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.