Deoxygenative Single-Carbon Atom Transfer: Accessing Strained Carbocycles From Alkenes and Aldehydes With Designer Dual-Functional Reagent.

Single-carbon atom transfer is an attractive approach to increasing molecular complexity through the concurrent formation of four new covalent bonds. Yet, the success of these methods depends largely on atomic carbon reagents that harness carbene reactivity, thereby constraining the repertoire of transformations attainable within this regime. Here, we report a deoxygenative single-carbon atom transfer strategy that directly couples alkenes and aldehydes to access substituted alkylidenecyclopropanes. The key enabling development is the identification of a novel iodomethylphosphonium reagent that orchestrates photocatalytic atom-transfer radical addition and cyclizative Wittig olefination at a single carbon center. Mechanistic studies reveal that the electronically tailored phosphonium motif endows the key radical intermediate with the desired polarity for carbon delivery and, at the same time, enhances the accessibility of phosphorus ylides en route to both ring closure and Wittig reaction. This operationally simple method provides a modular entry from two abundant starting materials to highly strained small carbocycles featuring four newly formed bonds.