Nitromethane → 5-(2-nitro-vinyl)-1H-indole
Reaction equation
[CH:1]([C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][CH:11]=1)[NH:8][CH:7]=[CH:6]2)=O.CCOC(C)=O.CCCCCC.[N+:24]([CH3:27])([O-:26])=[O:25]>>[N+:24]([CH:27]=[CH:1][C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][CH:11]=1)[NH:8][CH:7]=[CH:6]2)([O-:26])=[O:25]Participants
5
Procedure
5-Formyl indole (14.5 g) was refluxed with NH4OAc (10.0 g) in nitromethane ((100 mL) for 3 hours. The mixture was cooled and evaporated under reduced pressure. The residue was recrystallized from isopropanol to give the first portion of intermediate and the mother liquid was purified by chromatograph (EtOAc:hexane=1:4 to 2:3) to the second portion intermediate of 5-(2-nitro-vinyl)-1H-indole (2.09 g combined, in 11% yield), which was treated with NaBH4 (1.85 g) in methanol (150 mL) at room temperature for 35 min then quenched with acetic acid (4 mL), concentrated and followed by chromatography purification (EtOAc:hexane=1:9) to afford 5-(2-nitro-ethyl)-1H-indole (1.37 g) in 65% yield. This nitro compound was hydrogenated with Pd—C (10%) under atmosphere hydrogen in methanol overnight to afford 2-(1H-indol-5-yl)-ethylamine in 99% yield. LC-MS showed the product had the expected M+H+ of 161.