Competitive retro-cycloaddition reactions in heterocyclic fullerene bis-adducts ions: selective removal of the heterocyclic moieties

• Published in: Rapid communications in mass spectrometry 2015-03, Vol.29 (6), p.497-504
• Main Authors: Suárez, Margarita, Maroto, Enrique E., Filippone, Salvatore, Martín, Nazario, Martínez-Álvarez, Roberto
• Format: Article
• Language: English
• Subjects: Derivatives; Fragmentation; Ionization; Mass spectrometry; Nitrogen atoms; Radicals; Selectivity; Spectroscopy
• ISSN: 0951-4198; 1097-0231
• DOI: 10.1002/rcm.7131

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.