New pyridino-18-crown-6 ligands containing two methyl, two tert-butyl, or two allyl substituents on chiral positions next to the pyridine ring

Chiral 2,16-diallyl-, 2,16-dimethyl-, and 2,16-di-tert-butylpyridino-18-crown-6 Ligands have been. prepared by treating the appropriate chiral alpha,alpha'-disubstituted pyridinedimethanol with tetraethylene glycol ditosylate in the presence of base. In these reactions, chiral 2:2 dimers (dipyridino-36-crown-12 derivatives) were also obtained. The log K values for the interaction of these chiral ligands with the enantiomers of (alpha-phenylethyl)ammonium perchlorate (PhEt) and (alpha-(1-naphthyl)ethyl)-ammonium perchlorate (NapEt) were measured using an H-1 NMR titration method in a CDCl3/CD3OD (1/1) solvent mixture. The log K values indicate that these chiral pyridino-18-crown-6 ligands have high complexing abilities and some enantiomeric recognition for the chiral organic ammonium perchlorates. The H-1 NMR titration experiments also show that the phenyl ring of the guest PhEt is approximately parallel to the pyridine ring in the chiral diallyl- and dimethyl-substituted Ligand complexes with chiral PhEt and the phenyl ring is perpendicular to the pyridine ring in the chiral di-tert-butyl-substituted ligand complex with PhEt. These results were supported by MM2 calculations.