[CH2:1]([C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][CH:11]=1)[NH:8][CH2:7][CH2:6]2)[CH3:2].[N+:12]([O-])([O-:14])=[O:13].[K+].[OH-].[Na+]>OS(O)(=O)=O>[CH2:1]([C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][C:11]=1[N+:12]([O-:14])=[O:13])[NH:8][CH2:7][CH2:6]2)[CH3:2]To a solution of 5-ethyl-2,3-dihydro-1H-indole (2.5 g, 17 mmol) in H2SO4 (98%, 20 mL) was slowly added KNO3 (1.7 g, 17 mmol) at 0° C. After addition, the mixture was stirred at 0-10° C. for 10 min, carefully poured into ice, basified with NaOH solution to pH 9 and extracted with ethyl acetate. The combined extracts were washed with brine, dried over Na2SO4 and concentrated to dryness. The residue was purified by column chromatography on silica gel to give 5-ethyl-6-nitro-2,3-dihydro-1H-indole (1.9 g, 58%).
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