The N-Methyl-5-aminoindole2-carboxylic acid ethyl ester (2.4 g, 11 mmol) was added with 100 ml of CH2Cl2 and triethyl amine (2.3 ml, 16.5 mmol). The reaction mixture was brought to −78 degree (dry ice-acetone) under N2. After (CF3SO2)2O (2.0 ml, 12 mmol) was added into it slowly via a syringe, the reaction mixture was stirred at −78 degree for 30 min and slowly brought to room temperature. The reaction was treated with 300 ml of CH2Cl2 and washed with Sat. Na2SO4 (100 ml×3), H2O (100 ml×50, and brine. TLC (20% EA/Hexane) showed two components, the desired product with smaller Rf (0.4) value and the corresponding 5-(N, N-ditrifluoromethanesulfonyl)aminoindole (Rf 0.6). After the solvent was evaporated, the residue was purified either via recrystalization with CH2Cl2/Hexane or Flash Column (20% EA/Hexane). The purified product (1-Methyl-5-trifluoromethansulfonylamino-1H-indole-2-carboxylic acid ethyl ester) was obtained as a light orange solid (1.6 g). 1H-NMR (400 MHz, DMSO-d6) δ 11.69 (s, 1H, SNH-5), 7.64 (d, J=8.6 Hz, 1H, H-7), 7.60 (d, J=2.2 Hz, 1H, H-4), 7.31 (s, 1H, H-3), 7.23 (dd, J=2.2, 8.6 Hz, 1H, H-6), 4.33 (q, J=7 Hz, 2H, CH2CH3), 4.02 (s, 3H, NCH3), 1.33 (t, 3H, CH2CH3), MS m/z 349 [M−H].
