General procedure for the synthesis of monomethyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate from dimethyl 2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate:
(3) Preparation of 5-methoxycarbonyl-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylic acid
Dimethyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (0.01 mol) was mixed with 150 mL of methanol. Saturated aqueous NaOH solution (9 g, 0.225 mol) was slowly added to the mixture under stirring conditions. The reaction mixture was vigorously stirred at 70 °C for 6 hours. Upon completion of the reaction, about 80 mL of methanol was removed by evaporation under reduced pressure. 200 mL of water was added to the residue and unreacted feedstock was removed by filtration. The filtrate was adjusted to pH about 2.5 with 1 mol/L hydrochloric acid, at which point a yellow solid precipitated, which was filtered and dried to give a khaki colored powder. The resulting powder was recrystallized from methanol to give the title product 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylic acid monomethyl ester as a yellow solid (1.9 g, 57.2% yield).
