The intramolecular salt effect in chiral auxiliaries. Enhanced diastereoselectivity in a nitrile oxide cycloaddition via rational transition state stabilization

The use of ion pairs to control a nitrile oxide cycloaddition is demonstrated. A chiral phenylmaleimide derivative bearing an ionic group and an associated counterion provides enhanced selectivity in the cycloaddition of benzonitrile oxide. The intramolecular salt effect controls the orientation of the 1,3-dipolar reagent. The nature of the solvent is shown to be relevant in the selectivity of the reaction.