RECOGNITION BY NEW SYMMETRICALLY SUBSTITUTED CHIRAL DIPHENYL-BUTYLPYRIDINO-18-CROWN-6 AND DI-TERT-BUTYLPYRIDINO-18-CROWN-6 AND ASYMMETRICALLY SUBSTITUTED CHIRAL DIMETHYLPYRIDINO-18-CROWN-6 LIGANDS OF THE ENANTIOMERS OF VARIOUS ORGANIC AMMONIUM PERCHLORATES

Three new chiral pyridino-18-crown-6 ligands have been prepared. These ligands contain 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 prepare 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 CD2Cl2 of the enantiomers of [alpha-(1-naphthyl)ethyl]ammonium perchlorate (NapEt) was shown by the diphenyl- and di-tert-butyl-substituted crowns as measured by differences in the free energy of activation (DELTA-G(c) double-ended-dagger) values determined by temperature-dependent H-1 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 H-1 NMR technique.