Amines anodic oxidation

Very similar product mixtures are obtained from electrochemical decarboxylations or deoxidations 201 and deaminations 202 of the corresponding alcohols or amines. Anodic oxidation of cyclobutanecarboxylic acid affords in 30% yield a mixture of cyclopropylcarbinol, cyclobutanol and allylcarbinol identical in composition with that obtained from deamination of cyclobutylamine 203 Electrolysis of exo- or encfo-norbornane-2-carboxylic acid gave exo-norbornyl-2-... 

In general, treatment of carbonium ions with nitriles under a variety of conditions yields A -substituted amines. Anodic oxidation in acetonitrile converts selected aliphatic compounds to acetamides, e.g. adamantane to adamantylacetamide (equation 22). ... 

Triazoles and Benzotriazoles. - The alkenediazonium salt (431 Ar = P-NO2C6H4) is converted into the triazoles (432 R = H or alkyl) by the action of amines. Anodic oxidation of the oxime phenylhydrazone of benzil, HON=CPhCPh=NNHPh, gives the AA-oxide (433). The alkenyl-triazolines (434 R = H or alkyl) afford the aziridines (435) on flash vacuum py roly sis.Photolysis of the 4-alkylaminotriazoles (436 R = alkyl) yields 2-alkylpyrroles rather than the expected 3-alkyIpyrroles. The... 

Conversely, the use of elevated temperatures will be most advantageous when the current is determined by the rate of a preceding chemical reaction or when the electron transfer occurs via an indirect route involving a rate-determining chemical process. An example of the latter is the oxidation of amines at a nickel anode where the limiting current shows marked temperature dependence (Fleischmann et al., 1972a). The complete anodic oxidation of organic compounds to carbon dioxide is favoured by an increase in temperature and much fuel cell research has been carried out at temperatures up to 700°C. 

Oxidation of thiophene with Fenton-like reagents produces 2-hydroxythiophene of which the 2(570 One isomer is the most stable (Eq. 1) <96JCR(S)242>. In contrast, methyltrioxorhenium (Vn) catalyzed hydrogen peroxide oxidation of thiophene and its derivatives forms first the sulfoxide and ultimately the sulfone derivatives <96107211>. Anodic oxidation of aminated dibenzothiophene produces stable radical cation salts <96BSF597>. Reduction of dihalothiophene at carbon cathodes produces the first example of an electrochemical halogen dance reaction (Eq. 2) <96JOC8074>. 

A variety of amines have been used as mediators for electrochemical oxidation reactions. In these reactions, the amine is oxidized at an anode surface to form a radical cation. The amine radical cation then oxidizes a second substrate triggering a reaction of synthetic interest. The regenerated amine is then reoxidized at the anode... 

In addition to using amine oxidation products as mediators, anodic oxidation reactions can be used to functionalize amine compounds. These reactions include both - examples that generate imines and nitriles, as well as examples that lead to the addition of nucleophiles to the carbon alpha to the nitrogen. 

Scheme 5 Mediated anodic oxidation of amine to nitrile and carbonyl compound.

The oxidation of an amine can benefit from the use of an electroauxiliary [19-28]. Electroauxiliaries are substituents that both lower the initial oxidation potential of the substrate and control the formation of the subsequent reactive intermediates. To this end, the anodic oxidation of the 6-membered ring a-silylamines in the presence of cyanide was shown to afford a net displacement of the silyl... 

Finally, it is important to note that many of the anodic reactions discussed above cannot be duplicated with traditional chemical oxidants. For this reason, the anodic oxidation of nitrogen-containing compounds represents a powerful class of reactions that has the potential to open up entirely new synthetic pathways to complex molecules. From the work already accomplished, it is clear that employing such an approach is both feasible and beneficial, and that the ability to selectively oxidize amines and amides is a valuable tool for any synthetic chemist to have at their disposal. 

Anodic oxidations of secondary amines can provide radicals or radical cations. 

Specifically, the mediators (Med ) used were the radical cations of tris-(4-bromophenyl)amine and 2,3-dihydro-2,2-dimethylphenothiazine-6(17/)-one [59], The results of the oxidative cyclizations under the homogeneous oxidation conditions are parallel to those obtained by direct anodic oxidation. 

The catalytic effects and versatility of cerinm(IV) ammonium nitrate as a single-electron oxidant were recently reviewed (Nair and Deepthi 2007, Maulide et al. 2007). However, it should be kept in mind that this oxidative reagent is very powerful and some sensitive fnnctions are not compatible with it. Particularly, some amines are at least as easily oxidizable as the starting molecule bearing the protected group. Anodic oxidation was proposed as a usefnl alternative (De Lamo Martin et al. 2005). 

The ruthenium tetroxide dioxide catalytic system is effective for the oxidation of alkanols, although it will also react with any alkene groups or amine substituents that are present. The catalyst can be used in aqueous acetonitrile containing tetra-butylammonium hydroxide with platinum electrodes in an undivided cell Primary alcohols are oxidised to the aldehyde and secondary alcohols to the ketone [30]. Anodic oxidation of ruthenium dioxide generates the tetroxide, which is the effective oxidising agent. 

An electrochemical method for amination has been reported by Shono and co-workers.275 Derivatives of malonic esters containing an N-tosyl group were cyclized in high yields by anodic oxidation ... 

Table III collects and compares the rate date for the oxidation of some aliphatic amines and alcohols on nickel, silver, copper, and cobalt oxide anodes. Homologous alcohols always react 10 times slower than amines. The reaction rates on silver and on cobalt are sizeably slower than those on copper and nickel, so that silver and cobalt could be ruled out for technically applied anodic oxidation (190).

Anodic oxidation of enamine ketones or esters in CH30H-NaC104 at a graphite anode gives substituted pyrroles in 15-45% yield.101 Formation of the symmetrically substituted pyrroles 47 indicated radical dimerization of radical-cations formed as primary products from 46. This process leads to dications from which the pyrroles can be formed by cyclization and elimination of an amine [Eq. (44)]. 

The conversion of substituted diphenylamines and triphenylamines to carbazoles at platinum anodes in CH3CN-Et4NC104 takes place if the intermediate cation-radical is fairly stable. Thus the anodic oxidation of (V-ethylbis(p-fert-butylphenyl)amine (87) gave 3,6-di-ferf-butyl-Af-ethyl-carbazole (88) in 15% yield152 [Eq. (72)]. 

The a-methoxylated derivatives are shown to be versatile synthons because of the reactivity of the methoxy group near the nitrogen atom, a-Methoxycarbamates, prepared by anodic oxidation, were used as key intermediates in the synthesis of a-amino acids,200 a new carbon-phosphorus bond-forming reaction,200 and in a new method of acylation of aliphatic amines at the -position.201 The application of this reaction to the synthesis of pyrrolidine, piperidine, and tropane alkaloids is also described.202... 

These reactions have been used for the deblocking of protecting groups. In the case of amines, the formation of metabolites is possible because the anodic oxidation of amines equals the microsomal oxidation to a large extent. 

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