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J Am Chem Soc. 2008 Nov 12;130(45):14984-6. doi: 10.1021/ja806431d. Epub 2008 Oct 21.

Chiral anion-mediated asymmetric ring opening of meso-aziridinium and episulfonium ions.

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1
Department of Chemistry, University of California, Berkeley, California 94720, USA.

Abstract

Reactions proceeding through cationic intermediates that lack a Lewis or Brønsted basic site present a challenge for traditional asymmetric catalysis based on chiral metals or organocatalysts. We present an enantioselective ring opening of tetrasubstituted meso-aziridinium ions with alcohol nucleophiles proceeding through a chiral ion pair with a binaphthol-phosphate anion. The reaction is initiated by silver-induced ring closure of beta-chloroamines using the Ag salt of the chiral anion as in situ generated catalyst. Use of insoluble Ag2CO3 as silver source is essential to obtain high enantioselectivity; we believe the chiral phosphate acts as a "chiral anion phase transfer catalyst" to bring silver ion into the organic phase. The chiral anion concept can also be extended to the related asymmetric opening of meso-episulfonium ions generated by protonation of trichloroacetimidates vicinal to sulfides.

PMID:
18937464
DOI:
10.1021/ja806431d
[Indexed for MEDLINE]
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