ORGN 849 |
| Boron-mediated aldol reactions of methyl ketones are used extensively in natural product synthesis, although predicting selectivity remains a significant challenge. Since stereoselectivity is often in the opposite sense to that of substituted enolates, new models are required. We have used high-level transition state modeling to quantitatively account for the stereoselectivity observed in chiral ligand and substrate controlled reactions. This information has been used to construct a general molecular mechanics model able to predict levels of selectivity in the aldol-couplings of complex fragments, where multiple controlling factors are in competition. We present a new stereochemical model supported by ab initio calculations to account for the remarkable 1,5-anti selectivity shown by β-alkoxy methyl ketones, in which a formyl-hydrogen bond is important.
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Total Synthesis, Materials, Molecular Recognition, Process R&D, and Physical Organic Chemistry
8:00 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster
Sci-Mix
Division of Organic Chemistry |
