Abstract Condensation of ethyl 4-chloroacetoacetate with 4-amino-6-hydroxy-2- pyrimidinethiol produced ethyl 3-hydroxy-5-amino-7-oxothiazolino [3, 2-a] pyrimidin-3- acetate (7a) on crystallization. Subsequent ring closure of 7a produced the tricyclic 6a- hydroxy-5, 6, 6a, 7-tetrahydro-8-thia-1, 4-diazacycl [3.3. 2] azin-2, 5-dione (8). The structure of 8 was confirmed by crystal x-ray diffraction analysis.
![(5-amino-3-hydroxy-7-oxo-2,3-dihydro-7H-thiazolo[3,2-a]pyrimidin-3-yl)-acetic acid ethyl ester Structure](https://image.chemsrc.com/caspic/140/72195-12-1.png)
