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Stereomutations of Conformational Atropisomers of Hindered 1,2‐Diaryltetrahydropyrimidines
Author(s) -
Garcia M. Beatriz,
Grilli Stefano,
Lunazzi Lodovico,
Mazzanti Andrea,
Orelli Liliana R.
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200212)2002:23<4018::aid-ejoc4018>3.0.co;2-1
Subject(s) - atropisomer , chemistry , diastereomer , stereocenter , substituent , conformational isomerism , ring flip , enantiomer , stereochemistry , nuclear magnetic resonance spectroscopy , population , nmr spectra database , ring (chemistry) , crystallography , spectral line , molecule , organic chemistry , enantioselective synthesis , catalysis , physics , demography , astronomy , sociology
The barriers required to interconvert the conformational enantiomers (atropisomers) of three 2‐( o ‐halophenyl)‐1‐mesityl‐1,4,5,6‐tetrahydropyrimidines (the ortho ‐halogen substituents being I, Br, Cl) have been measured by low‐temperature 1 H NMR spectroscopy. In addition, the barrier for the inversion of the heterocyclic six‐membered ring has been determined by monitoring the 13 C NMR spectra at even lower temperatures. When the mesityl substituent is replaced by a 2,3‐dimethylphenyl group, two stereogenic axes are created, generating two diastereomeric conformers. These were identified by low‐temperature NMR as existing in a 10:1 population ratio, with a 11.5 kcal·mol −1 interconversion barrier. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)