The formation of N′-(benzoyloxy)benzenecarboximidamides and their subsequent cyclization to 3,5-disubstituted 1,2,4-oxadiazoles in different solvents were studied. A probable reaction mechanism was proposed on the basis of the obtained results.Compounds containing a 1,2,4-oxadiazole ring are active components of medical agents used for the treatment of asthma, ischemia, and Parkinson's disease. There are published data on antibacterial, anti-inflammatory, and anticancer properties of such compounds [1]. Therefore, studies on the formation of 1,2,4-oxadiazoles with a view to improve the existing methods of their synthesis and develop new more efficient procedures constitute an important problem.Several possible ways (a, b) for the formation of 1,2,4-oxadiazoles from N′-hydroxyamidines have been proposed. Ooi and Wilson [2] described a scheme for the reaction of carboxylic acid chlorides with N′-hydroxyamidines (Scheme 1, a). Here, the slow reaction step is the transformation of zwitterion into 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazol-5-ol via proton transfer from the nitrogen atom to oxygen. In the presence of strong bases [3, 4] 3,5-disubstituted 1,2,4-oxadiazoles are formed from O-acyl-N′-hydroxyamidines according to path b (Scheme 1).We examined [5-8] the formation of a series of 3,5-disubstituted 1,2,4-oxadiazoles (Scheme 2) and determined the rate constants k (k 1 + k 2 ) for the reaction I → III and the rate constants for the cyclization of preliminarily synthesized compound II (k 2 ). The latter was obtained by reaction of N′-hydroxybenzimidamide
