Abstract In a one-pot synthesis 6, 7-dimethyl-2-arylidine-5-H-thieno [2, 3-d] pyrimidine-3, 5- diones 2 were prepared via the reaction of a ternary mixture of 5, 6-dimethyl-2-thioxo-1, 2, 3, 4-tetrahydrothieno [2, 3-d] pyrimidin-4-one (1), chloroacetic acid, and a proper aldehyde. Compound 2 reacted with hydroxylamine to afford 2, 3-dihydro-7, 8-dimethyl-3-substituted-9 H-isoxazolo [5′, 4′: 4, 5] thiazolo [3, 2-a] thieno [2, 3-d] pyrimidin-9-ones (4). Reaction of ...