Design of Rigid Chiral Bipyridine-2No Tetradentate Ligands: Application in Asymmetric Catalysis

Expanding the chemical space of chiral N-oxides and chiral 2,2 '-bipyridine ligands is in great demand in asymmetric catalysis. Herein, a new class of C2-symmetric bipyridine-tertiary amine-derived chiral N,N '-dioxide (bipyridine-2NO) ligands, featuring structural fine-tunability, chemical stability, and ready accessibility, was rationally designed and developed, and the effectiveness was demonstrated in a Ni(ii)-catalyzed asymmetric Michael-type Friedel-Crafts alkylation reaction of indoles and beta,gamma-unsaturated alpha-keto esters. Excellent yields (up to 92%) and high enantioselectivities (up to 99% ee) were obtained for a wide range of substrates under mild conditions. These results demonstrated the promising potential of the chiral bipyridine-2NO scaffold as an efficient type of tetradentate ligand. A new class of chiral bipyridine-2NO ligands, which incorporate the advantages of both the bipyridine skeleton and the pyrroloimidazolone-based N-oxide moiety, was developed.