Green Synthesis of Dihydropyrimidines and Pyridines Utilizing Biginelli Reaction

A novel approach to the synthesis of functionally substituted pyrazolopyrimidine, utilizing Ultrasound irradiation (US), microwave energy, and reaction under pressure in Q-tube as green and environmentally friendly techniques. The reaction time and yield of the products were compared in the three methods. A new compound, 5-benzoyl-6-hydroxy-4-phenyl-3,4-dihydropyrimidin-2(1H)-one was synthesized by conducting a Biginelli reaction under ultrasound irradiation. By following a reaction between an enaminones, aromatic aldehydes, and urea, in acetic acid, we observed that product obtained was dependent on applied reaction conditions in the presence of ammonium acetate. 1,3,5-triaroylbenzene was formed under pressure in Q-tube. Ultrasound irradiation of the same mixture led to a different end product. The chemical structures of these reaction products were firmly established using X-ray crystallography. In addition, a reaction mechanism to account for the formation of the observed effect was proposed.