Transition Metal‐Free Activation of Carbon Monoxide: Ketenyl Anions by PPh3/CO Exchange

Ketenes (R2C=C=O) are important reactive intermediates in organic chemistry which are often challenging to access in stable form due to their polarized cumulenic structure and inherent high reactivity. Ketenyl anions (R(M)C=C=O) or metal ynolates (R−C≡C−OM) represent alternative, highly attractive synthetic targets, but are typically prepared in situ and their structure and synthetic access are little investigated. Now, a fundamentally new strategy utilizing an exchange reaction of a phosphine with carbon monoxide at a metalated ylide gives rise to a series of novel ketenyl anions. These compounds are flexible reagents and can easily be transferred with electrophiles into more complex building blocks for synthetic applications. Since carbon monoxide is an inexpensive C1 building block, the new exchange strategy is an elegant concept and a valuable new entry in the synthetic toolbox of organic synthesis. This article highlights the recent findings reported by Gessner and co‐workers in the synthesis of valuable ketenyl anions by an exchange of triphenylphosphine with carbon monoxide at a metalated ylide. The metal ketenyl/ynolate was structurally characterized and used as a reagent in organic synthesis.