Palladium-catalyzed hydroesterification of alkynes in the presence of p-toluenesulfonic acid under a normal pressure of carbon monoxide

JOURNAL OF

MOLECULAR CATALYSIS Journal of

MolecularCatalysis 89 ( 1994) 151-158

Palladium-catalyzed hydroesterification of alkynes in the presence of p-toluenesulfonic acid under a normal pressure of carbon monoxide Yuichi Kushino, Kenji Itoh, Masahiro Miura”, Masakatsu Nomura Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan (Received

September 9, 1993; accepted December 3, 1993)

Abstract Hydroesterification

of terminal

alkynes

with butanol

proceeds

smoothly

and efficiently

under

a

of carbon monoxide by using a catalyst system of Pd(dba),/PPh,/TsOH (dba = dibenzylideneacetone,TsOH =p-toluenesulfonic acid) to give the corresponding 2-substituted 2-propenoic acid butyl esters in good selectivity and yield. Internal alkynes can also be hydroesterified under similar conditions. normal

pressure

Key words; alkynes; carbon monoxide; hydroesterification;

palladium

1. Introduction

Palladium-catalyzed carbonylation of terminal alkynes can give rise to either 2- and/or 3-substituted acrylic acid derivatives or acetylenecarboxylic acid derivatives, depending on the catalyst systems employed [l-3]. It has been reported that arylacetylenes undergo regioselective carbonylation in the presence of palladium catalysts in methanol containing hydrogen iodide to give methyl 2-arylpropenoates [ 4,5] which can be useful precursors for optically active 2-arylpropionic acids known as antiinflammatory agents [ 5,6]. Torii et al. have demonstrated that hydroaminocarbonylation of terminal alkynes proceeds regioselectively in the presence of palladium complexes and iodide promoters in diethylamine under considerably mild conditions [ 71. Selective formation of 2-substituted acrylate esters in hydroesterification of terminal alkynes using palladium dppb (dppb = Ph,P( CH,),PPh,) under neutral conditions without addition of iodides was described by Ali and Alper [ 81; *Corresponding

author.

0304-5102/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSD10304-5102(93)E0324-A

Y. Kushino et 01. / Journd

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however higher temperatures and carbon monoxide pressures are required. Recently, they have also reported that in contrast to the hydroesterification, hydrocarboxylation of alkynes can be carried out in the presence of formic acid under much milder conditions [ 91. Drent et al. have disclosed an effective catalyst system consisting of palladium( II) species, 2pyridinylphosphine, and an acid for the carbonylation of alkynes, especially propyne to methyl methacrylate [ lo]. On the other hand, we have reported that terminal alkynes are efficiently carbonylated even under a normal pressure of carbon monoxide in the presence of Pd(PPh,), or Pd( OAc) ,-dppf (dppf = 1,l ‘-bis( diphenylphosphino) ferrocene) using weakly acidic 3-or 4-substituted phenols as nucleophiles to give 2substituted 2-propenoate aryl esters along with the corresponding 3-substituted isomers [ 1 I]. In the case of aliphatic terminal alkynes, addition of a catalytic amount of acetic acid was found to enhance the reaction, remarkably. Subsequently, we have undertaken the terminal alkyne hydroesterification using less expensive aliphatic alcohols under mild conditions. It was found that the reaction efficiently and smoothly proceeded under a normal pressure of carbon monoxide when a catalyst system of Pd( dba) ,/PPh,/TsOH (dba = dibenzylideneacetone, TsOH =p-toluenesulfonic acid) was used. Carbonylation of internal alkynes with the system has also been examined. These results are described herein.

RC=CH

co/R’OH l Pd(dbajj4PPhJrsOH

1

R\ ,c=cHz R’OOC 2

+

R\ ,c=c; H 3

H COOR

2. Results and discussion 2.1. Carbonylation

ofphenylacetylene

in the presence of n-butanol

When the reaction of phenylacetylene (1, R = Ph) ( 1 mmol) was carried out in toluene in the presence of n-butanol (2, R’ = Bu) (4 mmol) and Pd( PPh,), (0.04 mol) at 100°C under a normal pressure of carbon monoxide for 2 h, butyl2-phenyl-2-propenoate (44%) was formed along with butyl (E) -cinnamate (5%). Addition of trifluoroacetic acid or TsOH (0.04 mmol) was found to considerably increase the yield of the propenoate ester, whereas acetic acid reduced the product yield. The combinations of Pd( dba)? with PPh, and dppf could also be used in place of Pd(PPh,),. It was of interest that Pd(dba)+lPPh3 gave a superior result than Pd( PPh,), to afford the propenoate ester in 89% yield (85% after purification). While the ligand, dba is considered to have less donating ability compared with PPh,, Pd( PPh,),-2dba was also better than Pd( PPh3), alone. 2.2. Hydroesterijcation

with various terminal alkynes and alcohols

The results for the reaction using various terminal alkynes and alcohols in the presence of Pd( dba)2/PPh,/TsOH are summarized in Table 2.4-Chloro-, 4-methyl-, and 4-methoxyphenylacetylenes and 6-methoxy-2-naphthylacetylene were carbonylated in the presence of n-butanol to give the corresponding butyl2-aryl-2-propenoates in good yield and selectivity. The reaction of 1-heptyne was somewhat slow. The reaction of phenylacetylene with a

Y. Kushino et al. /.loumal Table 1 Carbonylation

of phenylacetylene

Catalyst

Pd(PPh,)., Pd(PPh,), Pd(PPh,), WPPW, Pd(PPW, Pd( dba), Pd( dba)* Pd(dba), Pd( dba) Z Pd(dba), Pd(dba)2 Pd( OAc)z

of Molecular Catalysis 89 (1994) 151-158

(1, R = Ph) in the presence of n-butanol”

Acid

Ligand

CHJOOH CF,COOH TsOH TsOH TsOH TsOH TsOH TsOH TsOH TsOH TsOH

Rin 1

4-MeC,H, 4-MeO&H, 4-Cl&H, 6-MeO-2-naphthyl Ph Ph Ph Ph n-Pentyld

( %)b

Products

2dba’ 2dba 2PPh, 4PPh, dppf dppf, 2PPh, 2dppf 2dba, 4PPh,

“The reaction was carried out in toluene under carbon nol] : [Pd] : [acid] = 1 :4:0.04:0.04 (in mmol). bDetermined by GLC analysis. ‘Dibenzylideneacetone. dNot detected. ‘Isolated yield. ‘1,l ‘-Bis( diphenylphosphino)ferrocene.

Table 2 Hydroesterification

153

Recovery of 1 (a)

2

3

44

5 2

26 62 72 80 d

4 4 _d

41 89 (85)’ 83 56 41 24

5 4 2 3 5 2

2

1

monoxide

( 1 atm)

at 100°C for 2 h.

1 2

4 44 2

[l] : [buta-

with various terminal alkynes and alcohols” R’OH

n-BuOH n-BuOH n-BuOH n-BuOH n-PrOH n-HexOH sec.-BuOH wt.-AmOH n-BuOH

Products ( %)b 2

3

15 92 88 76 85 14 72 88 53

2 1 4 _c 4 3 3 6 3

“The reaction was carried out in toluene under carbon monoxide ( 1 atm) at 100°C for 2 h by using Pd(dba),/ PPhJTsOH. [1]:[R’OH]:[Pd(dba),]:[PPh,]:[TsOH]=1:4:0.04:0.16:0.04(inmmol). “Determined by GLC analysis. ‘Not detected. dReaction for 4 h.

Y. Kushino et al. /Journnl

154

r,fMolecular

Catalpis

89 (1994) 151-158

number of aliphatic alcohols indicated that secondary and tertiary alcohols could be used as well as primary ones. 2.3. Curhonylation

of internal alkynes

Table 3 shows the results for the carbonylation of various internal alkynes by using the catalyst system of Pd( dba),/PPh,/TsOH. The reaction of 1,2_diphenylacetylene in the presence of n- and sec.-butanols gave n- and sec.-butyl (E)-2,3-diphenyl-2-propenoates in 8 1 and 89% yields. The reaction of 4-octyne with n-butanol was considerably slow. However, the use of dppp ( 1,3-bis( diphenylphosphino)propane) in place of PPh3 was found to enhance the reaction to afford the expected ester in 75% yield. The reaction of l-phenyl-lheptyne gave a mixture of butyl (E)-2-phenyl-2-octenoate and butyl (E)-3-phenyl-2pentyl-2-propenoate in a ratio of 61: 39. Similar product distributions were also observed Table 3 Carbonylation

of internal alkynes in the presence of n-butanol”

Alkyne

Yield (%)C

Product(s) (Ratio)b

81 (89)d

Ph.CIC-Ph 8 (75)e

n-Pr-CIC-n-Pr

x

u

/

-

\

CSC-n-Pentyl

R-CzC-COOMe

n_B;s;pentyl

n-BuOOC

x%rz,” X=H (61:39)

56

X=Me (58:42) X=0 (56:44)

85 79

H

R=Ph R=n-Pentyl

81 56

R-CrC I-l R=Ph (63:37) R=n-Pentyl (39:61)

56 88

“The reaction was carried out in toluene under carbon monoxide ( I atm) at 100°C for 2 h by using Pd(dba)?/ PPh,/TsOH. [Alkyne] : [R’OH] : [Pd(dba),] : [PPh,] : [TsOH] = 1:4:0.04:0.16:0.~4(in mmol). hDetermined by GLC or ‘H NMR analysis. ‘Isolated yield. ‘Reaction with sec.-BuOH in place of n-BuOH. ‘Reaction using dppp in place of PPh,.

Y. Kushino et al. /Journal

of Molecular Catalysis 89 (1994) 151-158

Pd(0) /

155

HPdoTs

Scheme

I.

in the reactions of 1- (4-chlorophenyl) - and 1- (4-methylphenyl) - 1-heptynes. Methyl 3phenyl-2-propynoate and methyl 2-octynoate were regio- and stereoselectively carbonylated to give the corresponding fumaric acid ester derivatives. The reactions of (E) -1,4-diphenyl1-buten-3-yne and (E) - I-phenyl- 1-nonen-3-yne also proceeded regioselectively to give the corresponding products carbonylated at the 3-position of the enynes. The products were mixtures of (E), (E) and (E), (Z) isomers. 2.4. Reaction scheme A probable mechanism for the carbonylation of terminal alkynes in the presence of TsOH is illustrated in Scheme 1 in which neutral ligands are omitted. The observed regio- and stereo-chemistries of the products appear to be mostly consistent with those in the alkyne carbonylations under acidic conditions reported previously [4,5,9]. Thus, it may be reasonable to consider that hydridopalladium complex formed by the reaction of palladium( 0) species with TsOH as the key intermediate [ 7,9]. This is also supported by the fact that a peak at - 7.11 ppm which is assignable to H-Pd species was observed in the ‘H NMR spectrum of a mixture of Pd(PPh3), and TsOH in toluene-butanol. The spectrum of a mixture of Pd(PPh3), and CF,COOH in benzene-d, also showed a peak at - 7.73 ppm. Addition of the hydrido complex to the alkyne may give a vinyl-palladium complex, and subsequent insertion of carbon monoxide followed by reaction with alcohol affords a product, regenerating palladium( 0) species. The hydrido and vinyl-palladium intermediates may exist as ion pair complexes, [ (H or vinyl) -PdL,] + -0Ts (L = neutral ligands). Tosylate and trifluoroacetate, compared with acetate, seem to be preferable for the formation of such species. This could make alkyne and carbon monoxide facile to incorporate to the corresponding complexes as the ligands, so that the whole reaction proceeded smoothly. Recently, reaction of Pd( dba), with PPh, has been throughly studied and it has also been demonstrated that iodobenzene reacts with Pd(dba)+PPh, more slowly than with Pd( PPh3)4, this being attributable to the stability of Pd( dba) ( PPh3)2 [ 121. ZPPh,

Pd( dba)*-

ZPPh,

Pd( dba) ( PPh,) 2 c;lPd(PPh3)‘, dba

In the present reaction, Pd( dba),APPh, gives better product yield than Pd(PPh3).+ A possible explanation for this could be that the coordination of dba to the palladium(O) species was also significant in the less donating solvent, toluene, which interfered with the

156

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et al. /Journd

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Catalwis

89 (1994)

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approach of two alkyne molecules to the complex to suppress formation of oligomeric products which could not be detected by GLC analysis, while the role of the ligand should be further investigated. Zargarian and Alper have demonstrated that in the palladiumcatalyzed hydrocarboxylation of alkynes, a mixed ligand system of PPh,-dppb shows significant ligand synergism in a number of cases [ 91. They suggested two or more metal centers in the reaction as the possible rationalization. In the present case, however, it seems less probable, since dba can not extend as dppb. The results of the carbonylation of the enyne compounds suggest that the configuration of the reaction intermediates partly isomerizes. Such an isomerization in vinyl-palladium complex has been discussed previously [ 9,131.

3. Experimental ‘H NMR spectra were obtained with a JEOL JNM-GSX-400 spectrometer for CDC13 solutions using tetramethylsilane as internal standard. GC-MS spectra were obtained with a JEOL JMS-DX-303 spectrometer or a Shimadzu GCMS-QP-2000A spectrometer. GLC analysis was carried out on a Shimadzu GC-8APF gas chromatograph with a silicon OV17 column (diameter 2.6 mm X 1.5 m) or with a CBP- 1 capillary column (diameter 0.5 mmX25 m). Terminal alkynes (R in 1; 4-methylphenyl, 4-chlorophenyl, 4-methoxyphenyl, and 6methoxy-2-naphthyl), 1-ary- 1-heptynes, methyl 3-phenyl-2-propynoate, methyl 2-octynoate, 1,4-diphenyl-3-buten-3-yne, and 1-phenyl- 1-nonen-3-yne were prepared according to the methods reported previously [ 141. The following typical procedure illustrates the carbonylation method. 3.1. Carbonylation

ofphenylacetylene

in the presence of n-butanol

A mixture of phenylacetylene ( I mmol), Pd( dba) 7 (0.04 mmol) ,p-toluenesulfonic acid monohydrate (0.04 mmol), PPh, (0.16 mmol), and n-butanol (4 mmol) in toluene (5 ml) was stirred under 1 atm of carbon monoxide at 100°C for 2 h. GC and GC-MS analyses confirmed formation of a mixture of butyl 2-phenyl-2-propenoate (89%) and butyl 3phenyl-2-propenoate (4%). The former ester (85%) was also isolated by column chromatography on silica gel. 3.2. Products The configurations of the following compounds were determined on the basis of their ‘H NMR spectra. Butyl (E)-2,3-diphenyl-2-propenoate: 6 0.91 (3H, t, J 7.3), 1.36 (2H, qd, / 7.3, 6.8), 1.64 (2H, tt,J6.8, 6.8), 4.20 (2H, t,J6.8), 7.03-7.39 (lOH, m), 7.82 (IH, s). Butyl (E) -2.prop@2-hexenoate: S 0.89-0.97 (9H, m), 1.37-l .52 (6H, m), 1.65 (2H, tt,J6.8, 6.8), 2.15 (2H, td, /7.3, 7.3), 2.27 (2H, t,J7.8), 4.13 (2H, t, J6.8), 6.74 (lH, t, J 7.3). Butyl (E) -2-phenyl-2-octenoate: 6 0.84 (3H, t, J 7.3), 0.90 (3H, t, ./ 7.3), 1.2 l-l .26

Y. Kushino et al. /Journal of Moleculnr Catuiwis 89 (1994) 151-158

157

(4H, m), 1.33 (2H, tt,J7.3,7.3), 1.42 (2H, tt,J7.3,7.3), 1.58-1.64 (2H,m),2.07 (2H, dt,J7.3, 7.3),4.14 (2H, t,J6.8),7.04 (IH, t,J7.3),7.15-7.37 (5H, m). Butyl (E)-2-pentyl-3-phenyl-2-propenoate: S 0.95 (3H, t, .I 7.3), 0.97 (3H, t, J 7.3), 1.31-1.36 (4H, m), 1.43-1.57 (4H, m), 1.67-1.74 (2H, m), 2.48-2.52 (2H, m), 4.21 (2H, t, J6.8), 7.15-7.39 (5H, m), 7.64 (IH, s). Butyl (E)-2-(4-methylphenyl)-2-ocrenoate: 6 0.85 (3H, t, J 6.8), 0.91 (3H, t, J 7.3), 1.21-1.25 (4H, m), 1.30-1.45 (4H, m), 1.57-1.64 (2H, m), 2.08 (2H, td,J7.3,7.3), 2.36 (3H, s),4.14 (2H, t,J6.8), 7.02 (IH, t,J7.8), 7.04-7.17 (4H, m). Butyl (E) -2-pentyl-3-(4-merhylphenyl) -2-propenoate: 6 0.90 (3H, t, J 6.8)) 0.97 (3H, t,J7.3), 1.28-1.36 (4H,m), 1.40-1.50 (2H,m), 1.51-1.57 (2H,m), 1.66-1.74 (2H,m), 2.37 (3H, s), 2.49-2.53 (2H, m), 4.21 (2H, t, J6.8), 7.18-7.28 (4H, m), 7.61 (IH, s). Bcltyl (E)-2-(4-chlorophenyl)-2-octenoate: 6 0.85 (3H, t, ./ 6.8), 0.91 (3H, t, J 7.3), 1.20-1.25 (4H,m), 1.31-1.38 (2H,m), 1.57-1.64 (2H,m),2.05 (2H, td,J7.3,7.3),4.14 (2H, t, J6.8), 7.06 (IH, t, J7.8). Butyl (E) -2.pentyl-3-(4-chlorophenyl)-2-propenoate: 6 0.89 (3H, t, J 7.3), 0.97 (3H, t,J7.3), 1.31-1.36 (4H,m), 1.40-1.56 (4H,m), 1.67-1.74 (2H,m),2.45-2.49 (2H, m), 4.21 (2H, t, J6.8), 7.26-7.37 (4H, m), 7.57 (IH, s). Methyl (E) -3-phenyl-3-butoxycarbonyl-2-propenoate: 6 0.9 1 (3H, t, J 7.3), 1.36 (2H, qt, J7.3, 7.3), 1.64 (2H, tt, J6.8, 7.3), 3.60 (3H, s), 4.21 (2H, t, J6.8), 6.99 (IH, s), 7.23-7.37 (5H, m). Merhyl (E)-3-butoxycarbonyl-2-octenoare: 6 0.89 (3H, t, J 6.8), 0.95 (3H, t, J 7.3), 1.31-1.35 (4H,m), 1.35-1.48 (4H,m), 1.64-1.71 (2H,m),2.78 (2H, t,J7.3), 3.77 (3H, s), 4.20 (2H, t,J6.8), 6.72 (IH, s). Butyl (Z) -2-( (E) -styryl) -3-phenyl-2-propenoute: 6 0.99 (3H, t, J 7.3)) 1.49 (2H, qt, J 7.3, 7.3), 1.73-1.80 (2H, m), 4.31 (2H, t, J 6.8), 7.06 (IH, d, J 16.4), 7.23-7.47 (IOH, m), 7.28 (IH, d, J 16.4), 7.57 (IH, s). Butyl (E) -2-( (E) -styryl) -3-phenyl-2-propenoute: 6 0.86 (3H, t, J 7.3)) 1.25 (2H, qt, J 7.3,7.3), 1.60-1.63 (2H, m), 4.27 (2H, t,J6.8), 6.64 (IH, d, J 16.4), 6.74 (IH, s), 6.88 (lH, d, J 16.4), 7.23-7.47 (IOH, m). Butyl (Z) -2-( (E) -sfyryl) -2-octenoute: S 0.89-0.92 (3H, m), 0.95-0.99 (3H, m), 1.301.36 (4H, m), 1.41-1.54 (4H, m), 1.67-1.76 (2H, m), 2.31 (2H, td,J7.3,7.3),4.28 (2H, t, J 6.8), 6.02 (IH, t, J 7.8), 6.58 (IH, d, J 16.4), 6.73 (IH, d, J 16.4), 7.20-7.39 (5H, m). Butyl (E) -2-( (E) -styryyl) -2-octenoute: 6 0.89-0.92 (3H, m) ,0.95-0.99(3H, m) , 1.301.36 (4H, m), 1.41-1.54 (4H, m), 1.67-1.76 (2H, m), 2.40 (2H, td,J7.3,7.3),4.21 (2H, t, J 6.8), 6.75 (IH, t, J 7.8), 6.90 (IH, d, J 16.4), 7.02 (IH, d, J 16.4), 7.20-7.39 (5H,

m).

4. References [I] R.F. Heck, Palladium Reagents in Organic Synthesis, Academic Press, New York, 1985. [21 A. Mullen, in J. Falbe (Ed.), New Synthesis with Carbon Monoxide, Springer-Verlag, New York/Heidelberg/Berlin, 1980, Ch. 3. [3] J. Tsuji, Organic Synthesis with Palladium Compound, Springer-Verlag, New York/Heidelberg/Berlin, 1980.

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