title: Mechanism and regioselectivity of reductive elimination of pi-allylcopper (III) intermediates.
abstract: Reductive elimination of a pi-allylcopper(III) compound leading to the formation of a C-C bond on an allylic terminal has been considered to occur via the corresponding sigma-allylcopper(III) species. The present B3LYP density functional study has shown however that the C-C bond formation occurs directly from the pi-allyl complex via an enyl[sigma+pi]-type transition state, which has structural features different from a simple sigma-allylcopper(III) intermediate. In the case of unsymmetrically substituted pi-allylcopper(III) compound that has a partial sigma-allylcopper(III) structure, the reductive elimination occurs preferentially at the sigma-bonded allylic terminal since, in this way, the copper atom can recover most effectively its d-electrons shared with the allyl system. The regioselectivity of the reductive elimination of a substituted pi-allylcopper(III) intermediate is mainly controlled by the electronic effect, and correlated well to the Hammett sigma(p)(+) constant. The analyses revealed mechanistic kinship between the allylic substitution and the conjugate addition reaction of organocopper reagents.
authors.affiliation: Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yamanaka
authors.forename: Seiichi
authors.initials: S
authors.lastname: Kato
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nakamura