Rationale: We have investigated the fragmentation reactions of ions from bis-adducts containing isoxazolino-, pyrrolidino- and methanofullerene moieties.
Methods: The fragmentation reactions induced by collision-induced dissociation (CID) of ions generated under electrospray ionization (ESI) in positive and negative modes of detection using an ion-trap spectrometer have been investigated.
Results: The competitive retro-cycloaddition process between isoxazoline and pyrrolidine rings fused to [60]fullerene reveals that it is strongly dependent on the experimental negative or positive ESI experimental conditions. Thus, whereas retro-cycloaddition reaction is favored in the pyrrolidine ring under negative conditions, the protonation occurring on the nitrogen atom of the pyrrolidine ring under positive conditions precludes its retro-cycloaddition and, therefore, only the isoxazoline ring undergoes the retro-cycloaddition process. The obtained experimental results are different from those reported when the reaction is carried out under thermal conditions. Competitive retro-cycloaddition reactions of isoxazolino- and methanofullerenes show that the heterocyclic ring undergoes cycloelimination, leaving the methanofullerene moiety unchanged. In this case, the same selectivity is observed under thermal and gas-phase conditions.
Conclusions: The observed selectivity in the heterocyclic removal in these [60]fullerene derivatives is reversed from negative conditions (radical anions) to positive conditions (protonated molecules). Moreover, the retro-cycloaddition reaction behaves differently under spectrometric and thermal conditions.
Copyright © 2015 John Wiley & Sons, Ltd.