DIRECT EVIDENCE ON THE MECHANISM OF THE OXIDATION OF 2,3-DIMETHYLINDOLE BY INORGANIC PEROXO ANIONS

The mechanisms of the 2,3-dimethylindole (1) oxidation to 3-methylindo le-2-carbaldehyde (3) by peroxodisulfate and peroxomonosulfate anions have been investigated in H2SO4/20 % v/v methanol-water solutions. Bec ause indolenines have been postulated as intermediates in the oxidatio n of some indole derivatives, we have also analyzed the reactivity of 3-hydroxy-2,3-dimethyl-3H-indole (2a) with both peroxo anions. From th ese and previous studies, it is concluded that the reactions proceed i n three steps: electrophilic attack of the peroxidic bond at the C-3 a tom of indole to form the indolenine intermediate, a second peroxo ani on attack on the enamine tautomer of this intermediate followed by hyd rolysis to give 3-methylindole-2-carbaldehyde (3).