Boric acid (H3BO3), tripropyl ester → 3-ethyl-1-phenyl-1H-indazol-6-ylboronic acid

Into a 250-mL 3-necked round-bottom flask purged and maintained with an inert atmosphere of nitrogen, was placed a solution of 6-bromo-3-ethyl-1-phenyl-1H-indazole (2 g, 6.64 mmol, 1.00 equiv) in tetrahydrofuran (20 mL). To the resulting mixture was then added a solution of n-BuLi (4 mL, 1.40 equiv) in tetrahydrofuran (5 mL) dropwise with stirring at −78° C. in 5 min. The resulting mixture was stirred for 30 min at the temperature. To the resulting mixture was then added a solution of tripropyl borate (1.49 g, 7.93 mmol, 1.20 equiv) in tetrahydrofuran (5 mL) dropwise with stirring at −78° C. in 5 min. The resulting solution was stirred for 1 h at −78° C. in a liquid nitrogen bath. The reaction was then quenched by the addition of water (30 mL). The resulting solution was extracted with ethyl acetate (2×50 mL), the organic layers combined and dried over anhydrous sodium sulfate, then concentrated under vacuum. The residue was applied onto a silica gel column with ethyl acetate/petroleum ether (1:5) to yield 3-ethyl-1-phenyl-1H-indazol-6-ylboronic acid as a white solid.