ORGN 573 |
| Rhodium-catalyzed oxidative cyclization of glucal 3-carbamates leads to oxazolidinone-protected mannosamine derivatives. The stereoselectivity at the anomeric center depends upon the nature of the protecting groups and the solvent. Of the three 4O,6O protecting groups that we have studied-- acetonide, tert-butyl silylene, and benzyl-- benzyl protection provides the highest α-selectivity. We have noted that less polar solvents, such as hexanes and benzene, also improve the anomeric ratio. A dihydro-4-pyranone byproduct is produced in these reactions. Mechanistic studies have shown that its formation requires the presence of a primary amide-containing carbamate starting material. The byproduct and minor β-stereoisomer may emerge from a common intermediate.
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Heterocycles, Aromatics, Metal-Mediated Reactions and Syntheses, Materials, Devices, and Switches
8:00 PM-10:00 PM, Wednesday, 29 March 2006 Georgia World Congress Center -- Ex. Hall B4, Poster
Division of Organic Chemistry |
