Process for preparing optically active cyclohexanol derivatives

Abstract: A process for producing an optically active cyclohexanol derivative represented by formula (I): wherein R 1 represents an alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or a protected hydroxyl group, comprising asymmetrically hydrogenating a cyclohexanone derivative in the presence of a catalyst system composed of a transition metal compound, for example, transition metal complex, a base such as KOH, and a nitrogen compound for example, an amine compound. Such cyclohexanol derivatives are useful in various applications for example as intermediate for pharmaceuticals or optically active ligands.

Description: This invention relates to a process for preparing optically active cyclohexanol derivatives, more particularly to a practical process for preparing optically active cyclohexanol derivatives useful in various applications, for example, as intermediate for pharmaceuticals or optically active ligands. Known methods for asymmetric synthesis of optically active alcohols include (1) an enzymatic method using bread yeast, etc. and (2) asymmetric hydrogenation of a carbonyl compound using a metal complex catalyst. In particular, many proposals have been made to date for the asymmetric hydrogenation route as follows. 1) Asymmetric hydrogenation of a carbonyl compound having a functional group using an optically active ruthenium catalyst (R. Noyori (ed.), Asymmetric Catalysis in Organic Synthesis , pp. 56-82 (1994)). 2) Hydrogen shift type reduction using a ruthenium, rhodium or iridium asymmetric complex catalyst ( Chem. Rev. , Vol. 92, pp. 1051-1069 (1992)). 3) Asymmetric hydrogenation using a tartaric acid- modified nickel catalyst ( Yukagaku , pp. 828-831 (1980) and Y. Izumi (ed.), Advances in Catalysis , Vol. 32, p. 215 (1983)). 4) Asymmetric hydrosilylation (J.D. Morrison (ed.), Asymmetric Synthesis , Vol. 5, Chap. 4 (1985) and J. Organomet. Chem. , Vol. 346, pp. 413-424 (1988)). 5) Borane reduction in the presence of an asymmetric ligand ( J. Chem. Soc., Perkin Trans. I , pp. 2039-2044 (1985) and J. Am. Chem. Soc. , Vol. 109, pp. 5551-5553 (1987)). 6) Asymmetric hydrogenation of an aromatic ketone using potassium hydroxide, an optically active diamine, and a ruthenium asymmetric complex catalyst ( J. Am. Chem. Soc. , Vol. 117, pp. 2675-2676 (1995)). 7) Diastereoselective asymmetric hydrogenation of a racemic carbonyl compound, e.g., asymmetric hydrogenation of a β-ketoester compound using a ruthenium asymmetric complex catalyst ( J. Am. Chem. Soc. , Vol. 111, pp. 9134-9135 (1989), ibid , Vol. 115, pp. 144-152 (1993), and J. Chem. Soc., Chem. Commun., pp. 609-610 (1991)). Of the above-described methods, the process of using an enzyme produces alcohols of relatively high optical purity but is limited in kind of applicable substrates. Besides, the absolute configuration of the resulting alcohols is limited. The processes using a transition metal catalyst for asymmetric hydrogenation produce optically active alcohols at high selectivity from substrates having a functional group in the molecule thereof, such as a keto-acid, but are unsatisfactory in terms of reaction rate and ineffective on simple carbonyl compounds having no functional group in the molecule thereof, and require a very expensive optically active amine compound. The diastereoselective asymmetric hydrogenation of a racemic carbonyl compound is effective only on those substrates which are accompanied with racemization through enolization, such as β-ketoester compunds. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly active catalyst system capable of diastereoselectively producing an optically active alcohol from a racemic carbonyl compound and a novel process for synthesizing an optically active alcohol using the catalyst system. The present invention relates to a process for producing an optically active cyclohexanol derivative represented by formula (I): wherein R 1 represents an alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or a protected hydroxyl group, comprising asymmetrically hydrogenating a cyclohexanone derivative represented by formula (II): wherein R 1 is as defined above, in the presence of a catalyst system for asymmetric hydrogenation composed of a transition metal compound, a base, and a nitrogen compound, and wherein said transition metal compound is a complex of a transition metal of the group VIII represented by formula (III): M 1 X m L n wherein M 1 represents a transition metal selected from Ru, Rh, Ir, and Pt; X represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, and an alkoxy group; L represents DM-BINAP; and m and n each represent an integer, and wherein said base is a compound represented by formula (IV); M 2 Y wherein M 2 represents an alkali metal and an alkaline earth metal; and Y represents a group selected from a hydroxyl group, an alkoxy group, a mercapto group, and a naphthyl group, or a quaternary ammonium salt, and wherein said nitrogen compound is an amine compound. DETAILED DESCRIPTION OF THE INVENTION The starting compound for use in the invention is a 2-substituted cyclohexanone compound represented by formula (II). In formula (II), R 1 represents an alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or a protected hydroxyl group. Specific examples of R 1 are alkyl groups, e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl groups; a hydroxyl group; and protected hydroxyl groups, e.g., methoxy, ethoxy, propoxy, isopropoxy, butoxy, benzyloxy, acetoxy, trimethylsilyoxy, triethylsilyoxy, tert-butyldimethylsilyloxy, dimethylphenylsilyloxy, and diphenylmethylsilyoxy groups. The transition metal compound which constitutes the asymmetric hydrogenation catalyst system according to the invention is a transition metal complex represented by formula (III). In formula (III), M 1 is a transition metal of the group VIII, selected from ruthenium, rhodium, iridium or platinum, with ruthenium being preferred. X is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group or an alkoxy group. L is the optically active phosphine ligand 2,2'-bis(di-3,5-dimethylphenylphosphino)-1,1'-binaphthyl (DM-BINAP). n for these bidentate phosphine ligands is 1 to 2. The group VIII transition metal complex is used usually at a molar ratio of 1/100 to 1/100,000, preferably 1/500 to 1/20,000, to the reaction substrate, 2-substituted cyclohexanone, which varying depending on the type of the reaction vessel, the type of the reaction, or economy. In formula (IV) representing the base to be used in the catalyst system of the invention, M 2 is an alkali metal or an alkaline earth metal, and Y is a hydroxyl group, an alkoxy group, a mercapto group or a naphthyl group. Examples of the base include KOH, KOCH 3 , KOCH(CH 3 ) 2 , KC 10 H 8 , NaOH, NaOCH 3 , LiOH, LiOCH 3 , and LiOCH(CH 3 ) 2 . Quaternary ammonium salts are also useful as a base. The base is used usually at a molar ratio of 1/10 to 1/1,000, preferably 1/20 to 1/100, to the 2-substituted cyclohexanone substrate. The nitrogen compound used in the catalyst system of the invention is an amine compound and possibly an optically active amine compound. The amine compound or optically active amine compound includes a monoamine represented by formula (V): NR 5 R 6 R 7 wherein R 5 , R 6 , and R 7 each represent a hydrogen atom, an alkyl group or an aryl group; an optically active monoamine represented by formula (V) in which at least one of R 5 , R 6 , and R 7 is an optically active group, and an optically active diamine compound represented by formula (VI): wherein R 8 , R 9 , R 14 , R 15 each represent a hydrogen atom, an alkyl group, an aryl group, a urethane group, a sulfonyl group, etc.; R 10 , R 11 , R 12 , and R 13 each represent a hydrogen atom, an alkyl group, an aryl group, a cycloalkyl group, etc.; in the optically active diamine compound R 10 , R 11 , R 12 , and R 13 , which may be the same or different, are selected from a hydrogen atom, an alkyl group, an aryl group, a cyclic hydrocarbon group, etc. so that the carbon atoms to which they are bonded may become asymmetric centers. Examples of the amine compounds are n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, benzylamine, dibenzylamine, triethylamine, aniline, 1,2-phenylenediamine, ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 1,2-butanediamine, 1,3-butanediamine, 1,4-butanediamine, 2,3-butanediamine, 1,2-pentanediamine, 1,3-pentanediamine, 1,4-pentanediamine, 1,5-pentanediamine, 2,3-pentanediamine, 2,4-pentanediamine, 2-methyl-1,2-propanediamine, 3-methyl-1,3-butanediamine, 4-methyl-2,3-pentanediamine, and 2-methyl-2,4-pentanediamine. Examples of the optically active amine compounds are phenylethylamine, α-naphthylethylamine, 2-butylamine, 1,2-diphenylethylenediamine, 1,2-cyclohexanediamine, 1,2-cycloheptanediamine, 2,3-dimethyl-2,3-butanediamine, 1-methyl-2,2-diphenylethylenediamine, 1-isobutyl-2,2-diphenylethylenediamine, 1-isopropyl-2,2-diphenylethylenediamine, 1-methyl-2,2-di(p-methoxyphenyl)ethylenediamine, 1-isobutyl-2,2-di(p-methoxyphenyl)ethylenediamine, 1-isopropyl-2,2-di(p-methoxyphenyl)ethylenediamine, 1-benzyl-2,2-di(p-methoxyphenyl)ethylenediamine, 1-methyl-2,2-dinaphthylethylenediamine, 1-isobutyl-2,2-dinaphthylethylenediamine, and 1-isopropyl-2,2-dinaphthylethylenediamine; and optically active diamine compounds of formula (VI) in which one or both of R 8 and R 14 is/are a sulfonyl group or a urethane group. The optically active amine compounds useful in the invention are not limited to the foregoing examples. Optically active propanediamine, butanediamine, and phenylenediamine derivatives are also useful. The monoamine compound or optically active monoamine compound is used in an amount of 1 to 4 equivalents, preferably 2 to 4 equivalents, to the transition metal complex, and the diamine compound or optically active diamine compound is used in an amount of 0.5 to 2.5 equivalents, preferably 1 to 2 equivalents, to the transition metal complex. The solvent to be used in the reaction is selected appropriately from those solubilizing the reaction substrate and the catalyst system. Suitable solvents include alcohols, such as methanol, ethanol, 2-propanol, butanol, and benzyl alcohol; ethers, such as ethyl ether, tetrahydrofuran, and dioxane; esters, such as ethyl acetate, isopropyl acetate, and butyl acetate; halogen-containing hydrocarbons, such as methylene chloride; and hetero atom-containing organic solvents, such as N,N'dimethylformamide and dimethyl sulfoxide. Alcohol solvents are preferred, with 2-propanol being still preferred. A mixture of two or more of the above-described solvents may be used for sparingly soluble substrates. The amount of the solvent to be used is decided according to the solubility of the reaction substrate and economy. In using 2-propanol, for example, the reaction can be carried out at a substrate concentration broadly ranging from 1% or even lower up to a nearly solvent-free condition. A preferred substrate concentration is 5 to 50% by weight. The asymmetric hydrogenation reaction can proceed under atmospheric pressure because of the high activity of the catalyst system. From the economical consideration a suitable hydrogen pressure is from 1.013 X 10 5 Pa to 1.013 X 10 7 Pa (1 to 100 atm), particularly 5.066 X 10 5 Pa to 5.066 X 10 6 Pa (5 to 50 atm). The reaction temperature is from -20° to 100°C, preferably -5° to 50°C, still preferably 0° to 30°C. The reaction time varies depending on the reaction conditions, such as substrate concentration, temperature, and hydrogen pressure. The reaction usually completes in several minutes to 24 hours. The reaction can be conducted either in a batch system or in a continuous system. The present invention will now be described in greater detail with reference to the following Examples, but it should be understood that the invention is not limited thereto, The products prepared were identified from the infrared absorption spectrum (IR) (Model IR-810, manufactured by Nippon Bunko Kogyo K.K.) and the 1 H nuclear magnetic resonance spectrum ( 1 H-NMR) (Model AM-400, manufactured by Bruker Inc.; internal standard: tetramethylsilane in CDCl 3 ). The conversions, diastereoselectivity, and enantioselectivity of the products obtained were confirmed by gas chromatography under the following conditions. Conversion: Gas Chromatograph: HP-5890 series II Plus, manufactured by Hewlett Packard Column: Neutrabond-1 (0.25 mm x 30 m), manufactured by G.L. Science Co., Ltd. Carrier gas: helium Injection temperature: 220°C Detector temperature: 250°C Initial temperature: 80°C Final temperature: 250°C Rate: 2°C/min Diastereoselectivity: Gas chromatograph: HP-5890, manufactured by Hewlett Packard Column: DB-WAX (0.53 mm x 15 m), manufactured by J&W Scientific Co. Carrier gas: helium Injection temperature: 200°C Detector temperature: 250°C Initial temperature: 60°C Final temperature: 200°C Rate: 2°C/min Enantioselectivity: Gas chromatograph: GC-14A, manufactured by Shimadzu Corp. Column: Chirasil-DEX CB (0.25 mm x 25 m), manufactured by Chrompack International b.v. Carrier gas: helium Injection temperature: 220°C Detector temperature: 250°C Initial temperature: 50°C Final temperature: 150°C Rate: 1°C/min EXAMPLE 1 In a 100 ml autoclave were charged 3.4 ml of a 0.1M solution of potassium hydroxide (0.34 mmol) in 2-propanol, 4.2 mg (0.02 mmol) of (1R,2R)-diphenylethylenediamine, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 9.5 mg (0.005 mmol) of RU 2 Cl 4 [(R)-dm-binap] 2 NEt 3 and 6.5 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at 50°C for 30 minutes and cooled to room temperature. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1S,2R)-2-methoxycyclohexanol. The optical purity of the product was found to be 98%d.e. and 96%e.e. by gas chromatography. Boiling Point: 80-82°C/31.997 X 10 2 Pa (80-82°C/24 mmHg) IR (neat) cm -1 : 3450, 1100 NMR (CDCl 3 ) : 1.2-1.4 (m, 2H), 1.45-1.7 (m, 2H), 1.7-1.9 (m, 2H), 2.22 (dd, J=1.0, 5.0Hz, 1H), 3.28 (ddd, J=3.1, 3.3, 10.0Hz, 1H), 3.37 (s, 3H), 3.8-3.9 (m, 1H) EXAMPLE 2 In a 100 ml autoclave were charged 3.4 ml of a 0.1M solution of potassium hydroxide (0.34 mmol) in 2-propanol, 4.2 mg (0.02 mmol) of (1S,2S)-diphenylethylenediamine, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 8.4 mg (0.005 mmol) of Ru 2 Cl 4 [(S)-binap] 2 NEt 3 , and 6.5 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at 50°C for 60 minutes and cooled to room temperature. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1R,2S)-2-methoxycyclohexanol. The optical purity of the product was found to be 97%d.e. and 92%e.e. by gas chromatography. EXAMPLE 3 In a 100 ml autoclave were charged 1.75 ml of a 0.2M solution of potassium hydroxide (0.35 mmol) in 2-propanol, 0.2 ml of a 0.1M solution of 1,3-propanediamine (0.02 mmol) in 2-propanol, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 8.4 mg (0.005 mmol) of Ru 2 Cl 4 [(S)-binap] 2 NEt 3 , and 8 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at room temperature for 1.5 hours. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1R,2S)-2-methoxycyclohexanol. The optical purity of the product was found to be 93%d.e. and 91%e.e. by gas chromatography. EXAMPLE 4 In a 100 ml autoclave were charged 1.5 ml of a 0.2M solution of potassium hydroxide (0.30 mmol) in 2-propanol, 1.1 mg of (0.005 mmol) of (1S,2S)-diphenylethylenediamine, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 1.9 mg (0.0001 mmol) of Ru 2 Cl 4 [(S)-dm-binap] 2 NEt 3 , and 8.5 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at room temperature for 3.5 hours. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1R,2S)-2-methoxycyclohexanol. The optical purity of the product was found to be 99%d.e. and 98%e.e. by gas chromatography. EXAMPLE 5 In a 100 ml autoclave were charged 1.50 ml of a 0.2M solution of potassium hydroxide (0.30 mmol) in 2-propanol, 4.2 mg (0.02 mmol) of (1R,2R)-diphenylethylenediamine, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 9.6 mg (0.01 mmol) of Rh(cod)[(R)-t-binap]BF 4 and 8.5 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at 50°C for 19 hours and cooled to room temperature. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1S,2R)-2(1S,2R)-2-methoxycyclohexanol. The optical purity of the product was found to be 34%d.e. and 14%e.e. by gas chromatography. EXAMPLE 6 In a 100 ml autoclave were charged 1.5 ml of a 0.2M solution of potassium hydroxide (0.30 mmol) in 2-propanol, 4.2 mg (0.02 mmol) of (1S,2S)-diphenylethylenediamine, 1.28 g (10.0 mmol) of 2-methoxycyclohexanone, 10.1 mg (0.01 mmol) of Ir(cod) [(S)-binap]BF 4 and 8.5 ml of 2-propanol in a nitrogen atmosphere, and hydrogen was introduced therein to 5.066 X 10 6 Pa (50 atm). The mixture was stirred at 50°C for 19 hours and cooled to room temperature. The disappearance of the starting material was confirmed by gas chromatography. The solvent was evaporated under reduced pressure, and the residue was distilled under reduced pressure to obtain (1R,2S)-2-methoxycyclohexanol. The optical purity of the product was found to be 78%d.e. and 31%e.e. by gas chromatography. EXAMPLES 7 TO 26 In the same manner as in Examples 1 to 6 the 2-substituted cyclohexanone shown below was asymmetrically hydrogenated in the presence of a catalyst system using the phosphine ligand shown below and the amine shown below under the reaction conditions shown in Table 1 to obtain the corresponding optically active cyclohexanol in high yield. The reaction results are shown in Table 1. 2-Substituted Cyclohexanone: 19: R=OCH 3 20: R=OC 2 H 5 21: R=CH 3 Phosphine Ligand: 1: Ar=C 6 H 5 (BINAP) 2: Ar=C 6 H 4 -p-Me(Tol-BINAP) 3: Ar=C 6 H 3 -3,5-Me 2 (DM-BINAP) 4: Ar=C 6 H 4 -p-MeO(p-MeO-BINAP) 5: Ar=C 6 H 4 -p-Cl(p-Cl-BINAP) 6: Ar=C 6 H 4 -p- t Bu(p- t Bu-BINAP) 7: Ar=C 6 H 3 -3,5-Me 2 (H 8 -DM-BINAP) 8: Ar=C 6 H 5 (BIPHEMP) 9: Ar=C 6 H 5 (CHIRAPHOS) As described and demonstrated above, the present invention makes it possible to obtain various optically active cyclohexanol derivatives at high purity and in high yield.

Claims: A process for producing an optically active cyclohexanol derivative represented by formula (I): wherein R 1 represents an alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or a protected hydroxyl group, comprising asymmetrically hydrogenating a cyclohexanone derivative represented by formula (II): wherein R 1 is as defined above, in the presence of a catalyst system for asymmetric hydrogenation composed of a transition metal compound, a base, and a nitrogen compound, and wherein said transition metal compound is a complex of a transition metal of the group VIII represented by formula (III): M 1 X m L n wherein M 1 represents a transition metal selected from Ru, Rh, Ir, and Pt; X represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, and an alkoxy group; L represents DM-BINAP; and m and n each represent an integer, and wherein said base is a compound represented by formula (IV): M 2 Y wherein M 2 represents an alkali metal and an alkaline earth metal; and Y represents a group selected from a hydroxyl group, an alkoxy group, a mercapto group, and a naphthyl group, or a quaternary ammonium salt, and wherein said nitrogen compound is an amine compound. The process according to any preceding claim, wherein said asymmetric hydrogenation is carried out in an organic solvent.

Inventors: MATSUMOTO TAKAJI, MIURA TAKASHI, MURAYAMA TOSHIYUKI, MATSUMOTO, TAKAJI, MIURA, TAKASHI, MURAYAMA, TOSHIYUKI
Applicants: TAKASAGO PERFUMERY CO LTD, TAKASAGO INTERNATIONAL CORPORATION
Application year: 1996
Main classification: C07B53
IPC codes: C07C35, C07C43, C07B61, C07C29, B01J31, C07C41