Efficient methods for the preparation of isomeric o, o′-diaminobibenzothiazoles (8a and 11a) and o, o′-diamino-2, 2′-dimethylbibenzothiazoles (8b and 11b), potentially valuable building blocks for construction of hitherto unknown dithiazolo annulated pentacyclic heterocycles, have been developed. The dithiazolo annulated benzo [c] cinnolines 9a, 9b, and 12a were prepared from the corresponding diamines by oxidation with PhI (OAc) 2 in ...