[OH:1]O.[O-]Cl=O.[Na+].[Br:7][C:8]1[C:15]([CH3:16])=[CH:14][C:11]([CH:12]=[O:13])=[C:10]([F:17])[CH:9]=1.Cl>O.CC#N>[Br:7][C:8]1[C:15]([CH3:16])=[CH:14][C:11]([C:12]([OH:1])=[O:13])=[C:10]([F:17])[CH:9]=1
NaH2PO4 (418 mg, 3.48 mmol) in H2O (17.6 ml), a 35% aqueous H2O2 solution (2.5 ml, 25.7 mmol) and NaClO2 (2.23 g, 24.7 mmol) in H2O (34.9 ml) were sequentially added to a mixture of 4-bromo-2-fluoro-5-methyl-benzaldehyde (3.74 g, 17.2 mmol) in MeCN (52 ml) at 0° C. The mixture was stirred at room temperature for 14 hours, and then made acidic (pH 3) with a 10% aqueous HCl solution and extracted with ethyl acetate (3×100 ml). The organic layers were washed with H2O (70 ml), and then dried over MgSO4 and concentrated under reduced pressure to give 4-bromo-2-fluoro-5-methyl-benzoic acid as a pale orange solid (4.02 g, 100%).
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