Synthesis of Cyclopentenones with Reverse Pauson-Khand Regiocontrol via Ni-Catalyzed C-C Activation of Cyclopropanone.

A formal [3 + 2] cycloaddition between cyclopropanone and alkynes via Ni-catalyzed C-C bond activation has been developed, where 1-sulfonylcyclopropanols are employed as key precursors of cyclopropanone in the presence of trimethylaluminum. The transformation provides access to 2,3-disubstituted cyclopentenones with complete regiocontrol, favoring reverse Pauson-Khand products, where the large substituent is located at the 3-position of the ring. In the process, the trimethylaluminum additive is thought to play multiple roles, including as a Bronsted base triggering the equilibration to cyclopropanone and liberation of methane, as well as a source of Lewis acid to activate the carbonyl group toward Ni-catalyzed C-C activation.