Ethyl 5-oxo-2,3-dihydro-5H-[1,3]thiazolo-[3,2-a]pyrimidine-6-carboxylateEthyl 5-oxo-2,3-dihydro-5H-pyrimido[2,1-b][1,3]thiazole-6-carboxylateethyl 5-oxo-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine-6-carboxylateEthyl 5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidine-6-carboxylate