Recent topics on catalytic asymmetric 1,4-addition

Tetrahedron Letters 58 (2017) 1793–1805

Contents lists available at ScienceDirect

Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet

Digest paper

Recent topics on catalytic asymmetric 1,4-addition Masahiko Hayashi ⇑, Ryosuke Matsubara Department of Chemistry, Graduate School of Science, Kobe University, Kobe 657-8501, Japan

a r t i c l e

i n f o

Article history: Received 10 February 2017 Revised 27 February 2017 Accepted 15 March 2017 Available online 4 April 2017 Keywords: Catalytic asymmetric reaction Chiral ligand 14-Addition Michael acceptor Non-linear effect

a b s t r a c t Catalytic asymmetric 1,4-addition (conjugate addition; Michael addition) is one of the most powerful methods for carbon-carbon bond formation. Following the first efficient catalyst system developed by Feringa, which is composed of Cu(OTf)2 and phosphoramidite with dialkylzincs, a variety of chiral catalysts have been reported for the catalytic asymmetric conjugate addition. In this digest review, we will first summarize novel chiral ligands that work efficiently for cyclic and acyclic enones and demonstrate the wide applicability of Michael acceptors. We will also introduce unique phenomena that include the nonlinear effect and reversal of enantioselectivity. Organomagnesium reagents have also been used instead of organozincs. Finally, we introduce the recent examples of the synthesis of natural products based on the catalytic asymmetric reaction. The rare experimental studies into the mechanism of copper-catalyzed 1,4-addition reported by Kitamura and Noyori’s group are also introduced. Ó 2017 Published by Elsevier Ltd.

Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Development of effective chiral ligands. . . . . . . . . . . . . . Trapping of zinc enolates by some electrophiles . . . . . . Experiment-based investigation of reaction mechanism Non-linear effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Switching of enantioselectivity54 . . . . . . . . . . . . . . . . . . . Combination of Grignard reagents with copper . . . . . . . Synthetic application to natural products . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

Introduction Catalytic asymmetric 1,4-addition is now recognized as one of the most reliable carbon-carbon bond forming reactions in organic synthesis.1,2 In 1988, Soai and his co-workers first reported the asymmetric 1,4-addition of chalcone with diethylzinc in the presence of Ni(acac)2 and chiral b-amino alcohol to furnish the

⇑ Corresponding author. E-mail address: [email protected] (M. Hayashi). http://dx.doi.org/10.1016/j.tetlet.2017.03.044 0040-4039/Ó 2017 Published by Elsevier Ltd.

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

1793 1794 1797 1797 1797 1799 1801 1803 1804 1804 1804

1,4-addition product in 75% yield with 45% ee.3 Subsequently, there have been many reports on asymmetric 1,4-addition reactions, most of which included the reactions of cyclic and acyclic enones with dialkylzincs in the presence of chiral copper complexes. A remarkable improvement was introduced by the combination of Cu(OTf)2 and chiral phosphoramidite 1 developed by Feringa in 1997 (Eq. 1).4,5

1794

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

Feringa (1997) O + Et2 Zn

PF6

O

2 mol% Cu(OTf) 2 __ chiral phosphoramidite 1

N

HO O

94% yield > 98% ee (S)

O

R 2 2Zn

+

O

CuOTf .0.5C 6H 6 (1 mol%) n-BuLi (2.5 mol%)

(eq. 2)

R2 R1

EtOAc, rt, 16 h

R1

O

(S,R,R)-1:

i-Bu 1 mol%

(eq. 1) Et

Ph

N

P N

up to 98% yield up to 98% ee

Ph

A general and rational mechanism underlying the copper-catalyzed 1,4-addition of a,b-unsaturated ketones using dialkylzincs and a Cu(OTf)2-chiral ligand system is outlined in Scheme 1.4,6,7, However, since it is not easy to isolate and analyze the reaction intermediates, the actual reaction mechanism is still under debate. In this article, we present an overview of the recent progress of catalytic asymmetric 1,4-addition.

Sakaguchi and his co-workers developed and reported a similar type of ligand, as shown below (Eq. 3). In this case, the chiral azolium salts themselves were found to work as catalysts. In addition, this group observed a unique phenomenon, reversal of enantioselectivity which will be discussed later.21 Sakaguchi (2010) O O

Development of effective chiral ligands

Cu(OTf) 2 , azolium salt

Following Feringa’s report,4 continuous efforts have been undertaken for the development of new chiral ligands that afford high reactivity and high enantioselectivity. In this regard, various binaphthol-derived phosphoramidites, phosphonites, and phosphites were reported. Some of the ligands that gave the 1,4-addition product in the reaction of 2-cyclohexen-1-one in >95% ee are summarized in Scheme 2.8–12 Other types of ligands that afford a high ee include chiral Schiff bases. The successful examples of chiral ligands for conjugate addition are shown in Scheme 3.13–15 In 2001, Fraser and Woodward reported a strong ligand acceleration effect upon the addition of N-heterocyclic carbene (NHC) in the reaction of various enones with diethylzinc, and proposed the transition state illustrated in Scheme 4.16 Based on this concept, Mauduit developed several chiral alkoxy NHC ligands (derived from alcohol and n-BuLi) (Scheme 5).17–19 The same authors recently reported the reaction of b-substituted cyclohexenones with dialkylzincs to afforded products possessing quaternary carbon centers, in up to 98% ee (Eq. 2).20

ZnR 2

L*n Cu

L*nCu

X

R

+

RZnX

OZnR O R

L*n Cu O

+ R 2 Zn

n

n H N

N N Cl

O

*

(eq. 3) R

t-Bu OH

Ph chiral azolium salt

For acyclic enones, the chiral ligands shown below exhibited high enantioselectivitiy (Scheme 6).22–33 Expansion of scope of Michael acceptors In most of the catalytic asymmetric 1,4-additions reported so far, cyclic and acyclic cyclohexenones such as 2-cyclohexen-1one and chalcone, respectively, were used as substrates. In this chapter, we will introduce various Michael acceptors other than the abovementioned simple enones. In 1999, Feringa reported the copper-phosphoramidite-catalyzed 1,4-addition of dialkylzincs to symmetric 4,4-disubstituted cyclohexadienones and unsymmetric 4,4-disubstituted cyclohexadienones to give the 1,4-addition products in high ee (Scheme 7).34 Feringa extended this methodology for the synthesis of both cisand trans-3,4,4,5-tetrasubstituted cyclohexanones by appropriate choice of (S,R,R)-1 or (R,S,S)-1. The reaction proceeded selectively with chiral catalyst control (Scheme 8).35 As Michael acceptors, nitroolefins were also used to give the corresponding nitroalkanes; however, only two substrates have been reported to give the product with high ee.36,37 Feringa reported the asymmetric conjugate addition of dialkylzinc reagents to a,b-unsaturated nitroacetates, which led to the enantioselective synthesis of b-aryl-nitroalkanes.

O Et

R

Zn R

X O

O

Et

Cu(OTf) 2 (1.2 mol%) (S,R,R)-1 (2.4 mol%)

NO2 + Et 2Zn

NO2 O

O

*

NO2

OH 92% ee (-)

R Scheme 1. Proposed mechanism for the copper-catalyzed 1,4-addition of organozincs to 2-cyclohexenone.

Cu(OTf) 2 (0.5 mol%) (R,S,S)-1 (1 mol%)

NO2 + Et 2Zn

Et *

NO2

94% ee (+)

1795

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

O P O O

P O

O

O

Fe

O

P O

P

O

2mol% Cu(OTf) 2 99% ee (R) Reetz (2002) 9

2mol% Cu(OTf) 2 97% ee (S) Chan (2002) 8

O

OPh O

O P O

O

O

O

O P O

O P O O

Bn N O

O

1 mol%CuOTf .0.5C 6H 6 96% ee (R) Tse & Wang (2010) 10

P O O

2 mol% CuOTf .0.5C 6H 6 95% ee (S) Wang (2013) 11

O O P

O

O O

P O

2 mol% CuTc 99% ee (R) Wang (2016) 12 Scheme 2. Binaphthol-derived ligands for asymmetric1,4-addition.

i-Pr N PPh 2

O

H N

N Mes = L

Mes N

O NHBu Bn

N i-Pr

N

III

‡

L

I

R Cu R

R Cu R O

N i-Pr

‡

L

O

N

Scheme 4. Mechanism of ligand accelerated catalysis in 1,4-addition. 2 mol% CuOTf.0.5C 6H 6 98% ee (R) Hoveyda (2001) 13

PPh2 0.1 mol% Cu(OTf) 2 0.25 mol% ligand 98% ee (S) Hayashi (2008) 14

PPh2 1 mol% Cu(OTf) 2 2.5 mol% ligand 98% ee (S) Hayashi (2012) 15

Scheme 3. Chiral Schiff base ligands for asymmetric conjugate addition.

Recently, Mauduit, and Campagne reported the coppercatalyzed enantioselective conjugate addition of dimethylzinc to unsaturated 2-acyl-N-methylimidazole using a chiral bidentate

PF6

PF6 N

PF6 N

N

N

N

i-Bu

N HO

OH 2 mol% Cu(OTf) 2 93% ee (R) Mauduit (2005) 17

OH 2 mol% Cu(OTf) 2 94% ee (R) Mauduit (2005) 18

2 mol% Cu(OTf) 2 93% ee (R) Cr évisy & Mauduit (2009) 19

Scheme 5. Chiral NHC ligands for asymmetric 1,4-addition.

1796

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

hydroxyalkyl-NHC ligand (Eq. 4).38 The 1,4-addition product, acylimidazole, was further converted to the corresponding aldehyde by treatment first with NaBH4, and then with MeI and 2 M NaOH. Me N

O R N

Cu(OTf) 2 (2 mol%) ligand 2 (3 mol%) + Me2 Zn

Me

O +

R 1O

toluene, -30 °C

OR 1

(eq. 4)

O

N

THF, 0 °C to rt, 16 h

R = alkyl, aryl PF6t-Bu N+

N ligand 2:

R 2 Zn (1.2 eq) Cu(OTf) 2 (2 mol%) ligand 1 (4.5 mol%)

R1 = Me, Et, -CH 2 CH2-, R = Me, Et -CH2 CH2 CH2 -, CH2C(Me) 2CH2 -

Me N

O

R *

n-BuLi (8 mol%)

(3 equiv)

O

up to 85% yield up to 95% ee

+

toluene, -30 °C

1

R = Me R1 = CH2 Ph R1 = OCH 2Ph

HO

up to 76% yield up to 99% ee O P N O

Et 2Zn (1.2 eq) Cu(OTf) 2 (2 mol%) ligand 1 (4.5 mol%)

R1

MeO

* R OR 1

R1 O

O

* * Et MeO R1 up to 66% yield up to 98% de up to 98% ee (major)

CH3 CH3

(S,R,R)-1

Scheme 7. Asymmetric conjugate addition of symmetric and unsymmetric 4,4disubstituted cyclohexadienones.

O

O Ar 1

+

Ar2

Ph

R 2Zn

Ar

R

1

Ar2

Me

Ph

N

Cu(OTf) 2 __chiral ligand

O

Me

N Mes

H N

Me P

Ph

Cu(OTf) 2 (2.5 mol%) 97% ee (S) Katsuki (2009) 22

P Me

R

Me PPh 2

CuCl2 2O (0.5 mol%) 98% ee (S) Endo & Shibata (2010) 23

H S Fc = ferrocenyl

Ph2P

Cu(OTf) 2 (1.5 mol%) 92% ee (R) Dogan & Bulut (2011) 25

HN

O

Cu(OTf) 2 (2 mol%) 98% ee (R) OH Crevisy & Mauduit (2012) 27 PPh 2

Ph2 P

t-Bu

N

CuCl2 .2H 2O or Cu(acac) 2 (5 mol%) 95% ee (R) Endo & Shibata (2012) 26

HO

Cu(OTf) 2.C 6 H6 (6 mol%) 96% ee (R & S) Sakaguchi (2012) 29 PPh 2

Cl

H N O

CH2OH CO2 Me

NH O

ONa

OH

Cl

N

O N P O Ph

PPh2 N

O

N

N

Ph

.2H

Fc

N

CuBr (1 mol%) 95% ee Huang (2010) 24

Me

Et

H O

P O O

OH Me Me OH

tBuONa

N

O

OH

CO2 Me

HOH 2C Cu(NO 3) 2 (5 mol%) 93% ee (R & S) Sakaguchi (2014) 31

OH OH

>99% ee Cu(OTf) 2 (1 mol%) Xu (2013) 30

OH OH OH Ph Ph

O O P

NEt2 CuCl2.2H 2 O (5 mol%) 97% ee (S) Cu(OTf) 2 (1 mol%) Endo & Shibata (2013) 32 95% ee (R) Jiang (2015) 33 Scheme 6. Efficient chiral ligands for acyclic enones.

Ph O P N O Ph

trans-(S,S,aR,S,S) Cu(OAc) 2.H 2O (1 mol%) 92% ee (S) in THF 99% ee (R) in toluene Zhang (2012) 28

1797

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

O

O +

MeO

Et 2Zn

2 mol% (S,R,R)-cat 1

OMe

C7H15 *

Me

MeO

OMe O

(R,S,S)-cat 1

MeO

OMe

cis 95%

Me Me

OMe

O

(R,S,S)-cat 1

97% ee

OMe

trans 98%

+ Et 2Zn

Me

OMe

cis 98% Scheme 8. Synthesis of cis- and trans-3,4,4,5-tetrasubstituted cyclohexanone.

The unsaturated acyl imidazole obtained after the HornerWadsworth-Emmons reaction was then employed for the asymmetric 1,4-addition to give the desoxypropionate unit (Scheme 9). As an application of this protocol, the authors achieved the enantioselective synthesis of ionone derivatives and (+)-ar-turmerone (Scheme 10). The same authors also reported a DFT study on the mechanism underlying the regioselective formation of the 1,4-addition product over the 1,6-addition product.39 Alexakis reported the asymmetric 1,4-addition of b,c-unsaturated a-ketoesters using trimethylaluminum instead of dialkylzinc.40

O OEt

R O

R = alkyl, aryl

Me 3Al (3 eq) CuTC (2 mol%) (R)-BINAP (5 mol%)

Me

O OEt

R

b)

Me N

Me Me O c)

C7H15 *

*

69% yield 95% de

Me N N

O O OMe P N EtO OEt

a) 1) NaBH4, MeOH, rt, 2 h; 2) MeI, EtOAc, 60 °C, 16 h; 3) 2 M NaOH, glycine, toluene, 80 °C, 5 h. b) 1) 3, NaH, THF, -78 o C to rt, 16 h; 2) NMI, n-BuLi, THF, -78 °C to rt, 5 h. c) Me 2Zn (3 equiv), Cu(OTf)2 (2 mol%), ligand 2 (3 mol%), nBuLi (8 mol%), THF, 0 °C to rt, 16 h. Scheme 9. Synthesis of desoxypropionate unit.

O 2 mol% (S,R,R)-cat 1

O

3:

trans 96%

+ Et 2Zn 97% ee

O

N 84% (E/Z > 99/1), 95% ee

2 mol% (S,R,R)-cat 1

H

85%

C7H15 * O

OMe

C7H15 *

OMe

76% yield 97% ee

MeO

Me O a)

N MeO

O

Me N

Me O

O up to 93% yield up to 99.5% ee

Using this catalyst system, the authors achieved the efficient synthesis of (S)-florhydral (Scheme 11) and unnatural a-amino acid precursors (Scheme 12).

multicomponent coupling can be realized. In their first report of asymmetric 1,4-addition in 1997, Feringa et al. described the reaction of a zinc enolate with aldehydes (Scheme 13).4b In 1999, Feringa also reported catalytic enantioselective annulations via 1,4-addition and aldol condensation to afford [n + 4] and [n + 3] annulation products. They reported three-component coupling using an allyl acetate and a catalytic amount of Pd(PPh3)4. A typical example of [n + 3] annulation is shown in Scheme 14.41 Alexakis and his-coworkers reported the reaction of zinc enolate with activated electrophiles such as nitroolefins and vinylsulfonates in the absence of a Pd catalyst (Schemes 15 and 16).42,43 We also investigated the direct trapping of the intermediate zinc enolates with allyl iodides. The results are summarized in Table 1. The reactions were carried out using 1 mol% of Cu(OTf)2 and 2.5 mol% of the ligand.7Table 2 Alexakis also reported the reaction of zinc or aluminum enolate with vinyl oxiranes, which led to the formation of optically active allylic alcohols with up to 98% ee. This methodology was applied to the formal synthesis of Clavularin B (Scheme 17).44 Huang reported a diastereo- and enantioselective dual tandem reaction that affords three contiguous stereocenters and disclosed the synthesis of functionalized pyrrolidine (Scheme 18).45 Experiment-based investigation of reaction mechanism As mentioned at the beginning of this article, detailed studies on the mechanism of 1,4-conjugate addition are very rare. As an exception, Kitamura and Noyori carefully elucidated the reaction mechanism for a dialkylzinc and copper(I)-sulfonamide system based on a kinetic study and structural analysis of the zinc enolate product by NMR and molecular weight measurements (Scheme 19).46 They proposed the mixed metal complex A as an active species. Complex A generates the catalyst/reagent/substrate complex B in an unfavorable equilibrium. The turnover limiting step is the following irreversible alkylation step, where alkyl group transfer is facile due to the sulfonamide spacer. The formation of stable dimeric alkylzinc enolate C is proposed to facilitate the regeneration of active species A.

Trapping of zinc enolates by some electrophiles Non-linear effect One of the characteristic features of copper-catalyzed 1,4-addition using dialkyl zincs is the generation of an intermediate zinc enolate. Therefore, if this zinc enolate is trapped by an electrophile,

Following the first discovery of the non-linear effect in catalytic asymmetric reactions by Kagan in 1986,47 numerous other reports

1798

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

O

Cu(OTf) 2 (2 mol%) ligand 2 (3 mol%)

Me N

+ Me 2 Zn

N

Me

n-BuLi (8 mol%) THF, 0 °C, rt, 24 h 83% yield 93% ee

O

Me N N

1) NaBH 4, MeOH, rt, 2 h 2) MeI, EtOAc, 60 C, 16 h 3) 2M NaOH, glycine toluene, 80 °C, 5 h Me

O H

70% yield 93% ee ionone derivatives O

Me N N

Cu(OTf) 2 (4 mol%) ligand 2 (6 mol%) + Me2 Zn

Me

O

n-BuLi (16 mol%) THF, 0 °C, rt, 24 h

Me N N

81% yield, 91% ee 1) BrMg Me

O

THF, 2h, rt 2) MeI, EtOAc, 60 °C, 16 h 3) DBU, toluene, 80 °C, 6 h

(+)-ar-turmerone 61% yield, 91% ee Scheme 10. Synthesis of (+)-ar-turmerone.

O OEt O

1) 2 equiv Me 3Al 5 mol% CuTC 5 mol% (R)-BINAP

Me

H

(S)

2) 3 drops H2 O 3 equiv NaBH 4 3) SiO 2-supported NaIO4

O

O

+

OZnR

Cu(OTf) 2 (1.2 mol%) ligand 1 (2.4 mol%)

R2 Zn

R O R 1 CHO

90% yield >99% ee >99% regioselectivity

H

OH

O

H

OH

R1 +

R1

R Scheme 11. Synthesis of (S)-florhydral.

R

trans-erythro

trans-threo 3:7

R = Me, Et; R 1 = Ph etc MeO

O

Scheme 13. Tandem 1,4-addition–aldol reaction.

O

Ph 2 equiv Me 3Al 5 mol% CuTC 5 mol% (R)-BINAP

MeO O

O

Me Ph

NaCNBH3 (4 equiv) p-anisidine (2 equiv) AcOH (4 equiv) CH 2Cl2, rt

MeO

O

MeO

Me

HN (R) (S) Ph

HN (S)

O

Me (S) Ph

+

OH

OH 88% yield 99% ee 50% de >99% regioselectivity

Scheme 12. Synthesis of unnatural a-amino acid precursors.

have discussed this phenomenon.48 In the asymmetric 1,4-addition carried out using a copper catalyst and dialkylzinc system, both positive and negative nonlinear effects were observed, which often give us useful information concerning the intermediate complexes, especially in the aggregation state. Feringa’s group also contributed to information regarding the non-linear effect in 1,4-addition, from an early stage. They

reported a positive non-linear effect (asymmetric amplification) in the reaction of chalcone or cyclohexanone with diethylzinc catalyzed by the Ni(acac)2-( )DAIB system,49 and a negative non-linear effect (asymmetric depletion) in the reaction of chalcone with diethylzinc catalyzed by the Cu(OTf)2-chiral phosphoramidite ligand.50 The work reported by Feng and his co-workers is noteworthy. They demonstrated remarkable asymmetric amplification in the 1,4-addition of thioglycolate to chalcones catalyzed by a chiral l-proline-derived N,N’-dioxide-La(OTf)3 complex (Eq. 5).51 La(OTf) 3 __chiral ligand (1:1; 10 mol%)

O Ph + HS

Ph

ligand:

O R

CO2Me

N N H O

O Ph

N OH N

O

R R = 2,6-diisopropylphenyl

S * Ph

CO2Me (eq. 5)

1799

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

Cu(OTf) 2 (2 mol %)

O

Me O P N O

Ph Me (4 mol %)

O +

Et 2 Zn

ligand 4: CuCl PdCl2 (10 mol%)

[Pd(PPh 3) 4] (2 mol %) 0 ºC, 12 h

Et

H O

Scheme 14. Catalytic enantioselective annulations via 1,4-addition and aldol cyclization.

Cu(OTf) 2 (1 mol %) Ph O P N O

+

Ph (2 mol %)

Et 2Zn

Et2 O, -30 ºC

(1.5equiv)

PivO

O

NO2 rt, 6 h

Et

NO2

72% trans:cis = 95:5 99% ee Scheme 15. Trapping of zinc enolate with nitroolefin.

O

n

OM

1st asymmetric 1,4-addition

n

O

R1

R3

NO2 or

PhO 2 S

SO2 Ph

O R3

n

2nd 1,4-addition (enolate trapping) R2

R1

R2 O R1

SO 2Ph or n

O

O

tert -butyl DiPPAM

Switching of enantioselectivity54

O

O

PPh2 N

DMF/H2 O, O2

88% trans:cis = 9:1 96% ee

O

(eq. 6) *

Na

O

KOtBu THF, rt

O

2) DBU

toluene, -30 ºC, 3 h

(1.0equiv)

AcO

Ph

1) (L + D)-ligand 4 (10 mol%) Cu(OTf) 2 (5 mol%) Et 2Zn (3 equiv)

R2 SO Ph 2 R1

Scheme 16. Trapping of metal enolate with nitroolefins or vinyl gem-disulfones.

Alexakis, Crévisy, and Mauduit reported asymmetric amplification in the enantioselective Cu/DiPPAM-catalyzed 1,6- and 1,4additions of diethylzinc to (di)enones (Eq. 6).52,53

A variety of compounds showing physiological activity, such as pharmaceuticals, pesticides, and perfumes have optically active moieties. In these compounds, one enantiomer often exhibits favorable physiological activity, while the other may exhibit no activity, inhibit favorable physiological activity, or even exhibit unfavorable physiological activity. Therefore, the development of a synthetic methodology that selectively produces one enantiomer with high ee is a very important and challenging topic of research. However, when amino acids or carbohydrates are to be used as a substrate or ligand, only one enantiomer of the product can be obtained. One of the solutions to overcome this limitation is reversal of enantioselectivity, which denotes the selective formation of both enantiomers from the same chiral origin. Reversal of enantioselectivity was observed by controlling the nature of the substituent in the catalyst and/or substrate, changing the central metal, or controlling the solvent, temperature, and additives. In asymmetric 1,4-addition, too, several unique methods to switch the stereochemistry of the products have been proposed. These reports are significant not only in terms of synthetic usefulness but also in providing relevant mechanistic information. In this chapter, we will introduce some recent examples in this regard. In 2009, Sakaguchi and his co-workers reported complete reversal of enantioselectivity in the Cu-catalyzed 1,4-addition of dialkylzinc to cyclic enone, in the presence of chiral azolium compound.21,55,56 Reversal of enantioselectivity was observed by changing the copper species. That is, 1,4-addition of diethylzinc to 2-cyclohexen-1-one catalyzed by Cu(OTf)2 combined with an azolium salt derived from (S)-leucinol produced the (S)-1,4-adduct in up to 81% ee, while the combination of the same ligand with Cu (acac)2 afforded the (R)-1,4-adduct in up to 82% ee. The same authors reported that the ee of each product was increased up to >99.5% and 86% by optimization of the substituents in the azolium salt and the type of dialkylzinc (Scheme 20). In 2012, the same authors reported that both Cu(OTf)2/CH2bridged ligand 5 and Cu(acac)2/(CH2)2-bridged ligand 6 combinations afforded the same enantiomer in up to 99% ee. On the other hand, the Cu(OTf)2/6 and Cu(acac)2/5 combinations afforded the opposite enantiomer in up to 84% ee (Scheme 21).57 Sakaguchi speculated that in the Cu(OTf)2/5 catalytic system, the anionic amidate/NHC-Cu species A might be involved, whereas the 1,4-addition catalyzed by Cu(acac)2/5 may proceed through model B, where the anionic acetylacetonate ligand coordinates to a Cu center (Scheme 22). Very recently, Sakaguchi reported that a change in the order of addition of the substrate (enone) and diethylzinc caused a reversal of enantioselectivity, as shown in Scheme 23.58c In 2012, Endo and Shibata reported the multinuclear Cu/Zn complex-catalyzed asymmetric 1,4-addition of organozinc

1800

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

Table 1 Enantioselective 1,4-addition, followed by trapping of zinc enolate with allyl iodides.

Cu(OTf) 2 (1 mol %)

N R2

N R3

O PPh2 (1.5 mol %) + R1 2Zn

a

CH 2Cl2, -40 ºC , time

I

O R3

(5 equiv) rt, 48 h

n R1

Entry

n

R1

R2

R3

Time/h

Yield/%a

trans:cis

ee of trans

1 2 3 4 5

1 1 1 1 0

Et Me Et Me Et

i-Pr i-Pr i-Pr i-Pr t-Bu

H H Me Me H

5 24 5 24 5

76 71 85 83 44

95:5 93:7 97:3 96:4 95:5

99 99 99 99 97

Combined yield of trans and cis isomers.

Table 2 Reaction of dienone 11. O

O O

Cu(OTf) 2 , ligand

Ar1

O

* 11

+

R

R

O 12

RM

1

Et2Zn

Ligand

Solvent

12/13

ee%

2-Me-THF

0/100

97

Et RH

O CH2Cl2

EtMgBr

N

>99/1

97

N

R'NHSO2Ar + ZnR 2

Cl HO

RZnNR'SO2 Ar + RH

CuX + ZnR 2

CuR + RZnX

RZnNR'SO2 Ar + CuR

(RZnNR'SO2Ar)(CuR) (A)

OH RM

O

R1

ZnR 2 or AlR 3 n

O

R1

O

ZnR 2

O

Kassoc

Cu(OTf) 2 , ligand (R,S,S)-1

n

R

R up to 74% yield up to 98% ee OH

O

1) Cu(OTf) 2 , ligand (R,S,S)-1 Me 2Zn 2)

O

O

Ar Ar

OAc

Ac2 O, NEt3, DMAP

R'

O

Me

Grubbs II catalyst

R'

O S

A

O

R

Cu R

N Zn

O S

O CuZnR 3

O

OZnR B

68% yield trans:cis = 2:1 98% ee (trans )

5 mol% Pd(OAc) 2 20 mol% PPh3 ammonium formate

1/2

Ar R 2 C

HO

N Zn R

Me

5 mol% Pd(P Ph3 )4

Ar 2

Scheme 18. Enantioselective tandem reaction to furnish pyrrolidines.

Na O

O

Ar1 H

N H H

PPh 2 N

2

N P O O

ligand:

H

up to 92% yield up to >99:1 dr up to 97% ee

H N

*

Ar2 NO2

Ar

O

13

O

H 1

Et 2O, -20 °C

Et 2Zn

*

O

Entry

CuCl (1 mol%) ligand (2 mol%)

+

DBU

RM (Et 2Zn or EtMgBr)

Ar 2

NO2

R' R

N Zn

O S

O

k

CuR OZnR

O

OH ZnI

Me Clavularin B

Scheme 17. Formal synthesis of Clavularin B.

Me

R Scheme 19. Catalytic cycle of the 1,4-addition of dialkylzincs to a,b-unsaturated ketones.

1801

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

+

O

O

cat. Cu(OTf) 2 (R 1 = Bn, R 2 = t-Bu)

O Bu 2Zn

Et 2Zn

Bu H N

N O

N

R1 +

Et 2 Zn

O

Cl

4 or 10 mol%

R2

O

>99.5% ee (R)a a

O

OH

cat. Cu(acac) 2 R 1 = Me, R2 = Bn

because of the rule of nomenclature

N N

Bn

H N 2 O

Et up to 74% ee (R)

OH

AgI

6 or 4 mol% Cu(OTf) 2 .C 6 H6

Et 86% ee (R)

rt or -20 °C 3h

O

Et

O

Et2Zn

in THF rt, 3 h

Scheme 20. Reversal of enantioselectivity by changing copper (II) sources.

Et up to 87% ee (R)

Scheme 23. Switching of enantioselectivity by modifying the addition order. O cat. Cu(OTf) 2/5 cat. Cu(acac) 2 /6

O +

R n 3 R3 R up to 99% ee O

R2 Zn

n R 3 R3

H N

N N R2 H

O

Cl

R1 OH

5

2 mol% of the ligand in THF afforded the 1,4-adduct in 94% yields and with 92% ee (S). On the other hand, the reaction in toluene gave the product in 96% yield and with 99% ee (R) (Eq. 7).

cat. Cu(OTf) 2/6 cat. Cu(acac) 2 /5

H N

N

n R 3 R3 R up to 84% ee

R2

N H

2 O

X

R1 OH

6

O R1

Scheme 21. Reversal of enantioselectivity by modifying the structure of the chiral ligand and metal combination.

Cu(OTf) 2/5

Ph N P O Ph

Cu(acac) 2 /5

R2 Et

N

N R1 Cu

N

Cu(OAc) 2.H2 O trans ligand L2 -50 °C, 16 h

Et

O

R1 *

Ph O P N O Ph

O

R2

in THF 92% ee (S) in toluene 99% ee (R)

(eq. 7)

trans-(S,S,aR,S,S) L2

O N

R2

+ Et2 Zn

N R2

O Cu Et

N

O

R1

O O

O

O LnZn

They explained this reversal phenomenon as shown in Scheme 26. The coordination of THF to the metal affects the asymmetric environment (refer to the original paper for more details).

O

ZnLn

A

B

O

Combination of Grignard reagents with copper

O

Et

Et

(S)

(R)

O

N N Bn

Cl 5

HN

i-Bu OH

Scheme 22. Explanation of the reversal of enantioselectivity by changing copper(II) sources.

reagents to acyclic and cyclic enones. In this reaction, regioisomeric SPINOL-PHOS ligands gave the opposite enantiomer of the product (Scheme 24).26 The authors proposed the structure of Zn- and Cu/Zn-complexes based on ESI-MS analysis (Scheme 25), although they did not mention the reason for the inversion of stereoselectivity. Zhang reported that the nature of the solvent dramatically inversed the enantioselectivity.28 That is, the reaction of chalcone with diethylzinc in the presence of 1 mol% of Cu(OAc)2
H2O and

The nucleophile used in copper-catalyzed 1,4-additions is not limited to dialkylzincs; other organometallic reagents such as Grignard reagents and organoaluminum reagents have been also studied. In 1988, Lippard reported the first enantioselective 1,4-addition of a Grignard reagent to an enone using a catalytic amount of copper amide complex, but the enantioselectivities were low.59 Subsequently, many reports on asymmetric1,4-addition have been published. However, the enantioselectivities were low except in two cases. In 2004, Feringa first reported the highly enantioselective (up to 96% ee) copper-catalyzed asymmetric conjugate addition of Grignard reagents to cyclic enones (Eq. 8).60

O + EtMgBr

CuCl (5 mol) (R,S)-TaniaPhos (6 mol%) Et 2O, 0 °C, 15 min NMe 2

Fe

PPh 2 PPh2

(R,S)-TaniaPhos

O (eq. 8) Et 100% coinv. 1,4- /1,2- =95/5 96% ee

1802

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

Et

O

Ph (S)

Ph

CuCl2.2H2O or Cu(acac)2(5 mol%) (S)-6,6'-SPINOL-PHOS SP1 (5 mol%)

CuCl2. 2H2O or Cu(acac)2(5 mol%) (S)-4,4'-SPINOL-PHOS SP2 (5 mol%)

O Ph

Ph

Et2Zn, THF, 0 °C

Et2Zn, THF, 0 °C

90% ee

Et

O Ph

Ph (R) 95% ee

Ph2P PPh2 OH

OH

OH

OH

PPh2 Ph2P

SP1

P O

Zn

O

Zn

P

SP2

Cu

Cu P

P

O

O O

O

P

P

Zn

Zn

P O O

P

Cu

Cu

Scheme 24. Concept of multinuclear Cu/Zn complex.

PPh2 Zn

O O

1,6-adduct 8 with high regio- and enantioselectivity. Only a trace amount (<2%) of the 1,4-adduct was formed, and the 1,2-addition product was not detected at all.

Ph2 P O O

Zn

R2 MgBr CuBr.SMe2 , (+)-7

O

PPh2 Ph 2P

R1

+

In 2008, Minnaard and Feringa reported the catalytic enantioselective 1,6-addition of Grignard reagents to linear dienones (Eq. 9).61 In the presence of (R,S)-( )-reversed josiphos 7 or (S,R)-(+)reversed josiphos (5.25 mol%) and CuBr
SMe2 (5 mol%), the addition of EtMgBr to b,c-unsaturated 1,6-addition proceeded to afford

P

Ar Me

O

P Me Me Ph

O O

Et

Me

O P

O

n

Ph

N Ph

P

Me P

O

Me

Ph

P OAr Me N

O

Cu

Ph

Ar

Me Et

Zn

L2-TS1 disfavored

OEt

+

R1

Me

O

Ph

N Ph

O OEt

(eq. 9)

10

Et Ph

O

Ar

Ar S product

O Zn O

n L2-THF-TS1 favored

Me O

1

N Me

Et

L2-THF-TS2 disfavored

Me

R2

O

Ph

P ArO Me

O

Ar

Ph

Me

Me

N Ph

O

8

9

Me Cu P Ar

Zn

R

2

69__88% yield, 8/10 = 95/5 __99/1, 73 __96% ee

Ph

N

O

Cu

P

Ph

Me

O

N Ph

Me

OEt

CH 2Cl2 -78 °C, 16 h R

Me

O

R1

OEt

Scheme 25. Proposed structure of Zn/SPI-complex.

Ph

R2

Me Me

O

P O Ar Me Cu P Et

Ph

O O

P Me N H

O

Me Me

Zn Ar L2-TS2 favored

Scheme 26. Reversal of enantioselectivity by choice of solvent.

Et

O

Ar

Ar R product

1803

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

Schmalz reported the enantioselective copper-catalyzed 1,4addition of Grignard reagents to 2-cyclohexen-1-one using a Taddol-derived phosphine-phosphite ligand in 2-methyl-THF as a solvent (Eq. 10).65⁄⁄

Me PCy 2 PPh 2

Fe

(R,S)-(-)- 6 , josiphos Me PPh2

Fe

5 mol% CuBr-SMe 2

Me

6 mol%

Ph2 P Cy 2P

PCy2

Fe O

(S,R)-(+)- 7, reversed josiphos

(R,S)-(-)- 7 , reversed josiphos

Br

P

Cu

P

Br

P Cu P

Et

A

P P

MgBr Br B

EtMgBr

(eq. 10)

up to 92% ee

2-Me-THF

Synthetic application to natural products In this chapter, we will demonstrate the total synthesis of natural products via a catalytic asymmetric conjugate reaction. Minnaard reported the total synthesis of phenolic glycolipid mycoside B and glycosylated hydroxybenzoic acid methyl ester HBAD-I, virulence markers of Mycobacterium tuberculosis (Scheme 29).68

P Br P CuIII Et

Et Cu

R

Thaler and Knochel reported the copper-catalyzed asymmetric 1,4-addition of magnesium organometallic reagents to provide chiral molecules, as shown in Scheme 28.66 In 2012, Guénée, Mauduit, and Alexakis reported the formation of quaternary stereogenic centers by NHC-Cu-catalyzed asymmetric 1,4-addition with Grignard reagents on polyconjugated cyclic enones. It is noteworthy that the reaction of 11 with diethylzinc exclusively furnished the 1,6-addition product 13.67

OEt

G

*

R = alkyl, aryl

OMgBr

EtMgBr

O

O

PPh2

+ R MgBr

Based on their own mechanistic study62 and the theoretical studies by Nakamura63 and Morokuma’s64 groups, Feringa proposed the mechanism shown in Scheme 27. The catalytic cycle starts with formation of reactive complex B from the dimeric resting state A of the catalyst. Intermediate B forms a p complex D with substrate C, followed by the formation of the copper (III) r complex E. Then, E undergoes sequential copper migration via r/p-allylcopper (III) complex F to the remote position. The catalytic cycle ends with reductive elimination to form product G. The preference for the 1,6-addition product over the 1,4-product is explained by the lower activation energy for the migration of the Cu complex as compared to that for alkyl addition at the 4-position, because this addition disturbs the conjugate system.

O

O O P O

OMgBr

Minnaard (2012)68 O

OEt

F

O

1. Cu(OTf) 2 (0.5 mol%) (S,R,R)-1 (1 mol%) Me2Zn, toluene, -25 °C

O Et

O

Me

OH

MeO

2. EtI, HMPA, 0 C,

O

OEt C

O

P Br P Cu MgBr O Et OEt D

O

P Br P CuIII Et

OMgBr OEt

HO

E

O HO OMe

Scheme 27. Proposed catalytic cycle for the asymmetric 1,6-addition of EtMgBr to ethyl sorbate.

mycoside B

Scheme 29. Synthesis of mycoside B.

CO2Me Et Pr

Pr

CO2Me

F3 C Me

0.5 mol%

1.5 mol% PPh2 Br Fe P Cu Cy2 2 CH2Cl2 , -75 °C

PCy2 Br Fe P Cu Ph 2 2 tBuOMe, -75 °C

99%, 93% ee

CO2 Me

Ph

Et Ph

EtMgBr Me

(E) CO2 Me

88%, 93% ee

Et CO2 Me

CO2 Me

EtMgBr

CuI (1 mol%) (S)-tol-BINAP (1.5 mol%) tBuOMe, -40 °C

F3C 99%, 96% ee

Ph (Z)

Et

CO2 Me

CuI (1 mol%) (S)-tol-BINAP (1.5 mol%) tBuOMe, -40 °C

Ph

Scheme 28. Copper-catalyzed 1,4-addition of organomagnesium reagents.

CO2 Me 86%, 94% ee

O

OMe

1804

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805

The same author reported the total synthesis of cyclo-archaeol (Scheme 30).69 Finally, we would like to show two recent reports of the enantioselective total synthesis of natural products, in which catalytic asymmetric 1,4-addition was used as the key step to generate the chiral center. Luo reported the synthesis of amphilectane and serrulatane diterpenoids. Asymmetric 1,4-addition was used for the synthesis of erogorgiaene (Scheme 31).70 Baran71 accomplished a 11-step synthesis of ( )-maoecrystal V starting from an enantioselective 1,4-addition modified by Schmalz’s catalyst and solvent system (Scheme 32).65

Schouten and Minnaard (2013)69 O

1. Cu(OTf) 2 (0.5 mol%)

O

(R,S,S)-1 (1 mol%) Me 2Zn, toluene, -25 °C 2. EtI, HMPA, 0 C,

1. Me2Zn 2.5 mol% Cu(OTf) 2(S,R,R)-1

OTMS 1) O , NaBH 3 4 2) MeOH, p-TSA

2. Et3N, HMPA TMSCl

O HO

OH

59% >99% de >99% ee

O cyclo-archaeol

Me 2Zn 2 mol% Cu(OTf) 2 4mol% Ph O PN O Ph

O

Et O

Et

H2N

then O EtO

O

O

EtO Me

EtO Me >95% ee

CN Me

Me Me

Me H Me erogorgiaene Scheme 31. Synthesis of erogorgiaene.

Baran (2016) 71 MgBr TMS 0.6 mol% CuI-SMe2 0.8 mol% Ph Ph

O

O

O O P O PPh2Ph

O

O

O

O

Me

Ph TMS

PhMe-2-MeTHF

O Me O O

80% yield 99% ee

Scheme 32. synthesis of maoecrystal V.

Acknowledgement

References

Scheme 30. Synthesis of cyclo-archaeol.

Luo (2016)70

We have summarized the recent progress in catalytic asymmetric 1,4-additions. Efforts for the development of chiral ligands and chiral catalysts toward 100% yield and 100% ee with a high TON and TOF will be continued for a variety of Michael acceptors. Attempts to extend catalytic asymmetric 1,4-addition to the synthesis of complex natural products have just been undertaken. In the early stages of research, dialkylzincs were the first choice for organometallic nucleophiles; however, Grignard reagents and other organometallic compounds such as organoborons72,73 have recently been used in copper-catalyzed 1,4-addition. Note that space constraints prevented us from including some significant reports on Rh, Ir, Pd-catalyzed74–87 and organocatalytic88,89 asymmetric 1,4-addition of organoboron reagents. More details of these studies can be found in the cited references.

We are grateful for the financial support by Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan and by Special Coordination Funds for Promoting Science and Technology, Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Innovative Bioproduction Kobe), MEXT, Japan.

O

OMe

Conclusion

maoecrystal V

Me

1. a) For books on asymmetric 1,4-addition, see: Perlmutter P. Conjugate addition reaction in organic synthesisTetrahedron organic chemistries series, Vol. 9. Oxford: Pergamon Press; 1992; b) Tomioka K, Nagaoka Y. In: Jacobsen EN, Pfaltz A, Yamamoto H, eds. Comprehensive asymmetric catalysis. Berlin, Heiderberg: Springer Velag; 1999. Chapter 31.1; c) Tomioka K, Nagaoka Y. In: Jacobsen EN, Pfaltz A, Yamamoto H, eds. Comprehensive asymmetric catalysis. Berlin, Heiderberg, New York: Springer Velag; 2004. Supplement to Chapter 31.1; d) Kotora M, Betik R. In: Cordova A, ed. Catalytic asymmetric conjugate reactions. Wiley-VCH; 2010. Chapter 2; e) Alexakis A, Krause N, Woodward S. In: Alexakis A, Krause N, Woodward S, eds. Copper-catalyzed asymmetric synthesis. Hoboken: Wiley; 2014. Chapter 2; f) Mauduit M, Baslé O, Clavier H, Crévisy C, Denicourt-Nowicki. In: Knochel P, Molander GA, eds. Comprehensive organic synthesis II, Vol. 4. Amsterdam: Elsevier; 2014:186. 2. a) For reviews on asymmetric 1,4-addition, see Alexakis A, Benhaim C. Eur J Org Chem. 2002;3221–3236; b) Hawner C, Alexakis A. Chem Commun. 2010;46:7295–7306; c) Jerphagnon T, Pizzuti MG, Minnaard AJ, Feringa BL. Chem Soc Rev. 2009;38:1039–1075; d) Alexakis A, Bäckvall JE, Krause N, Pàmies O, Diéguez M. Chem Rev. 2008;108:2796–2823. 3. Soai K, Hayasaka T, Ugajin S. J Chem Soc, Chem Commun. 1989;516–517. 4. (a) Feringa BL, Pineschi M, Arnold LA, Imbos R, de Vries AHM. Angew Chem Int Ed. 1997;36:2620–2622; (b) de Vries AHM, Meetsma A, Feringa BL. Angew Chem Int Ed. 1996;35:2374–2376. 5. Prior to Ref. 4. the pioneering work by Alexakis should be noted, see: Alexakis A, Frutos J, Mangeney P. Tetrahedron Asymmetry. 1993;4:2427–2430. 6. Schnnerl M, Seitz M, Kaiser A, Reiser O. Org Lett. 2001;3:4259–4262. 7. Kawamura K, Fukuzawa H, Hayashi M. Bull Chem Soc Jpn. 2011;84:640–647. 8. Liang L, A.-Yeung TT-L, Chan ASC. Org Lett. 2002;4:3799–3801. 9. Reetz MT, Gosberg A, Moulin D. Tetrahedron Lett. 2002;43:1189–1191. 10. Zhao Q-L, Tse MK, Wang L-L, Xing A-P, Jiang X. Tetrahedron Asymmetry. 2010;21:2788–2793. 11. Xing A-P, Bai C-B, Wang L-L. Tetrahedron. 2013;69:455–459. 12. Pang Z-B, Li H-F, Wang L-L. Chin Chem Lett. 2016;27:271–276. 13. Degrado SJ, Mizutani H, Hoveyda AH. J Am Chem Soc. 2001;123:755–756. 14. Kawamura K, Fukuzawa H, Hayashi M. Org Lett. 2008;10:3509–3512. 15. Ebisu Y, Kawamura K, Hayashi M. Tetrahedron Asymmetry. 2012;23:959–964. 16. Fraser PK, Woodward S. Tetrahedron Lett. 2001;42:2747–2749. 17. Clavier H, Coutable L, Guillemin J-C, Mauduit M. Tetrahedron Asymmetry. 2005;16:921–924. 18. Clavier H, Coutable L, Toupet L, Guillemin J-C, Mauduit M. J Organomet Chem. 2005;690:5237–5254. 19. Rix D, Labat S, Toupet L, Crévisy C, Mauduit M. Eur J Inorg Chem. 2009;1989–1999. 20. Jahier-Diallo C, Morin MST, Queval P, et al. Chem Eur J. 2015;21:993–997. 21. Shibata N, Okamoto M, Yamamoto Y, Sakaguchi S. J Org Chem. 2010;75:5707–5715.

M. Hayashi, R. Matsubara / Tetrahedron Letters 58 (2017) 1793–1805 22. 23. 24. 25. 26. 27. 28.

29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53.

54.

Uchida T, Katsuki T. Tetrahedron Lett. 2009;50:4741–4743. Endo K, Ogawa M, Shibata T. Angew Chem Int Ed. 2010;49:2410–2413. Guo S, Xie Y, Hu X, Xia C, Huang H. Angew Chem Int Ed. 2010;49:2728–2731. Dogan Ö, Bulut A, Polat S, Tecimer MA. Tetrahedron Asymmetry. 2011;22:1601–1604. Endo K, Hamada D, Yakeishi S, Ogawa M, Shibata T. Org Lett. 2012;14:2342–2345. Magrez M, Wencel-Delord J, Crévisy C, Mauduit M. Tetrahedron. 2012;68:3507–3511. a) Yu H, Xie F, Ma Z, Liu Y, Zhang W. Org Biomol Chem. 2012;10:5137–5142; b) Zhang H, Fang F, Xie F, Yu H, Yang G, Zhang W. Tetrahedron Lett. 2010;51:3119–3122. Dohi K, Kondo J, Yamada H, Arakawa R, Sakaguchi S. Eur J Org Chem. 2012;7143–7152. Ye F, Zheng Z-J, Deng W-H, et al. Chem Asian J. 2013;8:2242–2253. Kondo J, Harano A, Dohi K, Sakaguchi S. J Mol Catal A. 2014;395:66–71. Endo K, Yakeishi S, Hamada D, Shibata T. Chem Lett. 2013;42:547–549. Han L, Lei Y, Xing P, Zhao X-L, Jiang B. J Org Chem. 2015;80:3752–3757. Imbos R, Brilman MHG, Pineschi M, Feringa BL. Org Lett. 1999;1:623–625. Imbos R, Minnaard AJ, Feringa BL. Tetrahedron. 2001;57:2485–2489. Versleijen JPG, van Leusen AM, Feringa BL. Tetrahedron Lett. 1999;40:5803–5806. Alexakis A, Benhaim C. Org Lett. 2000;2:2579–2581. Drissi-Amraoui S, Morin MST, Crévisy C, et al. Angew Chem Int Ed. 2015;54:11830–11834. Drissi-Amraoui S, Schmid TE, Lauberteaux J, et al. Adv Synth Catal. 2016;358:2519–2540. Gremaud L, Alexakis A. Angew Chem Int Ed. 2012;51:794–797. Naasz R, Arnold LA, Pineschi M, Keller E, Feringa BL. J Am Chem Soc. 1999;121:1104–1105. Rathgeb X, March S, Alexakis A. J Org Chem. 2006;71:5737–5742. Germain N, Schlaefli D, Chellat M, Rosset S, Alexakis A. Org Lett. 2014;16:2006–2009. Welker M, Woodward S, Alexakis A. Org Lett. 2010;12:576–579. Guo S, Xie Y, Hu X, Huang H. Org Lett. 2011;13:5596–5599. Kitamura M, Miki T, Nakano K, Noyori R. Bull Chem Soc Jpn. 2000;73:999–1014; Kitamura M, Miki T, Nakano K, Noyori R. Tetrahedron Lett. 1996;37:5141–5144. Puchot C, Samuel O, Duñach E, Zhao S, Agami C, Kagan HB. J Am Chem Soc. 1986;108:2353–2357. For excellent review Girard C, Kagan HB. Angew Chem Int Ed. 1988;37:2922–2959. de Vries AHM, Jansen FGA, Feringa BL. Tetrahedron. 1994;50:4479–4491. Arnold LA, Imbos R, Mandoli A, de Vries AHM, Naasz R, Feringa BL. Tetrahedron. 2000;56:2865–2878. Hui Y, Jiang J, Wang W, et al. Angew Chem Int Ed. 2010;49:4290–4293. Magrez M, Wencel-Delord J, Alexakis A, Crévisy C, Mauduit M. Org Lett. 2012;14:3576–3579. (a) Other examples of non-linear effect in asymmetric 1,4-addition. See Zhou Q-L, Pfaltz A. Tetrahedron. 1994;50:4467–4478; (b) van Koten G. Pure Appl Chem. 1994;66:1455–1462. (a) For review on reversal of enantioselectivity, see Tanaka T, Hayashi M. Synthesis. 2008;3361–3376; (b) Tanaka T, Hayashi M. J Synth Org Chem Jpn. 2007;65:969–976.

1805

55. Okamoto M, Yamamoto Y, Sakaguchi S. Chem Commun. 2009;7363–7365. 56. Shibata N, Yoshimura M, Yamada H, Arakawa R, Sakaguchi S. J Org Chem. 2012;77:4079–4086. 57. Yoshimura M, Shibata N, Kawakami M, Sakaguchi S. Tetrahedron. 2012;68:3512–3518. 58. Matsumoto K, Nakano Y, Shibata N, Sakaguchi S. RSC Adv. 2016;6:7755–7759; . See alsoHarano A, Sakaguchi S. J Organometal Chem. 2011;696:61–67. 59. Villacorta GM, Rao CP, Lippard SJ. J Am Chem Soc. 1988;110:3175–3182. 60. Feringa BL, Badorrey R, Peña D, Harutyunyan SR, Minnaard AJ. PNAS. 2004;101:5834–5838. 61. den Hartog T, Harutyunyan SR, Font D, Minnaard AJ, Feringa BL. Angew Chem Int Ed. 2008;47:398–401. 62. Harutyunyan SR, López F, Browne WR, et al. J Am Chem Soc. 2006;128:9103–9118. 63. a) Yoshikai N, Yamashita T, Nakamura E. Angew Chem Int Ed. 2005;44:4721–4723; b) Yoshikai N, Yamashita T, Nakamura E. Chem Asian J. 2006;1:322–330. 64. Mori S, Uerdingen M, Krause N, Morokuma K. Angew Chem Int Ed. 2005;44:4715–4719. 65. Robert T, Velder J, Schmalz H-G. Angew Chem Int Ed. 2008;47:7718–7721. 66. Thaler T, Knochel P. Angew Chem Int Ed. 2009;48:645–648. 67. (a) Germain N, Magrez M, Kehrli S, Mauduit M, Alexakis A. Eur J Org Chem. 2012;5301–5306; (b) Tissot M, Poggiali D, Hénon H, et al. Chem Eur J. 2012;18:8731–8747. 68. Barroso S, Geerdink D, ter Horst B, Casa-Arce E, Minnaard AJ. Eur J Org Chem. 2013;4642–4643. 69. Ferrer C, Fordan P, Barroso S, et al. Org Biomol Chem. 2013;11:2482–2492. 70. Yu X, Su F, Yuan H, et al. J Am Chem Soc. 2016;138:6261–6270. 71. Cernijenko A, Risgaard R, Baran PS. J Am Chem Soc. 2016;138:9425–9428. 72. Yoshida M, Ohmiya H, Sawamura M. J Am Chem Soc. 2012;134:11896–11899. 73. Takatsu K, Shintani R, Hayashi T. Angew Chem Int Ed. 2011;50:5548–5552. 74. Gandi VR, Lu Y, Hayashi T. Tetrahedron Asymmetry. 2015;26:679–682. 75. Vlahovic S, Schädel N, Tussetschläger S, Laschat S. Eur J Org Chem. 2013;1580–1590. 76. Nishimura T, Kasai A, Nagaosa M, Hayashi T. Chem Commun. 2011;47:10488–10490. 77. Trost BM, Burns AC, Tautz T. Org Lett. 2011;13:4566–4569. 78. Chen G, Gui J, Li L, Liao J. Angew Chem Int Ed. 2011;50:7681–7685. 79. Shintani R, Takeda M, Nishimura T, Hayashi T. Angew Chem Int Ed. 2010;49:3969–3971. 80. Luo Y, Carnell AJ. Angew Chem Int Ed. 2010;49:2750–2754. 81. Chen J, Chen J, Lang F, et al. J Am Chem Soc. 2010;132:4552–4553. 82. Nishimura T, Wang J, Nagaosa M, et al. J Am Chem Soc. 2010;132:464–465. 83. Hu X, Zhuang M, Cao Z, Du H. Org Lett. 2009;11:4744–4747. 84. Shintani R, Tsutsumi Y, Nagaosa M, Nishimura T, Hayashi T. J Am Chem Soc. 2009;131:13588–13589. 85. Bürgi JJ, Mariz R, Gatti M, et al. Angew Chem Int Ed. 2009;48:2768–2771. 86. Nishimura T, Yasuhara Y, Sawano T, Hayashi T. J Am Chem Soc. 2010;132:7872–7873. 87. Kikushima K, Holder JC, Gatti M, Stoltz BM. J Am Chem Soc. 2011;133:6902–6905. 88. Inokuma T, Takasu K, Sakaeda T, Takemoto Y. Org Lett. 2009;11:2425–2428. 89. Turner HM, Patel J, Niljianskul N, Chong JM. Org Lett. 2011;13:5796–5799.