Reactivity of 3‐alkyl‐4‐arylazomethylene‐3,4‐dihydro‐1,2,3‐benzotriazines in protic solvents: 1,4‐Addition reactions and dimroth rearrangement

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Abstract 3‐Alkyl‐4‐arylazomethylene‐3,4‐dihydro‐1,2,3‐benzotriazines 5a and 5b undergo facile 1,4‐addition of methanol or ethanol to afford stable crystalline hydrazones, 6 and 8 which have been characterised by spectroscopic analysis. In particular, the nmr spectrum of 8 shows novel features due to the diastereotopic nature of the CH2 protons in the two O‐ethyl groups. Compound 5b shows a property unique to the compounds in this series; refluxing this arylazomethylenetriazine in ethanol affords a rearranged product, characterised as the 1‐aryl‐2‐cinnolinylhydrazine (9). The formation of 9 is rationalised as a ring opening‐ring closure process analogous to the Dimroth rearrangement. The cinnoline 9 displays some novel chemistry arising from the facility of the arylhydrazino substituent to react with acid to give a fragmentation product, 3‐methylindazole (7).