Study On Synthesis Of Thiophene And 4-hydroxythiazole Compounds Based On Inorganic Sulfur Source

Five-membered sulfur heterocyclic compounds,such as thiophenes and thiazoles,are a kind of important heterocyclic compounds containing sulfur atoms,which are widely used in the fields of natural products,medicines and functional materials.The conventional methods for the synthesis of thiophenes and thiazoles derivatives are always limited by the need for transition metal catalysis or harsh reaction conditions or easy oxidation of the substrate.As a consequence,simple and efficient methods for the synthesis of five-membered sulfur heterocycles have been attracted.Our research group has been committed to synthesizing various sulfur heterocyclic compounds through constructing two carbon-sulfur bonds by using environmentally friendly,stable,cheap and readily available inorganic sulfur sources.Based on these studies,my dissertation focuses on developing synthetic methods for synthesis of thiophenes and 4-hydroxythiazoles by using a metal sulfide and elemental sulfur as the sulfur source,which could be accomplished by the sulfuration/annulation of C（sp³）-H bonds without transition metal catalysis.This dissertation includes three chapters:In Chapter one,we have introduced the synthesis progress on thiophene and thiazole derivatives,and introduces the significane and content of this research subject.In Chapter two,we herein described a novel method for the synthesis of 2,4-disubstituted thiophene from potassium sulfide and acetylene alcohol compounds.This reaction system uses dodecylbenzenesulfonic acid as an acid additive without transition metal catalysis and reacts for 12 hours in a 140 oC nitrogen atmosphere.By cutting two C（sp³）-H bonds,the thiophene scaffolds is simply and efficiently constructed.Meanwhile,We have studied the mechanism of the reaction and believe that the reaction may be carried out through the process of dehydration/radical addition/radical cyclization under the action of protonic acid,This method provides an effective way to synthesize 2,4-disubstituted thiophene using an easily prepared substrate.In Chapter three,an efficient method was developed for the formation of 4-hydroxythiazole compounds via Metal-free catalyzed reaction of elemental sulfur and N-substituted amides.Under the action of DMSO/P₂O₅/HMPA system,using elemental sulfur as the sulfur source,4-hydroxythiazoles can be obtained in a relatively high yield through the sulfuration/annulation.The characteristics of this reaction are:1)No need to use metal catalyst;2)Environmentally friendly,stable,inexpensive and easily available elemental sulfur as sulfur source;3)a broad substrate scope;4)The formation of two C-S bonds involves the cleavage of four C（sp³）-H bonds.