GENERAL PROCEDURE: 3,4-Dimethoxyaniline (0.5 mmol, 1.0 eq.) was dissolved in methanol (1.0 mL), hydrochloric acid (0.5 mL, 1.5 mmol, 3.0 eq.) was slowly added, followed by water (0.5 mL). The reaction mixture was stirred for 2 min, then sodium nitrite solution (0.25 mL, prepared by dissolving 35 mg NaNO2 in 0.25 mL of water) was added. The reaction mixture was stirred at 0-5 °C for 30 min, followed by the addition of methanol (1.0 mL) and hydrochloric acid (135 mg, 1.5 mmol, 3.0 equiv). Stirring was continued for 60 min. Upon completion of the reaction, it was diluted with water (10 mL) and extracted with dichloromethane (50 mL, 3 times). The organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give 3,4-dimethoxyphenylboronic acid.
