SYNTHESIS OF PYRIMIDINE-ANNELATED HETEROCYCLES: THERMAL REARRANGEMENT OF 1,3-DIMETHYL-5-(PROP-2-ENYLTHIO)-PYRIMIDINE-2,4-DIONES

Abstract

Thermal [3,3] sigmatropic rearrangement of a number of 1,3-dimethyl-5-(prop-2-enylthio)uracils (3a–c) afforded pyrimidine-annelated heterocycles in 65–80% yields. While 3a and 3b gave 1,3-dimethyl-tetrahydropyrano[3,2-d]pyrimidine-2,4-dione (4a) and 1,3,6-trimethyl thieno[3,2-d]pyrimidine-2,4-dione (6b), 3c furnished 6,7-dihydro-1,3,6-trialkyl thieno[3,2-d]pyrimidine-2,4-dione (5c) and 3d gave 1,3-dimethyl-5-mercapto-6-(3-methylbut-2-enyl)pyrimidine-2,4-dione (8d). Product 5c on subsequent dehydrogenation with palladised charcoal in diphenyl ether gave 1,3-dialkyl-6-ethyl thieno[3,2-d]pyrimidine-2,4-dione (6c).

ACKNOWLEDGMENTS

We are thankful to CSIR (New Delhi) for financial assistance. Two of us (NKJ and SKG) are grateful to CSIR (New Delhi) for fellowships.