TEMPO oxidation, anode

M. Schamann and H. J. Schafer, TEMPO-mediated anodic oxidation of methyl glycosides and 1-methyl and 1-azido disaccharides, Eur. J. Org. Chem. (2003) 351-358. 

M. Schamann and H. J. Schafer, TEMPO-mediated anodic oxidation of methyl glycosides and... 

Tempo-mediated anodic oxidation of alcohols to aldehydes and ketones was successfully carried out in ionic liquids [23, 24]. High viscosity of the ionic liquids limiting the mass transport... 

Scheme 7 Selective anodic oxidation of diols with TEMPO as mediator.

In an enantiomer-differentiating oxidation at a poly-(L-valine)-coated Pb02 anode, rac-2,2-dimethyl-l -phenyl-1 -propanol was partially oxidized leaving 43% optically pure (5)-alcohol [371]. At a TEMPO-modified graphite felt anode rac-1-phenyl-ethanol has been enantioselectively oxidized in the presence of (-[-sparteine leaving 46% of the (/ [-alcohol with 99.6% ee [372]. However, under the same conditions, an exclusive dehydrogenation of (-[-sparteine to the iminium salt without oxidation of the alcohol was found [373]. 

Other organic mediators act as hydride atom-abstracting agents. This is true, for example, with 2,2-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and the oxoammonium ion which is anodically accessible from 2,2,6,6-tetramethylpiperidyl oxide (TEMPO). DDQ has been electrochemically regenerated either externally or internally The in situ electrochemical oxidation, of TEMPO to the active oxoammonium ion is performed in lutidine-containing acetonitrile. Thus, primary alcohols can be oxidized to the aldehydes, while secondary ones are stable Primary amines are transformed to nitriles. If water is present, the amines are cleaved via the Schiff bases to the corresponding carbonyl compounds... 

K. Schnatbaum and H. J. Shafer, Electroorganic synthesis. 66 Selective anodic oxidation of carbohydrates mediated by TEMPO, Synthesis, (1999) 864-872. 

Anodic oxidation of alcohols in water using water-soluble N-oxyl compounds (W S-TEMPOs, Figure 12.1) has been developed by Tanaka and co-workers [14]. An alcohol... 

Figure 12.2 General procedure for anodic oxidation of alcohols mediated by WS-TEMPOs.

Halide-free anodic oxidation of alcohols mediated by an anionic WS-TEMPO (Figure 12.3) was also accomplished. It was suggested that the anionic WS-TEMPO might form an anionic oil-in-water emulsion including alcohol, and the attractive force between the sulfonate ion and the positive charge of anode would facilitate direct electron transfer from the N-oxyl moiety to the anode. 

On the basis of these mechanistic insights, the authors developed the a-amino-xylation reaction using TEMPO and a synergistic combination of copper and chiral imidazolidinones [61 ]. A radical cation similar to IV has also been proposed by Jang and co-workers [62] for the organocatalytic a-oxidation of aldehydes using anodic oxidation. 

Benzyl alcohol anodic oxidation in water over TEMPO DE (V=1.4Vvs. Ag/AgCI)... 

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