Aromatic Substitution by the S_RN1 Reaction

The S_RN1 (Unimolecular Radical Nucleophilic Substitution) is a process through which nucleophilic substitution is achieved on aromatic and aliphatic compounds that do not react or react slowly through polar nucleophilic mechanisms. This transformation takes place through electron transfer steps with radicals and radical anions as intermediates.

The S_RN1 mechanism was proposed for the first time in 1966 for the substitution of alkyl halides with electron-withdrawing groups and in 1970 for the substitution of unactivated aryl halides. Since then, the scope of the process has increased considerably, and it constitutes an important synthetic method for achieving the substitution of unactivated aromatic and heteroaromatic substrates, vinyl halides, perfluoroalkyl iodides, and activated and non-activated alkyl compounds. Nucleophiles that can be used include anions derived from carbon or heteroatoms, which react to form a new carbon-carbon or carbon-heteroatom bond.

Several reviews have been published in relation to activated and non-activated aliphatic S_RN1 reactions, to aromatic photoinitiated reactions, to S_RN1 reactions at aromatic centers, to reactions performed with electrochemical techniques, and to the synthetic applications of the process. This chapter attempts to cover aromatic S_RN1 reactions including all the relevant literature up to the end of 1996.

Keywords: mechanism; aromatic substitution; initiation; SRN1 reactions; scope; limitation; electrophiles; nucleophiles; carbanions; hydrocarbons; enolate ions; ketones; esters; carboxylate ions; disubstituted amides; thioamides; nitriles; dicarbonyl carbanions; phenoxide ions; cyanide; nitronate ions; nucleophiles; tin; nitrogen; phosphorus; arsenic; antimony; sulfur; selenium; tellurium; ring closure reactions; comparison of methods; experimental conditions; experimental procedures; tabular survey