Electrochemical Conversion Studies Based On Carbon Radical And Carbocation Intermediates

Electrochemistry provides an alternative and sustainable redox strategy for organic transformations,particularly when regarding the increasing recognition of sustainable development.In the early studies,incredible transformations have been achieved by continuously increasing the voltage.However,these processes are limited in terms of reaction scopes and functional group compatibility due to the high voltage.Recently,synergistic electrochemical catalysis has become an enabling tool for those redox-retardant substrates by combining electrochemistry with metal catalysis,organocatalysis and biocatalysis.In this thesis,we have developed new synergistic strategies with a focus on electrochemical generation of carbon radical and carbocation intermediates at lower voltages and investigated their transformations.The major progresses include:(1)Using the photoluminescent LMCT strategy,the conversion of carboxylic acids to carbon radical intermediates was achieved at low voltages using cerium complex as the catalyst.It was then combined with redox reactions catalyzed by nickel to obtain a series of decarboxylated arylation products in moderate to high yields.The reaction showed wide scopes of simple primary and secondary carboxylic acids and tolerates a variety of functional groups.This represents a new protocol for the construction of Csp~3-Csp~2 bonds.(2)Under the mild conditions,asymmetric decarboxylative cyanation was achieved with high yields and enantioselectivities catalyzed by chiral copper complex.The reaction showed a broad scope of substrate and can be readily scaled up.The applicability has also been demonstrated in the late-stage functionalization of pharmerceuticals.(3)Asymmetric electrochemicalα-sulfuration of aldehyde with free thiol was developed by combining chiral primary amine catalysis and anodic oxidation.The secondary enamine from aldehyde and our primary amine catalyst is redox-labile and can be anodically oxidized to a chiralα-imino carbocation intermediate.Under the mild electrochemical conditions,the oxidative by-pathways normally associated with free thiol can be avoided.