Proceeding from 3-(4-methyl-6-oxo-2-phenyl-1,6-dihydro-5-pyrimidinyl)propanoic and 2-methylpropanoic acids by successive reactions of chlorination, amination, and heterocyclization 4-amino-substituted pyrimidines were synthesized: 5,6,7,8-tetrahydropyrido[2,3-d]pyrimidine derivatives and 4-methyl-2-phenyl-5,6-dihydrobenzo[4',5']imidazo[2',1':6,1]pyrido[2,3-d]pyrimidine which we had previously obtained by alternative method. Antibacterial properties of the synthesized compounds were studied.

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Heating a mixture of substituted malonic esters and 6-methoxy-1,3-benzothiazolyl-2-amine afforded new derivatives of benzo [4,5]thiazolo[3,2-a]pyrimidine, 3-substituted 2-hydroxy-4Н-benzo[4,5]thiazolo[3,2-a]pyrimidine-4-ones. The choice between the possible tautomers was carried out basing on the Xray diffraction analysis of 3-formyl-2-chloro derivative synthesized by formylation of unsubstituted heterocycle by Vilsmeier reaction.The interest to the synthesis and investigation of derivatives of fused pyrimidines is due to the wide range of the biological activity exhibited by this class of heterocycles, including antitumor, antibacterial, antiviral, antiinflammation, neurotrophic, and other types of action [1,2].