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 .