Thionation of bisindole derivatives with P4S10 or elemental sulfur

Abstract

Thionation reactions of several bisindole derivatives using elemental sulfur or P4S10 in pyridine have been studied, leading to formation of several novel structures. The reaction of indigo or isatin with P4S10 gave the structurally new salt 10, which could be transformed into the ethyl derivative 11. The first example of a thionated indigo derivative, monothioindigo (6), was isolated in low yield from the thionation of isatin. Treatment of 3,3′-biindolyl with sulfur in hot DMF produced the previously known tetrasulfide 1, which was studied by X-ray crystallography, thus also establishing that 1 is chiral in the crystalline state. The structure of an additional thionation product, the thienoindole derivative 34 was also solved using X-ray crystallography.