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 tint 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 degrees C to attach the crown to silica gel. Preliminary results of the separation of [alpha-(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.