title: Preparation of sigma- and pi-allylcopper(III) intermediates in SN2 and SN2' reactions of organocuprate(I) reagents with allylic substrates.
abstract: The first pi-allyl complexes of CuIII have been prepared and characterized by using rapid injection nuclear magnetic resonance spectroscopy (RI-NMR). The prototype, (eta3-allyl)dimethylcopper(III), was prepared by injection of allyl chloride into a THF-d8 solution of iodo-Gilman reagent, Me2CuLi.LiI (A), spinning in the probe of an NMR spectrometer at -100 degreesC. A sigma-allyl ate complex, lithium (eta1-allyl)trimethylcuprate(III), was prepared in high yield by including 1 equiv of tributylphosphine in the reaction mixture or by using allyl acetate as the substrate. Cyano ate complex, lithium cis-(eta1-allyl)cyanodimethylcuprate(III) was obtained in high yield by injecting allyl chloride or allyl acetate into the cyano-Gilman reagent, Me2CuLi.LiCN (B), in THF-d8 at -100 degrees C. Reactions of A with allylic substrates show a definite dependence on leaving group (chloride vs acetate), whereas those of B do not. Moreover, these reagents have different regioselectivities, which in the case of A vary with temperature. Finally, the exclusive formation of cis-cyano sigma-allyl CuIII intermediates in both the 1,4-addition of B to alpha-enones and its SN2alpha reaction with allylic substrates now makes sense in terms of pi-allyl intermediates in both cases, thus unifying the mechanisms of these two kinds of conjugate addition.
authors.affiliation: Department of Chemistry, University of North Carolina-Charlotte, Charlotte, North Carolina 28223, USA.
authors.forename: Erika R
authors.initials: ER
authors.lastname: Bartholomew
authors.forename: Steven H
authors.initials: SH
authors.lastname: Bertz
authors.forename: Stephen
authors.initials: S
authors.lastname: Cope
authors.forename: Michael
authors.initials: M
authors.lastname: Murphy
authors.forename: Craig A
authors.initials: CA
authors.lastname: Ogle