Development of Highly Diastereo- and Enantioselective Direct Asymmetric Aldol Reaction of a Glycinate Schiff Base with Aldehydes Catalyzed by Chiral Quaternary Ammonium Salts

Takashi Ooi, Minoru Kameda, Mika Taniguchi, and Keiji Maruoka*
Contribution from the Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
J. Am. Chem. Soc., 2004, 126 (31), pp 9685–9694
DOI: 10.1021/ja048865q
Publication Date (Web): July 16, 2004
Copyright © 2004 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.

, maruoka@kuchem.kyoto-u.ac.jp

Abstract

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A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention of an unfavorable yet inevitable retro aldol process involving the chiral catalyst. On the basis of this information, a reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-β-hydroxy-α-amino esters almost exclusively in an essentially optically pure form.

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History

  • Published In Issue August 11, 2004
  • Received February 29, 2004

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