2,3 -dihydropyrazine with alkali

The 1,4-dihydropyrazine system has been prepared by reductive silylation of pyrazine with alkali metals and halogenosilanes. Thus pyrazine with lithium and trimethylchlorosilane gives l,4-bis(trimethylsilyl)-l,4-dihydropyrazine (623). Reduction of pyrazine with sodium in ethanol gives piperazine (22). 

The reactions in the decomposition of 13,6-trimethyl-2-oxo-l, 2-dihydropyrazine methiodide with alkali metal hydroxide to give 1,4,6-trimethyl-3-methylene-2-oxo-1,2,3,4-tetrahydropyrazine (1105) and its reaction with benzenediazonium chloride or phenylhydrazine to give l,4,6-trimethyl-2-oxo-3-phenylazomethylene-l,2,3,4-tetrahydropyrazine (1105,1132) have been described. 

Fierz-David and Ziegler (301) first applied this method to azo compounds. Ethyl acetoacetate and various aromatic amines (aniline, o- and p-toluidines, m-xylidine, o-anisidine, and chloroanilines) were convereted to acetoacetanilides and then coupled with diazotized sulfanilic acid. The azo dyes (38) were reduced with stannous chloride in hydrochloric acid to the corresponding aminoaceto-acetanilides (39), which in alkali formed the dihydropyrazines (40). Catalytic reduction of o-hydroxyphenylglyoxal phenylhydrazone in acetic acid over palladium has been shown also to give 2,5-bis(o-hydroxyphenyl)pyrazine (302). Reduction of chemical means has been shown to give... 

The condensation of a, dicarbonyl compounds (49) with aj3-diamino compounds (50), which proceeds through the dihydropyrazine (51), has been much used for the synthesis of alkyl- and arylpyrazines (52). These reactions are usually carried out in methanol, ethanol, or ether in the presence of sodium or potassium hydroxide. The dihydropyrazines may be isolated, or oxidized directly to the pyrazine. Dehydrogenating agents that have been employed include oxygen in aqueous alkali (329), air in the presence of potassium hydroxide (330), sodium amylate in amyl alcohol (330a), alcoholic ferric chloride (24), and copper chromite catalyst at 300° (331) (see also Section 1). Pyrazines prepared by this method and modifications described below are listed in Table II.8 (2, 6, 24, 60, 80,195, 329-382) and some additional data are provided in Sections VI. 1 A, VlII.lA(l), and IX.4A(1). 

The ultraviolet spectra in aqueous solution (821) of the methiodides isolated from the methylation of 2-amino- and 2-dimethylaminopyrazines with methyl iodide in methanol (821) differed from those obtained by protonation of 2-amino-and 2-dimethylaminopyrazine, respectively. This methiodide of 2-aminopyrazine was rapidly decomposed by aqueous alkali but did not form l-methyl-2-oxo(or imino)-l, 2-dihydropyrazine or 2-methylaminopyrazine (821). These and other observations were consistent with protonation of 2-amino(2-methylamino or 2-dimethylamino)pyrazine at N, and with the methiodides isolated involving quater-nization at N4 (821). It has been claimed from studies of ultraviolet and infrared spectra and from reactions with cyanoguanidine that in 2-aminopyrazine p-toluenesulfonate, the amino group is protonated (1189). 

Diphenyl-5,6-dihydropyrazine reacts with alcoholic alkali to form 2,3-... 

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