反应详情

A mixture of dimethyl 2-methyl-4-(2-cyanophenyl)-6-formyl-1,4-dihydropyridine-3,5-dicarboxylate (2.4 g), hydroxylamine hydrochloride (539.3 mg) and sodium acetate (752.3 mg) in acetic acid (15 ml) was stirred at room temperature for 55 minutes to form dimethyl-2-methyl-4-(2-cyanophenyl)-6-hydroxyiminomethyl-1,4-dihydropyridine-3,5-dicarboxylate. To the reaction mixture was added acetic anhydride (2.375 g), and the mixture was heated at 110° C. for 4 hours with stirring. The reaction mixture was concentrated and treated with water (30 ml). The resultant acidic solution was adjusted to pH 7.5 to 8 with an aqueous sodium bicarbonate solution, and extracted twice with ethyl acetate. The organic layer was washed with water, saturated aqueous sodium chloride solution, and evaporated to dryness under reduced pressure. The residue was kept overnight in a refrigerator for crystallization. The resultant crystals were collected by filtration and washed with small portion of cold methanol to give crystals of dimethyl 2-methyl-4-(2-cyanophenyl)-6-cyano-1,4-dihydropyridine-3,5-dicarboxylate (1.71 g). Additional crop (0.9 g) was recovered from the mother liquor. The combined crystals (2.61 g) were recrystallized from methanol to give pure crystals (1.2 g), m.p. 166°-166.5° C.