Trimethyl borate → tert-butyl-[2-(1H-indol-5-yl)propan-2-yloxy]silane;[1-[(2-methylpropan-2-yl)oxycarbonyl]indol-2-yl]boronic acid

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Reaction Steps

To a stirred solution of 5-(tert-Butyl-dimethyl-silanyloxymethyl)-indole-1-carboxylic acid tert-butyl ester (3-3, 38.6 g, 106.7 mmol) in tetrahydrofuran (400 mL) was slowly added at −78 deg C. a solution of lithiun diisopropylamide in tetrahydrofuran (2M, 80.1 mL, 160.1 mmol, 1.5 equiv). The reaction mixture was stirred at the same temperature for 1 h, treated with trimethylborate, warmed up to ambient temperature, and partitioned between ethyl acetate and 0.5N-HCl. The organic layer was washed with brine, separated, dried (MgSO4) and concentrated in vacuo to give the crude solid. Trituration of the crude product with hexanes followed by filtration and air-drying afforded the desired boronic acid (3-4, 41.3 g, 95%) as a white powder; 1H NMR (400 MHz, CDCl3) δ 7.96 (d, 1H, J=6.8 Hz), 7.54 (s, 1H), 7.47 (s, 1H), 7.32 (d, 1H, J=6.8 Hz), 7.10 (s, 1H), 4.82 (s, 2H), 1.74 (s, 9H), 0.95 (s, 9H), 0.11 (s, 6H).

Provenance & Evidence