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
Contribution from the Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801
J. Am. Chem. Soc., 2005, 127 (11), pp 3774–3789
DOI: 10.1021/ja047339w
Publication Date (Web): February 23, 2005
Copyright © 2005 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, denmark@scs.uiuc.edu

Abstract

Abstract Image

The concept of Lewis base activation of Lewis acids has been reduced to practice for catalysis of the aldol reaction of silyl ketene acetals and silyl dienol ethers with aldehydes. 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. This species has proven to be a competent catalyst for the aldol addition of acetate-, propanoate-, and isobutyrate-derived silyl ketene acetals to conjugated and nonconjugated aldehydes. Furthermore, vinylogous aldol reactions of silyl dienol ethers are also demonstrated. The high levels of regio-, anti diastereo-, and enantioselectivity observed in these reactions can be rationalized through consideration of an open transition structure where steric interactions between the silyl cation complex and the approaching nucleophile are dominant.

View: Full Text HTML | Hi-Res PDF

Tools

History

  • Published In Issue March 23, 2005
  • Received May 6, 2004

Recommend & Share

Related Content

Other ACS content by these authors: