Benzo cinnoline dioxide

The reduction of nitro compounds should initially produce nitroso compounds. This area has not been systematically explored because the nitroso group can be more easily introduced by alternative methods such as direct nitrosation, condensation and oxidative procedures. - In fact, there have been few instances in which nitroso compounds have been isolated as intermediates in reductions of nitro compounds. For example, it was initially believed that w-trifluoromethylnitrobenzene produced the corresponding nitroso compound upon reduction, but subsequently the product was shown to be w-trifluoromethylazox-ybenzene. - Low yields of an intramolecular dimeric, nitroso compound, benzo[c]cinnoline dioxide (1), can be obtained by reducing 2,2 -dinitrobiphenyl with zinc or sodium sulfide (equation I). - ... 

Only pyrazine and its benzo derivatives are easily converted into di-A-oxides, although di-A-oxides have been reported, for example, in the pyridazine, pyrimidine and cinnoline series. Oxidation of 3-amino-1,2,4-triazine 2-oxide with H202 in polyphosphoric acid at 24°C affords 3-amino-1,2,4-triazine 2,4-dioxide (78). However, 3-amino-1,2,4-triazine with peracetic or... 

Controlled reduction of 2,2 -dinitrobiphenyl is achieved with 2, 1, and 0.5 molar equivalents of sodium borohydride in the presence of palladium on carbon and sodium hydroxide to give benzo[c]cinnoline, its /V-oxide, and AT V -dioxide, respectively, in high yields (Scheme 6). 

Orientation in the nitration of the 5-oxide of benzo[c]cinnoline (11.20) depends upon conditions. With nitric acid alone it gives 69% of the 9-nitro 5-oxide and 13.5% of the 2-nitro 5,6-dioxide (62JCS2454). But with nitric acid/sulfuric acid, the products appear to be the 1- and 7-nitro 5-oxides in 43 and 26% yields, respectively. One group gives the yields as 43 and 26%, respectively (62JCS2454), whereas another finds the latter to be the major product (62JCS4384). 2,9-Dimethylbenzo[c]cinnoline 5-oxide and the 3,8-dimethyl isomer are nitrated at the 1- and 4-positions, respectively, as expected (62JCS4384). 

Several mechanisms are possible for these cyclizations. Formation of the dioxide (4) from the unknown 2,2 -dinitrosobiphenyl would parallel the dimerization observed with acyclic nitrosoarenes, and all the other cycliza-tion steps shown in Scheme 1 could be simple condensations, or involve radical anions, or radicals. Where deoxygenating reagents are used, there is also the possibility of cyclization via nitrene intermediates. It has been reported that low yields of benzo[c]cinnolines result from reduction of 2,2 -dinitrobiphenyls with carbon monoxide in the presence of iron penta-carbonyF or by heating in triethyl phosphite. In polarographic reduction studies, Ross et al - claimed to have demonstrated the sequence ... 

Oxidations of 2,2 -diaminobiphenyls with sodium perborate, phenyl iodosodiacetate, ° or manganese dioxide have given benzo[c]cinnolines with hydrogen peroxide in acetic acid, cyclization is accompanied by N-oxidation. These reactions, which parallel the oxidation of arylamines... 

The benzo[c]cinnoline ring system is resistant to oxidation by chromic acid, but is oxidized to pyridazinetetracarboxylic acid by alkaline permanganate. " Benzo[c]cinnoline has been oxidized to the 5-oxide with hydrogen peroxide in acetic acid at 0°C, and further to the 5,6-dioxide at 110°-120 C. The JV-oxidation of various other derivatives has been reported, although the main method for the preparation of N-oxides has been by the reduction of 2,2 -dinitrobiphenyls (Section II,A,2). In the case of unsymmetrically substituted compounds, both of the above methods usually give mixtures of 5- and 6-oxides. Selectivity is occasionally observed, thus 4-bromobenzo[c]cinnoline is oxidized to the 6-oxide, presumably owing to steric factors. Benzo[c]cinnoline oxides of known orientation have been obtained by the cyclization of 2-amino-2 -nitro-biphenyl derivatives (Section II,A,2). 

Benzo[c]cinnoline-5,6-dioxide is a colorless, high-melting (243°C), non-basic compound, sparingly soluble in organic solvents. There has been discussion of spectroscopic evidence as to whether it has a di-JV-oxide or a nitroso-dimer type structure, hut there has been little investigation of its chemistry and there appears to be no chemical evidence for its behaving as 2,2 -dinitrosobiphenyl i.e., it shows no nitroso group reactions. 

Benzo[c]cinnoline (114) (3%) was separated from a complex mixture of colored products obtained from the oxidation of 9 with active manganese dioxide formation of 114 suggests the stepwise loss of nitrogen, 10- 113-+ 1, and 1,4-dipolar cycloaddition of benzyne to 113.16 Oxidation of 9 with (diacetoxyiodo)benzene gave azobenzene (4%), 1-phenylbenzotriazole (112)... 

JV,JV -Dioxides or IV-oxides may be formed as intermediates in these reactions, depending on the stage at which N—N bond formation takes place (Scheme 1) and on the vigor of the subsequent reduction. By suitable choice of reaction conditions these may be isolated for example, reduction of 2,2 -dinitrobiphenyl with sodium hydrosulfide gives high yields of benzo[c]-cinnoline 5-oxide (5),11 while catalytic hydrogenation in solutions containing sodium hydroxide can be stopped at the 5,6-dioxide (4), or carried further.151618... 

The past year has seen the publication of Comprehensive Organic Chemistry, one volume of which contains much information on the six-membered ring systems to be reviewed in this article a monograph on the chemistry of condensed pyrazines has also appeared. Reviews on 1,4-thiazines, l,3-benzothiazines," pyridazines, benzo[c]cinnolines, quinazolines, purines, pyrrolo[3,2-c]quino-lines, 1,10-phenanthroline and its complexes, polyaza-phenanthrenes, and 1,9- and 1,10-diaza-anthracenes have been published. Other specialist reviews are devoted to catalytic methods of obtaining pyridine bases pyridine N-oxides the stereochemistry of quinolizines, indolizines, and pyrrolizines benzothiazinone dioxides 2-quinazolones and their cyclic homologues (e.g. 

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