Iron-Catalyzed Direct Aldehyde-to-Carbene Conversion via Ketyl Radicals

Carbene chemistry is at the forefront of modern synthetic methodology due to its ability to unlock a plethora of chemical transformations. Traditional reliance on diazo compounds, while effective, is hindered by their inherent instability, toxicity, and limited functional group tolerance. Recent advances have explored alternative carbene precursors, yet the direct catalytic generation of carbenes from aldehydes remains underexplored. Here, we report a mild iron-catalyzed carbene transfer protocol that directly accesses carbene intermediates from aldehydes via a ketyl radical mechanism. This method obviates the need for prefunctionalized precursors, enabling the synthesis of diverse functionalized cyclopropanes with good efficiency and functional group compatibility. Mechanistic investigations, including radical trapping, σ-bond insertion, and olefin metathesis experiments, corroborate the intermediacy of ketyl radicals and iron carbenes. This work expands the synthetic utility of aldehydes, offering a robust platform for carbene transfer reactions and the synthesis of valuable cyclopropane scaffolds.