Synthesis and characterization of a cyclic vinylpalladium(II) complex: vinylpalladium species as the possible intermediate in the catalytic direct olefination reaction of enamide

A six-membered cyclic vinylpalladium complex was synthesized via alkenyl C-H bond direct palladation, which was probed in detail by 1 H NMR spectroscopy and characterized by X-ray analysis. The cyclic vinylpalladium complex was propounded to be the intermediate during the olefination reaction of enamides. An efficient catalytic system for oxidative cross-coupling reaction of enamides with electron-deficient olefins catalyzed by palladium(II) acetate and 1 atm oxygen as sole oxidant was developed. The corresponding products were obtained in moderate to good yields under mild conditions.