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

The title reaction has been studied both in CD3OD and (t)BuOK/CD3OD by means of H-1 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 meagre and 3-acetylamino-5-aryl-1,2,4-oxadiazoles are more stable than the 3-aroylamino-5-methyl isomers. Vice-versa, when anions are involved the substituent effect is remarcable 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.