Py-2NO ligand enabled Ni(ii)-catalyzed asymmetric Michael addition reaction of indoles with β,γ-unsaturated α-keto esters

Abstract

The development of chiral ligands to fine-tune stereocontrol in asymmetric catalysis is of great demand. To diversify the Py-2NO ligand library recently developed by our group, herein, we synthesized six new Py-2NO ligands, determined the absolute configuration via X-ray crystallographic study of ligand L1g, and applied these ligands in the Ni(II)-catalyzed asymmetric Michael addition reaction of indoles and β,γ-unsaturated α-keto esters. Excellent yields (up to 93%) and high enantioselectivities (up to 99% ee) were obtained for a wide range of substrates under mild conditions. In addition, we discovered the presence of axial chirality in the C(aryl)–N(amide) bond in the tertiary amine-derived N-oxide product via X-ray crystallographic study. Owing to the intriguing characteristics of atropisomerism, we believe that this reaction will add an important member to the axial chiral family.