One-pot synthesis of dihydropyrimidinones catalysed by lithium bromide: an improved procedure for the Biginelli reaction

Maiti and co-workers have found that lithium bromide (10 mol%) efficiently catalyses the three component condensation reaction of an aldehyde, a b ketoester and urea in refluxing acetonitrile to afford the corresponding dihydropyrimidinones in high yields (85-90%).  A wide variety of aromatic aldehydes (alkoxy- and dialkoxybenzaldehydes, hydroxy-, nitro-, and chlorobenzaldehydes), furfuraldehyde and n-hexanal all react well under these conditions.  Thiourea has also been used successfully in place of urea to generate the corresponding thio derivatives.  (Tet. Lett., 2003, 44, 2757-2758).