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 theZ-phenylhydrazone (4b) of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant triazoles 5a and5b 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 onepreviously evidenced for some Z-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, the study ofthe reactivity in the presence of TCA has most interestingly evidenced a general-acid-catalyzedrearrangement for “both” 4a and 4b. Thus, 4a offers the first example of a solvent-dependentdichotomic 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.