[NH2:1][C:2]1[NH:3][C:4]2[C:9]([C:10]=1[C:11]#[N:12])=[CH:8][CH:7]=[C:6]([N+:13]([O-:15])=[O:14])[CH:5]=2.CO[CH:18]1[CH2:22][CH2:21][CH:20](OC)O1.[C:25](=[O:28])(O)[O-].[Na+].C(=O)=O>C(O)(=O)C.O>[N+:13]([C:6]1[CH:5]=[C:4]2[C:9]([C:10]([C:11]#[N:12])=[C:2]([N:1]3[CH:18]=[CH:22][CH:21]=[CH:20]3)[NH:3]2)=[CH:8][CH:7]=1)([O-:15])=[O:14].[CH2:18]([N:3]1[C:4]2[C:9](=[CH:8][CH:7]=[C:6]([O:28][CH3:25])[CH:5]=2)[C:10]([C:11]#[N:12])=[CH:2]1)[CH3:22]A solution of 2-amino-6-nitro-1H-indole-3-carbonitrile (362 mg, 1.79 mmol) in acetic acid (5 mL) is treated with 2,5-dimethoxytetrahydrofuran (0.30 mL, 2.27 mmol), and the solution is heated to reflux for 14 h. After cooling to ambient temperature, the solution is poured into water (100 mL), and solid sodium bicarbonate is added until CO2 evolution ceased. The mixture is extracted with EtOAc (2×100 mL), and the extracts are washed with saturated brine, combined, dried over MgSO4, filtered and concentrated. The residual material is separated by silica gel chromatography (EtOAc/hexanes, 1/4) to afford 6-nitro-2-pyrrol-1-yl-1H-indole-3-carbonitrile, compound 5, as a yellow solid (232 mg, 51%).
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