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Stereoselective synthesis of alpha,alpha-chlorofluoro carbonyl compounds leading to the construction of fluorinated chiral quaternary carbon centers.

The preparation of fluorine-containing organic molecules has attracted considerable attention in the field of pharmaceutical and agricultural chemistry.[1] One of the most challenging synthetic operations used to access these molecules is the stereoselective construction of a fluorinated chiral carbon center.[2] Various stereoselective electrophilic fluorination reagents have been developed for this purpose.[3] Following a study by Hintermann and Togni,[4a] efficient catalytic asymmetric fluorination reactions of β-ketoesters have been reported.[4b, e] Organocatalytic enantioselective α-fluorination reactions of aldehydes have also been successfully realized.[5] Although the field of asymmetric α-fluorination is progressing steadily, a flexible route for the stereoselective construction of fluorinated quaternary carbon centers is still required. We propose the synthesis of optically active α,α-chlorofluoro carbonyl compounds, which can be stereoselectively converted into various chiral molecules with a fluorinated quaternary carbon by nucleophilic substitution (Scheme 1). Surprisingly little attention has been given to the synthesis of optically active α,α-chlorofluoro carbonyl compounds[6] or their selective transformation.[7] Herein, we disclose the first enantioselective synthesis of α,α-chlorofluoro carbonyl compounds from simple aldehydes or ketones, and their subsequent transformation into a variety of optically active molecules in which the fluorinated quaternary carbon center is adjacent to the carbonyl group.