Methyl 3-aminocrotonate → 4-(2-Chlorophenyl)-2-[[2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)ethoxy]methyl]-1,4-dihydro-6-methyl-3,5-pyridinedicarboxylic Acid 3,5-Dimethyl Ester

92.1 g of methyl 2-(o-chlorobenzylidene)-4-(2-phthalimidoethoxy)acetoacetate was dissolved in 108 ml of 2-propanol at 80° C. 31.3 g of methyl-3-aminocrotonate was added and the mixture was heated at the same temperature for 24 hours. The mixture was evaporated to dryness. The residue was dissolved in 162 ml of glacial acetic acid at 80° C. The mixture was cooled to 15° C. and stirred at the same temperature for 20 hours. The solid was filtered off and washed with 83 ml of glacial acetic acid. The solid was suspended in 68 ml of methanol and agitated for 30 minutes. The solid was filtered off, washed with 23 ml of methanol and dried. The product was recrystallized from ethyl acetate.