Electron impact mass spectral fragmentation of 3a,5-disubstituted 1,3-diphenyl-3a,4,5,6-tetra-hydro-3H-1,2,4-triazolo[4,3-a][1,5]benzo-diazepines

The mass spectrometric behaviour of six 3a,5-disubstituted 1,3-diphenyl-3a, 4,5,6-tetrahydro-3H- 1,2,4-triazolo[4,3-alpha][1,5]benzodiazepines has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization, All compounds show a tendency to eliminate (substituted) styrene molecules, aryl radicals , arylmethyl radicals or phenylnitrene (PhN:), All of the resulting fragmen t icons, except [M - PhN:](+.), could further undergo a reverse [2 + 3] cyc loaddition, The [M - PhN:](+.) ions could further lose styrene derivatives and undergo a ring enlargement rearrangement. The molecular ions also show a tendency to eliminate a phenyl radical, and the [M - Ph]+ ions could elim inate styrene derivatives. The [M - R1CH = CH2](+.) ions could further lose NH2 to yield stable tetracyclic 1,3-diphenyl-1,2,4-triazolo[4,3-d]phenanth ridine ions, which could further lose benzonitrile, or undergo a reverse [2 + 3] cycloaddition, The molecular ions could also undergo a reverse [2 + 3 ] cycloaddition to produce N-phenylhenzonitrile imine ions and 2,4-disubsti tuted 2,3-dihydro-1H-1,5-benzodiazepine ions, whose further fragmentations were also investigated. Copyright (C) 2000 John Wiley & Sons, Ltd.