20.5 g of 2-nitratopropyl acetoacetate, 15.1 g of 3-nitrobenzaldehyde and 1.5 g of piperidine acetate in 74 ml of benzene were heated at reflux under azeotropic dehydration conditions for 2 hours. The reaction solution was washed, in turn, with 25 ml of water, 25 ml of an aqueous 1N sodium bisulfite solution and 25 ml of water and dried over anhydrous sodium sulfate, and the benzene was evaporated under reduced pressure. To the residue thus obtained was added 15.4 g of 2-cyanoethyl 3-aminocrotonate, and the mixture was taken up in 44 ml of isopropyl alcohol, heated at reflux for 3 hours and cooled on ice. The crystals which precipitated were collected by filtration, dried, applied to a silica gel column chromatography [eluent: a mixture of hexane and ethyl acetate (1:1)] and recrystallized from isopropyl alcohol to give 31.2 g of 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-(2-cyanoethyl) ester 5-(2-nitratopropyl) ester.
