Synthesis and reactivity of 3-(benzothiazol-2-yl)-3-oxopropanenitrile

The versatile, hitherto unreported 3-(benzothiazol-2-yl)-3-oxopropanenitrile (3) was prepared by two convenient routes: either by the reaction of ethyl 2-benzothiazolecarboxylate (1) with acetonitrile in the presence of sodium hydride or by treatment of 2-bromoacetylbenzothiazole (2) with potassium cyanide. Reaction of 3 with heterocyclic diazonium salts furnished the corresponding hydrazones 6, 7 and 13, respectively. The latter products underwent intramolecular cyclization into the corresponding pyrazolo[5,1-c]-1,2,4-triazine, 1,2,4-triazolo[5,1-c]-1,2,4-triazine and 1,2,4-triazolo[4,3-a]benzimidazole derivatives 8, 9 and 14, respectively, upon boiling in pyridine. Compound 3 coupled also with diazotized aromatic amines and gave the corresponding arylhydrazones 16a-c which undergo cyclocondensation with hydrazine and phenylhydrazine to afford the pyrazole derivatives 17a-c and 18a-c, respectively. Cyclocondensation of compound 3 with hydrazine derivatives afforded the corresponding aminopyrazoles 19 and 20, respectively in good yields.