OXIDATION OF 4-, 6- AND 7-HYDROXYINDOLES.

Article abstract of DOI:10.1016/S0040-4020(01)89145-6

Oxidation of 4-, 6- and 7-hydroxyindoles with sodium periodate in phosphate buffer at pH 7.0 leads to complex mixtures of oligomeric products, the majority of which have been isolated and characterised as the O-acetyl derivatives. 7-Hydroxyindole (6) gives predominantly the dimers 9 and 10 as well as the trimer 11 and the tetramer 12 in smaller amounts.The 4- and 6-hydroxy isomers 7 and 8 follow less clear-cut reaction paths, characterised by the formation of the oligomers 13-16 and 17-19 respectively, along with polymeric materials.The observed mode of polymerisation of hydroxyindoles 6-8 is apparently consistent with a mechanism involving nucleophilic addition of the starting indoles to the electrophilic positions of transient quinonimine or phenoxonium-like intermediates.