Synthesis of 2,2′-(1,4-Phenylene)bis-3,4-dihydro-2H-1,3-thiazin-4-ones and their Facile Recyclization to 2,2′-(1,4-Phenylene)bis(pyrimidin-4-one) and/or 2,2′-(1,4-Phenylene)-bis-(thieno[2,3-d]pyrimidin-4(1H)-one) Derivatives

1,3-Thiazines are an important type of heterocycles showing a wide variety of pharmacological properties. Thus, 1,3-thiazine derivatives have recently been reported as cholecystokinin antagonists [1], antimycobacterial agents [2], cannabinoid receptor agonists [3], and inhibitors of NO synthase (NOS) [4], as antibacterial [5], antipyretic [6], anti-inflammatory [6, 7], analgesic [7], antitumor [8], and antioxidant [9] agents, and as calcium channel modulators [10]. Furthermore, the antibiotic activity of cephalosporin is due to the presence of the 1,3-thiazine moiety [11]. A few methods have been reported in the literature for the preparation of 1,3-thiazines [12 – 21], but to the best of our knowledge, there are no reports in the literature for the formation of 2,2′-(1,4-phenylene)bis(3,4-dihydro2H-1,3-thiazin-4-one). Considering the above reports in conjunction with our recent work on the synthesis of bis[22 – 26] and polyheterocyclic systems [27 – 35], we wish to describe herein an efficient and direct procedure for the synthesis of 2,2′-(1,4-phenylene)bis(3,4dihydro-2H-1,3-thiazin-4-one) derivatives and their base-catalyzed recyclization to bis-pyrimidin-4-one and bis-thieno[2,3-d]pyrimidin-4-one derivatives.