Palladium-Catalyzed Direct C–H Alkenylation with Enol Pivalates Proceeds via Reversible C–O Oxidative Addition to Pd(0)

We report a direct tandem C–O/C–H activation approach to C–C bond formation using palladium catalysis. This reaction combines C–O oxidative addition at enol pivalates with concerted metalation–deprotonation of functionalized heterocycles to achieve base-free direct C–H alkenylation. Preliminary mechanistic studies revealed that the C–O oxidative addition to Pd(0) is reversible under these conditions and that C–H activation occurs directly from the Pd(II) C–O oxidative addition product. In situ 31P NMR spectroscopy further revealed that the (Cy3P)2Pd(alkenyl)(OPiv) species is a major catalyst resting state during the reactions.