On the use of multi-parameter free energy relationships: the rearrangement of (Z) arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole into (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas

By using a multi-parameter approach (a combination of Hammett/Ingold-Yukawa-Tsuno/Fujita-Nishioka free energy relationships) the mononuclear rearrangements of heterocycles (MRH) rates for five new ortho-substituted and ten new di-, tri-, or tetra-substituted (Z)-arylhydrazones of 5-amino-3-benzoyl- 1,2,4-oxadiazole into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas (in dioxane/water and in a large range of pSþ values) have been related to the electronic and proximity effects exerted by the present substituents, also considering previous results on some mono meta- and para-substituted (Z)- arylhydrazones. In every case, excellent correlation coefficients have been calculated (r2 or R20.996). Once more the study of MRH has furnished an interesting panel of different reactivity (three pathways of reaction have been evidenced: general-base-catalyzed, uncatalyzed, and specific-acid-catalyzed) and this has been useful in enlightening how polysubstitution can differently affect the MRH rates. Moreover 2,6- disubstitution on the (Z)-arylhydrazono moiety causes a significant increase of the reactivity in all of the three studied pathways. All of the collected data appear useful for understanding structure-reactivity/ activity relationships in polysubstituted compounds.