Cinchona alkaloids-derived chiral ligands for Mn-catalyzed ATH of ketones: Improvement of enantioselectivity through π-π stacking-induced hydrogen bond

Abstract

Inexpensive and readily available manganese metals combined with novel chiral ligands derived from cinchona alkaloids catalyzed the asymmetric transfer hydrogenation of aromatic ketones. All tested aromatic ketones were highly enantioselectively converted to the corresponding chiral alcohols, obtaining up to 99.4% ee. Based on control experiments and density functional theory (DFT) calculations, a plausible mechanism was discussed. During catalysis, π-π stacking in the catalyst promoted the formation of hydrogen bonds between the substrate and the catalyst, and the stronger the stacking, the stronger the hydrogen bonds, while stronger hydrogen bonds were more favourable for achieving high enantioselectivity in manganese-catalyzed asymmetric transfer hydrogenation.