A deep insight into the mechanism of the acid‐catalyzed rearrangement of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole in a non‐polar solvent

Abstract

The conversion of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole (1a) into the relevant 1,2,3‐triazole (2a) has been quantitatively studied in toluene in the presence of several halogenoacetic acids (HAAs, 3a–h). Again, the occurrence of two reaction pathways has been pointed out: they require one or two moles of acid, respectively, thus repeating the situation previously observed in the presence of trichloroacetic acid. The observed rate constant ratios (kIII/kII) are only slightly affected by the nature of the acid used. To gain a deeper insight into the action of the acids used we have measured the association constants of the HAAs (3a–h) with 4‐nitroaniline (4) in toluene. Also in this case, the formation of two complexes requiring one (K2) or two (K3) moles of acid has been evidenced, but now the K3/K2 ratios are significantly affected by the strength of the acid examined. The variation of the K3/K2 ratios larger than those concerning the kIII/kII ratios appears useful to enlighten the very nature of the acid‐catalyzed pathways in toluene, which has been elucidated also carrying out the rearrangement in the presence of mixtures of tribromo‐ and trichloro‐acetic acids at different concentrations. Copyright © 2010 John Wiley & Sons, Ltd.

Proton transfer reactions in apolar aprotic solvents

“…While investigating the mechanism of acid or base catalysis in a monocyclic rearrangement of Z ‐arylhydrazones of 3‐benzoyl‐5‐amino‐1,2,4‐oxadiazole in toluene into the relevant 1,2,3‐triazole (Scheme ), Spinelli et al . found that kinetics of the rearrangement exhibit general acid or general base catalysis involving either only one acid (e.g., 2,2‐dichloropropionic acid)/base (e.g., di‐isobutylamine) molecule or both one and two molecules of the acid (e.g., trichloroacetic acid)/base (e.g., piperidine).…”

“… 4Refs . and and Lange's Handbook of Chemistry , 13th edition (Ed: J.A. Dean), McGraw‐Hill Book Company, New York, 1985.…”

Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations

“…The mononuclear rearrangement of heterocycles (MRH) reaction (also called the Boulton–Katritzky rearrangement) has been a historically efficient method for synthesizing five-membered heteroaromatic rings. − Heterocycles containing nitrogen atoms are critical in many areas of chemistry including synthesis, medicinal efforts, and materials; extensive reviews are available. − Of specific interest is the MRH of the Z -phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole (Scheme ) reported by D’Anna and co-workers . The MRH reaction’s ring-to-ring interconversion mechanism represents a special case of S N 2 displacement that proceeds via an intramolecular nucleophilic substitution (S Ni ) reaction that features a bicyclic quasi-aromatic 10π transition state. − …”