Harnessing Molecular Strain to Program 1,2-Migration in Boronic Ester Chemistry

Strain in small-ring systems has emerged as a powerful intrinsic driver for stereospecific 1,2-metalate rearrangements in boronic ester chemistry, offering an alternative to classical electrophilic activation. By embedding stored strain energy within nitrogen-containing rings, cyclopropanes, epoxides, and bicyclo[1.1.0]butanes, otherwise disfavored carbon migrations can be selectively and predictably promoted. Release of this strain lowers activation barriers, enforces concerted pathways, and enables faithful transfer of stereochemical information from boron to carbon. Both transition-metal-mediated and metal-free triggers convert the latent strain into productive bond reorganization, allowing efficient access to complex, sp³-rich frameworks from simple precursors. This review highlights how deliberate exploitation of molecular strain provides a general, programmable strategy for controlling 1,2-migration, expanding the synthetic toolbox for constructing stereochemically defined, densely functionalized molecules.