Resolution of the first nonracemic diquats.
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 DeltaG(++) 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.
Vachon
Jérôme
J
Organic Chemistry Department, University of Geneva, quai Ernest Ansermet 30, 1211 Genève 4, Switzerland.
Bernardinelli
Gérald
G
Lacour
Jérôme
J