[CH2:1]([N:3]1[C:11]2[C:6](=[CH:7][CH:8]=[C:9]([N+:12]([O-:14])=[O:13])[CH:10]=2)[CH:5]=[C:4]1[CH3:15])[CH3:2].[Br:16]NC(=O)CCC(N)=O.C(OCC)(=O)C>C1COCC1>[Br:16][C:5]1[C:6]2[C:11](=[CH:10][C:9]([N+:12]([O-:14])=[O:13])=[CH:8][CH:7]=2)[N:3]([CH2:1][CH3:2])[C:4]=1[CH3:15].[CH2:1]([N:3]1[C:11]2[C:6](=[CH:7][CH:8]=[C:9]([N+:12]([O-:14])=[O:13])[CH:10]=2)[CH:5]=[C:4]1[CH3:15])[CH3:2]Stir a solution of 1-ethyl-2-methyl-6-nitro-1H-indole, 19 (0.36 g, 1.76 mmol) and N-bromosuccinamide (0.31 g, 1.76 mmol) in anhydrous THF (10 mL) under inert atmosphere at ambient temperature for 14 hours. Quench the reaction with saturated aqueous sodium bicarbonate, add ethyl acetate, and wash with saturated aqueous sodium bicarbonate followed by saturated aqueous brine. Dry the organic layer over sodium sulfate, filter, and concentrate in vacuo. Chromatograph over silica gel using hexanes/ethyl acetate (9:1) to afford the title compound and unreacted 1-ethyl-2-methyl-6-nitro-1H-indole (0.37 g) in a 4:1 mixture which can be used in the subsequent step without further purification. LRMS (API ES+)=: 283, 285 (M, M+2M).
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