Cinnoline photolysis

The photodecomposition of benzotriazine A/ -oxides produced 3-substituted 2,1-benzisoxazoles (Scheme 183) (73JA2390). The photolysis of cinnoline 1-oxides produced 3-methyl-2,1-benzisoxazoles (Scheme 183) (74TL2643, 74T2645). 

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. ... 

Benzo[c]cinnoline 5-oxide is formed when 2-azido-2 -nitrosobiphenyl is heated in toluene, possibly by cyelization to the dipolar intermediate (12), followed by elimination of nitrogen [Eq. (6)], or via 2-nitrosobiphenyl-2 -nitrene. The quantitative eonversion of 2,2 -diazidobiphenyl into benzo-[c] cinnoline by low-temperature photolysis was argued to provide evidence for a stepwise process through the azidonitrene and the dinitrene [Eq. (7)]. ... 

Photochemical reactions of pyridazines, phthalazines and cinnolines were extensively reviewed in CHEC-I <84CHEC-l(3B)l>, with many reactions proceeding via ring contraction. Since 1985, the photolysis of 4-azidopyridazines to give significant yields of ring expansion products, unsaturated... 

The major reaction observed in the sensitized (by benzophenone) and nonsensitized photolysis of benzo[c]cinnoline N-imine and N-acylimines is N—N bond fission. Small amounts of carbazole are formed as a by-product from irradiation of benzo[c]cinnoline N-imine.44... 

Electron Spin Resonance. A study has been made of the ESR spectra for radicals derived by photolysis of cinnoline and related substrates. ... 

The photolysis of cinnoline absorbed on colloidal silver has been studied by Raman spectral means the final product was formulated as the N,/)/ -disilver derivative (16) of o-(2-aminovinyl)aniline. ... 

Cinnoline 1-oxide (108, R = H) resisted photolysis, but 4-methylcinnoline 1-oxide (108, R = Me) gave a separable mixture of the deoxygenated product, 4-methylcinnoline (109), and 3-methyl-2,l-benzisoxazole (110) (MeOH, hv, N2, 84 h 42% and 11%, respectively also minor products) similar treatment of 4-metiiylcinnoline 2-oxide (111) also gave 4-methylcinnoline (109) (58%) but accompanied by 3-methyl-l//-indazole (112) (25%) and... 

An intramolecular version of this process, the photolytic conversion of 2,2 -diazidobiphenyl (36) to benzo[c]cinnoline, is also an unfavored reaction when carried out at room temperature. 4-Azidocarbazole is the main product but photolysis of 36 in a glass at 77 K gives a quantitative yield of benzo[c]cinnoline. Presumably conformational effects play a crucial role in this reaction but it should be pointed out that nitrene intermediacy has not been confirmed. 

Neiman found that 2-azido-2 -nitrobiphenyl cyclizes readily to benzo[c]cinnoline-iV-oxide on photolysis or thermolysis. The intermolecular counterpart of this reaction now has been found to be equally facile in some cases. Heating a- or jS-naphthyl azide and p-nitroso-iV, -dimethylaniline at reflux in bromobenzene produces the azoxy compounds 40 and 41 in virtually quantitative yield (Np = naphthyl). 

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