Synthesis
To a 2L round bottom flask was added 1-bromo-4-chloro-2-fluorobenzene (50 g, 238.7 mmol) and anhydrous tetrahydrofuran (900 ml), and the mixture was cooled to -78°C with stirring. Slowly n-butyllithium (2.5 M hexane solution, 100 ml, 250 mmol) was added dropwise and stirred continuously for 1 hour at this temperature. Subsequently, trimethyl borate (31.9 ml, 286 mmol) was added slowly and the reaction was continued for 30 minutes. After completion of the reaction, 1N aqueous hydrochloric acid solution (600 ml) was added and gradually warmed up to room temperature while stirring. The organic layer was separated, dried with anhydrous magnesium sulfate and filtered. The solvent was removed by distillation under reduced pressure, and the concentrated product was extracted with a mixture of chloroform and hexane solvents, and finally purified by recrystallization to afford 4-chloro-2-fluorophenylboronic acid (33.7 g, 193.3 mmol) in 81% yield.
