Enantioselective Synthesis and Application to the Allylic Imidate Rearrangement of Amine-Coordinated Palladacycle Catalysts of Cobalt Sandwich Complexes

The reaction of ((5)-(N,N-dimethylaminomethyl)cyclopentadien-yl)((4)-tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)-N-acetylphenylalanine gave planar chiral palladacycle di--chloridebis[((5)-(S-p)-2-(N,N-dimethylaminomethyl)cyclopentadienyl,1-C,3-N)((4)-tetraphenylcyclobutadiene)cobalt]dipalladium [(S-p)-Me-2-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 (S-p)-Me-2-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 5mol% of the latter [(S-p)-Pyrr-CAP-Cl] and AgNO3 (3.8equiv) 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.