A series of substituted thieno[2,3-d]pyrimidines was synthesized starting from ethyl 2- amino-4,5-dimethylthiophene-3-carboxylate and ethyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene- 3-carboxylate. Reaction of 2-hydrazino-5,6-dimethylthieno[2,3-d]pyrimidin-4(3H)-one, 2-hydrazino- 5,6,7,8-tetrahydro-3H-benzo[4,5]thieno[2,3-d]pyrimidin-4-one and its 3-allyl analogue with different reagents afforded thieno [2,3-d]triazolo[4,3-a]pyrimidines and thieno[3,2-e]triazolo[4,3- a]pyrimidines, beside open chain derivatives.