2-Isopropyl-3 -methylpyrazine

Alkyl-2-methoxypyrazines exhibit a base peak at miz 124 in the mass spectrum. The peak corresponds to a molecular ion in 2-methoxy-3-methylpyrazine (24a) and to a fragment ion, resulting from a McLafferty rearrangement of an alkyl group, in 3-isopropyl-2-methoxypyrazine (24b) and 3-5cc-butyl-2-methoxy pyrazine (24d) (97). 

With chiral racemic oxiranes one enantiomer reacts faster than the other the degree of kinetic resolution is very high for L-valine/alanine-based dialkoxydihydropyrazines. For example, in the reaction of one equivalent of (2.S )-2,5-dihydro-2-isopropyl-3,6-dimethoxy-5-methyl-pyrazine (1, R1 = CH3) with two equivalents of fW-(//,/ )-2,3-dimethyloxirane (R2,R4 = CH3 R = H) virtually only the (2//,3/ )-oxirane enantiomer reacts with the lithiated dihydropyrazine to give exclusively the (l /, 2/, 2 / )-configuratcd adduct i.e., (2/ ,5S)-2,5-dihydro-5-isopropyl-3,6-dimethoxy-2-[(l/ ,2/ )-2-(2-methoxyethoxymethoxy)-l-methylpropyl]-2-methylpyrazine, entry 7. Likewise, kinetic resolution (intramolecular) occurs upon reaction with rac-7-oxabicy-clo[4.1.0]heptane (entry 8). 

Dimethoxy-3-isopropyl- -6-methylpyrazine OCH3 i-C3H7 och3 X u... 

Flavour and off-flavour compounds of black and white pepper (P. nigrum L.) were evaluated by Jagella and Grosch (1999a,b). Enantioselective analysis of optically active monoterpenes indicated ( )-linalool, (+)-a-phellandrene, (-)-limonene, myrcene, (-)-a-pinene, 3-methylbutanal and meth-ylpropanal as the most potent odorants of black pepper. Additionally, 2-isopropyl-3-methoxypyrazine and 2,3-diethyl-5-meth-ylpyrazine were detected as important odorants of the black pepper sample from Malaysia, which had a mouldy, musty off-flavour. Omission tests indicated a-and (3-pinene, myrcene, a-phellandrene, limonene, linalool, methylpropanal, 2- and 3-methylbutanal, butyric acid and 3-meth-ylbutyric acid as key odorants. A storage experiment revealed that for ground black pepper, losses of a-pinene, limonene and 3-methylbutanal were mainly responsible for deficits in the pepper-like, citrus-like, terpene-like and malty notes after 30 days at room temperature. The musty/mouldy off-flavour of a sample of black pepper was caused by a mixture consisting of 2,3-diethyl-5-methylpyrazine (2.9pg/kg) and 2-isopropyl-3-methoxypyrazine (0.2 (xg/kg). 

Galbanum Ferula gummosa (-)-/3-Pinene, (3E,5Z)-1,3,5-undecatriene (77), 2-methoxy-3-isopropyl-5-methylpyrazine(78) 95,96... 

Isopropyl-3-methoxy-5-methylpyrazine gave 2-isopropyl-3-methoxy-5-[3-(pyran-2-yloxy)propyl]pyrazine (289) [2-(3-bromopropoxy)pyran, PT2NK (made in situ), THF, A, -78°C, 3 h 83%] 298 also analogues likewise.295,298... 

A Ally /V -methyl-3,5-bismethylamino-2,6-pyrazinedicarboxamide 2-Allyloxycarbonylamino-3,5,6-trichloropyrazine 2-Allyloxy-3-chloropyrazine 2-Allyloxy-6-chloropyrazine 2-Allyloxy-6-iodopyrazine 2-Allyloxy-3-isopropyl-5,6-dimethylpyrazine 2-Allyloxy-3-methylpyrazine... 

Chloro-3-isopropyl-5,6-dimethylpyrazine 2-Chloro-3-isopropyl-5,6-diphenylpyrazine 2-Chloro-3-isopropyl-5-methylpyrazine 2-Chloro-3-isopropyl-6-methylpyrazine 2-Chloro-6-isopropyl-3-methylpyrazine 2-Chloro-3-isopropyl-6-methylpyrazine 1 -oxide 2-Chloro-6-isopropyl-3-methylpyrazine 1-oxide 2-Chloro-3-isopropylpyrazine... 

Guanidinopropyl)-3-isopropyl-2(l//)-pyrazinone 3,6,AA V,X-Hexamethyl-2,5-pyrazinedicarboxamide 2-Hexylamino-3,6-dimethylpyrazine 2-Hexylamino-3,6-dimethylpyrazine 4-oxide 2-Hexylaminopyrazine 2-Hexylaminopyrazine 4-oxide 2- Hexyl- 3,6-dimethylpyrazine 2- Hexyl- 5,6- dimethy lpy razi ne 2- Hexyl -3,6- dimethy lpy razi ne 1,4- dioxide 2-Hexyl-3-methoxypyrazine 2- Hexyl- 3-methylpyrazine... 

Isopropylamino-2-pyrazinecarboiiitrile 2-Isopropyl- 3,5-dimethoxy-6-methylpyrazine 2-Isopropyl-3,6-diniethoxy-5-methylpyrazine 2-Isopropyl-3,6-dimethoxy-5-propionylpyrazine 2-Isopropyl-3,6-dimethoxypyrazine... 

Isopropylthio-2,5-pyrazinedicarboxamide 2-Isopropyl-3,5,6-triphenylpyrazine 2-Isovaleryl-3-methylpyrazine 2-Isovaleryl-5-methylpyrazine 2-Isovaleryl-6-methylpyrazine 2-Isovalerylpyrazine 5-Isovaleryl-2-pyrazinecarbonitrile 5-Isovaleryl-2,3-pyrazinedicarbonitrile 2-Isovaleryl-3,5,6-trimethylpyrazine 2-Mercaptomethylpyrazine... 

Recent work has shown the presence of pyrazine and 2,6-dimethylpyrazine in leek (75), pyrazine and alkylpyrazines in the volatile constituents of tamarind (76), five alkylpyrazines in soong-neung (extract of cooked and roasted rice) (77) and in shoyu (soy sauce) (78), and alkylpyrazines in white bread (79). Murray and Whitfield (80) have examined vegetable tissue for 2-isopropyl-, 2is-butyl-, and 2-isobutyl-3-methoxypyrazines and observed at least one of these compounds in 23 of the 27 samples studied. 2-Methylpyrazine and 2,5- and 2,6-dimethylpyrazines have been determined in black tobacco and in the smoke of nonfilter cigarettes made from these tobaccos (81). 

Pyrazines have been prepared by heating 1,2-dicarbonyl compounds with a-amino acids. Thus Rizzi (308) observed that under the conditions of the Strecker degradation, equimolar amounts of DL-valine (44) and butane-2,3-dione in refluxing bis(2-methoxyethyl) ether, diglyme, gave isobutyraldehyde, tetra-methylpyrazine (9%), and a mixture of cis- and trans-2-isopropyl-4,5-dimethyl-3-oxazoline (4%). He proposed a reductive amination mechanism in which butane-23-dione was converted to 2-aminobutan-3-one which underwent self-condensation to the pyrazine. Tetramethylpyrazine was also prepared when the same reactants were heated in dimethylformamide at 123° for 5 hours (and other pyrazines prepared similarly) (308a). 

Chloro-3-methylpyrazine (101,535) and 2-chloro-5-phenylpyrazine (363, 365a, 377, 824, 825) have been prepared from the corresponding hydroxy compound and phosphoryl chloride, 2-chloro-6-methylpyrazine from 2-hydroxy-6-methylpyrazine and phosphoryl chloride with one drop of dimethylformamide (681), and 2-benzyl(or s-butyl, isobutyl, or isopropyl)-3phosphoryl chloride with a trace of concentrated sulfuric acid (80). 2-Chloro-6-methyl-3-propyl- (826), 3[Pg.99]

Pepper, black Musty, mouldy 2,3-Diethyl-5-methylpyrazine, 2-Isopropyl-3-methoxypyrazine [83]... 

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