Evidence for the intermediacy of (eta(3)-allyl)palladium complexes in the palladium-catalyzed acryloxylation of cycloalkenes: Unexpected oxidation of1,5-cyclooctadiene

Palladium-catalyzed acryloxylation of several cycloalkenes in the presence of the Pd(OAc)(2)/p-benzoquinone/MnO2 catalytic system is reported. This ox idation reaction yields allylic acrylates as the sole products through the intermediacy of an eta(3)-allyl complex. However, with 1,5-cyclooctadiene ( 3), cyclooct-4-enone (4) is the major reaction product. Its formation resul ts from oxidation, which is also observed in the palladium-catalyzed acetox ylation of 3. It has been shown that this is the result of a 1,2-trans addi tion (acryloxy-palladation), followed by a P-hydride elimination, which yie lds an enol acrylate or acetate. A second Markovnikov-oriented 1,2-trans-ac ryloxy-palladation on the latter yields a palladium complex, rearrangement of which gives 4.