Lewis base activation of Lewis acids: Catalytic, enantioselective addition of silyl ketene acetals to aldehydes

Scott E Denmark, Gregory L. Beutner, Thomas Wynn, Martin D. Eastgate

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)3774-3789
Number of pages16
JournalJournal of the American Chemical Society
Volume127
Issue number11
DOIs
StatePublished - Mar 23 2005

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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