Preparation of indoles from 4H-3,1-benzothiazines by extrusion of sulfur

Prolonged heating of a series of α -hydroxy-α-aryl-o-toluidines in the presence of base and carbon disulfide afforded the corresponding 4H-3,]-benzothiazine-2-thiones. Treatment of the thiolalkyl ethers of these compounds with strong bases led to ring contraction to the corresponding 2-thioalkyl indole with concommitant extrusion of sulfur. The scope of the reaction was examined.