Construction Of Csp~3-Csp~2 Bond By Direct Electrochemical Synthesis:Alkylation Of Benzonitrile Derivatives

Alkylarenes serve as many uses in biomedicine,materials,pesticides and other fields.Therefore,the construction of Csp~3-Csp~2 bond to incorporate structural complexity of alkylarenes has important application value.Direct electrochemical synthesis achieves redox process through the exchange of electrons between electrodes and substrates,which may avoid expensive metal catalysts and be operated under mild conditions.Therefore,it is widely considered as a green and efficient synthetic method.In this thesis,the cross-coupling of benzonitrile derivatives and alkyl halides were developed using direct electrochemical approach,which allowed Csp~3-Csp~2 bond constructions without transition metals at mild conditions.The substrate scope as well as the mechanism were studied.The main content is listed as follows:Firstly,the influencing factors,such as solvent,supporting electrolytes,voltage,electrode materials and the ratio of substrates,were optimized in various electrochemical reactions.The optimal conditions were established with graphite as anode and Cu as cathode under a constant voltage,and three alternative electrolytes[acetonitrile（A）,ethylenediamine/acetonitrile（B）and ethylenediamine（C）]aiming at certain substrates were developed.The standard reaction from 1,4-dicyanobenzene and bromocyclohexane was proceeded with 100%conversion,affording the desired up to 90%yield under the optimal conditions.Subsequently,benzonitrile derivatives were efficiently coupled with alkyl halides.Secondly,Minisci reaction was further explored in electrolyte system based on acetonitrile（A）.Various nitrogen-containing heteroarenes were tolerated to give alkylarene products in high yields and regioselectivity,which avoid using of transition metals and stoichiometric redox agents in traditional Minisci-type reactions.Finally,a series of controlling experiments,such as cyclic voltammetry（CV）studies,divided cell experiment and gas chromatography（GC）,were performed to gain preliminary insight of the reaction,and a reasonable mechanism was proposed for the Csp~3-Csp~2 bond formation,which involved the anodic solvent oxidation and cathode activated free radical process.The direct electrochemical allows construction of Csp~3-Csp~2 bond without the aid of transition metals and redox agents,providing important experience for the preparation of value-added alkylarenes in an economical and green fashion.