Oxidation of 2,3-Bis(hydroxymethyl)indole

Oxidation of 2,3-bis(hydroxymethyl)indole (1) with MnO2 yields as intermediate 3-formyl-2-hydroxymethylindole (2) and finally 2,3-diformylindole (3). The structure of 2 was proved by both chemical methods and 13C n.m.r. spectra. Use of DMSO acetic anhydride mixture as the oxidative agent, however, yields the 3,3′-diindolylmethane derivative 4, instead of 2 or 3.