A prominent class of phase transfer catalysts are cinchona alkaloids and their derivatives. Structurally, this class of alkaloids has two distinct subunits where the C9 position functions as a molecular hinge with internal rotations around the C8-C9 (t1) and C9-C4' (t2) bonds giving rise to four low energy conformers. From the perspective of designing new catalysts with improved performance, a way to control this internal rotation is desirable. By substituting the C9 carbinol centre by a configurationally defined fluorine, a fluorine-ammonium gauche effect encodes for two out of the four possible conformers partially solving the problem of conformational dynamics. The merit of this approach was displayed in the application of this novel class of chiral, fluorinated cinchonium salts for the enantioselective, electrophilic fluorination of �-ketoesters. Furthermore, X-Ray crystallography, solution phase conformational analysis and NMR studies were successfully undertaken to gain insight into the catalysts mode of enantioinduction. 

Designing fluorinated cinchona alkaloids for enantioselective catalysis: Controlling internal rotation by a fluorine-ammonium ion Gauche effect (?NCCF)

243rd National Meeting (2012)

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