An Environmentally Benign One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and -thiones Using Tetrabutylammonium Hexatungstate [TBA]2[W6O19] as a Recyclable Catalyst

Abstract

Tetrabutylammonium hexatungstate [TBA]2[W6O19], an isopolytungstate, was found to be a highly efficient and recyclable heterogeneous catalyst for Biginelli reaction of ethyl acetoacetate, an aryl aldehyde, and urea or thiourea under solvent-free conditions, giving rise to 3,4-dihydropyrimidin-2(1H)-ones and -thiones. Good to high yields, short reaction times, easy workup, and absence of any volatile and hazardous organic solvents are just a few of the advantages of this procedure. Furthermore, the catalyst can be recycled after a simple workup, and can be used at least three times without substantial reduction in its catalytic activity.