Abstract
Homochiral N-enoylimidazolidin-2-ones 5-8 are readily accessible, practical, and highly diastereoselective dienophiles in dialkylaluminium-promoted Diels-Alder reactions. Acrylate, methacrylate, and (E)-crotonate derivatives bearing ephedrine-based imidazolidin-2-one auxiliaries 1 and 2 undergo rapid, face-selective cycloadditions under mild conditions. High yields of diastereomerically homogeneous products 11-14 are readily obtained by crystallisation or chromatography. The reactivity scope of these systems is extended to less reactive dienes through auxiliary tuning by the application of alternative asparagine-based imidazolidin-2-one auxiliaries 3 and 4.