Ethyl 2-Amino-5-ethylthiophene-3-carboxylate is used as a reagent in the synthesis of 2-amino-4-oxo-5-substituted-6-ethylthieno[2,3-d]pyrimidines as dual thymidylate synthase and dihydrofolate reductase inhibitors and as antitumor agents. Also used as a reagent in the synthesis of the necroptosis inhibitor, Necrostatin-5 (Nec-5).