2-Bromobenzofuran (5.0 mmol) was dissolved in dry 20 mL of tetrahydrofuran, and the mixture was cooled to -78 degrees C. n-Butyllithium (5.5 mmol, 2.43 M, 1.1 eq.) was then added slowly and dropwise to the mixture, and the reaction mixture was stirred for about 30 minutes before triisopropyl borate (10 mmol, 2.0 eq.) was added dropwise to the reaction system. The reaction mixture was then stirred for 30 minutes, allowed to warm up to zero degrees Celsius and stirred the reaction mixture at 0 degrees Celsius for 1 hour. At the end of the reaction, the reaction was quenched with 1 M hydrochloric acid (40 mL), then the reaction mixture was extracted with ethyl acetate (3 x 50 mL), the combined organic phases were dried over MgSO4 and filtered, and the filtrate was concentrated under reduced pressure to give the target product molecule benzofuran-2-boronic acid.
