The general procedure for the synthesis of 2,3-difluoro-4-bromophenol from 4-bromo-2,3-difluoroanisole was as follows: to a stirred solution of 1-bromo-2,3-difluoro-4-methoxybenzene (3 g, 13.45 mmol) in dichloromethane (DCM, 30 mL) was slowly added dropwise to a dichloromethane (DCM) solution of 1 M boron tribromide (BBr3) (26.9) at -20 °C. The dropwise addition time was controlled to 10 min. mL, 26.9 mmol), and the dropwise addition time was controlled over 10 min. The cooling bath was removed and the reaction mixture was continued to be stirred at room temperature for 12 hours. Subsequently, the reaction mixture was cooled to 10 °C and the reaction was quenched with saturated aqueous sodium bicarbonate solution (100 mL). The mixture was diluted with dichloromethane (DCM, 150 mL) and the organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product 4-bromo-2,3-difluorophenol (2 g, 9.47 mmol, 70% yield) in the form of a dark red oil. NMR hydrogen spectrum (400MHz, chloroform-d): δ 7.15-7.21 (m, 1H), 6.69-6.76 (m, 1H), 5.30-5.31 (m, 1H) ppm.
