An Expedient One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-Ones and -Thiones Catalyzed by ZIRCONIA Nanopowder. An Improved Protocol for the Biginelli Cyclocondensation Compounds in ‘Dry Media’

A general and practical Green Chemistry route to the Biginelli cyclocondensation multicomponent reaction had been carried out by the three-component coupling of β-ketoesters, various structurally diverse aldehydes including heterocyclic aldehydes and urea/thiourea in the presence of Zirconia (ZrO2) nanopowder catalyst in dry media under microwave irradiation and a comparative study was also done under thermal conditions giving 3,4-dihydropyrimidin-2(1H)-ones and -thiones (DHPMs) in excellent yields. Besides, it was highlighted that ZrO2 nanopowder can be reused up to six times after simple washing with ethyl acetate, thus exposing the process economical and environmentally benign.