The Studies Of Visible-Light-Promoted Oxidative Transformations Of Alkenes

Energy crisis and environment problem are getting more and more serious based on an increasing consumption of irreversible energy sources,such as coal,oil and gases,for the rapid development of society.As a widely-existed,clean,non-toxic and sustainable energy source,visible light energy has been widely utilized to generate electricity,split water and so on.In recent decades,as a novel and powerful strategy,visible light photoredox catalysis has been widely used in organic synthetic chemistry and provided a new impetus to organic chemistry.Alkenes are widely existed,readily available,as well as important building blocks.Directly constructing polycyclic skeletons is very rare during the oxidative transformations of alkenes.High regioselective difunctionalizations of alkenes,especially hydroxyfunctionalization using air as both oxygen source and terminal oxidant under mild conditions is still a challenge.In the dissertation,we described the recent development of the oxidative transformations of alkenes and their derivatives.Focused on this field,four sections of work have been developed by us as follows:1.Visible-light-promoted oxidative[4+2]cycloadditions of ?,3-unsaturated silyl enol ethers have been developed to diastereoselectively and efficiently construct polycyclic core skeletons under mild conditions using Ru(bpy)3(PF6)2,(NH4)S2O8 and methanol as starting materials.The diastereoselectivities of the transformation were dependent on the stereoconfiguration of silyl enol ether,electric properties of substitutions on aryl rings,as well as substitutions on the link.Moreover,the intermediates have been trapped by TEMPO,oxygen or methanol.Mechanistic studies indicated that the reaction was initiated by one-electron oxidation of the silyl enol ether.2.A highly efficient visible-light-promoted metal-free aerobic hydroxyazidation of alkenes has been developed utilizing Acr+MesClO4-as photosensitizer,TMSN3 as azide source and toluene as solvent in 4 hours.This protocol was operationally simple with broad substrate scope using relatively simple and readily available starting materials,such as alkenes and air,to construct high-valued ?-azido alcohols which are significant building blocks to build N-containing compounds.The dioxygen plays roles of oxygen source and terminal oxidant.The distinct possible mechanisms were proposed to explain the mechanism and high regioselectivity via the generation of alkene radical cation and azido radical.3.An efficient visible light promoted metal-free dihydroxylation of styrenes with dioxygen and water has been developed for the construction of vicinal alcohols.The protocol was operationally simple with a broad substrate scope.The mechanistic studies demonstrated that one of the hydroxyl groups came from molecular oxygen and the other one came from water.Additionally,the P-alkyoxy alcohols could also be obtained using a similar strategy.4.On the basis of the development of the hydroxyazidation of alkenes developed by us,the azidoalkylation of alkenes has been achieved utilizing photocatalyst to oxidize TMSN3 to azido radical.The azido radical was then captured by alkenes to generate the new carbon-centered radicals which were then reduced by one-electron transfer to afford carbon anions.As a result,the desired azidaoalkylation products were obtained through Michael addition.Another way,the new carbon-centered radicals could also be captured by alkenes bearing electron-withdrawing groups and then be reduced/protonated to deliever the desired product.This strategy is suitable for both the aryl alkenes and aliphatic alkenes.Other Michael acceptors could also be transferred into the azidoalkylated products.In summary,polycyclic core skeletons have been constructed efficiently under mild conditions and the hydroxyazidation,dihydroxylation and azidoalkylation of alkenes have been powerfully achieved through our studies,which diversified the oxidative transformations of alkenes.Further extended to other difunctionalizations and asymmetric transformations of alkenes will be the next stage of work.