Arene activation via π-bond localization: concepts and opportunities

Dearomatization reactions of aromatic feedstocks constitute a highly efficient and conceptually powerful class of transformations for the synthesis of complex, three-dimensional molecular architectures with tailored physicochemical properties. Despite notable advances in dearomative methodologies over the past decades, the selective and controlled disruption of the aromatic core continues to represent a fundamental challenge in synthetic chemistry. In this review, we delineate the potential of π-bond localization within the aromatic framework as a general strategy for arene activation and dearomatization. Four distinct approaches are discussed, encompassing localization of the arene π-bonds through small-ring annelation as well as transition metal coordination to aromatic fragments in an η 2 -, η 3 -, and η 4 -fashion. The structural and reactivity consequences of these perturbations are analyzed in detail, and representative examples of stoichiometric and, where available, catalytic applications in synthesis are highlighted. Collectively, these concepts create a roadmap for the development of new strategies that harness π-bond localization to expand the synthetic utility of aromatic compounds.