Thiourea dioxide catalyzed multi-component coupling reaction for the one step synthesis of naphthopyran derivatives

An aqueous solution of thiourea dioxide was used to catalyze a one-pot three-component coupling reaction of an aromatic aldehyde, malononitrile, and α- or β-naphthol for the synthesis of various naphthopyran derivatives in excellent yields. At the end of the reaction, the product was isolated by filtration or extraction and the remaining aqueous solution of thiourea dioxide was reused as such for several subsequent runs.