Dimethylformamide → t-Butyl 5-nitroindole-2-carboxylate

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To a stirred solution of 9 (12.8 g, 61.2 mmol) in dry THF (200 mL) under argon was added oxalyl chloride (12.0 mL, 137.5 mmol) followed by DMF (0.1 mL), which caused a vigorous evolution of gas. After 40 min, the reaction mixture was evaporated to dryness. The resulting solid was re-dissolved in THF (150 mL), cooled to ˜30° C., and stirred under argon. A solution of potassium t-butoxide (1.0 M in THF, 140 mL, 140 mmol) was then added dropwise over 45 min, and stirring was continued for an additional 45 min. The reaction was quenched with 600 mL of water, neutralized with few drops of a 10% aqueous solution of H3PO4 and extracted with ethyl acetate (3×400 mL). The organic extracts were washed with saturated aqueous NaHCO3, water, and then dried over magnesium sulfate, filtered, concentrated and crystallized with ethanol/hexane to afford compound 10 (9.62 g, 85% yield). Rf=0.35 (1:5 Ethyl acetate/Hexane); 1H NMR (CDCl3), 11.63 (s, 1H), 8.66 (dd, 1H, J=0.5, 1.3Hz), 8.20 (dd, 1H, J=0.5, 9.0 Hz), 7.48 (dd, 1H, J=0.5, 9.1 Hz), 7.28 (dd, 1H, J=0.9, 11.1 Hz), 1.63 (s, 9H); 13C NMR 160.39, 142.12, 138.11, 132.10, 126.78, 120.22, 119.83, 111.98, 109.82, 82.91, 28.26; MS m/z 285.43 (M+Na)+.

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