General procedure for the synthesis of 4-fluoro-3-methoxyphenylboronic acid from 2-fluoro-5-bromoanisole: To a solution of 2-fluoro-5-bromoanisole (2.7 g, 13.1 mmol) in tetrahydrofuran (THF, 25 mL) was slowly added n-butyllithium (n-BuLi, 1.6 M solution in hexane, 11.0 mL, 17.7 mmol) at -78 °C. The reaction mixture was stirred continuously at -78 °C for 40 min, followed by the addition of trimethyl borate (2.7 mL, 24.3 mmol). The reaction system was slowly warmed from -78 °C to room temperature and stirring was continued at this temperature for 18 hours. Upon completion of the reaction, the reaction was quenched with 1.0 N hydrochloric acid (40 mL) and subsequently extracted with ethyl acetate (EtOAc). The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate (Na2SO4). After removal of solvent by evaporation under reduced pressure, the crude product obtained was purified by grinding with a solvent mixture of ethyl acetate/hexane (1:4, v/v). After filtration, the target product 4-fluoro-3-methoxyphenylboronic acid (0.75 g, 35% yield) was obtained as a white solid. The structure of the product was confirmed by 1H NMR (400 MHz, methanol-d4) with chemical shifts of δ 3.86 (s, 3H) and 7.03-7.45 (m, 3H).
