Electrochemically Catalyzed Aromatic Nucleophilic Substitution. Phenoxide Ion as Nucleophile

Article abstract of DOI:10.1021/jo00242a029

Cyclic voltammetry and preparative-scale electrolysis of aryl halides in the presence of phenoxide ions, a nucleophile reputed as unreactive S_RN1 reactions, show the formation, in liquid ammonia or in dimethyl sulfoxide, of coupling products along an electrochemically catalyzed S_RN1 aromatic substitution process.Coupling occurs at carbons of the phenyl ring rather than at the phenolic oxygen.The mechanism of the reaction is estabilished on kinetic grounds.Determination of the coupling rate constant between phenoxide ions and aryl radicals and comparison with other n ucleophiles shows that phenoxide ions are quite efficient nucleophiles in S_RN1 reactions.The reaction can as well be viewed as an homolytic aromatic substitution.Mechanistic implications concerning the latter type of reaction are discussed.With mediated electrochemical induction of the substitution reaction, it is possible to raise the yield in coupling product up to about 80percent, which renders the reaction an attractive route to the synthesis of electron donor-electron acceptor biaryls.