New N-Heterocyclic Carbene Ligand and Its Application in Asymmetric Nickel-Catalyzed Aldehyde/Alkyne Reductive Couplings

A new chiral N-heterocyclic carbene ligand has been prepared and examined in nickel-catalyzed, asymmetric reductive couplings of aldehydes and alkynes. In comparison with related structures that have been largely examined in asymmetric ring-closing metathesis reactions, the new ligand provides superior yields and enantioselectivities in the nickel-catalyzed reductive couplings. The scope of asymmetric couplings in intermolecular variants as well as a 14-membered macrocyclization is illustrated.