Visible-Light-Driven C-C(Si) Bond Formation And Cleavage Reaction Using Alkoxy Radical

Solar energy is one of the green renewable resources whose conversion and utilization is one of the current research hotspots.Photocatalytic organic reactions can effectively convert light energy into chemical energy,which is able to produce active intermediates such as radicals and radical ions under mild conditions.Alkoxy radicals are highly reactive intermediates,which can participate in one of three elementary reactions,such as hydrogen atom transfer,alkene addition andβ-scission.Compared with traditional methods,the photocatalytic strategy can generate alkoxy radicals under mild conditions and has better functional group compatibility.This dissertation focuses on the use of visible-light-mediated highly active alkoxy radicals to build new C-C bonds and C-Si bonds and realize the cleavage ofβ-C–C bonds of lignin model compound.Firstly,visible-light-driven alkoxycarbonylation of alkenes using alkoxy radical was developed.Alkene difunctionalization initiated by the addition of alkoxycarbonyl radicals is a particularly efficient transformation that simultaneously introduces an ester group and constructs another C-C or C-X bond.Visible-light mediated alkoxyl radicals could abstract hydrogen atom from alkyl formate to generate alkoxycarbonyl radical,which could initiate alkoxycarbonylation of alkenes under metal-free and mild conditions.Through this strategy,a variety of substituted alkanoates,includingβ-alkoxy,β-hydroxy,β-dimethoxymethoxy andβ-formyloxy alkanoates could be facilely accessed with high functional group tolerance and high efficiency.Among them,the yield ofβ-alkoxy alkanoates is up to 88%.On this basis,the later-stage modification of the pharmaceutically active molecules was successfully realized.Moreover,the mechanism study revealed thatβ-hydroxy alkanoates were generated by a selective decomposition of orthoformates promoted by the N-alkoxyazinium salt.Next,visible-light-driven silylfunctionalization of alkenes using alkoxy radical was developed.Visible-light mediated alkoxy radicals are used to capture hydrogen atoms of hydrosilane to generate silicon radicals and realize the silylfunctionalization of alkenes through radical addition.This method enables the rapid construction of complex silicon-containing motifs via the simultaneous introduction of a C-Si bond and another functional group.Various nucleophiles,such as alcohols,thiols,H₂O,and indoles,are compatible with the catalytic system,providingβ-alkoxy,β-alkylthio,β-hydroxy,andβ-indolyl silanes in good yields.Among them,the yield ofβ-alkoxy silanes is up to 96%.In addition,vinylsilanes were successfully produced in good yields in the absence of nucleophiles.Finally,visible-light-driven C-C bond cleavage of lignin model compounds using alkoxy radical was developed.Through alkoxy radical mediatedβ-cleavage strategy,a visible-light-induced selective C-C bond cleavage ofβ-O-4 motifs using the cyclic iodine（III）reagent cyanobenziodoxolone（CBX）as the oxidant is established.Through this strategy,lignin model compounds could be converted into aldehydes in moderate yields.In addition,acetal ester is another product of this reaction,which could conveniently furnish formaldehyde and phenols by alcoholysis.The mild reaction conditions provide a new path for the utilization of lignin...