ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 12, pp. 2752–2758. © Pleiades Publishing, Ltd., 2016. 2752 Synthesis and Characterization of Novel 5-Allyl-6-{(benzo[d]thiazol-2-yl)methyl}- 2-(alkylsulfanyl)oxopyrimidine Derivatives 1 N. M. Khalifa a,b *, M. A. Al-Omar a , and A. E. Amr a,c a Pharmaceutical Chemistry Department, Drug Exploration & Development Chair (DEDC), College of Pharmacy, King Saud University, Riyadh, 11451 Saudi Arabia *e-mail: nagykhalifa@hotmail.com b Department of Therapeutical Chemistry, Pharmaceutical and Drug Industries Division, National Research Centre, Dokki, Cairo, 12622 Egypt c Applied Organic Chemistry Department, National Research Centre, Dokki, Cairo, 12622 Egypt Received November 26, 2015 Abstract—A series of novel S-DABO analogues bearing thiazolo[3,2-a]pyrimidine and pyrimido[2,1- b][1,3]thiazine has been developed starting from 5-allyl-6-{(benzo[d]thiazol-2-yl)methyl}-2,3-dihydro-2-thioxopyrimidin- 4(1H)-one. Selective S-alkylation was achieved to give the title compounds which were cyclized and oxidized to the corresponding sulfones. Keywords: S-DABO analogues, benzo[d]thiazoles, pyrimidine-4-one derivatives, synthesis 1 The text was submitted by the authors in English. Previously, we synthesized and evaluated several S- DABOs and HEPT analogues containing benzo[d]- thiazole linked to the pyrimidine-2-thione nucleus at C 6 position [1]. Recently, we reported that certain of our newly Pyrimidine and condensed pyrimidines have been synthesized and evaluated as antimicrobial, analgesic, anti-inflammatory, anti-HIV, and anti-HSV- 1 activities [2–6]. In addition, pyrimidinone derivatives were recently reported as cytotoxic agents. In most of these derivatives, alkylation of the 2-thio group es- pecially with alkylamino moiety was reported to en- hance the cytotoxic activity of the resulting pyrimidine derivatives [7–9]. On the other hand, benzothiazoles represent a class of heterocyclic compounds of great importance in biological chemistry [10,11]. Aiming to get S-DABOs derivatives with potential biological significance, we report herein the combination of the two active pharmacophores benzothiazoles and pyri- midines in one molecule bearing various S-(alkyl and amino alkyl) moieties at position-2. Synthetic approach for preparation of the title products is summarized in (Schemes 1‒4). Selective S-alkylation of the key intermediate 5-allyl-6-{(benzo[d]- thiazol-2-yl)methyl}-2,3-dihydro-2-thioxopyrimidin- 4 (1H)-one (1) with appropriate alkyl or aryl halides in presence of K 2 CO 3 afforded the designed compounds 2a–2h. Reaction of compound 1 with 2-bromo- acetaldehyde acetal in the presence of K 2 CO 3 at 65°C gave compound 3 which on treatment with N,O-bis- (trimethylsilyl)acetamide (BSA) in the presence of a TMS triflate catalyst yielded the target 6-allyl-5- {(benzo[d]thiazol-2-yl)methyl}-3-ethoxy-2,3-dihydro- thiazolo[3,2-a]pyrimidin-7-one (4) (Scheme 1). In addition, treatment of compound 1 with 1,2- dibromoethylene or 1,3-dibromopropane in presence of triethylamine (TEA) afforded five- or six-membered- ring-fused pyrimidine derivatives: thiazolo[3,2-a]- pyrimidine 5 or pyrimido[2,1-b]thiazine 6, respectively (Scheme 2). Moreover, treatment of compound 1 with cyclo- pentyl or cyclohexyl bromide gave the corresponding S-cycloalkyl derivatives 7a or 7b, respectively (Scheme 3). Finally, The latter compound 7b was reacted with 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane- 2,4-dithione (Lawesson’s reagent) to afford 5-allyl-6- {(benzo[d]thiazol-2-yl)methyl}-2-(cyclohexylsulfanyl)- pyrimidine-4(3H)-thione (8). Sulfide 7b was also DOI: 10.1134/S1070363216120367