Studies On The Green Biginelli Synthesis Of Dihydropyrimidinethiones

Green chemistry and sustainable development demand the designing chemical processes with a view of reduction or even elimination of the use and production of hazardous materials. Recent studies have focused on the limiting the use of organic solvents and replacing them with new, environmentally benign media. The chemical industry is interested in these cost-effective, alternative solvents and processes. The most commonly used green reaction media are supercritical fluids, ionic liquids, water, and solvent-free conditions, etc.Pyrimidine rings, as the essential structure unit in biological systems, exist widely in nature. Studies on the synthesis and conversions, biological activity and metabolism of pyrimidine derivatives are significant.In recent years, much attention has been focused on the synthesis of 3, 4- dihydropyrimidin-2(1H)-thiones due to their significant biological activities and pharmacological properties. The best known procedure for the preparation of 3, 4- dihydropyrimidin-2(1H)-thiones is the classical Biginelli reaction. However, this method involves a long reaction time, harsh reaction conditions and unsatisfactory yields. A number of improved procedures have been reported, but many of them suffer from drawbacks such as hazardous organic solvents, expensive catalysts and tedious work-up. These are not acceptable in the context of green synthesis.In the present thesis, three series of 3, 4-dihydropyrimidin-2(1H)-thiones have been synthesized under microwave irradiation and solvent-free conditions.1. Under solvent-free conditions, 42 compounds have been synthesized by the Biginelli reaction of aldehydes, acetoacetate and thiourea with iodine as catalyst under microwave irradiation: 42 compounds of 3, 4-dihydropyrimidin-2(1H)-thiones.2. Under solvent-free conditions, 17 compounds have been synthesized with the Biginelli reaction of aldehydes, ethyl benzoylacetate and thiourea with iodine as catalyst under microwave irradiation: 17 compounds of 3, 4-dihydropyrimidin-2(1H)-thiones.3. In the thesis, fifty nine compounds have been synthesized and seventeen of them are new ones. The structures of the compounds prepared have been characterized by the 1H NMR and IR spectra and new compounds have also been confirmed by 13C NMR and MS spectra and elemental analysis. Nine crystal structures of the compounds have been achieved by single crystal X-ray crystallographic analysis and the molecular structures have been confirmed unambiguously. Eight single crystal structures were not found in the literature.The green synthesis of 3, 4-dihydropyrimidin-2(1H)-thiones have been performed and studied successfully in aqueous medium or under solvent-free microwave irradiation conditions in this thesis. These protocols have the advantages of environmentally benign, economy, short reaction time, high yields, and simple work-up procedure, which are acceptable in the context of green chemistry.