[Br:1][C:2]1[C:3]([F:22])=[C:4]([F:21])[CH:5]=[C:6]2[C:11]=1[N:10]([CH:12]1[CH2:14][CH2:13]1)[CH:9]=[C:8]([C:15]([O:17]CC)=[O:16])[C:7]2=[O:20].C(O)(=O)C.S(=O)(=O)(O)O>O>[Br:1][C:2]1[C:3]([F:22])=[C:4]([F:21])[CH:5]=[C:6]2[C:11]=1[N:10]([CH:12]1[CH2:14][CH2:13]1)[CH:9]=[C:8]([C:15]([OH:17])=[O:16])[C:7]2=[O:20]A mixture of ethyl 8-bromo-1-cyclopropyl-6,7-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylate (1.0 g), acetic acid (4 ml), water (3 ml) and concentrated sulfuric acid (0.5 ml) was heated on an oil bath (90°-100° C.) for an hour under stirring, then for an hour at room temperature and poured into ice water (20 ml). The resulting precipitate was collected by filtration and washed with water to give the title compound (0.82 g), mp 224°-225.5° C.
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