title: On the mechanism of the thermal retrocycloaddition of pyrrolidinofullerenes (retro-Prato reaction).
abstract: In contrast to N-methyl or N-unsubstituted pyrrolidinofullerenes, which efficiently undergo the retrocycloaddition reaction to quantitatively afford pristine fullerene, N-benzoyl derivatives do not give this reaction under the same experimental conditions. To unravel the mechanism of the retrocycloaddition process, trapping experiments of the in-situ thermally generated azomethine ylides, with an efficient dipolarophile were conducted. These experiments afforded the respective cycloadducts as an endo/exo isomeric mixture. Theoretical calculations carried out at the DFT level and by using the two-layered ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) approach underpin the experimental findings and predict that the presence of the dienophile is not a basic requirement for the azomethine ylide to be able to leave the fullerene surface under thermal conditions. Once the 1,3-dipole is generated in the reaction medium, it is efficiently trapped by the dipolarophile (maleic anhydride or N-phenylmaleimide). However, for N-unsubstituted pyrrolidinofullerenes, the participation of the dipolarophile in assisting the 1,3-dipole to leave the fullerene surface throughout the whole reaction pathway is also a plausible mechanism that cannot be ruled out.
authors.affiliation: Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Filippone
authors.forename: Marta Izquierdo
authors.initials: MI
authors.lastname: Barroso
authors.forename: Angel
authors.initials: A
authors.lastname: Martín-Domenech
authors.forename: Sílvia
authors.initials: S
authors.lastname: Osuna
authors.forename: Miquel
authors.initials: M
authors.lastname: Solà
authors.forename: Nazario
authors.initials: N
authors.lastname: Martín