[3+2] Cycloaddition of Dialkyl (E)-Hex-2-en-4-ynedioates to [60]Fullerene by Phosphane-Promoted Tandem α(δ′)-Michael Additions

Organophosphanes promote the [3+2] cycloaddition reactions of dialkyl (E)-hex-2-en-4-ynedioates and [60]fullerene, giving a series of cyclopenteno-fullerenes 3a–k bearing phosphorus ylides. This cycloaddition reaction is initiated by the attack of nucleophilic phosphanes at the α(δ′)-C atom of the dialkyl (E)-hex-2-en-4-ynedioate, which generates a 1,3-dipolar species. These 1,3-dipoles then react with C60 followed by intramolecular cyclization to give cyclopenteno-fullerenes in moderate-to-good yields. In a cyclic voltmmetry study, these novel fullerenes show a larger cathodic shift in their first reduction potential relative to [6,6]phenyl-C61 methyl butyrate, which indicates that these new derivatives possess higher LUMO energy levels.