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Tertiary aromatic amides bearing stereogenic centres ortho to the amide group may adopt two diastereoisomeric conformations which interconvert slowly on the NMR timescale at ambient temperature, and are therefore detectable by NMR. Certain classes of stereogenic centre--particularly sulfoxides, ephedrine-derived oxazolidines, and proline-derived imidazolidines--strongly bias the population of the two conformers. We propose a model, supported by molecular mechanics calculations, which rationalises the sense and magnitude of the conformational selectivity attained in terms of the steric and electronic properties of the controlling centre. The control over conformation may be exploited either by trapping the favoured conformer as an atropisomer, or by using it to relay information about the stereochemistry of the controlling centre.

Original publication

DOI

10.1039/b514557k

Type

Journal article

Journal

Org Biomol Chem

Publication Date

07/02/2006

Volume

4

Pages

424 - 443

Keywords

Alkylation, Amides, Crystallography, X-Ray, Ephedrine, Hydroxylation, Kinetics, Magnetic Resonance Spectroscopy, Models, Chemical, Molecular Conformation, Oxazoles, Proline, Stereoisomerism, Sulfur, Thermodynamics