Isomerization of Hydrofluorocyclopentenes Promoted by Fluoride Anion

The isomerization of hydrofluorocyclopentenes promoted by fluoride anion was investigated. It was found that two processes were responsible for interconversion of the isomers: an allylic syn-addition/elimination of fluoride anion that does not change the mutual positions of hydrogen atoms but is responsible for transfers of fluorine atoms, and a fluoride anion-assisted deprotonation/protonation which does not change the mutual positions of fluorine atoms but is responsible for transfers of hydrogen atoms. In the deprotonation, HF can easily capture excess fluoride anion to form HF2- anion which can probably inhibit the protonation.