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

Article abstract of DOI:10.1021/jo00010a028

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 <α-(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 avtivation (ΔG_c^*) 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.