In methylene chloride (30 ml) is suspended methyl (+)-5-carboxy-2-cyano-6-methyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylate (3.12 g) followed by addition of phosphorus pentachloride (2.46 g) with ice-cooling, and the mixture is stirred for 30 minutes. Then, a solution of isopropyl alcohol (1.4 g) in methylene chloride (10 ml) is added dropwise over a period of 10 minutes. The mixture is stirred for 20 minutes, at the end of which time 5% aqueous sodium carbonate solution (30 ml) is added and the mixture is stirred at ambient temperature for one hour. The organic layer is separated and the water layer is extracted with methylene chloride. The organic layers are combined, washed with aqueous sodium chloride solution, dried over anhydrous magnesium sulfate and distilled under reduced pressure to remove the solvent. The residue is purified by silica gel (75 g) column chromatography, elution being carried out with benzeneethyl acetate (10:1). The solvent is removed from the eluate under reduced pressure and the residue is crystallized from diisopropyl ether to provide 5-isopropyl 3-methyl (+)-2-cyano-6-methyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate (3.34 g).
