New Pyridino-18-crown-6 Ligands Containing Two Methyl, Twotert-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 α,α‘-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 (α-phenylethyl)ammonium perchlorate (PhEt) and (α-(1-naphthyl)ethyl)ammonium perchlorate (NapEt) were measured using an 1 H NMR titration method in a CDCl 3 /CD 3 OD (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 1 H 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.