Benzotriazole 1-oxide ring

Anions 207, derived from l-(diarylmethyl)benzotriazoles 206, can be oxidized with mild oxidants to relatively stable triaryl radicals 208. One of the possible reactions of radicals 208 is ring opening to give radicals 209. Elimination of nitrogen from 209 produces unstable species 210 that undergo intramolecular cyclization to phenan-thridines 211 (Scheme 25) <1996JHC607, 1998JOC1467>. When substituents X and Y are identical, products 211... 

Oxidation of benzotriazoles and other fused triazoles by potassium permanganate is a well-established route to lif-triazole 4,5-dicarboxylic acid derivatives. Many of the triazolo[d]pyrimidines, synthesized as purine analogs, can be degraded to monocyclic triazoles by acidic or basic hydrolysis (in other triazolopyriraidines, however, the triazole ring is cleaved preferentially ), e.g. Scheme 24. 

UV irradiation of 2-arylbenzotriazoles (144), including the commercially available photostabilizer Tinuvin P, in an aerated solvent results in oxidation of the benzo ring to give the 2-aryl-l,2,3-triazole-4,5-dicarboxylic acid (146), possibly via the intermediate 2-arylbenzotriazole-4,7-dione (145) (Scheme 25). Indeed, when the independently synthesized l-phenyl-2. -benzotriazole-4,7-dione (145, R = = H) is irradiated under the same conditions, compound (146 R = R = H) is formed, and... 

Considerable effort has been invested in attempts to explore the total replacement of CH groups by nitrogen in cyclopentadienide anions or benzene. The ability of aryl groups to stabilize free radicals, cations or anions is due to extension (conjugation) of re-orbitals. More than a century ago, it was observed that alkylbenzenes afford benzoic acid on oxidation and that the stability of arylazoles toward oxidants and acids increased with the number of N atoms, so that the oxidants attack the benzene ring in phenylpyrazole, and that benzotriazole survives refluxing with aqua regia. 

Heating 2,2 -diazidoazobenzene (371) at a temperature not higher than 58 °C leads to 2-(2-azidophenyl)-2H-benzotriazole (372), while above that temperature, e.g. at 170 C, the l,3a,4,6a-tetraazapentalene (373) is formed in 93% yield (67ja2618>. Most probably, the second step also involves nitrene intermediates. Benzotriazoles are also accessible by ring contraction reaction of bicyclic systems, like l,2,4-benzotriazin-3(2H)-one (374). This is converted into IH-benzotriazole on treatment with chloramine (an aminating oxidant) in ether (71CC532). 

Interestingly, oxidation of benzotriazole with KMn04 cleaves the benzene ring and produces l,2,3-triazole-4,5-dicarboxylic acid thus documenting the stability of the triazole system against oxidation. 

Photochemistry of N-heterocyclics Benzotriazole 1-oxide from pyrazole ring... 

The reduction of several indolo[2,3-a]quinolizidines by BY gave novel products resulting from reduction of the indole double bond, cleavage of the C-D ring junction, or reduction of a lactame to a carbinol amine [371]. The known reduction of aromatic nitro compounds has been used as a key step in the synthesis of 2-aryl-2/f-benzotriazoles. Thus, treatment of the o-nitrophenylazo dye 342 gave the 2-aryl-2/7-benzotriazole-l-oxides 343 in good yields [513]. 

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