Enantiomeric recognition and separation of chiral organic ammonium salts by chiral pyridino-18-crown-6 ligands

Optically pure allyloxy and dimethyl-substituted pyridino-18-crown-6 (8) was attached to silica gel by the following reactions. 4-Allyloxy-2,6-pyridinedimethyl ditosylate (23) was first prepared from chelidamic acid. Ditosylate 23 was treated with (S,S)-dimethyl-substituted tetraethylene glycol to form 8. Ligand 8 was treated with triethoxysilane using a platinum catalyst. The resulting chiral crown-substituted triethoxysilane 32 was reacted with silica gel in toluene at 90 C to attach the crown to silica gel. Preliminary results of the separation of [α-(1-naphthyl)ethyl]ammonium perchlorate into its (R) and (S) forms using the bound chiral crown with acetone/methanol (7/3) (v/v) as the eluant are reported. The preparation of chiral dimethyl(allyloxyphenyl)pyridino-18-crown-6 (9) that could be attached to silica gel on the side opposite to the pyridine ring is also reported.