Sodium hydride → 1-(2-trimethylsilanylethanesulfonyl)-1H-indole-5-carboxylic acid ethyl ester

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A solution of 1H-indole-5-carboxylic acid ethyl ester (10.31 g, 58.8 mmol) in dimethylformamide (50 mL) was added dropwise at 0° C. to a mixture of sodium hydride (1.83 g, 76.4 mmol) in dimethylformamide (150 mL). The resulting mixture was stirred at 0° C. for 30 min, then a solution of 2-trimethylsilanyl-ethanesulfonyl chloride (17.7 g, 88.2 mmol) in dimethylformamide (100 mL) was added slowly at 0° C. to the above mixture. After 2 h, sat. aqueous ammonium chloride (200 mL) was added, and the mixture was extracted with ethyl acetate (300 mL). After separation, the aqueous layer was extracted with ethyl acetate (2×150 mL). The combined organic layers were washed with brine (3×150 mL), and dried over anhydrous sodium sulfate. Solvents were removed in vacuo and the residue was subjected to flash chromatography on silica gel using 1:1.5 methylene chloride/hexanes as eluent to afford the title compound as a white solid (15.8 g, 79%). 1H-NMR (CDCl3, 500 MHz) δ 8.36 (d, J=1.5 Hz, 1H), 8.03 (dd, J 9.0, 2.0 Hz, 1H), 7.92 (d, J=8.5 Hz, 1H), 7.50 (d, J=3.5 Hz, 1H), 6.75 (d, J=3.5 Hz, 1H), 3.94 (s, 3H), 3.21-3.18 (m, 2H), 0.84-0.80 (m, 2H), −0.06 (s, 9H). 13C-NMR (CDCl3, 125 MHz) δ 167.3, 137.7, 130.3, 128.3, 125.9, 125.5, 124.0, 112.8, 108.3, 52.2, 51.2, 10.1, −2.1. Mass spec. 354.12 (MH)+.

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