BX₃-Mediated Directed Electrophilic Borylation: Advances, Applications, and Mechanistic Insights

ConspectusOrganoboron compounds have emerged as indispensable tools in modern chemical science, which are prized for their low toxicity and exceptional functional versatility. As key intermediates in pharmaceutical development and advanced materials synthesis─including functional polymers and hydrogels─their significance continues to expand. Traditional synthetic approaches, which predominantly rely on organolithium or Grignard reagents, are frequently constrained by limited functional group tolerance and demanding operational conditions. The advent of C-H borylation has represented a transformative advance, enabling the direct introduction of boron into complex molecular architectures without the need for prefunctionalization. Nevertheless, the continued reliance on precious transition-metal catalysts such as iridium, rhodium, and palladium remains a critical economic and practical limitation. Thus, there exists a compelling need to establish efficient, atom-economical, and cost-effective synthetic platforms for the preparation of organoborons and their derivatives. This Account summarizes our research group's contributions since 2019 toward addressing this challenge through the development of directed electrophilic borylation mediated by boron trihalides (BX₃) under mild conditions. We highlight the chelation-assisted activation of both C-H and C-C bonds facilitated by tailored directing groups, encompassing substrates based on indoles, pyrroles, amides, phosphines, enamides, and cyclopropanes.The Account is structured to guide readers through the conceptual development, substrate scope, limitations, and mechanistic foundations of these directed electrophilic transformations. Mechanistic insights, derived from integrated experimental and computational studies, are presented to clarify key intermediates and reaction pathways that govern the selectivity and reactivity. In the concluding section, we acknowledge significant contributions from other research groups, outline persisting challenges, and suggest future directions essential for advancing the field─with the aim of inspiring further research and innovation.