Pyridazines from 1,2-dicarboxylic anhydrides

Condensation of pyrazine-2,3-dicarboxylic anhydride with hydrazine furnishes pyrazino[2,3-diols from pyrazine-2,3-dicarboxylic esters (see Section 7.4.9.1,1.1.). 

Acetic acid acetic anhydride Pyridazin-3,6-diol ring from dicarboxylic acids... 

Pyrazino[2,3-d]pyridazine-5,8-dione (420) can be prepared from pyrazine-2,3-dicarboxylic acid anhydride (419). Condensation of hydrazine with ethyl 5-acylpyridazine-4-carboxylates (421) gives pyridazino[4,5-d]pyridazin-l(2//)-ones (422) (79M365). 

Good yields of a pyridazine (rather than the bishydrazide) are obtained from a dicarboxylic acid by first converting the latter into its anhydride by heating with acetic anhydride, and then adding a hydrazine. A related pyridine diester is cyclized vnth hydrazine hydrate [2733] (sometimes with hydrochloric acid present [3918]) at ambient tem()erature to the dihydrazide, which may be converted to the dione by heating with hydrazine [2733], and to the imide on acidification with acetic acid. The pyridazinedione may also be prepared from the imide (80J) by heating with hydrazine hydrate [2797]. 

In analogy to phthalazine syntheses, 5,7-dihydrofuro 3,4-A pyridinc (pyndine-2,3-dicarboxylic acid anhydride) and hydrazine readily condense in refluxing aqueous solution,42 refluxing acetic acid, or alternatively with lower yield in refluxing ethanol, to give pyrido[2,3-r/]-pyridazine-5,8(6/7,7//)-dione (la).78 A similar reaction is observed starting from pyridine-2,3-dicarboxylic acid anhydride and hydrazine hydrate in refluxing acetic acid.45... 

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See also in sourсe #XX -- [ , ]

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