Study Of Distal Radical Migration Reactions Via Visible Light Photocatalysis

Radical-mediated distal migration reaction can rapidly isomerize functional groups and remodify distal inert sites,it has good selectivity and wide applicability.Therefore,this strategy has attracted extensive attention in the precise activation and functionalization of inert C-H and C-C bonds.In the early stage,the long-distance radical migration process was generally realized by the harsh conditions of ultraviolet,high temperature,excessive strong oxidants and radical initiators.However,these systems have great limitations,for example,poor tolerance of functional groups,difficulties in practical application,and so on.In recent years,based on the needs of ecological priority and green sustainable development strategies,safe,clean and simple visible light photoredox catalysis is very popular,and has become one of the effective means to trigger radical distal migration.With this mild method,molecular skeleton can be reconstructed efficiently and selectively,which greatly enriches the research contents of selective activation and diversity transformation of intramolecular distal inert chemical bonds.In this paper,we conducted an in-depth study on the distal functionality migration initiated by carbon and oxygen radicals through visible light photoredox catalysis.The main work was divided into the following two parts:Part ?:We developed the visible light-catalyzed tandem ?-difluoroalkylation and?-alkynylation of unactivated olefins.Under mild reaction conditions,the activation and functionalization of the inert C(sp)-C(sp3)bonds were achieved by the intramolecular 1,4-alkynyl migration strategy induced by alkyl carbon radicals,which provided a simple,ingenious and general protocol for synthesizing the small molecule block of difluoroalkynyl alkynylated chain ketone.Part ?:By utilizing the advantages of visible-light photoredox neutral catalysis,the first carboxyl-directed intermolecular functionalization of benzyl C(sp3)-H bond was realized.In this system,the aromatic carboxylic acid didn't require preactivation,and could directly generate a highly electrophilic carboxyl radical through a mild single-electron oxidation process.Thereby the carboxyl radical initiated an intramolecular selective 1,5-hydrogen atom transfer,followed by radical addition or radical coupling reaction,so as to accomplish the conversion of secondary and tertiary alkyl C-H bonds to C-C bonds.