Hexahydropyrido pyridazines

Hexahydropyrido[l,2-6]pyridazin-8-ones 178 and a 2,3-tetramethylene derivative were formed on the intramolecular cycloaddition of 177, formed in situ by dehalogenation of hydrazones of the hex-5-enoic acid derivatives 176 [87JCS(P1)2511]. Intramolecular cycloaddition of hydrazones 179 in... 

Arylidene-substituted Meldrum s acids 290 were reacted with 5-amino-6-phenyl-3(2//)-pyridazinone 291 to yield 4-aryl-2,5-dioxo-8-phenyl-l,2,3,4,5,6-hexahydropyrido[2,3-r/]pyridazines 292 in one step in good yields... 

The pyridazine part of 4,4a,5.6,7,8-hexahydropyrido[4,3-c]pyridazin-3(2f/)-ones is aromatized by treatment with bromine in refluxing chloroform to give product l.142... 

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