Linear and branched aldehydes are asymmetrically α‐fluorinated with L‐proline‐ and pyrrolidine‐based organocatalysts (see scheme; NFSi: N‐fluorobenzenesulfonamide). In the first case, yields and enantioselectivities were high; in the second, the yields remained high and the enantioselectivities were moderate. Significantly, linear aldehydes were only monofluorinated.

We acknowledge that Drs. Zoe Pikramenou and Peter Glover (University of Birmingham) first prepared and provided a sample of the nonfluorinated Er(tpip) 3 compound for initial studies, though none of the work detailed in this paper has utilized that sample.

A fluorogenic method for the determination of cysteine concentration has been developed.