Energy‐Transfer‐Enabled Copper‐Catalyzed Direct Site‐Selective Cycloaddition of Unprotected Oximes with Alkenes

Abstract While methodologies for N─O bond scission in O‐functionalized oximes are well established, the analogous activation of free oximes remains challenging, largely due to the formidable hurdles associated with selective N─O bond cleavage and competing side reactions involving the acidic O─H moiety. Herein, we report a dual photo‐ and copper‐catalyzed strategy that directly promotes homolytic cleavage of the N─O bond in free oximes through photosensitization of oxime‐ligated copper complexes, thereby overcoming prior limitations. Mechanistic studies, including full characterization of key copper intermediates, support an energy transfer (EnT) pathway. This distinctive activation mode enables a previously elusive intermolecular cyclization between unprotected oximes and alkenes, delivering valuable 1‐pyrrolines with high efficiency.