Asymmetric Direct α-Hydroxylation of β-Oxo Esters Catalyzed by Chiral Quaternary Ammonium Salts Derived from Cinchona Alkaloids

Cinchona alkaloid-derived chiral quaternary ammonium organocatalysts were developed. The catalyst with a bulky 1-adamantoyl group at the C-9 position promoted the enantioselective alpha-hydroxylation of beta-oxo esters and resulted in the corresponding products in 35-95% yields and 58-90% ee. The reaction was successfully scaled to a gram-quantity scale with a similar yield without loss of enantioselectivity.