Cyclocondensation of 5-amino-6-methyl-2-morpholinopyrimidine-4-thiol (1) and 2-bromo-5,5-dimethylcyclohexane-1,3-dione (2) under mild reaction condition afforded 4,7,7-trimethyl-2-morpholino-7,8-dihydro-5H-benzo[b]pyrimido[5,4-e][1,4]thiazin-9(6H)-one (3). The 1H and 13C NMR data of compound (3) are demonstrated that this compound exists primarily in the enamino ketone form. Reaction of compound (3) with phosphorous oxychloride gave 4-(9-chloro-4,7,7-trimethyl-7,8-dihydro-6H-benzo[b]pyrimido[5,4-e][1,4]thiazin-2-yl)morpholine (4). Nucleophilic substitution of chlorine atom of compound (4) with typical secondary amines in DMF and K2CO3 furnished the new substituted derivatives of 4-(4,7,7-trimethyl-7,8-dihydro-6H-benzo[b]pyrimido[5,4-e][1,4]thiazin-2-yl)morpholine (5a-h). All the synthesized products were characterized and confirmed by their spectroscopic and microanalytical data.

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