Synthesis of Functionalized 2,3‐Dihydrothieno[2,3‐d]pyrimidin‐4(1H)‐ones and Their Recyclization to 2,3‐Dihydrothieno[3,4‐d]pyrimidin‐4(1H)‐ones.

Abstract

Fused pyrimidine derivatives R 0515 Synthesis of Functionalized 2,3-Dihydrothieno[2,3-d]pyrimidin-4(1H)-ones and Their Recyclization to 2,3-Dihydrothieno[3,4-d]pyrimidin-4(1H)-ones. -Thiazinones (II) are subjected to reactions with alkylating agents (III) undergoing heterocyclization into thieno[2,3-d]pyrimidinones (IV). Recyclization of the latter into thieno[3,4-d]pyrimidinones (V) occurs on treatment with toluenesulfonic acid. The reaction rate of this recyclization is significantly affected by the medium acidity, temperature, as well as the nature of the substituents at positions 1 and 2 of the dihydropyrimidine ring. A straightforward formation of recyclized product (VII) in the reaction of (VI) with (IIIa) results from steric hindrances by bulky substituents and preclude the thieno[2,3-d]pyrimidine ring closure. -(VOVK*, M. V.; SUKACH, V. A.; PYROZHENKO, V. V.; BOL'BUT, A. V.; Heteroat. Chem. 17 (2006) 2, 104-111; Inst. Org. Chem., Acad. Sci. Ukr., Kiev 253094, Ukraine; Eng.) -H. Hoennerscheid 31-145