131223-51-3Relevant articles and documents
Mononuclear Heterocyclic Rearrangements. Effect of the Structure of the Side Chain on the Reactivity. Part 1. Rearrangement of Some 3-Arylureines of 5-Phenyl-1,2,4-oxadiazole into 1-Aryl-3-benzoylamino-1,2,4-triazolin-5-ones in Acetonitrile, Benzene, and Dioxane-Water
Frenna, Vincenzo,Spinelli, Domenico,Consiglio, Giovanni
, p. 1289 - 1295 (2007/10/02)
The effect of the structure of the side chain both on the mechanism and the reactivity in mononuclear heterocyclic rearrangements has been studied by comparing the base-catalysed rearrangement of some 3-arylureines of 5-phenyl-1,2,4-oxadiazole with that of some arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole.In acetonitrile and in benzene, in the presence of amines, on changing from the side chain CNN (arylhydrazones) to the side chain NCN (arylureines), a strong decrease of the reactivity has been observed (rate ratios ca. 103), but the reaction mechanism is the same for the two series of compounds.In contrast, in dioxane-water, the reactivity variation is much less (rate ratios ca. 25 in the pS+-dependent range) and a change of mechanism is observed.For arylureines and for arylhydrazones, specific- and general-base catalysis respectively has been shown.This is in keeping with the high acidity of arylureines, which in the presence of a strong base can be converted into the corresponding anions and then rearrange to the 1,2,4-triazolin-5-ones.
