Abstract:
An optically active arylacetic acid derivative of the formula: ##STR1## wherein R 1  and R 2  are the same or different and are each an hydrogen atom, a lower alkyl group or a phenyl group; and Ar is a group of the formula: ##STR2## a group of the formula: ##STR3## wherein R 3  and R 4  are the same or different and are each a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a difluoromethoxy group, a trifluoromethyl group or a phenyl group is prepared in good conversion and optical yield by asymmetrically reducing an ethylenically unsaturated compound of the formula: ##STR4## wherein R 1 , and R 2  and Ar are the same as defined above with hydrogen in the presence of a metal catalyst modified with a ligand selected from the group consisting of a specific optically active metallocenyl phosphine derivative and a specific optically active binaphthyl derivative.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for preparing an optically active arylacetic acid derivative. More particularly, the present invention relates to a process for preparing an optically active arylacetic acid derivative useful as an intermediate for the preparation of medicines and agricultural chemicals. 
     2. Description of the Prior Art 
     It is known from U.S. Pat. No. 4,409,397 to use a catalyst of the formula: 
     
         LM(olefin).sub.2.sup.+ X.sup.-                             (V) 
    
     wherein M is a rhodium atom, a ruthenium atom or an iridium atom, L is an asymmetric ligand of ferrocenyl phosphine or pyridinyl phosphine, (olefin) 2  represents 2,5-norbornadiene or 1,5-cyclooctadiene, and X is ClO 4 , BF 4  or PF 6  in the preparation of optically active phenylacetic acid by asymmetric reduction with hydrogen. As ferrocenyl phosphine, disclosed in this patent is an optically active ferrocenyl phosphine of the formula: ##STR5## wherein R 5  &#39; and R 6  &#39; are each a lower alkyl group, a C 5  -C 8  cycloalkyl group, a phenyl group or a C 5  -C 6  heterocyclic group, Q is a lower alkyl group, an alkenyl group or a group of the formula: 
     
         C(R.sub.7 &#39;)(R.sub.8 &#39;)-Y&#39; 
    
     wherein R 7  &#39; and R 8  &#39; are each a hydrogen atom, a lower alkyl group or an aryl group or together form a cycloalkyl group, and Y&#39; is an hydrogen atom, a hydroxyl group, an acyloxy group or a group of the formula: 
     
         Z&#39;(R.sub.10 &#39;).sub.2 or PR.sub.10 &#39;R.sub.11 &#39; 
    
     wherein Z&#39; is N, P, As or Sb, R 10  &#39; and R 11  &#39; are each a hydrogen atom or an alkyl group or (R 10  &#39;) 2  forms a heterocyclic group containing N or P in Z&#39; and optionally additional N or O; and n is 0 (zero) or 1 (one). 
     The process for preparing the optically active phenylacetic acid derivative by using a metal catalyst modified with such optically active ferrocenyl phosphine compounds is not industrially satisfactory since it cannot necessarily produce the desired compound in a high optical yield and conversion. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a process for preparing an optically active arylacetic acid derivative in a high yield and high conversion. 
     Another object of the present invention is to provide a process for preparing an optically active arylacetic acid in the presence of a metal catalyst modified with an optically active metallocenyl phosphine derivative or an optically active binaphthyl derivative. 
     These and other objects of the present invention are achieved by a process for preparing an optically active arylacetic acid derivative of the formula: ##STR6## wherein R 1  and R 2  are the same or different and are a hydrogen atom, a lower alkyl group or a phenyl group; and Ar is a group of the formula: ##STR7## a group of the formula: ##STR8## wherein R 3  and are R 4  are the same or different and each a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a difluoromethoxy group, a trifluoromethyl group or a phenyl group, which comprises asymmetrically reducing an ethylenically unsaturated compound of the formula: ##STR9## wherein R 1 , R 2  and Ar are the same as defined above with hydrogen in the presence of a metal catalyst modified with a ligand selected from the group consisting of: 
     an optically active metallocenyl phosphine derivative of the formula: ##STR10## wherein R 5  and R 6  are the same or different and are each a lower alkyl group, a C 5  -C 8  cycloalkyl group, an aryl group or a C 5  -C 6  heterocyclic group; R 7  and R 8  are the same or different and are each a hydrogen atom or a lower alkyl group; X is a methylene group, an oxygen atom or a group of the formula: -NR 9  wherein R 9  is an hydrogen atom or a lower alkyl group; Z is an alkylene group, or a group of the formula: ##STR11## Y is a group of the formula: -OR 10  or ##STR12## wherein R 10 , R 11  and R 12  are the same or different and are each a hydrogen atom or a lower alkyl group or R 11  and R 12  together form a heterocyclic group containing the nitrogen atom to which they are bonded and optionally an additional oxygen or nitrogen atom; M is Fe, Ru or Os; and n is 0 (zero) or 1 (one) and an optically active binaphthyl derivative of the formula: ##STR13## wherein R is a phenyl group, a p-tolyl group, a p-methoxyphenyl group or a cyclohexyl group. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the context of the present invention, &#34;halogen&#34; is intended to mean fluorine, chlorine, bromine and iodine, the terms &#34;lower alkyl&#34; or the &#34;lower alkoxy&#34; are intended to include those having 1 to 6 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, isobutyl, isoamyl, pentyl, hexyl, or methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, pentyloxy or hexyloxy, the &#34;aryl group&#34; is intended to encompass phenyl, p-tolyl, p-methoxyphenyl, etc., the &#34;alkylene group&#34; is intended to mean a divalent lower alkenyl group having 1 to 6 carbon atoms such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, ethylethylene, methyltetramethylene, and the heterocyclic group formed by R 11  and R 12  is intended to mean pyrrolidinyl, piperidino, morpholino, piperazyl, hexahydro-1H-azepinyl, 4-methylpiperazyl, etc. 
     As the ethylenically unsaturated compound (II) used in the process of the present invention, there are exemplified 2-phenyl-3-methylcrotonic acid, 2-(4-chlorophenyl)-3-methylcrotonic acid, 2-(4-methoxyphenyl)-3-methylcrotonic acid, 2-(4-difluoromethoxyphenyl)-3-methylcrotonic acid, 2-(4-isobutylphenyl)acrylic acid, 2-(6-methoxynaphthyl-2)acrylic acid, 2-phenylacrylic acid, 2-phenyl-3-ethylpentenoic acid, 2-(4-chlorophenyl)-3-ethylpentenoic acid, 2-(2-naphthyl)-3-methylcrotonic acid, 2-phenyl-3-methylcinnamic acid, 2-phenyl-3-methyl-2-pentenoic acid, etc. These and other compounds of the formula (II) can be prepared by an analogous process to that described in U.S. Pat. No. 4,409,397, the disclosure of which is hereby incorporated by reference. 
     Among the optically active metallocenyl phosphine derivatives, a derivative (III) wherein the metal atom M is an iron atom is preferred. Preferably, R 5  and R 6  are independently a t-butyl group, a cyclohexyl group or a phenyl group; R 7  is a hydrogen atom; R 8  is a methyl group; X is NMe; Z is a methylene group, an ethylene group, a trimethylene group, a tetramethylene group or a carbonyl group; Y is --N(R 11 )(R 12 ) wherein R 11  and R 12  are independently a lower alkyl group. 
     According to one embodiment of the present invention, a metal catalyst modified with such metallocenyl phosphine derivative (III) is used. Preferred examples of the metal component in the catalyst are transition metals such as rhodium, iridium and ruthenium. 
     Specific examples of the metal catalyst are as follows: ##STR14## Rh[(R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  ](NBD)BF 4 , Rh[(R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  ] 2  ClO 4 , 
     Ru 2  Cl 4  [(R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  ] 2   
     wherein ##STR15## and (R)-(S)-BPPF-NMeCH 2  -CH 2  NEt 2  represent (R)-N-methyl-[2-(1-piperidine)ethyl]-1-[(S)-1&#39;,2-bis(diphenylphosphino)-ferrocenyl]ethylamine and (R)-N-methyl-[2-(diethylamino)ethyl]-1-[(S)-1&#39;,2-bis(diphenylphosphino)ferrocenyl]ethylamine, respectively, and NBD represents 2,5-norbornadiene. 
     The modified metal catalyst can be prepared by a per se conventional process according to those described in Bull. Chem. Soc. Jpn., 53, 1138 (1980), Acc. Chem. Res., 15, 395, (1982), J. Am. Chem. Soc., 99, 6262 (1977) and J. Am. Chem. Soc., 108, 6405 (1986). 
     For example, (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  is prepared by reacting (R)-(S)-BPPF-OCOMe with HNMeCH 2  CH 2  NEt 2  according to the following reaction formula: ##STR16## 
     Rh[(R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  ](NBD)BF 4  is prepared by reacting Rh(NBD)2BF 4  with (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  in methanol to replace NBD with (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2 . 
     Specific examples of the metal catalyst modified with the optically active binaphthyl derivative (IV) are 
     Rh(BINAP)(COD)BF 4 , 
     Rh(BINAP) 2  ClO 4 , and 
     Ru 2  Cl 4  (BINAP) 2   wherein BINAP represents 2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl and COD represents 1,5-cyclooctadiene. These catalysts are prepared by a per se conventional process according to those described in Tetrahedron, 40, 1245 (1984), J. Chem. Soc., Chem. Commun., 922 (1985), Japanese Patent Kokai Publication Nos. 61587/1985 and J. Org. Chem., 51, 629 (1986). For example, Rh(BINAP)(COD)BF 4  is prepared by reacting Rh 2  (COD) 2  Cl 2  with BINAP in methanol in the presence of AgBF 4  to replace COD with BINAP. 
     In the process according to the present invention, the catalyst is used in an amount of 0.001 to 10% by mole, preferably 0.01 to 1% by mole, based on the amount of the ethylenically unsaturated compound (II). 
     Usually, the reaction of the present invention is carried out in a solvent. Specific examples of the solvent are organic solvents such as methanol, ethanol, isopropanol, butanol, methyl acetate, benzene, toluene, xylene, tetrahydrofuran, and water or mixtures thereof. Among them, methanol and ethanol are preferred. The solvent is used in an amount of 1 to 500 parts by weight, preferably 10 to 200 parts by weight, per part by weight of the ethylenically unsaturated compound (II). 
     The pressure of hydrogen to be supplied to the reaction system is usually from atmospheric pressure to 500 kg/cm 2 , preferably from 10 to 150 kg/cm 2 . 
     The reaction temperature is usually from 0° to 150° C., preferably from room temperature to 150° C. 
     The reaction time is not critical in the present invention and is usually from 1 to 90 hours. 
     To the reaction system, a tertiary amine such as triethylamine and tri-n-propylamine may be added in an amount of 0.1 to 100 moles, preferably 1 to 20 moles per mole of the catalyst. 
     According to the process of the present invention, the optically active arylacetic acid derivative (I) is prepared in good conversion and good optical yield. By changing the configuration of the modifying compound of the metal catalyst, the configuration of the produce arylacetic acid derivative (I) is controlled. 
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Practically and presently preferred embodiments of the present invention are shown in the following examples. 
    
    
     EXAMPLE 1 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR17## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 20 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (211.8 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      93.8% (+isomer)______________________________________ 
    
     Conversion, selectivity and optical yield were calculated from the results of liquid chromatography using an optically active column and an angle of rotation. 
     EXAMPLE 2 
     Rh(NBD) 2  BF 4  (1.9 mg, 0.005 mmol) and (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  (4.5 mg, 0.00625 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the autoclave was cooled and hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (213 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      85.4% (+isomer)______________________________________ 
    
     (R)-(S)-BPPF-NMeCH 2  CH 2  Am has the chemical structure of the formula: ##STR18## wherein Am is NEt 2  or ##STR19## 
     EXAMPLES 3-11 
     In the same manner as in Example 2 but using an optically active ferrocenyl phosphine derivative shown in Table 1 in place of (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2 , the reaction and post-treatment were carried out to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid. The results are shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________ExampleFerrocenylphosphine derivative                        Conver-                             Selecti-                                  Configu-                                       OpticalNo.  (R)(S)BPPFW             sion (%)                             vity (%)                                  ration                                       yield (%)__________________________________________________________________________3    (R)(S)BPPFNMeCH.sub.2 CH.sub.2 NMe.sub.2                        100  &gt;98  S(+) 66.74    (R)(S)BPPFNMeCH.sub.2 CH.sub.2 N(i-Pr).sub.2                        100  &gt;98  S(+) 75.25    (R)(S)BPPFNMeCH.sub.2 CH.sub.2 N(n-Bu).sub.2                        100  &gt;98  S(+) 77.9 ##STR20##              100  &gt;98  S(+) 70.67 ##STR21##              100  &gt;98  S(+) 66.88 ##STR22##              100  &gt;98  S(+) 84.99 ##STR23##              100  &gt;98  S(+) 42.310   (R)(S)BPPFNMeCH.sub.2 CH.sub.2 CH.sub.2 NEt.sub.2                        100  &gt;98  S(+) 74.711   (S)(R)BPPF NMeCH.sub.2 CH.sub.2 NMe.sub.2                        100  &gt;98  R(-) 66.7__________________________________________________________________________ 
    
     (R)-(S)-BPPF-W has a chemical structure of the formula: ##STR24## 
     EXAMPLES 12 and 13 
     In the same manner as in Example 2 but proceeding the reaction under conditions as specified in Table 2, the reaction and post-treatment were carried out. The results are also shown in Table 2. 
     
                       TABLE 2______________________________________Example No.         12       13______________________________________Hydrogen pressure (kg/cm.sup.2)               10       50Reaction temp. (°C.)               50       20Reaction time (hrs) 4        20Conversion (%)      99       96Selectivity (%)     &gt;98      &gt;98Configuration       S(+)     S(+)Optical yield (%)   85.0     80.7______________________________________ 
    
     EXAMPLE 14 
     Rh(COD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), (R)-(S)-BPPF-NMeCH 2  CH 2  NEt 2  (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg. 0.05 mmol) were dissolved in ethanol (7.5 ml) in the same autoclave as used in Example 1. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the autoclave was cooled and hydrogen gas was purged, ethanol was evaporated off. The residual mixture was extracted with alkali, precipitated with an acid and extracted with ether followed by concentration to obtain S-2-(4-chlorophenyl)-3-methylbutyric acid (213 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      89.0% (+isomer)______________________________________ 
    
     EXAMPLE 15 
     Rh(COD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), (S)-(R)-BPPF-NMeCH 2  CH 2  NEt 2  (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in the same autoclave as used in Example 1. To the resulting solution, 2-phenylacrylic acid (148 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 16 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with alkali, precipitated with an acid and extracted with ether followed by concentration to obtain S-2-phenylpropionic acid (149.4 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      80.7% (+isomer)______________________________________ 
    
     EXAMPLE 16 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR25## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-phenyl-3-methylcrotonic acid (176 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 20 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-phenyl-3-methylbutyric acid (177 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      95.8% (+isomer)______________________________________ 
    
     EXAMPLE 17 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR26## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-methoxyphenyl)-3-methylcrotonic acid (206 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 20 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-methoxyphenyl)-3-methylbutyric acid (205.5 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      91.9% (+isomer)______________________________________ 
    
     EXAMPLE 18 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR27## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(2-naphthyl)-3-methylcrotonic acid (226 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 6 hours at 50° C. 
     After the autoclave was cooled and hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(2-naphthyl)-3-methylbutyric acid (226 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      91.3% (+isomer)______________________________________ 
    
     EXAMPLE 19 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR28## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-phenyl-3-methylcinnamic acid (238.3 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 100 kg/cm 2 , and the solution was stirred for 50 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain erythro-2,3-diphenylbutyric acid (240.2 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      83.2% (-isomer)______________________________________ 
    
     EXAMPLE 20 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR29## (4.5 mg, 0.00625 mmol) and triethylamine (3.5 mg, 0.025 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, (E)-2-phenyl-3-methyl-2-pentenoic acid (95.1 mg, 0.5 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 100 kg/cm 2 , and the solution was stirred for 90 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain erythro-2-phenyl-3-methylpentanoic acid (96.0 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      90.1% (-isomer)______________________________________ 
    
     EXAMPLE 21 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol) ##STR30## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in a mixed solvent of methanol and tetrahydrofuran (1:4) (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-phenyl-3-methylcrotonic acid (176 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 20 hours at room temperature. 
     After hydrogen gas was purged, the solvents were evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-phenyl-3-methylbutyric acid (177 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      97.6% (+isomer)______________________________________ 
    
     EXAMPLE 22 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR31## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in a mixed solvent of methanol and tetrahydrofuran (1:4) (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 40 hours at room temperature. 
     After hydrogen gas was purged, the solvents were evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (213 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      97.4% (+isomer)______________________________________ 
    
     EXAMPLE 23 
     Rh 2  (NBD) 2  Cl 2  (1.2 mg, 0.0025 mmol), AgBF 4  (1.0 mg, 0.005 mmol), ##STR32## (4.5 mg, 0.00625 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in a mixed solvent of methanol and tetrahydrofuran (1:4) (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(2-naphthyl)-3-methylcrotonic acid (226 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 65 hours at room temperature. 
     After hydrogen gas was purged, the solvents were evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(2-naphthyl)-3-methylbutyric acid (226 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      96.7% (+isomer)______________________________________ 
    
     COMPARATIVE EXAMPLE 1 
     According to the process described in U.S. Pat. No. 4,409,397, Rh(NBD) 2  BF 4  (1.9 mg, 0.005 mmol), (R)-(S)-BPPF-NMe 2  (3.9 mg, 0.00625 mmol) and triethylamine (2.5 mg, 0.025 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg, 1 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 . Under the same pressure, the solution was stirred for 4 hours at 80° C. 
     After the reaction was completed, the reaction mixture was treated in the same manner as in Example 1 to obtain S-2-(4-chlorophenyl)-3-methylbutyric acid (212 mg). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      15.8% (+isomer)______________________________________ 
    
     (R)-(S)-BPPF-NMe 2  has the chemical structure of the formula: ##STR33## 
     COMPARATIVE EXAMPLE 2 
     In the same manner as in Comparative Example 1 but using ##STR34## in place of (R)-(S)-BPPF-NMe 2  and no triethylamine, the reaction and post-treamtment were carried out to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (211 mg). 
     
         ______________________________________Conversion:        92%Selectivity:      &gt;98%Optical yield      25.8% (+isomer)______________________________________ ##STR35## has a chemical structure of the formula: ##STR36## 
    
     COMPARATIVE EXAMPLE 3 
     In the same manner as in Comparative Example 1 but using ##STR37## in place of (R)-(S)-BPPF-NMe 2  and no triethylamine, the reaction and post-treatment were carried out to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (212 mg). 
     
         ______________________________________Conversion:        99%Selectivity:      &gt;98%Optical yield      27.2% (+isomer)______________________________________ ##STR38## has a chemical structure of the formula: ##STR39## 
    
     EXAMPLE 24 
     Rh 2  (2,5-norbornadiene) 2  Cl 2  (2.3 mg, 0.005 mmol), R(+)-2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl (7.8 mg, 0.0125 mmol), AgBF 4  (1.9 mg, 0.01 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (15 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (0.42 g, 2 mmol) was dissolved. After replacing the autoclave interior with hydrogen gas three times, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the reaction was completed, the catalyst was filtered off and the reaction mixture was concentrated to obtain S-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:       &gt;98%Selectivity:      &gt;98%Optical yield      69% (+isomer)______________________________________ 
    
     EXAMPLES 25 and 26 
     In the same manner as in Example 24 but pressurizing the autoclave to pressure as shown in Table 3, the reaction and post-treatment were carried out to obtain S-2-(4-chlorophenyl)-3-methylbutyric acid. The results are shown in Table 3. 
     
                       TABLE 3______________________________________Example No.         25       26______________________________________Hydrogen pressure (kg/cm.sup.2)               30       100Conversion (%)      91       &gt;98Selectivity (%)     &gt;98      &gt;98Optical yield (%) (+isomer)               69       70.5______________________________________ 
    
     EXAMPLE 27 
     In the same manner as in Example 24 but using S(-)-2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl in place of R(+)-2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl, the reaction and post-treatment were carried out to obtain (R)-2-(4-chlorophenyl)-3-methylbutyric acid. 
     
         ______________________________________Conversion:       &gt;98%Selectivity:      &gt;98%Optical yield      69% (-isomer)______________________________________ 
    
     EXAMPLE 28 
     Rh 2  (1,5-cyclooctadiene) 2  Cl 2  (2.5 mg, 0.005 mmol), R(+)-2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl (7.8 mg, 0.0125 mmol), AgBF 4  (1.9 mg, 0.01 mmol) and triethylamine (10.2 mg, 0.10 mmol) were dissolved in methanol (15 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (0.42 g, 2 mmol) was dissolved. After replacing the autoclave interior with hydrogen gas three times, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the reaction was completed, the catalyst was filtered off and the reaction mixture was concentrated to obtain S-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:       &gt;98%Selectivity:      &gt;98%Optical yield      65.0% (+isomer)______________________________________ 
    
     EXAMPLE 29 
     Ru(2,5-norbornadiene)Cl 2  (2.6 mg, 0.01 mmol), S(-)-2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl (7.8 mg, 0.0125 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (15 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (0.42 g, 2 mmol) was dissolved. After replacing the autoclave interior with hydrogen gas three times, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the reaction was completed, the catalyst was filtered off and the reaction mixture was concentrated to obtain R-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:       &gt;98%Selectivity:      &gt;98%Optical yield      68% (-isomer)______________________________________ 
    
     EXAMPLE 30 
     Rh 2  (NBD) 2  Cl 2  (2.3 mg, 0.005 mmol), AgBF 4  (1.9 mg, 0.01 mmol), S(-)-cyclohexyl-BINAP (8.1 mg, 0.0125 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (15 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (0.42 g, 2 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 24 hours at room temperature. 
     After hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:        100%Selectivity:      &gt;98%Optical yield      76.5% (+isomer)______________________________________ 
    
     EXAMPLE 31 
     Rh 2  (NBD) 2  Cl 2  (2.3 mg, 0.005 mmol), AgBF 4  (1.9 mg, 0.01 mmol), R(+)-p-tolyl-BINAP (8.5 mg, 0.0125 mmol) and triethylamine (5.1 mg, 0.05 mmol) were dissolved in methanol (15 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (0.42 g, 2 mmol) was added and dissolved. After the interior space of the autoclave was replaced with hydrogen gas, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the autoclave was cooled and hydrogen gas was purged, methanol was evaporated off. The residual mixture was extracted with an alkali, precipitated with an acid and extracted with ether followed by concentration to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:        95%Selectivity:      &gt;98%Optical yield      63.0% (+isomer)______________________________________ 
    
     EXAMPLE 32 
     In the same manner as in Example 30 but using R(+)-p-CH 3  O-BINAP (9.3 mg, 0.0125 mmol) in place of R(+)-p-tolyl-BINAP, the reaction and post-treatment were carried out to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (0.42 g). 
     
         ______________________________________Conversion:        95%Selectivity:      &gt;98%Optical yield      57.9% (+isomer)______________________________________ 
    
     COMPARATIVE EXAMPLE 4 
     According to the process described in U.S. Pat. No. 4,409,397, Rh 2  (1,5-norbornadiene) 2  Cl 2  (2.3 mg, 0.005 mmol), (R)-(S)-PPFA (5.5 mg, 0.0125 mmol), AgBF 4  (1.9 mg, 0.01 mmol) and triethylamine (5.1 mg, 0.005 mmol) were dissolved in methanol (7.5 ml) in a 35 ml autoclave. To the resulting solution, 2-(4-chlorophenyl)-3-methylcrotonic acid (211 mg, 1 mmol) was added and dissolved. After replacing the autoclave interior with hydrogen gas three times, hydrogen gas was injected to pressurize the autoclave to 50 kg/cm 2 , and the solution was stirred for 4 hours at 80° C. 
     After the reaction was completed, the catalyst was filtered off and the reaction mixture was concentrated to obtain (S)-2-(4-chlorophenyl)-3-methylbutyric acid (211 mg). 
     
         ______________________________________Conversion:        10%Selectivity:      &gt;98%Optical yield       3% (+isomer)______________________________________ 
    
     (R)-(S)-PPFA has a chemical structure of the formula: