Pyrimido pyrimidine-6-carboxylates 5-hydroxy

The cyclization of ethyl 3-(4-chloro-2-substituted-pyrimidin-5-yl)-2-diazo-3-oxopropanoates 4 (prepared from the corresponding pyrimidine-5-carbonyl chlorides and ethyl diazoacetate) in the presence of triphenylphosphane yields the corresponding 7-substituted ethyl 4-hydroxy-pyrimido[4,5-c ]pyridazine-3-carboxylates 544 [for a similar reaction of 4 (R = SMe) with hydrazine hydrate cf. ref 50]. 

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