Synthesis of Thioindoles Using an Intramolecular Friedel-Crafts Reaction

Significance

Reported is the synthesis of thieno[2,3-b]indoles from 2-furyl arylisothiocyanates using excess aluminum trichloride. The thieno[2,3-b]indoles were synthesized in good yield from the parent anilines, which in turn were obtained from the nitro compounds. A limited investigation into the scope of the reaction makes it difficult to predict the generality of the reaction; however, in the examples shown, the yields are reasonably good. A potential mechanism for the reaction is proposed and shown above. No evidence for this mechanism is given, but it appears to us to be plausible.