[Cl:1][C:2]1[CH:10]=[CH:9][CH:8]=[C:7]2[C:3]=1[C:4]([CH:11]=O)=[CH:5][NH:6]2.C([O-])(=O)C.[NH4+].[N+:18]([CH3:21])([O-:20])=[O:19]>O>[Cl:1][C:2]1[CH:10]=[CH:9][CH:8]=[C:7]2[C:3]=1[C:4](/[CH:11]=[CH:21]/[N+:18]([O-:20])=[O:19])=[CH:5][NH:6]2A mixture of 4-chloroindole-3-carbaldehyde (314 mg, 1.75 mmol) and ammonium acetate (404 mg, 5.25 mmol) in nitromethane (6 mL) was stirred at 100° C. for 20 min. The reaction mixture was cooled, diluted with water and extracted with EtOAc (2×40 mL). The combined organic layers were washed with brine, dried over MgSO4 and concentrated under reduced pressure. The crude material was purified by silicagel column chromatography (50-100% EtOAc/heptane) to give compound B19-1 (224 mg, 58%) as an orange solid.
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