Twisted 9, 10-phenanthrenequinones: Chromatographic enrichment of enantiomers and barriers to racemization

An approach to discriminating 25 commercial chiral stationary phases from structural data sets extracted from a molecular database

“…As steric effects often play a major role in the molecular environment of axial or planar dissymmetrical compounds its not surprising to find on the same side the descriptor CHI. As could be expected from literature trends, the CSPs CTA and OT show a good success for such chiral compounds (Roussel et al, 1988;Mannschreck et al, 1987;Meurer et al, 1985). In the same way, the behaviour of the other CSPs may be summarized as following: -OK and OB located at the neighbourhood of ROR and EST (ether and ester) appear to be CSPs of choice for oxygenated solutes -OA, SPH, OJ have a good affinity for solutes containing an asymmetric centre on a cycle -Derivatization of carboxylic acids in ester is recommended for OA, OB, OK, OJ, SPH, OT, CTA -OA, OB, OK have a very low affinity for basic solutes -OF and OJ show good results in the resolution of basic compounds -PCO and PIO (Pirkle ionic) exhibit good results when carboxylic acids are derived in amides or esters respectively.…”

Twisted Arenes

“…As a result, the torsional angle y is increased to 32.9 . The combination of the buttressing effect and the presence of the two methyl groups at the C1 and C8 positions increases the activation barrier of 9c to 25.1 kcal/mol at 49 C [23,26]. With a sterically hindered tert-butyl group at the C4 position and a methyl group at the C5 position as depicted in 2,4-di-tert-butyl-5,7-dimethylphenanthrene (11), the activation barrier further increases to 26.6 kcal/mol at 80 C [25].…”

“…Overcrowded 4,5-bis(2-pyridyl)phenanthrenes 28a and 28b were prepared from the Diels-Alder reactions between 4a,5a-diazoniapentaphene diperchlorate (26) and ketene acetals 27a and 27b, respectively (Scheme 5) [16]. The X-ray structure Twisted Arenes 37 of 28b shows that each pyridine is intramolecularly hydrogen bonded to the neighboring hydroxyl group, creating a twofold axis of symmetry ( Fig.…”

ESR and ENDOR investigations of phenanthrenesemiquinones

“…anthrenequinone, were separated semipreparatively by liquid chromatography on optically active ~orbents.~ Thermal racemizations of (M)-or (P)-I1 at 50-140°C resulted in free enthalpies of activation of 117-131 kJ mol-', which means that the planar transition state is destabilized by repulsions between the two substituents R and between the two oxygen atoms. 3 The question arises of whether the corresponding semiquinones IIa also differ from species such as Ia which bear no substituents in the 4-and 5-positions. Although ESR spectroscopy has been a successful method for the investigation of various phenanthrenesemiquinones,4 it is normally unable to distinguish enantiomers such as (M)-and (P)-IIa.…”