Enantioselective protonation of monofluorinated silyl enol ethers by cooperative cation‐binding catalysis

Herein, we report on the successful enantioselective protonation of a range of silyl enol ethers of cyclic ketones with labile chiral secondary CF bonds by using Song's chiral oligoethylene glycols (oligoEGs) as cation‐binding catalysts in the presence of CsF and a proton source. Highly enantioselective protonations of an array of silyl enol ethers of α‐fluoro tetralones and α‐fluoro benzosuberones were achieved, producing corresponding chiral α‐secondary α‐fluoro cyclic ketones in full conversion, with up to 96% ee. Furthermore, this protocol has successfully been extended to access chiral α‐choro and α‐bromo cyclic ketones. This successful in situ generated fluoride ion‐based stereoselective catalysis was driven by creating a densely confined chiral cage from the chiral catalyst, substrate, and CsF. Herein, we report highly enantioselective organocatalytic protonation of a range of monofluorinated silyl enol ethers of cyclic ketones by using Song's chiral oligoethylene glycols as cation‐binding catalysts in the presence of CsF and a proton source, producing chiral α‐secondary α‐fluoro cyclic ketones in excellent yields, with up to 96% ee. This protocol was also successfully extended to the synthesis of chiral α‐choro and α‐bromo cyclic ketones.