Asymmetric Morita-Baylis-Hillman reactions catalyzed by chiral Brønsted acids.
Chiral BINOL-derived Brønsted acids catalyze the enantioselective asymmetric Morita-Baylis-Hillman (MBH) reaction of cyclohexenone with aldehydes. The asymmetric MBH reaction requires 2-20 mol % of the chiral Brønsted acid 2e or 2f and triethylphosphine as the nucleophilic promoter. The reaction products are obtained in good yields (39-88%) and high enantioselectivities (67-96% ee). The Brønsted-acid-catalyzed reaction is the first example of a highly enantioselective asymmetric MBH reaction of cyclohexenone with aldehydes.