Fast-atom bombardment mass spectrometric studies of trisubstituted 3a,4,5,11-tetrahydro-6H-1,2,4-oxadiazolo [4,5-a][1,5]benzodiazepines

The mass spectrometric behaviour of seven 1,3a,5-trisubstituted 3a,4,5,11-t etrahydro-6H-1,2,4-oxadiazolo[4,5-a] [1,5]benzodiazepines has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and exact mas s measurements using fast-atom bombardment ionization, All compounds show a tendency to eliminate a neutral substituted or unsubstituted styrene from the diazepine ring to yield 1,2,4-oxadiazolo [4,5-a] [1,3]benzimidazole ion s, and further undergo reverse 1,3-dipolar cycloadditions to give benzimida zole ions. The formation of stable conjugated fused tetracyclic systems, su bstituted 1,2,4-oxadiazolo[4,5-f]phenanthridine ions, was also observed. Co pyright (C) 1999 John Wiley & Sons, Ltd.