Chelation-induced axially chiral palladium complex system with tetraoxazoline ligands for highly enantioselective Wacker-type cyclization.

A new family of chelation-induced axially chiral palladium complexes by using biphenyl ligands 2 with four identical chiral oxazoline groups at four ortho positions has been developed. Although there is no axial chirality in ligands 2 due to the molecular symmetry, when they chelated with one or two palladium ions, the axial chirality could be induced by destroying the molecular symmetry. Significantly, only one diastereomeric metal complex with (S)-axial configuration was produced during the chelation-induced process. The chelation-induced axially chiral catalytic system, 2c-Pd(CF3COO)2 (1:1 molar ratio), showed excellent catalytic activities and enantioselectivities in the Wacker-type cyclization of allylphenols with up to 99% ee.