Biginelli Reaction Using Propylene Carbonate as Green Solvent: An Elegant Methodology for the Synthesis of Dihydropyrimidinones and Dihydropyrimidinthiones

Background: The reaction named for Pietro Biginelli was first reported in 1891. The method consists of the reaction of an aromatic aldehyde, urea and ethyl acetoacetate leading to dihydropyrimidinones. Currently, the scientific movement to develop economically viable green methods using compounds that are reusable, nonvolatile, easily obtained, etc., is growing. Objective: A synthetic method was developed for the preparation of dihydropyrimidinones and dihydropyrimidinthiones with a focus on green chemistry based on the Biginelli reaction, using propylene carbonate as solvent and molecular iodine as the catalyst. Method: A mixture of arylbenzaldehyde, ethyl acetoacetate, urea or thiourea, molecular iodine and propylene carbonate was stirred and heated at 70 degrees C for 4 hours. At the end of 4 hours, the mixture was treated with sodium thiosulfate and washed three times with hot water. The pure solid was obtained after filtration. Results: We developed a synthetic method for the preparation of dihydropyrimidinones and dihydropyrimidinthiones based on the Biginelli reaction using PC as the solvent with yields ranged from 22-76% with high purity. Conclusion: This methodology uses a green and inexpensive solvent and catalyst and has the advantage of being a non-complex purification method: only sodium thiosulfate is required for catalyst removal, hot water to remove the solvent. The yields obtained range from moderate to high.