Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Silyl Ketene Acetals to Aldehydes
Scott E. Denmark,* Gregory L. Beutner, Thomas Wynn and Martin D. Eastgate
*Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, Email: denmarkscs.uiuc.edu
S. E. Denmark, G. L. Beutner, T. Wynn, M. D. Eastgate, J. Am. Chem. Soc., 2005, 127, 3774-3789.
The weakly acidic species, silicon tetrachloride (SiCl4), can be activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral Lewis acid for catalysis of the aldol reaction of silyl ketene acetals and silyl dienol ethers (vinylogous aldol reactions) to conjugated and nonconjugated aldehydes. The high levels of regio-, anti diastereo-, and enantioselectivity observed are discussed.
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β-Hydroxy Esters, Mukaiyama Aldol Addition, Homoallylic Alcohols, α,β-unsaturated compounds