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Synfacts 2005(0): 0044-0044  
DOI: 10.1055/s-2005-869913
Metal-Catalyzed Asymmetric Synthesis and Stereoselective Reactions
© Georg Thieme Verlag Stuttgart · New York

Molecular Weight Induced Enantioreversal in Sharpless Asymmetric Epoxidation

Contributor(s): Hisashi Yamamoto, Matthew Boxer
N. N. Reed, T. J. Dickerson, G. E. B oldt, K. D. Janda*
The Scripps Research Institute, La Jolla, USA
Enantioreversal in the Sharpless Asymmetric Epoxidation Reaction Controlled by the Molecular Weight of a Covalently Appended Achiral Polymer
J. Org. Chem.  2005,  70:  1728-1731  
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Publication History

Publication Date:
20 July 2005 (online)

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Key words

asymmetric epoxidation - enantioreversal - polymers

Significance

The molecular weight of the poly(ethylene glycol) monomethyl ether (MPEG) can reverse the enantioselectivity for Sharpless epoxidation. A relatively narrow molecular weight range of 800 is sufficient to provide the enantioreversal.

Comment

While the Sharpless asymmetric epoxidation is one of the most powerful synthetic tools, this finding stands to expand on this reaction. So far, various mechanistic investigations are reported for this important transformation. This paper provides completely new insights for the mechanism. The observed enantioreversal was proposed to occur as a result of 2:1 titanium-ligand complex, as opposed to the 2:2 titanium-ligand complex of normal Sharpless asymmetric epoxidation.

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