Heterogeneous Photoinduced Homolytic Aromatic Substitution of Electron‐Rich Arenes with Perfluoroalkyl Groups in Water and Aqueous Media – A Radical‐Ion Reaction

Abstract

The photoinduced electron transfer (PET) substitution reaction of electron‐rich aromatic nuclei with perfluoroalkyl Rf groups was carried out in water or aqueous mixtures to render substitution products resulting from replacement of aromatic H atoms with the Rf moiety in good yields (57–88 %). Some mechanistic aspects are discussed, supporting the notion of a PET reaction leading to a classical radical homolytic aromatic substitution (HAS) followed by an electron transfer (ET) and then a proton transfer (PT) sequence. A radical mechanism superimposed on a redox process is proposed to account for product formation. Evidence for the radical cation species (as an initiation event) generated from electron‐rich arenes in the presence of perfluoroalkyl halides is provided by the UV/Vis transient spectra obtained by Nanosecond Laser Flash Photolysis techniques.

A new era for homolytic aromatic substitution: replacing Bu3SnH with efficient light-induced chain reactions

“…39,40 For example, N,N-dimethyl-1-naphthylamine 5 is converted to 4-substitution product 6 in water using a medium pressure Hg lamp (Scheme 10). UV-irradiation of dioxime oxalates generates iminyl radicals by decarboxylation.…”

Perfluoroalkylation reactions of (hetero)arenes

“…66 The Scheme 33 Scope of the Ru-catalyzed perfluoroarylation of arenes. 66 The Scheme 33 Scope of the Ru-catalyzed perfluoroarylation of arenes.…”

“…66 The mechanism of the reaction is illustrated in Scheme 39. 66 The mechanism of the reaction is illustrated in Scheme 39.…”

“…66 Scheme 35 Reaction mechanism of the photochemical perfluorobutylation of a-cyanoarylacetates. This constitutes the initiation step.…”

“…5-8 C Ar-H peruoroalkyl-group radical substitution reactions of arenes can be classied into thermal and photoinduced methods. [12][13][14][15][16][17][18] Photoinduced methods either through direct homolysis of X-C n F 2n+1 bonds, 19,20 or by means of photoinduced electron transfer (PET) reactions 21 are capable of generating per-uoroalkyl radicals C n F 2n+1 even in aqueous systems 22 (Fig. 1) or else be non-metal catalyzed, among which, the use of the Baran reagent 14 or per-uoroalkylsulnate salts 15 in the presence of organic peroxide 16 or azo initiators 17 (Fig.…”