Synthesis Of 1,3,4-thiadiazol-2-ylcarbamates And Benzothiazol-2-ylcarbamates Via Seleniumcatalyzed Carbonylation

Heterocyclic carbamates such as 1,3,4-thiadiazol-2-ylcarbamates and benzothiazol-2-ylcarbamates usually posses biological,pharmacological and reactive activities due to the different substituted peptide bonds?-NHCO-?and nitrogen,oxygen,sulfur and other heteroatoms contained in their molecules.They are a class of important fine chemicals and have wide applications in the fields of pesticides,medicine and organic synthesis.At present,the methods for the synthesis of 1,3,4-thiadiazol-2-ylcarbamates and benzothiazol-2-yl-carbamates mainly include triphosgene method,phosgene derivative method?such as chloroformate method,isocyanate method,isothiocyanate method,carbonate method,etc.?,thiourea cyclization method and carbon dioxide method,etc.These methods have the defects of complicated reaction steps,difficult separation,corrosion of equipment by highly toxic phosgene and its by-products,environmental pollution,complex catalyst structure,complicated preparation,high cost,etc.With the increasingly severe environmental problems,protecting the environment has become the common voice of people.Therefore,it is urgent to develop a green,economical and simple approach to these two kinds of compounds.For these reasons,Se/CO system,which has the advantages of low cost,high atomic economy,relatively environmental friendliness,and convenient operation,has been successfully applied to the synthesis of 1,3,4-thiadiazol-2-ylcarbamate compounds and benzothiazol-2-ylcarbamate compounds.Thus,a new way for the synthesis of these two heterocyclic carbamate compounds with short steps,convenient operation,high atomic economy,low cost and relatively environmental friendliness has been developed,respectively.This article is divided into three chapters:In the first chapter,the applications and their main synthetic methods of 1,3,4-thiadiazol-2-ylcarbamates and benzothiazol-2-ylcarbamates,and the discovery and applications of Se/CO catalytic system were summarized,respectively.On this basis,the design idea of this dissertation are proposed.In the second chapter,the selenium-catalyzed oxidative carbonylation of 2-amino-1,3,4-thiadiazole with alcohol to 1,3,4-thiadiazol-2-ylcarbamate was studied.The main factors affecting the reaction,such as temperature,time,total pressure and volume ratio of CO and O₂,the amount of ethanol,the amount of catalyst,and the type and amount of alkali,were optimized.Under the optimized conditions,a series of alcohols and 2-amino-1,3,4-thiadiazole were applied in this protocol to produce the corresponding1,3,4-thiadiazol-2-ylcarbamates.In chapter 3,selenium-catalyzed oxidative carbonylation of 2-amino-benzothiazole with a series of alcohols was studied in a similar way to chapter 2,and the optimal reaction conditions were obtained.A series of benzothiazol-2-ylcarbamates were synthesized under the optimized reaction conditions.