To a three-neck flask equipped with a Dean-Stark splitter was added 30 mL of toluene followed by 2-methylphenylboronic acid (0.21 g, 1.55 mmol) and pinacol (0.22 g, 1.86 mmol). The reaction mixture was heated to reflux for 2 hours. Upon completion of the reaction, the mixture was washed three times with 30 mL of water to remove unreacted pinacol and phenylboronic acid. The organic phase was separated and the toluene solvent was removed by evaporation under reduced pressure to give the crude product. The crude product was dissolved in 50 mL of dichloromethane and washed again with 30 mL of water. Anhydrous sodium sulfate was added to the organic phase to dry, and the dried solution was evaporated under reduced pressure to give 0.32 g of crude product. The resulting crude product (0.32 g, 1.47 mmol), N-bromosuccinimide (NBS, 0.39 g, 2.2 mmol) and azobisisobutyronitrile (AIBN, 0.003 g, 0.018 mmol) were dissolved in 10 mL of acetonitrile. The reaction solution was refluxed at 90 °C for 2 hours. After the reaction was completed, it was cooled to room temperature and the solvent was removed by distillation under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography using petroleum ether (60~90 °C)/ethyl acetate (v/v = 1:1) as eluent to obtain the target product 2-bromoethylphenylboronic acid pinacol ester as white solid (0.53 g, 80% yield).
