Research On The Iodine-promoted C-S Bond Formation Reactions By Using BAST Reagent As A Sulfur Source

C-S bonds are commonly found in natural products,bioactive molecules and material molecular structures.The construction of C-S bonds is an important research topic in the field of synthesis and catalysis.However,traditional methods for constructing C-S bonds often require the use of repulsive odor thiolating agents,stoichiometric oxidants,transition metal catalysts,and harsh reaction conditions,which limit the application of these methods.Imidazopyridines are a class of nitrogen-containing fused heterocyclic compounds with excellent biological activity and photoelectric properties.They are widely used in medicine,agriculture,materials science and other fields.Therefore,it is of great significance to transform and modify the structure of imidazolopyridine heterocycles.Bis（2-methoxyethyl）aminosulfur trifluoride（BAST）is a nucleophilic fluorinating reagent with sulfur element in its structure,which is mainly used to introduce fluorine atoms into molecular structure.In this paper,the BAST reagent is used as a sulfur source and imidazolopyridine compounds are used as substrate,two transformations of imidazolopyridine compounds into symmetrical monothioethers or 1,2,4-thiadiazoles were successfully achieved in the presence of iodide salt by using the formation of C-S bond as the key step.The main contents are as follows:In the first part,iodide-promoted construction of monothioether based on BAST reagent.By optimizing the conditions of additives,solvents and feeding ratio,it was found that the high yield of symmetrical monothioethers could be obtained by taking sodium iodide as a promoter,the BAST reagent as sulfur source and imidazolopyridine compounds as substrate at room temperature in one hour.Electronic effects and steric hindrance effects have no obvious influence on the reaction.Mechanism studies indicated that 1-iodine-imidazopyridine compounds may be the key reaction intermediates.In this method,BAST reagent was used as a novel sulfur source to construct C-S bond for the first time.It has the advantages of short reaction time,wide substrate range,high yield,and no need of transition metals and exogenous oxidants.In the second part,construction of 1,2,4-thiadiazoles by a three-component reaction involving BAST reagent.In the presence of ammonium iodide（NH₄I）,imidazo[1,5-a]pyridine heterocycles can undergo a ring conversion reaction with BAST reagent at room temperature,and imidazo[1,5-a]pyridine heterocycles can be converted to 1,2,4-thiadiazole heterocycles.NH₄I serves as both a promoter for the reaction and as a nitrogen source to construct the 1,2,4-thiadiazole.The same process can be achieved by replacing ammonium iodide with a combination of sodium iodide and ammonium chloride.Mechanism studies have shown that the process of transcyclization may involve free radical reactions,and monosulfide is the key intermediate of the reaction.This method has a unique reaction mechanism,simple and mild reaction conditions,and provides a new strategy for the synthesis of 1,2,4-thiadiazole compounds.Figure[39]table[14]reference[84]...