Conformational arm-wrestling: battles for stereochemical control in benzamides bearing matched and mismatched chiral 2- and 6-substituents.
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.
Clayden
Jonathan
J
School of Chemistry, University of Manchester, Oxford Road, Manchester, UKM13 9PL. clayden@man.ac.uk
Foricher
Yann J Y
YJ
Helliwell
Madeleine
M
Johnson
Paul
P
Mitjans
David
D
Vinader
Victoria
V
D000447:Aldehydes / Q000138:chemical synthesis / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D001549:Benzamides / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004809:Ephedrine / Q000737:chemistry; D048288:Imidazolines / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010080:Oxazoles / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D012451:Safrole / Q000031:analogs & derivatives / Q000737:chemistry; D013237:Stereoisomerism; D014297:Trimethylsilyl Compounds / Q000737:chemistry
D000447:Aldehydes; D000588:Amines; D001549:Benzamides; D048288:Imidazolines; D010080:Oxazoles; D014297:Trimethylsilyl Compounds; C064210:oxazolidine; D011392:Proline; D004809:Ephedrine; D012451:Safrole; C005746:sulfoxide