Bridgehead nitrogen heterocycles. I. 2H(and 4H)-Pyrimido[1,2-b]pyridazin-2(and 4)-one. 3H-Imidazo[1,2-b]pyridazin-2-one, and 7H-(1,3,4-)thiadiazolo[3,2-a]pyrimidin-7-one systems
Bridgehead nitrogen heterocycles. I. 2H(and 4H)-Pyrimido[1,2-b]pyridazin-2(and 4)-one. 3H-Imidazo[1,2-b]pyridazin-2-one, and 7H-(1,3,4-)thiadiazolo[3,2-a]pyrimidin-7-one systems