A MASS-SPECTROMETRIC INVESTIGATION ON SOME 4,7-DIOXO-4,5,6,7-TETRAHYDROINDOLE DERIVATIVES

The mass spectrometric behaviour of a series of 2-aryl substituted 4,7 -dioxo-4,5,6,7-tetrahydroindoles has been studied in different ionizat ion conditions (Electron Ionization and Fast Atom Bombardment), with t he aid of the metastable ion studies. In electron ionization condition s all the compounds exhibit a highly favoured, primary H-2 loss giving rise to the corresponding indole-4,7-diones; in the usual spectra no evidence for the molecular ions in the enolic form was found, while th e OH' loss observed in the MIKE (mass analyzed ion kinetic energy) spe ctra of molecular ions suggests that species at low internal energy co ntent isomerize to the corresponding tautomeric enolic form. FAB mass spectra show easy formation of an unusual [M + 2H]+. species, together with abundant [M + H]+ and M+. cations.