[NH2:1][C:2]1[CH:7]=[C:6]([Br:8])[C:5]([F:9])=[CH:4][C:3]=1[OH:10].C([O-])([O-])=O.[K+].[K+].Cl[CH2:18][C:19](Cl)=[O:20].O>CN(C=O)C>[Br:8][C:6]1[C:5]([F:9])=[CH:4][C:3]2[O:10][CH2:18][C:19](=[O:20])[NH:1][C:2]=2[CH:7]=1
To a 0° C. mixture of 2-amino-4-bromo-5-fluorophenol (38.0 g, crude from previous step) and K2CO3 (76.0 g, 553 mmol) in DMF (100 mL) was added 2-chloroacetyl chloride (23.0 g, 15.3 mL, 203 mmol) drop-wise. The reaction mixture was heated at 80° C. overnight then cooled to ambient temperature and poured into water (300 mL). The precipitate was collected by filtration, washed with water and dried to give 6-bromo-7-fluoro-4H-benzo[1,4]oxazin-3-one (41.0 g, 90%). 1H NMR (DMSO-d6, 400 MHz): δ 7.13 (m, 2H), 4.62 (s, 2H). The amide proton was not observed.
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