Recent Advances on Radical Nucleophilic Substitution Reactions

Abstract

The radical nucleophilic substitution mechanism or SRN1 is a chain process, in which radicals and radical anions are intermediates. This process has been extensively used to effect substitution on a wide variety of substrates. The SRN1 reaction has been studied from both mechanistic and synthetic standpoints. The SRN1 mechanism requires an initiation step. Spontaneous electron transfer (ET) from the nucleophile to the substrate has been observed in a few systems; light stimulation, electrodes, alkali metals or inorganic salt-mediation is used otherwise. There are systems that are totally inert or undergo rather slow substitutions by classical polar mechanisms. Their lack of reactivity is usually due to strain (cycloalkyl and polycycloalkyl halides), steric (cycloalkyl, polycycloalkyl and neopentyl halides), or electronic factors (unactivated aromatic, vinyl halides and perfluoroalkyl halides). For these families of compounds, the nucleophilic substitution can be accomplished by the SRN1 mechanism. Conversely, there is a class of substrates, for which substitution can be achieved through both polar and ET mechanisms; however, the ET pathway is favored in some systems (i.e.: alkyl halides with EWG). We propose to undertake a compilation and critical review on SRN1 reactions dealing with substitutions on aromatic substrates, cycloalkyl, bridgehead, neopentyl, vinyl halides, perfluoroalkyl iodides, aliphatic substrates with EWG in the _ position and N,N-Dialkyl-p-toluenesulfonamides. With this aim in mind, we expect to cover recent SRN1 substitutions, with an emphasis on the scope of the process in terms of synthetic capability and target applications.