Cation Radical‐Mediated Nucleophilic Aromatic Substitution (S <i> _N </i> Ar): A Modern Realization of an Old Discovery

Beginning in 2017, the groups of Nicewicz, Burton, Lambert, and others have reported an ever‐widening array of formally redox neutral nucleophilic aromatic substitution (S N Ar) reactions that proceed via an aromatic radical cation intermediate. However, the roots of this reaction extend far back more than 50 years to foundational work by Nyberg, Kochi, Cornelisse, and Eberson. Unfortunately, much of this early precedent appears to have been overlooked, despite the fact that it offers many potentially useful mechanistic insights into the more modern transformations. Additionally, it is found that this early work has not previously been reviewed in the unified context of nucleophilic aromatic substitution. In this review, a glimpse into the past is provided before discussing the exciting developments of the last decade in this area. The review is concluded with an overview of some of the potential growth opportunities that remain.