Benzo cinnolines 9,10-dihydro

By controlling the potential the reaction can be stopped at the N-oxide stage at more negative potentials the reduction can be controlled to give either benzo[c]cinnoline or its dihydro derivative. 

F. A. Neugebauer, M. Bock, S. Kuhn-hauser, H. Kurreck, Darstellung, ESR-und ENDOR-Untersuchung von Radi-calkationen des Tetraphenylhydrazins, des 5,6-Dihydro-5,6-diphenylbenzo[c]-cinnolins und des Benzo[c]benzo[3, 4]cinnolino[l,2-a]cinnolines, Chem. Ber. 1986, 119, 980-990. 

Cinnoliniumperchlorate 3 with 2nKOH in dioxan-acetonitrile gives 2,4-diphenyl-5-hydroxy-6-(2, 4, 6 -triphenylphenyl)-5,6-dihydro-benzo[c]cinnoline, m.p. 227-228 °C (44% yield). Perchloric acid leads back to the cinnolinium perchlorate 3. 

However, another study by Emerson and Rees found that benzo[c]-cinnoline (1) was reduced more easily than the oxides 4 and 5 thus all three are probably reduced directly to the dihydro compound 6 under these conditions. They also concluded that 2,2 -dinitrobiphenyl (3), the most easily reduced of all, is converted into 2,2 -bis(hydroxylamino)biphenyl (7) in an eight-electron step and thence into 6 [Eq. (2)]. More recent studies by cyclic voltammetry indicate that some steps may be more complex. " It has also... 

Phenyllithium adds to the N=N bond of benzo[c]cinnoline giving, on work-up, the air-sensitive, 5,6-dihydro-5-phenylbenzo[c]cinnoline (53). In an attempt to generate the radical corresponding to triphenylhydrazyl from 53, Wittig and Schumacher S found that oxidation with silver oxide or lead tetraacetate produced instead the quinonimine 54, analogous to the product formed by methylating 2-hydroxybenzo[c]cinnoline (Section V,D). On reductive acetylation, the quinonimine is converted into the 5,6-dihydro... 

Early reports indicate that N-aminopyridinium salts react with aromatic aldehydes in the presence of base to give nitriles as the major products.1 Completely different reaction courses emerge when the l-methyl-3-amino-benzimidazolium salt 23 and 2-methyl-3-aminobenzothiazolium salt 25 are allowed to react with benzaldehyde under the similar conditions, affording a benzaldehyde phenylhydrazone 24151 and a 2,3-dihydro-1,3,4-benzothia-diazine 26,152 respectively likely reaction pathways are suggested in Eqs. (16) and (17). Benzo[c]cinnoline JV-imine reacts with p-anisaldehyde to give the bis-lV-imine 27.44... 

Benzo[c]cinnolines from 9,10-dihydro-9-aza-10-boraphenanthrenes s. 19, 541 Sodium salt Na ... 

Syntheses and mechanisms are proposed for the preparation of a series of 4,4a,5,6-tetrahydro- and 5,6-dihydro-benzocinnolinones and their subsequent dehydrogenation and amination to give new benzo[fe]cinnolines (110 = H) and their 4-amino... 

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