Microwave-Assisted Synthesis of New Dihydropyrimidine Derivatives and Mechanism of the Reactions

5-benzoyl-4-aryl-6-phenyl-1,2,3,4-tetrahydro-2-thioxopyrimidines were synthesized via Biginelli cyclocondensation reaction. The diethyl 2-(4-aryl-5-benzoyl-6-phenyl-3,4-dihydropyrimidin-2(1H)-ylidene) malonates were prepared by the reaction of thioxopyrimidines with diethyl 2-bromomalonate in dioxane/pyridine (10/1 v:v) under microwave irradiation and conventional conditions. The reaction of diethyl 2-(5-benzoyl-4,6-phenyl-3,4-dihydropyrimidin-2(1H)- ylidene) malonate with hydrazine hydrate and urea yielded the compounds of (E)-ethyl 2-(5-benzoyl-4,6-diphenyl-3,4- dihydropyrimidin-2(1H)-ylidene)-3-hydrazinyl-3-oxopropanoate and (E)-ethyl 2-(5-benzoyl-4,6-diphenyl-3,4- dihydropyrimidin-2(1H)-ylidene)-3-oxo-3-ureidopropanoate, respectively. All of these new derivatives were characterized by analytical and spectroscopic studies. The structure of the diethyl 2-(5-benzoyl-4,6-diphenyl-3,4-dihydropyrimidin- 2(1H)-lidene) malonate was identified by a single crystal X-ray diffraction analysis, and the reaction mechanism was also discussed.