Enantioselective reactions with trisoxazolines

A series of homochiral and heterochiral trisoxazolines were synthesized by a direct or modular approach. These trisoxazoline-derived metal complexes function as enantioselective Lewis acid catalysts for Friedel-Crafts, Kinugasa, 1,3-dipolar cycloaddition, cyclopropanation, and Diels-Alder reaction. In these catalyzed processes, trisoxazoline-derived chiral metal complexes exhibit excellent reactivity, good to excellent selectivity, and high tolerance towards moisture. In some cases, the reaction selectivity could be easily tuned by changing reaction parameters such as temperature and solvent. In these reactions, trisoxazoline-derived chiral catalysts achieved better enantiofacial control, higher catalytic activity, and higher tolerance of impurities than the corresponding bisoxazoline derived ones. In light of these features, it is assumed that the coordination of the oxazoline sidearm to the metal center improves the stability, activity, and chiral environment of the catalyst.