1 //-Benzo cinnolines

Cinnolin-4(lH)-one, 8-hydroxy-iodination, 3, 21 Cinnolin-4-ones synthesis, 3, 56 Circular dichroism indolizidines, 4, 450 pyridines and benzo derivatives, 2, 126... 

Even though data for a quantitative comparison are lacking, the effect of the position of benzo-fusion onto pyridazines is analogous to that with pyridines in producing the very poorly reactive 3-chloro-cinnoline (396) and highly reactive 1-chlorophthalazine (Table XV, lines 8 and 9). 

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 ... 

Isolated and benzo-fused diazine rings are key structural elements in many natural and synthetic compounds of current interest. This contribution relates highlights from many of the studies on the diazines pyridazine, pyrimidine, pyrazine, and their benzo-fused derivatives cinnoline, phthalazine, quinazoline, quinoxaline, and phenazine published in English in the journal literature during 1996, as covered by Chem. Abstr. through volume 126, issue 5. 

Benzo[r]bcnzo[3,4]cinnolino[l,2- ]cinnoline 61 and a series of 5,6-dihydrobenzo[c]cinnoline derivatives, including compounds 62, were studied by cyclic voltammetry. The unusual shape of the voltammograms of the investigated compounds can be explained by an EiE-DISP mechanism with a slow disproportionation reaction <1996JA5020>. 

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,... 

Cinnolines, one of the two benzo derivatives of pyridazines, attracted considerable attention due to the variety of pharmacological activities exhibited by these heterocycles. 

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. ... 

Antwerp (2004), and Strasbourg (2006) in the covered period of this chapter. Certainly there has been a lot of activity in the pyridazine and benzo derivative field in the 1996-2006 period. A search on the Web of Science revealed 1756 articles for the topic pyridazin , 574 for phthalazin and 168 for cinnolin . The same search on the Scifinder database revealed 5203, 1943 and 462 hits for the concepts pyridazin , phthalazin , and cinnolin , respectively. Patents have only been taken into account in Section 8.01.12. In this chapter emphasis has been put on new and adapted older methods, as well as new interesting examples of well established methods. Selections necessarily had to be made due to the large amount of material published within the considered timeframe. Fully conjugated pyridazines, phthalazines and cinnolines as well as (partly) reduced and oxo forms (both only in the 1,2-diazine ring) are covered in this work. 

Microbial deoxygenation of benzo[f]cinnolin-5-ium oxide with Bakers yeast-NaOH in EtOH/water at reflux yielded 90% of benzo[f]cinnoline <1997TL845>. The same deoxygenation has been achieved in a similar yield via heating in EtOH with NaOEt at 160°C in a sealed tube <2004JOC7720>. 

The annelation of benzo rings on pyridazines was covered in CHEC-II(1996) <1996CHEC-II(6)1>. Maes and Matyus reported new examples in their synthesis of the dibenzo[// ]phthalazin-l(27r)-one and dibenzo[//]cinnolin-3(27/)-one skeleton. Palladium-catalyzed intramolecular arylation of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2//)-one yielded 2-benzyldibenzo[/,4]phthalazin-l(2//)-one. The synthesis of this new tetracyclic pyridazinone from 2-benzyl-5-(2-aminophenyl) -phenylpyridazin-3(2//)-one via a Pschorr-type reaction was also investigated. Similarly, the con-stmction of 2-methyldibenzo[/, ]cinnolin-3(2//)-one from 2-methyl-5-(2-bromophenyl)-6-phenylpyridazin-3(27T)-one and 2-methyl-5-(2-aminophenyl)-6-phenyl-pyridazin-3(2//)-one was performed <2003T5919>. 

The interest for applications of pyridazines, phthalazines, and cinnolines as pharmaceuticals, agrochemicals, and materials certainly increased in the period 1996-2006. The database Scifinder revealed that 669 patents containing the topic pyridazine were published in this time frame. Similarly, for the benzo analogs phthalazine and cinnoline ... 

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