Electrochemical reduction indoles

In this paper, the selectivity of the ECH method for the reduction of nitro compounds to the corresponding amines on RCu electrodes will be compared with that of reduction by RCu alloy powder in alkaline aqueous ethanol. In the latter method (termed chemical catalytic hydrogenation (CCH)), chemisorbed hydrogen is generated in situ but by reduction of water by aluminium (by leaching of the alloy) (equation [12]). The reductions by in situ leaching must be carried out in a basic medium in order to ensure the conversion of insoluble Al(OH)3 into soluble aluminate (equation [12]). The selectivity and efficiency of the electrochemical reduction of 5-nitro-indoles, -benzofurane, and -benzothiophene at RCu electrodes in neutral and alkaline aqueous ethanol will also be compared with that of the classical reduction with zinc in acidic medium. 

The electrochemical reduction of indole derivatives 4U-413) and tetrahydrocarbazole 413) has been carried out industrially. The reduction products have been required as dye intermediates. 

Indolines and indoles were prepared by a direct electrochemical reduction of arenediazonium salts. As a result, radical intermediates were generated from which 3,4-disubstituted tetrahydrofuran skeleta were constructed <02OL2735>. A short and stereoselective total synthesis of furano lignans was realized by radical cyclization of epoxides using a transition-metal radical source <02JOC3242>. Other preparations of tetrahydrofurans using radical cyclization include the synthesis of novel amino acids L-bis-... 

Oxazolone itself can be easily obtained from oxazolidinone through electrochemical reduction as described in CHEC-II(1996). A similar sequence was utilized in the synthesis of indole-substituted 2(3//)-oxazolone 244 (Scheme 71) <1997CPB733>. Electrochemical oxidation of 2-oxazolidinone in methanol gave a 4-methoxy oxazolidinone 241, which reacted with an organomagnesium indole reagent 242 in the presence of BF3-Et20, followed by... 

Another methods for the electrochemical formation of the active carbanion is the cathodic reduction of iminium salts. When an iminium salt is reduced in the presence of a suitable alkylating agent, an alkyl group is introduced to the carbon atom of the imine. Some isoquinoline and indole type alkaloids are synthesized by using this substitution method as exemplified bellow by the synthesis of laudanosine 51 37>. 

Electrochemical detectors are based upon the volta-metric oxidation or reduction of separated analytes at a micro- or thin-film electrode. A number of pharmacologically active compounds that are aldehydes, ketones, or quinones (such as doxorubicin), or nitro compounds (such as nitrofurantoin) are amenable to reduction at a mercury or platinum electrode electron-rich indole derivatives and catecholamines can be oxidized at these electrodes. An important condition that must be fulfilled for electrochemical detection to be practicable is that the mobile phase must be capable of conducting an electrical current. This makes electrochemical detection particularly useful in reversed-phase liquid chromatography, where buffered water mixed with one or more organic cosolvents is usually the mobile phase. 

A titanium(O) colloid, prepared by the reduction of TiCU with KBEtsH, has been used in the synthesis of indoles [260]. Nanostructured titanium clusters, produced electrochemically by using a titanium sacrificial anode as the metal source and Bu4NBr in THF as the electrolyte and stabilizer, were found to induce olefin-forming McMurry-type coupling of oxoamides, aromatic aldehydes, and ketones [261]. 

Experimental studies of the electrochemical oxidation and reduction of nitro SP compounds in different environments show that oxidation takes place on the indole part of the SP and reduction at the NO2 group of the benzopyran part of the SP [57-60]. Without a NO2 group, SP does not exhibit electroactivity [61]. We report in this section on the isomerization reaction pathways for the anion and the cation of S-SPl conformer. The isomerization pathways are summarized in Fig. 8 and compared with field and protonation effects. 

In an attempt to help clarify the apparently complex oxidation chemistry of indolic compounds found in the CNS we have begun a systematic study of this chemistry using electrochemical and other analytical approaches. Modern electroanalytical and related techniques are particularly well suited to studies of the oxidation (and reduction) of biologically significant molecules. In this report some aspects of the electrochemical oxidation of 5-HT and 5-HTPP will be described. 

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