121-43-7

6627-55-0

259209-21-7

General method: n-Butyllithium (1.7 M hexane solution, 38 mL) was slowly added dropwise to a solution of 2-bromo-4-methylphenol (30 mmol) or 2-bromo-1-ethoxy-4-methylphenol (30 mmol) in anhydrous ethyl ether (80 mL) cooled to -80°C under argon protection. After the dropwise addition was completed, the reaction mixture was allowed to gradually warm up to room temperature and stirred continuously under argon atmosphere for 2 hours. Subsequently, the reaction mixture was cooled again to -80 °C and trimethyl borate (5.58 mL, 50 mmol) was added quickly. After stirring at -80 °C for 0.5 h, the mixture was moved to room temperature and continued to stir under argon atmosphere for 15 h. The reaction was completed with the addition of trimethyl borate (5.58 mL, 50 mmol). After the reaction was completed, 2M HCl aqueous solution (20 mL) was slowly added to the ice-cold reaction mixture and stirred for 0.5 h until the milky emulsion became clear. The ether layer was separated and the aqueous layer was extracted with ether (3 x 100 mL). All ether layers were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The residue was recrystallized with a solvent mixture of hot ether and toluene (3:7 v/v) to give the white solid product (2-hydroxy-5-methylphenyl)boronic acid.