NEW PYRIDINO-18-CROWN-6 LIGANDS CONTAINING 2 METHYL, 2 TERT-BUTYL, OR2 ALLYL SUBSTITUENTS ON CHIRAL POSITIONS NEXT TO THE PYRIDINE RING

Chiral 2,16-diallyl-, 2,16-dimethyl-, and 2,16-di-tert-butylpyridino-1 8-crown-6 Ligands have been. prepared by treating the appropriate chir al alpha,alpha'-disubstituted pyridinedimethanol with tetraethylene gl ycol 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 enan tiomers 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 l og K values indicate that these chiral pyridino-18-crown-6 ligands hav e high complexing abilities and some enantiomeric recognition for the chiral organic ammonium perchlorates. The H-1 NMR titration experiment s also show that the phenyl ring of the guest PhEt is approximately pa rallel to the pyridine ring in the chiral diallyl- and dimethyl-substi tuted Ligand complexes with chiral PhEt and the phenyl ring is perpend icular to the pyridine ring in the chiral di-tert-butyl-substituted li gand complex with PhEt. These results were supported by MM2 calculatio ns.