Single electron transfer oxidation

Eq. 2). The free radical intermediates obtained frequently undergo second single-electron transfer oxidation to yield carbenium ions. 

The process is induced photochemically and involves the single-electron transfer oxidation of cubane then completed with a backward electron transfer to the transient radical cations. A Li+ salt with a weakly coordinating anion is able to induce pericyclic transformations, including the rearrangement of cubane to cuneane, quadricyclane to norbomadiene, and basketene to Nenitzescu s hydrocarbon 392... 

Irradiation of 3-methylthiophene in hexafluoropropan-2-ol with added methanesulfonic acid brings about single electron-transfer oxidation and this yields a species that has been identified as the Z>w-protonated radical-cation of (289). Irradiation of 2-acetyl-5-iodothiophene leads to cleavage of the C-I bond and the resultant radical adds to acrylonitrile to afford the adduct (290) in moderate yield. Reactions of this type have also been described for iodofuran and iodopyrrole derivatives and in the latter case 4,5-diiodo-l//-pyrrole-2-carboxaldehyde reacts photochemically with thiophene to give... 

Radical cations of triaiylamines are known to be single electron transfer oxidizing agents. Very recently, these substances have been used as efficient mediators for gcm-difluorodesulfurization as shown in Scheme 56. ° Furthermore, triarylamines have recently been shown to be highly effective mediators for monofluorodesulfurization of P-lactams. Severe passivation of the anode takes place during anodic fluorination of P-phenylthio- P-lactams, which is quite different from the case of a-phenylthio-P-lactams 60. However, selective anodic fluorodesulfurization proceeds efficiently without passivation when tris(2,4-dibromophenyl)amine is employed as a mediator as shown in Scheme 57. ... 

Different from the hydroxyalkylation reactions using carbonyl compounds as substrates, Nicolaou s and Macmillan s groups developed independently the intramolecular asymmetric Friedel-Crafts-type a-arylation of aldehydes with electron-enriched arenes based on the SOMO activation strategy. Using chiral imidazolidione as catalyst, a series of cyclic aldehydes were obtained in good yields and enantioselectivities with cerium ammonium nitrate (CAN) as single electron transfer oxidant [46]. 

Mella, M., Freccero, M., and Albini, A., The photochemical approach to the functionalisation of open-chain and cyclic alkanes. 1. Single electron transfer oxidation. Tetrahedron, 52, 5523, 1996. 

Although single-electron-transfer (SET) processes would be expected to be important in reactions that use metals as reagents, this type of process has also been recognized in the reduction of carbonyl groups that involve 1,4-dihydronicotinamide derivatives . Recent work by Oae and coworkers" has shown that an SET process is operative in the reduction of dibenzothiophene S-oxide by l-benzyl-l,4-dihydronicotinamide when the reaction is catalyzed by metalloporphins. The reaction is outlined in equation (18), but the study gave results of much more mechanistic than synthetic value. This type of study is relevant to understanding biochemical mechanisms since it is known that methionine sulphoxide is reduced to methionine by NADPH when the reaction is catalyzed by an enzyme isolated from certain yeasts . 

Kinetic studies of the oxidation of diaryl sulfoxides by Cr led to the proposition of a single electron transfer as in the case of aryl methyl sulfoxides . These reactions were performed in aqueous acetic acid/perchloric acid medium, HCrOs" being the active... 

In an anionic/radical domino process an interim single-electron transfer (SET) from the intermediate of the first anionic reaction must occur. Thus, a radical is generated which can enter into subsequent reactions. Although a SET corresponds to a formal change of the oxidation state, the transformations will be treated as typical radical reactions. To date, only a few true anionic/radical domino transformations have been reported in the literature. However, some interesting examples of related one-pot procedures have been established where formation of the radical occurs after the anionic step by addition of TEMPO or Bu3SnH. A reason for the latter approach are the problems associated with the switch between anionic and radical reaction patterns, which often do not permit the presence of a radical generator until the initial anionic reaction step is finished. 

In contrast to [L Pd], oxidative addition of aryl halides on [L Ni] often proceed by single electron transfer mechanism [2, 197]. SN2 and SNAr types of oxidative addition as a step of the catalytic dehalogenation have also been proposed in the literature for low-valent Ti [40, 114], Zr(II) [115], Ru(II) [20, 74, 81, 98],... 

Single electron transfer to dialkylzirconocenes Single-electron oxidation of dialkylzirco-nocenes, e. g. with a ferrocinium [13] or silver salt [14,15], induces the following reaction leading to a cationic zirconocene [13] ... 

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