Asymmetric Counteranion‐Directed Catalysis

Exceedingly high enantioselectivity in a catalytic reaction can be realized even when the chirality resides only in the counteranion of the catalyst. A salt (1) composed of an achiral ammonium cation and a chiral phosphate counteranion catalyzes asymmetric transfer hydrogenations of aromatic and aliphatic α,β-unsaturated aldehydes with a Hantzsch ester in excellent enantioselectivities (see scheme).