Acenes represent interesting platforms on which to add fullerenes via Diels-Alder cycloaddition reactions[1]. For unsubstituted acenes, the most reactive positions are the center-most rings. Thus for pentacene, [60]fullerene cycloaddition occurs across the 6,13 positions. In the presence of 6,13-diphenyl substituents, two [60] fullerene cycloadditions are observed across the 5,14 and 7,12 positions of the acene backbone yielding highly interesting cis-bis[60]fullerene adducts. The [60]fullerene additions are syn diastereoselective due to favorable pi-pi stacking interactions between adjacent [60]fullerene moieties. In this presentation, we highlight the chemistry between [60]fullerene and 6,13-bis(2,6-dimethylphenyl)pentacene where we observe only one [60]fullerene cycloaddition across the 5,14 position of the acene backbone. A second cycloaddition is presumably slowed due to steric interference. Surprisingly, this [60]fullerene monoadduct does not persist in air. Instead, singlet oxygen adds regioselectively across the remaining 7,12 position of the acene backbone with both syn and anti products observed (4:1, respectively). The [60]fullerene moiety is implicated in a highly efficient formation (sensitization) of singlet oxygen.

[1] J. Briggs and G.P. Miller, “[60]Fullerene-Acene Chemistry: A Review,” Comptes Rendus Chimie 2006, 9(7-8), 916-927.