An Allylpalladium(IV) Intermediate in the Synthesis of Highly Substituted Benzoxepines and Benzopyrans via Reactions of Stable Pallada(II)cycles with Allyl Bromides

Stable pallada(II)cycles L₂Pd-1-C₆H₅-2-OCHCO₂Et, featuring a Pd-bonded sp³-hybridized stereogenic carbon and bipyridine or bis(imine) auxiliary ligands (L-L), reacted with allyl bromides via a Pd(II)−Pd(IV)-mediated process involving a direct C(sp²)−H functionalization to afford highly substituted benzoxepines or benzopyrans. An allylpalladium(IV) complex, which was detected by low-temperature ¹H NMR analysis and characterized by X-ray crystallography, was shown to operate as an intermediate in the reaction sequence.