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.