Slowly add n-BuLi (98.1 mL, 0.102 mol, 1.6 M hexane solution) dropwise to a stirred solution of 4-(3-bromophenyl)morpholine (16.5 g, 0.068 mol) in anhydrous THF (300 mL) at -70°C to -78°C. Maintaining this temperature, the reaction mixture was continued to be stirred for 2 hours. Subsequently, triisopropyl borate (30.5 mL, 0.150 mol) was slowly added dropwise to the reaction mixture while maintaining the same temperature. The dry ice-acetone bath was removed and the reaction mixture was allowed to gradually warm up to room temperature and stirred continuously at room temperature overnight. Upon completion of the reaction, the mixture was poured into saturated aqueous ammonium chloride solution, diluted with an appropriate amount of water and subsequently extracted with ethyl acetate. The organic phases were combined, dried with anhydrous MgSO4, concentrated under reduced pressure, and the temperature was controlled below 40°C to remove the solvent. The resulting residue was ground with a solvent mixture of hexane and ether to give 3-morpholin-4-ylphenylboronic acid (12 g, 85% yield) as a off-white solid. Mass spectrum (ES+): m/z 208 [M+H]+. 1H NMR (d6-DMSO) δ: 3.05 (4H, m), 3.72 (4H, m), 6.95 (1H, d), 7.18 (1H, t), 7.21 (1H, d), 7.38 (1H, br s), 7.94 (2H, s).
