4-Methoxy-2-methylphenylboronic acid was synthesized as follows: 4-bromo-3-methylanisole (10 g, 0.050 mol) was used as starting material, and reacted with n-butyllithium (24 mL of 2.5 M hexane solution, 0.055 mol) under anhydrous and anaerobic conditions at a low temperature (-78°C) to generate the corresponding aryl lithium intermediate. Subsequently, triisopropyl borate (57.7 mL, 47.02 g, 0.25 mol) was added to the reaction system, slowly warmed to room temperature and stirred overnight. Upon completion of the reaction, the crude product was obtained by acidic hydrolysis treatment and purified to give 5.7 g of 4-methoxy-2-methylphenylboronic acid white solid in 69% yield. The product was characterized by mass spectrometry (ESI), m/z 313 (2M-H2O-H)-.
