Electron Ionization Induced Fragmentation of some 3-Aroylamino-5-Methyl-1,2,4- Oxadiazoles and 3-Acetylamino-5-Aryl-1,2,4-Oxadiazoles

Background and Objectives: 1,2,4-Oxadiazoles show a high reactivity and represent starting compounds for the synthesis of several other heterocycles. Some their derivatives can give the so called Boulton-Katritzky Reactions (BKR) which opens the way to the synthesis of several azoles. For this reason we have registered the mass spectra of several 3-aroylamino-5-methyl-1,2,4-oxadiazoles and 3-acetylamino-5-aryl1,2,4-oxadiazoles.Methods and Results: Thus, studying the mass spectra of the isomeric couple 3-benzoylamino-5-methyl-1,2,4-oxadiazole (1A) and 3-acetylamino-5-phenyl-1,2,4-oxadiazoles (1B) we have observed that MIKE and CID MIKE spectra of their molecular ions and of the [M - CH2CO](+). evidence that several fragmentation processes arise from common structure(s).Conclusions: These findings lead to suggest that the BKR could occur also under electron ionization. In order to evidence possible substituent effects the EI-MS spectra of a large series of 3-aroylamino-5-methyl-1,2,4-oxadiazoles (2A-19A) and of the corresponding 3-acetylamino-5-aryl-1,2,4-oxadiazoles (2B-19B) have been examined.