C2-Symmetric Chiral Bisoxazolines as Hydrogen-Bond-Acceptor Catalysts in Enantioselective Aldol Reaction of β-Carbonyl Acids with Trifluoroacetaldehyde Hemiacetals.

A simple C2-symmetric chiral bisoxazoline is demonstrated to use hydrogen bonding to catalyze an important family of aldol reactions of trifluoroacetaldehyde hemiacetals with various β-carbonyl acids. This reaction is highly enantioselective, delivering chiral nonracemic trifluoromethylated alcohols with excellent optical purity and good isolated yields. This concept of relaying chiral information via a chiral hydrogen-bond acceptor should be applicable to a vast number of organocatalytic processes.