Electron-impact induced fragmentation of some 5,10-di- hydrophenazastannines

The electron-impact induced fragmentation of four 5,10-dihydrophenazastannides [(I)-(IV)] was studied by low and high resolution mass spectrometry. Two of the compounds contain tin in the spiro position. To identify energetically favorable reaction paths, low electron-energy scans (12 eV) were taken along with 70 eV ones. The molecular ions fragment by consecutive ejection of the 10-substituents or, alternatively, by loss of R₂Sn. Subsequent fragmentation is accompanied by complex skeletal rearrangements and hydrogen migrations. An example of SnBr bond formation has been discovered. Ions of the phenanthridine type (m/e 179, C₁₃H₉N) are formed via enlargement of the center heterocyclic ring and rearomatization. Tentative mechanistic pathways are derived for all major fragmentation sequences on the basis of computer-aided correlation of metastable peaks, accurate mass measurements (elemental composition) and shifts resulting from specific deuterium labelling.