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RESEARCH PRODUCT

On the application of the extended Fujita-Nishioka equation to polysubstitued system. A kinetic study of the rearrangement of several poly-substitued Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 2-aryl-4-benzoylamino-5-phenyl-1,2,3-triazoles in dioxane/water

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Abstract The rearrangement rates of several di-, tri-, tetra- or penta-substituted Z -arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole ( 1a – 18a ) into the relevant 2-aryl-4-benzoylamino-5-phenyl-1,2,3-triazoles ( 1b – 18b ) have been determined in 1:1 (v:v) dioxane/water in a wide range of p S + (3.80–12.50) at different temperatures. The kinetic data obtained have been correlated with those previously collected for the rearrangement of ortho -, meta - and para -substituted Z -arylhydrazones ( 19a – 38a ) by means of an extension of the linear free-energy relationship (LFER) proposed by Fujita and Nishioka, thus considering steric ( E s ) and field ( F o ) proximity effects in addition to the normal electronic effects ( σ o,m,p ). Excellent correlation coefficients have been calculated ( R ≥0.999), with susceptibility constants ( ρ , δ and f ) close to those previously obtained for 19a – 38a , when only excluding data for the 2,6-bis- ortho -substituted Z -arylhydrazones 11a and 16 – 18a , which show a reactivity much higher than foreseeable, evidencing the first case of ‘steric acceleration’ in mononuclear rearrangements of heterocycles. A rationale for such a behaviour is proposed.