Thieno[2,3-d]Pyrimidine-4-Ones. Part 5.# Hydrogen Chloride Promoted Synthesis of 2-Substituted Thieno[2,3-d]Pyrimidine-4-Ones and their Structural Investigations

Synthesis of some novel 2-substituted thieno[2,3-d]pyrimidine-4-ones have been studied. It was found that in this case the 2-amino-4,5-dimethylthiophene carboxamide (1) can serve effective synthone for the synthesis 2-aryl-5,6-dimethyl-3,4-dihydrothieno[2,3-d]pyrimidine-4-ones (3-13). Interaction of amide 1 with substituted aromatic aldehydes in the presence of concentrated hydrochloric acid leads to the formation of compounds 3-13. It was impossible to isolate intermediates (2), substances with asymmetric carbon atom in position 2. It was revealed that intermediates 2 by oxidation on air easily turn into 2-arylthieno[2,3-d]pyrimidine-4-ones. The structure of synthesized compounds was confirmed by IR- and 1H NMR-spectroscopy.