Studies on the chemistry of thienoanellated O,N- and S,N-containing heterocycles. 3. Synthesis of tricyclic thieno[2,3-b][1,4]thiazines via nucleophilic substitution of activated precursors†

Starting from thieno[2,3-b][1,4]thiazin-2-one 1 new synthetic pathways to the tricyclic compounds thieno[2,3-b]-1,2,4-triazolo[4,3-d]-1,4-thiazine derivatives (5, 12, 13, 14), 1,2,4-oxadiazolo[4,3-d]thieno[2,3-b]-1,4-thiazine derivative (20), and the tetracyclic ring system thieno[3',2':5,6]-1,4-thiazino[3,4-b]quinazoline derivative (19), are described. Under mild reaction conditions some intermediates can be isolated. Reaction of 2-methylthiothieno[2,3-b]-1,4-thiazine (8) with several amines leads to the amidines 2-aminothieno[2,3-b]-1,4-thiazine derivatives (15-18)