a) Synthesis of dimethyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate
A mixture of 75.5 g (0.50 mol) of 3-nitrobenzaldehyde, 116 g (1.00 mol) of methyl acetoacetate, and 55 mL (1.50 mol) of 28% ammonia solution was heated to reflux for 5 hours in 150 mL of methanol. After completion of the reaction, the precipitate was collected by filtration and the filter cake was purified by washing with hot anhydrous ethanol to give 133.5 g of yellow powdery product. The melting point (determined by Kofler's method) was 208°C. The yield was 77.2%.
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