Selectivity in electroreductive carbon-carbon bond forming Reactions: Redox chemistry of activated alkenes, quinonemethides and quinodimethanes

Abstract

Electroreductive carbon-carbon bond forming reactions are surveyed with emphasis on those which involve combination of radical-anions cathodically generated from electron-poor alkenes and from quinonemethides. Carbon-carbon bond forming reactions of quinodimethanes formed by 1,4-electroreductive elimination of halides are included. Recent advances in the understanding of the formation, characterisation and reactivity of these intermediates are described with special attention to chemical and stereoselectivity. Several general conclusions are drawn. Radical-anion/radical-anion combination is the rule for electrohydrodimerisation reactions, and the stereochemical consequences of the required orthogonal approach to the transition state are highlighted. The cathodic generation of p-quinodimethanes, either by direct reduction or via redox catalysis, is the basis of clean and convenient routes to poly-p-xylylenes (PPXs) and poly-(p-phenylenevinylenes) (PPVs). Similar generation of o-quinodimethanes is mediated by easily reducible dienophiles which, when used in situ, participate in subsequent and preparatively useful cycloaddition. © Acta Chemica Scandinavica 1998.