Various monocyclic 1,2-dithiines 6a,b,d-t were prepared via (Z,Z)-1,4-difunctionalized butadienes (4–11,19,20). A twisted cyclic structure A is unequivocally proved rather than of the ringopened valence isomer B. The reactivity of these 1,2-dithiines is described. Thermal as well as day-light induced sulfur extrusion is an important feature of their chemistry. The latter mode of sulfur extrusion depends