Pyrazine 2.3- dicarboxylic acid anhydride, reactions

Pyrazino[2,3-d]pyridazine-5,8-dione (104) can be prepared from either pyrazine-2,3-dicarboxylic acid anhydride (212) or dimethyl pyrazine-2,3-dicarboxylate (213) by reaction with hydrazine hydrochloride or hydrazine hydrate, respectively. The preparation based... 

Pyrazino[2,3- / pyridazine-5,8-dione 420 can be prepared from pyrazine-2,3-dicarboxylic acid anhydride 419 (Scheme 218). Likewise, the reaction of a pyridazine-4,5-dicarboxylic acid derivative with hydrazine is the most convenient approach to pyridazino[4,5-d]pyridazines <2000TL2863, CHEC-III(10.19.2.1.3)984> a related synthesis of pyridazino[4,5- /]pyridazin-l(2//)-ones 422 from ethyl 5-acylpyridazine-4-carboxylates 421 is shown in Scheme 219 <1979M365>. 

Reference has already been made to the partial decarboxylation of pyrazinedicarboxylic acids.219 Both pyrazine itself,232 and 2,3-dimethylpyrazine,207 are conveniently prepared by decarboxylation of the appropriate dicarboxylic acids. The decarboxylation of pyrazine-2,3-dicarboxylic acid is carried out by heating in din-butyl phthalate and gives pyrazine in 90% yield. The 2,3-dicarboxylic acid forms an anhydride in the normal way. Pyrolysis of the anhydride at 800°/0.05 mm through a silica tube gives in 80% yield an approximately 1 1 mixture of maleonitrile and fumaronitrile (Scheme 19). 2,3-Dehydropyrazine is thought to be an intermediate in this reaction and a strong peak of m/e 78, corresponding to the dehydropyrazine ion, is observed in the mass spectrum of the anhydride.233... 

Catalytic hydrogenation of the imide 24 (R = H) over palladium on charcoal results in partial reduction of the pyrazine ring to give the tetrahydro compound 37. The anomalous products 31 and 32 from the reaction of the anhydride of pyrazine-2,3-dicarboxylic acid and hydrazine were presumed to have been formed by reduction of the pyrazine ring by diimide. This could have been formed in situ by oxidation of hydrazine... 

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