The Research On Cyclization Of Mercaptobenzimidazoles With Carbonyls

Heterocyclic compounds containing nitrogen and sulfur are widely exist in the molecular skeleton of drugs,which are of importance to human life and development.Since the first report on the efficacy of benzimidazole against Trichinella spiralis has appeared,many benzimidazothiazoles and benzimidazolylazines heterocyclic drugs derived from benzimidazoles have been synthesized under experimental conditions and exhibit anticancer and antiparasitic activities.In recent years,with the development of green chemistry,more environmentally friendly and mild experimental synthesis methods have been appreciated and recognized.In this paper,2-mercaptobenzimidazole was used as a raw material to cyclize cyclohexanones,aldehydes,alkenones and acroleins respectively by environmentally friendly photocatalytic or operational easily acid-catalyzed method.The details are as follows:1.Developed a synthesis methods for benzimidazolylazole by dehydrocyclization reaction of 2-mercaptobenzimidazole with cyclohexanone and aldehydes under visible light catalysis.In this reaction,the inexpensive and non-toxic dye Bengal Rose is used as a visible photocatalyst.Under an oxygen atmosphere,cyclohexanones or aldehydes were activated by Lewis acid cyclized with2-mercaptobenzimidazole in the form of an enol to form a series of polycyclic heterocyclic compounds.The reaction is mild,which has good functionality tolerance to six-membered cyclic ketones,and branched and linear aldehydes.2.Developed synthesis methods for the benzimidazolylazines by cyclization reaction of 2-mercaptobenzimidazole with acroleins under Lewis acid catalysis or2-mercaptobenzimidazole with cyclopentenone under visible light catalysis.In this system,2-mercaptobenzimidazole directly undergoes a Michael addition reaction with acroleins,and the reaction is catalyzed by Lewis acid in an open system at room temperature to obtain a good yield.It is worth noting that 2-mercaptobenzimidazole and cyclopentenone do not undergo Michael addition reaction in the Lewis acid catalyst system,but in the visible light catalytic system,oxidative cyclization can occur and a novel bridged ring compound can be acquired.In this paper,the visible light catalysis of 2-mercaptobenzimidazole and cyclohexanone,aldehyde,cyclopentenone were investigated.As a result,a series ofpolycyclic fused heterocyclic compounds were synthesized under simple mild conditions.Additionally,some simple Michael addition products of2-mercaptobenzimidazole and alkenal were obtained under simple acid catalysis for the first time.