On the dichotomic behaviour of the Z-2,4-dinitrophenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole with acids in toluene and in dioxane/water: rearrangement versus hydrolysis

The mononuclear rearrangement (MRH) of the Z-2,4-dinitrophenylhydrazone (4a) and of the Z-phenylhydrazone (4b) of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant triazoles 5a and 5b in toluene has been quantitatively investigated in the presence of trichloroacetic acid (TCA) and of piperidine at 313.1 K. While the behavior in the presence of piperidine recalls the one previously evidenced for some Z-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, the study of the reactivity in the presence of TCA has most interestingly evidenced a general-acid-catalyzed rearrangement for “both” 4a and 4b. Thus, 4a offers the first example of a solvent-dependent dichotomic behavior in MRH processes on 1,2,4-oxadiazole derivatives as far as it undergoes an “acidic hydrolysis” in dioxane/water and a “rearrangement” in toluene.