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Vinylogous Aldol Additions

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A highly regioselective vinylogous aldol reaction catalyzed by SiCl4 and a chiral phosphoramide, provides δ-hydroxy enones for a variety of aldehyde and dienol ether structures in good yields, excellent enantioselectivities, and in some cases excellent anti diastereoselectivities.
S. E. Denmark, G. L. Beutner, J. Am. Chem. Soc., 2003, 125, 7800-7801.


N,O-Silyl dienyl ketene acetals are useful reagents for highly enantioselective vinylogous aldol additions to various aldehydes in the presence of SiCl4 and the catalytic action of a chiral phosphoramide.
S. E. Denmark, J. R. Heemstra, Jr., J. Am. Chem. Soc., 2006, 128, 1038-1039.


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.
S. E. Denmark, G. L. Beutner, T. Wynn, M. D. Eastgate, J. Am. Chem. Soc., 2005, 127, 3774-3789.