In combination with various Lewis acids, forms a number of catalyst systems for asymmetric reactions including Diels-Alder, allylation and aldol reactions: Angew. Chem. Int. Ed., 30, 455 (1991). For use in enantioselective catalytic Diels-Alder reactions, see: J. Am. Chem. Soc., 111, 5493 (1989); Org. Synth. Coll., 9, 67 (1998).