Selective mono- and difluorination of enolates

Fe(III)/NaBH4-Mediated Free Radical Hydrofluorination of Unactivated Alkenes

“…In contrast, the reaction of 6 provided the cyclized products 7 and 8 , inconsistent with an ionic mechanism and further supportive of free radical intermediates generated under these reaction conditions. 19 It is not yet clear whether the reaction involves generation of an initiating Fe–H and its unusual Markovnikov migratory insertion onto the alkene followed by subsequent homolytic cleavage of the resulting C–Fe bond for alkyl radical generation, or whether an Fe–H or oxidized borane/borohydride (e.g., BH 3 ·/BH 4 ·) simply serve as an initiating hydrogen atom donor.…”

Metal-Catalyzed Decarboxylative Fluoroalkylation Reactions

“…Thus, convergent and functional group tolerant strategies for forming these substructures can enable access to the next generation of biological probes and therapeutic candidates. Currently, the most common strategies for creating α,α-difluoroketones involve non-convergent functional group interconversions, such as electrophilic fluorination 15 and deoxyfluorination, 14a,16 that require harsh and/or oxidizing fluorinating reagents. Alternatively, Lewis acid-assisted alkylation of α,α-difluoroenoxysilanes can generate α-functionalized products, but only two groups have exploited this transformation that uses stoichiometric metals.…”

Selectfluor: Mechanistic Insight and Applications

“…Differding and coworkers were the first to use radical clocks to monitor the reaction for the presence of intermediate radicals. [73,74] Their experiment was based on the following logic: If the potassium enolate 25 a were to react in an SET process, the resulting radical 25 b would undergo cyclization to the radical 25 c (Scheme 29). The recombination of 25 c and atomic fluorine would produce some amount of 26 c and 26 d, thus proving the existence of radicals in the reaction.…”

“…[79] Selectfluor and the other compounds of this general class are the only electrophilic fluorination reagents for which no clear evidence has been found for the intermediacy of radical Table 10: Yields of products (in %) from reactions of fluorinating reagents with 25 a (see Scheme 29). [73,74] [ 10] intermediates. The DesMarteau reagent (2, Scheme 2) is inhibited by p-dinitrobenzene, [12] an efficient electron-transfer quencher, and N-fluoropyridinium reagents display CT bands indicative of SET, as described previously.…”