2-Ethyl-3- pyrazine, oxidation

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... 

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. 

Oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) converted ethyl l,2,3,4-tetrahydropyrido[2,3-A]-pyrazine-2-carboxylate 203 into the conjugated pyridopyrazine 205, while the 3-isomer 204 could not be oxidized to the corresponding aromatic heterocycle <2002T5241>. 

Bourguignon and coworkers in their preparation of thieno[2,3-6]pyrazine used methyl-pyrazine (364 Scheme 107) (80JHC257) as starting material. The chlorination of (364) yields 2-chloro-3-methyl- and 2-chloro-6-methyl-pyrazine in a ratio of 80 20. Without separation this mixture is treated with ethyl mercaptoacetate in the presence of sodium ethoxide to give (365) in 91% yield (based on 2-chloro-3-methylpyrazine). Oxidation of the methyl group to an aldehyde function and subsequent base catalyzed ring closure yields (366), which is transformed to (363) by the method depicted already in Scheme 106. 

Pyrazine, 3-alkyl-2-ethyl-oxidation, 3, 168 Pyrazine, amino-bromination, 3, 177 reactions... 

Oxidation of 3-hydroxymethyl-2,3-dihydro-5H-pyrido[l,2,3-cfe][1,4] benzoxazin-5-ones with o-iodoxybenzoic acid in DMSO and with Dess-Martin periodinate in CH2CI2 afforded 3-formyl derivatives (08WOP2008/ 120003). Dehydrogenation of ethyl 10-[2-(ferf-butoxycarbonyl)-l,2,3,4,6,8a-hexahydropyrrolo[l,2-a]pyrazin-7-yl]-9-fluoro-3(S)-methyl-7-oxo-2,3-dihydro-7H-pyrido[l,2,3-de][l,4]oxazine-6-carboxylates in the presence of Pd/C with air in MeOH afforded 10-[2-(ferf-butoxycarbonyl)-l, 2,3,4-tetrahydropyrrolo[l,2-a]pyrazin-7-yl] derivatives, which then were deprotected (09BML4933). 

Polyurethanes (PU) The odor of many polyurethanes is caused by fishy smelling low molecular weight amines, mostly methylamines like trimethylamine, degradation products of the amine catalysts used during production. In some cases after evaporation of the fishy smelling amines, other odor qualities remain. One noticeable odor of PU samples was earthy, nutty, which can often be attributed to substituted pyrazines, formed by condensation of two a-aminoketones, subsequent oxidation or alkylation by aldehydes. One example is 2-ethyl-3,5-dimethylpyrazine (Mayer and Breuer, 2006). 

Hydrogenation of 2,3,5,6-tetramethylpyrazine over platinum oxide was unsuccessful in alcohol or in ethyl acetate, and proceeded only to small extents in acetic acid. However, the anhydrous hydrochloride of the pyrazine was rapidly and quantitatively hydrogenated in absolute ethanol with the addition of acetic acid.162 The methiodide of the tetramethylpirazine was also successfully hydrogenated over platinum oxide in ethanol with the addition of a little water.163... 

Amino-IV-ethyl-6-phenyl-2-pyrazine-carboxamide 4-oxide... 

Ethyl 3-amino-3-pyrazinecarboxylate 4-oxide Ethyl 5-azidocarbonyl-2-pyrazinecarboxylate 2-Ethyl-3,6-bis(2-hydroxyethyl)pyrazine... 

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... 

Pyrazin-l-oxid 2-Amino-3-cyan-5-ethyl- E9b/2, 283 [HO-N=CH-CO-C2H5 + NC-CH(NH2)-CN]... 

Dimethyl-3-ethyl-2-hydroxy-E9b/2, 268f, (Gloxal + H2N-CHR-CO-NH2) 2-Hydroxy-3-isopropyl-5-methyl-E9b/2, 268f. (H3C-CO-CHO + H2N-CHR-CO-NH2) 2-Hydroxy-5(or6)-methyl-3-propyl-E9b/2, 268 f. (H3C-CO-CHO -I- H2N-CHR-CO-NH2) Pyrazin-1,4-bis-oxid 2,5-Diethyl-E9b/2, 309 (N-Oxidat.) Pyrazin-l-oxid... 

Phenol 3-(2-Cyan-ethoxy)-2-(2-cyan-ethyl)- VI/lc, 501 Pyrazin-l,4-bis-oxid 2,5-DimethyI-3-phenyl- E9b/2, 305 (N-Bis-oxidat.)... 

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