Benzo quinoxalines preparations

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 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). 

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... 

The generation of other heteroq cles from Bfx and Fx has been the subject of exhaustive investigation. The most important transformation of Bfx to other heterocycles has been described by Haddadin and Issidorides, and is known as the Beirut reaction . This reaction involves a condensation between adequate substituted Bfx and alkene-type substructure synthons, particularly enamine and enolate nucleophiles. The Beirut reaction has been employed to prepare quinoxaline 1,4-dioxides [41], phenazine 5,10-dioxides (see Chap. Quinoxahne 1,4-dioxide and Phenazine 5,10-dioxide. Chemistry and Biology ), 1-hydroxybenzimidazole 3-oxides or benzimidazole 1,3-dioxides, when nitroalkanes have been used as enolate-producer reagent [42], and benzo[e] [ 1,2,4]triazine 1,4-dioxides when Bfx reacts with sodium cyan-amide [43-46] (Fig. 4). 

The pyrazine ring is stable toward permanganate oxidation, and this explains a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines or benzo-fused quinoxalines. In contrast, alkyl side chains on pyrazines are effectively oxidized by permanganate, selenious acid, selenium dioxide, or dichromate to afford the corresponding carboxylic acids (Section 8.03.7.1). Oxidation of pyrazines with hydrogen peroxide or percarboxylic acids gives pyrazine A -oxides and/or A, A -dioxides (Section 8.03.5.2). 

The preparation of quinoxaline derivatives carrying a substituent in the benzene ring requires suitably substituted o-phenylenediamines. These have been prepared by reductive cleavage (SnCl2) of appropriately substituted 2,1,3-benzoselenadiazoles (I9).21 Benzo-selenadiazoles, readily prepared from 1,2-diaminobenzenes and selenium dioxide, undergo halogenation at positions 4 and 7 and sulfonation at C-4. 5,6-Dichloro- 2,3-diphenylquinoxaline has been synthesized from benzil and l,2-diamino-3,4-dichlorobenzene, the diamine in turn was obtained from 4,5-dichloro-2,l,3-benzoselenadiazole.22... 

Isomerization of benzo[/]-l,5-diazabicyclo[3,2,2]nonene in 8.8 N HBr at 140°C yielded l,2,3,5,6,7-hexahydropyrido[l,2,3-de]quinoxaline (83 KGS677). Photolysis of dimethyl l-(quinolin-8-yl)-l,2,3-triazole-4,5-di-carboxylates in MeCN resulted in stable an/tydro-2,3-dimethoxycarbonyl-3//-pyrido[l,2,3-de]quinoxalin-4-ium hydroxides [87JCS(P1)403]. 6-Hy-droxymethyl-2-methyl-7-methoxy-l,2,3,4-tetrahydro-6//-pyrazino-[1,2-h]isoquinolin-4-one (138) was prepared from 5- [A-methyl-Ar-(ethoxy-... 

Biologically interesting benzo[ ]furyl quinoxalines were prepared by sequential oxidation and condensation (Scheme 83) <2004T6063>. 

Compound 777 of this type of acyclo C-nucleoside was prepared from the benzo[g]quinoxalin-3-yl precursor 776 (Section XII,O) by reaction with phenylhydrazine (58CB113) (Scheme 203). 

The pyrazine ring is stable to permanganate oxidation, and this accounts for a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines, benzo-fused quinoxalines including phenazines, and pyrido-fused pyrazines . In other fused systems, particularly pter-idines, the pyrimidine ring is easily hydrolyzed under either acidic or basic conditions to give numerous 3-aminopyrazinecarboxylic acid derivatives. 

Quinoxalinyl ketones have been prepared by application of the classical quinoxaline synthesis, an o-phenylenediamine being condensed with an appropriate 1,2,3-tricarbonyl compound. Reactions of this type do not provide an unambiguous synthesis of quinoxalinyl ketones, since an alternative mode of condensation is possible leading to a benzo-1,5-diazepinone. The latter possibility is eliminated in the example cited in Scheme 1 because NMR examination of the condensation product... 

The pyridazino[l,6-a]quinoxaline ring system, which is the only known benzologue, can be prepared from 1-substituted benzo triazoles (78) with two moles of DM AD (Equation (18)). The reaction presumably proceeds via pyridazino[l,2-a]benzotriazoles, which undergo ring scission by N—N bond cleavage followed by recyclization to (79). The reaction is sensitive to the solvent in... 

A number of preparations of different types of imidazoquinoxalines were reported in 2013. Ma and coworkers devised an efficient one-pot synthesis of benzo[4,5]imidazo[l,2-a]quinoxalines via a copper-catalyzed process... 

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