[CH:1]1([N:4]2[C:13]3[C:8](=[C:9]([N+:18]([O-:20])=[O:19])[C:10]([F:17])=[C:11]([F:16])[C:12]=3[O:14][CH3:15])[C:7](=[O:21])[CH:6]([C:22]([O:24][CH2:25][CH3:26])=[O:23])[CH:5]2[CH3:27])[CH2:3][CH2:2]1>C(Cl)Cl.[O-2].[O-2].[Mn+4]>[CH:1]1([N:4]2[C:13]3[C:8](=[C:9]([N+:18]([O-:20])=[O:19])[C:10]([F:17])=[C:11]([F:16])[C:12]=3[O:14][CH3:15])[C:7](=[O:21])[C:6]([C:22]([O:24][CH2:25][CH3:26])=[O:23])=[C:5]2[CH3:27])[CH2:2][CH2:3]1A suspension of ethyl 1-cyclopropyl-6,7-difluoro-1,2,3,4-tetrahydro-8-methoxy-2-methyl-5-nitro-4-oxoquinoline-3-carboxylate (1.42 g, 3.69 mmol) and manganese dioxide (16.1 g, 185 mmol) in CH2Cl2 (80 mL) was stirred at room temperature for 36 h. The catalyst was removed by filtration over Celite and the filtrate was concentrated in vacuo. The crude product was purified by column chromatography (Hexane:EtOAc 5:1→1:1) to yield ethyl 1-cyclopropyl-6,7-difluoro-1,4-dihydro-8-methoxy-2-methyl-5-nitro-4-oxoquinoline-3-carboxylate (225 mg, 16%) as a colorless solid.
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