Abstract Dibenzo [b, f]-1, 4-thiazepin-11 (10H)-ones IIa-IIc reacted with phosphorus pentasulfide in pyridine under the formation of the thiones IIIa-IIIc which were transformed by treatment with hydrazine hydrate in 1-butanol to the hydrazine derivatives IVa-IVc. Reactions with triethyl orthoformate in ethanol in the presence of sulfuric acid effected cyclization to dibenzo [b, f]-1, 2, 4-triazolo [4, 3-d]-1, 4-thiazepine (Va) and its chloro derivatives Vb, Vc ...