Studies On The Photoinduced,photocatalyst-free Construction Of Csp~2-C And C-N Bonds

The construction of C-N and Csp²-C bonds with aryl halides or alkenes is a very common and useful chemical transformation in organic synthesis.Those reactions were be used to introduce aryl groups into the structure of N-containing compounds,or synthesize the azo-heterocyclic compounds,or achieve the alkene functionalization.Consequently,they have found wide application in pharmaceutical preparation and material processing.Traditional methods to achieve these transfomations always involved the use of noble transition-metal catalysts,or conducted with high temperature,which severely limited their population and application.As a green synthetic tool,Organic photochemical reactions has attracted much attention due to their clean and mild reaction conditions.In this thesis,we systematically developed the photoinduced reactions of1,2-diiodobenzenes with secondary amines,o-iodoanilines with alkenes and alkenes with 4-acyl-1,4-dihydropyridines,by taking advantage of UV-light and visible-light synthetic techniques without the use of any photocatalysts.Various tertiary amines,carbazoles,indolines and carbonyl compounds were effectively prepared by the construction of C-N and Csp²-C bonds.With the irradiation of 300nm low-pressure mercury lamp,tertiary arylamines were prepared through the C_sp2-N coupling reactions between1,2-diiodobenzenes with secondary aliphatic amines（35%-73%）.When the substrates were secondary arylamines,the C_sp2-N coupling products were further transformed into the carbazole derivatives through cross-dehydrogenative coupling（24%-71%）.Both the photoreactions were feasible in the absence of additives or photosensitizers and showed good generality and functional group tolerance.Such a photochemical protocol provides a simple and mild strategy for construction of carbazole scaffold,which effectively avoided the complex steps and harsh conditions in traditional methods.When K₂HPO₄ was employed as additive,DMSO as solvent and300nm low-pressure mercury lamp as light source,a highly regioselective[3+2]cyclization occurred between aryl alkenes and o-iodoanilines by the construction of C-C and C-N bonds.In this protocol,2-mono substituted indolines were effectively prepared via terminal alkene carboamination（35%-74%）.The reaction of gem-substituted alkenes yielded2,2-disubstituted indolines（32%-73%）.When the structure of alkene was cycloalkane fused-benzene,such a photochemical protocol produced valuable spiroindoline products（55%-72%）.This synthetic method proceeded with the use of no catalyst,available substrates,and showed good tolerance with many functional groups.Control experiments suggested the reaction was trigged by UV-light.The radical quenching experiment indicated a radical process was involved in the reaction.This synthetic strategy offered an alternative for indoline skeleton construction to the traditional methods,which suffered from many issues such as the preparation of complex substrates,the use of transition-metal catalysts and tedious procedures,greatly improving the synthetic efficiency.With the aids of visible-light,an alkene functionalization was realized by the construction of C_carbonyl-C bond,which introduced a carbonyl group into unsaturated alkenes without the use of photocatlysts.The reaction was proceeded with Cs₂CO₃as additive,4-acyl-1,4-dihydropyridines as the acyl resource.By the direct absorption of visible-light,4-acyl-1,4-dihydropyridine produced an acyl radical via bond homolytic cleavage,which then reacted with alkenes to give the hydroacylation products via hydrogen atom transfer step.The reaction displayed a broad substrate scope and good functional group tolerance.The gram-scale experiment was successfully conducted.A variety of carbonyl compounds were prepared in 35%-99%yields.By use of this method,the acylation reactions were accomplished with natural products,medicines and drug intermediates as substrates.Under the irradiation of visible-light,in the presence of of NiCl₂.DME as catalyst,alkenene diacylation was realized by the reactions of aromatic alkenes and 4-acyl-DHPs.This protocol provided an access to a wide range of 1,4-dicarbonyl compounds（34%-76%）,which were further used to effectively synthesize the pyrrole and furan derivatives.The UV-visible spectroscopy and radical trapping experiments confirmed the fact that 4-acyl-1,4-DHPs absorp visible-light and provide the acyl radical.The analysis of byproduct suggested a hydrogen atom transfer process was involved in the alkene hydroacylation.This developed stategy is a successful exploration in the non-photocatalyst and simple metal salt promoted visible-light reactions,which avoided the decarbonylation and poor selectivity issues in traditional methodologies,and widened the electron-rich substrate scope.