Visible Light-Induced Synthesis Of Sulphur-Containing Compounds Based On C-H Functionalisation Reactions

Sulphur-containing heterocyclic compounds are a common class of heterocyclic compounds that are widely used in biologically active drugs as well as in some functional materials.Therefore,it is important to develop efficient methods for the heterocyclic sulphur-containing compounds.Visible photocatalysis is a relatively green and efficient means of reaction that allows single electron transfer,energy transfer or atom transfer between catalyst and reactant under mild conditions.In recent years,with the further development of visible photocatalysis,the construction of sulphur-containing heterocyclic compounds by visible photocatalysis has become an important research direction for scientists.In this thesis,we aim at the construction of sulphur-containing heterocyclic compounds by using Eosin Y,an organic dye photocatalyst,in the direction of C（sp³）-H bond activation on benzoylacetonitrile and pyrazolone,to achieve visible light-induced construction of sulphur-containing heterocyclic compounds through a single-electron transfer pathway.The specific studies in this thesis are as follows:（1）Starting from the background of visible light redox catalysis,the significance of visible light redox catalysis,the mechanism of photocatalytic reactions and the types of photocatalysts are introduced;followed by the importance of sulphur-containing heterocyclic compounds and the progress of research on the involvement of visible light in the intramolecular and intermolecular reactions for the construction of sulphur-containing heterocyclic compounds.（2）A strategy for the construction of sulfur-containing heterocyclic compounds using benzoylacetonitrile was used to study the visible light-induced synthesis of2-aminothiazoles.The reaction was carried out under green light irradiation for 12 h at room temperature using benzoylacetonitrile and thioureas as substrates,Eosin Y as photocatalyst and ethanol:water=1:1 as solvent,and a series of 2-aminothiazole derivatives were obtained in 72%to 94%yields.The method has the advantages of being green,eliminating the need for excess oxidants,being substrate universal and having mild conditions.（3）The C（sp³）-H thiocyanation reaction of pyrazolinones was investigated using a photoredox-catalyzed thiocyanation strategy for heterocyclic compounds.The reaction was carried out using pyrazolinone and NH₄SCN as substrates,Eosin Y as photocatalyst and ethanol as solvent.Under blue light irradiation,a series of thiocyanated pyrazolinone derivatives were obtained in 61%to 85%yields at room temperature.The reaction is characterized by easy availability of raw materials and simple operation.（4）A strategy for the synthesis of isothioureas from pyrazolinones and thioureas was investigated using thioureas as substrates for the construction of sulfur-containing heterocyclic compounds.The reaction uses pyrazolinone and thiourea as substrates,and also uses Eosin Y as a photocatalyst and ethanol as a solvent.Under green light irradiation,the reaction can synthesize a series of isothiourea derivatives at room temperature,and this method has the advantages of green solvent,universal substrate and high efficiency of the reaction.