Sulfuric Acid → Ethyl 1-cyclopropyl-7-(4-ethoxycarbonyl-1-piperazinyl)-6-fluoro-8-methyl-1,4-dihydro-4-oxoquinoline-3-carboxylate

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Reaction Steps

To a solution of diethyl [N-cyclopropyl-N-[3-(4-ethoxycarbonyl-1-piperazinyl)-2-methyl-4-fluoro-6-nitrophenyl]aminomethylene]malonate (1.0 g) in acetic anhydride (5 ml) is added conc. sulfuric acid (2 ml) with keeping at 50°-70° C. After stirring for 30 minutes, the reaction mixture is poured into ice water, and neutralized with potassium carbonate. The mixture is extracted with ethyl acetate, and the solvent is distilled off, and the resulting residue is purified by silica gel column chromatography (solvent, dichloromethane:methanol=10:1) and then recrystallized from ethyl acetate to give ethyl 1-cyclopropyl-7-(4-ethoxycarbonyl-1-piperazinyl)-6-fluoro-8-methyl-1,4-dihydro-4-oxoquinoline-3-carboxylate (0.19 g), as colorless prisms, m.p. 200°-202° C.

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