Process for the preparation of dihydropyridinecarboxylic acids

A process for the preparation of an optically pure 1,4-dihydropyridinemonocarboxylic acid of formula I ##STR24## in which R1 denotes 1-4C-alkyl,

• R2 denotes 1-4C-alkyl,
• R3 denotes 1-4C-alkyl or benzyl, and either
• A denotes hydrogen and
• B denotes a 2-chlorophenyl, 3-chlorophenyl, 2,3-dichlorophenyl, 2-nitrophenyl, 3-nitrophenyl, benzoximidazolyl (4-benzofurazanyl), 2-trifluoromethylphenyl, 2,3-methylenedioxyphenyl or 2-difluoromethoxyphenyl radical, or
• A denotes a 2-chlorophenyl, 3-chlorophenyl, 2,3-dichlorophenyl, 2-nitrophenyl, 3-nitrophenyl, benzoximidazolyl (4-benzofurazanyl), 2-trifluoromethylphenyl, 2,3-methylenedioxyphenyl or 2-difluoromethoxyphenyl radical and
• B denotes hydrogen,
• which comprises hydrolysing a compound of the formula II ##STR25## in which R1, R2, R3, A and B have the abovementioned meanings, in an alcohol R1--OH R1 being 1-4C-alkyl using aqueous alkali metal hydroxide, and resolving the resultant acid III ##STR26## into the enantiomers in a customary manner.

A process for the preparation of an optically pure 1,4-dihydropyridinemonocarboxylic acid of the formula I ##STR27## in which R1 denotes 1-4C-alkyl,

• R2 denotes 1-4C-alkyl,
• R3 denotes 1-4C-alkyl or benzyl, and either
• A denotes hydrogen and
• B denotes a 2-chlorophenyl, 3-chlorophenyl, 2,3-dichlorophenyl, 2-nitrophenyl, 3-nitrophenyl, benzoximidazolyl (4-benzofurazanyl), 2-trifluoromethylphenyl, 2,3-methylenedioxyphenyl or 2-difluoromethoxyphenyl radical, or
• A denotes a 2-chlorophenyl, 3-chlorophenyl, 2,3-dichlorophenyl, 2-nitrophenyl, 3-nitrophenyl, benzoximidazolyl (4-benzofurazanyl), 2-trifluoromethylphenyl, 2,3-methylenedioxyphenyl or 2-difluoromethoxyphenyl radical and
• B denotes hydrogen,
• by partial hydrolysis of a compound of the formula II ##STR28## in which R1, R2, R3, A and B have the abovementioned meanings, to give an acid III ##STR29## and resolution into the enantiomers in a customary manner, which comprises employing the undesired enantiomer, after ester formation with the compound R1--X in which R1 has the abovementioned meaning and X represents a leaving group or a halocarbonyloxy group, again as the starting compound II.

A process for the preparation of an 1,4-dihydropyridinemonocarboxylic acid of the formula III ##STR30## in which R1 denotes 1-4C-alkyl,

• R2 denotes 1-4C-alkyl,
• R3 denotes 1-4C-alkyl or benzyl, and
• A denotes hydrogen and
• B denotes a 2-chlorophenyl, 3-chlorophenyl, 2,3-dichlorophenyl, 2-nitrophenyl, 3-nitrophenyl, benzoximidazolyl (4-benzofurazanyl), 2-trifluoromethylphenyl, 2,3-methylenedioxyphenyl or 2-difluoromethoxyphenyl radical,
• which comprises hydrolysing a compound of the formula II ##STR31## in which R1, R2, R3, A and B have the abovementioned meanings, in an alcohol R1--OH R1 being 1-4C-alkyl using aqueous alkali metal hydroxide.