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.