Visible Light Promoted 2‐Bromotetrafluoroethylation of Nitrones

Abstract

A reaction of nitrones with 1,2-dibromotetrafluoroethane affording bromodifluoroethylsubstituted hydroxylamines is described. The process is performed in the presence of a ruthenium photocatalyst and ascorbic acid as a stoichiometric reducing agent and is mediated by blue light irradiation. The fluroalkylation products can undergo chemoselective transformations involving either NÀO or CÀBr bonds furnishing various tetrafluorinated compounds.

Synthesis of tetrafluorinated piperidines from nitrones via a visible-light-promoted annelation reaction

“…In case of 3n there was some unidentified side product formed under the standard conditions. In the previous research on the radical addition to nitrones we sometimes encountered a fluoroalkylation of the aromatic rings, if an excess of the fluorinated alkyl iodide was used [22][23][24]. This prompted us to attempt the reaction with an equimolar amount of the iodide 2b, which resulted in a cleaner process.…”

“…Recently, we disclosed a photoredox method for the reductive radical fluoroalkylation of nitrones [22][23][24]. We have also eval- uated the construction of fluorinated tetrahydroisoquinoline structures starting from nitrones, but this required four consecutive reactions with different conditions and chromatographic separation at each step [25] (Scheme 1).…”

N-(Hetero)arylations with Metalated (Hetero)aryls: Recent Advances in First-Row Transition-Metal-Mediated Cross-Couplings

“…In 2018, Dilman et al showed that fluorides containing hydroxylamines can be obtained by addition of a radical derived from 1,2-dibromotetrafluoroethane to nitrones under photocatalytic conditions. 67 The resulting hydroxylamine can be benzoylated and then used as a substrate in a coppercatalyzed electrophilic cross-coupling with phenylaluminum reagent (prepared in situ from phenylmagnesium chloride and Et 2 AlCl, Scheme 52).…”

Boron Chelates Derived from N-Acylhydrazones as Radical Acceptors: Photocatalyzed Coupling of Hydrazones with Carboxylic Acids

“…Radical addition at the CN bond is an important process, serving as a key step in many synthetic methods. , These reactions have become even more popular due to the advent of photoredox catalysis, which provided convenient ways for the generation of free radicals. − Indeed, photocatalytic reactions of azomethines with alkyl halides, − redox active esters, − sulfinates and sulfides, the C–H bond, − borates, and siliconates have been described . Herein we report that difluoroboryl complexes 2 can serve as efficient acceptors of alkyl radicals (Scheme ).…”