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-2 H-1,2,3-triazol-4-yl)ureas

Abstract

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-2 H-1,2,3-triazol-4-yl)ureas (in dioxane/water and in a large range of p S + 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 ( r 2 or R 2≥0.996). 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.