A Highly Regio- and Stereoselective Synthesis of α‑Fluorinated Imides via Fluorination of Chiral Enamides

A highly π-facial selective
and regioselective fluorination
of chiral enamides is described. The reaction involves an enantioselective
fluorination exclusively at the electron-rich enamide olefin with
N–F reagents such as Selectfluor and N-fluoro-benzene­sulfonimide
[NFSI] accompanied by trapping of the β-fluoro-iminium cationic
intermediate with water. The resulting N,O-hemiacetal
could be oxidized using Dess-Martin periodinane, leading to an asymmetric
sequence for syntheses of chiral α-fluoro-imides and optically
enriched α-fluoro-ketones.