Asymmetric Direct α-Hydroxylation of β-Oxo Esters by Phase-Transfer Catalysis Using Chiral Quaternary Ammonium Salts

The first enantioselective direct alpha-hydroxylation of beta-oxo esters was developed by using phase-transfer catalysis. 1-Indanone-derived 1-adamantyl (1-Ad) beta-oxo esters, in the presence of commercially available cumyl hydroperoxide and a cinchonine-based ammonium salt, resulted in the corresponding products with 69-91% yield and 65-74% ee. The reaction had also been successfully scaled-up to a gram quantity, and a similar yield was obtained without loss of the enantioselectivity.