B(Br)(Br)Br.[OH:5][C:6]1[C:14]([C:15]([F:18])([F:17])[F:16])=[CH:13][C:9]([C:10]([OH:12])=[O:11])=[CH:8][C:7]=1[O:19]C.O>C(Cl)Cl>[OH:19][C:7]1[CH:8]=[C:9]([CH:13]=[C:14]([C:15]([F:16])([F:17])[F:18])[C:6]=1[OH:5])[C:10]([OH:12])=[O:11]Boron tribromide (392 μL, 4.15 mmol) was added to a suspension of 4-hydroxy-3-methoxy-5-(trifluoromethyl)benzoic acid (4) (392 mg, 1.66 mmol) in DCM (10 mL) at 0° C. The reaction mixture was allowed to warm to RT and stirred for 70 h. The reaction mixture was cautiously added to stirring iced water (50 mL) and stirred for 10 min. The product was extracted with DCM (2×20 mL), and then the combined organic extracts were washed with brine (2×20 mL). The solvent was removed in vacuo and the residue was purified by silica chromatography (12 g, 0-10% MeOH in DCM) to afford 3,4-dihydroxy-5-(trifluoromethyl)benzoic acid (5) (257 mg, 68%) as a white solid: m/z 221 [M−H]− (ES−); 1H NMR (400 MHz, DMSO-d6) δ: 12.83 (1H, br s), 10.45 (2H, br d), 7.56 (2H, dd).
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