Green and Regioselective Alkylation of Dihydropyrimidinthiones through Michael Addition

Dihydropyrimidines are one of the most important heterocyclic ring systems having a serious place in medicinal and organic synthesis. In this paper, a new series of dihydropyrimidines consisting of sulfur atoms were synthesized using inorganic base K2CO3 and TBAB as an organic salt to make high polarity in reaction media. Interestingly, different 3,4-dihydropyrimidin-2(1H)-thiones re-acted smoothly with various acrylic esters to afford adducts via highly regioselective N3-Michael addition reaction was carried out at 100^oC in 12 h. result: Unfortunately, the reaction failed with fumaric esters owing steric effects. Avoiding organic solvents during this reaction effectively led to the development of an economic approach. Structures of the new compounds were established on the basis of¹H NMR,¹³C NMR, and IR spectral data.