Quinoxalin-2-ones nitration

Electrophilic substitution reactions of unsubstituted quinoxaline or phenazine are unusual however, in view of the increased resonance possibilities in the transition states leading to the products one would predict that electrophilic substitution should be more facile than with pyrazine itself (c/. the relationship between pyridine and quinoline). In the case of quinoxaline, electron localization calculations (57JCS2521) indicate the highest electron density at positions 5 and 8 and substitution would be expected to occur at these positions. Nitration is only effected under forcing conditions, e.g. with concentrated nitric acid and oleum at 90 °C for 24 hours a 1.5% yield of 5-nitroquinoxaline (19) is obtained. The major product is 5,6-dinitroquinoxaline (20), formed in 24% yield. 

Quinoxalin-2-ones, unlike quinoxaline itself, may be nitrated under mild conditions. Nitration of quinoxalin-2-one in acetic acid gives mainly the 7-nitro derivative in sulfuric acid, the 6-nitro compound is formed (Scheme 6). ... 

Quinoxalin-2-one is a very weak base (pK — 1.37) and so the different orientation of substitution in acetic and sulfuric acids may mean that in acetic acid the principal species undergoing nitration is the neutral molecule, and in sulfuric acid, the mono-cation. Treatment of quinoxaline-2,3-dione, or its iViV -dimethyl derivative in sulfuric acid, with 1 equivalent of potassium nitrate, results in nitration at position 6 with 2 equivalents of potassium nitrate, 6,7-dinitro compounds are formed. When quinoxaline is boiled with aqueous nitric acid, 6-... 

The stereoselective intramolecular Diels-Alder reaction of 3-alkenyl(oxy)-2(l//)-pyrazinones leading to tricyclic ring systems was investigated <02TL447>. A one-pot 7-alkoxylation of 6-arylpyrazino[2,3-c][l,2,6]thiadiazine 2,2-dioxides 169 was accomplished by using N-halosuccinimides <02EJ02109>, and the nitration of 2-(5-methyl-2-furyl)quinoxaline was shown... 

Reductive cyclization of (2-nitroanilino)acetic acid derivatives yields the 3,4-dihydro-quinoxalin-2(l/i/)-ones 1 and, after air oxidationor oxidation with hydrogen peroxide, potassium permanganate, or silver(I) nitrate, quinoxalin-2(lif)-ones 2 are formed. 

The regiospecific oxidative nitration of 3,4-dihydro-6,7-disubstituted quinoxalin-2(l//)-ones utilizing fuming nitric acid in trifluoroacetic acid gives 5-nitro-6,7-disubstituted quinoxa-line-2,3(l/f,4/f)-diones in good yields. 

The nitration of quinoxaline presumably involves the conjugate acid formed by addition of a proton to one of the nitrogen atoms.Direct nitration of quinoxaline under forcing conditions using concentrated nitric acid and oleum gives a mixture of 5-nitro- and 5,6-dini-troquinoxaline in 1.5% and 24% yield, respectively. - The formation of a mixture of... 

The benzene ring of quinoxalin-2(177)-ones is activated towards electrophilic substitution, and nitration results in the formation of the 7-nitro derivative when the reaction is carried out in acetic acid solution in concentrated sulfuric acid, where the base is present in a protonated form, the 6-nitro compound is formed. - ... 

Nitration of quinoxaline-2,3(l//,4//)-dione proceeds at the 6- and 7-positions, e.g. nitration with one or two equivalents of potassium nitrate in concentrated sulfuric acid yields the 6-nitro and 6,7-dinitro compounds, respectively. Nitration of 8-(carbamoy methy )su fonyl-benzo[/]quinoxaline-2,3(17/,4//)-dione with potassium nitrate in concentrated sulfuric acid gives the 6-nitro derivative in 52% yield. 

Electrophilic substitution of quinoxaline-2,3-dione and its 1,4-dimethyl derivative occxu at positions 6 and 7. For example, treatment of a solution of quinoxaline-2,3-dione in concentrated sulfuric acid with one equivalent of potassium nitrate yields the 6-nitro derivative, whereas with two equivalents of potassium nitrate 6,7-dinitroquinoxaline-2,3-dione is formed. 6-Bromo and 6,7-dibromoquinoxaline-2,3-dione have been prepared by bromination of the 2,3-dione in sulfuric acid with bromine and silver sulfate, and chlorination is found to occur under similar conditions. Treatment of quinoxaline-2,3-dione with fuming sulfuric acid yields the... 

This approach for the synthesis of macrocycles with quinoxaline moieties involves the development of methods for the introduction of amino groups to the adjacent carbon atoms of the planned unit of the macrocycle system. Two methods (Crossley et al. 1996a) have been developed for the synthesis of diaminoporphyrin 6. The first involves the reduction of the nitro group to the amino group of the compound 53 with sodium borohydride in the presence of the Pd/C and subsequent regioselective nitration (Scheme 5.13). The second one is the nucleophilic substitution of hydrogen by NaNHCHO and subsequent hydrolysis. Both methods lead to... 

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