Synthesis of 1,4-dihydropyridine carboxylic acids (III)

2,6-Dimethyl-4-(3′-nitrophenyl)-3-methoxylaminocarbonyl-1,4-dihydropyridine-5-carboxylic acid methylester,3b reacted with 2-cyanoethanol or benzylalcohol to give the corresponding cyanoethylurethane compound6c in 40.6% yield and benzylurethane compound6d in 32% yield. The cyanoethylurethane6c was hydrolized in ethanolic NaOH to give 2,6-dimethyl-4-(3′-nitrophenyl)-1,4-dihydropyridine-3-amino-5-carboxylic acid 5-methyl ester. HCl8 in 64.8% yield. Another acid hydrolysis of benzylurethane6d gave 2,6-dimethyl-4-(3′-nitrophenyl)-1,4-dihydropyridine-3-amino-5-carboxylic acid 5-methylester. HBr11 in 54.7% yield.