title: Enantioselective synthesis and application to the allylic imidate rearrangement of amine-coordinated palladacycle catalysts of cobalt sandwich complexes.
abstract: The reaction of (η(5)-(N,N-dimethylaminomethyl)cyclopentadien-yl)(η(4)-tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)-N-acetylphenylalanine gave planar chiral palladacycle di-μ-chloridebis[(η(5)-(Sp)-2-(N,N-dimethylaminomethyl)cyclopentadienyl,1-C,3'-N)(η(4)-tetraphenylcyclobutadiene)cobalt]dipalladium [(Sp )-Me2 -CAP-Cl] in 92% ee and 64% yield. Enantiopurity (>98% ee) was achieved by purification of the monomeric (R)-proline adducts and conversion back to the chloride dimer. Treatment with AgOAc gave (Sp)-Me2-CAP-OAc which was applied to asymmetric transcyclopalladation (up to 78% ee). The (R)-N-acetylphenylalanine mediated palladation methodology was applicable also to the corresponding N,N-diethyl (82% ee, 39% yield) and pyrrolidinyl (>98% ee, 43% yield) cobalt sandwich complexes. A combination of 5 mol % of the latter [(Sp)-Pyrr-CAP-Cl] and AgNO3 (3.8 equiv) is a catalyst for the allylic imidate rearrangement of an (E)-N-aryltrifluoroacetimidate (up to 83% ee), and this catalyst system is also applicable to the rearrangement of a range of (E)-trichloroacetimidates (up to 99% ee). This asymmetric efficiency combined with the simplicity of catalyst synthesis provides accessible solutions to the generation of non-racemic allylic amine derivatives.
authors.affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK).
authors.forename: Doyle J
authors.initials: DJ
authors.lastname: Cassar
authors.forename: Gennadiy
authors.initials: G
authors.lastname: Ilyashenko
authors.forename: Muhammad
authors.initials: M
authors.lastname: Ismail
authors.forename: James
authors.initials: J
authors.lastname: Woods
authors.forename: David L
authors.initials: DL
authors.lastname: Hughes
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Richards
keywords: asymmetric synthesis; catalysis; metallacycles; palladium; sandwich complexes