Metathesis Mechanism of Zinc-Catalyzed Fluorination of Alkenes with Hypervalent Fluoroiodine

Density functional theory calculations are used to unravel the mechanism of the Zn-catalyzed fluorocyclization reaction of alkenes using fluoro-benziodoxole reagent. In the initial step Zn coordinates to the fluorine atom of the fluoro-benziodoxole reagent. An important activation step for the fluorination involves Zn-mediated isomerization of the benziodoxole reagent. The activation is followed by a metathesis step to form the C–F bond and a nucleophilic substitution, closing the ring to yield the final aminofluorination product. This mechanism has feasible energy barriers and accounts for the observed selectivity outcome. An alternative mechanism involving an iodocyclopropylium cation intermediate is shown to be associated with high energies.