Dibenzofuran-4,6-bis(oxazoline) (DBFOX). A novel trans-chelating bis(oxazoline) ligand for asymmetric reactions

The trans-chelating bis(oxazoline) ligand (R,R)-4,6-dibenzofurandiyl-2,2′-bis(4-phenyloxazoline) [(R,R)-DBFOX/Ph] coordinates metal ions to give C₂-symmetric complexes which effectively catalyze a variety of asymmetric reactions. (R,R)-DBFOX/Ph·Ni(ClO₄)₂·3H₂O, whose crystal structure is octahedral with three aqua ligands, can be stored under air for several months without loss of catalytic activity and promotes highly enantioselective reactions even in the presence of excess amounts of water, alcohols, amines, and acids. The complex shows remarkable chiral amplification in asymmetric Diels–Alder (DA) reactions. This review focuses on enantioselective reactions catalyzed by (R,R)-DBFOX/Ph·metal complexes.