Study Of Single-Electron-Transfer-Induced C-C Bond Cleavage

As a common inert chemical bond,C-C bond is the core part of the basic framework of organic compounds.The cleavage and reorganization of C-C bonds is a vital technology for crude oil refining in industry.The controllable and selective C-C bonds cleavage under mild reaction conditions is of special use for fine chemical production and new reaction innovation in laboratory,but generally remains challenging.Small ring systems,in particular three-and four-membered rings,are privileged precursors in C-C bond activation as the release of ring strain facilitates the cleavage of inert C-C bond.With the development of transition metal catalysts and reaction systems,selective carbon-carbon bond cleavage catalyzed by transition metals such as rhodium,palladium and ruthenium has been comprehensively and deeply developed.In recent years,the research of radical driven C-C bond cleavage is one of the most popular topics in organic chemistry methodology,which were mainly divided into radical migration and ?-carbon scission.We were devoted to the research of the cleavage and fuctionalization of inert bonds.Among them,the cleavge of C-C bonds is also one of our research subjects.Based on the literatures and experimental results,the main research content of this dissertation is the single-electron-transfer-induced selective C-C bond cleavage.In this dissertation,we study copper-catalzed intermolecular Heck-like coupling of cyclobutanone oximes initiated by selective C-C bond cleavage,single-electron-transfer(SET)-induced fragmentation-rearrangement sequence of cycloketoxime esters and photoinduced C-C bond cleavage and oxidation of cycloketoxime esters.Part 1:The activation and functionalization of C-C single bonds by transition metal complexes is of fundamental interest and plays an important role in the synthesis of complex organic molecules.Because of the presence of multiple C-C bonds in an organic molecule with subtle difference in activation barrier,controlling the positional selectivity represents the key challenge.Cyclobutanones and their derivatives are very useful intermediates,which are widely used in total synthesis of nature products.We have reported copper-catalyzed intermolecular Mizoroki-Heck(M-H)type reaction of cyclobutanone derivatives with olefins in which nitrile products are derived via a formal C-C cleavage of the cyclobutanone oximes.The protocol is distinguished by mild reaction conditions that avoid ligand,oxidant and base.A wide scope of cyclobutanones and olefin coupling components can be used without compromising efficiency and scalability.The alternative visible-light-driven photoredox process for this coupling reaction was also uncovered.Part 2:Ketoximes and their derivatives have found wide applications in organic synthesis.The venerable Beckmann rearrangement is the skeletal rearrangement of ketoximes in the presence of acids,to give amides or lactams.However,certain ketoximes.particularly those having a quarternary carbon anti to the hydroxyl,are likely to undergo the Beckmann fragmentation to form alkene nitriles.Another classical Neber rearrangement has been recognized as one of the promising methods for the preparation of a variety of a-amino ketones.In this context,the discovery of a simple and reliable transformation of ketoxime derivatives is apparently beneficial.Herein,we have reported a novel structural reorganization of cycloketoxime esters involving C-C bond cleavage and carboxyl group migration to produce cyano-containing benzoates.Different from the traditional rearrangements that require strong acidic or base media,this mild transformation is triggered by iminyl radical in the presence of photocatalysis or copper salts.Part 3:The cleavage and reorganization of C-C bonds is strategically important to shift paradigm in retrosynthetic analysis.It offers a way of disconnecting inert bonds,providing a simultaneous construction of two new chemical bonds from simple starting materials.Strategies for C-C bond cleavage can be divided into several mechanistic categories mainly including oxidative addition,?-carbon elimination,migration and rearrangement.The most ideal candidate to cleave a C-C bond utilizes small(three-and four-membered)rings,in which the strain-release energy associated with the cleavage event provides the major driving force.Catalytic activation of unstrained C-C.bonds is much rarer due to energetically less favourable C-C cleavage process.Baeyer-Villiger oxidation is a namely reaction that ketone was transformed into ester in the presence of peroxide reagent.With the application and development of traditional Swern oxidation and Kornblum oxidation,DMSO.as a readily available and mild oxidant,is widely applied in the synthesis of organic compounds.Herein,we report a novel transformation of photocatalytic selective C-C bond cleavage of cycloketoxime esters to construct cyano-containing ketones,in which a functional compound containing cyano and carbonyl groups is obtained while a carbon-carbon bond is selectively cleavage.Further applications in late-stage modification of complex and chiral molecules have also been reported.