Scope and Limitations of Chiral B-[3,5-Bis(trifluoromethyl)phenyl]oxazaborilidine Catalyst for Use in the Mukaiyama Aldol Reaction
Kazuaki Ishihara, Shoichi Kondo, Hisashi Yamamoto*
*Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, Email: yamamotouchicago.edu
K. Ishihara, S. Kondo, H. Yamamoto, J. Org. Chem., 2000, 65, 9125-9128.
DOI: 10.1021/jo001271v
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Abstract
A new chiral oxazaborolidine catalyst is much more active than Corey's original catalyst for the Mukaiyama aldol reaction of aldehydes with silyl enol ethers. The observed syn selectivities and re-face attack of silyl enol ethers on carbonyl carbon of aldehydes imply that the extended-transition state model is applicable.
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proposed extended-transition
state assembly
Details
The document discusses the development and application of a new chiral oxazaborolidine catalyst derived from 3,5-bis(trifluoromethyl)phenylboron dichloride and N-(p-toluenesulfonyl)-(S)-tryptophan for the Mukaiyama aldol reaction. This catalyst demonstrates higher activity and enantioselectivity compared to Corey’s original catalyst. The catalyst is prepared in situ and shows significant improvements in yield and enantioselectivity for the aldol reaction of aldehydes with silyl enol ethers. The study highlights the importance of electron-withdrawing substituents in enhancing the catalytic activity of boron-based chiral Lewis acids. The new catalyst, referred to as 2d, achieves high yields and enantioselectivities with various substrates, indicating its broad applicability in enantioselective synthesis. The document also provides detailed experimental procedures for the preparation of the catalyst and its application in the Mukaiyama aldol reaction, along with supporting data on yields and enantioselectivities. The results suggest that the extended-transition state model is applicable, and the catalyst's efficiency makes it suitable for large-scale synthesis.
M. Wadamoto, N. Ozasa, A. Yanagisawa, H. Yamamoto, J. Org. Chem., 2003, 68, 5593-5601.
Key Words
Mukaiyama Aldol Addition, chiral oxazaborolidines, silyl enol ethers
ID: J42-Y2000-080