The general procedure for the synthesis of 3-ethylphenylboronic acid from 3-bromoethylbenzene was as follows: 1-bromo-3-ethylbenzene (2.80 g, 15 mmol) was dissolved in tetrahydrofuran (40 mL) under nitrogen protection, cooled to -78 °C and stirred. n-Butyllithium (10 mL, 16 mmol) was slowly added and stirring was continued for 10 minutes. Subsequently, triisopropyl borate (6.92 mL, 30 mmol) was added and the reaction mixture was allowed to gradually warm to room temperature. Upon completion of the reaction, 1 M hydrochloric acid (50 mL) was added for acidification and then extracted with ether (100 mL). The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated. The crude product was purified by recrystallization in water and washed with hexane to give 0.591 g of 3-ethylphenylboronic acid in 26% yield. Mass spectrometry analysis showed (M + ACN)+ peak of 195.
