2-Hydroxy-5-methoxy-3,6-diphenylpyrazine

Reductive debenzylation. 2-Benzyloxy-3,6-diisobutyl-5-methoxypyrazine 4-oxide (21) gave 3,6-diisobutyl-5-methoxy-2(l//)-pyrazinone 4-oxide (22) (H2, Pd/C, EtOH, h 90% structure confirmed by X-ray analysis) 310 2,5-dibenzy-loxy-3,6-diphenylpyrazine likewise gave 5-hydroxy-3,6-diphenyl-2(l//)-pyrazinone (23) (43%).82... 

V-Hydroxy-6-propylthio-2-pyrazinecarboxamide V-Hydroxy-6-propylthio-2-pyrazinecarboxamidine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisobutylpyrazine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisobutylpyrazine 4-oxide 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisopropylpyrazine 2- (3-Hydroxyprop-1 -ynyl)-3,6-diisopropylpyrazine 4-oxide 2- (3-Hydroxyprop-1 -ynyl)-3,6-dimethylpy razi ne 2-(3-Hydroxyprop-1 -y nyl)-3,6-dimethylpyrazine 4-oxide 2-(3-Hydroxyprop-l-ynyl)-3,5-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-3,6-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-5,6-diphenylpyrazine 2-(3-Hydroxyprop-l-ynyl)-5,6-diphenylpyrazine 4-oxide 2-(3-Hydroxyprop-l-ynyl)-6-methoxy-5-(2-methylprop-l-enyl)pyrazine 2- (3-Hydroxyprop-1 -ynyl )-6-methoxypyrazine N-Hydroxy-2-pyrazinecarboxamide Af-Hydroxy-2-pyrazinecarboxamide 4-oxide... 

Methoxypyrazines (31) have been prepared by diazomethane methylation of 2-hydroxy-3-isobutylpyrazine (60, 311, 367), 2-hydroxy-3-isopropylpyrazine (59, 367), 2-hydroxy-3-propyl(ethyl or hexyl)pyrazine (367), 3-hydroxy-2-isobutyl-5(and 6)methylpyrazine and 2-hydroxy-3-isobutyl-5,6-dimethylpyrazine (368), 2,3-dihydroxypyrazine (832), 2-hydroxy-5-methoxy- and 2,5-dihydroxy-3,6-diphenyl-pyrazine (832), 2-hydroxy-6-methoxy(and benzyloxy)pyrazine (832), 2,6-dihydroxy-3,5-diphenylpyrazine (873), 2,3,5-trifluoro-6-hydroxypyrazine (851), 2-chloro-6-hydroxy-3,5-diphenylpyrazine (873), 2-chloro-6-hydroxy-5-methyl-3-phenylpyrazine (873), 2-chloro-6-hydroxy-3-methyl-5-phenylpyrazine (873), 5,6-dichloro-1 -cyclohexyl-34iydroxy-2-oxo-l, 2-dihydropyrazine (853), 2-chloro-5-hydroxy-3-methoxy-6-methoxycarbonylpyrazine (881), 2-(4 -amino-3, 5 -dibromo-phenylsulfonamido)-3Tiydroxy-6-methoxypyrazine (881), 2-amino-3-hydroxy-... 

Pyrolyses and thermal stabilities of 2-hydroxy-, 2-ethoxy-, and 2-isopropoxy-pyrazines have been studied. 2-Hydroxypyrazine was very stable, but the alkoxy-pyrazines underwent thermal elimination of olefin to yield 2-hydroxypyrazine (668a). Electrochemical reductions of l-methyl-2-oxo-5,6-diphenyl-l,2-dihydro-pyrazine and 54iydroxy(and 5-methoxy)-2,3-diphenylpyrazine are reported to involve the intermediate enamine, for example, 6-hydroxy-1-methyl-2,3-diphenyl-1,4-dihydropyrazine (54) (1096, cf. 1097). When tested on mice 2-carbamoyl-5-methoxypyrazine had less anti tubercular activity than did pyrazinamide (1098). 

Khydroxypyrazine (which was converted into its jV -dimethyl derivative by treatment with dimethyl sulfate and alkali) gave, on reaction with an excess of ethereal diazomethane a mixture of its N,N-, 0,N-, and 0,0-dimethyl derivatives (58-60) (832). 2-Hydroxy-5-methoxy- and 2,5-dihydroxy-3,6-diphenylpyrazine with ethereal diazomethane gave predominantly 2,5-dimethoxy-3,6-diphenyl-pyrazine and only minor amounts of A -methylated products (832). Methylation of 2-hydroxy-6-methoxypyrazine with ethereal diazomethane produced a mixture of 0- and A -methyl derivatives in which the 0-methyl derivative predominated but the corresponding reaction of 2-benzyloxy-6-hydroxypyrazine gave almost exclusively the 0-methyl derivative (832) [the results of these methylations were correlated with the carbonyl stretching frequency (1103) in the parent lactam (832)]. 

Chloro-3-methoxycarbonyl-5,6-diphenylpyrazine refluxed with sodium methoxide gave 2-carboxy-3-methoxy-5,6-diphenylpyrazine (371) and the attempted Schmidt reaction of 2,5-dimethoxycarbonylpyrazine, in concentrated sulfuric acid with trichloroacetic acid at 60° with subsequent addition of sodium azide, gave 2,5-dicarboxypyrazine (1176). 2-Methoxy-3-methoxycarbonyl-5,6-diphenylpyrazine, when refluxed with cuprous chloride in dry dimethylformamide, gave 2-carboxy-3-methoxy-5,6-diphenylpyrazine (10%) 2-hydroxy-3-methoxycarbonyl-5,6-diphenyl-pyrazine similarly treated gave 5-hydroxy-2,3-diphenylpyrazine (30%) (837). 

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