2- pyrazine salt

Inductive and resonance stabilization of carbanions derived by proton abstraction from alkyl substituents a to the ring nitrogen in pyrazines and quinoxalines confers a degree of stability on these species comparable with that observed with enolate anions. The resultant carbanions undergo typical condensation reactions with a variety of electrophilic reagents such as aldehydes, ketones, nitriles, diazonium salts, etc., which makes them of considerable preparative importance. 

An alternative approach to the use of a-aminoketones involves acetals (72JOC221) and pyrazine-2,3-diones have been synthesized by this route (Scheme 58). The acetals are readily available from the phthalimido derivatives via the a-chloroketones. Hemiacetals have also served as a starting point for pyrazine synthesis, although in most cases hemiacetals are too labile to be easily prepared examples are common in the 2-amino-2-deoxy sugar series 2-amino-2-deoxy-D-glucose for example dimerizes to the pyrazine (101) when generated in situ from the hydrochloride salt (68JAP6813469). 

No systematic study of the mass spectra of pyridopyrazines has been noted, but those of 2,3-dialkyl and 2,3-diaryl derivatives have been recorded 750MS97), and mass spectrometry has been used in the elucidation of problems in the reactions of pyrido[2,3-f ]pyrazines with amide ion (including use of and derivatives) (79JHC305), and of pyrido[2,3-f ]pyrazinium salts with indoles (78ZOR431). The mass spectra of some 1-deazaflavins have been recorded (74JCS(P1)1965). 

Pyrido[l,2-a]pyrazin-5-ium salts — see 2-Azaquinolizinium salts E rido[2,3-b]pyrazinium salts mass spectra, 3, 250... 

The quaternization of pyrazine compounds has not been extensively studied, and, therefore, a detailed discussion of the effect of substituents is not possible. Recently Cheeseman has shown, from spectroscopic evidence, that 2-amino- and 2-diethylamino-pyrazine (50, Y = NH2 and NEt2) quatemize at N-4, although protonation occurs at position-1. Other substituted pyrazines from which quaternary salts of structure 51 are formed include 2-chloro- and 2-... 

Phase transfer catalysts were used for nucleophilic displacement reactions of activated leaving groups by hydroxyfurazanyl anions. For example, tetrachloro-pyrazine was found to react with hydroxyfurazans in benzene/Na2C03/tetraalkyl-ammonium salts giving products of mono- or disubstitution (Scheme 173) (94MI1). The course of the reaction depends on the ratio of the reactants and the nature of the ammonium salt. 

Treatment of the appropriate pipecolic amide 396 with NEta afforded optically active or racemic perhydropyrido[l,2-a]pyrazine-l,4-dione (397) (97USP5703072). (9a5)-Perhydropyrido[l,2-a]pyrazin-3-one (400) was obtained by cyclization of piperidine 398, and the catalytic hydrogenation of quaternary salt 399 over Pd/C (99H(51)2065). 

As no simple copper-perrhenate salts previously existed to serve as a model for structural relationships to [Cu2(pzc)2(H20)2Re04], our attention turned to the syntheses of the isoelectronic silver-perrhenate systems. Shortly after an analysis of the structure above, a synthesis of the new pyrazine-pillared (=pyz) AgRe04(pyz) solid was found [30], and is shown in Fig. 17.3 alongside the re-... 

Because silylation with HMDS 2/TCS 14 in acetonitrile at ambient temperature converts the unreactive a-chloroketone moiety of 743 into an /Z-mixture of reactive alkyl 4-chloro-3-trimethylsilyloxycrotonates 746a, b [230, 231] which can be isolated and distilled, if humidity is excluded, silylation of 743a, b in the presence of ami dine salts such as 745 gives the desired ethyl or methyl imidazole(4,5)-acetates 748a, b via IMz and 747b. The reaction of formamidine acetate with 746a,b affords 745 (with R=H) in up to 70% yield [232, 233] (Scheme 5.79). As side reactions one must, e.g., take into account the reaction of 746 with ammonia to give 755 which subsequently dimerizes to the pyrazine 756, as discussed in Section 5.5.3. 

Oxazoles (191) are producedwhen triphenylphosphine is treated simultaneously with an a-azidocarbonyl compound and an acyl halide. The intermediate iminophosphoranes (189) react with the acyl halide before they can react with themselves to give pyrazines. Elimination of phosphine oxide from the resulting salts may give the intermediate halo-genoimines (190), or the oxazoles may be formed via the betaines (192). 

High density brine completion fluids also often require the use of corrosion inhibitors (8,9). Blends of thioglycolates and thiourea alkyl, alkenyl, or alkynyl phosphonium salts thiocyanate salts mercaptoacetic acid and its salts and the reaction products of pyridine or pyrazine derivatives with dicarboxylic acid monoanhydrides have been used as high density brine corrosion inhibitors. 

Figure 2.3 ESR spectrum of the potassium salt of pyrazine radical anion simulated using hyperfine couplings from ref. 2.

The quinoxaline 100, with self-contained donor-acceptor properties, has potential in optoelectronic <06JACS10992>. Electroactive dendrimeric bis-quatemary salts have been prepared by direct quatemisation of pyrazine using dendrimeric benzyl bromides <06TL4711>. 

This method can be used with heteroaromatic bases, such as thiazoles or pyrazines, which complex with the silver salt and reduce its catalytic activity. A disadvantage of the method is that the heteroaromatic base can be only partially protonated under these conditions. 

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