Synthesis of cyclopropanes via Pd(II/IV)-catalyzed reactions of enynes

This report describes a new Pd-catalyzed oxidation reaction for the stereospecific conversion of enynes into cyclopropyl ketones. Unlike related Pd-II/0, Au, and Pt-catalyzed cyclopropane-forming reactions, these transformations proceed with net inversion of geometry with respect to the starting olefin. This result is consistent with a Pd-II/IV mechanism in which the key cyclopropane-forming step involves nucleophilic attack of a tethered olefin onto the Pd-IV-C bond.