A FACILE SYNTHESIS OF ISOXAZOLO [5′,4′:4,5]THIAZOLO[3,2-a]THIENO PYRIMIDINES A NEW RING SYSTEM

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-9H-isoxazolo[5′,4′:4,5]thiazolo [3,2-a] thieno[2,3-d]pyrimidin-9-ones (4). Reaction of 1 with 3-chloropent-2,4-dione in ethanolic potassium hydroxide yielded the S-acetylacetone derivative 5d. The latter compound reacted with hydrazines and thiourea affording the 2-pyrazolthio and the 2-pyrimidinylthio derivatives 11 and 12, respectively. Compound 5d also underwent cyclization on boiling with acetic anhydride/pyridine solution to yield 2-acetyl-3,6,7-trimethyl-5H-thieno[2,3-d]thiazolo[3,2-a]pyrimidin-5-one (13). The 2-methylthioderivative 5a was converted into the corresponding 2-methyl sulphone derivative 9 on treatment with hydrogen peroxide.