Under nitrogen protection, (3-fluoro-5-methoxyphenyl)boronic acid (500 mg, 2.942 mmol) was dissolved in dichloromethane (15 mL) and cooled to 0°C. A dichloromethane solution of 1 M boron tribromide (14.7 mL, 14.7 mmol) was slowly added dropwise. The reaction mixture was stirred at room temperature for 3 h. The progress of the reaction was monitored by thin layer chromatography (TLC). After completion of the reaction, the mixture was concentrated under reduced pressure. Water (15 mL) was added to the residue and the pH was adjusted to 2 with 1 M aqueous hydrochloric acid. the product was extracted with ethyl acetate (2 x 25 mL). The organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give (3-fluoro-5-hydroxyphenyl)boronic acid (430 mg) as an off-white solid.
