Ph ₂ SCCO: A New Versatile CCO‐Fragment Transfer Reagent

ketenylidene (C₂O) is an electronically intriguing small molecule with significant potential as a C₂ synthon in organic synthesis. However, its high reactivity has thus far precluded practical applications. Herein, we report the synthesis of a new reagent, the heterocumulene Ph₂S═C═C═O (1), a well-defined C₂O equivalent that accurately replicates the chemical reactivity profile of C₂O in a controlled manner. 1 uniquely integrates ketene-like and classical carbene reactivity. In the presence of Brønsted acids, 1 undergoes initial 1,2-addition to form a sulfur ylide intermediate, which can be exploited for subsequent reactions including cyclopropanation, epoxidation, or X-H addition. The CCO fragment transfer strategy, starting from simple precursors, enables efficient access to α-cyclopropyl- as well as α-epoxy-carbonyl derivatives and structurally complex bicyclic cyclopropanes.