4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-1H-indazole

73183-34-3

186407-74-9

885618-33-7

To a solution of 4-bromo-1H-indazole (500 mg, 2.54 mmol) and bis(pinacolato)diboron (1.5 eq, 3.81 mmol) in dimethyl sulfoxide (DMSO, 20 mL) was added dry potassium acetate (3.0 eq, 7.61 mmol, 747 mg) and PdCl2(dppf)2 (3 mol%, 0.076 mmol, 62 mg). The reaction mixture was degassed with argon and the reaction was heated at 80 °C for 40 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was partitioned between water (50 mL) and ether (3 x 50 mL). The organic layers were combined, washed with brine (50 mL), separated and dried over anhydrous magnesium sulfate (MgSO4). The crude product was purified by column chromatography using 30%-40% ethyl acetate/petroleum ether as eluent to give a non-separable 3:1 mixture of 1H-indazole-4-boronic acid pinacol ester (369 mg, 60%) and unreacted 4-bromo-1H-indazole (60 mg, 20%). The mixture was a yellow gel that solidified to an off-white solid upon standing.1H NMR (400 MHz, DMSO-d6) data were as follows:1H-indazole-4-boronic acid pinacol ester (70): δ 1.41 (12H, s), 7.40 (1H, dd, J = 8.4 Hz, 6.9 Hz), 7.59 (1H, d, J = 8.4 Hz), 7.67 (1H, d, J = 6.9 Hz), 10.00 (1H, br s), 8.45 (1H, s); 4-bromo-1H-indazole: δ 7.40 (1H, m), 7.18 (1H, t, J = 7.9 Hz), 7.50 (1H, d, J = 9.1 Hz), 7.77 (1H, d, J = 7.9 Hz), 8.09 (1H, s). The impurity peak appeared at δ 1.25.