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

A simple C-2-symmetric chiral bisoxazoline is demonstrated to use hydrogen bonding to catalyze an important family of aldol reactions of trifluoroacetaldehyde hemiacetals with various beta-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 organo catalytic processes.