Sodium ethoxide → 5-[2-(4-Benzhydryl-1-piperazinyl)ethyl] 3-ethyl 2-amino-1,4-dihydro-6-methyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate

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Reaction Steps

Sodium (0.20 g) was dissolved in dry ethanol (10 ml) and the thus-obtained sodium ethylate solution was added dropwise to a solution of 2-(4-benzhydryl-1-piperazinyl)ethyl 2-(3-nitrobenzylidene)acetoacetate (4.37 g) and ethyl amidinoacetate hydrochloride (1.42 g) in dry ethanol (10 ml) with stirring under reflux over a period of about 15 minutes. The mixture was further refluxed for 5 minutes. The resulting NaCl was filtered off and the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (120 g). From the eluate with ethyl ether-ethyl acetate (10:1, v/v), there was obtained 5-[2-(4-benzhydryl-1-piperazinyl)ethyl] 3-ethyl 2-amino-1,4-dihydro-6-methyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate as a yellow powder. Yield 3.22 g. To a solution of 2.48 g of this product in ethanol was added a solution of oxalic acid in ethanol to give the oxalate as crystals. Yield 2.52 g. Recrystallization from ethanol-ethyl ether gave yellow crystals (1.83 g). m.p. 152°-153° C.

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