Selenium atom transfer enables selective bridged alkene-arylamine cycloaddition.

Cycloaddition reactions are central to building cyclic molecular architectures for drug discovery and materials science. However, controlling single-atom-bridged cycloaddition remains elusive. Herein, we describe a selenium-atom transfer [3 + 2 + 1] heterocycloaddition of readily available arylamines, alkenes and diselenides, enabling rapid, modular access to diverse selenium- and nitrogen-containing heterocycles, including selenomorpholines and polycyclic 1,4-selenazinanes. This metal-free method operates under mild, simple conditions with scalability, showcasing broad substrate generality and functional group tolerance, is amenable to scalable synthesis, and demonstrates utility in the late-stage skeletal diversification of complex molecules. Mechanistic and computational studies reveal a Se-bridged cycloaddition pathway involving alkene aminoselenylation, followed by electrophilic selenocyclization and deprotonative rearomatization. This heteroatom-driven annulation opens opportunities for the development of reactions for the construction of multi-heteroatom cyclic scaffolds and broader application in selenium-based medicinal chemistry.