Fragmentation of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones under electron ionization

A series of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo3.3. 1]nonan-9-ones was prepared, and the details of their fragmentation under electron ionization (EI) were elucidated. The molecular ions of each compound under consideration were quite abundant in their EI spectra. Full-scan spectra exhibited a number of fragment ions which were clearly assigned using MS/MS and accurate mass measurements. The basic fragmentation of 3,7-dialkyl-1,5-diphenylbispidinones was due to the cleavage of C(1)-C(2) bond followed by a hydrogen migration similar to an odd-electron McLafferty rearrangement. Alternatively, the C(1)-C(2) bond cleavage was followed by the elimination of an imine molecule, Alk-N=CH(2). Further fragmentation resulted in ions at m/z 234 and 103, present in the spectra of all the compounds under study. The fragmentation pathways proposed in this paper are based on the substituent shifts, accurate mass measurements and collision-induced dissociation spectra of selected ions. The results of the present work can be useful in selecting the fragment ions suitable for identification and quantitation of bispidinones in biological matrices.