Biginelli and Hantzsch-Type Reactions Leading to Highly Functionalized Dihydropyrimidinone, Thiocoumarin, and Pyridopyrimidinone Frameworks via Ring Annulation with β-Oxodithioesters

An efficient and highly convergent route to dihydropyrimidinones (DHPMs) and hitherto unreported dihydropyridopyrimidinones has been developed by one-pot, three-component cyclocondensation of aromatic aldehydes, β-oxodithioesters, and urea/6-amino-1,3-dimethyluracil in the presence of recyclable SiO2-H2SO4. On the other hand, salicylaldehyde, β-oxodithioester, and urea reacted under similar conditions to afford the 3-aroyl/heteroaroyl-2H-chromen-2-thiones in high yields instead of Biginelli product. The attractive feature of this approach is the synthesis of three important bioactive heterocyclic frameworks from the same β-oxodithioester under the similar reaction conditions, making this new strategy highly useful in diversity-oriented synthesis (DOS).