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Atropisomerism in the 2-arylimino-N-(2-hydroxyphenyl)thiazoline series: influence of hydrogen bonding on the racemization process.

Authors
  • Roussel, Christian
  • Vanthuyne, Nicolas
  • Bouchekara, Mohamed
  • Djafri, Ayada
  • Elguero, José
  • Alkorta, Ibon
Type
Published Article
Journal
The Journal of Organic Chemistry
Publisher
American Chemical Society
Publication Date
Jan 18, 2008
Volume
73
Issue
2
Pages
403–411
Identifiers
PMID: 18088138
Source
Medline
License
Unknown

Abstract

A series of original atropisomeric iminothiazolines 1 in which X = OH or (and) Y = OH were prepared from the corresponding methoxy precursors. The resolution of the atropisomeric enantiomers on chiral support is reported, and the barriers to enantiomerization are given. These barriers were determined either by off-line racemization studies or by treatment of the plateau-shape chromatogram during chromatography on chiral support. When X = OH, the barriers are quite low due to the development of a hydrogen bond between the proton of the OH group and the nitrogen of the imino group. For these compounds, plateau shape chromatograms were obtained during HPLC on chiral support. DFT calculations confirmed the occurrence of hydrogen bonding all along the rotation process and produced calculated barriers in close agreement with the experimental data. Compound 1i (OH, OH) in which both X and Y are hydroxy groups was particularly easy to prepare by demethylation with BBr3 of the dimethoxy precursor. Since the above-mentioned precursor is readily available from N,N'-bis(2-methoxyphenyl)thiourea and 1-chloropropan-2-one, 1i (OH, OH) is a good candidate for further functionalization. Atropisomerism in a 12-membered bridged bisether prepared from 1i (OH, OH) is reported as an illustrating example.

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