Studies On The Electrochemical Cross-coupling Of C-C/C-N Bonds In Aqueous Media And Copper Catalyzed Decarboxylative Cross-Coupling Reaction

Electro-organic synthesis is a highly attractive method for the preparation of organic compounds,wherein the electric current provides a stoichiometric amount of the oxidizing or reducing agent.This approach avoids waste originating from the reagents and catalysts employed.Electro-synthetic processes are considered to be?green chemistry?,and have great technical significance.Alkylzinc or Grignard reagents are widely employed in coupling reactions.However,prior stoichiometric formation of organometallic reagents,air/moisture sensitivity,and poor functional-group compatibility limit their synthetic applications.During the course of our studies on aqueous Barbier-Grignard-type allylation alkylation of the carbonyl and imine compounds,the electrochemical method was an alternative approach to efficient transformation in organic chemistry.In this proposal,electrochemical supported Barbier-Negishi-type coupling reactions in water was studied.This work focued on the study of the reaction mediated by?active Zn?.This new methodology provided a straightforward means of effecting transition metal catalyzed C_sp3-C_sp3 bond constructions in the absence of a stoichiometricallypreformedorganometalliccouplingpartner.Meanwhile,alcohol-to-heterocycle reactions require high selectivity to achieve dehydrogenation of the C-H and N-H bonds in one pot,and the electric current could provide a stoichiometric amount of the oxidizing or reducing agent to synthesize nitrogen-heterocyclic compounds via C-C and C-X bonds formation.On the other hand,compared to noble-metals,copper has many advantages such as cheap,low toxicity,stability,easy operation,and so on.Our group has successfully furnished copper catalyzed green oxidation to develop fluoroalkylations to achieve copper-catalyzed decarboxylative difluoroalkylation and perfluoroalkylation of?,?-unsaturated carboxylic acids.A series of new results are presented in the following chapters:In chapter two,we developed a straightforward and ligand-free method for the Pd-catalyzed electrochemical coupling between alkyl and allylic halides.This protocol is efficient for the coupling reaction of substituted allylic halides with a variety of alkyl halides,including unactivated primary,secondary and tertiary halides as well as activated halides.Prior formation of organiczinc reagent,strict exclusion of moisture and air,and protection–deprotection of acidic hydrogen in the substrates are avoided.In chapter three,we reported an electrochemical strategy for the synthesis of benzazoles directly from benzilic alcohols with o-substituted anilines with catalytic amount of cobalt.This method is atom-economic and is carried out in a one-compartment cell at room temperature under the air conditions.Meanwhile,enhanced by water,the reaction gives2-substituted benzimidazoles,benzothiazoles and benzoxazoles in moderate to excellent yields with a wide range of functional groups.Inchapterfour,copper-catalyzeddecarboxylativedifluoroalkylationand perfluoroalkylation of?,?-unsaturated carboxylic acids was studied.The method offered a reliable tool to produce fluoroalkylated motifs in good to excellent yields from commonly available fluoroalkyl iodides and bromides.With a wide substrate scope and excellent functional-group tolerance,the reaction proceeds in excellent E selectivity under mild reaction conditions.Preliminary mechanism study suggested that radical pathway was involved in the catalytic cycle and dialkyl phosphite had played an indispensible role in this reaction.