Visible-Light Catalyzed Sulfur Dioxide Insertion Reactions Using Sodium Metabisulfites And Synthesis Of Dithiocarbamates

Sulfur-containing compounds are widely found in a number of functional materials,drug molecules and natural products,which have the extremely important application value in chemistry research and pharmaceutical industry.In particular,sulfur compounds containing sulfonyl and alkyl dithiocarbamate structure units have attracted a great attention of chemists due to their important application value.From the point of synthetic chemistry,metabisulfites and carbon disulfide as cheap and readily available sulfur source are ideal reagents to synthesize sulfonyl compounds and alkyl dithiocarbamates.Although some sulfur dioxide insertion reactions using metabisulfites to synthesize sulfonyl compounds and the reactions using of CS₂to construct alkyl dithiocarbamates had been developed during the past several years,most of them needed high reaction temperature and metal reagents.Therefore,the development of mild and green method is highly desirable.In this thesis,we have developed some visible-light catalyzed sulfur dioxide insertion reactions using sodium metabisulfites to synthesize biologically important sulfonyl compounds and CS₂insertion reactions to access alkyl dithiocarbamates.Meanwhile,based on the study of detailed reaction mechanism,the present thesis will provide a useful theoretical and experimental support for the development of new visible-light-induced multi-component reactions and their applications in drug discovery and development.The main contents are demonstrated as the following:1)A visible-light-mediated strategy has been established for the synthesis of unsymmetrical thiosulfonates via sulfur dioxide insertion reaction of aryldiazonium,sodium metabisulphite and thiols.This strategy,simply utilizes cheap sodium metabisulfite as SO₂surrogate,Rhodamine 6G（1 mol%）as the photocatalyst,and 3W white LED as light source,provides a variety of unsymmetrical thiosulfonates in moderate to good yields.The present reaction could be scaled up to gram scale without any significant loss of its efficiency,which show the synthetic application value in organic synthesis.2)A visible-light-promoted protocol has been developed for the preparation of 3-β-sulfonylalkyl quinoxalin-2-ones via four component sulfur dioxide insertion reaction of quinoxalin-2-ones,alkenes,aryldiazonium,and sodium metabisulfite.The optimized reaction conditions were obtained through the investigation of various reaction conditions such as photocatalyst,loading of photocatalyst,solvent,light source,the ratio of substrates.Under the optimized reaction conditions in hand,we examined the substrate scope of this visible-light mediated sulfur dioxide insertion reaction.A series of substituted quinoxalin-2-ones,alkenes,and aryldiazonium were all compatible with the reaction conditions,and the corresponding products were obtained in good yields.3)A visible-light photoredox catalyzed four-component sulfur dioxide insertion reaction has been developed for the synthesis of a series of 3-quinoxalin-2-one-substituted vinyl sulfones from alkynes,sodium metabisulfite,aryldiazonium,and quinoxalin-2-ones.This tandem reaction using of cheap sodium metabisulfite as SO₂surrogate,Rhodamine 6G（2 mol%）as metal-free photocatalyst,and 3W white LEDs as light source,provided a highly selective approach to access Z configuration dominant 3-quinoxalin-one-substituted vinyl sulfones.4)A visible-light-promoted method has been developed for the synthesis of alkyl dithiocarbamates through multicomponent reactions ofα-diazoesters,CS₂and amines.A series of structurally diverse four-component coupling products with the incorporation of the ring-opening of THF could be obtained when the reaction ofα-aryldiazoesters,amines and CS₂was performed in THF by simply using DBU（50 mol%）as the additive.Three-component reactions ofα-diazoesters,CS₂and amines could be efficiently obtained in 1,4-dioxane.In summary,we have developed visible-light photoredox catalyzed sulfur dioxide insertion reactions for the synthesis of sulfonyl compounds including thiosulfonates,3-β-sulfonylalkyl quinoxalin-2-ones,and3-quinoxalin-2-one-substituted vinyl sulfones and the reactions for the construction of S-alkyl dithiocarbamates using of CS₂.These photocatalytic multicomponent strategies conform to the concept of green chemistry,which have some advantages such as clean energy source,readily available materials,mild conditions,non metal pollution and favourable functional group tolerance.