2-Methoxy-3-methylpyrazine oxidation

Certain a-chloromethylpyrazine A -oxides have been deoxygenated with phosphorus trichloride. Treatment of 2-amino-5-chloromethyl-3-cyanopyrazine 1-oxide (and 2-amino-3-cyano-5-methoxymethylpyrazine 1-oxide) with phosphorus trichloride at room temperature in tetrahydrofuran resulted in smooth deoxygenation to 2-amino-5-chloromethyl-3-cyanopyrazine (and 2-amino-3-cyano-5-methoxy-methylpyrazine) (529), whereas 2-amino-6-chloromethyl-3-cyanopyrazine 1-oxide was best deoxygenated to 3-amino-5-chloromethyl-2-cyanopyrazine by phosphorus trichloride in refluxing tetrahydrofuran (534). The more vigorous conditions necessary for the last reaction may be a reflection of increased steric hindrance at the fV-oxide grouping (529). Use of solvents like chloroform or dioxane led to slow reactions which were accompanied by the formation of numerous unidentified by-products (534). 

The preparation of extranuclear alkoxypyrazines from extranuclear halogeneo-pyrazines has been described in Section V.6A (654, 672,679,685, 687,688,694, 756, 872, 1027). 2-Amino-3-cyano-5-methoxymethylpyrazine 1-oxide with phosphorus trichloride in tetrahydrofuran afforded 2-amino-3-cyano-5-methoxy-methylpyrazine (529) and 3-(bromoacetamido)-l-ethoxy4-oxopentane (44) with alcoholic ammonia gave 5-hydroxy-3-(2 -ethoxyethyl)-2-methylpyrazine (45) (248). 

Alkoxy groups again direct attack to the more remote nitrogen site, probably for steric reasons. Thus, 2-ethoxypyrazine gave 45% and 2-methoxy-3-methylpyrazine 82% of the 4-oxides (64JOC2623). Isolation of an almost quantitative yield of 4-oxide from 2-methoxy-3-phenylpyrazine oxidation... 

Chloromethyl-3-methoxy-5-methylpyrazine 1-oxide (28, R = H) gave 2-chloro-6-chloromethyl-5-methoxy-3-methylpyrazine 1-oxide (28, R = Cl) OV-chIorosuccinimide, Me2NCHO, 20°C, 12 h 90%).333 Also other examples.321,599,1460... 

Chloromethyl-3-methoxy-5-methylpyrazine 1-oxide (232) and indole-l( )-yl-magnesium bromide (233) (made in situ) gave 3-(3-methoxy-5-methyl-l-oxi-dopyrazin-2-ylmethyl)indole (234) (Et20—PhMe, 0 — 20°C, 12 h 77%).333 Also other examples.1614... 

Methoxy-3,6-dimethylpyrazine 4-oxide (283) gave only 2-acetoxymethyl-3-methoxy-5-methylpyrazine (284) (neat AC2O, reflux, 1 h 88%) 324 in contrast, the homologous substrate, 2,5-dibenzyl-3-methoxypyrazine 1-oxide (285), gave a separable mixture of 2-(a-acetoxybenzyl)-5-benzyl-3-methoxy-pyrazine (286) and 2-acetoxy-3,6-dibenzyl-5-methoxypyrazine (287) (neat Ac20, reflux, 90 min 55 and 20%, respectively).312... 

Acetoxymethyl- -chloropyrazine 2-Acetoxymethyl-3,6-dichloro-5-methylpyrazine 2-Acetoxymethyl-3,6-dichloro-5-methylpyrazine 1-oxide 2-Acetoxymethyl-3-ethoxypyrazine 2-Acetoxymethyl-5-isobutyl-3-methoxypyrazine 2-Acetoxymethyl-5-isobutyl-3-methoxypyrazine 1-oxide 2-Acetoxymethyl-3-methoxy-5-methylpyrazine 2-Acetoxymethyl-5-methoxy-6-methylpyrazine 2-Acetoxymethyl-3-methoxy-5-methylpyrazine 1-oxide 2-Acetoxymethyl-3-methylpyrazine 2-Acetoxymethyl-5-methylpyrazine... 

Chloromethyl-3-ethoxy-5-methylpyrazine 2-Chloromethyl-3-methoxy-5-methylpyrazine 1-oxide 2-Chloromethyl-3-methylpyrazine... 

Dimethylamino-7V-hydroxy-2-pyrazinecarboxamide 6-Dimethylamino-7V-hydroxy-2-pyrazinecarboxamidine 2-Dimethylamino-5-iodopyrazine 2-Dimethylamino-6-iodopyrazine 2-Dimethylamino-5-iodopyrazine 4-oxide 2-Dimethylamino-3-isobutylpyrazine 2-Dimethylamino-6-isobutylpyrazine 2-Dimethylamino-5-methoxy-3,6-dimethylpyrazine 2-Dimethylaminomethyl-3,6-bismethylthiopyrazine 2-Dimethylamino-6-methyl-5-phenylpyrazine 4-oxide 2-Dimethylamino-3-methylpyrazine 2-Dimethylamino-6-methylpyrazine 2-Dimethylamino-3-methylpyrazine 4-oxide Dimethyl 5-amino-6-oxo-1,6-dihydro-2,3-pyrazinedicarboxylate 2-Dimethylamino-5-phenylpyrazine 2-(3-Dimethylaminopropyl)-6-methylpyrazine... 

Isobutyl-3-methoxy-5-methylpyrazine 2-Isobutyl-3-methoxy-5-methylpyrazine 2-Isobutyl-6-methoxy-5-methylpyrazine 4-oxide 2-Isobutyl-3-methoxypyrazine... 

Both 2-methylpyrazine 1- and 4-oxides (625) (obtained by oxidation of 2-methyl-pyrazine with peroxyacetic acid) on treatment with phosphoryl chloride have been claimed to give 2-chloro-3-methylpyrazine(626)but the 2-methylpyrazine-4-oxide used is now known to have been a mixture of the 1- and 4-isomers (734). More recently other workers (735, 736) have claimed that the mixed 2-methylpyrazine 7V-oxides with phosphoryl chloride gave a mixture of 2-chloro-3-, -5-, and -6-methylpyrazine but Nakel and Haynes (686) have shown that 2-methylpyrazine 1-oxide with phosphoryl chloride followed by sodium methoxide gave 2-methoxy-3-methylpyrazine and 6-methoxy-2-methylpyrazine, and 2-methylpyrazine 4-oxide (3-methylpyrazine 1-oxide) similarly treated gave only 2-methoxy-6-methylpyrazine. 3-Trifluoromethylpyrazine 1-oxide with benzenesulfonyl chloride at 1(X)° has been shown to give 2-chloro-6-trifluoromethylpyrazine (44%) (759). 

The following alkoxypyrazine Af-oxides have been prepared from the corresponding chloropyrazine A-oxides and sodium alkoxide in the appropriate alcohol (unless otherwise specified) 3-methoxypyrazine 1-oxide (838) 2-methoxypyrazine 1-oxide (no details (838) 3-ethoxypyrazine 1-oxide (978) 3-ethoxy-2-methylpyrazine 1-oxide (potassium hydroxide in ethanol) (978) 3-ethoxy-2,5-dimethylpyrazine 1-oxide (sodium ethoxide or potassium hydroxide in ethanol) (872, 978) and 3-methoxy-2,5-dimethylpyrazine 1-oxide (588). 

Alkoxypyrazine A-oxides may also be prepared by oxidation of the alkoxypyrazine with peroxyacetic acid. In this way the following have been prepared 3-ethoxypyrazine 1-oxide (100°/20h) (978) 3-(trideuteromethoxy)pyrazine 1-oxide (757l9h) (975) 3-ethoxy-2-methylpyrazine 1-oxide (65-75724h) (978) 3-methoxy-2-phenylpyrazine 1-oxide (55720 h) (817) 3-ethoxy-2,5-dimethyl-pyrazine 1-oxide (56716 h) (872) 3-carbamoyl-2-methoxypyrazine 1-oxide (80720h) (881) and 2-cyano-5-ethoxy-3,6-dimethylpyrazine A-oxide (55720h) (288). 

Amino-3with sodium methoxide overnight has been shown to give 3-amino-2-cyano-5-methoxy-6-methylpyrazine 1-oxide (532). 

Dimethylamino-23-dimethylpyrazine 1-oxide in boiling acetic anhydride gave 2-acetoxymethyl-3-dimethylamino-5-methylpyrazine (793) which was not isolated but saponified directly to 3-dimethylamino-2-hydroxymethyl-5-methylpyrazine (793). 2-Amino-3-cyano-5-methylpyrazine 1,4-dioxide refluxed with (a) acetic anhydride gave 3-acetamido-2-cyano-5-hydroxy-6-methylpyrazine 1-oxide (532) and (6) sodium methoxide gave 3-amino-2-cyano-5-methoxy-6-methylpyrazine 1-oxide (532). 

Alkylpyrazines with other substituents have been oxidized to carboxylic acids as follows 2-acetamido-6-methylpyrazine was oxidized in aqueous magnesium sulfate with potassium permanganate to 2-acetamido-6aqueous potassium permanganate at room temperature to 2-carboxy-3-chloropyrazine, which was also obtained by oxidation of 2-chloro-3-methylpyrazine with selenium dioxide in boiling aqueous pyridine (947). Oxidations of 2-methoxy-3-methyl-... 

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