Regioselective synthesis of 1,3-thiazines by sequential 4-oxothiazolidine to 1,2-dithiole to 1,3-thiazine transformations: role of intramolecular non-bonded S⋯O interactions

A new synthetic approach to 2,3-dihydro-4H-1,3-thiazine derivatives based upon reductive rearrangement of 1,2-dithiole-3-ylidene thiones has been developed. In turn, the 1,2-dithiole derivatives were prepared by an efficient ring-opening–closing process of 2-alkylidene-4-oxothiazolidines, induced in the presence of Lawessonʹs reagent by intramolecular non-bonded 1,5-type S⋯O interactions in the 4-oxothiazolidine precursors.