[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 C ₆₀ 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-C ₆₁ methyl butyrate, which indicates that these new derivatives possess higher LUMO energy levels.