Appropriately substituted 2,3-dihydro-7H-thiazolo[3,2-a]pyrimidin-7-ones 9-12 and 18 were considered as annulated analogues of HEPT (1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)-thymine), and some of these compounds were also found active against HIV-1, the most active one being 2,3-dihydro-5-[(3,5-dimethylphenyl)methyl]-3-ethoxy-6-ethyl-7H- thiazolo[3,2-a]pyrimidin-7-one (10b). S-Alkylation of 5-alkyl-6-(arylmethyl)-2-thiouracils 1-4 was performed with 2-bromoacetaldehyde acetals to furnish the S-[bis(alkoxy)ethyl] derivatives 5-8 and with allyl bromide to furnish S-allyl derivatives 17. The target compounds 9-12 were obtained by an N1 regioselective intramolecular cyclization reaction of silylated 5-8 using trimethylsilyl trifluoromethanesulfonate (TMS triflate) as the catalyst. Treatment of the S-allyl derivatives 17 with bromine in dry methylene chloride afforded the 3-(bromomethyl) derivatives 18.