A ligand-free copper(II)-catalyzed three-component reaction in poly(ethylene glycol) medium: a versatile protocol for the preparation of selected 3-indole derivatives

An efficient and eco-friendly method has been developed for the synthesis of selected 3-indole derivatives via a copper-catalyzed condensation between indole, aldehydes, and malononitrile in polyethylene glycol. The reagent system (PEG solvent plus catalyst) could be recycled up to 5 times for reaction with the same aldehyde and it was used also with at least three different aldehydes successively. This multi-component reaction (MCR) occurs first through Knoevenagel condensation followed by Michael addition of indole.