The general procedure for the synthesis of 3-chloro-2-fluorophenylboronic acid from 3-chloro-2-fluorobromobenzene was as follows: 16 g (72 mmol) of 1-bromo-3-chloro-2-fluorobenzene was added to a 500 mL three-necked flask and the air in the flask was displaced with nitrogen. Subsequently, 200 mL of tetrahydrofuran was added and the solution was cooled to -80 °C under a stream of nitrogen. 48 mL (76 mmol) of n-butyllithium (1.6 mol/L hexane solution) was slowly added dropwise with a syringe to this cooled solution, and after the dropwise addition was completed, the reaction mixture was continued to be stirred at the same temperature for 1.5 hours. After that, 9.0 mL (80 mmol) of trimethyl borate was added to the reaction mixture and gradually warmed up to room temperature (20 °C), where stirring was continued for about 19 hours. Upon completion of the reaction, about 100 mL of 1 mol/L hydrochloric acid was added to the resulting solution and the mixture was stirred. The organic layer was separated, washed with water, and the aqueous layer was extracted twice with toluene. The organic layer and the toluene extract were combined and washed with saturated aqueous sodium chloride solution. The combined organic layers were dried with anhydrous magnesium sulfate followed by gravity filtration. The filtrate was concentrated to give 4.5 g of the light yellow solid product 3-chloro-2-fluorophenylboronic acid in 35% yield.
