Visible Light Mediated Construction Of N-S Bonds For The Synthesis Of Thiazole And Thiadiazine Derivatives

Nitrogen-sulfur bond is a common type of chemical bond and widely existed in organic compounds.Its construction is a key step in the synthesis of many drug molecules,pesticides,and biological materials.Thus,various methods of constructing nitrogen-sulfur bond were reported.The nitrogen-sulfur bond was mainly formed via transition metal catalyzed cross-coupling reactions.However,the reaction conditions are stringent and dangerous reagents are used,which limit its application in chemical industry.Visible light catalyzed reactions with environment-friendly,mild reaction conditions and high atom utilization have attracted widespread attention.This thesis is focusing on the development of atom-economic andenvironmentally friendly strategy for the synthesis of thiazole and thiadiazine derivatives via visible light mediated construction of N-S bonds,it contains three parts.In the first part,the visible light promoted N-S bond oxidative coupling reaction for synthesis of thiadiazoles was developed.In this protocol,we used thioureas as substrates,without external additives,a kind of thiadiazoles derivatives is synthesized by visible light promoted N-S bond oxidative coupling reaction.The present protocol provides a novel route for synthesis of disubstituted thiadiazole derivatives.In the second part,a visible light promoted method for the synthesis of benzisothiazol-3（2H）-ones from 2-mercaptobenzamides was realized.This reaction proceeds through intramolecular N-H/S-H coupling cyclization reaction under visible light.Under the irradiation of blue light of 20 W,Rhodamine 6G as photocatalyst,tetrabromoethane as additive,and DIPEA as base,a kind of benzisothiazoles derivatives were obtained.In the third part,a novel method for the synthesis of 1,2,4-benzothiadiazine derivatives was developed.Under the irradiation of blue light of 20 W,Ru（bpy）₃Cl₂ as photocatalyst,tetrabromoethane as additive,and 2,6-Lutidine as base,a series of 1,2,4-benzothiadiazine oxides derivatives were obtained through intramolecular N-S bond coupling reaction,which provides an efficient means of accessing biologically important compounds.This approach has numerous advantages including the mild conditions and readily available starting materials.Finally preliminary exploration of the reaction mechanism was conducted,and the reaction involved the radical pathway.