Hydrogen migration in the electron impact induced retro diels-alder fragmentation of N-aryl-4 H-5,7a-epoxyisoindolines.

The electron impact induced fragmentations of the C-5 unsubstituted and 5-methyl N-aryl-4 H-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-4 H-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. [ABSTRACT FROM AUTHOR]