Benzo c,cinnolines

The parent dibenzotriazepine is converted into a mixture of benzo[c]cinnoline 5-imide (5), benzo[c]cinnoline (6) and carbazole (4) on irradiation.331... 

Moderate yields of the 1- (47%) and 4- (51%) fluoro derivatives of benzo[c]cinnoline were obtained by fluorodenitration of the nitro precursors using tetrabutylammonium fluoride. The 2- and 3-fluoro isomers have been made by Schiemann reactions, though yields were only 25 and 35%, respectively (92SC545). 

Die kathodische Cyclisierung von 2,2 -Dinitro-biphenyl zu Benzo-[c]-cinnolin verlauft anBlei-Kathodcnin Natronlauge nahezu quantitativ1 ebenso leicht bilden sich 3,8-disub-stituierte Bcnzo-[c]-cinnoline2 ... 

Oxidative photocyclization of benzylideneaniline appears to proceed efficiently only in the presence of strong acid. The phenanthridine 31, however, has been prepared by irradiation of the imine 3228 few other examples of the photocyclization of arylimines have been reported.29 Strong acid is also required for successful photocyclization of azobenzenes to benzo-[c]cinnolines. Here, protonation is claimed to lower the reactive n, n excited state below the level of the unreactive n, it state. 2-Phenylazopyridine,... 

F. W. Schulze, H. J. Petrick, H. K. Cammenga, H. Z. Klinge. Thermodynamic Properties of the Structural Analogues Benzo[c]cinnoline, trans-Azobenzene and cis-Azobenzene. Z. Phys. Chem. 1977, 107, 1-19. 

Dinitrobiphenyl, in an alkaline solution, is reduced to benzo[c]cinnoline N-oxide (Scheme 83) [122,123]. 

Scheme 83 Benzo[c]cinnoline by cathodic cyclization of 2,2 -dinitrobiphenyl.

Fig. 14 Reduction of PhjCSPh by electrochemically generated aromatic anion radicals (in DMF at 25°C). Variation of the rate-determining step rate constant, A , with the standard potential of the aromatic anion radical, p,g (from left to right azobenzene, benzo[c]cinnoline, 4-dimethylaminoazobenzene, terephthalonitrile, naphthacene, phlhalonitrile, perylene, fluoranthene, 9,10-diphenylanthracene). The dotted lines are the theoretical limiting behaviours corresponding to the concerted (right) and stepwise (left) pathways. (Adapted from Severin et al 1988.)...

When 2,2 -biphenyldiamines are tetrazotized and the resulting salts are heated, benzofurans are obtained, but benzo[c]cinnolines may be byproducts. This method has been litttle used. 2,3,7,8-Tetramethyldibenzo-furan (47) has been obtained in 40% yield from 4,4, 5,5 -tetramethyl-2,2 -biphenyldiamine by this method. " ... 

Benzo[c]cinnoline is reduced by visible-light photolysis in isopropanol to 5,6-dihydrobenzo[c]cinnoline irradiation of this at a shorter wavelenth converts it to carbazole. ... 

Auf ahnliche Weise laBt sich die thermische Bildung von 3-Phenyl-1,2,4-oxadiazolen aus [Pg.483]

A variation of this procedure is given in Preparation 3-3, in which a mixed solvent is used in the preparation of benzo[c]cinnoline by a lithium aluminum hydride reduction [67]. 

Preparation of Benzo[c]cinnoline by Lithium Aluminium Hydride Reduc-... 

Azobenzene is oxidatively cyclized to benzo(c)cinnoline (CIX) when exposed to sunlight in strongly acidic solutions,172 or in an acetic acid and ferric chloride mixture.124 As irradiation of azobenzene in neutral solutions is known to result in cis-trans equilibration, it seems that the... 

Benzo[c]cinnoline derivatives of different oxidation levels are prepared by N-N bond formations from suitable 2,2 -disubstituted biphenyls as outlined in Scheme 5. 

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). 

Benzo[c]cinnoline is also available by irradiation of azobenzene. 

There are also reviews on the biological activity of certain phthalazines (59MI21203) and on Reissert compounds from phthalazines (80H(14)1033). The chemistry of benzo[c]cinnolines has also been covered (79AHC(24)l5l). 

It has been known for some time that irradiation of azobenzene (324) in either 22 N sulfuric acid350 351 or acetic acid with added ferric chloride 352 yields benzo[c]cinnoline (325). This is accompanied by the formation of an almost equal quantity of benzidine (326), undoubtedly arising by rearrangement of hydrazobenzene (327). The mechanism of this reaction differs, therefore, from that of the stilbene cyclodehydrogenation, and azobenzene itself functions as the hydrogen acceptor. Yields of not more than 50% of benzo[c]cinnoline are generally observed. 

In contrast to 4-methylcinnoline, benzo[c]cinnoline with DM AD in methanol450 or without solvents451 gave tetramethyl benzo[c]pyrida-... 

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