Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 16, Issue 9, Pages 2797-2805Publisher
WILEY-BLACKWELL
DOI: 10.1002/chem.200902562
Keywords
chirality; configuration determination; diquats; racemization barriers; resolution
Categories
Funding
- Departement d'Instruction Publique (Geneva)
- Swiss National Science Foundation
- State Secretariat for Education and Research
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Three tricyclic diquats with an eight-membered ring were prepared and shown to be the first configurationally stable derivatives of their kind. Resolution was achieved by using chiral hexacoordinated phosphorus BINPHAT and TRISPHAT anions. The diquat cations were obtained in high diastereo- and enantiomeric purity (ee > 96% in most cases). X-ray diffraction analysis coupled with circular dichroism (CD) measurements allowed a precise determination of the relative and absolute configuration of the salts. The barriers to racemization of these compounds were calculated by using CD time-course measurements at different temperatures, affording Delta G(not equal) values above 25 kcal mol(-1). Derivatives 4a, 4b, and 4c are the first eight-membered-ring derivatives with only three ring constraints to be resolved. This manuscript also reports the first procedure to remove TRISPHAT anions after diastereomeric separation.
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