Studies on azole-to-azole interconversions. Substituent effects on the ring-degenerate equilibration between 3-aroylamino-5-methyl-1,2,4-oxadiazoles and 3-acetylamino-5-aryl-1,2,4-oxadiazoles

Article abstract of DOI:10.1016/0040-4020(95)98709-Q

The title reaction has been studied both in CD₃OD and (t)BuOK/CD₃OD by means of ¹H NMR measurements. The equilibrium composition and the effect exerted thereon by X-substituents in the aryl moiety have been found to be quite different whether neutral or anionic forms are involved. In the first case the effect of X is meager and 3-acetylamino-1,2,4-oxadiazoles are more stable than the 3-aroylamino-5-methyl isomers. Vice-versa, when anions are involved the substituent effect is remarkable and the equilibrium can be, for strongly electron-withdrawing X-groups, even largely shifted towards the anions of the 3-aroylamino-5-methyl-1,2,4-oxadiazoles.