The SRN1 reaction

Abstract

Since its discovery, the radical nucleophilic substitution, or SRN1 reaction, has been widely used to achieve new CC or C-heteroatom bonds. The mechanism involves a chain propagation cycle with radicals and radical anions as intermediates. The initiation step is an electron transfer to a substrate to form its radical anion, which fragments to afford a radical and the anion of the leaving group. The radical thus formed couples with a nucleophile to give a new radical anion which, in the next propagation step, transfers its extra electron to the substrate, closing the cycle. Here we discuss SRN1 reactions of aromatic substrates with carbanions and heteroaromatic nucleophiles as well as ring-closure reactions to obtain heterocycles by different approaches. SRN1 reactions of vinylic halides with nucleophiles and the competing mechanisms are also examined. Reactions of aliphatic substrates that do not react or are poorly reactive toward polar nucleophilic substitutions (cycloalkyl, bridgehead, neopentyl, and perfluoroalkyl halides) are discussed in terms of mechanistic requirements to follow an SRN1 process. In addition, the reactions of alkyl substrates with electron-withdrawing groups also are presented. Every year, new synthetic strategies and mechanistic studies involving SRN1 reactions are reported, which constitute a useful tool in the field of organic chemistry.