BX₃-Mediated Arene Borylation: Concepts, Scope, and Mechanistic Insight

Transition metal-free arene C‒H borylation has emerged as a promising strategy for the synthesis of arylborane compounds under mild, sustainable, and cost-effective conditions, thus avoiding the limitations associated with precious metal-catalyzed reactions. Central to these approaches is the use of highly electrophilic boron trihalides, which directly interact with the π-electron systems of arenes to facilitate efficient borylation. This review article provides a critical analysis of the mechanistic pathways underlying such metal-free transformations, with a particular emphasis on the elementary steps involved in the BX₃-mediated C-H bond functionalization of arenes. Our discussion provides a conceptual framework to support both the interpretation of existing studies and the rational design of future methodologies in metal-free borylation chemistry.