HYDROGEN MIGRATION IN THE ELECTRON-IMPACT INDUCED RETRO DIELS-ALDER FRAGMENTATION OF N-ARYL-4H-5,7A-EPOXYISOINDOLINES

The electron impact induced fragmentations of the C‐5 unsubstituted and 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines (where aryl is pheny, p‐tolyl, p‐methoxyphenyl, o‐methoxyphenyl and p‐chlorophenyl) were investigated. The fragmentation patterns deduced were supported by exact mass measurements of prominent ions and by deuterium labelling. The retro Diels‐Alder fragmentation turned out to be a predominant process in all the compounds investigated. In the mass spectra of the 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines hydrogen migration preceding fragmentation occurred. From the mass spectrum of the specifically deuterated compound it was concluded that the transferred hydrogen originates exclusively from the 5‐methyl group. Copyright © 1979 John Wiley & Sons, Ltd.