Ring contractions of dihydro- and tetrahydro-1,5-benzodiazepines in electron ionization mass spectrometry

Electron ionization mass spectra of a series of 2,4-disubstituted dihydro- and tetrahydro-1,5-benzodiazepines are discussed. The fragmentation of these compounds is dominated by ring contractions of diazepine, which give both five- and six-membered rings, benzimidazoles and quinoxalines. Tetrahydro compounds showed a tendency to eliminate one nitrogen from the ring system and give quinoline rings through NH₂ and NH₄ eliminations. The electron ionization spectra of cis and trans isomers of tetrahydro compounds are identical.