ORGN 365 |
| Metalloporphyrin-catalyzed alkene epoxidation has been a subject of extensive studies for decades. By judicious modification of the macrocyclic ligand, steric and electronic properties of metalloporphyrin catalysts can be fine-tuned for stereo- and enantioselective alkene epoxidations. Epoxides of allyl-substituted alkenes are versatile synthetic intermediates for organic synthesis. Significant successes have been achieved in cis-selective epoxidation of cyclic allylic alcohols through hydrogen bonding. However, for epoxidation of alkenes without syn-directing group, anti-epoxides would be obtained as major product, and such anti-selectivities are generally poor. Here, we reported that highly diastereoselective epoxidations of allyl-substituted alkenes including allylic alcohols, esters, and amines can be achieved by using sterically bulky metalloporphyrins [Mn(TDCPP)Cl] and [Ru(TDCPP)CO] as catalysts. Our epoxidation protocols afforded anti-epoxides selectively in good yields (up to 99%) with up to >99:1 anti-selectivity. The synthetic utilities of this epoxidation method are highlighted, and transition-state geometries are proposed to rationalize the diastereoselective epoxidation reaction. |
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Bioorganic, Metal-Mediated Reactions, and Molecular Recognition
8:00 PM-10:00 PM, Tuesday, 30 August 2005 Washington DC Convention Center -- Hall A, Poster
Division of Organic Chemistry |