Catalytic asymmetric protonation of achiral lithium enolates mediated by a chiral tetraamine ligand with water as a proton source

Catalytic protonation of achiral lithium enolates (derived from 2-substituted-1-tetralones), mediated by a chiral tetraamine ligand [(R,R)-N,N′-bis[1-phenyl-2-(1-piperidinyl)ethyl]-1,3-propanediamine (0.10 equiv.)], was achieved with high enantioselectivity (up to 93% ee) by using water (10% aqueous citric acid) as a proton source. A possible mechanism of highly efficient catalytic turnover of the chiral tetraamine ligand is discussed.