Trimethyl borate → 5-Bromo-2-chlorophenylboronic acid

4-Bromo-1-chloro-2-iodobenzene (10.35 g, 33 mmol) is dissolved in anhydrous tetrahydrofuran (60 ml) and the solution is cooled to −75° C. under an atmosphere of argon. Isopropylmagnesium chloride (17.1 ml, 34 mmol, 2M solution in tetrahydrofuran) is added dropwise over 30 minutes, maintaining the internal temperature below −70° C. by external cooling. Once the addition is complete, the reaction mixture is stirred at approximately −70° C. for 30 minutes and then allowed to warm to room temperature and stirred for 1 hour. The reaction mixture is then cooled to −78° C. and trimethyl borate (7.3 ml, 65 mmol) is added dropwise. The mixture is stirred at −78° C. for 30 minutes and then the cooling bath is removed and the mixture is stirred at room temperature for 1.5 hours. 2M Aqueous hydrochloric acid (30 ml) is added, and the crude product is extracted with ethyl acetate. The organic phase is washed with water and brine, dried over anhydrous magnesium sulfate, filtered and the filtrate evaporated in vacuo. Trituration with hexane gives 5-bromo-2-chlorophenylboronic acid (6.16 g) as an off-white solid.