Synthese und Eigenschaften von Thiazolo[3,2‐ a ]pyrimidinen und Thiazolo [3,2‐ a ] pyrrolo [2,3‐ d ]pyrimidinen

From the alkali‐catalysed reaction of thiouracil with bromoacetaldehyde diethyl acetal three products are isolated in nearly the same quantity: 2‐(2, 2‐diethoxyethylthio)‐uracil ( 2 ) and two cyclization products: 3 , a thiazolo[3, 2‐ a ]pyrimidin‐5‐one, and 4 , athiazolo[3, 2‐ a ]pyrimidin7‐one. By warming with acid both 2 and 4 yield 3 . Rearrangement of 4 to 3 proceeds also by heating the hydrochloride. Similar cyclizations leading to thiazolo[3, 2‐ d ]pyrrolo[2, 3‐d]pyrimidin‐5‐ones are also described. Bromine substitutes 3 in position 6. The bromo derivative 6 on treatment with primary or secondary amines affords 7‐amino compounds.