3-Mercaptobenzo [b] thiophene (1) is transformed with assistance of bases, especially of amines, into the benzo [b]-thieno-annellated 1, 2-dithiine 6 and not into the originally claimed" Dithioxo-thioindigo" trans-3. Primarily, the formation of 6 from 1 involves oxidation to the disulfide 4 which may also be used separately. Conceivable rationalizations are discussed. The same compound is accessible (in lower yield) by thionation of thioindigo ...