[NH:1]1[CH2:6][CH2:5][NH:4][CH2:3][CH2:2]1.[CH3:7][O:8][C:9]([C:11]1[C:20](=[O:21])[C:19]2[C:14](=[CH:15][C:16](Cl)=[C:17]([F:22])[CH:18]=2)[N:13]([CH2:24][CH3:25])[CH:12]=1)=[O:10]>N1C=CC=CC=1>[CH3:7][O:8][C:9]([C:11]1[C:20](=[O:21])[C:19]2[C:14](=[CH:15][C:16]([N:1]3[CH2:6][CH2:5][NH:4][CH2:3][CH2:2]3)=[C:17]([F:22])[CH:18]=2)[N:13]([CH2:24][CH3:25])[CH:12]=1)=[O:10]A mixture of 1.7 g of anhydrous piperazine and 1.4 g of 1-ethyl-6-fluoro-7-chloro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid methyl ester in 3 ml of pyridine was refluxed with stirring for 5 hrs. The reaction mixture was cooled to give crude crystals. The crude crystals were recrystallized from a mixture of methylene chloride and methanol to give 1.55 g (77.5% yield) of 1-ethyl-6-fluoro-7-(1-piperazinyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid methyl ester. mp: 179°-181° C.
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