Crab-shaped tridentate HoQ-Sulidines as bifunctional anionic ligands: empowering asymmetric addition reactions of indoles with β,γ-unsaturated α-ketoesters

Abstract

Herein, we report a modular one step synthesis of a new series of crab-shaped bipyridine/hydroxyquinoline-based imidazolidine-type ligands, designated Bpy/HoQ-Sulidines. Among these, the tridentate chiral HoQ-Sulidine ligands could serve as the anionic ligands upon deprotonated activation, allowing for the deprotonated oxygen anion as the chelating site for coordination with earth-abundant metal, cooperatively activating both nucleophiles and electrophiles to form a highly enantioselective bifunctional catalyst, exhibiting superior performance in the asymmetric addition reactions of indoles with β,γ-unsaturated α-ketoesters to afford functionalized chiral indole derivatives (up to 92% yield, up to 96% ee). Especially, our work is the first example of utilizing a hydroxyquinoline group as the bidentate chelating unit for the synthesis of C1-symmetric monochiral arm ligands.