0.1 equiv.) n-Bu4NCl (1.5 equiv.) MeO OTs KH2PO4 (2 equiv.)

OMe (45)

DMF, 120 °C, 7 h (2.5 equiv.)

81%

4.3. After addition to acrolein diethyl acetal

4.4. After intramolecular addition

The arylation of acrolein diethyl acetal can lead to mixtures.136,137 Cacchi’s team discovered experimental conditions, which lead to the arylation of the terminal carbon with subsequent selective elimination of either the b-H or the b0 -H (Scheme 38). After hydrolysis, these methods provide either cinnamaldehydes (path a)138 or ethyl 3-arylpropanoates (path b).139 The authors did not propose any explanation. From the different conditions they used to reach selective procedures, it seems that chloride and acetate anions have decisive roles. Thus, a tentative clarification could be based on a subsequent report they published with Norrby’s team, in which DFT calculations on the hydride elimination from PhCH2C(PdX)CH2OMe under phosphine-free conditions indicated that X¼OAc favours the b-H elimination, whereas the b0 -H elimination would be preferred when X¼Cl (Scheme 39).51 We suspect that DFT studies on the transformation of PhCH2C(PdX)CH(OEt)2 could lead to the same indications.

The cyclisation of o-(2-butenyl)phenol occurs via the 5-exo140 or the 6-endo141 pathway, depending on the experimental conditions (Scheme 40).142 The main compound resulting from the exo cyclisation corresponds to a b0 -H elimination, whereas the minor compound would be obtained from either the isomerisation of the main compound62 or the b-H elimination followed by migration of the C]C bond.143 As for the endo cyclisation, the formation of 2-methyl-2Hchromene also corresponds to a b0 -H elimination, but Larock et al. noted that this reaction could involve the h3-allylpalladium chemistry.141,144 The 5-exo cyclisations of allylic N-hydroxymethylcarbamates are also followed by selective b0 -H eliminations (Eq. 46 145).146 In contrast to the above examples, the h1-palladium complexes 41A147 and 42A148 obtained from exo cyclisations evolved via the cleavage of the internal C-alkoxy bond (Scheme 41) or the CeOAr bond (Scheme 42), respectively, although the availability of a syn b0 H. Sinou et al. suspected an ionic pathway, rather than a concerted mechanism, for the cleavage of the C-alkoxy bond.147

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

CO2Me Boc

N

10089

CO2Me

OH Pd(OAc)2 (0.05 equiv.) Boc O2 (1 atm)

N

O (46)

DMSO, 65-70 °C, 2 h 80%

1) Pd(OAc)2 (0.03 equiv.), n-Bu4NOAc (2 equiv.) K2CO3 (1.5 equiv.), KCl (1 equiv.) O Ar DMF, 90 °C, 1.5 h 2) aq. HCl Ar = p-IC6H4: 88% (a) β-H elimination OEt (b) β'-H elimination OEt (3 equiv.) Ar O 1) Pd(OAc)2 (0.03 equiv.) n-Bu4NCl (1 equiv.), n-Bu3N (2 equiv.) OEt DMF, 90 °C, 3 h Ar = p-IC6H4: 91% 2) aq. HCl

ArI +

Scheme 38.

Ph

OMe

β-H elimination

PdX Ph

X = OAc

OMe β

β'-H elimination

Ph

OMe

X = Cl

β'

Scheme 39.

Pd(OAc)2 (0.2 equiv.) Cu(OAc)2.H2O (0.5 equiv.) slow stream of O2 MeOH/H2O (25:2), 55 °C, 1 d

OH Pd(dba)2 (0.05 equiv.) KHCO3 (1.1 equiv.) DMSO/H2O (9:1) air, 60 °C, 3 d

+ O 54%

O traces

O 80% Scheme 40.

TBDMSO O O Br

Pd(OAc)2 (0.05 equiv.) TBDMSO PPh3 (0.1 equiv.) NEt3 (2.5 equiv.) OEt O n-Bu4NHSO4 (1 equiv.) MeCN/H2O (5:1) 80 °C, 1 d Scheme 41.

TBDMSO O

OH OEt PdBr

41A

OEt

O 57%

10090

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

TBDMSO O O Br

TBDMSO

TBDMSO Pd(OAc)2 (0.1 equiv.) OAr PPh3 (0.2 equiv.) O NEt3 (2.5 equiv.)

O

O OAr

n-Bu4NHSO4 (1 equiv.) DMF, 80 °C, 2 d

O

PdBr 55%

Ar = p-(t-Bu)C6H4

42A Scheme 42.

5. Competitions between hydrogen(s) and halide or arylsulfonyl

The coupling of 4-methylbenzenesulfonohydrazide with allylsulfonylbenzene occurred with selective b-H elimination (Eq. 50).153

In AcOH containing LiCl, the rate of the halide elimination is higher than those of the OAc, OR, OH and H eliminations.6,68 Halide ions could coordinate to palladium and, thus, promote the dehalogenation via an E2-like mechanism.7,149 These conditions are, however, not required to obtain the halide elimination, as exemplified in Eqs. 47,150 48 151 and 49.44,152 For the coupling depicted in Eq. 42, we suspect that the silver salt mainly functions as a base.133

6. Competitions between hydrogen(s) and amino derivative

N

LiPdCl3 (1 equiv.)

Cl

PhHgCl +

Ph

MeCN, rt, overnight

MeB(C6F5)3 Me Pd +

1) CD2Cl2, - 78 °C 2) rt, 30 min

OMe CO2H Br

+

+

SO2NHNH2 +

(48)

+

95% 5%

Pd(OAc)2 (0.1 equiv.) Cu2O (0.01 equiv.) Ag2CO3 (3 equiv.)

OMe

(49) PhMe/DMSO (95:5) 110 °C, 2 h

OMe

(1.2 equiv.)

(47) 61%

Cl (103 equiv.) ClCD2Cl

N

The XPdCaeCNR2 intermediates are not prone to elimination of the nitrogen substituent.154 This allowed the efficient amination of styrene in the presence of triethylamine (Eq. 51).155,156 Although the nitro group is an efficient leaving group for TsujieTrost-type reactions,157 the HeckeMatsuda reaction of allylic

88%

OMe

Pd(OAc)2 (0.1 equiv.) O2 (1 atm) SO2Ph DMSO/MeNO2 (1:1) 70 °C, 5 h

SO2Ph (50) 90%

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

O O

PdCl2(MeCN)2 (0.05 equiv.) O CuCl2 (0.05 equiv.) Ph NEt3 (0.1 equiv.) NH + Ph O N O2 (1 atm) (6 equiv.) DME, 60 °C, 24 h 99%

NO2 PhN2BF4 + (3 equiv.)

96% ee

(1.2 equiv.)

NH Ts

NHCbz

N(Boc)2

SO2NHNH2

X

77%

(1.1 equiv.)

+

(53)

CO2H

DMF, 50 °C, 6 h

Pd2(dba)3 (0.02 equiv.) AcONa (3 equiv.)

N2BF4 + MeO

(52)

bond usually arises via the b-H elimination, leading to the allylamine derivative (Eqs. 53,160 54 161 and 55 153).131,162 In contrast, b0 -H eliminations are involved for intramolecular reactions under Stahl’s experimental conditions (Eq. 56 163).164e168

Pd(OAc)2 (0.1 equiv.) P(o-tol)3 (0.2 equiv.) n-Bu4NCl (1 equiv.) CO2H K CO (5 equiv.) 2 3 NHCbz (1.04 equiv.)

(51)

NO2 Pd2(dba)3 (0.05 equiv.) NaOAc (3 equiv.) Ph OCbz OCbz MeCN, rt, 8 d 78% yield, 96% ee

nitro compounds can occur effectively with selective b-H elimination and the complete retention of configuration at the tertiary nitro C atoms, as shown in Eq. 52.158,159 When b-H and b0 -H are available from the CaePd intermediate generated by an intermolecular addition, the C]C

+ OTf

10091

N(Boc)2

MeCN, rt, 3 h

90%

MeO

Pd(OAc)2 (0.1 equiv.) O2 (1 atm) NHTs DMSO/MeNO2 (1:1) 70 °C, 5 h

Pd(OCOCF3)2(DMSO)2 (0.05 equiv.) O2 (4 atm), 3 Å MS

X

PhMe, 60 °C, 24 h

N

Ts X = O (76%), CH2 (92%), NTs (71%)

(54)

NHTs (55) 77%

(56)

10092

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

The exchange reaction shown in Eq. 57, which afforded, in a low yield, but with preservation of the configuration of the chiral centres, a key intermediate of the total synthesis of rhizobitoxine, is an example of the methoxy elimination in the presence of eliminatable hydrogens and N-substituents.169 Both vinylamine and allylamine derivatives can be obtained from the same substrate. Indeed, Filippini and co-workers observed

NHCO2Bn BnO

OH +

7.1. After addition to a vinylic silane In 1982, Hallberg and Westerlund disclosed the Pd-catalyzed reaction of vinyltrimethylsilane with aryl iodides (Eq. 60).176 The styrenes being the main products, the authors assumed that pal-

PdCl2(PhCN)2 (0.5 equiv.) NaH2PO4 (4.5 equiv.) 4 Å MS CO2Bn BnO

MeO

(3.2 equiv.)

NHCO2Bn

N

NHCO2Bn

DME, -20 °C, 21 h

a strong influence of the nature of the solvent on the vinylN/allylN ratio for the reaction of phenyl iodide with 1-(2-methylallyl)piperidine (Scheme 43).170 To explain this solvent effect, these authors assumed that the b-H elimination is favoured when the N atom of the piperidino moiety is coordinated to Pd, and that this chelation is disadvantaged in polar solvents. From a comparison with the results of Eq. 46, which are also obtained in DMF, the chelation efficiency would also be dependent on the nitrogen substituents.

PhI +

7. Competitions between hydrogen(s) and silane

O

CO2Bn

17%

NHCO2Bn

(57)

ladium promotes the cleavage of the vinylic silicon bond, rather than envisaging the b-SiMe3 elimination. The desilylation was also observed by Kikukawa and co-workers, who used arene diazotetrafluoroborates instead of aryl iodides, but they proposed a cleavage mediated by the fluoride ion.177e179 Using deuterated substrates, these authors assumed that both syn- and anti-elimination of Pd0 and SiMe3 can occur, as exemplified in Scheme 45.177 Cis addition of ArPdþ to the (Z)-PhCH]CDSiMe3 affords s-alkyl complexes 45A1 and 45B1. Cis b-H elimination from 45A1 leads to

PdCl2(PPh3)2 (0.01 equiv.) K2CO3 (2 equiv.) solvent, 80 °C, 2 h

XPd N Ph

(3.1 equiv.)

β'

β

X = I or Cl HPdX

Ph

+

N

PhMe: EtOH: DMF:

85% 60% 2%

Ph

N 10% 20% 72%

Scheme 43.

Allylic phthalimides are the main products from the coupling of phthalimide with cyclic alkenes (Eq. 58 171).172,173 Stahl and co-workers assumed a cis-aminopalladation of the cyclic alkene174 followed by a selective syn b0 -H elimination.171,172 The isomeric compounds would arise via Pd-hydride-mediated migration of the double bond.171

O

Pd(OAc)2 (0.1 equiv.) O2 (4 atm)

NH +

p-complex 45A2. Cis-readdition of HPdþ gives 45A3, which suffers anti-elimination mediated by fluoride to deliver (E)-Ar(Ph)C] CHD. As from 45B1, syn-elimination leads to (E)-PhCH] CDAr.177,180

O N

PhCN, 60 °C, 24 h (1.2 equiv.) O A b-N elimination is a key step of a cascade reaction generating benzo[c]phenanthridines (Eq. 59).175 This elimination is caused by the absence of hydride syn to Pd in intermediate 44A obtained from the insertion of the ArPdI species into the C]C bond of the azabicycle (Scheme 44). Consequently, 44A evolves by cleavage of the syn CeN bond to afford 44B and, subsequently, the amide.

75% O

isomeric + products

(58)

8%

For the reaction of p-iodoanisole with the substrates shown in Eq. 61, the teams of Blart and Ricci assumed that the isolated compounds are the result of syn-eliminations of Me3SiPdI (Scheme 46).181 Since Hallberg and Karabelas proposed that the elimination of SiMe3 is promoted by iodide,182 we suspect that this step could rather lead to Me3SiI and Pd0, as suggested in Scheme 47.

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Pd(PPh3)2Cl2 (0.02 equiv.) ZnCl2 (0.5 equiv.) Zn (10 equiv.) NEt3 (0 or 8 equiv.)

BocN I

O

10093

+

O O (59)

CO2Me THF, 60 °C, 12 h

O (1.2 equiv.)

NH 90% O

O L2PdCl2 Zn

HN O

ZnCl2

I

PdLn

O

CO2Me ZnCl2 Zn, L LnIPd

PdILn

MeO2C NBoc

CO2Me

O

BocN

O CO2Me

O 44B

BocN

MeO2C

O

O PdILn

O

44A Scheme 44.

PhI +

Pd(OAc)2 (0.02 equiv.) PPh3 (0.04 equiv.) SiMe3 (2.5 equiv.) DMF, 125 °C, 0.5 h

Ph Ph

+

Ph

60%

The influence of the halide ion on the SiMe3 elimination is exemplified with the use of ArPdOAc instead of ArPdI as the arylating species, this mainly leading to the arylated alkenylsilanes via the syn-elimination of HPdOAc (Scheme 48).183 As shown in Scheme 46, path a, the SiMe3 elimination is subsequent to the elimination/readdition of HPdI. This SiMe3 elimination can be prevented in the presence of silver nitrate (Schemes 49176,182,184 and 50185). This was explained by the silver-mediated abstraction of iodide from the aryl (or alkenyl) palladium iodide leading to a cationic palladium complex, which adds to the vinylsilane.182,185 In agreement with this proposal, the use of alkenyl triflate instead of alkenyl iodide also provided effectively the corresponding 2-alkenylvinylsilane, even in the absence of the silver salt.185,186

SiMe3 + 5-25%

(60) SiMe3 traces

7.2. After addition to an allylic silane187 The Pd-catalyzed addition of phenyl iodide to allyltrimethylsilane mainly occurs to the terminal position. Hallberg’s team demonstrated that the corresponding subsequent elimination is highly dependent on additives and the temperature (Eq. 62).188 At 120  C in MeCN, the elimination from PhCH2CH(PdI)CH2SiMe3 mainly concerned a benzylic hydrogen, slight elimination either of the b0 -H or of the trimethylsilyl group being observed. With the addition of silver nitrate, the intermediate would be the cationic complex PhCH2CHPdþCH2SiMe3, and the b0 -H elimination increased. Under these conditions, the decrease of the temperature to 50  C led selectively to (E)-trimethyl-(3phenylprop-1-enyl)silane, i.e., to the b0 -H elimination as the main reaction pathway, without SiMe3 elimination.189

10094

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

ArN2BF4 SiMe3

BF4

Ar

Ph

Pd

D MeCN, 25 °C

H

Ar

Pd(dba)2 (0.2 equiv.)

N2 ArPd

Ph

Ar = p-NO2C6H4

H

Pd

Ph

Pd

Ar

D

H

Pd SiMe3 D

Ph

D SiMe3

Ph

SiMe3

H 45B1 D

H 45A1 D

SiMe3

Pd Ar

SiMe3 Ph +

H F3B-F Ar

HPd

SiMe3

Ph 45A2 D

Ar

Pd H

Pd0 + Me3SiF + BF3 H

SiMe3 Ar

Ph 45A3 D

D Ph 10%

Ph

F-BF3

Ar

D Ar H 77%

Scheme 45.

ArI + (2 equiv.)

R

Pd(OAc)2 (0.05 equiv.) dppb (0.1 equiv.) R NEt3 (2.5 equiv.) SiMe3

MeCN

R = CH2NHBoc, 80 °C, 16 h: Ar = p-MeOC6H4 R = CH2OCH(Me)OEt, 65 °C, 48 h: R = CH2OMe, 80 °C, 48 h:

Ar + R

(61)

Ar 65% 40% 24%

The influence of the presence of silver oxide on the differentiation between b0 -H and b0 -SiMe3 eliminations has been reported by Tietze’s team for an intramolecular reaction (Scheme 51).190,191 Jeffery proposed procedures, which led to either b-H elimination or b0 -SiMe3 elimination, thanks to the appropriate selection of the base, the additive and the solvent (Scheme 52),192 their respective role on the selectivity remaining rather elusive.193

7.3. After addition to an alkene Recently, Watson’s team disclosed experimental conditions leading efficiently to vinylic and allylic silanes from the coupling of iodotrimethylsilane with styrenes and terminal alkenes, respectively (Eqs. 63 and 64).194 Thus, these reactions involve the selective elimination of a b-H (Eq. 63) or a b0 -H (Eq. 64). The competing formation of the vinylic silane from the two terminal alkenes shown in Eq. 65 was, however, observed,194 indicating, for these substrates, the competition between the b-H and b0 -H eliminations. 8. Competitions between hydrogen(s), alkoxy and ester or hydroxy or arylsulfonyl A number of examples with such potential competition have been presented in a recent review devoted to oxaheterocyclizations.195 Consequently, only a few examples are included in this section.

6.5% 39% 1% The formation of 3-oxopropyl acetate, as the main compound, from allyl acetate under Wenzel conditions (Eq. 66) would arise via the alkoxypalladation leading to 53A, and then a b-H elimination and subsequent attack of the coordinated vinyl ether by traces of water, as depicted in Scheme 53, path a.133,196 The plausible formation of the t-butyl acetal 53B has been suspected as an alternative intermediate (Scheme 53, path b). From 53A, the b0 -OAc elimination is a minor reaction pathway (Scheme 53, path c). A similar b-H elimination rather than b0 -tosyl or b-methoxy would be involved in the cycloacetalisation of 2-tosyl-3-butenols (Scheme 54).197 The exo Wacker-type cyclisation of allylic esters (Eq. 67)198 and alcohols (Eq. 68)199 having a hydroxylated tether occurs with b0 elimination of the heterosubstituent. 9. Competitions between hydrogen(s), aryloxy and acetoxy or trichloroacetimidate We envisaged that the Pd-catalyzed addition of phenol to ethyl 2-(acetoxymethyl)acrylate under neutral conditions could involve a Heck-type reaction (Scheme 55).200 This would imply that the HPdOAc elimination is, for this reaction, preferred to the PdH2 and HPdOPh eliminations. Recently, Overman’s team prepared 2-vinylchromanes, 2vinyl-1,4-benzodioxanes and 2,3-dihydro-2-vinyl-2H-1,4enantioselective benzoxazines via the PdII-catalyzed

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10095

ArPdI R

H Me3Si

ArPdI

R

Me3Si

H (a)

Ar PdI

H Me3Si

R

H

Ar

IPd

R

Me3Si

H

HPdI

H

H

Me3Si Me Si Ar 3

PdI

H

R

H

IPd

R

Ar

H

H H

Me3Si

H

Me3Si Me3Si H

R Ar

H H

H

PdI

Ar

R

Me3SiPdI Ar

Ar

H

R PdI

H

R

Ar R

Me3SiPdI Scheme 46.

I Me3Si

Me3Si

PdI

Pd

+ Me3SiI + Pd0

R R

R

Scheme 47.

PhN(NO)Ac Pd(dba)2 (0.2 equiv.) N2 Ph

PhPdOAc

Ph

SiMe3

Ph

MeCN 40 °C, 2 h

Ph + SiMe3

HPdOAc

SiMe3 + Ph

Ph + Ph

Ph

Ph

69%, 42:33:12:13

0

Pd + AcOH Scheme 48.

Pd(OAc)2 (0.02 equiv.) PPh3 (0.04 equiv.) NEt3 (1.36 equiv.)

Ph

PhI + 60%

DMF, 125 °C, 0.5 h

SiMe3 (2-2.5 equiv.) Scheme 49.

Pd(OAc)2 (0.03 equiv.) PPh3 (0.06 equiv.) AgNO3 (1 equiv.) NEt3 (1.2 equiv.) Ph MeCN, 50 °C, 5 h

74%

SiMe3

10096

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

+ 100 °C 15 h I +

57% conversion: 70%

SiMe3

12%

Pd(OAc)2 (cat.) SiMe3 (3 equiv.)

DMSO AgNO3 (1 equiv.) NEt3 (3 equiv.) 50 °C, 3 h

64%

SiMe3

Scheme 50.

PhI +

SiMe3

Pd(OAc)2 (0.05 equiv.) P(o-tol)3 (0.3 equiv.) AgNO3 (0 or 1 equiv.) NEt3 (1.2 equiv.)

(62)

MeCN Ph

SiMe3 β

+

SiMe3

β

+

Ph

SiMe3 β'

Ph

without AgNO3, 120 °C, 7 h: 60% β/β'-H ratio: 30.5 46% with AgNO3, 120 °C, 3 h: β/β'-H ratio: 1.88 with AgNO3, 50 °C, 48 h: 15% β/β'-H ratio: 0.37

SiMe3 +

Ph

Ph

+

1%

2%

9%

9%

15%

1%

25%

13%

7%

7%

3%

48%

16%

0%

1%

Pd(OAc)2 (0.05 equiv.) PPh3 (0.1 equiv.) Pr4NBr (1 equiv.) KOAc (3 equiv.) DMF, 55 °C, 3 h NCOCF3

Ph +

NCOCF3

81%

(a)

I (b)

Pd2(dba)3 (0.025 equiv.) PPh3 (0.1 equiv.) Ag2O (1 equiv.) DMF, 55 °C, 3 h

SiMe3

NCOCF3 NCOCF3 +

5%

64%

SiMe3

Scheme 51.

intramolecular addition of a phenolic unit to an allylic acetate or trichloroacetimidate (Eq. 69).201 These results imply that the elimination of the acetate and the trichloroacetimidate is, under the used experimental conditions, preferred to that of b-hydrogen, b0 -hydrogen and aryloxy groups. According to deuteriumlabelling and computational experiments, these cyclisations occur through anti-oxypalladation followed by the syn-deoxypalladation (Scheme 56).

10. Competitions between hydrogen(s), amino derivative or trichloroacetimidate and hydroxy or acetate or carbonate or alkoxy or carbamate or halide 10.1. After addition to vinyl acetate or a vinyl ether The Pd-catalyzed reactions of nitrogen nucleophiles with vinyl acetate (Eqs. 70 202 and 71 203) or vinyl ethers (Eq. 72 204) lead to the

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10097

Pd(dba)2 (0.03 equiv.) Ph SiMe3 Ph DABCO (2.5 equiv.) SiMe3 + Ph + n-Bu4NCl (1 equiv.) β 79% 8% β' MeCN, rt, 19 h β/β'-H ratio: 9.88 (a) SiMe3 PhI + (b) (1.75-5 equiv.) Pd(dba)2 (0.03 equiv.) Ph PPh3 (0.09 equiv.) 95% n-Bu4NOAc (2.5 equiv.) MS 4 Å, DMF, 50 °C, 24 h

12%

Scheme 52.

Me3SiI + (2 equiv.)

(COD)Pd(CH2SiMe3)2 (0.05 equiv.) R t-BuPPh2 (0.105 equiv.) Me3Si NEt3 (2.2 equiv.)

R (63)

PhMe, 50 °C, 24 h

R = H (95%), m-OMe (97%), p-OMe (96%), p-F (83%), p-Cl (96%), p-Ac (84%), p-CO2Et (81%)

Me3SiI + (2 equiv.)

(COD)Pd(CH2SiMe3)2 (0.025 equiv.) t-BuPPh2 (0.053 equiv.) NEt3 (2.2 equiv.) Me3Si R

R

(64)

PhCF3, rt, 24 h

R = Ph (57%), Bn (64%), p-MeOC6H4 (67%), (CH2)6Me (60%), SiMe3 (49%)

Me3SiI + (2 equiv.)

AcO

(COD)Pd(CH2SiMe3)2 (0.025 equiv.) t-BuPPh2 (0.053 equiv.) NEt3 (2.2 equiv.) Me3Si R PhCF3, rt, 24 h

PdCl2 (0.025 equiv.) RCN (0.1 equiv.) CuCl (0.05 equiv.) AcO NaCl (0.05 equiv.) O2 (40 psi), t-BuOH, 1 h R = Me, 50 °C: R = p-NO2C6H4, 60 °C:

R + Me3Si

R

(65)

R = (CH2)2OPiv: 58%, 90:10 R = CH(OTBS)Ph: 78%, 68:32

O CHO + AcO 48% 55%

Ot-Bu

+

8% 18%

5% 0%

(66)

10098

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

HPdCl AcO

Ot-Bu

PdCl

PdCl2 AcO

AcO t-BuOH

β'

AcO 53B AcOPdCl

Ot-Bu

CHO

H2O Ot-Bu

β

53A

HCl

AcO

t-BuOH

(b)

(a)

H2O

(c)

Ot-Bu Ot-Bu

Scheme 53.

PdCl2 + MeOH

Ts

Ts

HCl

PdCl

Ts

HPdCl

β' β

R

R

OH

OMe

OH

R

OH

H+ or PdII PdCl2 (0.5 equiv.) CuCl2 (3 equiv.) MeC(OEt)3 (0.4 equiv.) Me2NCONMe2 (5 equiv.) MeOH, reflux, 5 h

OMe HPdCl

Ts

Ts

OMe R

O R = (CH2)2Ph (95%), Ph (69%), CH2i-Pr (81%), Me (69%)

R

OMe

O

HPdCl

PdCl

H

Scheme 54.

TBSO C12H25

TBSO

TBSO PdCl2(MeCN)2 (0.1 equiv.) OH

DME, rt, 12 h

C12H25

O

OH

CH2OBz

( )n

O

CH2OBz

PdCl2(MeCN)2 (0.1 equiv.) THF, 0 °C, 15 min

(67) O

R = t-Bu: 23%, 81:19 R = Ph: 29%, 83:17 R = biphenyl: 99%, 90:10

OCOR

HO

+ C12H25

( )n n = 0: 87%, 95% e.e. n = 1: 92%, 98% e.e.

(68)

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10099

PhOH

OAc

Pd(dba)2 (0.05 equiv.) dppe (0.05 equiv.) OAc PhOPdH

O OEt

O

O

HPdOAc

OEt

OEt HPd

THF, rt, 29 h

52% OPh

OPh Scheme 55.

2

Pd

OAc i-Pr N R or S

Ph

2

R

O Ph (0.005-0.05 equiv.) R2 Ph

Co

OH Ph OR1

Z Z = CH2, O, S R1 = Ac, C=NH(CCl3)

O R or S

solvent, 23-60 °C

(69)

Z up to 98% yield and 98% ee

R OH

Y

R L*PdIIOAc

HOAc

O

Z

H

PdL*

D

O

H D Y = NH and R = CCl3 or Y = O and R = Me

Z

O Z

O

Y

D

L*Pd

II

L*Pd OCR=Y

O

H

Y

R O

D H Z Scheme 56.

formation of CeN bonds and to the elimination of the acetate or ether unit. According to Xu and co-workers, the N-vinylation of arylsulfonamides and acylamides with vinyl acetate (Eq. 71) occurs via the formation, mediated by potassium carbonate, of a PdeN bond (Scheme 57). Subsequent aminopalladation of the substrate is followed by b-OAc elimination.203 For the formation of enamides from butyl vinyl ether catalyzed with (4,7-diphenyl-1,10-phenanthroline)palladium(II) trifluoroacetate complex (Eq. 72), Stahl and co-workers suggested

O

a mechanism (Scheme 58),204 which differs from Xu’s proposal (Scheme 57). According to Stahl’s team, coordination of the olefin to palladium would afford the cationic complex 58A, which suffers addition of the nitrogen nucleophile leading to the h1 complex 58B and trifluoroacetic acid. The latter would remove the butyloxy group of 58B giving n-butanol and 58C, liberation of enamide from 58C regenerating the catalyst. According to this mechanism, there is no concomitant elimination of palladium and the leaving group; this contrasts with most mechanisms suggested for the formation of the C]C bonds.

O Na2PdCl4 (0.009 equiv.)

NH +

OAc (2.5 equiv.)

reflux, 20 h

N 85%

(70)

10100

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Pd(OAc)2 (0.01 equiv.) Ii-Pr (0.02 equiv.) K2CO3 (1 equiv.) OAc R1R2N air, rt, 12 h R1 = Ph, R2 = Ts: 92% R1 = PhCO, R2 = H: 36%

R1NHR2 +

R1NHR2 +

(71)

(dpp)Pd(OCOCF3)2 (0.05 equiv.) R1R2N On-Bu air, 75 °C (10 equiv.) R1 = Me, R2 = Ts, 2 h: 64% R1-R2 = (CH2)3C=O, 3 h: 89% R1-R2 = (CH2)2OC=O, 1.3 h: 91%

L2Pd(OAc)2

NR1R2

(72)

R1NHR2 + K2CO3

KHCO3 + KOAc

AcO

L2 Pd

NR1R2 OAc OAc

L2Pd

NR1R2

OAc Scheme 57.

10.2. After addition to an allylic alcohol This section, which concerns the PdII-catalyzed addition of nitrogen nucleophiles to allylic alcohols, is limited to intramolecular

couplings. Indeed, the corresponding intermolecular additions seem to only involve h3-allylpalladium intermediates formed thanks to the participation of additives,75,205 whereas the intramolecular additions can provide h1-alkylpalladium intermediates.75

L2Pd(OCOCF3)2

On-Bu

1 2

NR R

L2Pd

L2Pd NR1R2

CF3CO2

CF3CO2

On-Bu

CF3CO2 58A

58C

n-BuOH

CF3CO2H

OCOCF3

R1NHR2

L2Pd R1R2N

On-Bu 58B

Scheme 58.

CF3CO2H

CF3CO2

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

According to various examples collected in a previous review75 and new reports, the exo cyclisations of allylic alcohols substituted at C2 by a tether bearing a nitrogen nucleophile lead to the elimination of the hydroxyl group (Eqs. 73,206 74 207 and 75 116 199,208 ).

10.3. After addition to an allylic alcohol derivative or an allylic halide In 1997, Hirai’s team disclosed the PdCl2(MeCN)2-catalyzed intramolecular N-addition of oxazolidin-2-one to an allylic ether,

CO2Me PdCl2(PhCN)2 (0.15 equiv.)

HO

NHBoc

OBn

10101

CO2Me

N

THF, rt, 12 h 77%

(73)

Boc

OBn OBn

THF, rt, 3 h

NH Boc

OBn

PdCl2(MeCN)2 (0.1 equiv.)

(74) N Boc 90%

OH

OH Boc

Boc CO2t-Bu N

HN CO2t-Bu PdCl2(MeCN)2 (0.1 equiv.)

(75)

MeCN, 90 °C, 24 h

N Boc

76%, cis/trans = 5:1

The five-membered nitrogen heterocycles shown in Eqs. 76,209 77 210 and 78 210 are formed from 5-endo-trig cyclisations and, mainly, elimination of the hydroxyl group, the minor compounds resulting from the b-H or b0 -H elimination (Scheme 59). These results agree with the syn-eliminations of HOPdCl and HPdCl.

N Boc which occurred with elimination of the ether group (Eq. 79).211 A few years later, Lu and co-workers reported that PdCl2(PhCN)2 did not catalyze the intramolecular reaction of an N-tosylcarbamate with an allylic tosylcarbamate, the reaction becoming efficient in the presence of LiCl; the best procedure was with a catalytic

OH ArCH2O HN

PdCl2(MeCN)2 (0.3 equiv.) ArCH2O THF, 20 °C, 1.5 h

(76) N

67%, 97% ee CO2Bn

Ar = p-MeOC6H4 CO2Bn

O

OH PdCl2(MeCN)2 (0.2 equiv.) R

HN

THF, rt, 21-22 h R

Ts R = H: R = Me:

N Ts 55% 77%

+ R

+ N Ts 22% 5%

R

(77) N Ts 4%

10102

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

OH PdCl2(MeCN)2 (0.1 equiv.) THF, rt, 1.5 h

HN

+

(78) N

N 83%

Ts

Ts

Ts

ClPd

OH ClPdOH

OH

OH

β'

β

HCl

7%

N

N

R

R

OH

PdCl2 Cl2Pd HN

HN

ClPd

R

R

OH

H PdCl

β'

β

HCl

N

β

-H2O

N

R

R

OH

O

N Hβ'PdCl

Ts

N

N

R

R

Scheme 59.

amount of Pd(OAc)2 and an excess of lithium bromide or chloride (Eq. 80).212 These conditions were also effective for the intramolecular addition to an allylic acetate, carbonate or chloride (Eq. 80).212 The selective OAc elimination also occurred for the 6-exo cyclisation occurring by addition of a tosylamide (Eq. 81).213 For this last reaction, Poli’s team demonstrated the irreversibility of the nucleophilic addition under the Pd(OAc)2/LiCl conditions.213

11. Competitions between hydrogen(s), acetoxy and alkyl groups From their study of the Pd-catalyzed intramolecular reaction of dimethyl [40 -acetoxy-20 -bromo-(20 Z)-butenyl]-2-propenylmalonate, Steinig and de Meijere showed that b-H, b-OAc and b-C eliminations were competitive reaction pathways (Scheme 61), the

PhOCO

PhOCO H

PdCl2(MeCN)2 (0.2 equiv.) NH

OMOM

H

O

O

O

NH

77%

O

O

O

(79)

N

THF, rt, 2 h

Pd(OAc)2 (0.05 equiv.) LiBr (4 equiv.) Z O THF, rt, 10 min

O (80)

N

Ts Ts Z = OCONHTs (97%), OAc (95%), OCO2Me (78%), Cl (96%) Intermolecular enantioselective additions of organic acids214,215 and phenols216,217 to allylic trichloroacetimidates have been disclosed by Overman’s team using chiral complexes such as that shown in Scheme 60.214,216 The mechanism of the formation of allylic esters has been particularly studied. According to a variety of experiments and DFT computational studies, their liberation from the Pd intermediates occurs via a syn-deoxypalladation pathway.218

ratio between them depending on the reaction conditions.219 5exo-trig Cyclization provides 61A, which evolves via either the b-H elimination giving the 1-acetoxymethyl-1,3-diene derivative, or the 3-exo-trig cyclisation leading to 61B. b-OAc elimination from 61B affords a bicyclic vinylcyclopropane, whereas a b-C elimination leads to 61C, which suffers the b-H elimination, liberating the cyclohexene derivative.

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

Bn O

10103

Bn

N

Pd(OAc)2 (0.2 equiv.) O LiCl (5 equiv.)

N (81)

OAc DMF, 80 °C, 4 h

NH Ts

N

98%, cis/trans = 85:15 Ts OAc 2

Pd

n-Pr 88%, 94% ee

OAc i-Pr N R or S

O n-Pr

NH

O Ph (0.01 equiv.)

Co

Ph

AcOH (3 equiv.) 23 °C, 17 h

Ph

Ph

CCl3

OPh

CH2Cl2 PhOH (3 equiv.) 38 °C, 36 h

n-Pr 86%, 92% ee

Scheme 60.

H E

Pd0

Br

E

PdBr β-H elimination

E

E

E

OAc

E

61A

E = CO2Me

H

H E

E

E

E

OAc

OAc

β-OAc elimination E PdBr

E

61B

BrPd

OAc

OAc β-C elimination PdBr β-H elimination

E

E E

E 61C

OAc

OAc Scheme 61.

12. Competitions between hydrogens The competition can arise between b-H and b0 -H, even in the presence of a b0 -heteroatom, as depicted in Scheme 62. Thus, the Cheteroatom bond can be preserved. This is exemplified in various above examples, especially with the arylation of acyclic substrates (Scheme 62, Nu¼Ar), the HPdX elimination giving the styrenyl derivative (Eqs. 8, 12, 15e19, 21, 28, 39e42, 50, 54, 55 and 62, Schemes 13, 14, 18, 19, 37, 43 and 52) or the allylic derivative (Eqs. 41 and 62,

Schemes 43 and 52), which evolves to the carbonyl compound when Z¼OH (21, 22 and 27e33, Schemes 27, 28, 30 and 38). Recently, the selective b-H elimination was observed in the course of the mono- and di-phenylation of 9-allyl-9H-purine (Eq. 82).220 In contrast, the phenylation of 1-alkenes yielded a mixture of arylated compounds (Eqs. 83 131 and 84 59,221).222 Besides the competitive hydride eliminations, there is the problem of the migration of the C]C bond due to either the readdition/elimination of HPdII species61 or the subsequent Pd

10104

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

PhI +

Pd(OAc)2 (0.05 equiv.) PPh3 (0.1 equiv.) N NaOAc (3 equiv.)

N

N N

OMe

OMe

OMe

N

or

N

N

DMF, 100 °C,, 8 h

N

N

N

N

N

Ph using 1.2 equiv. of PhI: using 3 equiv. of PhI:

(82)

Ph

Ph

88% 78%

O

O Ph

S Ph (0.1 equiv.) Pd(OAc)2 benzoquinone (2 equiv.) AcOH (4 equiv.)

C8H17

PhB(OH)2 + (1.5 equiv.)

(83)

dioxane, rt, 4 h Ph C8H17 Ph +

Ph

C8H17

C8H17

+

68%, 4:4:1; β/β'-H ratio: 1

O S Ph (0.1 equiv.) Pd(OAc)2 benzoquinone (2 equiv.) AcOH (4 equiv.) O

Ph

n-Pr

PhB(OH)2 + (1.5 equiv.)

(84)

dioxane, rt or 45 °c, 4 h Ph Ph

n-Pr β

+

Ph

β'

n-Pr

n-Pr

+

at rt: 78%, 10:7:1; β/β'-H ratio: 1.4 at 45°C: 75%, 8:1:1; β/β'-H ratio: 8

PdX α

H β Nu

β-H elimination H β'

Z

Nu

Z β'

(a) (b) β'-H elimination

Nu

Z

Z = OH

Nu

O

β

Z = leaving group

Scheme 62.

catalysis.62,223 Consequently, mixtures can be obtained, as observed for the couplings shown in Eqs. 58 171 and 85 224 and Scheme 63.225 The plausible C]C migration can lead to uncertainty in the initial hydride elimination. This is the case in Eqs. 41,51 62,188 65,194 83,131 84 59,221 and 86,41 and Schemes 43 170 and 52,192 where the reactions involve either both b-H and b0 -H eliminations, or b-H elimination and subsequent C]C migration. For the

phenylation of 3-methylhex-1-ene (Eq. 84), the dependence of the 1-phenyl-3-methylhex-1-ene/1-phenyl-3-methylhex-2-ene ratio on the temperature leads us to suspect the migration of the C]C bond. In contrast, the results depicted in Eqs. 19,60 87 60 and 88 226 clearly imply the C]C migration, since the H-elimination from the CaePd intermediate can only deliver the terminal double bond. The HeckeMatsuda reaction leading to 1-phenylcyclohexene

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

O O

CO2Me

O Pd(OAc)2 (0.1 equiv.) DMSO (5 equiv.) O2 (1 atm) O

10105

O +

PhMe, 45 °C, 84 h

O

(85)

conversion: 86%, yield: 51%, exo/endo = 2:1 Ot-Bu

Ot-Bu

Pd(OAc)2 (0.05 equiv.) n-Bu 4NCl (1 equiv.) I KOAc (3 equiv.) DMF, 90 °C, 43 h

+

H

H

44%

(2 equiv.)

45%

Ot-Bu Ot-Bu Br

H

Ph (2.40 equiv.)

Ot-Bu

+

Pd(OAc)2 (0.1 equiv.) PPh3 (0.22 equiv.) Ag3PO4 (2.45 equiv.) Ph DMF, 110 °C, 60 h conversion: 50%

H 39%

Ph

4%

Scheme 63.

under the experimental conditions of Eq. 89 227 likely involved also a C]C migration, because the CaePd intermediate has a syn hydride only in the b0 position. The C]C migration was, however, not observed for the HeckeMatsuda coupling depicted in Eq. 90, which also occurs from an intermolecular reaction with a cyclic alkene.228 In contrast, isomerised and non-isomerised coupling products were obtained from the reaction of 2,3-dihydrofuran with phenyl triflate shown in Eq. 91, the isomeric selectivity depending on the base.229 The 6-endo cyclisation depicted in Scheme 64, path a, involves, apparently, the selective b-H elimination;230 nevertheless, b0 -H elimination followed by migration of the C]C bond leading to the thermodynamic compound could also occur.61,223 In fact, the b0 -H

Ph OAc PhI +

elimination arose when the starting C]C bond was not terminal (Scheme 64, path b). b0 -H elimination occurred for the 6-exo cyclisation shown in Eq. 92,225 probably because of the anti relationship between Pd and b-H at the level of the h1-palladium intermediate. For the oxidative Heck arylations affording CaePd intermediates having a b-H, a b0 -H, a b-Ar and a b0 -carbonyl group, White’s team reported, in 2008, experimental conditions, which mainly gave the corresponding conjugated ketone or ester via, apparently, the b0 -H elimination (Eq. 93).131 As shown from the arylation of methyl but3-enoate, the selectivity was, however, greatly dependent on the substitution of the aryl group. Two years later, Sigman and Werner discovered that the b-H/ b0 -H selectivity of oxidative Heck arylations depends on the

OAc

Pd(OAc)2 (0.05 equiv.) AgOAc (0.6 equiv.)

Ph

OAc

+

air, PhMe, reflux

(86)

65%, 12:88

PhB(OH)2 +

OEt (2 equiv.)

Pd(OAc)2 (0.02 equiv.) dppp (0.03 equiv.)

Ph

Ph OEt +

acetone, 70 °C, 20 h

<5%

OEt 76%

(87)

10106

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

OTBS MeO

OTBS

PdCl2(MeCN)2 (0.2 equiv.) MeO LiCl (10 equiv.) benzoquinone (1.5 equiv.)

N NH

N (88) N

K2CO3 (3 equiv.) THF, 25 °C, 105 mn

100%

Pd(OAc)2 (0.005 equiv.) HO Ph Cl Bn

N

N (0.1 equiv.) (89)

PhN2BF4 +

EtOH, 36 °C, 3 h

Ph

(2 equiv.)

F3C

N2BF4 + (2 equiv.)

82%

Pd(OCOCF3)2 (0.1 equiv.) O O (0.2 equiv.) N N PhCH2 CH2Ph

CO2Me

CO2Me 2,6-di-(t-butyl)-4-methylpyridine (1 equiv.) CO2Me MeOH, 60 °C, 20 min

F3C

CO2Me

(90)

83%, 84% ee

O Pd2(dba)3 (0.015 equiv.) base (3 equiv.) PhOTf + (5.1 equiv.)

O

PPh2 PPh2 O (0.06 equiv.)

dioxane, 100 °C, 7 d

with EtN(i-Pr)2 as base: with 1,8-bis(dimethylamino)naphthalene as base: catalyst (Eq. 94).231 They also observed the influence of the substitution of the arylboronic ester (Eq. 95, Procedure A); the unusual Hammett correlation (i.e., break of linearity) between their electronic nature and the selectivity of the arylation of methyl but-3-enoate suggested a change in the reaction mechanism.231 From their results and preliminary mechanistic studies, the

Ph

+ O

90%, 77% ee 66%, 79% ee

Ph

+ O 1% 2%

Ph

(91) O

10%, 40% ee 33%, 44% ee

authors recently suspected that the electrophilic nature of the catalyst could allow for predictable determination of which CeH bond is cleaved.232 Subsequently, these authors observed that the b-H/b0 -H selectivity of the HeckeMatsuda arylation depended not only on the electronic properties of the arylating agent (Eq. 95, Procedure B),

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

10107

OMe

Ph Ph N

MeO OMe

Ph

N

MeO

Pd(OAc)2 (0.25-0.45 equiv.) P(o-tol)3 (0.43 equiv.) (a) R = H NEt3 (10 equiv.) Ph (b) MeCN, 100 °C, 15 h

96%

OMe

Ph

R = Me

Br

Ph N

MeO

R

94% Scheme 64.

Ot-Bu

o-tol P o-tol

Ot-Bu

PdOAc (0.02 equiv.) 2

H Br

n-Bu4NOAc (2.5 equiv.)

H (92)

H

DMF/MeCN/H2O (1:1:0.2) MeO 115 °C, 4.5 h

99%

MeO

O

O

Ph

ArB(OH)2 + (1.5 equiv.)

S Ph (0.1 equiv.) Pd(OAc)2 O benzoquinone (2 equiv.) AcOH (4 equiv.) Ar R dioxane β

O

O R

+ Ar β'

R

(93)

R = CH(NHBoc)Bn, Ar = Ph, 45 °C, 48 h: 62%, β/β'-H ratio: <0.05 R = OEt, Ar = 2-BrC6H4, rt, 4 h: 50%, β/β'-H ratio: 0.056 R = OMe, Ar = 2,5-F2C6H3, rt, 4 h: 51%, β/β'-H ratio: 0.058 R = OMe, Ar = Ph, rt, 4 h: unknown yield, β/β'-H ratio: 0.25

but also on the nature of the solvent (Eq. 96).66 According to the results shown in Eq. 95, the procedure also influences the selectivity towards the styrenyl or the aryl allyl compound. Under experimental conditions used for the synthesis of lactams,233 the intramolecular reaction of a-bromovinylsulfonamides derived from allylic amides generated a mixture of 5exo and 6-endo cyclisation compounds.234 Use of silver and thallium salts as additives favoured the 5-exo process, the

elimination only occurring with an exocyclic hydrogen; some migration of the C]C bonds can arise, but this was prevented with TlOAc (Eq. 97). Stahl and co-workers studied the mechanism of the cyclisation of N-(hex-4-enyl)-4-methylbenzenesulfonamide.166 From various isotopic labelling studies, including those depicted in Eqs. 98 and 99, they demonstrated the absence of the crossover product and the reversibility of the hydride elimination reaction.

10108

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

O Ph

PdLnX2 (0.06 equiv.) CuX2 (0.06 equiv.) O2 (balloon)

O +

B

OMe

O (3 equiv.)

(94)

DMA, 40 °C, 22 h O

i-Pr

i-Pr

Ph

Ii-Pr: N

N

i-Pr

i-Pr

O arylating agent +

O OMe

Pd(OAc)2, Cu(OAc)2: Pd(OAc)2, Cu(OTf)2: Pd(MeCN)2(OTf)2, Cu(OTf)2: Pd(Ii-Pr)(Cl)2, Cu(OTf)2: Pd(Ii-Pr)(OTs)2, Cu(OTf)2: White's conditions (Eq. 93):

Procedure A or B OMe DMA

R

+ Ph

OMe

35%, 6.2:1 56%, 2.0:1 99%, 3.4:1 61%, 4.4:1 96%, 9.8:1 1.2:1

R

O

O (95)

+ OMe

OMe

β β' (3 equiv.), Pd(Ii-Pr)(OTs)2 (0.06 equiv.), Cu(OTf)2 (0.06 equiv.), 40 °C, 22 h β/β'-H ratio: R = H (0.34), OMe (1.14), CO2Me (0.93), F (1.45) O Procedure B. ArN2BF4 (1.1 equiv.), Pd2(dba)3 (0.03 equiv.), rt, 20 min. β/β'-H ratio: R = H (6.03), OMe (7.87), CO2Me (7.69), F (6.12) O

Procedure A. Ar

B

O PhN2BF4 + (1.1 equiv.)

Pd2(dba)3 (0.03 equiv.) (96)

OMe solvent, rt, 15 min O Ph

O OMe

+ Ph

OMe

in DMA: 99%, 10.7:1 in MeCN: 15%, 0.3:1 in MeOH: 20%, 0.2:1

O2S

Bn N

Bn N O2S

Bn N +

O2S

Bn N + O2S

+

6-endo cyclisation compounds

Br

Pd(OAc)2 (0.05 equiv.), P(o-tol)3 (0.11 equiv.), n-Bu4NCl (2 equiv.), Na2CO3 (2 equiv), MeCN, reflux, 1 h: 10% 5% 10% 50% Pd(OAc)2 (0.1 equiv.), P(o-tol)3 (0.11 equiv.), Ag3PO4 (2 equiv), MeCN, reflux, 29 h: 58% 10% Pd(OAc)2 (0.1 equiv.), P(o-tol)3 (0.11 equiv.), Tl2CO3 (2 equiv), MeCN, reflux, 14 h: 52% 5% Pd(OAc)2 (0.1 equiv.), P(o-tol)3 (0.11 equiv.), TlOAc (2 equiv), MeCN, reflux, 2.5 h: 73%

(97)

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

NHTs

10109

CH3/CD3 Pd(OAc)2 (0.02 equiv.) pyridine (0.08 equiv.) O2 (1 atm), PhMe, 80 °C

(98)

kH/kD = 1.20 ± 0.05 C2H3 + N Ts

C2H2D +

C2HD2 +

N Ts

C2D3

N Ts

N Ts

54:0:38:8

Pd(OAc)2 (0.02 equiv.) pyridine (0.08 equiv.) CH2D O2 (1 atm) NHTs

PhMe, 80 °C

H/D N Ts

+ H D

N Ts 43:43:14

13. Conclusions As exemplified from the various examples gathered in this review, the formation of C]C bonds from alkylpalladium complexes can involve complicated chemo- and regioselectivities. Indeed, the elimination reaction depends on various factors, especially the nature of the leaving group and the ligands. Thus, additives such as silver or thallium salts, halide ions and nitrogen compounds, as well as the solvent and the nature, cationic or neutral, of the palladium intermediates may have a determining effect on the selectivity. Nevertheless, the amount of reported studies now allows, according to the experimental conditions, a relatively good anticipation of the main elimination pathway and, hence, the extensive applications of the corresponding catalytic palladium procedures in organic synthesis. References and notes 1. The MizorokieHeck Reaction; Oestreich, M., Ed.; Wiley: Chichester, UK, 2009. 2. (a) Davies, S. G. Organotransition Metal Chemistry: Applications to Organic Synthesis; Pergamon: Oxford, UK, 1982; (b) Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic Molecules; University Science Books: Mill Valley, 1994; (c) Campagne, J. M.; Prim, D. Les complexes du palladium en synth ese organique; CNRS Editions: Paris, 2001. 3. Zeni, G.; Larock, R. C. Chem. Rev. 2004, 104, 2285e2309. 4. Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, UK, 2004; 15. 5. Zhao, H.; Ariafard, A.; Lin, Z. Organometallics 2006, 25, 812e819. 6. Zhu, G.; Lu, X. Organometallics 1995, 14, 4899e4904. 7. Zhang, Z.; Lu, X.; Xu, Z.; Zhang, Q.; Han, X. Organometallics 2001, 20, 3724e3728. 8. These reactions occur via the isomerisation of the h3-allylpalladium intermediate into the corresponding h1-allylpalladium complex and subsequent b-H elimination; for reviews, see: (a) Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, UK, 2004; 494e499; (b) Muzart, J. Eur. J. Org. Chem. 2011, 4717e4741 For reports concerning syn and anti hydride eliminations via such reactions, see: (c) Takahashi, T.; Nakagawa, N.; Minoshima, T.; Yamada, H.; Tsuji, J. Tetrahedron Lett. 1990, 31, 4333e4336; (d) Takacs, J. M.; Lawson, E. C.; Clement, F. J. Am. Chem. Soc. 1997, 119, 5956e5957; (e) Andersson, P. G.; Schab, S. Organometallics 1995, 14, 1e2; (f) Schwarz, I.; Braun, M. Chem.dEur. J. 1999, 5, 2300e2305. 9. For a review, see: Muzart, J. Eur. J. Org. Chem. 2010, 3779e3790. 10. For reviews of these reactions with b-H eliminations, see: (a) Tsuji, J. Tetrahedron 1986, 42, 4361e4401; (b) Tsuji, J.; Minami, I. Acc. Chem. Res. 1987, 20, 140e145; (c) Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, UK, 2004; 500e506.

H/D

H/D + D H

N Ts

H

(99)

H

11. For the synthesis of a-methylene ketones via cascade reactions involving a b-ester, b-OH or b-OMe elimination as the last step, see: (a) Tsuji, J.; Nisar, M.; Minami, I. Tetrahedron Lett. 1986, 27, 2483e2486; (b) Tsuji, J.; Nisar, M.; Minami, I. Chem. Lett. 1987, 23e24. 12. Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5535e5542. 13. For the formation of a five-membered palladacycle from the chelation of an acetate group to palladium, see: Williams, B. S.; Leatherman, M. D.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2005, 127, 5132e5146. 14. Kasahara, A.; Izumi, T.; Fukuda, N. Bull. Chem. Soc. Jpn. 1977, 50, 551e552. 15. Lautens, M.; Tayama, E.; Herse, C. J. Am. Chem. Soc. 2005, 127, 72e73. 16. Muzart, J. J. Mol. Catal. A: Chem. 2009, 308, 15e24. 17. Kikuwa, K.; Naritomi, M.; He, G.-X.; Wada, F.; Matsuda, T. J. Org. Chem. 1985, 50, 299e301. 18. Choudary, B. M.; Ravichandra Sarma, M. Tetrahedron Lett. 1990, 31, 1495e1496. 19. Arai, I.; Daves, G. D., Jr. J. Org. Chem. 1979, 44, 21e23. 20. Pan, D.; Jiao, N. Synlett 2010, 1577e1588. 21. Cheng, J. C. Y.; Daves, G. D., Jr. Organometallics 1986, 5, 1753e1755. 22. Daves, G. D., Jr. Acc. Chem. Res. 1990, 23, 201e206. , M. R. Organometallics 23. Munro-Leighton, C.; Adduci, L. L.; Becker, J. J.; Gagne 2011, 30, 2646e2649. 24. Mariampillai, B.; Herse, C.; Lautens, M. Org. Lett. 2005, 7, 4745e4747. 25. Liu, Y.; Yao, B.; Deng, C. L.; Tang, R. Y.; Zhang, X. G.; Li, J. H. Org. Lett. 2011, 13, 1126e1129. 26. (a) Dieck, H. A.; Heck, R. F. J. Org. Chem. 1975, 40, 1083e1090; (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457e2483. ~ as, M.; Pe rez, M.; Pleixats, R. J. Org. Chem. 1996, 61, 2346e2351. 27. Moreno-Man 28. Ramnauth, J.; Poulin, O.; Rakhit, S.; Maddaford, S. P. Org. Lett. 2001, 3, 2013e2015. 29. Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009e3066. 30. Ohmiya, H.; Makida, Y.; Tanaka, T.; Sawamura, M. J. Am. Chem. Soc. 2008, 130, 17276e17277. 31. Ohmiya, H.; Makida, Y.; Li, D.; Tanabe, M.; Sawamura, M. J. Am. Chem. Soc. 2010, 132, 879e889. 32. Makida, Y.; Ohmiya, H.; Sawamura, M. Chem. Asian J. 2011, 6, 410e414. 33. Yao, B.; Liu, Y.; Wang, M. K.; Li, J. H.; Tang, R. Y.; Zhang, X. G.; Deng, C. L. Adv. Synth. Catal. 2012, 354, 1069e1076. 34. Li, Deng and co-workers assumed the formation of the arylating palladium complex from the insertion of Pd0 species into the AreB bond,33 instead of the usually admitted BIII/PdII transmetalation when Pd(OAc)2 is the catalyst.26,27 For the study of the reaction of arylboronic acids with Pd0 complexes, see Ref. 27 35. According to the authors,33 the second arylation would involve an allylpalladium intermediate 36. Zhang, Q.; Lu, X.; Han, X. J. Org. Chem. 2001, 66, 7676e7684. 37. Henry, P. M. Acc. Chem. Res. 1973, 6, 16e24. nin, F.; Muzart, J. Organometallics 2001, 20, 1683e1686. 38. Aït-Mohand, S.; He 39. Zhang, Q.; Xu, W.; Lu, X. J. Org. Chem. 2005, 70, 1505e1507. 40. Zhang, Q.; Lu, X. J. Am. Chem. Soc. 2000, 122, 7604e7605. 41. Pan, D.; Chen, A.; Su, Y.; Zhou, W.; Li, S.; Jia, W.; Xiao, J.; Liu, Q.; Zhang, L.; Jiao, N. Angew. Chem., Int. Ed. 2008, 47, 4729e4732. 42. Chen, W.; Xu, M.; Bo, D. L.; Jiao, N. Chin. J. Org. Chem. 2010, 30, 469e473.

10110

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113

43. Evdokimov, N. M.; Kornienko, A.; Magedov, I. V. Tetrahedron Lett. 2011, 52, 4327e4329. 44. Wang, J.; Cui, Z.; Zhang, Y.; Li, H.; Wu, L. M.; Liu, Z. Org. Biomol. Chem. 2011, 9, 663e666. 45. Liu, Z. Personal communication on the structure of 2-(2,4,5-trimethoxybenzyl) allyl acetate, April 13, 2011. 46. Zhang, Y.; Li, Z.; Liu, Z. Q. Org. Lett. 2012, 14, 226e229. 47. Mino, T.; Koizumi, T.; Suzuki, S.; Hirai, K.; Kajiwara, K.; Sakamoto, M.; Fujita, T. Eur. J. Org. Chem. 2012, 678e680. 48. Su, Y.; Jiao, N. Org. Lett. 2009, 11, 2980e2983. 49. Hudnall, T. W.; Chiu, C. W.; Gabbai, F. P. Acc. Chem. Res. 2009, 42, 388e397. 50. Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. J. Am. Chem. Soc. 2005, 127, 13754e13755. 51. Ambrogio, I.; Fabrizi, G.; Cacchi, S.; Henriksen, S. T.; Fristrup, P.; Tanner, D.; Norrby, P. O. Organometallics 2008, 27, 3187e3195. 52. (a) Moro, A. V.; Cardoso, F. S. P.; Correia, C. R. D. Org. Lett. 2009, 11, 3642e3645; (b) Soldi, C.; Moro, A. V.; Pizzolatti, M. G.; Correia, C. R. D. Eur. J. Org. Chem. 2012, 3607e3616. 53. For a review on dehydrogenative Heck reactions, see: Le Bras, J.; Muzart, J. Chem. Rev. 2011, 111, 1170e1214. 54. Shang, X.; Xiong, Y.; Zhang, Y.; Zhang, L.; Liu, Z. Synlett 2012, 259e262. 55. Pan, D.; Yu, M.; Chen, W.; Jiao, N. Chem. Asian J. 2010, 5, 1090e1093. 56. Kubota, A.; Emmert, M. H.; Sanford, M. S. Org. Lett. 2012, 14, 1760e1763. 57. Li, Z.; Zhang, Y.; Liu, Z. Q. Org. Lett. 2012, 14, 74e77. 58. Zhang, Y.; Cui, Z.; Li, Z.; Liu, Z. Q. Org. Lett. 2012, 14, 1838e1841. 59. Delcamp, J. H.; White, M. C. J. Am. Chem. Soc. 2006, 128, 15076e15077. 60. Ruan, J.; Li, X.; Saidi, O.; Xiao, J. J. Am. Chem. Soc. 2008, 130, 2424e2425. 61. For the migration of the C]C bonds via the readdition/elimination of HPdII species, see: Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2e7. 62. For the PdII-catalyzed migration of the C]C bonds, see: (a) Harrod, J. F.; Chalk, A. J. J. Am. Chem. Soc. 1964, 86, 1776e1779; (b) Bingham, D.; Hudson, B.; Webster, D. E.; Wells, P. B. J. Chem. Soc., Dalton Trans. 1974, 1521e1524. 63. Xiang, S.; Cai, S.; Zeng, J.; Liu, X. W. Org. Lett. 2011, 13, 4608e4611. 64. It is usually considered that the elimination of HPd species requires the syn relationship between the palladium unit and the hydrogen: (a) Ref. 1. (b) Tsuji, J. Palladium Reagents and Catalysts, Innovations in Organic Synthesis; Wiley: ̈ Chichester, UK, 1995; 127. A number of reports concern however Heck-type cyclisations arising via the formal anti b-H elimination; for a review, see: (c) Ikeda, M.; El Bialy, S. A. A.; Yakura, T. Heterocycles 1999, 51, 1957e1970 see also: (d) Shea, K. M.; Lee, K. L.; Danheiser, R. L. Org. Lett. 2000, 2, 2353e2356; (e) Lautens, M.; Fang, Y. Q. Org. Lett. 2003, 5, 3679e3682; (f) Imbos, R.; Minnaard, A. J.; Feringa, B. L. Dalton Trans. 2003, 2017e2023 and the references cited in these reports. For a recent intermolecular reaction involving the formal anti b-H elimination, see: (g) Fu, H. Y.; Chen, L.; Doucet, H. J. Org. Chem. 2012, 77, 4473e4478. 65. Werner, E. W.; Urkalan, K. B.; Sigman, M. S. Org. Lett. 2010, 12, 2848e2851. 66. Werner, E. W.; Sigman, M. S. J. Am. Chem. Soc. 2011, 133, 9692e9695. 67. Hosokawa, T.; Sugafuji, T.; Yamanaka, T.; Murahashi, S.-I. J. Organomet. Chem. 1994, 470, 253e255. 68. Lu, X. Top. Catal. 2005, 35, 73e86. 69. Hacksell, U.; Daves, G. D., Jr. Organometallics 1983, 2, 772e775. 70. Huang, J. M.; Zhou, L.; Jiang, H. F. Angew. Chem., Int. Ed. 2006, 45, 1945e1949. 71. For the dependence of the stereochemistry of the halopalladation of triple bonds with the experimental conditions, see: Zhu, G.; Lu, X. J. Organomet. Chem. 1996, 508, 83e90. 72. Jiang, H.; Qiao, C.; Liu, W. Chem.dEur. J. 2010, 16, 10968e10970. 73. Wang, F.; Li, S.; Qu, M.; Zhao, M.-X.; Liu, L.-J.; Shi, M. Chem. Commun. 2011, 12813e12815. 74. For the formation of substituted cyclohexenones via oxo-h3-allylpalladium intermediates, the equilibrium between the C-enolate and the O-enolate has been proposed to assume a syn b-H elimination instead of the apparent anti b-H elimination.64c,f 75. Muzart, J. Tetrahedron 2005, 61, 4179e4212. 76. Le Bras, J.; Muzart, J. Synthesis 2011, 3581e3591. 77. Melpolder, J. B.; Heck, R. F. J. Org. Chem. 1976, 41, 265e272. 78. Chalk, A. J.; Magennis, S. A. J. Org. Chem. 1976, 41, 273e278. 79. Heck, R. F. Organotransition Metal Chemistry; Academic: New York, NY, 1974, pp 105e106. 80. (a) Smadja, W.; Ville, G.; Cahiez, G. Tetrahedron Lett. 1984, 25, 1793e1796; (b) Smadja, W.; Czernecki, S.; Ville, G.; Georgoulis, C. Organometallics 1987, 6, 166e169. 81. Wen, Y.; Huang, L.; Jiang, H.; Chen, H. J. Org. Chem. 2012, 77, 2029e2034. lez, I.; Bouquillon, S.; Roglans, A.; He nin, 82. Zawisza, A. M.; Ganchegui, B.; Gonza F.; Muzart, J. J. Mol. Catal. A: Chem. 2008, 283, 140e145. 83. Keith, J. A.; Oxgaard, J.; Goddard, W. A., III. J. Am. Chem. Soc. 2006, 128, 3132e3133. 84. Keith, J. A.; Henry, P. M. Angew. Chem., Int. Ed. 2009, 48, 9038e9049. 85. (a) B€ ackvall, J. E.;  Akermark, B.; Ljunggren, S. O. J. Am. Chem. Soc. 1979, 101, 2411e2416; (b) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals, 2nd ed.; Wiley: New York, NY, 1994; 195. 86. Kikukawa, K.; Nagira, K.; Wada, F.; Matsuda, T. Tetrahedron 1981, 37, 31e36. nin, F.; Muzart, J. J. Organomet. 87. Masllorens, J.; Bouquillon, S.; Roglans, A.; He Chem. 2005, 690, 3822e3826. 88. Perez, R.; Veronese, D.; Coelho, F.; Antunes, O. A. C. Tetrahedron Lett. 2006, 47, 1325e1328. 89. Barbero, M.; Cadamuro, S.; Dughera, S. Synthesis 2006, 3443e3452.

90. Bernocchi, E.; Cacchi, S.; Ciattini, P. G.; Morera, E.; Ortar, G. Tetrahedron Lett. 1992, 33, 3073e3076. 91. Zhu, M.; Song, Y.; Cao, Y. Synthesis 2007, 853e856. 92. Jeffery, T. J. Chem. Soc., Chem. Commun. 1991, 324e325. 93. Jeffery, T. Tetrahedron Lett. 1991, 32, 2121e2124. 94. Jeffery, T. Tetrahedron Lett. 1993, 34, 1133e1136. 95. Trost, B. M.; Corte, J. R.; Gudiksen, M. S. Angew. Chem., Int. Ed. 1999, 38, 3662e3664 In footnote 19, the authors noted that the effect of silver salts on the H elimination selectivity is opposite to that normally observed. 96. Jeffery, T. Tetrahedron Lett. 1990, 31, 6641e6644. 97. Jeffery, T. J. Chem. Soc., Chem. Commun. 1984, 1287e1289. 98. Heim-Riether, A. Synthesis 2008, 883e886. 99. van de Sande, M.; Gais, H. J. Chem.dEur. J. 2007, 13, 1784e1795. , V.; Nacci, A.; Monopoli, A.; Ferola, V. J. Org. Chem. 2007, 72, 2596e2601. 100. Calo 101. Kumar, N. S. C. R.; Raj, I. V. P.; Sudalai, A. J. Mol. Catal. A: Chem. 2007, 269, 218e224. 102. Krishna, J.; Reddy, A. G. K.; Ramulu, B. V.; Mahendar, L.; Satyanarayana, G. Synlett 2012, 375e380. 103. Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. J. Org. Chem 1992, 57, 3558e3563. 104. Knowles, J. P.; Whiting, A. Org. Biomol. Chem. 2007, 5, 31e44. 105. Jutand, A. In The MizorokieHeck Reaction; Oestreich, M., Ed.; Wiley: Chichester, UK, 2009; pp 1e50. 106. Proutiere, F.; Schoenebeck, F. Synlett 2012, 645e648. 107. Kang, S. K.; Lee, H. W.; Jang, S. B.; Kim, T. H.; Pyun, S. J. J. Org. Chem. 1996, 61, 2604e2605. 108. See Ref. 91. 109. Ambrogio, I.; Cacchi, S.; Fabrizi, G.; Goggiamani, A.; Sgalla, S. Synlett 2009, 620e624. 110. For reviews on the Pd-catalyzed oxidation of alcohols, see: (a) Muzart, J. Tetrahedron 2003, 59, 5789e5816; (b) Hayashi, M. Organometallic News 2003, 40e45 Chem. Abstr., 139, 133050; (c) Stoltz, B. M. Chem. Lett. 2004, 33, 362e367; (d) Zhan, B.-Z.; Thompson, A. Tetrahedron 2004, 60, 2917e2935; (e) Nishimura, T.; Uemura, S. Synlett 2004, 201e216; (f) Stahl, S. S. Angew. Chem., Int. Ed. 2004, 43, 3400e3420; (g) Sigman, M. E.; Jensen, D. R. Acc. Chem. Res. 2006, 39, 221e229; (h) Kaneda, K.; Ebitani, K.; Mizugaki, T.; Mori, K. Bull. Chem. Soc. Jpn. 2006, 79, 981e1016; (i) Parmeggiani, C.; Cardona, F. Green. Chem. 2012, 14, 547e564. 111. Sabino, A. A.; Machado, A. H. L.; Correia, C. R. D.; Eberlin, M. N. Angew. Chem., Int. Ed. 2004, 43, 2514e2518. ~ as, M. Chem. 112. For reviews, see: (a) Roglans, A.; Pla-Quintana, A.; Moreno-Man Rev. 2006, 106, 4622e4643; (b) Taylor, J. G.; Moro, A. V.; Correia, C. R. D. Eur. J. Org. Chem. 2011, 1403e1428; (c) Felpin, F.-X.; Nassar-Hardy, L.; Le Callonnec, F.; Fouquet, E. Tetrahedron 2011, 67, 2815e2831. 113. The mechanism of the arylations with arenediazonium salts in the absence of base is an intriguing question (a) Beletskaya, I. P.; Cheprakov, A. V. In The MizorokieHeck Reaction; Oestreich, M., Ed.; Wiley: Chichester, UK, 2009; p 59 ) which, at the present time, remains unsolved; (b) Roglans, A. Personal communication, February 14, 2012. 114. Chen, B.; Xie, X.; Lu, J.; Wang, Q.; Zhang, Q.; Tang, S.; She, X.; Pan, X. Synlett 2006, 259e262. 115. Chen, M.; Wang, J.; Chai, Z.; You, C.; Lei, A. Adv. Synth. Catal. 2012, 354, 341e346. 116. Ku, J. M.; Jeong, B. S.; Jew, S.; Park, H. J. Org. Chem. 2007, 72, 8115e8118. 117. (a) Yokoyama, Y.; Matsumoto, T.; Murakami, Y. J. Org. Chem. 1995, 60, 1486e1487; (b) Berthiol, F.; Doucet, H.; Santelli, M. Appl. Organomet. Chem. 2006, 20, 855e868. 118. (a) Patonay, T.; Vasas, A.; Kiss-Szikszai, A.; Silva, A. M. S.; Cavaleiro, J. A. S. Aust.  nya, K.; Silva, A. M. J. Chem. 2010, 63, 1582e1593; (b) Vasas, A.; Patonay, T.; Ko S.; Cavaleiro, J. A. S. Aust. J. Chem. 2011, 64, 647e657; (c) Fekete, S.; Patonay, T.; Silva, A. M. S.; Cavaleiro, J. A. S. Arkivoc 2012, v, 210e225. 119. (a) Arylation and alkenylation of tertiary allyl alcohols can lead to epoxides through the suspected intramolecular addition of the aryl(or alkenyl)palladium alcoholate to the C]C bond: Hayashi, S.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2009, 131, 2052e2053; (b) Other allylic alcohols can also lead to epoxides, but this would be restricted to the reaction with polyfluoralkyl halides under basic conditions; the addition of the polyfluoralkylpalladium halide to the C]C bond was thus proposed: Fuchikami, T.; Shibata, Y.; Urata, H. Chem. Lett. 1987, 521e524. ~ o, R.; C 120. Sauza, A.; Morales-Serna, J. A.; García-Molina, M.; Gavin ardenas, J. Synthesis 2012, 272e282. 121. (a) Hallberg, A.; Westfelt, L.; Holm, B. J. Org. Chem. 1981, 46, 5414e5415; (b) Larhed, M.; Andersson, C.-M.; Hallberg, A. Tetrahedron 1994, 50, 285e304. 122. Andersson, C.-M.; Hallberg, A. J. Org. Chem. 1989, 54, 1502e1505. 123. Gaikwad, D. S.; Park, Y.; Pore, D. M. Tetrahedron Lett. 2012, 53, 3077e3081. 124. Jeffery, T.; David, M. Tetrahedron Lett. 1998, 39, 5751e5754. 125. Fitzpatrick, M. O.; Muller-Bunz, H.; Guiry, P. J. Eur. J. Org. Chem. 2009, 1889e1895. 126. Kishida, M.; Akita, H. Tetrahedron 2005, 61, 10559e10568. 127. Berthiol, F.; Doucet, M.; Santelli, M. Eur. J. Org. Chem. 2005, 1367e1377. 128. Zhou, Z.; Xie, Y.; Du, Z.; Hu, Q.; Xue, J.; Shi, J. Arkivoc 2012, vi, 164e172. 129. Du, X.; Suguro, M.; Hirabayashi, K.; Mori, A.; Nishikata, T.; Hagiwara, N.; Kawata, K.; Okeda, T.; Wang, H. F.; Fugami, K.; Kosugi, M. Org. Lett. 2001, 3, 3313e3316. 130. Nokami, J.; Furukawa, A.; Okuda, Y.; Hazato, A.; Kurozumi, S. Tetrahedron Lett. 1998, 39, 1005e1008. 131. Delcamp, J. H.; Brucks, A. P.; White, M. C. J. Am. Chem. Soc. 2008, 130, 11270e11271.

J. Le Bras, J. Muzart / Tetrahedron 68 (2012) 10065e10113 132. For the required precautions to interpret the deuterium kinetic isotope effects, see: Simmons, E. M.; Hartwig, J. F. Angew. Chem., Int. Ed. 2012, 51, 3066e3072. 133. For the decarboxylation mechanism and the double role (base and oxidant) of Ag2CO3, see: (a) Myers, A. G.; Tanaka, D.; Mannion, M. R. J. Am. Chem. Soc. 2002, 124, 11250e11251; (b) Tanaka, D.; Romeril, S. P.; Myers, A. G. J. Am. Chem. Soc. 2005, 127, 10323e10333. 134. Wenzel, T. T. J. Chem. Soc., Chem. Commun. 1993, 862e864. 135. Awasaguchi, K.; Miyazawa, M.; Uoya, I.; Inoue, K.; Nakamura, K.; Yokoyama, H.; Kakuda, H.; Hirai, Y. Synlett 2010, 2392e2396. 136. The arylation of acrolein diethyl acetal usually occurs at the terminal carbon, but without high selectivity of the subsequent hydride elimination: (a) Zebovitz, T. C.; Heck, R. F. J. Org. Chem. 1977, 42, 3907e3909; (b) Davies, S. G.; Mobbs, B. E.; Goodwin, C. J. J. Chem. Soc., Perkin Trans. 1 1987, 2597e2604; (c) Ref. 118. 137. Experimental conditions for the selective arylation at the central carbon of acrolein diethyl acetal have been recently disclosed: Qin, L.; Ren, X.; Lu, Y.; Li, Y.; Zhou, J. Angew. Chem., Int. Ed. 2012, 51, 5915e5919. 138. Battistuzzi, G.; Cacchi, S.; Fabrizi, G. Org. Lett. 2003, 5, 777e780. 139. Battistuzzi, G.; Cacchi, S.; Fabrizi, G.; Bernini, R. Synlett 2003, 1133e1136. 140. Hosokawa, T.; Okhata, H.; Moritani, I. Bull. Chem. Soc. Jpn. 1975, 48, 1533e1536. 141. Larock, R. C.; Wei, L.; Hightower, T. R. Synlett 1998, 522e524. 142. For the similar dependence for the cyclisation of methyl 2-allyl-4,5,6-tribromo3-hydroxybenzoate, see: Khan, F. A.; Soma, L. Tetrahedron Lett. 2007, 48, 85e88. 143. Hosokawa, T.; Miyagi, S.; Murahashi, S.; Sonoda, A. J. Org. Chem. 1978, 43, 2752e2757. 144. According to a subsequent review from the same laboratory, it seems that the oxypalladation is the preferred pathway for this cyclisation. Indeed, this report was included in the review, whereas the authors indicated in the introduction that heterocycles prepared via h3-allylpalladium intermediates chemistry will not be considered.3 145. Van Benthem, R. A. T. M.; Hiemstra, H.; Michels, J. J.; Speckamp, W. N. J. Chem. Soc., Chem. Commun. 1994, 357e361. 146. (a) Van Benthem, R. A. T. M.; Hiemstra, H.; van Leeuwen, PW. N. M.; Geus, J. W.; Speckamp, W. N. Angew. Chem., Int. Ed. Engl. 1995, 34, 457e460; (b) Van Benthem, R. A. T. M.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1992, 57, 6083e6085. 147. Nguefack, J.-F.; Bolitt, V.; Sinou, D. J. Org. Chem. 1997, 62, 1341e1347. 148. Bedjeguelal, K.; Bolitt, V.; Sinou, D. Synlett 1999, 762e764. 149. (a) Alcaide, B.; Almendros, P.; Martíez del Campo, T.; Soriano, E.; MarcoContelles, J. L. Chem.dEur. J. 2009, 15, 1909e1928; (b) Alcaide, B.; Almendros, P.; Martiez del Campo, T.; Soriano, E.; Marco-Contelles, J. L. Chem.dEur. J. 2009, 15, 9127e9138. 150. Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5531e5534. 151. Foley, S. R.; Stockland, R. A., Jr.; Shen, H.; Jordan, R. F. J. Am. Chem. Soc. 2003, 125, 4350e4361. 152. See also: (a) Ref. 5. (b) Bergstrom, D. E.; Ruth, J. L.; Warwick, P. J. Org. Chem. 1981, 46, 1432e1441; (c) Ma, S.; Yu, Z. J. Org. Chem. 2003, 68, 6149e6152; (d) Foley, S. R.; Shen, H.; Qadeer, U. A.; Jordan, R. F. Organometallics 2004, 23,  ski,  s, M. T.; Gadzin 600e609; (e) Alcaide, B.; Almendros, P.; Alonso, J. M.; Quiro P. Adv. Synth. Catal. 2011, 353, 1871e1876. 153. Yang, F. L.; Ma, X. T.; Tian, S. K. Chem.dEur. J. 2012, 18, 1582e1585. 154. Nitrogen substituents have nevertheless leaving properties as exemplified either in the generation of h3-allylpalladium intermediates from allylic amine derivatives and Pd0 complexes: (a) Zhang, Y.; DeKorver, K. A.; Lohse, A. G.; Zhang, Y.-S.; Huang, J.; Hsung, R. P. Org. Lett. 2009, 11, 899e902; (b) Li, M.-B.; Wang, Y.; Tian, S.-K. Angew. Chem., Int. Ed. 2012, 51, 2968e2971 or from isomerisation reactions: (c) Ferber, B.; Lemaire, S.; Mader, M. M.; Prestat, G.; Poli, G. Tetrahedron Lett. 2003, 44, 4213e4216; (d) Oshitari, T.; Akagi, R.; Mandai, T. Synthesis 2004, 1325e1330. 155. Timokhin, V. I.; Anastasi, N. R.; Stahl, S. S. J. Am. Chem. Soc. 2003, 125, 12996e12997. 156. In the absence of an effective Brønstedt base, the aminopalladation can be a reversible process: Timokhin, V. I.; Stahl, S. S. J. Am. Chem. Soc. 2005, 127, 17888e17893. 157. (a) Tamura, R.; Kamimura, A.; Ono, N. Synthesis 1991, 423e434; (b) Barco, A.; Benetti, S.; Spalluto, G.; Casolari, A.; Pollini, G. P.; Zanirato, V. J. Org. Chem. 1992, 57, 6279e6286. 158. Nakano, T.; Miyahara, M.; Itoh, T.; Kamimura, A. Eur. J. Org. Chem. 2012, 2161e2166. 159. It has been noted that the use of NEt3 as base decomposes PhN2BF4.158 160. Crisp, G. T.; Glink, P. T. Tetrahedron 1992, 48, 3541e3556. 161. Cacchi, S.; Fabrizi, G.; Goggiamani, A.; Sferrazza, A. Org. Biomol. Chem. 2011, 9, 1727e1730. 162. (a) Kao, L.-C.; Stakem, F. G.; Patel, B. A.; Heck, R. F. J. Org. Chem. 1982, 47, 1267e1277; (b) Malek, N. J.; Moormann, A. E. J. Org. Chem. 1982, 47, 5395e5397; (c) Arcadi, A.; Bernocchi, E.; Cacchi, S.; Caglioti, L.; Marinelli, F. Tetrahedron Lett. 1990, 31, 2463e2466; (d) Crisp, G. T.; Gebauer, M. G. Tetrahedron 1996, 52, 12465e12474; (e) Busacca, C. A.; Dong, Y. Tetrahedron Lett. 1996, 37, 3947e3950; (f) Dong, Y.; Busacca, C. A. J. Org. Chem. 1997, 62, nisson, Y.; Correia, C. R. D. J. Org. 6464e6465; (g) Prediger, P.; Barbosa, L. F.; Ge Chem. 2011, 76, 7737e7749; (h) Deng, Y.; Jiang, Z.; Yao, M.; Xu, D.; Zhang, L.; Li, H.; Tang, W.; Xu, L. Adv. Synth. Catal. 2012, 354, 899e907; (i) Kore, A. R.; Shanmugasundaram, M. Tetrahedron Lett. 2012, 53, 2530e2532; (j) Jiang, Z.; Zhang, L.; Dong, C.; Ma, B.; Tang, W.; Xu, L.; Fan, Q.; Xiao, J. Tetrahedron 2012, 68, 4919e4926. 163. Lu, Z.; Stahl, S. S. Org. Lett. 2012, 14, 1234e1237. 164. Fix, S. R.; Brice, J. L.; Stahl, S. S. Angew. Chem., Int. Ed. 2002, 41, 164e166.

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165. Kotov, V.; Scarborough, C. C.; Stahl, S. S. Inorg. Chem. 2007, 46, 1910e1923. 166. Ye, X.; Liu, G.; Popp, B. V.; Stahl, S. S. J. Org. Chem. 2011, 76, 1031e1044. 167. Redford, J. E.; McDonald, R. I.; Rigsby, M. L.; Wiensch, J. D.; Stahl, S. S. Org. Lett. 2012, 14, 1242e1245. 168. Under Stahl’s experimental conditions, a Wacker-type addition rather than an allylic CeH activation leading to a Tsuji/Trost-type reaction was assumed on the basis of experiments and DFT computational studies.166,167 Using different experimental conditions, White’s team reported 5- cyclisations of alkenes bearing tethered N-tosyl(or nosyl)carbamates, which occur via a h3-allylpalladium intermediate: (a) Fraunhoffer, K. J.; White, M. C. J. Am. Chem. Soc. 2007, 129, 7274e7276; (b) Jiang, C.; Covell, D. J.; Stepan, A. F.; Plummer, M. S.; White, M. C. Org. Lett. 2012, 14, 1386e1389. 169. Keith, D. D.; Tortora, J. A.; Ineichen, K.; Leimgruber, W. Tetrahedron 1975, 31, 2633e2636. 170. Filippini, L.; Gusmeroli, M.; Riva, R. Tetrahedron Lett. 1993, 34, 1643e1646. 171. Rogers, M. M.; Kotov, V.; Chatwichien, J.; Stahl, S. S. Org. Lett. 2007, 9, 4331e4334. 172. Brice, J. L.; Harang, J. E.; Timokhin, V. I.; Anastasi, N. R.; Stahl, S. S. J. Am. Chem. Soc. 2005, 127, 2868e2869. 173. Allylamines can be also obtained from the Pd-catalysed addition of amines to linear alkenes, but, such reactions would involve h3-allylpalladium intermediates, i.e., TsujieTrost type reactions, rather than aza-Wacker reactions followed by b0 -H eliminations: Liu, G.; Yin, G.; Wu, L. Angew. Chem., Int. Ed. 2008, 47, 4733e4736. 174. This contrasts with the reported stoichiometric trans-aminopalladation of  , K.; Sjo € berg, K.; linear alkenes: (a)  Akermark, B.; B€ ackvall, J. E.; Siirala-Hansen Zetterberg, K. Tetrahedron Lett. 1974, 15, 1363e1366; (b)  Akermark, B.; B€ ackvall, n, K.; Sjo € berg, K. J. Organomet. J. E.; Hegedus, L. S.; Zetterberg, K.; Siirala-Hanse Chem. 1974, 72, 127e138. 175. Lv, P.; Huang, K.; Xie, L.; Xu, X. Org. Biomol. Chem. 2011, 9, 3133e3135. 176. Hallberg, A.; Westerlund, C. Chem. Lett. 1982, 1993e1994. 177. Kikukawa, K.; Ikenaga, K.; Wada, F.; Matsuda, T. Chem. Lett. 1983, 1337e1340. 178. (a) Kikukawa, K.; Ikenaga, K.; Kono, K.; Toritani, K.; Wada, F.; Matsuda, T. J. Organomet. Chem. 1984, 270, 277e282; (b) Ikenaga, K.; Matsumoto, S.; Kikukawa, K.; Matsuda, T. Chem. Lett. 1988, 873e876. 179. Another possibility would be a transmetalation promoted by fluoride ion: Hatanaka, Y.; Hiyama, T. Synlett 1991, 845e853 The transmetalation process occurs from alkenylpentafluorosilicates (Yoshida, J.; Tamao, K.; Yamamoto, H.; Kakui, R.; Uchida, T.; Kumada, M. Organometallics 1982, 1, 542e549.), alkenylsilanoates (Denmark, S. E.; Regens, C. S. Acc. Chem. Res. 2008, 41, 1486e1499.) and intramolecularly activated vinylsilanes (Matsumoto, K.; Shindo, M. Adv. Synth. Catal. 2012, 354, 642e650. Omote, M.; Tanaka, M.; Ikeda, A.; Nomura, S.; Tarui, A.; Sato, K.; Ando, A. Org. Lett. 2012, 14, 2286e2289.).. 180. Ikenaga, K.; Kikukawa, K.; Matsuda, T. J. Chem. Soc., Perkin Trans. 1 1986, 1959e1964. 181. Alvisi, D.; Blart, E.; Bonini, B. F.; Mazzanti, G.; Ricci, A.; Zani, P. J. Org. Chem. 1996, 61, 7139e7146. 182. Karabelas, K.; Hallberg, A. J. Org. Chem. 1986, 51, 5286e5290. 183. (a) Kikukawa, K.; Ikenaga, K.; Wada, F.; Matsuda, T. Tetrahedron Lett. 1984, 25, 5789e5792; (b) Ikenaga, K.; Kikukawa, K.; Matsuda, T. J. Org. Chem. 1987, 52, 1276e1280. 184. Karabelas, K.; Hallberg, A. Tetrahedron Lett. 1985, 26, 3131e3132. 185. Karabelas, K.; Hallberg, A. J. Org. Chem. 1988, 53, 4909e4914. 186. For other efficient conditions with ArI, which preserve the trimethylsilyl group, see: Jeffery, T. Tetrahedron Lett. 1999, 40, 1673e1676. 187. The arylation and alkenylation of allylic trifluorosilanes are out of the scope of this review, because these reactions proceed through Si/Pd transmetalations: (a) Hatanaka, Y.; Ebina, Y.; Hiyama, T. J. Am. Chem. Soc. 1991, 113, 7075e7076; (b) Hatanaka, Y.; Goda, K.; Hiyama, T. Tetrahedron Lett. 1994, 35, 1279e1282; (c) Hatanaka, Y.; Goda, K.; Hiyama, T. Tetrahedron Lett. 1994, 35, 6511e6514. 188. Karabelas, K.; Westerlund, C.; Hallberg, A. J. Org. Chem. 1985, 50, 3896e3900. 189. Under these conditions, the traces of propen-2-ylbenzene would be due to the subsequent desilylation of trimethyl(2-phenylallyl)silane.188 190. Tietze, L. F.; Schimpf, R. Angew. Chem., Int. Ed. Engl. 1994, 33, 1089e1091. 191. The eliminations of the SiMe3 group reported by Tietze’s team for similar intramolecular reactions when using Pd2(dba)3, (S)- or (R)-Binap, Ag3PO4 (Ref.190. Tietze, L. F.; Raschke, T. Synlett 1995, 597e598; Tietze, L. F.; Raschke, T. Liebigs Ann./Recueil 1996, 1981e1987) are, in our opinion, surprising. This leads us to suspect other intermediates than those of the Heck-type reaction, possibly h3-allylpalladium complexes.; formation of such complexes from allylic trimethylsilanes and PdII salts has been reported: Kliegman, J. M. J. Organomet. , N.; Gue rin, C. J. Organomet. Chem. Chem. 1971, 29, 73e77; Corriu, R. J. P.; Escudie 1984, 271, C7eC9; Hayashi, T.; Konishi, M.; Okamoto, Y.; Kabeta, K.; Kumada, M. J. Org. Chem. 1986, 51, 3772e3781; Fugami, K.; Oshima, K.; Utimoto, K.; Nozaki, H. Bull. Chem. Soc. Jpn. 1987, 60, 2509e2515; For corresponding catalytic reactions, ri, I.; Szabo , see: Muzart, J.; Riahi, A. Organometallics 1992, 11, 3478e3481. Macsa K. J. Chem.dEur. J. 2001, 7, 4097e4106. These reactions involve transmetalation reactions. 192. Jeffery, T. Tetrahedron Lett. 2000, 41, 8445e8449. 193. Jeffery considered that (E)-prop-1-enylbenzene was obtained from the isomerisation of allylbenzene.192 We suspect that this compound is rather generated by desilylation of cinnamyltrimethylsilane, as proposed by Hallberg’s team for the formation of prop-1-en-2-ylbenzene (Eq. 55).188,189 194. McAtee, J. R.; Martin, S. E. S.; Ahneman, D. T.; Johnson, K. A.; Watson, D. A. Angew. Chem., Int. Ed. 2012, 51, 3663e3667.

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195. Muzart, J. J. Mol. Catal. A: Chem. 2010, 319, 1e29. 196. Water is mentioned as an additive in author’s patent: Wenzel, T. T. U.S. Patent 5,136,105, 1992; Chem. Abstr. 1993, 118, 21944. Moreover, water is generated from the reoxidation of Pd0 into PdII under these reaction conditions: Muzart, J. Tetrahedron 2007, 63, 7505e7521. 197. Igarashi, S.; Haruta, Y.; Ozawa, M.; Nishide, Y.; Kinoshita, H.; Inomata, K. Chem. Lett. 1989, 737e740. 198. (a) Hattori, Y.; Furuhata, S.; Okajima, M.; Konno, H.; Abe, M.; Miyoshi, H.; Goto, T.; Makabe, H. A. Org. Lett. 2008, 10, 717e720; (b) Furuhata, S.; Hattori, Y.; Okajima, M.; Konno, H.; Abe, M.; Miyoshi, H.; Goto, T.; Makabe, H. A. Tetrahedron 2008, 64, 7695e7703. 199. Uenishi, J.; Vikhe, Y. S. Heterocycles 2010, 80, 1463e1469. nin, F.; Muzart, J. Tetrahedron 2000, 56, 8133e8140. 200. Roy, O.; Riahi, A.; He 201. Cannon, J. S.; Olson, A. C.; Overman, L. E.; Solomon, N. S. J. Org. Chem. 2012, 77, 1961e1973. 202. Bayer, E.; Geckeler, K. Angew. Chem., Int. Ed. Engl. 1979, 18, 533e534. 203. Xu, J.; Fu, Y.; Xiao, B.; Gong, T.; Guo, Q. Tetrahedron Lett. 2010, 51, 5476e5479. 204. Brice, J. L.; Meerdink, J. E.; Stahl, S. S. Org. Lett. 2004, 6, 1845e1848. 205. Muzart, J. Eur. J. Org. Chem. 2007, 3077e3089. 206. Eustache, J.; Van de Weghe, P.; Le Nouen, D.; Uyehara, H.; Kabuto, C.; Yamamoto, Y. J. Org. Chem. 2005, 70, 4043e4053. 207. Yokoyama, H.; Ejiri, H.; Miyazawa, M.; Yamaguchi, S.; Hirai, Y. Tetrahedron: Asymmetry 2007, 18, 852e856. 208. (a) Yokoyama, H.; Kobayashi, H.; Miyazawa, M.; Yamaguchi, S.; Hirai, Y. Heterocycles 2007, 74, 283e292; (b) Yokoyama, H.; Hirai, Y. Heterocycles 2008, 75, 2133e2153; (c) Yokoyama, H.; Hayashi, Y.; Nagasawa, Y.; Ejiri, H.; Miyazawa, M.; Hirai, Y. Tetrahedron 2010, 66, 8458e8463. 209. Saito, S.; Hara, T.; Takahashi, N.; Hirai, M.; Morikawe, T. Synlett 1992, 237e238. 210. Kimura, M.; Harayama, H.; Tanaka, S.; Tamaru, Y. J. Chem. Soc., Chem. Commun. 1994, 2531e2533. 211. Hirai, Y.; Watanabe, J.; Nozaki, T.; Yokoyama, H.; Yamaguchi, S. J. Org. Chem. 1997, 62, 776e777. 212. Lei, A.; Liu, G.; Lu, X. J. Org. Chem. 2002, 67, 974e980. 213. Ferber, B.; Prestat, G.; Vogel, S.; Madec, D.; Poli, G. Synlett 2006, 2133e2135. 214. Cannon, J. S.; Kirsch, S. F.; Overman, L. E. J. Am. Chem. Soc. 2010, 132,15185e15191.

215. (a) Kirsch, S. F.; Overman, L. E. J. Am. Chem. Soc. 2005, 127, 2866e2867; (b) Cannon, J. S.; Frederich, J. H.; Overman, L. E. J. Org. Chem. 2012, 77, 1939e1951. 216. Kirsch, S. F.; Overman, L. E.; White, N. S. Org. Lett. 2007, 9, 911e913. 217. Olson, A. C.; Overman, L. E.; Sneddon, H. F.; Ziller, J. W. Adv. Synth. Catal. 2009, 351, 3186e3192. 218. Cannon, J. S.; Kirsch, S. F.; Overman, L. E.; Sneddon, H. F. J. Am. Chem. Soc. 2010, 132, 15192e15203. 219. Steinig, A. G.; de Meijere, A. Eur. J. Org. Chem. 1999, 1333e1334. 220. Guo, H. M.; Rao, W. H.; Niu, H. Y.; Jiang, L. L.; Liang, L.; Zhang, Y.; Qu, G. R. RSC Adv. 2011, 1, 961e963. 221. This reaction of 3-methylhex-1-ene is only disclosed in the Supplementary data of the report.59 222. (a) Heck, R. F. J. Am. Chem. Soc. 1971, 93, 6896e6901; (b) Dieck, H. A.; Heck, R. F. J. Am. Chem. Soc. 1974, 96, 1133e1136. 223. For the Pd0-catalyzed migration of the C]C bonds, see: (a) Carless, H. A.; Haywood, D. J. J. Chem. Soc., Chem. Commun. 1980, 980e981; (b) Hoshino, Y.; Takeno, N. Bull. Chem. Soc. Jpn. 1994, 67, 2873e2875; (d) Zhang, Y. Q.; Zhu, D. Y.; Li, B. S.; Tu, Y. Q.; Liu, J. X.; Lu, Y.; Wang, S. H. J. Org. Chem. 2012, 77, 4167e4170. 224. Takeda, K.; Toyota, M. Heterocycles 2012, 84, 1271e1276. €bel, T.; Spescha, M. J. Am. Chem. Soc. 1998, 120, 8971e8977. 225. Tietze, L. F.; No , A. S.; Lau, C. K. Synlett 1997, 1312e1314; (b) Zakrzewski, 226. (a) Gowan, M.; Caille P.; Gowan, M.; Trimble, L. A.; Lau, C. K. Synthesis 1999, 1893e1902. 227. Pefiel, I.; Pastor, I. M.; Yus, M. Eur. J. Org. Chem. 2012, 3151e3156. 228. Correia, C. R. D.; Oliveira, C. C.; Salles, A. G.; Santos, E. A. F. Tetrahedron Lett. 2012, 53, 3325e3328. 229. (a) Andersen, N. G.; Parvez, M.; Keay, B. A. Org. Lett. 2000, 2, 2817e2820; (b) Andersen, N. G.; Parvez, M.; McDonald, R.; Keay, B. A. Can. J. Chem. 2004, 82, 145e161. 230. Black, D. St. C.; Keller, P. A.; Kumar, N. Tetrahedron 1992, 48, 7601e7608. 231. Werner, E. W.; Sigman, M. S. J. Am. Chem. Soc. 2010, 132, 13981e13983. 232. Sigman, M. S.; Werner, E. W. Acc. Chem. Res. 2012, 45, 874e884. 233. Pinho, P.; Minnaard, J.; Feringa, B. L. Org. Lett. 2003, 5, 259e261. 234. Merten, S.; Froehlich, R.; Kataeva, O.; Metz, P. Adv. Synth. Catal. 2005, 347, 754e758.

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Biographical sketch

Jean Le Bras Jean Le Bras was born in Brest and obtained his Engineering Diploma from  Pierre et Marie Curie. In 1996, ENSCP-Paris and his M.Sc. degree (DEA) from Universite he joined the group of Dr. Hani Amouri where he studied iridium mediated phenols functionalization and obtained his Ph.D. in 1998. He then joined the group of Professor John A. Gladysz as a post-doctoral fellow in Salt Lake City (USA) and in Erlangen (Germany) and has worked on the synthesis of organometallic complexes with 17 valence  de electrons and polyynediyl chains. In 2000, he became a CNRS fellow at Universite Reims Champagne Ardenne. Its current interests are concentrated on transition metal-catalysis with particular emphasis on oxidations, CeH activation and valorization of agricultural by-products.

Jacques Muzart Jacques Muzart was born in 1946, in Vienne la Ville, a small village in  de the Argonne area, 200 km east of Paris. He studied chemistry at the Universite  Champagne-Ardenne and received his degrees (Doctorat de 3eme cycle in 1972, Docte on photochemical rearrangements of torat d’Etat in 1976) for his work with J.-P. Pe a,b-epoxyketones and b-diketones. He was appointed at the Centre National de la Recherche Scientifique in 1971, and spent 15 months (1977e1978) as a post-doctoral fellow of National Science Foundation working with E. J. Corey at Harvard University on natural product synthesis. On his return to Reims, he mainly studied the photoreactivity of h3-allylpalladium complexes and anionic activation by supported reagents. Dirite since 2011, his research interests concentrate on recteur de Recherche Em e transition metal-catalysis with particular emphasis on oxidations, CeH activation and mechanisms. He is also involved in the valorisation of agricultural by-products.