Asymmetric Catalysis
Application of Metallacycles
Nucleophilic Catalysis
Ligand Diversity

In collaboration with the Overman group (UC Irvine), we have applied palladacycle 1 to the allylic imidate rearrangement of trifluoroacetimidates. Both E- and Z-isomers react enantioselectively to provide, following deprotection, either the (S)- or (R)-enantiomer of an allylic amine building block.1

Further work has concentrated on the use on minimising the catalyst loading for the rearrangement of (E)-trichloroacetimidate substrates, for which just 0.25 mol% of dimer 1 is required.2 Palladacycle 1 is now commercially available or is readily synthesised.3
A home grown reaction is the Michael addition of activated nitriles such as ethyl a-cyanopropionate to unsaturated carbonyls.4 This is catalysed by as little as 1mol% of the cationic pincer complexes 2, with similar results arising from the palladium and platinum species. Although the highest enantioselectivity obtained to date is somewhat modest, this reaction displays some unusual non-linear phenomena that have reawakened our interest in this process.5
[1] L. E. Overman, C. E. Owen, M. M. Pavan and C. J. Richards, Org. Lett., 2003, 5, 1809. [2] H. Nomura and C. J. Richards, Chem. Eur. J. 2007, 13, 10216 [3a] Preparation of (h5-(S)-2-(4-Methylethyl)oxazolinylcyclopentadienyl)(h4-tetraphenylcyclobutadiene)cobalt. C. E. Anderson, L. E. Overman, C. J. Richards, M. P. Watson and N. White, Organic Syntheses, 2007, 84, 139. [3b] Preparation of the COP Catalysts: [(S)-COP-OAc]2, [(S)-COP-Cl]2, and (S)-COP-hfacac. C. E. Anderson, S. F. Kirsch, L. E. Overman, C. J. Richards and M. P. Watson, Organic Syntheses, 2007, 84, 148. [4] M. A. Stark, G. Jones and C. J. Richards, Organometallics, 2000, 19, 1282. [5] J. S. Fossey and C. J. Richards, manuscript in preparation.