Studies of the regioselective ring-opening–closing mode of functionally different thiazolidine type enaminones: en route to the synthesis of trithiaazapentalene derivatives

Trithiaazapentalene derivatives were prepared by the reaction of 2-alkylidene-4-oxothiazolidines with Lawessonʹs reagent. They are classified as two structurally different trithiaazapentalene compounds that have different contributions of monocyclic 1,2-dithiole and 1,2,4-dithiazole structures and degrees of aromaticity of the bicyclic trithiaazapentalene system. The electron-donating ability of substituents at the C(5) position of the trithiaazapentalene system is recognized as the main cause for changes in π-electron distribution. This is the first complete study of substituent effects on the structure of trithiapentalenes.