Radical Carbofluorination of Alkenes with Arylhydrazines and Selectfluor: Additives, Mechanistic Pathways, and Polar Effects

Radical carbofluorination reactions starting from arylhydrazines and nonactivated alkenes, in which the C-F bond is formed through the use of Selectfluor, can be improved through the addition of anisole. Because direct trapping products could be detected only in trace amounts, anisole does primarily act as a reversible scavenger for the highly reactive ammonium radical dication released from Selectfluor in the C-F bond-forming step. As shown for three diverse substitution patterns, the main role of anisole is to prevent, or at least reduce, the undesired addition of the ammonium radical dication to the alkene, which in turn leads to an unfavorable consumption of the arylhydrazine-derived precursors required for carbofluorination. Moreover, besides the remarkable polar effects in radical trapping, this study shows that the Selectfluor-derived nitrogen-centered radical dication may add directly to alkenes, which has not been described so far.