2- 2 - ethyl pyrazine

The odor threshold of the pyrazines range from 0.006 ppb in water for 2—propyl—3-methoxypyrazine (29) to 43 ppm in water for 2,5—dimethyl—3-ethyl pyrazine (30). A excellent review of the pyrazines found in food products has been prepared by Maga (31). 

Diethyl-3-methyl pyrazine 2.5- Dime 3 ethyl pyrazine + +... 

Dimethy1-3-ethyl pyrazine 6,7-Dihydro-2-ethyl-5(H)-cyclopentapyrazine + +... 

Amino-3-phenylisoxazol-4-yl)pyrazine (168) gave 2-phenylethynylpyrazine (169) (NaN02, AcOH—H20, 20°C, 1 h 80% mechanism suggested).795 2-(Benzo[ ]thien-2-yl)-3,6-dim ethyl pyrazine (170) underwent desulfurization to 2,5-dimethyl-3-phenacylpyrazine (171) (Raney Ni, EtOH, reflux, 8 h ... 

Vinylpyrazine (333, R = H) gave 2-[2-(ethylamino)ethyl]pyrazine (334) (EtNH2, MeOH, AcOH, 60°C, 24 h >90%).1662 Also other examples.847... 

Dibenzyloxy-3-isobutyl-6-(tetrahydropyran-2-yloxymethyl)pyrazine 4-oxide (171) gave 2-benzyloxy-3-isobutyl-5-methoxy-6-(tetrahydropyran-2-yloxym-ethyl)pyrazine 4-oxide (172) (NaH, Bu4NBr, MeOH, Mc2NCHO, 20°C, N2, 40 min 91% the selective transalkoxylation of the 5-benzyloxy group may be due to activation by the adjacent /V-oxidc entity).848... 

Acetylpyrazine gave its semicarbazone, 2-(l-semicarbazonoethyl)pyrazine (298) (H2NHNC0NH2.HC1, AcONa, EtOH—H20, 95°C, 15 min 90%)mo 2-[2-(Pyrazin-2-yl)acetyl]pyrazine (299) and 2-hydrazinopyrazine (300) gave 2-[2-(pyrazin-2-yl)-1 -(pyrazin-2-ylhydrazono)ethyl]pyrazine (301) (EtOH, reflux, 3 h %) 730 analogues likewise.730,731 Also other examples.283,866... 

Triisobutyl-6-methylpyrazine 2-[2-(Trimethylammonio)ethyl] pyrazine iodide... 

Pyrazine-based heterocycles examined by X-ray crystallography included N,N -bis[2-(2-pyridyl)ethyl]pyrazine-2,3-dicarboxamide <07JCS(D)633>, diimidazo[l,5-a T,5 -J]pyrazine-... 

Halogenations with A/-halogenosuccinimides have also been studied. Treatment of 2-methyl- and 2,5-dimethylpyrazine with one equivalent of A -chlorosuccinimide and a small quantity of benzoyl peroxide gave the unstable 2-chloromethyl (679, 690) and 2-chloromethyl-5-methylpyrazine (679). 2-Ethyl-3-methylpyrazine and 23-diethylpyrazine with V-bromosuccinimide in the presence of benzoyl peroxide gave 2-(l -bromoethyl)-3-methyl(and 3-ethyl)pyrazine, respectively (691,692). 

A series of aminoethylpyrazines (C4H3N2CH2CH2N=) has been prepared by the reaction of vinylpyrazine with amines in the presence of methanolic acetic acid or metallic sodium as the catalyst (730) and likewise 2-[2 -(r -oxocyclohexan-2" yl)ethyl] pyrazine from vinylpyrazine and cyclohexanone (731). 

Normal nucleophilic substitution reactions of alkyl and aryl chloropyrazines have been examined as follows 2-chloro-3-methyl- and 3-chloro-2,5-dimethyl(and diethyl)pyrazine with ammonia and various amines (535, 679, 680) 2-chloro-3(and 6)-methylpyrazine with methylamine and dimethylamine (681, 844), piperidine and other amines (681, 921) 2-chloro-5(and 6)-methylpyrazine with aqueous ammonia (362) alkyl (and phenyl) chloropyrazines with ammonium hydroxide at 200° (887) 2-chloro-3-methylpyrazine with aniline and substituted anilines (929), and piperazine at 140° (759) 2-chloro-3-methyl(and ethyl)pyrazine with piperidine (aqueous potassium hydroxide at reflux) (930,931) [cf. the formation of the 2,6-isomer( ) (932)] 2-chloro-3,6-dimethylpyrazine with benzylamine at 184-250° (benzaldehyde and 2-amino-3,6-dimethylpyrazine were also produced) (921) 2-chloro-3,5,6-trimethylpyrazine with aqueous ammonia and copper powder at 140-150° (933) and with dimethylamine at 180° for 3 days (934,935) 2-chloro-6-trifluoromethylpyrazine with piperazine in acetonitrile at reflux (759) 2-chloro-3-phenylpyrazine with aqueous ammonia at 200° (535) 2-chloro-5-phenylpyrazine with liquid ammonia in an autoclave at 170° (377) 2-chloro-5-phenylpyrazine with piperazine in refluxing butanol (759) but the 6-isomer in acetonitrile (759) 5-chloro-2,3-diphenylpyrazine and piperidine at reflux (741) and 5-chloro-23-diphenylpyrazine with 2-hydroxyethylamine in a sealed tube at 125° for 40 hours (834). 

Amino-5-bromomethyl-3-cyanopyrazine with ethyl acetoacetate and sodium hydride in tetrahydrofuran gave 5-[(2 -acetyl-2 -ethoxycarbonyl)ethyl]-2-amino-3-cyanopyrazine (1031) [which with sodium chloride in aqueous dimethyl sulfoxide at 155-170° for 6 hours gave 5-(2 -acetylethyl)-2-amino-3-cyanopyrazine] and a similar reaction with ethyl y-ethoxyacetoacetate gave 2-amino-3-cyano-5-[(2 -ethoxycarbonyl-2 -ethoxymethylcarbonyl)ethyl]pyrazine [which with sodium chloride in aqueous dimethyl sulfoxide at 155-170° for 6 hours gave 2-amino-3-cyano-5-(2 -ethoxymethylcarbonyl)ethylpyrazine] (1031). 

Vinylpyrazine undergoes a Michael condensation with cyclohexanone, cyclo-pentanone, and acetophenone for example, 2-vinylpyrazine with cyclohexanone and sodium gave 2-[2 -(r -oxocyclohexan-2"-yl)ethyl]pyrazine, and with acetophenone and sodamide in liquid ammonia gave low yields of 2-(3 -benzoylpropyl)pyrazine (monopyrazylethylation) and the bis Michael adduct (731). 

Typical preparations have been described for 2-(r-hydroxyiminomethyl)pyrazine (138) 2-(4 -dimethylamino-T-hydroxyiminobutyl)pyrazine (1186) 2-(2 -hydroxy-iminopentyl)-6-methylpyrazine (645) 2-(2 -hydroxyimino-3, 3 -dimethylbutyl)-6-methylpyrazine (645) 2-[r-hydroxyimino-2-(pyridin-2"-yl) (hyl]pyrazine (642) 2-[2 -hydroxyimino-2 -(pyridin-2"-yl, pyrazin-2"-yl, or pyrimidin-4 -yl)ethyl]pyrazine (642) 2-[l, 2 -bishydroxyimino-2 -(pyridin-2"-yl)ethyl]pyrazine (642) 2-12 -(2",4"-dinitrophenylhydrazono)-3 -methylbutyl]-6-methylpyrazine (645) 2-[ 1-(substituted hydrazono)ethyl]pyrazine (1196) 2-[l -phenyl-1 -(substituted hydrazono)methyl]-pyrazine (1196) 2-(r-thiosemicarbazonoethyl)pyrazine (138) 2-(2 -chloro-l -thiosemicarbazonoethyOpyrazine (138) and 2,5-dimethyl-3,6-bis(r-semicarbazono-ethyl)pyrazine (1196). 

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