A mixture of 3-methoxycarbonyl-2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-5-carboxylic acid (3.32 g, 0.01 mole), 1-bromo-2-chloroethane (1.43 g, 0.01 mole) and triethylamine (1.01 g, 0.01 mole) is stirred at 120° C. for 8 hours. The reaction mixture is dissolved in a mixture of ethyl acetate/methanol/ammonia (80:30:3) and subjected to chromatography on a silica gel column (2×35 cm). Thus, there are obtained chloroethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (0.75 g, 19.8%) and the dimeric ethylene glycol-di-/2,6-dimethyl-4-(m-nitrophenyl)-5-methoxycarbonyl-1,4-dihydropyridyl-3/dicarboxylate (0.1 g, 1.5%) as oily substance.
