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

Abstract

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.

Current Advances in Meerwein-type Radical Alkene Functionalizations

“…2b Based on this pioneering study, an improved carbofluorination was recently developed, in which the addition of anisole led to a reduced formation of side products (Scheme 21). 71 Scheme 21 Selectfluor-mediated fluoroarylation of non-activated alkenes 71 Similar to the earlier study, Selectfluor (50) serves as an oxidant to generate aryl radicals from phenylhydrazines 48, while phenyldiazenes XXXVIII occur as intermediates. In addition, Selectfluor enables fluorine atom transfer 72 to the alkyl radicals II leading to the carbofluorination products 49 as well as the Selectfluor-derived radical dication XXX-IX.…”

Visible‐Light‐Assisted Gold‐Catalyzed Fluoroarylation of Allenoates

“…By judiciously integrating ease of carbon radical generation, through either transition‐metal catalysis or photocatalysis, with productive fluorination techniques, considerable progress has been attained in the arena of fluoroalkylation reactions,– although most of the reported methods still show a heavy reliance on electrophilic fluorination reagents . However, the fluoroarylation counterpart is comparatively underdeveloped, probably due to a relative lack of efficient avenues for the easy production of aryl radical intermediates –…”

The Morita–Baylis–Hillman reaction for non-electron-deficient olefins enabled by photoredox catalysis

“…Furthermore, several recent reports also suggested that a tertiary aminium radical derived from Selectuor could also undergo the addition to olens for the catalytic oxidative functionalization of alkenes. [45][46][47] Thus, the quinuclidinium radical intermediate derived from quinuclidine as a tertiary amine should also perform the addition process with olens. In order to detect this mechanistic paradigm, a radical probe experiment was designed.…”