3-Bromo-l,2,4-benzotriazine

The treatment of 3-amino-1,2,4-triazine 2-oxides 1 or 3-amino-1,2,4-benzotri-azine 1-oxides 29 with nitrous acid proceeds as a diazotization reaction, but the diazo compounds have never been isolated owing to the easy displacement of the di-azo group with nucleophiles. Thus the reaction of 3-amino-1,2,4-triazine 2-oxides 1 with sodium nitrite in hydrochloric or hydrobromic acids leads to the corresponding 3-halogen-1,2,4-tiiazine 2-oxides 119 or 3-bromo-l,2,4-benzotriazine 1-oxides 120 (77JOC546, 82JOC3886). 

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). 

When the bromo compounds 9 were irradiated with UV light, 3-aryl-l, 2,3-benzotriazin-4(3//)-ones were isolated.222... 

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... 

---