A facile synthesis of Tyrian purple based on a biosynthetic pathway

Abstract

A facile synthesis of Tyrian purple, a valuable purple dye derived from gastropod mollusks in ancient times, has been accomplished. Tyrian purple, 6,6′-dibromoindigo, was easily obtained by three steps of reactions from the commercially available 6-bromoindole, on the basis of a biosynthetic pathway of indigo and biological precursors of the purple. Iodination of 6-bromoindole, followed by acetoxylation with silver acetate in acetic acid, afforded 6-bromo-3-acetoxyindole, whose alkaline hydrolysis accompanying air oxidation produced Tyrian purple.