4-Bromodiphenyl ether (6.2 g, 25.0 mmol) was dissolved with isopropanol pinacol borate (10.3 mL, 50 mmol) in anhydrous tetrahydrofuran and the reaction system was cooled to -78 °C under nitrogen protection. Slowly n-butyllithium (2.5 M, 18 mL, 45 mmol) was added dropwise, and after completion of the dropwise addition, the reaction mixture was stirred at -78 °C for 6 hours, followed by a slow warming to -40 °C and kept for 12 hours. Upon completion of the reaction, the mixture was quenched by pouring it into saturated ammonium chloride solution and extracted three times with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure and the crude product was purified by column chromatography to give 5.4 g of 4-phenoxyphenylboronic acid pinacol ester in 72% yield.
