Electrochemical reductive cleavage

A much more precise investigation of the variation of a with the electrode potential has been reported recently.44 It concerns the electrochemical reductive cleavage of the O—O bond in a series of five organic peroxides ... 

Fig. 9 Electrochemical reductive cleavage of aryl halides in a poor H-atom donor solvent. Cyclic voltammetry as a function of the scan rate, v. E, Electrode potential i, current. Reduction (cathodic) currents are represented as being upwards.

Reductive cleavages by low-valent metal ions 4.8.2.13 Electrochemical reductive cleavages... 

Electrochemical reductive cleavage of a-amino ketones becomes easier as the acidity of the medium is increased, indicating that they are reduced as their conjugate acids. As with a-ketols (Section 4.8.3.1.3), reductive cleavage of the carbon-heteroatom bond is frequently accompanied by reduction of the carbonyl group (equation 28). ... 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Cyano substituents have important influences on the electrochemical reductive cleavage of C—O bonds of 2-, 3- and 4-cyanoanisoles in DMF. Under cyclic voltammetric conditions reversible electron transfer, generating radical anions, was observed for 2- and... 

Andrieux, C. R, Le Gorande, A., and Saveant, J.-M. 1992. Electron transfer and bond breaking. Examples of passage from a sequential to a concerted mechanism in the electrochemical reductive cleavage of arylmethyl halides. /. Am. Chem. Soc. 114 6892. 

The characterization of reaction mechanisms and intermediates of complex chemical reactions forms a central topic in electrochemistry [113-118]. The electrochemical reductive cleavage of carbon-halogen bonds is an important process in electro-organic synthesis, waste stream treatment and electron-transfer mechanisms. Benzyl chloride (PhCH2Cl) reduction in organic solvents has been widely investigated following debate as to whether the carbon-chlorine bond would be reductively cleaved via a concerted or a nonconcerted reaction pathway. Recent studies have shown that Pd, Cu - and especially Ag - cathodes... 

Photo-induced additions of ferrocene to electron-deficient alkynes, giving 1-ferrocenylalkenes, photo-ethoxycarbonylation of ferrocene derivatives ( v-CCU-EtOH), and electrochemically-initiated additions of alkyl radicals (from RCOg ) to ferricenium cation have been reported. Electrochemical reductive cleavage of the ring-metal bonds in carbonyl-substituted ferrocenes has been achieved using polarographic methods. ... 

Andrieux, C.P., Saveant, J.-M., Su, K.B. Kinetics of dissociative electron transfer. Direct and mediated electrochemical reductive cleavage of the carbon-halogen bond. 7. Phys. Chem. 1986,90, 3815-3823. 

Electrochemical reductions of sulphones have been reviewed212, and have been discussed at intervals213-215. There is evidence that the cathodic reduction reaction proceeds via a radical anion, followed by a cleavage reaction, as outlined in equation (91)212,213. 

Horner has extended this reaction to the electrochemical reduction of optically active arsonium salts (68, X = As), which also undergo cleavage with retention of stereochemical configuration at arsenic M 65). This is a convenient synthetic route of optically active arsines of known configuration. 

While electrochemical cleavage of several other kinds of single bonds has been reported, stereochemical information is sparse. Erickson and Fischer examined the electrochemical reduction of O-benzoylatrolactic acid (76, R = H) and its methyl ester (76, R = CH3) 69>. The products (77, R = H and CH3) of the... 

Cobaloxime(I) generated by the electrochemical reductions of cobaloxime(III), the most simple model of vitamin Bi2, has been shown to catalyze radical cyclization of bromoacetals.307 Cobalt(I) species electrogenerated from [ConTPP] also catalyze the reductive cleavage of alkyl halides. This catalyst is much less stable than vitamin Bi2 derivatives.296 It has, however, been applied in the carboxylation of benzyl chloride and butyl halides with C02.308 Heterogeneous catalysis of organohalides reduction has also been studied at cobalt porphyrin-film modified electrodes,275,3 9-311 which have potential application in the electrochemical sensing of pollutants. 

It should, however, be emphasized that the relaxation from (X ) -l-i to X (+) does not always require a negligible energy. Counterexamples where the homolytic cleavage of an ion radical appears to be endowed with a sizable internal reorganization energy can be found in the electrochemical reduction of perbenzoates,60 where the observation of a transition between a concerted and a stepwise mechanism fits with an exothermic cleavage of the anion radicals. 

This procedure illustrates a general method for the preparation of amines by reductive cleavage of sulfonamides by hydrobromic acid in the presence of phenol.9 The present synthesis makes 1,3-dihydroisoindole readily accessible and is superior in certain respects to the other two practical methods of preparation. Thus the method here described is shorter and gives a higher overall yield than the three-step synthesis of Neumeyer,7 and obviates the special apparatus and careful control required by the electrochemical process of Dunet, Rollet, and Willemart.4... 

FIGURE 2.27. Redox catalysis of the reductive cleavage of 1-chloronaphthalene by the electrochemically generated anion radical of 4-methoxybenzophenone in DMSO at 0.05 V/s for excess factor of 0.5. Fitting of the experimental data points. 

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