Synthesis, Antimicrobial and Antioxidant Activity of 3-Aryl-6,7-Dihydro-5H-[1,3]Thiazolo[3,2-a]Pyrimidines

A series of 3-aryl-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidines was obtained by cyclocondensation of tetrahydropyrimidin-2(1H)-one with 2-bromo-1-arylethanones. It was established that the nature of the substituent in the aromatic nucleus of phenacyl bromide significantly affects the course of this type of reaction. In particular, in the case of 2-bromo-1-(4-hydroxyphenyl)ethanone, the target bicyclic product is formed as a result of boiling in ethanol for 4 hours, whereas the reaction time for the cyclocondensation of tetrahydropyrimidine-2(1H)-thione with other bromomethylaryl ketones was 10 hours. It was found that the result of the interaction of tetrahydropyrimidine-2(1H)-thione and 2-bromo-1-(4-chlorophenyl)ethanone for 4 hours is the S-alkylation product, 1-(4-chlorophenyl)-2-[(1,4,5,6-tetrahydropyrimidin-2-yl)thio]ethanone, intramolecular cyclization of which leads to 3-(4-chlorophenyl)-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine under the action of H3PO4. The results of bioscreening of the synthesized 3-aryl-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidines demonstrated their moderate antimicrobial activity and made it possible to identify a potential synthetic antioxidant, 3-(4-fluorophenyl)-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine (I = 88.2%).