1-(+)-Dehydroabietylimidazolium Salts as Enantiomer Discriminators for NMR Spectroscopy

Nine new (+)-dehydroabietylimidazolium salts were synthesised and studied as chiral solvating agents for several different racemic aromatic and non-aromatic carboxylate salts. These cationic chiral solvating agents resolve racemic ionic analytes better than non-ionic ones. Bis(dehydroabietylimidazolium) bis(trifluoromethanesulfonimide) gave the best discrimination for the enantiomers of carboxylate salts. Its resolution behaviour was studied by an NMR titration experiment, which indicated 1 : 1 complexation with the racemic analyte. The dehydroabietylimidazolium salts were also useful in enantiomeric excess (ee) determinations, and for the recognition of chirality of racemic aromatic and non-aromatic α-substituted carboxylic acids.