5-Cyano-4-oxo-6-phenyl-2-thioxo-l,2,3.4-tetrahydro pyrimidine1 (I) reacts with alkyl or alkaryl halides to give the corresponding 2-alkyl (alkaryl) derivatives (118-g); and with chloroacetic acid ethyl chloroacetate to give compounds 111 and IV respectively further reaction of IV with ammonia and amines yielded 5-cyano-2(glycolamidethio)-6-phenyl pyrimidine-4(3H) one derivatives (Va-g). The parent thiazolo[3,2-a]pyrimidine (VI) was prepared from compound 111 by refluxing with acetic anhydride. Also compound I reacted with hydrazine hydrate to give 2-hydrazino derivative IX was converted into a variety of triazolo(4.3-a] pyrimidine derivatives. The biological activity of the new compounds was tested as microbicidal and bioregulator agents, the results obtained were correlated with their structure