Reactions of Nitropyrazines

The action of either thionyl chloride or phosphoryl chloride upon 2-hydroxy-3-nitro-5,6-diphenylpyrazine was abnormal and resulted in loss of the nitro group and 

2-Hydroxy-3-nitro-5,6-diphenylpyrazine heated with aqueous hydrazine gave 2-hydrazino-34iydroxy-5,6-diphenylpyrazine (1124) whereas when refluxed with hydrazine and Raney nickel in methanol it gave 2-amino-3-hydroxy-5,6-diphenyl-pyrazine (1065). 

2-Hydroxy-3-nitro-5,6-diphenylpyrazine was converted with 72% sulfuric acid at 82° to benzil (24%), 23-dihydroxy-5,6-diphenylpyrazine (41%), and an unidentified solid (20%) (1065). The formation of benzil under these conditions was proof that neither of the phenyl groups in the starting material was nitrated (1065). 2-Hydroxy-3-nitro-5,6-diphenylpyrazine refluxed with acetic-6Af hydrochloric acid (1 1) for 1 hours also gave 2,3-dihydroxy-5,6-diphenylpyrazine (94%) (817). 

2-Hydroxy-5-nitro-3-phenylpyrazine with phosphoryl chloride at reflux gave 2-chloro-5-nitro-3-phenylpyrazine but at 170° gave 2,5-dichloro-3-phenylpyrazine (817). Phenylhydroxynitropyrazines are claimed not to react with dimethyl sulfate in alkaline solution or with sodium ethoxide and ethyl iodide in hot ethanol (817). 

Reduction of 2,6-diamino-3,5-dinitropyrazine in dimethylacetamide with hydrogen over platinum oxide (or with sodium sulfide and ammonium chloride in water at room temperature) gave 2,3,5-triamino-6-nitropyrazine (1180), but reduction with hydrogen and 10% palladium on charcoal at 50p.sJ. gave tetraamino-pyrazine (1180). 2-Amino-5 hloro-6-ethylamino-3-nitropyrazine with 1,1-dimethylurea and hydrochloric acid at reflux gave 2-chloro-5-(3, 3 -dimethylureido)- 

There is little recent information in this area. The tine structure of 3-acetoxy-l, 4-dinitro-2-piperazinol (14) has been elucidated by X-ray analysis.1212 Treatment of 5,6-dichloro-3-nitro-2-pyrazinamine (15) with refluxing ethanolic sodium cyanide for 4 days induced displacement of the nitro by a cyano group as well as ethanoly-sis of one chloro substituent to afford 3-amino-6-chloro-5-ethoxy-2-pyrazinecar-bonitrile (16) in 55% yield.1313 L-Methyl-4-(/ nitrobenzoyl)pipcrazine (17) gave I -(/ -aminobenzoyl)-4-methy I piperazine (18) (75%) on refluxing in ethanolic hydrazine hydrate with a little Raney nickel catalyst for 6 h 135, cf 1032 other reduction procedures have been reported.496,1741 

There is little recent information in this area. The fine structure of 3-acetoxy-l, 

4-dinitro-2-piperazinol (14) has been elucidated by X-ray analysis. Treatment of 

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Like 2-aminopyridines and 2-aminopyrimidine, 2-aminopyrazine (39) (Scheme 29) has been converted into the nitroso compound (121) by reaction with dimethyl sulfide and NCS followed by deprotonation of the resulting sulfonium salt with sodium methoxide to the 5, 5-dimethylsulfilimine and then oxidation with MCPBA <82JOC552>. The extremely reactive nitrosopyrazine (121) condenses with 1,3-dienes to give 3,6-dihydro-1,2-oxazines and with aromatic amines in the presence of acid to gives azo compounds, and is smoothly oxidized with ozone or sodium hypochlorite to 2-nitropyrazine (122). Methyl 3-aminopyrazinecarboxylate reacts with thiophosgene to produce the... 

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