Solvent-free approach to 3,4-dihydropyrimidin-2(1H)-(thio)ones: Biginelli reaction catalyzed by a Wells-Dawson reusable heteropolyacid

The Biginelli reaction is performed in an efficient, simple, solvent-free procedure, using a small amount of H6P2W18O62 center dot 24H(2)O, a reusable heteropolyacid catalyst with Wells-Dawson structure. Both aromatic and aliphatic aldehydes, and different beta-dicarbonyl compounds and urea or thiourea, were used as starting materials. Seventeen examples of dihydropyrimidinones and dihydropyrimidinethiones were prepared by heating the reactants either in refluxing acetonitrile or in the absence of solvent. Operational simplicity, the use of a noncorrosive, reusable catalyst in solventless conditions, short reaction times, and very good to excellent yields in most of the selected examples are the main advantages of the method.