[Br:1][C:2]1[C:7]([C:8]([OH:10])=[O:9])=[C:6]([F:11])[C:5]([F:12])=[CH:4][CH:3]=1.OS(O)(=O)=O.[CH3:18]O>>[Br:1][C:2]1[C:7]([C:8]([O:10][CH3:18])=[O:9])=[C:6]([F:11])[C:5]([F:12])=[CH:4][CH:3]=1A stirred solution of 6-bromo-2,3-difluorobenzoic acid and conc. H2SO4 in MeOH was heated at reflux for 18 h. The reaction mixture was cooled to rt and concentrated under reduced pressure. To the residue was carefully added a satd. aq. NaHCO3 solution. The resulting mixture was extracted with CH2Cl2. The combined extracts were dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The residue obtained was dried under high vacuum to afford the title compound. ESI MS (M+H) 251.
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