Under nitrogen protection, 2-bromo-5-phenylthiophene (compound 111, 2.50 g, 10.4 mmol) was dissolved in anhydrous THF (50 mL) and cooled to -78 °C. Slowly n-butyllithium (n-BuLi, 8.4 mL of a 2.5 M hexane solution) was added dropwise. The reaction mixture was stirred at -78 °C for 1 h. Trimethyl borate (2.40 mL, 20.9 mmol) was slowly added. Stirring was continued at -78 °C for 30 min, followed by removal of the cooling bath to allow the reaction mixture to gradually warm to room temperature and stirring for 3 h at 37 °C. Upon completion of the reaction, the reaction was quenched with 1N HCl (100 mL) and subsequently extracted with ethyl acetate. The organic layers were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure. The crude product was slurried with petroleum ether, filtered and dried to afford (5-phenylthiophen-2-yl)boronic acid (Compound 112, 1.04 g, 48.8% yield).
