Indole electrolytic oxidation

Electrolytic oxidation of acetonitrile solutions of monomer mixtures of dithioenopyrrole 23 and dithienothiophene 15a using tetrabutylammonium perchlorate as an electrolyte can produce poly(dithienopyrrole-dithienothiophene) copolymer which shows good electrochromic <1994EAC2159> characteristics. Similarly, films of poly(dithienopyrrole-thionapthene indole) and poly(dithienopyrrole-thionapthene indole) co-polymers can be obtained from DTT and DTP with thionapthene indole 85 (TNI) <1996SM(82)11>. 

An interesting compound (205), isolated in ca. 15% yield, is obtained from the electrochemical oxidation of indole in acetonitrile using tetraethylammonium perchlorate as an electrolyte (78MI30503). Although it is obvious that the 3-substituent arises from the tetraethylammonium ion, no mechanism for the reaction is immediately apparent. 

Intramolecular cyclization is a general reaction in the anodic oxidation of substituted amino alkenes. Thus, the already mentioned A-methyl-A-phenyl-1,2,2-triphe-nylvinylamine leads to a new 3/7-indole by anodic oxidation in the presence of 2,6-lutidine [149,150]. The corresponding enediamine undergoes an electrolytic double cyclization to form an indolooxazolidine [149]. The formation of isoquinolines, benzaze-pines, and tetrahydrocarbazoles may also be obtained by anodically initiated intramolecular cyclization of A-benzyl, A- S-phenethyl, and anilino enaminones [Eq. (30)] [158]. 

Pyrrole is not polarographically reducible but can be reduced at a lead cathode in dilute sulfuric acid to pyrroline and further to pyrrolidine [203]. Under similar conditions 1,2-dimethylpyrroline [204] is also reduced to the pyrrolidine and indoles [205-207] to indo-lines or dimerized products [208]. 1-Methylindole can be reduced to 2,3-dihydro-1-methyl-indole in aqeuous THE at very negative potentials using TBAOH as electrolyte [209]. Pyrrole may also be oxidized anodically oxidation of pyrrole may result in the formation of polypyrrole useful for preparation of conducting polymers (Chapter 32). 

DiMarco et al. [195] oxidatively polymerized yV-vinyl-thionaphthene-indole in methylene chloride at 1.2 V (versus SCE). Tetrabutylammonium perchlorate was added as the supporting electrolyte the monomer was used in concentrations greater than 5 x 10" M. Elemental analysis and mass spectroscopy results indicate that the polymer consists of four or more monomer units and that the benzene rings... 

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