Silica Gel-Supported Polyphosphoric Acid (PPA-SiO2) Catalyzed One-Pot Multi-Component Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and -thiones: An Efficient Method for the Biginelli Reaction

A green and efficient method for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones and -thiones through one-pot three-component reaction of ethyl acetoacetate, an aryl aldehyde, and urea or thiourea in acetonitrile using silica gel-supported polyphosphoric acid (PPA-SiO2) as catalyst is described. Compared to the classical Biginelli reaction conditions, the present methodology offers several advantages such as high yields, relatively short reaction times, mild reaction condition and a recyclable catalyst with a very easy work up.