Atropisomeric bisoxazoline ligands with a bridge across the 5,5′-position of biphenyl for asymmetric catalysis

A new family of atropisomeric bisoxazoline ligands 2 with a bridge across the 5,5′-position of biphenyl has been developed. The axial chirality of this type of ligands can be retained by macro-ring strain produced by 5,5′-linkage of biphenyls even without 6,6′-substituents on biphenyls. The Pd(II)-2d complex as catalyst showed high catalytic activity and enantioselectivity for asymmetric Wacker-type cyclization of allylphenols.