A facile synthesis of Tyrian purple, a valuable purple dye derived from gas
tropod mollusks in ancient times, has been accomplished. Tyrian purple, 6,6
'-dibromoindigo, was easily obtained by three steps of reactions from the c
ommercially available 6-bromoindole, on the basis of a biosynthetic pathway
of indigo and biological precursors of the purple. Iodination of 6-bromoin
dole, followed by acetoxylation with silver acetate in acetic acid, afforde
d 6-bromo-3-acetoxyindole, whose alkaline hydrolysis accompanying air oxida
tion produced Tyrian purple.