Cation radicals from phenylated amines

Principally the same, but chemically simpler, sequence was used to prepare arylnitro anion-radicals from arylamines, in high yields. For instance, aqueous sodium nitrite solution was added to a mixture of ascorbic acid and sodium 3,5-dibromo-4-aminobenzenesulfonate in water. After addition of aqueous sodium hydroxide solution, the cation-radical of sodium 3,5-dibromo-4-nitro-benzenesulfonate was formed in the solution. The latter was completely characterized by its ESR spectrum. Double functions of the nitrite and ascorbic acid in the reaction should be underlined. Nitrite takes part in diazotization of the starting amine and trapping of the phenyl a-radical formed after one-electron reduction of the intermediary diazo compound. Ascorbic acid produces acidity to the reaction solution (needed for diazotization) and plays the role of a reductant when the medium becomes alkaline. The method described was proposed for ESR analytical determination of nitrite ions in water solutions (Lagercrantz 1998). 

Fleischmann et al s 34 report cyclic voltammetry data for the oxidation of a series of aromatic hydrocarbons in a molten salt electrolyte, AlCl3-NaCl-KCl at 150°. Electrooxidation in this medium occurs at unusually low oxidation potentials. Tris-(p-substituted phenyl)amines, with the exception of tri (p-nitrophenyl) amine, yield very stable radical cations by all electrochemical criteria 380>S42 Mono- and bis-p-substituted triphenylamines, however, dimerize with rate constants ranging from 101 to 10s M 1 sec 1 to benzidines 176 (Eq. (237)), which subsequently are oxidized to the radical cations 177, whose ESR-spectra are observed. Dimerization is fastest with the p-N02 andp-CN-derivative, in accordance with HMO calculations, which predict the highest spin sensity in the p-position of these compounds 542 ... 

Products of addition to styrene double bonds can arise as a result of light induced electron transfer reactions. Lewis has studied the intramolecular reaction of l-phenyl-w-amino alkenes (422) 289,290 products arise from electron transfer from the amine nitrogen to the excited state of the styryl group followed by intramolecular proton transfer in the radical ion pair produced. The resultant biradical then couples to yield the isolated products (423) and (424). Sensitisation of the intermolecular analogue of this reaction by 1,4-dicyanobenzene has been reported and is proposed to occur by electron transfer from the styrene to the excited state of the sensitiser followed by attack of an amine on the styrene radical cation. This ultimately leads to the product of anti-Markovnikov addition of the amine across the double bond of the styrene. This is similar to the sequence long since established by... 

Homolytic intramolecular amination allows the synthesis of tetrahydroquinoline 28 from the 3-phenyl-propylamine 27 (n = 2). The yield of indoline 30 is lower because the aminium cation radical 29 generated from A-chloro-2-phenethylamine 27 (n = 1) undergoes an easy jff-scission reaction to form the benzyl radical (Scheme 9). 

Product studies have demonstrated that I-phenyl and 1,1-diarylalkene radical cations react with nitrogen-centered nucleophiles such as amines and pyridines by both addition and deprotonation. The addition reactions occur by a mechanism analogous to that shown in Scheme I for methanol addition. Deprotonation by an amine or pyridine base is an alternate possibility for radical cations derived from 2-alkyl-substituted alke-nes and leads to an allylic radical (Eq. 19). Reduction of this radical by the sensitizer radical anion generates an anion that is protonaled at either the original position to regenerate starting... 

There have been several papers dealing with the oxidation reactions of nitrogen and sulfur-based compounds. Hindered amines, such as substituted 2,2,6,6-tetramethylpiperidines, are easily oxidized by electron-transfer reactions to the corresponding cation, by the sulfate radical anion, and by sensitized electron transfer to carbonyl triplets. Radicals derived from tertiary piperidines were observed directly by optical spectroscopy and deprotonated to a-alkylamine radicals. The amine radical cation derived from secondary piperidines deprotonated to give aminyl radicals. In the presence of oxygen, both classes were oxidized to give nitroxyl radicals, but by different proposed mechanisms. Both oxidation and fragmentation pathways have been observed in the photochemical reaction of alkyl phenyl sulfides with tetranitromethane. The oxidation of various A-(arylthio)-4-substituted-2,6-diarylanilines (18) with PbOa yielded, in most cases, persistent radicals that could... 

Although the Capdevielle reaction for one-pot conversion of aldehydes to nitriles is a very convenient and widely applicable synthetic procedure, 3-substituted furoxans appear to be susceptible to rearrangement when substitutions with amine nucleophiles are attempted, even under relatively mild conditions (Scheme 29) <1999JOC8748>. The formation of the final product 107 in this reaction was explained via phenyl abstraction by carbamoyl radical cation from the second molecule of intermediate product 106 < 1999JOC8748>. 

J.K. Cha et al. developed a stereocontrolled synthesis of bicyclo[5.3.0]decan-3-ones from readily available acyclic substrates. Acyclic olefin-tethered amides were first subjected to the intramolecular Kulinkovich reaction to prepare bicyclic aminocyclopropanes. This was followed by a tandem ring-expansion-cyclization sequence triggered by aerobic oxidation. The reactive intermediates in this tandem process were aminium radicals (radical cations). The p-anisidine group was chosen to lower the amine oxidation potential. This substituent was crucial for the generation of the aminium radical (if Ar = phenyl, the ring aerobic oxidation is not feasible). 

To the more usual homolytic fragmentation of aryl halides (from the excited state or from the radical anion, the well known SrnI reaction, for a recent example see the arylation of aromatics), the heterolytic version of the reaction which produces phenyl cations has more recently joined. A theroretic study on the photodissociation of fluorinated iodobenzenes has been published. The perfluoroallgrlation of various alkenes has been obtained by irradiation in the presence of iodoperfluorobutane. The formation of phenyl cations is exemplified in many arylation reactions and, in the case of o-chlorostannane, also a benzyne has been reported. In the field of polymer chemistry, iodonium salts are model cationic photoinitiators. In particular the truxene-acridine/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ringopening polymerization of an epoxide, whereas the truxene AD/allq l halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. ... 

---