2-Methyl-6-vinylpyrazine

Chloromethyl-5-methylpyrazine (160) gave 2-methyl-5-triphenylphospho-niomethylpyrazine chloride (161) (PPh3, Me2NCHO, 75°C, 6 h 81%), and thence 2-methyl-5-vinylpyrazine (162) (HCHO, Na2C03, H20—CH2C12, 20°C, 2 h 37%).1446... 

Pyrazine, 2-ethenyl-5-methyl-, 2-methyl-5-vinylpyrazine, 2-ethenyl-5-methylpyrazine [13925-08-1] FEMA 3211... 

Minuscule quantities of naturally-occurring pyrazines have been found in some foodstuffs and are largely responsible for their flavor and aroma. For example, 3-isopropyl-2-methoxypyrazine is isolated from green peas and wine and a seasoned wine connoisseur can identify a ppt quantity. In addition, 2-methyl-6-vinylpyrazine exists in coffee. 

Methylpyrazine reacts with formaldehyde and dimethylamine to give the expected product (40) of Mannich reaction. This is converted in 63% overall yield to vinylpyrazine (41) by quaternization with methyl iodide followed by sodium hydroxide treatment.196... 

Ethylthio-2-pyrazinecarbonitrile 6-Ethylthio-2-pyrazinecarbonitrile 6-Ethylthio-2-pyrazinecarbothioamide 3-Ethylthio-2-pyrazinecarboxamide 6-Ethylthio-2-pyrazinecarboxamide 3-Ethylthio-2-pyrazinecarboxylic acid 6-Ethylthio-2-pyrazinecarboxylic acid 3-Ethylthio-2,5-pyrazinedicarboxamide 2-Ethylthiopyrazine 1-oxide 2-Ethyl-3,5,6-trimethylpyrazine 2-Ethyl-3,5,6-triphenylpyrazine 2-Ethyl-3-vinylpyrazine 2-Ethynyl-3,6-dimethylpyrazine 2-Ethynyl-3-methylpyrazine 2-Fluoro-5,6-dimethoxy-3-methylpyrazine 2- Fluoro- 5,6-dimethoxypyrazine 2-Fluoro-3,6-dimethylpyrazine 2-Fluoro-3-(l-hydroxyethyl)pyrazine 2-Fluoro-3-iodopyrazine 2-Fluoromethyl-5-methyl-3,6-diphenylpyrazine 2- Fluoro- 5-phenylpyrazine 2-Fluoro-3-phenylthiopyrazine... 

To illustrate further the general methods of preparation described above, literature preparations of methyl-, dimethyl- and vinylpyrazine are summarized below. 

Ethoxyethyl)-5-hydroxy-2-methylpyrazine heated in acetic acid saturated with hydrogen bromide formed a crystalline bromine-containing compound which with 5% sodium carbonate gave 5-hydroxy-2-methyl-3-vinylpyrazine (248). Heteromacrocyclic ethers have been quaternized (989). 

Dimethylaminoethyl)pyrazine was quaternized by methyl iodide to give 2-(2 -trimethylammonioethyl)pyrazine iodide (48) (which with aqueous sodium hydroxide gave 2-vinylpyrazine) (657) and 2-hydroxy-3-nitro-5,6-diphenylpyrazine... 

Treatment of diphenylacetonitrile in toluene with sodium amide and 2-chloro-pyrazine gave 2-(C-cyano-C,C-diphenylmethyl)pyrazine (1021), and 2-vinylpyrazine with phenylacetonitrile and sodium heated at 120-130° for 10 minutes gave 2-(3 -cyano-3 -phenylpropyl)pyrazine (731). 2-Amino-5-bromomethyl-3-cyano-pyrazine with sodium hydride and methyl cyanoacetate in tetrahydrofuran formed the dialkylated product (56) (1031). 2-Amino-3-mercapto-5,6-dimethylpyrazine in methanol with potassium hydroxide and chloroacetonitrile gave 2-amino-3-cyanomethyIthio-5,6-dimethylpyrazine (1229), and 2-carboxypyrazine refluxed with chloroacetonitrile and triethylamine in ethyl acetate for 45 minutes gave the cyanomethyl ester (1317). 2-Hydroxy 5-methyl-3-propylpyrazine with cyanogen halides in aqueous sodium hydroxide-dimethylformamide at 0-5° gave l-cyano-5-methyl-2-oxo-3-propyl-l, 2-dihydropyrazine (1123). 

Identified in roasted coffee flavor by Goldman et al. (1967). According to Silwar et al. (1987) the concentration is 1.2-1.3 ppm. Silwar and Liillmann (1993b) observed that, during roasting, the vinylpyr-azines were not formed before 190 °C, and the content of vinylpyrazine itself increased continuously until 260 °C (compare with methyl and dimethylpyrazines). 

The synthesis has been carried out by Kamal et al. (1962) through an Hofmann exhaustive methylation of the Mannich product obtained by reaction of methylpyrazine with formaldehyde and dimethylamine hydrochloride. Goldman (1963) prepared vinylpyrazine by pyrolysis of pyrazine-ethanol. 

Pyrazine, 2-ethenyl-6-methyl-, 2-methyl-6-vinylpyrazine, 2-vinyl-6-methylpyrazine [13925-09-2]... 

Pyrazine, 2-ethenyl-3-ethyl-5-methylpyrazine, 3-ethyl-5-methyl-2-vinylpyrazine 1181589-32-2]... 

Pyrazine, 3-ethenyl-2-ethyl-5-methyl-, 2-ethyl-5-methyl-3- vinylpyrazine [181589-33-3]... 

Others. For example, the odour of 2,5-dimethylpyrazine resembles roasted hazelnuts, and 2,6-dimethylpyrazine and trimethylpyrazine have a chocolate-like odour. Important components of coffee aroma include a number of pyrazines, such as 2,3-diethyl-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. The flavour-active components of popcorn and white bread are acetylpyrazine, 2-ethyl-3-methylpyrazine, 3-ethyl-2,5-dimethylpyrazine and 5-methyl-6,7-dihydro-5H-cyclopenta[fo] pyrazine. Cyclopentapyrazines, specihcaUy 6,7-dihydro-5H-cyclopenta[fo]pyrazines, are formed in reactions of cyclopen-tenolones with aminoketones and ammonia. 

Significant aliphatic sulfur compounds are methional, 3-methyl-but-2-ene-1-thiol, 3-mercapto-3-methylbutan-l-ol (8-124), its ester 3-mercapto-3-methylbutyl formate, methanethiol and dimethyltrisulfide. 3-Mercapto-3-methyl-l-ol also occurs in passion fruit and blackcurrant, and as a putative cat pheromone in cat urine, where it is formed as a degradation product of amino acid L-felinine (see Section 2.2.1.2.2). Of more than 70 known pyrazines, the most important compounds in roasted coffee are isopropylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. Pyridine and its alkyl derivatives and bicyclic pyridines have a negative impact on the quality of coffee aroma. Important aromatic... 

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