Concerning the mechanism of formation of 3-phenyl-5-trifluoromethyl-1,2,4-oxadiazole from O-vinylbenzamidoxime and trifluoroacetic anhydride in the presence of pyridine

A more appropriate mechanism of formation of the title compound from O-vinylbenzamidoxime and trifluoroacetic anhydride in pyridine is suggested. Careful analysis of electron densities and electronic charges at different reactive atoms using ab initio molecular orbital calculations supported this proposal. Comparative computations of the transition energies at N-2 and N-4 of O-vinylbenzamidoxime 1 and trifluroacetic anhydride 2 furnished inspiring results favoring the trifluoroacetylation at N-2.