Enantioselective Synthesis and Application to the Allylic Imidate Rearrangement of Amine‐Coordinated Palladacycle Catalysts of Cobalt Sandwich Complexes |
| |
Authors: | Doyle J Cassar Dr Gennadiy Ilyashenko Dr Muhammad Ismail James Woods Dr David L Hughes Dr Christopher J Richards |
| |
Institution: | 1. School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK);2. Current address: Department of Chemistry, Karakoram International University, University Road, Gilgit‐15100 (Pakistan) |
| |
Abstract: | The reaction of (η5‐(N,N‐dimethylaminomethyl)cyclopentadien‐yl)(η4‐tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)‐N‐acetylphenylalanine gave planar chiral palladacycle di‐μ‐chloridebis(η5‐(Sp)‐2‐(N,N‐dimethylaminomethyl)cyclopentadienyl,1‐C,3′‐N)(η4‐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. |
| |
Keywords: | asymmetric synthesis catalysis metallacycles palladium sandwich complexes |
|
|