Phosphoryl Radicals from Trivalent Iminyl Phosphines: A Photocatalytic Approach to <i>N</i> ‐Phosphoryl Azetidines

We report that iminyl phosphines, a class of bench-stable and readily accessible trivalent P-centered radical precursors, enable the synthesis of N-phosphoryl azetidines via formation of a key phosphoryl radical under visible-light single-electron transfer (SET) catalysis. Mechanistic investigations reveal that SET oxidation of the iminyl phosphine engages a previously unexplored SET-triggered polar pathway that channels the reaction away from classical phosphine oxidation toward the controlled generation of a P-centered radical. A combination of experimental evidence, including electron paramagnetic resonance (EPR) spectroscopy and optical studies, supported by density functional theory (DFT) calculations, were used to shed light on this unconventional reaction manifold. This cooperative radical-polar mechanism facilitates the radical ring-opening of azabicyclo[1.1.0]butanes (ABBs), granting access to previously inaccessible P-N bonds.