The general procedure for the synthesis of 3-(N,N-dimethylamino)phenylboronic acid from 3-bromo-N,N-dimethylaniline was as follows: 3-bromo-N,N-dimethylaniline (500 mg, 2.50 mmol) was dissolved in tetrahydrofuran (THF, 8 mL) and the solution was cooled to -78 °C. At -78 °C, n-butyllithium (1.6 M in hexane, 1.56 mL, 3.75 mmol) was slowly added dropwise, and after the drop was completed, the reaction mixture continued to be stirred for 5 min by maintaining this temperature. Subsequently, trimethyl borate (1.11 mL, 10.0 mmol) was added and stirred at -78 °C for 1 h, followed by a slow warming to -20 °C over 20 min. 2 M hydrochloric acid (3 mL) was added and after stirring for 5 min, the reaction mixture was neutralized with saturated sodium bicarbonate (NaHCO3) solution. The mixture was extracted with ethyl acetate (3 × 10 mL), the organic phases were combined, and the crude product was concentrated under reduced pressure. Purification by silica gel fast column chromatography with acetone/dichloromethane (1:1, v/v) as eluent gave the target product 3-(N,N-dimethylamino)phenylboronic acid (251 mg, 61% yield).
