Divergent ring-opening coupling betweencyclopropanols and alkynes under cobalt catalysis

摘要

Cobalt–diphosphine catalysts promote ring-opening coupling reactions between cyclopropanols andunactivated internal alkynes, affording either b-alkenyl ketones or multisubstituted cyclopentenolderivatives in good yields with good to excellent regioselectivities. The chemoselectivity between theseb-alkenylation and [3 + 2] annulation reactions, which likely share a cobalt homoenolate as a keycatalytic intermediate, is exquisitely controlled by the reaction conditions, with the solvent being a majorcontrolling factor. The reactions are proposed to involve ring opening of cobalt cyclopropoxide intohomoenolate, migratory insertion of the alkyne into the Co–C bond, and protodemetalation orintramolecular carbonyl addition of the resulting alkenylcobalt species. The feasibility of these reactionsteps was supported by DFT calculations.