3- Phenyl-1,2,4-benzotriazine 1 -oxide

In some cases, the position of the N-oxidation depends on the temperature. The reaction of 3-phenyl-1,2,4-benzotriazine 172 with peracetic acid atfords 3-phenyl-1,2,4-benzotriazine 1-oxide 173 at 50°C and 2-oxide 174 at room temperature (57JCS3186). Only the 1-oxide 175 was obtained by the oxidation of 3-unsubstituted 1,2,4-benzotriazine 176. The oxidation of 3-methyl-1,2,4-benzotriazine 176 (R = Me) under the same conditions results in a mixture of 3-methyl-1,2,4-benzotriazine 1-oxide 175 and 2-oxide 177 in 25 and 10% yields, respectively. 

The benzo fused system (579) is produced in good yield by the oxidative ring closure of (578) or by the action of zinc and aqueous sodium hydroxide on (577) (55CB1284). It rearranged in dilute acetic acid to give 3-phenyl-l,2,4-benzotriazine. 

Pyrolysis of 4-phenyl-l,2,3-benzotriazine 3-oxide (100) at 420 °C gave 3-phenylbenz-isoxazole (101), 3-phenylindazole (102) and acridin-9-one (103). However, the pyrolysis of 4-phenylnaphtho[2,3-. 

Electrochemical oxidation of 2-hydroxylaminobenzohydrazide (148) affords (10), and similar treatment of l-(2-hydroxylaminobenzyl)-l-phenylhydrazine (149) yields 3-phenyl-3,4-dihydro-l,2,3-benzotriazine (150) (76BSF433). 

Phenyl-l,2,4-benzotriazine 2-oxide (254 R = Ph) has been shown to rearrange to the 1-oxide (253) on prolonged heating at 45-50 °C (57JCS3186). 

Catalytic reduction of the 2-nitrophenyIhydrazones (745) and subsequent air oxidation of the tetrahydro-l,2,4-benzotriazines (746) which are formed is used for the synthesis of 3,4-dihydro-1,2,4-benzotriazines (747) (80FES715). In another cyclization of an o-nitro group, which somewhat resembles others (e.g. 736 —> 737) described earlier, treatment of l,l-dialkyl-2-(2-nitrophenyl)hydrazines (748) with acids affords 2-alkyl-1,2,4-benzotriazinium salts (749) (77JCS(P1)478). The 2-nitrophenylbromohydrazone (750) with sodium ethoxide and ethyl cyanoacetate forms 6-bromo-3-phenyl-l,2,4-benzotriazine (751) a mechanism for this interesting transformation, in which the cyanoacetate plays no part, has been proposed (79JHC33). 

V -(2-Aminophenyl)hydrazides are cyclized to 5 and oxidized to 1,2,4-benzotriazines 6 when treated with hydrochloric acid and sodium 3-nitrobenzenesulfonate.5,147 Similarly, A -(2-nitro-phenyl)hydrazides give 1,2-dihydro-l, 2,4-benzotriazines 5 when the nitro group is reduced with sodium amalgam in ethanol. In most cases, the initially formed dihydro compounds are not isolated, but are oxidized by potassium hexacyanoferrate(III) to the aromatic 1,2,4-benzotriazines 6.148 Reduction of the nitrohydrazones or the tautomeric azo compounds with zinc, catalytic hydrogenation,332 or elcctrochemically246 affords 1,2,4-benzotriazines 6.148 Electrochemical reduction of A"-(2-nitrophenyl)hydrazides yields 3-substituted 1,2,4-benzotriazines 6.140... 

Phenyl-1,2,4-benzotriazine 2-oxide rearranges to the 1-oxide on prolonged heating at... 

Methyl-,242 3-phenyl-,450 or 3-amino-l,2,4-benzotriazine 1-oxide or -2-oxide afford benzo-triazoles 4 when treated with sodium hydroxide377 The same reaction is observed for pyrido-[2,3-e]-l,2,4-triazin-3-amine or pyrido[4,3-e]-l,2,4-triazin-3-amine 1-oxide in sodium hydroxide affording the corresponding products in 77 and 40% yield, respectively.370 379... 

Phenyl-1,2,4-benzotriazin-3-one 1 -oxide (54), which exists as such in the crystal, gives in solution the 2-isocyanato-azoxybenzene (55) <85JCS(Pl)l47i>. 

Careful thermolysis of 3-(o-nitrophenyl)-4-phenyl-l,2,3,5-oxathiadiazole 2-oxide (476) in toluene led to the isolation of 2-phenyl-l,2,4-benzotriazin-3(2if)-one 1-oxide (54). In solution a reversible equilibrium of (54) with the ring-opened o-isocyanato-azoxybenzene (55) is observed (Scheme 87) <85JCS(P1)1471>. 

In view of these results it must be concluded that the other anthranil JV-oxides obtained by oxidation of o-nitrobenzaldehyde phenylhydra-zones,243 or by solvolysis of their a-bromo derivatives,244 should be reformulated as benzotriazinium JV-oxides. However, it is quite likely that 3-arylazoanthranil JV-oxides are intermediates in these reactions and also in the photolytic rearrangement of a-bromo-o-nitrobenzaldehyde phenyl-hydrazones to 3-aryl-l,2,3-benzotriazin-4-ones.245... 

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