Pyridazine 1,2-dioxide, 3,6-dimethyl

Pyrido[2,3-, pyridazine derivatives 48 have been synthesized by refluxing equimolar amounts of an appropriate 5-benzylidene-2,2-dimethyl-l,3-dioxane-4,6-dione 47 with 5-amino-6-phenylpyridazin-3(2/7)-one 46 in methanol or a methanol acetic acid mixture. The electron-poor carbon atom of the polarized carbon-carbon double bond of 47 is the electrophile attacking C-4 of the 5-aminopyridazinone 46. Imino-enamine tautomerization of the intermediate is followed by ring closure and subsequent loss of acetone and carbon dioxide affording the reaction products 48 as stable crystalline solids in 70-90% yield (Scheme 9) <2000T2473>. 

N-Oxidation of 3,3 -bipyridazines is influenced by substituents in a similar way to that for pyridazines. Thus, the nitrogen atoms adjacent to an aryl or methoxy substituent are not oxidized. Thus, the 6,6 -dimethyl compoimd (124) gives with hydrogen peroxide the l,l -dioxide (125), and with peroxy-benzoic acid a mbcture of the monoxide (126) and a small amount of the dioxide (125). No isomeric 2-oxides were formed. Similar results were obtained with 3,3 -bipyridazine itself. On the other hand, the 6,6 -dimethoxy analog (127) affords the 2,2 -dioxide (128) with hydrogen peroxide, and. a... 

Dimethyl-3,5-bis(methylsulfanyl)-1.2,4-triazepine undergoes addition of maleic anhydride, the intermediate then rearranges with loss of carbon dioxide, hydrogen, or methanethiol to give 2,4-dimethyl-5,7-bis(methylsulfanyl)pyrido[3,4- f]pyridazin-l(277)-one (1 20%) and 2,4-dimethyl-7-(methylsulfanyl)pyrido[3,4-ii]pyridazin-l(2/7)-one (2 40%).133... 

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