Regioselectivity in Wacker oxidations of internal alkenes: antiperiplanar effects?

Abstract

Computational chemistry, with considerable effort, was used to elucidate the reason for regioselectivity (12:1 distal:proximal product distribution) in a published Wacker oxidation of internal alkenes with a homoallylic lactam ring. Such a distribution is reproduced by a non-chelating reaction pathway; chelated intermediates are found to be too high in energy. Despite much speculation of chelation effects in the literature, this particular result is most probably an antiperiplanar field effect with no chelation. Partial charge data are provided to support the proposed antiperiplanar effect. The great care needed in modelling Wacker oxidations is emphasized, but optimism is offered that its various product mysteries can be elucidated on a case-by-case basis.