A New Chiral Brønsted Acid Catalyst

Significance

Yamamoto and Cheon present the new designer chiral Brønsted acid catalyst 1 and its application to the enantioselective protonation of silyl enol ethers. Several new catalysts were tested and it turned out that N-triflyl thiophosphoramides were the most effective catalysts. Using catalyst 1, the catalyst loading can be reduced down to 0.05 mol% without any significant loss in enantioselectivity although the reaction time is longer. A plausible two-step mechanism is suggested.