Synthesis, characterization and RHF/ab initio simulations of 2-amino-1,3,4-thiadiazole and its annulated ring junction pyrimidine derivatives

Michael addition reaction of the 2-amino-1,3,4-thiadiazole to chalcone as biselectrophile afforded 5,7-diphenyl-6-[1,3-diphenylpropan-1-on-3-yl][1,3,4]thiadiazolo[3,2-a]pyrimidine (3) instead of 5,7-diphenyl-5H-[1,3,4]thiadiazolo[3,2-a]pyrimidine (5) via further Michael addition at C5 in pyrimidine moiety. The structure 3 was established through the aspect of ab initio calculations, elemental analysis and spectral data.