Pyridazino pyridazine-1,4,6,9-tetrone

Pyridazino[l,2-pyridazine derivatives are easily reduced with either hydrogen over a catalyst or with metal hydrides. Reaction of the pyridazino[l,2- ]pyridazine-l,4,6,9-tetrone (44) with hydrogen over platinum oxide gives the hydrogenated product (45) (66JOC1311). This product can be further reduced with lithium aluminum hydride to give the octahy-dropyridazino[l,2- ]pyridazine (24) (67JA4875). 

Another pathway which is often used in the preparation of this ring system involves the Diels-Alder reaction. 3,6-Pyridazinedione (139) is known to be exceptionally reactive toward dienes. This dienophile readily condenses with butadiene, 2,3-dimethylbutadiene and coumalic acid to give the respective Diels-Alder adducts (140). 3,6-Pyridazinedione is also reported to decompose with evolution of nitrogen gas at temperatures below 0 °C, giving the pyridazino[l,2-a]pyridazine-l,4,6,9-tetrone (44) as the major product (62JA966). 

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