ORGN 90 |
| Michael W. Fennie, Erin F. DiMauro, Venkatachalam Annamalai, Erin M. O'Brien, and Marisa Kozlowski. Department of Chemistry, University of Pennsylvania, 231 S 34th St, Philadelphia, PA 19104 |
| Metal complexes of C2-symmetric bifunctional Lewis acid/ Lewis base salen ligands provide an excellent example of ligand accelerated catalysis in the enantioselective diethylzinc addition to aldehydes (up to 92% ee), and in the addition of diethylzinc to alpha-ketoesters (up to 88% ee). alpha-Ketoesters alone serve as their own ligands to promote racemic 1,2-addition of diethylzinc. In such instances, beta-hydride reduction of the carbonyl via a metalloene pathway is often the major product. Simple Lewis acid catalysis does not accelerate enantioselective 1,2-addition over these two competing pathways. Bifunctional salen catalysts, however, rapidly provide enantioenriched 1,2-addition products in excellent yield and with complete chemoselectivity. Results for the asymmetric alpha-ketoester additions detailing the scope, mechanism, and utility in pharmaceutical agent synthesis will be presented. Applications of these bifunctional salen catalysts to other transformations will also be discussed. |
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Asymmetric Reactions and Syntheses, Metal-Mediated Reactions, Materials, Molecular Recognition
8:00 PM-10:00 PM, Sunday, August 22, 2004 Pennsylvania Convention Center -- Hall D, Poster
Division of Organic Chemistry |