Issue 19, 2001

Unusual stereoselectivity in the alkylation of pyroglutamate ester urethanes1

Abstract

Previous studies on the alkylation of pyroglutamate ester urethanes have led to a consensus that alkylation at C-4 occurs to give a mixture of diastereoisomers, the major isomer of which usually has the alkyl group trans to the ester group at C-2. We have now discovered that this generalisation is not invariably correct and that, although for SN1-type electrophiles stereoselectivity is in fact trans, SN2-type electrophiles can give the thermodynamically less stable cis compounds as the predominant products. Use of the bulky proton source 2,6-di-tert-butylphenol to quench these reactions yields the cis isomers as the only products in good yield, thus making direct alkylation of pyroglutamic acid derivatives a useful alternative to our hydrogenation approach to these synthons.

Graphical abstract: Unusual stereoselectivity in the alkylation of pyroglutamate ester urethanes1

Supplementary files

Article information

Article type
Paper
Submitted
19 Jul 2001
Accepted
08 Aug 2001
First published
07 Sep 2001

J. Chem. Soc., Perkin Trans. 1, 2001, 2367-2371

Unusual stereoselectivity in the alkylation of pyroglutamate ester urethanes

J. Charrier, J. E. S. Duffy, P. B. Hitchcock and D. W. Young, J. Chem. Soc., Perkin Trans. 1, 2001, 2367 DOI: 10.1039/B106451G

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