CHIRAL REDUCTIONS OF IMINES LEADING TO THE SYNTHESES OF OPTICALLY ACTIVE AMINES

Abstract: A process for preparing an R enantiomer of a compound of formula (I) wherein Me is methyl, Ar is 3-methoxyphenyl, 3-chlorophenyl, or 1-naphthyl, and X is independently selected from the group consisting of H, F, Cl, Br, I, phenyl, CF3, CF2H, CFH2, lower alkyl (e.g., Me), O-lower alkyl (e.g., OMe), OCH2CF3, OH, CN, NO2, C(O)-lower alkyl (e.g., C(O)Me), C(O)O-lower alkyl (e.g., C(O)OMe), C(O)NH-lower alkyl (e.g., C(O)NH-Me), C(O)N-lower alkyl2 (e.g., C(O)NMe2), OC(O)-lower alkyl (e.g., OC(O)Me), and NH-C(O)-lower alkyl (e.g., NH-C(O)Me), where "lower alkyl" is selected from a group consisting of 1 to 6 carbon atoms, and m is an integer between 1 and 5, by asymmetrically and enantioselectively reducing an imine with a reducing agent/chiral auxiliary agent complex so as to produce an enantiomeric excess of R enantiomer of the compound of formula (I) over the S enantiomer of the compound of formula (I). The process is especially useful to produce compounds (R)-(+)-N-[1-(3-methoxyphenyl)ethyl]-3-(2-chlorophenyl)propanamine and (R)-(+)-N-[1-(3-methoxyphenyl)ethyl]-3-(phenyl)propanamine. Enantiomeric excess of the R enantiomer over S enantiomer of greater than 65 % have been achieved.

Description: CHIRAL REDUCTIONS OF IMINES LEADING TO THE SYNTHESES OF OPTICALLY ACTIVE AMINES Background of the Invention Technical Field: The invention relates to methods for reducing an imine to an amine, and more specifically to the enantioselective reduction of an imine using a chiral reducing agent to generate a chiral amine product of enhanced enantiomeric excess. Background Art: As disclosed in Fox et al. , "A First Generation Calcimimetic Compound (NPS R-568) that Acts on the Parathyroid Cell Calcium Receptor: A Novel Therapeutic Approach for Hyperparathyroidism," Journal of Bone and Mineral Research. 8: S181 , Abstract 260 (Suppl. 1 , Aug. , 1993), compounds such as (R)-(+)-N-[l-(3-methoxyphenyl)ethyl]-3-(2- chlorophenyl)propanamine (chem. abstr. index name, also known as, e.g. , (/?)-(+)- N-[3-(2-chlorophenyl)propyl- -methyl-3-methoxybenzylamine or (R)-( + )-N-[3-(2- chlorophenyl)propyl]- 1 -(3-methoxyphenyl)ethylamine) , i.e. : have utility in the treatment of hyperparathyroidism and possibly other bone and mineral-related disorders and diseases such as osteoporosis. As disclosed in Zhu et al. "Asymmetric Reductions of Carbon- Nitrogen Double Bonds. A Review" , Organic Preparation and Procedures International.. 26 (2)193-236 (1994): "Reagents prepared from reaction of LiAJH 4 with (-)-menthol or (-f-)-borneol were used to reduce several aliphatic imines to the corresponding amines, but the enantiomeric excesses obtained were low (i.e. , 1.8- 9.9% ee). Also, the use of optically active α-phenylethylamine-borane complex for the reductive amination of prochiral ketones to produce chiral amines has also been investigated, but gave very low enantioselectivities (1.1-1.6% ee). " Although the successful chiral reduction of ketones to alcohols has been thoroughly documented in the literature, the reductions of imines to chiral amines, as indicated above (from Zhu et al.), has given, at best, poor yields ( < 10% ee). A straightforward chemical synthesis yielding (R)-(+)-N-[3-(2- chlorophenyl)propyl]-l-(3-methoxyphenyl)ethylamine, and similar analogs (in greater than 10% ee), using readily available inexpensive, and achiral starting materials would be an improvement in the art. Disclosure of the Invention The invention includes a process for preparing the R enantiomers of compounds of the general formula (I): where Ar is 3-methoxyphenyl, 3-chlorophenyl, or 1 -naphthyl, and X is independently selected from the group consisting of H, F, Cl, Br, I, phenyl, CF 3 , CF 2 H, CFH 2 , lower alkyl (e.g. , methyl or "Me"), 0-lower alkyl (e.g. , OMe), OCH 2 CF 3 , OH, CΝ, ΝO 2 , C(O)-lower alkyl (e.g. , C(O)Me), C(O)O-lower alkyl (e.g. , C(O)OMe), C(O)NH-lower alkyl (e.g. , C(O)NH-Me), C(O)N-lower alkyl, (e.g., C(O)NMe 2 ), OC(O)-lower alkyl (e.g. , OC(O)Me), and NH-C(O)-lower alkyl (e.g., NH-C(O)Me), where "lower alkyl" is preferably a saturated branched or unbranched hydrocarbon having one to six carbon atoms, e.g. methyl, ethyl ("Et"), or isopentyl, and where m is an integer between 1 and 5. These compounds are produced by the enantiomeric reduction of an imine of the formula (II): with a chiral reducing agent so as to produce an enantiomeric excess (% ee) of the R enantiomer of the compound of formula (I) over the S enantiomer of the compound of the formula (I) . The preferred compounds produced by this process are as follows: The process is especially useful to produce the most preferred compounds (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine and (R)- 30 (+)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl)ethylamine ((R)-(+)-N-[l-(3- methoxyphenyl)ethyl]-3-(2-chlorophenyl)propanamine and (R)-( +)-N-[ 1 (3- methoxyphenyl)ethyl]-3-(phenyl)propanamine): In one such process, the imine in is formed by the condensation of 3- phenyl-1 -propylamine with 3'-methoxyacetophenone. The intermediate imine DI is then reduced with a chiral reducing agent to yield the product IV ((R)-(+)-N-(3- phenylpropyl)-l-(3-methoxyphenyl)ethylamine), with an enantiomeric excess greater than 10%. "Chiral ov The same process is used to prepare (/?)-( +)-N-[3-(2-chloro- phenyl)propyl]-l-(3-methoxyphenyl)ethylamine. Condensation of 3(2-chloro)phenyl- 1 -propylamine with 3'-methoxyacetophenone generates the imine V which is then reduced with a chiral reducing agent to yield (/?)-(+ )-N-[3-(2-chlorophenyl)propyl]- l-(3-methoxyphenyl)ethylamine, with an enantiomeric excess greater than 10% . Brief Description of the Figures FIG. 1 is a bar graph depicting the results of Tables A and B. FIG. 2 is a bar graph depicting the results of Table C. Best Mode for Carrying Out the Invention The preferred reducing agents for use in the process include lithium aluminum hydride or borane in combination with a chiral auxiliary selected from the group consisting of (S)-(+)-2-(anilinomethyl)pyrrolidine, (S)-(-)-nicotine, (S)-(-)- l , l '-bi-2-naphthol, (lR,2S)-(-)-ephedrine, (lfl,2S),-(-)-N-methylephedrine, (S)-(+)- l-(2-pyrrolidinylmethyl)pyrrolidine, (S)-(-)-l-methyl-2-pyrrolidinemethanol, (R)- (+)-α,α-diphenyl-2-pyrrolidinemethanol, (R)-(+)-l , 1 '-bi-2-naphthol, (lR,2S)-(-)-N- methylpseudoephedrine, (2S,3R)-(+) 4 dimethylamino- 1 ,2-dipheny l-3-methyl-2- butanol, and (S)-(-)-αr,o.-diphenyl-2-pyrrolidinemethanol. When the reducing agent is lithium aluminum hydride, the preferred chiral auxiliaries are (S)-(-(-)-2-(anilinomethyl)pyrrolidine, (lR,2S)-(-)-ephedrine, (lR,2S),-(-)-Ν-methylephedrine, and (R)-(+)-l . l '-bi-2-naphthol. When the reducing agent is borane, the preferred chiral auxiliary is (S)-(+)-l-(2-pyrrolidmylmethyl)pyrrolidine. The invention is further explained by reference to the following illustrative EXAMPLES. EXAMPLES The following abbreviations have been assigned to the solvents or reagents used: IPA = isopropanol DEA = diethylamine THF = tetrahydrofuran Et 2 O = diethyl ether EXAMPLE I Preparation of 1 -methyl- 1 -(3-methoxy)phenyl-5-phenyl-2-aza- 1 - pentene (imine IQ). A 500 ml round-bottomed flask containing about 22.5 g (167 mmol) of 3-phenyl-l -propylamine (Aldrich Chemical Co., Milwaukee, WI, USA) and about 20.2 g (167 mmol) of 3'-methoxyacetophenone (Aldrich Chemical Co. , Milwaukee, WI, USA) was heated at about 150°C with stirring, under vacuum (water aspirator) for about 3 hours. The reaction was then heated at about 100°C under vacuum 10 (microns) for about 15 minutes. This process afforded 1-methyl- l-(3-methoxy)phenyl-5-phenyl-2-aza-l -pentene (imine IQ), a single component, as analyzed by GC/EI-MS: m/z (rel. int.) 267 (M + , 5), 252 (1), 276 (5), 162 (100), 148 (8), 132 (14), 121 (15), 104 (4), 91 (38), 77 (100). EXAMPLE II Reduction of imine m with (S)-(+)-2- (an-J-inomethyl)pyrrolidine/LiAlH 4 complex. A solution of (S)-(+)-2-(anilinomethyl)pyrrolidine (about 250 mg. [1.4 mmol]) in diethyl ether (about 5 ml) was added to a stirred solution of LiAlH 4 (about 54.6 mg [1.4 mmol]) in diethyl ether (about 5 ml). The reaction was stirred for about 2 hours at room temperature (about 23 °C) and treated with a solution of the imine UI (about 300 mg [1.1 mmol]) in diethyl ether (about 3 ml). The reaction was stirred for about 60 hours and quenched by the addition of saturated NH 4 CI. The resulting mixture was basified by the addition of a sufficient amount ION ΝaOH to raise the mixture above a pH of about 12 and extracted with diethyl ether. GC/EI-MS analysis of this solution showed complete reduction of the imine HI to yield (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine (100%). The ether extract was concentrated to an oil and a portion of this material chromatographed on a silica gel plate using 5% methanol in chloroform. The product was collected from the plate (R f 0.75) and subjected to chiral HPLC (High Pressure Liquid Chromatography) analysis. Chromatography through CHIRALCEL OD (0.46 x 25 cm) using 0.6% IPA in hexane containing 0.1 % DEA at 1 ml/min. measuring optical density at 260 mm, showed an enantiomeric excess R) enantiomer) of 17% . The results are reported in Table A. EXAMPLE m Reduction of imine HI with (S)-(-)-nicotine/LiAlH,. A suspension of LiAlH 4 (about 39 mg [1 mmol]) in diethyl ether (about 10 ml) was cooled to about -78°C and treated, dropwise, with a solution of (S)-(-)-nicotine (about 162 mg [1 mmol]) in diethyl ether. The reaction was stirred at room temperature for about 4 hours, cooled to about -78°C, and treated with a solution of the imine D (about 267 mg [1 mmol]) in diethyl ether (about 1 ml). The reaction was allowed to warm slowly to room temperature where it was stirred for about 72 hours. The reaction was quenched with a sufficient amount of 6N HC1, then basified to a pH above about 12 with ION NaOH, and extracted with diethyl ether. GC/EI-MS analysis showed a 78% yield of (R)-(+)-N-(3- phenylpropyl)-l-(3-methoxyphenyl) ethylamine. Preparative TLC (thin layer chromatography) and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (S enantiomer) of 3 % . The results are reported in Table A. EXAMPLE IV Reduction of imine ID with (S)-(-)-l ,l '-bi-2-naphthol/LiAlH». Reduction of imine ID was performed in a manner similar to that of Example m using (S)-(-)-l , l '-Bi-2-naphthol as the chiral auxiliary. GC/EI-MS analysis showed a 24% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl) ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (5 enantiomer) of 16%. The results are reported in Table A. EXAMPLE V Reduction of imine DI with (lR,2S)-(-)-ephedrine/LiAlH t . Reduction of imine DI was performed in a manner similar to that of Example HI using (l/?,2S)-(-)-ephedrine as the chiral auxiliary. GC/EI-MS analysis showed about a 3% yield of (/?)-( +)-N-(3-phenylpropyl)-l-(3-methoxyphenyl) ethylamine. The product was not analyzed by chiral HPLC. The results are reported in Table A. EXAMPLE VI Reduction of imine ID with (lR,2S)-(-)-N-methylephedrine/LiAlH 4 . Reduction of imine ID was performed in a manner similar to that of Example HI using (lR,2S)-(-)-N-methylephedrine as the chiral auxiliary. GC/EI-MS analysis showed a 64% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl) ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (R enantiomer) of 68 % . The results are reported in Table A. EXAMPLE VD Reduction of imine DI with (S)-(+)-l-(2-pyrrolidinylmethyl) py rrolidine/LiAlH 4 . Reduction of imine ID was performed in a manner similar to that of Example ID using (S)-(+)-l-(2-pyrrolidinylmethyl)pyrrolidine as the chiral auxiliary. GC/EI-MS analysis showed a 47% yield of (R)-(+)-N-(3-phenylpropyl)- l-(3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (R enantiomer) of 1 % . The results are reported in Table A. EXAMPLE VID Reduction of imine ID with (S)-(-)-l-methyl-2-pyrrolidine methanol/LiAlH 4 . Reduction of imine ID was performed in a manner similar to that of EXAMPLE DI using (S)-(-)-l-methyl-2-pyrrolidinemethanol as the chiral auxiliary. GC/EI-MS analysis showed a 67% yield of (Λ)-(+)-N-(3-ρhenylpropyl)-l-(3- methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (S enantiomer) of 1 % . The results are reported in Table A. EXAMPLE IX Reduction of imine ID with (R)-(+)-α,c.-diphenyl-2-pyrrolidine ethanol/Li A1H 4 . Reduction of imine ID was performed in a manner similar to that of Example DI using (R)-(+ )-α,α-diphenyl-2-pyrrolidinemethanol as the chiral auxiliary. GC/EI-MS analysis showed a 53 % yield of (R)-(+)-N-(3-phenylpropyl)- l-(3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example H) showed an enantiomeric excess (S enantiomer) of 1 % . The results are reported in Table A. EXAMPLE X Reduction of imine ID with (S)-(+)-2- (anilinomethyl)pyrrolidine/borane complex. A I M solution of borane-THF complex (about 1 ml [1 mmol]) was added to a cooled solution (about -78°C) of diethyl ether (about 9 ml) and treated, dropwise, with a solution of (S)-(+)-2-(anilinomethyl)pyrrolidine (about 176 mg, 1 mmol) in diethyl ether. The reaction was stirred a room temperature for about 4 hours, cooled to about -78°C, and treated with a solution of the imine DI (about 267 mg [1 mmol]) in diethyl ether (about 1 ml). The reaction was allowed to warm slowly to room temperature where it was stirred for about 72 hours. The reaction was quenched with 6N HCl, basified to a pH above about 12 with ION ΝaOH and extracted with diethyl ether. GC/EI-MS analysis showed a 75 % yield of (R)-(+)-N- (3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (S enantiomer) of 7% . The results are reported in Table B. EXAMPLE XI Reduction of imine HI with (S)-(-)-nicotine/BH,. Reduction of imine ID was performed in a manner similar to that of Example X using (S)-(-)-nicotine as the chiral auxiliary. GC/EI-MS analysis showed a 55 % yield of (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in example D) showed an enantiomeric excess (S enantiomer) of 4% . The results are reported in Table B. EXAMPLE XD Reduction of imine DI with (S)-(-)- 1 , 1 '-bi-2-naphthol/BH>. Reduction of imine DI was performed in a manner similar to that of Example X using (S)-(-)-l ,l '-bi-2-naphthol as the chiral auxiliary. GC/EI-MS analysis showed a 2% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3- methoxyphenyl)ethylamine. The product was not analyzed by chiral HPLC. The results are reported in Table B. EXAMPLE XID Reduction of imine DI with (lR,2S)-(-)-ephedrine/BI^. Reduction of imine DI was performed in a manner similar to that of Example X using (lR,2S)-(-)-ephedrine as the chiral auxiliary. GC/EI-MS analysis showed a 74% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine. Preparative TCL and chiral HPLC analysis (as in Example X) showed an enantiomeric excess (S enantiomer) of 1 %. The results are reported in Table B. EXAMPLE XIV Reduction of imine ID with (lR,2S)-(-)-N-methylephedrine/BH,. Reduction of imine HI was performed in a manner similar to that of Example X using (lR,2S)-(-)-N-methylephedrine as the chiral auxiliary. GC/EI-MS analysis showed a 45 % yield of (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl) ethylamine. Preparative TLC and chiral HPLC analysis (as in Example X) showed no enantiomeric excess. The results are reported in Table B. EXAMPLE XV Reduction of imine ID with (S)-(-l-)-l-(2-pyrrolidinyl methy l)pyrrolidine/BH 3 . Reduction of imine ID was performed in a manner similar to that of Example X using (S)-(+)-l-(2-pyrrolidinylmethyl)pyrroUdine as the chiral auxiliary. GC/EI-MS analysis showed a 54% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3- methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example X) showed an enantiomeric excess (R enantiomer) of 10% . The results are reported in Table B. EXAMPLE XVI Reduction of imine ID with (5)-(-)-l-methyl-2-pyrrolidine methanol/BH 3 . Reduction of imine ID was performed in a manner similar to that of Example X using (S)-(-)-l-methyl-2-pyrrolidine methanol as the chiral auxiliary. GC/EI-MS analysis showed a 60% yield of (R)-(+)-N-(3-phenylpropyl)-l-(3- methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example X) showed no enantiomeric excess. The results are reported in Table B. EXAMPLE XVO Reduction of imine ID with (R)-(+)-α,c.-diphenyl-2-pyrrolidine methanol/BH 3 . Reduction of imine ID was performed in a manner similar to that of Example X using (R)-(+)-α,o.-diphenyl-2-pyrrolidinemethanol as the chiral auxiliary. GC/EI-MS analysis showed a 96% yield of (Λ)-(+)-N-(3-phenylpropyl)- l-(3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example X) showed an enantiomeric excess (S enantiomer) of 5 % . The results are reported in Table B. EXAMPLE XVDI Preparation of l-methyl-l-(3-methoxy)phenyl-5-(2-chloro)phenyl-2- aza-1 -pentene (imine V). The imine V was prepared in a manner similar to that of imine ID in Example I using 3-(2-chlorophenyl)propylamine and 3'-methoxyacetophenone. 3-(2- chlorophenyl)propylamine was obtained by the reduction (BH^SMe, complex) of 2- chlorohydrocinnamonitrile (Aldrich Chemical Co., Milwaukee, WI, USA). This process afforded l-methyl-l-(3-methoxy)phenyl-5-(2-chloro)phenyl-2-aza-l-pentene (imine V), a single component, as analyzed by GC/EI-MS: m/z (rel. int.) 301 (M + , 1), 266 (22), 162 (100), 125 (26), 91 (13), 77 (9). EXAMPLE XIX Reduction of imine V with (/?)-( +)-l,l '-bi-2-naphthol/LiA-H,. Reduction of imine V was performed in a manner similar to that of Example ID using (R)-(+)-l , 1 '-bi-2-naphthol as the chiral auxiliary. GC/EI-MS analysis showed a 15 % yield of (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l-(3- methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (R enantiomer) of 12 % . The results are reported in Table C. EXAMPLE XX Reduction of imine V with (S)-(-)-2-pyrrolidinemethanol/LiAIH l . Reduction of imine V was performed in a manner similar to that of Example ID, using (S)-(+)-2-pyrrolidinemethanol as the chiral auxiliary. No (R)- (+)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl)ethylamine was detected from the reaction as analyzed by GC/EI-MS. The results are reported in Table C. EXAMPLE XXI Reduction of imine V with (lR,2S)-(-)-ephedrine/LiAlH 4 . Reduction of imine V was performed in a manner similar to that of Example ID using (lR,25)-(-)-ephedrine as the chiral auxiliary. GC/EI-MS analysis showed a 3% yield of (Λ)-(+)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl) ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (R enantiomer) of 40 % . The results are reported in Table C. EXAMPLE XXD Reduction of imine V with (lR,2S)-(-)-N-methylephedrine/LiAlH 4 . Reduction of imine V was performed in a manner similar to that of Example ID using (lR,2S)-(-)-N-methylephedrine as the chiral auxiliary. GC/EI-MS showed a 31 % yield of (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl) ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (R enantiomer) of 41 % . The results are reported in Table C. EXAMPLE XXDI Reduction of imine V with (l/?,2S)-(-)-N-methylpsuedo ephedrine/LiAJH 4 . Reduction of imine V was performed in a manner similar to that of Example HI using (lR,2S)-(-)-N-methylpsuedoephedrine as the chiral auxiliary. GC/EI-MS analysis showed a 28% yield of (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l- (3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (S enantiomer) of 31 % . The results are reported in Table C. EXAMPLE XXIV Reduction of imine V with (2S,3R)-(+)-4-dimethylamino-l ,2- diphenyl-3-methyl-2-butanol/LiAlH 4 . Reduction of imine V was performed in a manner similar to that of Example ID using (2S,3R)-(+)-4-dimethylamino-l ,2-diphenyl-3-methyl-2-butanolas the chiral auxiliary. No (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l-(3- methoxyphenyl)ethylamine was detected from the reaction as analyzed by GC/EI- MS. The results are reported in Table C. EXAMPLE XXV Reduction of imine V with (S)-(+)-l-(2-pyrrolidinylmethyl) pyrrolidine/LiAlH 4 . Reduction of imine V was performed in a manner similar to that of Example ID using (S)-(+)-l-(2-pyrrolidinylmethyl)pyrrolidine as the chiral auxiliary. No (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl)ethylamine was detected from the reaction as analyzed by GC/EI-MS. The results are reported in Table C. EXAMPLE XXVI Reduction of imine V with (S)-(-)-α,α-diphenyl-2-pyrrolidine methanol/LiAlH 4 . Reduction of imine V was performed in a manner similar to that of Example ID using (S)-(-)-o-,α-diphenyl-2-pyrrolidinemethanol as the chiral auxiliary. GC/EI-MS analysis showed a 6% yield of (R)-(+)-N-[3-(2-chlorophenyl)propyl]-l- (3-methoxyphenyl)ethylamine. Preparative TLC and chiral HPLC analysis (as in Example D) showed an enantiomeric excess (S enantiomer) of 8 % . The results are reported in Table C. EXAMPLE XXVD Reduction of imine V with (S)-(+)-2-(anilinomethyl) py rrolidine/LiAlH 4 . Reduction of imine V, was performed in a manner similar to that of Example ID using (S)-(+)-2-(Anilinomethyl)pyrrolidine as the chiral auxiliary. No (/?)-( +)-N-[3-(2-chlorophenyl)propyl]-l-(3-methoxyphenyl)ethylamine was detected from the reaction as analyzed by GC/EI-MS. The results are reported in Table C. TABLE A Chiral reduction" of imine ID yielding (R)-(+)-N-(3-phenylpropyl)-l-(3-methoxyphenyl)ethylamine Example Product" ee% c Percentage Yield D 100 17 (R) m 78 3 (S) IV 24 16 (S) V 3 ΝA d VI 64 68 (R) VD 47 1 (R) vm 67 1 (S) IX 53 1 (S) a Lithium aluminum hydride-chiral auxiliary complex (see Examples D-IX). b As analyzed by GC/EI-MS. c As analyzed by chiral HPLC. d Not analyzed. (S) indicates an enantiomeric excess ("ee") of the (S) enantiomer (R) indicates an enantiomeric excess ("ee") of the (R) enantiomer TABLE B Chiral reduction" of imine yielding (R)-( + )-N-(3-phenylpropyl)- 1 -(3-methoxyphenyl)ethylamine Example Product b ee% c Percentage Yield X 75 7 (S) XI 55 4 (S) XD 2 ΝA d xm 74 1 (S) XIV 45 0 XV 54 10 (R) XVI 60 0 XVD 96 5 (S) * Borane-chiral auxiliary complex (see Examples X-XVD). b As analyzed by GC/EI-MS. c As analyzed by chiral HPLC. d Not analyzed. (S) indicates an enantiomeric excess ("ee") of the (S) enantiomer (R) indicates an enantiomeric excess ("ee") of the (R) enantiomer TABLE C Chiral reduction" of imine V yielding (R)-( +)-N-[3-(2-chlorophenyl)propyl]- 1 -(3-methoxyphenyl)ethylamine Example Product b ee% c Percentage Yield XIX 15 12 (R) XX 0 NA d XXI 3 40 (R) XXD 31 41 (R) xx 28 31 (S) XXIV 0 NA d XXV 0 NA d XXVI 6 8 (S) xxvπ 0 NA d " Lithium aluminum hydride-chiral auxiliary complex (see Examples XVD-XXVI). b As analyzed by GC/EI-MS. c As analyzed by chiral HPLC. d Not analyzed. (S) indicates an enantiomeric excess ("ee") of the (S) enantiomer (R) indicates an enantiomeric excess ("ee") of the (R) enantiomer Although the invention has been described with the use of various examples and preferred embodiments, these are illustrative only, and the scope of the invention is to be determined by the appended claims.

Claims: CLAIMS What is claimed is: 1. A process for preparing an R enantiomer of a compound having a formula (I): wherein Me is methyl, Ar is 3 -methoxyphenyl, 3 -chlorophenyl, or 1 -naphthyl, and X is independently selected from the group consisting of H, F, Cl, Br, I, phenyl, CF 3 , CF 2 H, CFH 2 , lower alkyl, O-lower alkyl, OCH 2 CF 3 , OH, CN, NO 2 , C(O)- lower alkyl, C(O)O-lower alkyl, C(O)NH-lower alkyl, C(O)N-lower alkyl 2 , OC(O)- lower alkyl, and NH-C(O)-lower alkyl, wherein m is an integer between 1 and 5, said process comprising: asymmetrically and enantioselectively reducing an imine having a formula (D): with a reducing agent modified by a chiral auxiliary agent so as to produce an enantiomeric excess of the R enantiomer of the compound of formula (I) over the S enantiomer of the compound of formula (I) . 2. The process according to claim 1 wherein said chiral auxiliary agent is selected from the group consisting of (S)-(+)-2-(anilinomethyl)pyrrolidine, (S)-(- )-nicotine, (S)-(-)-l ,l '-bi-2-naphthol, (lΛ,2S)-(-)-ephedrine, (lR,2S)-(-)-N- methylephedrine, (S)-(+)-l-(2-pyrrolidinylmethyl)pyrrolidine, (S)-(-)-l-methyl-2- pyrrolidinemethanol, (R)-(+)-α,α-diphenyl-2-pyrrolidinemethanol, (R)-(+)-l , 1 '-bi- 2-naphthol, (lR,2S)-(-)-N-methylpseudoephedrine, (2S,3R)-(+)-4-dimethylamino- l ,2-diphenyl-3-methyl-2-butanol, and (S)-(-)-c.,α-diphenyl-2-pyrrolidinemethanol. 3. The process according to claim 2 wherein said reducing agent is lithium aluminum hydride, and said chiral auxiliary agent is selected from the group consisting of (S)-(+)-2-(anilinomethyl)pyrrolidine, (lR,2S)-(-)-ephedrine, (\R,2S),- (-)-N-methylephedrine, and (R)-(+)-l,l '-bi-2-naphthol. 4. The process according to claim 2 wherein said reducing agent is borane, and said chiral auxiliary is (S)-(+)-l-(2-pyrrolidinylmethyl)pyrrolidine. 5. The process according to claim 1 wherein the compound of formula (I) is (R)-(N)-[l -(3-methoxyphenyl)ethyl]-3-(2-chlorobenzene)propanamine. 6. The process according to claim 1 wherein the compound of formula (I) is (7?)-(N)-[l-(3-methoxyphenyl)ethyl]-3-(phenyl)propanamine. 7. The process according to claim 5 wherein said reducing agent is lithium aluminum hydride, and said chiral auxiliary agent is (lR,2S)-(-)-N- methy lephedrine. 8. The process according to claim 1 wherein the imine of formula (D) is formed by the condensation of 3-(2chlorophenyl)propylamine with 3'- methoxyacetophenone. 9. The process according to claim 1 where the compound of formula (I) is produced in an enantiomeric excess of the R enantiomer over the S enantiomer in an amount greater than 10%. 10. The process according to claim 1 where the compound of formula (I) is produced in an enantiomeric excess of the R enantiomer over the 5 enantiomer in an amount greater than 40%. 11. The process according to claim 1 where the compound of formula (I) is produced in an enantiomeric excess of the R enantiomer over the S enantiomer in an amount greater than 65 % .

Inventors: BARMORE ROBERT M, VAN WAGENEN BRADFORD C, BARMORE, ROBERT, M., VAN WAGENEN, BRADFORD, C.
Applicants: NPS PHARMA INC, NPS PHARMACEUTICALS, INC.
Application year: 1996
Main classification: C07C209
IPC codes: C07C209, C07C211, C07C213, C07C215, C07C217, C07C227, C07C229, C07C231, C07C237, C07C253, C07C255