Synthesis of Fluoroalkene Dipeptide Isosteres by an Intramolecular Redox Reaction Utilizing N-Heteorocyclic Carbenes (NHCs)

(Z)-Fluoroalkene dipeptide isosteres (FADIs 16) have served as potential dipeptide mimetics possessing the substitution of fluoroalkenes for parent peptide bonds. Previously, we synthesized FADIs by reduction of γ,γ-difluoro-α,β-enoates with organocoppers or SmI₂, which prompted us to use an intramolecular redox reaction mediated by N-heterocyclic carbenes (NHCs) for the preparation of FADIs. Instead of the enoates, γ,γ-difluoro-α,β-enal 20 and γ,γ-difluoro-α,β-enoylsilane 34 were converted to FADIs by an NHC-mediated intramolecular redox reaction, whereby aldehyde components reduced the allylic difluoride component in an S_N2′ manner with accompanying monodefluorination.