Pyrazine-2,3-dicarboxylic anhydride,

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... 

Interest in the synthesis and reactions of pyrrolo[3,4- ]pyrazines is focused on two goals. The first is the development of analogs of zopiclone 256, a hypnotic agent <2001MI27>. Analogs of 256 are typically prepared from pyrazine-2,3-dicarboxylic anhydride (a furo[3,4- ]pyrazine) and a variety of aliphatic or aromatic amines <1996MI26, 1997MI28>. 

Pyrazine-2,3-dicarboxylic anhydride gave no products of the reaction of the corresponding heteroaryne with pyridine however, it gave a small but definite amount of phenylpyrazine with benzene, suggesting the formation of pyrazyne. This anhydride is readily converted by ring opening and rearrangement to succinonitrile (Brown et al., 1966). 

Heteroatomic dicarboxyhc anhydrides also lose CO 2 and CO on electron impact or thermolysis.72,73,74) Jq the case of pyrazine-2,3-dicarboxylic anhydride, the initially formed aiyne rearranges to a 1 1 mixture of maleo-nitrile and fumaronitrile 73) Eq. (33). Quinoxaline-2,3-dicarboxylic an-... 

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.). 

The parent polythieno[3,4-Z ]pyrazine (19, R = H) has recently been prepared by reaction of 2,3-pyrazine-dicarboxylic anhydride (92) with P4S10 (Scheme 8) as a black powder whose dedoped conductivity was 10 -10 S/cm. Doping with NO BF4, I2. or FeCU gave conductivities of (5-7) x 10 S/cm [22]. A similar reaction using 2,3-pyridinedicarboxylic anhydride (93) produced polythieno[3,4-/>]pyridine (94), whose dedoped conductivity was 10 S/cm and whose conductivities after doping with NO BF4 . I2. and FeCIi were 2 X 10 3 X 10 , and6 x 10 S/cm, respectively [22]. No band gap data were presented for either polymer. 

Stepwise addition of the aniline moieties in analogy to Scheme 7 (Route A) allows the preparation of asymmetrically substituted derivatives.55,56 The use of pyridine-3,4-dicarboxylic acid anhydride similarly results in the formation of mixtures of 5- and 6-azaphthalides.57 Quinoline-2,3-dicarbo-xylic anhydride has also been converted into the corresponding azaphthal-ides in a similar manner.58 Pyrazine-2,3-dicarboxylic acid anhydride yields... 

Pyrazine-2,3-dicarboxylic acid anhydride has also been shown69 to react according to Scheme 8, yielding 4,7-diazaphthalides very similar in... 

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). 

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... 

The O-carboxyhydroxamic acid, prepared by treatment of pyrazine 2,3-dicarboxylic acid anhydride with hydroxy la mine, gives an O-benzoyl derivative. This forms a sodium salt which is isolated as a methanolate and which on heating in boiling toluene gives a mixture of 24% 3-aminopyrazine 2-carboxylic acid and 55% of the corresponding methyl ester (Scheme 20a).253a... 

Pyrazine-2,3-dicarboxylic acid anhydride (180) serves as the basis for the preparation of a series of pyrrolo[3,4-6]pyrazine derivatives <89JSC233>. Thus, treatment with a series of amino acids yields compounds of the type (181) (Equation (62)). 

Synthesis of a tetracyclic analog of 294 is also reported from the anhydride of pyrazine-2,3-dicarboxylic acid and a tetralin derivative under Friedel-Crafts conditions (85JCR(S)338). A representative of the o-quinonoid system (296) was prepared from 2,3-dichloro-1,4-naphthoquinone and o-phenyl-enediamine (63JOC1019). 

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... 

The anhydride 1 is readily prepared from pyrazine-2,3-dicarboxylic acid by treatment with thionyl chloride or acetic anhydride. The 2,3-dimethyl-substituted analogue of 1 has been similarly prepared using... 

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