Photoinduced Selective Construction of Densely Functionalized Spirocyclic Ethers With Carbyne Equivalents.

Carbyne equivalents represent ideal trivalent carbon synthons, capable of forming C─C and C─X bonds through their three nonbonded electrons. This unique reactivity profile offers high modularity for rapid assemble complicate molecular scaffolds. However, the selective introduction of three σ-bonds at a single carbon center remains a formidable challenge, owing to the multifaceted reactivity of the carbyne center. Herein, we report a cascade reaction, which sequentially regulates the radical, nucleophilic, and electrophilic reactivity of carbyne equivalents under light irradiation. This cascade enables precise spatial and temporal activation, facilitating the selective and efficient construction of densely functionalized spirocyclic ethers from allylic and homoallylic acetates, with three σ-bonds introduced at the carbyne center. A wide range of spirocyclic ethers bearing diverse functional groups and structural motifs was obtained with excellent diastereoselectivity, underscoring the capability of carbyne equivalents for rapid construction of drug-like molecules. The reaction was readily scalable up to 50 mmol, either in batch mode or using a high-speed circulation-flow reactor. Mechanistic studies, including UV-vis spectroscopy, cyclic voltammetry, radical trapping, structure-reactivity relationship experiments, isotope labeling, as well as theoretical calculations, provide insights into the dynamic evolution of reactive intermediates, shedding light on the diverse reactivity of carbyne equivalents in organic synthesis.