Construction Of Sulfur-Containing Heterocyclic Compounds Based On Potassium Xanthate Enyne Cyclization

Sulfur-containing heterocycles are important structural backbones in organic heterocycles.Among many biologically active drug molecules and natural products,isothiazole and thiophene derivatives play an important role in their unique heterocyclic structure.They have been widely used in pharmaceutical pesticides,chemical reagents,photovoltaic materials,industry,dyes,polymer additives and other fields.The synthesis of isothiazole and thiophene has developed rapidly in recent years,but most of the methods for synthesizing heterocyclic rings are harsh,difficult to prepare and requirement of expensive transition metals or ligands which acts as a catalyst.Acetylene compounds are also widely used in the construction of heterocyclic rings,we think it is necessary to develop a green system that base on acetylene cyclization to construction of sulfur-containing heterocycles,and meanwhile holding easy to get starting materials,easy operation,free-metal catalysis,and mild reaction conditions features is an important research project.In the first chapter,the cyclization reactions of olefins,alkynes and conjugated alkynes and their applications in the construction of heterocyclic compounds in the past decades has been reviewed from the aspects of different cyclization modes and the use of transition metals or not.And then,the research progress of isothiazole and thiophene and their applications in some common fields in the last decadesare introduced.Finally,the purpose,content and significance of this research are discussed.The second chapter,the synthesis of substituted isothiazole compounds by [3+1+1] cyclization of aryl isopropylene derivatives was discussed.Potassium xanthate was used as sulfur source and ammonium iodide as nitrogen source to synthesize various isothiazole derivatives through free radical process.The isothiazole compounds can also produce diisothiazole by self-coupling or cross-coupling reaction in the presence of palladium complexs.The method has the characteristics of novel,efficient,easy to prepare,mild conditions and good compatibility.The third chapter,based on the synthesis of isothiazole,we have developed a method for the synthesis of polysubstituted thiophenes by using of potassium xanthate and conjugated alkyne bromine derivatives.A series of thiophene derivatives can be synthesized smoothly under intramolecular cyclization reaction without any catalysts.It has good functional group tolerance,and the corresponding target products can be obtained in good to high yields.This method has the advantages of simple operation,low cost and easy availability of starting materials.In summary,we have developed two new methods for the efficient synthesis of isothiazole and thiophene skeletons base on potassium xanthate by olefin and alkyne cyclization reaction,separately.These methods have the advantage of green sustainability and so on.