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 Brønsted 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.