ORGN 514 |
| An asparagine-derived asymmetric auxiliary is designed for stereoselective Diels-Alder reactions in aqueous media to study metal counter-ion influences on the stereochemical course of the transformation. The system is designed to determine how diverse metals can uniquely impact the syn/anti conformational equilibrium of the dienophile, in addition to Lewis acid catalysis. The complexation between the carboxylate metal and the acrylamide carbonyl in the sterically disfavored syn conformer impacts both the equilibrium constant and catalytic activity. The complexation is geometrically inaccessible to the anti conformer and thus impact should be minimal. In the study, metallated dienophiles were prepared and the conformational equilibrium values and cycloaddition stereoselectivities of each were determined. These data provide a quantitative measure of the rate enhancement afforded by diverse Lewis acid catalysts in water. A comparison of the impacts of the metals on equilibria and cycloaddition diastereoselectivity indicates that metal influence on complexation and catalysis are non-identical processes.
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Physical Organic Chemistry, Metal-Mediated Reactions, Asymmetric Reactions and Syntheses
8:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Organic Chemistry |
