2-Butenoic acid, 3-amino-, 1-methylethyl ester → 4-(2-Cyanophenyl)-5-methoxycarbonyl-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3-carboxylic acid

A mixture of methyl 2-(2-cyanobenzylidene)-4,4-dimethoxyacetoacetate (10.1 g) and isopropyl 3-aminocrotonate (5.51 g) was heated for 40 minutes at 78° C. for 5.5 hours at 120° C. with stirring, followed by heating for an hour at 125° C. without the stirring. After the reaction mixture was allowed to stand overnight, it was dissolved in ethyl acetate. This solution was washed twice with water, dried and then evaporated to dryness under reduced pressure to give a residue, which was crystallized from ethyl ether. The crystals were collected by filtration and washed with a small amount of ethyl ether to give crude powder of isopropyl ester of 4-(2-cyanophenyl)-5-methoxycarbonyl-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3-carboxylic acid (8.96 g.). Further, the crude product (0.77 g) was recovered from the filtrate. 0.5 g of this crude product was recrystallized from isopropyl ether to give purified white powder of the same product (0.37 g), mp 171°-172.5° C.