Isothiazolopyrimidines are of interest not only for the heterocyclic systems but also as compounds which uses as kinasin spindle protein (ksp) inhibitors, sedatives and anti-inflammation agents [1,2]. Some methods for the preparation of these heterocyclic system are involves treatment of 4-thiocyanatopyrimidine-5-carbaldehyde with ammonium acetate in the presence of 2-propanol [3] or condensation of 5-aminoisothiazole-4-carbonitrile with formamide [4] and also by the treatment of 5-amino-3-methylisothiazole-4-carbonitrile with orthoesters and acetic anhydride to give the related iminoethers. Ammonia in methanol converts iminoethers to the corresponding amidine which requires treatment with strong base [5]. In this study, the reaction of 4,5-dihydro-4-imino-6-(methylthio)-N,5-diphenyl-isothiazolo[3,4-d]pyrimidin-3-amine (1) with hydrazine hydrate afforded the corresponding hydrazine derivative (2) in boiling ethanol. Further treatment of this compound with orthoesters in acetic acid gave the desired [1,2,4]triazolo[3ʹ,4ʹ:2,3]pyrimido[4,5-c]isothiazoles (3a-c).

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