Regioselective green synthesis of some novel indole-substituted 1H-benzo[f]chromenes via one-pot three-component reactions in water-ethanol media.

A regioselective, efficient and environmentally friendly method was developed for the synthesis of novel indole-substituted 1H-benzo[f]chromene derivatives through one-pot multicomponent condensation reaction of 3-cyanoacetyl indole, 2,7-dihydroxynaphthalene, and various aryl, heteroaryl and aliphatic aldehydes in EtOH/H2O under reflux conditions. The domino reaction proceeded via a piperidine-catalyzed Knoevenagel condensation between 3-cyanoacetyl indole and an aldehyde, followed by a Michael addition of 2,7-dihydroxynaphthalene and subsequent intramolecular heteroannulation. The attractive features of this method are operational simplicity, regioselectivity, green process, broad substrate scope, metal-free, shorter reaction time, easy workup, good to excellent yields and easy purification of products without utilization of any chromatography. The structures of the compounds were confirmed by FT-IR, 1H-NMR, and 13C-NMR spectroscopy and mass spectrometry.