An Efficient, Solvent-Free and Green One-Pot Protocol for the Rapid Access to Polyfunctionalized Carbazoles

The solvent-free one-pot p-extension reaction of indole to carbazole has been carried out very efficiently on the surface of a basic alumina as an inexpensive reusable solid support by involving several 2-(3-formyl-1H-indol-2-yl) acetophenones/acetates and a wide range of 2-aryl/hetero-aryl/alkyl-substituted nitroolefins (or in situ generated nitroolefins from aldehydes and nitromethane)/nitrodienes/chalcones/cinnamyl esters as acceptors under aerobic conditions. This oxidant-free one-shot protocol delivers high to excellent yields (76-92%) of a novel series of 3-nitro/benzoyl/carboxylate carbazole derivatives in eco-friendly and economical manners and allows a variety of sensitive functional groups on aromatic rings. Moreover, the synthesized 3-nitrocarbazoles are valuable synthons for the easy access to tetra cyclic pyrido[ 3,2-c] carbazoles, 3-iodo/arylacetylenyl-substituted carbazoles and (Z)-N-carbazole-substituted nitroenamine (Z/E= 99:1).