The final steps of the Oppolzer cyclization: mechanism of the insertion of alkenes into allylpalladium(II) complexes

We report here the results of a computational study on the the mechanism of the Oppolzer cyclization. These results lead us to conclude that the insertion of olefins in Pd-allyl complexes probably takes place directly from the eta(3)-allyl species. The presence of a phosphane ligand in the reagents plays the role of enhancing the electron density on the Pd atom; this makes the alkene moiety more reactive towards insertion by back-donation from the metal. The results also indicate that the configuration of the new stereogenic centers is fixed in the insertion of the alkene into the (eta(3)-allyl)palladium species.