Indium(III) bromide-catalyzed preparation of dihydropyrimidinones: improved protocol conditions for the Biginelli reaction

Indium(III) bromide efficiently catalyzes the three-component coupling of beta-keto esters, aldehydes and urea (or thiourea) to afford the corresponding dihydropyrimidinones. This new protocol for the Biginelli reaction includes the following important features: produces excellent yields, allows the recycling of catalyst with no loss in its activity, and leads to zero-discharge during the process. The reaction of ethyl acetoacetate, salicylaldehyde and thiuourea produced 13-ethoxycarbonyl-9-methyl-11-thioxo-8-oxa-10,12-diazatricyclo [7.3.1.0(2,7)]-trideca-2,4-6-triene, which had its crystal structure determined by X-ray crystallography. (C) 2002 Elsevier Science Ltd. All rights reserved.