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

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.