Four-Component Reaction of Substituted β-Nitrostyrenes, Cyclohexanones, Activated Methylene Compounds, and Ammonium Acetate: Efficient Strategy for Construction of Tetrahydroindole Skeletons

An efficient one-pot four-component reaction was developed for the synthesis of two different stereochemical classes of substituted 2-aminotetrahydroindoles from substituted β-nitrostyrenes, cyclohexanones, ammonium acetate, and activated methylene compounds, such as Meldrum’s acid, 4-hydroxycoumarin, cyclohexanediones, cyclopentane-1,3-dione, or alkyl cyanoacetates. Both electron-donating and electron-withdrawing groups are tolerated in the aryl ring of the β-nitrostyrene. The reaction utilizes the triethylamine-promoted formation of new C–C and C–N bonds, and simultaneous aromatization in a domino fashion.