Pyrazine-2,3-dicarboxylic anhydride pyrolysis

Didehydropyrazine is believed to be an intermediate in the pyrolysis of pyrazine-2,3-dicarboxylic anhydride. According to DFT calculations, this molecule has a triplet ground state with a singlet state about 10 kcal/mol higher in... 

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... 

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