Dehydrative Cp*Co(III)-Catalyzed C–H Bond Allenylation

An efficient, unprecedented reactivity of Cp*Co­(III) for the synthesis of tetrasubstituted allenes under mild conditions is disclosed. Electron-rich and highly nucleophilic cobalt facilitates the dehydrative C–H bond allenylation directly from propargylic alcohols without any derivatization. The reaction proceeds via reversible cyclometalation followed by alcohol-directed regioselective alkyne insertion and β-hydroxy elimination to provide the tetrasubstituted allenes.