3- Cyanopyrazine 1-oxide

Amino-3-cyanopyrazine 1,4-dioxide was selectively monodeoxygenated with phosphorus trichloride in tetrahydrofuran at 25° to 3-amino-2-cyanopyrazine 1 -oxide (538). 

Cyanopyrazine 1-oxide and 3-cyanopyrazine 1-oxide each with alkaline 3% hydrogen peroxide at 55° gave 2-carbamoylpyrazine 1-oxide and 3-carbamoyl-pyrazine 1-oxide, respectively (838). 3-Amino-2-cyanopyrazine 1-oxide refluxed with trifluoroacetic anhydride in triHuoroacetic acid for 5 hours gave 3-amino-2-carbamoylpyrazine 1-oxide (538), and 2-amino-3-cyano-5-methylpyrazine 1-oxide with sulfuric acid (d. 1.8) at 100° gave 2-amino-3-carbamoyl-5-methylpyrazine 1-oxide (1255). 2-Amino-6-chloro-3-cyano-5-methylpyrazine 1-oxide with 0.5N sodium hydroxide at room temperature for 48 hours formed a mixture of 2-amino-3-cyano-6-hydroxy-5-methylpyrazine 1-oxide (56%) and 2-amino-3-carbamoyl-6-chloro-5-methylpyrazine 1-oxide (22%)(533). 3-7V-Acetylcarbamoylpyrazine 1-oxide was hydrolyzed by hot 10% sodium hydroxide to 3-carboxypyrazine 1-oxide (1057). 

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. 

Various 4-aminopteridine 3-oxides have recently been obtained by cyclization of 2-amino-3-cyanopyrazine derivatives (81H(15)293). 

The reductive decyanation of cyanopyrazine using H2 and Pt/C under acidic conditions has been reported <2002TL6747>, that is, 2-amino-3-cyano-5-phenylpyrazine 1-oxide 73 is hydrogenated to 2-amino-5-phenylpyra-zine 74 in 90% yield (Equation 11). The double reduction has also been shown to be realized with sodium dithionite. 

The synthetic strategy of preparing pyrazines by condensation of 2-keto aldoximes with a-amino nitriles is well represented by Taylor s pteridine synthesis, in which a variety of 2-amino-3-cyanopyrazine 1-oxides have been prepared by using aminomalononitrile <2002TL6747> as the amino nitriles. In the same fashion, some other a-amino nitriles, which are often the Strecker synthesis products, are converted into 2-aminopyrazine 1-oxides 160 (Scheme 44). The condensations are realized by treatment with iV-methylmorpholine <1993JOC7542>, and... 

Oxidation of one of the nitrogen atoms of 2-chloro-3-cyanopyrazine to form a mono-iV-oxide allows for an identical sequence of reactions to generate the corresponding W-oxide 484 <1999W09957122, 2000JME1586>. 

Swern oxidation of 2-(3-cyanopyrazin-2-yl)-6-hydroxymethylperhy-dropyrido[l,2-aJpyrazine at 78 °C gave 6-aldehyde (07USA2007/ 037816). 

The synthesis of 2-amino-5-chloromethyl-3-cyanopyrazine 1-oxide (529) from aminomalononitrile and chloromethyl hydroxyiminomethyl ketone, and of 2-amino-6-chloromethyl(and chloroalkyl)-3-cyanopyrazine 1-oxide (534) from aminomalononitrile and -chloro-a-hydroxyiminopropionaldehyde (prepared from the addition of nitrosyl chloride to acrolein) has been described in Section III.l. 

Chloropyrazine 1-oxide with cuprous cyanide in A(-methylpyrroIidine or dimethylformamide did not give 3-cyanopyrazine 1-oxide (838). 

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). 

Amino-5-chloromethyl-3-cyanopyrazine 1-oxide was also deoxygenated by sodium hydrosulfite (dithionite) in boiling water to give a poor yield of 2-amino-5-chloromethyl-3-cyanopyrazine, but 2-amino-6-chloromethyl-3-cyanopyrazine 1-oxide under the same conditions underwent both deoxygenation and reductive dehalogenation to 2-amino-3-cyano-6-methylpyrazine (529,534). 

Amino-5-chloromethyl-3-cyanopyrazine 1-oxide with triphenylphosphine in dimethylformamide at 80-90° gave 2-amino-3-cyano-5-(triphenylphosphonio)-methylpyrazine 1-oxide chloride (97) (520) and the 5-bromomethyl analogue reacted similarly with triphenylphosphine in propan-2-ol (542). Compound (97) on hydrolysis with 30% aqueous ethanol containing a small amount of triethylamine gave 2-amino-3-cyano-5-methylpyrazine 1-oxide and thus enabled removal of the chloro substituent from the chloromethylpyrazine (529) compound (97) with triethylamine and acetaldehyde (and other aldehydes) in chloroform at room temperature gave 2-amino-3-cyano-5-(prop-l -enyl)pyrazine 1-oxide (and other alkenyl analogues) (529). 

An analogous series of reactions was observed from 2-amino-6-chloromethyl-3-cyanopyrazine 1-oxide and the 2-amino-3-cyano-6-(triphenylphosphonio)-methylpyrazine 1-oxide chloride with aqueous sodium bicarbonate gave the betaine (98) (534). 

Amino-5-chloromethyl-3-cyanopyrazine 1-oxide at reflux in methanol gave... 

Condensation of 2-amino-5-bromomethyl-3-cyanopyrazine 1-oxides with the appropriate substituted amine afforded a series of 2-amino-5-([(aryl and aralkyl)-amino]methyl -3-cyanopyrazine 1-oxides (1040), and with p-chlorophenol and arylthiols gave 2-amino-5-[(p-chlorophenoxy)methyl]-3-cyanopyrazine 1-oxide and 2-amino-5[(arylthio)methyl]-3-cyanopyrazine 1-oxides (1041). 

Amino-2prepared from 2-amino-3-cyanopyrazine 1-oxide by reflux with acetic acid-acetic anhydride followed by ready deacetylation by refluxing in methanol (538), and in a similar manner 3-amino-2-ethoxycarbonyl-5-hydroxypyrazine has been prepared from 2-amino-3-ethoxycarbonylpyrazine 1 -oxide through 3-acetamido-2-ethoxycarbonyl-5 ydroxy-pyrazine (538), and 2-amino-3-carbamoyl-6-hydroxy-5-methylpyrazine from 2-amino-3-cyano-5-methylpyrazine 1-oxide (538). The preparation of 24 ydroxy-6-methoxycarbonylpyrazine (10) has been claimed from 3-methoxycarbonylpyrazine 1-oxide with acetic anhydride followed by hydrolysis (1057) [cf. Nov Cek et al. (839), who claim it to be the 5-isomer, and Foks (744)]. 

Diisobutyl-3miethoxypyrazine 1,4-dioxide (107) with phosphorus trichloride in ethyl acetate at 40° gave 2,5-diisobutyl-3-methoxypyrazine (980). 2-Amino-5-[(/7-chlorophenoxy)methyl]-3-cyanopyrazine 1-oxide was deoxygenated with triethyl phosphite in dimethylformamide at 120° (1041). 

Cyanopyrazine A -oxides have been prepared from a-amino nitriles and a-hydroxyimino carbonyl compounds as summarized in Section III. 1 (528-530, 532-534, 537, 540, 542). Oxidation of 2-cyanopyrazine with perhydrol gave 3-cyanopyrazine 1-oxide (575), 2-cyano-5-ethoxy-3,6-dimethylpyrazine with 30% hydrogen peroxide in acetic acid at 55° gave 2-cyano-5-ethoxy-3,6-dimethylpyrazine iV-oxide (288), and the oxidations of 2-amino-3-cyanopyrazine 1-oxide (538) and... 

The oxidations of 2-amino-3-cyanopyrazine 1-oxides to the 1,4-dioxides are described in Section VIII.3A(4) and deoxygenations of some 2-amino-3-cyano-pyrazine 1-oxides and 1,4-dioxides with phosphorus trichloride or sodium dithionite in Section VIII.3C(4). Deoxygenation and chlorination of aminocyanopyrazine 1-oxides are reported in Section V.IG, and deoxygenation and acetoxylation or alkoxylation of 2-amino-3-cyano-5-methylpyrazine 1,4-dioxide in Section VIII.3C(5). Hydrolysis of cyanopyrazine Y-oxides to carbamoylpyrazine Af-oxides are given in Section 10A(3) and ring closure reactions of 2-amino-3-cyanopyrazine 1-oxides to pteridine 8-oxides in Section V11I.3C(3). 

Hydrogen-deuterium exchange rates ofH2 in 3-cyanopyrazine 1-oxide (pA 1.12 ... 

For the pyrazine A -oxides, there is a table for each substituent type, and compounds are listed (once only) at the first opportunity. For example, 2-amino-6-chloromethyl-3-cyanopyrazine 1-oxide is listed in Table A.31 (aminopyrazine A -oxides) and 2-hydroxy-5-methoxycarbonylpyrazine 1-oxide in Table A.32 (carboxypyrazine A -oxides). 

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