2.5- Diethyl-3-hydroxypyrazine

Diazotization of 2-aminopyrazine with nitrous acid in dilute or concentrated sulfuric acid gave 2 hydroxypyrazine (to 67% yield) (86, 477, 720, 818). Many such conversions have been described, mostly using nitrosylsulfuric acid in concentrated sulfuric acid solution. Preparations of hydroxypyrazines from the aminopyrazines are summarized as follows 2-hydroxy-3-methylpyrazine (sodium nitrite in concentrated sulfuric acid-acetic acid) (681), 2Jiydroxy-3,5-dimethylpyrazine (aqueous nitrous acid, then at 60°) (524), 3-hydroxy-2,5-dimethylpyrazine (477), 2,5-diethyl-3-hydroxypyrazine (aqueous nitrous acid) (478), 2-hydroxy-6-phenyl-pyrazine (365a), 24iydroxy-3,5-diphenylpyrazine (nitrous acid in N hydrochloric acid) (524), 3-hydroxy-2,5-diphenylpyrazine (282), 2-s-butyl-3-hydroxy-5-isobutyl-pyrazine (93), 5TS-butyl-3 hydroxy-2-isobutylpyrazine (92, 536), 2,5-di-s-butyl-3-hydroxypyrazine (89, 720), 3-hydroxy-2-isobutyl-5-isopropylpyrazine (103, 525), 2,3-dihydroxypyrazine (from 2 amino-3-hydroxypyrazine) (757, 1055) and its... 

The sodium salt of 2-hydroxypyrazine with thiophosphoryl chloride at room temperature gave 2-(dichlorophosphinothioyloxy)pyrazine (1112, 1113) and in N-methyl-2-pyrrolidone with ( ,6)-diethyl phosphorochloridothioate [(EtO)2P(=S)Clj it gave 2-(diethoxyphosphinothioyloxy)pyrazine (1114, 1115), also prepared in the absence of A(-methyl-2-pyrroIidone (1116). The potassium salt of 2-hydroxy-pyrazine in t-butanol-dioxane with 0,0-diphenyl phosphorochloridothioate... 

Amino-5-carboxypyrazine in anhydrous dimethylformamide with triethyl-amine and ethyl chloroformate and then diethyl glutamate and stirred at room temperature gave 2-amino-5-(l, 3 -diethoxycarbonylpropyl)carbamoylpyrazine (24) (1244). Similarly a mixture of 2-carboxypyrazine and triethylamine in methylene dichloride with ethyl chloroformate and morpholine gave 2-( -morpholinocarbonyl)-pyrazine (1351). 2-Carboxy-3-hydroxypyrazine refluxed with phosphorus tris(A-methylanilide) in toluene gave 2-hydroxy-3-(A-methyl-A-phenyIcarbamoyl)pyrazine (1055), and 2-hydroxy-3-(A -methyl-A -p-tolylcarbamoyl)pyrazine was prepared similarly (1055). Tetracarboxypyrazine heated with sulfur tetrafluoride (SF4) at 150° gave tetra(trifluoromethyl)pyrazine (899). 

The irradiation of pyrazine derivatives with an a-carbonyl substituent under an atmosphere of nitrogen gave hydroxypyrazines and 1,4-dihydropyrazines (solvent adducts). Thus irradiation of 2,5-dimethoxycarbonyl-3,6-dimethylpyrazine in diethyl ether with a 450-W high-pressure mercury lamp gave two significant photoproducts, 2-hydroxy-5-methoxycarbonyl-3,6-dimethylpyrazine and l(r-ethoxy-ethyl)-2,5-dimethoxycarbonyl-3,6-dimethyl-l,4-dihydropyrazine (1064). The mechanism of the reaction has been investigated and discussed (1064). 

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