C2-symmetric chiral bis(oxazoline) ligands in asymmetric catalysis

This review covers the history of box ligands since their introduction in 1991 by Corey and Evans to the spring of 2005. Box ligands are synthesized by the construction of the oxazolidine rings, the substitution of two hydrogen atoms with two identical groups on the spacer of a preformed box and the manipulations of either the chiral groups on the oxazoline rings (C1) or the groups on the spacer (C2). The capacity of the box's to behave as chiral ligands in the formation first of complexes with inorganic salts and then of reaction complexes makes these heterocyclic derivatives a precious source of catalysts whose versatility has been demonstrated in a number of catalytic asymmetric syntheses.