4-Hydroxy-3,4-dihydro-1,2,4-triazine, open

Open-chain tautomerism is a general feature of 4-hydroxy-3,4-dihydro-1,2,4-triazines, including cr -adducts at position 3 of the 1,2,4-triazine 4-oxides. Thus triazahexatrienes 85 are the open-chain form of cr -adducts 86 and can be aromatized by oxidation with KMn04, yielding 3-amino-1,2,4-tiiazine 4-oxides 88 (98ZOR418). 

Amino-4,5-dihydro-5-hydroxy-l,2,4-triazine (82B) exhibits a temperature-dependent equilibrium with the open-chain hydrazide-hydrazone derivative 82A in CDCI3 solution, as shown by the H-NMR data (85LA78). 

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