Synthesis of Planar-Chiral [2.2]Paracyclophane-Based Oxazole-Pyrimidine Ligands and Application in Nickel-Catalyzed 1,2-Reduction of α,β-Unsaturated Ketones

The planar-chiral ligands have been widely applied as a class of unique and significant ligands in asymmetric catalysis. Among them, chiral [2.2]paracycyclophane has emerged as a privileged type of planar-chiral framework and has been utilized as an important toolbox due to their structural stability. Herein, we design and synthesize [2.2]paracyclophane-derived oxazole-pyrimidine ligands (abberviated as PYMCOX). These N,N-ligands with stable properties, rigid structure and large steric hindrance performed successfully in nickel-catalyzed asymmetric 1,2-reduction of alpha,beta-unsaturated ketones, affording the chiral allylic alcohols with up to 99% yield and 99% ee. Meanwhile, this reduction reaction could be conducted on gram-scale without loss of activity and enantioselectivity, and the chiral ligand could be conveniently recovered with high yield.