Methylpyrazines irradiation

Recently some interesting ring isomerization reactions of pyrazines have been reported. Both under photolytic and pyrolytic conditions pyrimidines are formed. Lahmani and Ivanoff irradiated pyrazine in various organic solvents and pyrazine, methyl-, and 2,5- and 2,6-dimethylpyrazine in the vapor phase.163,164 The products of these reactions are shown in Scheme 13. The presence of 2-methylpyrimidine in the photolysis products of 2-methylpyrazine was suspected, but not proved. The authors interpret the above data as indicative of the... 

The irans-benzylidene derivative (188), obtained as the major product of condensation of 3-methylpiperazine 2,5-dione and benzaldehyde in the presence of acetic anhydride, undergoes photoisomerization to the cis isomer (191) on irradiation in methanol. Both isomers have been converted into tetrahydropyrazine imino ethers (189) and (192) by treatment with triethyloxonium fluoroborate. The trans compound reacts more slowly and gives a lower yield of imino ether and this is attributed to steric hindrance. Compounds 188 and 191 are de-acetylated on treatment with methanolic 2 N potassium hydroxide. The trans and cis isomers (187) and (190), so produced are converted into 3-benzyl-2,5-dihydroxy-6-methylpyrazine (144) when heated at 100° with sodium hydroxide.384 Treatment of the dichloroacetyl derivative of phenylalanine with methylamine gives l-methyl-3-benzylidenepiperazine 2,5-dione with the stereochemistry shown.384a... 

Dilution and concentration experiments on samples of dried black pepper berries from India and Malaysia, as well as enantioselec-tive analysis of optically active monoterpenes, indicated ( )-linalool, (-i-)-a-phellandrene, (-)-limonene, myrcene, (-)-a-pinene, 3-methylb-utanal and methylpropanal as the most potent odorants of black pepper. Additionally, 2-iso-propyl-3-methoxypyrazine and 2,3-diethyl-5-methylpyrazine were detected as important odorants of the black pepper sample from Malaysia, which had a mouldy, musty off-flavour (Jagella and Grosch, 1999a). Gamma irradiation was an effective means of decon-... 

Irradiation of 2-methylpyrazine and 2,5- and 2,6-dimethylpyrazine at 254 nm has been shown to give various methyl- and dimethylpyrimidines (632). Pyrolyses and thermal stabilities of 2,5-dialkylpyrazines have been examined (688a). 

Irradiation at 313 nm of benzene solutions of 2-butylpyrazine and 2-(2 -hydroxy-ethyOpyrazine gave 2-methylpyrazine (722). 

Support for the postulate of a hot methylene- C insertion into carbon hydrogen bonds had already been obtained from observations on the yields of labeled hexanes produced in the irradiation of pentane plus 2-methylpyrazine (Table 11). The statistical nature of the product... 

The dried day-lily flowers contained volatile components including ethyl formate, ethyl acetate, nonanol, 3-methylbutanol, isoamyl alcohol, methylpyrazine, 2,6-di-methylpyrazine, furfural, acetic acid, terpinolene, furfuryl formate, furfuryl acetate, phenylacetaldehyde and furfuryl alcohol. A low dose (0.5 kGy) of irradiation could control mold contamination and insect infestation in dried day-lily flowers. No significant difference in the volatile compositions between the irradiated (0.5, 1.0, 2.0 and 5.0 kGy) and unirradiated dried day-lily flowers were found. However, the quality of dried day-lily flowers was acceptable after irradiation (at 0.5 kGy) (Yang, 1994). 

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