Lewis Base Activation of Lewis Acids in Asymmetric Aldol Reactions of Silyl Ketene Acetals
Beutner, Gregory Louis
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/84145
Description
Title
Lewis Base Activation of Lewis Acids in Asymmetric Aldol Reactions of Silyl Ketene Acetals
Author(s)
Beutner, Gregory Louis
Issue Date
2004
Doctoral Committee Chair(s)
Denmark, Scott E.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
The concept of Lewis base activation of Lewis acids has been effectively reduced to practice for catalysis in the chiral phosphoramide catalyzed/SiCl 4 promoted aldol reaction of silyl ketene acetals and silyl dienol ethers with aldehydes. The weakly acidic species, silicon tetrachloride (SiCl 4), is activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral silyl cation. This species has proven a competent catalyst for the aldol addition of acetate-, propanoate- and isobutyrate-derived silyl ketene acetals to conjugated and non-conjugated 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. Kinetic studies undertaken using ReactIR spectroscopy show that the reaction displays saturation kinetics in SiCl4. This suggests that the phosphoramide bound silyl cation complex is the catalyst resting state. Spectroscopic studies have garnered support for this conclusion through the observation of the phosphoramide bound silyl cation complex by 29Si NMR.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
