Recognition by New Symmetrically Substituted Chiral Diphenyl-and Di-tert-butylpyridino-18-crown-6 and Asymmetrically Substituted Chiral Dimethylpyridino-18-crown-6 Ligands of the Enantiomers of Various Organic Ammonium Perchlorates

摘要

Three new chiral pyridino-18-crown-6 ligands have been prepared. These ligandscontain either two phenyl, two tert-butyl, or two methyl substituents on chiral macroring carbon atoms. The chiral di-tert-butyl-substituted diester crown analogue was also prepared. The starting chiral di-tert-butyl-substituted tetraethylene glycol needed to prepared the two di-tert-butyl-substituted crowns was obtained from chiral tert-butyl-1,2-ethanediol, which was resolved from its bis(hydrogen phthalate) brucine salt. A high degree of chiral recognition in CD2CI2 of the enantiomers of ALPHA(1-NAPTHTHYLammonium perchlorate (NapEt) was shown by the diphenyl-and di-tert-butyl-substituted crowns as measured by differences in the free energy of activation values determined by temperature-dependent 1H NMR spectroscopy. The diphenyl-and di-tert-butyl-substituted crowns also exhibited high chiral recognition for the enantiomers of NapEt and other chiral organic ammonium salts in methanol and methanol-chloroform mixtures as shown by a large difference in the log K values determined by a direct 1H NMR technique.