2-Acetyl-3-ethylpyrazine

Some 2 -dialkylpyrazines have been oxidized in one step with sodium dichromate in acetic acid, in good yields, to the corresponding 2-acyl-3-alkylpyrazines (678). Thus 2-ethyl-3-methylpyrazine gave 2-acetyl-3-methylpyrazine, 23-diethylpyrazine gave 2-acetyl-3-ethylpyrazine, and 2-ethyl-3,5(or 3,6)-dimethylpyrazine gave 2-acetyl-3,5(or 3,6)-dimethylpyrazine (678). 

Mookherjee B.D., Giacino C., Karoll E. and Vock M.H. (1974) Odorous and flavoring 2-acetyl-3-ethylpyrazine. Deutsche Offen. 2166323. 

Bromination using NBS has been used to provide acetylpyrazine derivatives from the corresponding ethylpyrazines. Bromination of 2-ethyl-3-methylpyrazine gives 2-bromoethyl-3-methylpyrazine in quantitative yield this may be oxidized using the sodium salt of 2-nitropropane or with pyridine AT-oxide to yield 2-acetyl-3-methylpyrazine in yields of 66 and 25% respectively (Scheme 14). 

Direct oxidation of ethylpyrazines to the corresponding acetylpyrazines may also be carried out in favourable circumstances using hot chromic acid (75JOC1178). Treatment of 2-ethyl-3-alkylpyrazines with chromic acid yields the corresponding 2-acetyl-3-alkyl-pyrazines in yields of 50-70%. In the absence of the 3-alkyl substituent the yields fall dramatically to less than 10%. Acetylpyrazines are more generally prepared by the inverse addition of a Grignard reagent to a cyanopyrazine. 

The use of an isotope dilution assay is the best method to quantify labile and low level odorants. He applied this technique to the determination of 2-acetyl-l-pyrroline and 2-methyl-3-ethylpyrazine, the two compounds which showed the highest FD-factors among the compounds with roasty odor notes in extracts from wheat or rye bread crust, respectively ( 7, 38). The results are summarized in Table III. The high level of the acetylpyrroline in the crusts of the wheat breads was striking compared to the level in the rye breads. These quantitative data confirm that 2-acetyl-l-pyrroline is a character impact odor compound of the wheat bread crust. 

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). 

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