Silica sulfuric acid efficiently catalyzes the three-component Biginelli reaction between an aldehyde, a -dicarbonyl
compound and urea or thiourea in refluxing ethanol to afford the corresponding dihydropyrimidinones in high yields. The catalyst
is reusable and can be applied several times without any decrease in the yield of the reactions. © 2003 Elsevier Science Ltd. All
rights reserved.