Tributyl borate → (5-Isopropyl-1H-indazol-4-yl)boronic acid

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A solution of 4-bromo-5-isopropyl-1H-indazole (1.6 g, 6.9 mmol) in Et2O (4 mL) is added slowly to a suspension of KH (1.0 g of 30% dispersion in mineral oil, 7.7 mmol) in Et2O (20 mL) at 0° C. and the mixture is stirred for 20 min. After cooling to −78° C., t-BuLi (8.9 mL of 1.7 M in Hex, 15 mmol) is added and the resulting mixture is stirred for 40 min at −78° C. To this is added B(On-Bu)3 (5.6 mL, 21 mmol) and the mixture is stirred for 24 h at room temperature. The reaction mixture is quenched with 1N H3PO4 and extracted with Et2O. The combined Et2O layers are back-extracted with 1N NaOH (3×10 mL). The combined NaOH extracts are acidified with 1N H3PO4 and extracted with EtOAc. The EtOAc extracts are washed with saturated brine, dried (MgSO4), and concentrated to yield 5-isopropyl-1H-indazole-4-boronic acid. 1H NMR (CDCl3) 7.85 (s, 1H), 7.42 (d, 1H), 7.37 (d, 1H), 3.6 (br s, 2H), 2.88 (m, 1H), 1.32 (d, 6H).

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