Spin Delocalization of Nitrile-Ligated Diarylboryl Radicals Enables Photochemical Boracycle Synthesis via <i>N</i>-Borylimidoyl Radicals

Tetracoordinate boracycles are important motifs in organic synthesis and materials science, yet their synthesis remains constrained by two-electron processes requiring directing groups or highly reactive boron reagents. Herein, we report a photochemical strategy enabling the modular, single-step assembly of tetracoordinate boron-nitrogen heterocycles from olefins, nitriles, and tetraarylborates. This method bypasses traditional directing groups and strong boron electrophiles, providing access to previously inaccessible boracyclic architectures. More importantly, mechanistic experiments and DFT calculations reveal a distinct radical-mediated cyclization mechanism involving a novel class of <i>N</i>-borylimidoyl radicals, which are generated from nitrile-ligated diarylboryl radicals via spin delocalization. Preliminary studies demonstrate that these imidoyl radicals could also be leveraged to access tri- and tetrasubstituted 2-fluoropyrroles and bridged boracycles.