A New Efficient Method for the Synthesis of Fused [1,2,5]Thiadiazoles and Their Dearomatization with C-Nucleophiles

General method for the annulation of [1,2,5]thiadiazole ring to pyridine and benzene cycle has been developed using sulfur monochloride as a sulfur source. On this basis a number of [1,2,5]thiadiazolo[4,3-b]pyridines and benzo[c]thiadiazoles were synthesized. The most pi-deficient [1,2,5]thiadiazolo[4,3-b]pyridines readily react with neutral carbon nucleophiles such as CH-acids, indoles, pyrrole and phloroglucinol to give 1,4-adducts. An efficient method for the synthesis of fused [1,2,5]thiadiazoles by the reaction of ortho-diaminopyridines and benzenes with S2Cl2 has been developed. This method is suitable for those cases when conventional procedures applying thionyl chloride do not work. The most pi-deficient compounds react with neutral carbon nucleophiles under mild conditions to give the corresponding 1,4-adducts to the pyridine ring.image