Quinoxalinones nitration

When activating substituents are present in the benzenoid ring, substitution usually becomes more facile and occurs in accordance with predictions based on simple valence bond theory. When activating substituents are present in the heterocyclic ring the situation varies depending upon reaction conditions thus, nitration of 2(177)-quinoxalinone in acetic acid yields 7-nitro-2(177)-quinoxalinone (21) whereas nitration with mixed acid yields the 6-nitro derivative (22). The difference in products probably reflects a difference in the species being nitrated neutral 2(177)-quinoxalinone in acetic acid and the diprotonated species (23) in mixed acids. 

Nitration of 6,7-disubstituted 3,4-dihydro-2(l//)-quinoxalinones with fuming nitric acid in trifluoroacetic acid produces the 5-nitro-2,3(1/7, 4//)-quinoxalinediones in good yields <1995JOC5838>. Methyl 6-methyl-2,3(l//,4//)-quinoxalinedione-5-carboxylate is regioselectively nitrated with a mixture of potassium nitrate in concentrated sulfuric acid to give the corresponding 7-nitro derivative <1999JHC1271>. 

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