An appropriate one-pot synthesis of 3,4-dihydropyrano[c]chromenes and 6-amino-5-cyano-4-aryl-2-methyl-4H-pyrans with thiourea dioxide as an efficient, reusable organic catalyst in aqueous medium

An efficient, convenient method for the synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives by one-pot, three-component reaction of aldehydes, malononitrile/cyanoacetate, and 4-hydroxycoumarin in the presence of a catalytic amount of thiourea dioxide, an efficient, reusable organic catalyst, is described. A variety of 3,4-dihydropyrano[3,2-c]chromene derivatives were obtained, and 6-amino-5-cyano-4-phenyl-2-methyl-4H-pyran-3-carboxylic acid ethyl esters were obtained by condensation of aldehydes, malononitrile and ethyl acetoacetate in the presence of thiourea dioxide in aqueous medium. The salient features of the protocol are mild reaction conditions, high yields, short reaction time, safety, high atom-economy, eco-friendly standards, easy isolation of products, no column chromatographic separation and reusability of the catalyst.