2- benzo / quinoxalines

The numbering for benzo[/]quinoxaline (4) and benzo[ ]quinoxaline (5) is shown. 

In a similar manner, substituted benzo[/]quinoxaline derivatives can be prepared from naphthalene-1,2-diamine derivatives with oxalic acid dihydrate in 2 M hydrochloric acid. ... 

The reaction of benzene-1,2-diamines with nitromethyl phenyl ketone in the presence of sodium dithionite gives 2-phenylquinoxalines. In the same manner, naphthalene-1,2-diamine affords the corresponding benzo[/]quinoxalines. ... 

Condensation of 4-arylaminonaphthoquinones with diaminomaleonitrile affords 6-arylamino-benzo[/]quinoxaline-2,3-dicarbonitriles, and with ethane-1,2-diaminc, 6-arylaminobenzo-[/Jquinoxalincs are 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. 

The pyrazine ring is relatively stable to oxidation, and many pyrazine-carboxylic acids have been prepared from quinoxalines, phenazines, and other fused pyrazines by oxidation with potassium permanganate. This reaction has been most used for the oxidation of quinoxalines, for example, 77 -> 78. The oxidations are usually carried out with potassium permanganate in alkali (397), but may also be effected without added base (398). Crippa and Perroncito (399) have also used chromic oxide in acetic acid-acetic anhydride to oxidize benzo(/]quinoxalines (79). Pyrazines prepared by this method are summarized in Table 11.9 (397-419). 

O. Benzo[/]quinoxaline Acyclo C-Nucleosides 1. Benzo[fJquinoxalin-2- and 3-yl Acyclo C-Nucleosides... 

Reaction of 2-(D-araf //io-tetritol-l-yl)benzo /]quinoxaline (772) (Section XII,O) with three molar equivalents of phenylhydrazine gave the 3-(D-eryt/ira-l,2,3-hydroxypropyl)benzo[g]flavazole 773 (58CB113) (Scheme 201). 

Benzo[/]quinoxalines were formerly named 5,6-benzoquinoxalines, and thus 3-substituted benzo[/]quinoxalines were formulated as 2-substituted 5,6-benzoquinoxalines (1). A potential source of confusion is the alternative designation of 2-substituted benzo[/]quinoxalines as 2-substituted 7,8-benzoquinoxalines (2). 

The ultraviolet spectrum of benzo[/]quinoxaline has been measiured in ethanol and shows the expected three-banded structure these bands are... 

The condensation of 1,2-diaminonaphthalene with an a-dicarbonyl compound to give a benzo[/]quinoxaline represents a simple extension of the classical quinoxaline synthesis. As a result of the unsymmetrical structure of the diamine, isomeric mixtures of benzo[/]quinoxalines can in principle be formed when the dicarbonyl compound is also unsymmetrical (Scheme 1). In practice only one isomer may be formed in appreciable quantities and be thus readily isolated. The orientation of a number of the products obtained from the condensation reactions of 1,2-diaminonaphthalene is uncertain, though, as discussed in the following sections, unambiguous syntheses of benzo[/]quinoxalines may be achieved using o-aminonitroso- and o-aminophenylazonaphthalenes. 

The condensation of 4-aziridinyl-l,2-naphthoquinone (20) with 1,2-diaminoethane gives the benzo[/]quinoxaline 21. In simpler systems dihydro derivatives are isolated from the condensation of dicarbonyl compounds and 1,2-diaminoethane, but in this case the fully aromatic product is obtained. ... 

There have been two reports of the photochemical synthesis of benzo[/]quinoxalines. On irradiation of rmns-2-styrylpyrazine (22), photoisomerization occurs, and the resulting cis isomer 23 then undergoes... 

An interesting reaction sequence based on 1-tetralone (26) leads to an unambiguous synthesis of 2-amino-3-cyano-5,6-dihydro-benzo[/]-quinoxaline (27). The isomeric 3-amino-2-cyano compound is similarly obtained from 2-tetralone. ... 

Oxidation of the parent base with hydrogen peroxide in formic acid gives a high yield of mono-N-oxide and a little di-N-oxide N-Oxidation is assumed to proceed preferentially at the less hindered 4-nitrogen. A number of substituted benzo[/]quinoxaline 4-oxides have been prepared, the majority by oxidation of the appropriate benzo[/]quinoxaline with peracids. " Treatment of benzo[/]quinoxaline 4-oxide with phosphoryl chloride gives mainly 3-chlorobenzo[/]quinoxaline. An isomeric mono-chloride, m.p. 104-104.5°, is also isolated from this reaction which is shown by independent synthesis not to be the 2-chloro derivative. A dichloro derivative, m.p. 187-188°, of unknown structure is obtained by treatment of the parent base with chlorine in glacial acetic acid. A disubstitution product of unknown orientation and m.p. 288° is obtained by nitration of... 

Several transformations of 2- and 3-D-arabotetrahydroxybutyl benzo[/]quinoxalines have been reported. Thus oxidation of the 2-tetrahydroxybutyl derivative with hydrogen peroxide in dilute sodium hydroxide gives the 2-carboxylic acid, m.p. 185°, and oxidation with potassium periodate in dilute acetic acid gives the 2-aldehyde,... 

Benzo[/]quinoxalines have been patented for use as catalysts for the silver dye bleaching process and as dyestuff intermediates. The latter compounds have been derived by nitration, sulfonation, or chlorosulfona-tion of either 2,3-dioxo- or 2,3-dichlorobenzo[/]quinoxaline. 

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