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

Abstract

The mass spectrometric behaviour of six 3a,5-disubstituted 1,3-diphenyl-3a,4,5,6-tetrahydro-3H-1,2,4-triazolo[4,3-a][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 fragment ions, except [M − PhN:]+·, could further undergo a reverse [2 + 3] cycloaddition. 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 eliminate 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]phenanthridine 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-phenylbenzonitrile imine ions and 2,4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepine ions, whose further fragmentations were also investigated. Copyright © 2000 John Wiley & Sons, Ltd.