Redirecting radical phosphonylation via energy-transfer-enabled diradical rearrangement.

Radical phosphonylation has traditionally relied on single-electron transfer mechanisms. In contrast, strategies using energy-transfer pathways to enable scaffold rearrangement are rare. Here, we report an energy transfer catalysis strategy that diverts reactivity toward a previously unexplored pathway: a direct photochemical diradical rearrangement between homoallylic alcohols and phosphorus(III) reagents. Mechanistic studies, supported by computational calculation, provide definitive support for an energy-transfer-mediated diradical mechanism. This operationally simple and mild process, driven by visible light, forges strained phosphorylated cyclopropanes with high efficiency via diradical intermediates that undergo radical addition to phosphorus, β-scission, and recombination. With broad substrate compatibility and excellent functional group tolerance, this method delivers diverse three-membered rings containing phosphine oxide in good to excellent yields. This work establishes a new reaction manifold for organophosphorus synthesis, demonstrating how energy transfer catalysis can redirect traditional reactivity to access valuable strained architectures through previously inaccessible rearrangement pathways.