An efficient and facile approach has been proposed for the regioselective synthesis of 4-aryl (heteroaryl)-6-methyl-5-phenyl-3,4-dihydropyrimidine-2(1H)-thiones in the presence of nano-K2CO3. Nano K2CO3 activates the one-pot three component condensation of phenyl acetone, aromatic aldehydes, and thiourea, resulting in the formation of Biginelli-type products in high yields (79–92%). Some of the synthesized compounds showed moderate activity against Staphylococcus aureus. The DFT study for 6-methyl-4,5 diphenyl-3,4-dihydropyrimidine-2(1H)-thione was performed. High regioselectivity, mild basic conditions, simple procedure, good to high yield, and no need of chromatographic purification are significant features of the proposed protocol.