Cobalt-Catalyzed Regio- and Diastereoselective Formal [3 + 2] Cycloaddition between Cyclopropanols and Allenes

A cobalt–diphosphine catalyst has been found to promote a formal [3 + 2] cycloaddition reaction between a cyclopropanol and an allene via cyclopropanol ring opening, which affords a 3-alkylidenecyclopentanol derivative with high regio- and diastereoselectivities. The reaction tolerates monosubstituted, 1,1-disubstituted, and 1,3-disubstituted allenes and various functional groups. The reaction is proposed to proceed through carbometalation of the allene with a cobalt homoenolate followed by intramolecular carbonyl allylation of the resulting allylcobalt species.