Collect. Czech. Chem. Commun. 1981, 46, 3278-3284

Electrochemical oxidation of methylindoles

Miroslav Jandaa, Jan Šrogla and Petr Holýb

a Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6
b Institute of Haematology and Blood Transfusion, 128 20 Prague 2


Electrochemical oxidation of 1-methylindole (I), 1,3-dimethylindole (II) and 1,2-dimethylindole (III) on a platinum anode in methanol, containing ammonium bromide, was studied. A more profound oxidation as compared with benzofuran or benzothiophene derivatives is indicated by the obtained products: 1-methyl-2,2-bis(1-methylindol-3-yl)-3-indolinone (IV), 1,1'-dimethyl-Δ3,3-biindolin-2,2'-dione (V), 3,3-dibromo-1-methyl-2-indolinone (VI), 3,3,5-tribromo-1-methyl-2-indolinone (VII), 3-bromo-1-methyl-2,3-indoledione (VIII), 3-methoxy-1,3-dimethyl-2-indolinone (IX), 3-hydroxy-1,3-dimethyl-2-indolinone (X), 3,5-dibromo-1,3-dimethyl-2-indolinone (XI) and 3-bromo-1,2-dimethylindole (XII). The ratio of the products can be significantly influenced by the electrolysis conditions. The oxidation takes place in positions 2 and 3 of the indole molecule, the position 2 influencing decisively the oxidation path.