Synthesis
Under argon protection, 20 g (100 mmol) of 4-bromo-N,N-dimethylaniline was dissolved in 400 mL of anhydrous tetrahydrofuran and the mixture was cooled to -40°C. The reaction was carried out with the aid of a liquid solution of 1.6 M n-butyllithium in hexane. Subsequently, 63 mL (100 mmol) of a hexane solution of 1.6 M n-butyllithium was slowly added dropwise, stirring was maintained and the reaction mixture was gradually warmed to 0 °C for 1 hour. The reaction mixture was again cooled to -78 °C and 50 mL of anhydrous tetrahydrofuran was added. A solution containing 26 g (250 mmol) of trimethyl borate was added dropwise, followed by raising the reaction mixture to room temperature and stirring for 5 hours. After completion of the reaction, 200 mL of 1 N hydrochloric acid solution was added and stirred for 1 h. The aqueous layer was separated and discarded. The organic layer was dried with anhydrous magnesium sulfate and subsequently concentrated under reduced pressure. The resulting solid was washed with toluene to afford 12.38 g (75 mmol) of the target product 4-(N,N-dimethylamino)phenylboronic acid in 75% yield.
