Pyrazinium salts

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). 

Substituted pyrido[2,3-(i]pyrazinium salts form cycloadducts with quinones (75HCA2529), similar to those formed by quinoxalinium salts. 

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

Pyrido[2,3-b]pyrazinium salts, N-aryl-2,3-dimethyl-nucleophilic attack, 3, 253 Pyrido[2,3-(i]pyrazinium salts reactions... 

Hydrolytic ring opening of the isomeric [l,2,3]triazolopyrimidinium salt 99 yielded the amide 100. The same team also described <1997T9393> the analogous transformation of the [l,2,3]triazolo[l,5- ]pyrazinium salts 101 reaction of this quaternary salt with a secondary amine (e.g., with pyrrolidine) led to the formation of the azadieneamine 102. For the formation of this product, a similar mechanism to that with 96 was anticipated. 

A three-component one-pot condensation of 2-aminomethylpyridines 446, aldehydes, and isocyanides afforded 3-substituted 4-aminopyrido[l,2-fl] pyrazinium salts 447 (05OL2517) and not 4-(2-pyridyl)imidazols 448, as was stated earlier (05OL39). 

Pyrazine diquatemary salts of types 16lB1 and 17152 are known and also 6,7-dihydro derivatives of 16.152a The diquaternary salt (17) was originally formulated as the monohydrate of 18, but attempts to dehydrate 17 to 18 have not been successful.152 Dipyrido[l,2-a 2, l -c]pyrazinium dibromide (16) has herbicidal properties it is reduced in aqueous solution to a stable radical cation.183 The related pyrido[l,2-a]pyrazinium salts of type 19 have also been prepared.153,1B4a... 

Few examples of N-amination of azines have been reported. The use of such reagents as 0-mesitylenesulfonylhydroxylamine has led to the direct synthesis of /V-aminopyridazinium, -pyrimidinium, and -pyrazinium salts (80CPB2676), and 1-aminobarbituric acids (72CPB1814), while 0-(2,4-dinitrophenyl)hydroxylamine was a useful amino-transfer reagent in the direct synthesis of 1 -amino-6-methylthio-1,2,4-triazin-4( 17/)-ones from 2-methylthio-1,2,4-triazin-5( 1H)-ones (82JHC1583). 

In the secondary addition of methanol to the monomethoxy adducts 42-44, their reactivities vary to the greater extent. It has been established by 1H-NMR spectroscopy that diaddition of sodium methoxide in methanol-d4 occurs at 20°C with the 1,4-diazinium salts 36e, 37a,c,f, and 40d (Scheme 40) (86KGS1380). Monosubstituted pyrazinium salts 36c,d as well as the pteri-dinium cations 40a,b do not produce any detectable quantities of the dimethoxy adducts 45. 

Pyrazine 1-oxide (288) gave a 1 1 mixture of 2-chloropyrazine (289) and the l-(pyrazin-2-yl)pyrazinium salt (290), of which the second afforded 2-pyrazi-namine (291) during mildly alkaline work up [POCl3, 70°C, 2 h removal of (289) residue to pH 10 11% of amine (291)] the intermediate salt (290) was subsequently isolated and purified (POCl3, 20°C, 10 min 70%).574... 

Methylpyrazine is methylated with methyl iodide in dimethyl sulfoxide at room temperature to give l-methyl-3-methylpyrazinium iodide and i-methyl-2-methyl-pyrazinium iodide, in a ratio of 3.9 I. The rate of methylation relative to pyrazine was 2.06 (666). The reaction of 2,5-dimethylpyrazine with iodo- or bromoacetic acid to give the 1,2,5-trimethylpyrazinium salt has been investigated (3). A kinetic study of the reaction of sodium hydroxide on quaternary pyrazinium salts (667, 668) has been made using a conductivity method to follow the progress of the reaction (11=5 12). In the case of 1,2,5-trimethylpyrazinium hydroxide, equilibrium lies toward (11), which slowly disappears, presumably forming the ether (13) (668). When 1,2,5-trimethylpyrazinium bromide was heated in a sealed tube trimethyl- and tetramethylpyrazine were produced (660). 

The reactions of pyrazine with sodium amide in liquid ammonia to give the anion of 2-amino-1,2-dihydropyrazine (608), and of 3-substituted 1-methylpyrazinium ions with liquid anunonia to give 3(or 5)-substituted 2-amino-1-methyl-1,2-dihydro-pyrazines (609) have been described in Section IV. 1C. Similar reactions of pyrazine with phenyllithium at —45° in tetrahydrofuran (720a) and of 1,2,5-trimethyl-pyrazinium salts in liquid ammonia with nitromethide and ethanethiolate anions (721) have been described in Section IV.2C(8). 

Several lower iodoalkanes have been used to alkylate the parent compound, furnishing the 6-alkylpyrido[3,4-6]pyrazinium salts.67... 

Various 1,5-diketones of type 30 have been cyclized using ammonium acetate in acetic acid to give 1,3-disubstituted pyrido[l,2-a]pyrazinium salts (31). Similar treatment of the ester 32 gave the oxo compound 33. 

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