5-Cyano-4-oxo-6-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidine (I) reacts with P2S5in pyridine to give pyrimidine-2,4-dithione (II). Further reaction of II with ethyl chloroacetate, chloroacetanilide, phenacyl bromide, bromoacetone and chloroacetonitrile gave the corresponding thieno[2,3-d]pyrimidine derivatives (III-VI). Interaction of compoundIVawith hydrazine hydrate in ethanol or diluted ethanol gave the hydrazide and hydrazino derivatives (VII, IX), which reacted with aromatic aldehydes to give the corresponding hydrazones (VIIIa-c, Xa-c). Alkaline hydrolysis of IV, using KOH gave the acidXIwith extrusion of thioglycolic acid.