A family of chiral 4,4′-BOX ligands has been recently developed in the NUI group.1 These ligands, based on arabinol and xylitol scaffolds, have a chiral
backbone and, in some cases, chiral sidearms too. The main difference with the traditional 2,2’-BOX ligands is that the stereogenic atoms of the chiral
backbone are placed at the central bridge, instead of at the carbon atoms bearing the substituents (see Scheme below). These new ligands have been
applied as copper complexes to the asymmetric cyclopropanation reaction of styrene with ethyl diazoacetate. Enantioselectivities of up to 70% were
obtained. The multiple chiral centers in the ligand resulted in a substantial additive effect, which is not easy to rationalize.