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 PdII/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 PdII/IV mechanism in which the key cyclopropane-forming step involves nucleophilic attack of a tethered olefin onto the PdIV−C bond.