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Conformational arm-wrestling: battles for stereochemical control in benzamides bearing matched and mismatched chiral 2- and 6-substituents.

Authors
  • Clayden, Jonathan
  • Foricher, Yann J Y
  • Helliwell, Madeleine
  • Johnson, Paul
  • Mitjans, David
  • Vinader, Victoria
Type
Published Article
Journal
Organic & biomolecular chemistry
Publication Date
Feb 07, 2006
Volume
4
Issue
3
Pages
444–454
Identifiers
PMID: 16446801
Source
Medline
License
Unknown

Abstract

The orientation of a tertiary amide group adjacent to an aromatic ring may be governed by the stereochemistry of an adjacent chiral substituent. With a chiral substituent in both ortho positions, matched/mismatched pairs of isomers result. Evidence for matched stereochemistry is provided by the clean NMR spectra of single conformers, while mismatching gives poor or unexpected selectivities in the formation of chiral substituents, or mixtures of amide conformers. Attempts to use the match-mismatch effect to select for racemic pairs of enantiomeric substituents, and hence develop a "racemate-sequestering" reagent, are described, along with the use of "matching" to scavenge a single enantiomer of a diamine from material of incomplete enantiomeric purity.

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