Pyrazolo[1,5­a]pyrimidines, which are synthetic analogs of purines, exhibit a wide variety of biological activity, such as enzymatic, antibacterial, antiphlogistic and antiparasitic activities [1]. They are also used as intermediates in the dyestuff industry [2]. Besides, thiazine and 1,4­ benzothiazine derivatives possess a wide spectrum of biological and pharmacological activities, such as calcium channel blockers, phosphodiesterase 7 inhibitors, 5­HT3 antagonists, antipsychotics, sedatives and NaH exchange inhibitors [3]. Due to the widespread biological activities of fused heterocyclic systems, in this study, we synthesized a novel benzo[b]pyrazolo[5\',1\':2,3]pyrimido[4,5­e][1,4]thiazine heterocyclic system. In our protocol, the desired compound were obtained from the reaction of pyrazolo[1,5­ a]pyrimidine (1) with POCl 3 and then with o­aminothiophenol. As shown in scheme 1, the resulting compound was alkylated with various alkylhalides to give the corresponding products (2) in good yields.

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