Deoxygenative [3 + 2] Annulation of α,β-Unsaturated Carbonyl Compounds and Electron-Rich Olefins via Photocatalytic Umpolung of Triarylphosphine.

A visible-light-driven deoxygenative [3 + 2] annulation between α,β-unsaturated carbonyl compounds and electron-rich olefins was developed, which proceeded under mild conditions with a broad substrate scope and functional group tolerance, enabling straightforward access to diverse substituted cyclopentenes. This cascade annulation strategy exploited the reactivity of phosphine radical cations, generated from triarylphosphines by the oxidation with the excited-state iridium-based photocatalysts, toward olefins to form the corresponding distonic radical cations with a chain length pertinent to constructing cyclopentene scaffolds via sequential radical addition and intramolecular Wittig reaction.