Regioswitchable Bingel Bis-Functionalization of Fullerene C₇₀ via Supramolecular Masks

Isomer-pure functionalized fullerenes are required to boost the development of fullerene chemistry in any field, but their multiple functionalization renders a mixture of regioisomers that are very difficult to purify by chromatography. For the specific case of C-70, its nonspherical geometry makes its regioselective functionalization more challenging than that of spherical C-60. In this work, the supramolecular mask approach is applied for the first time to C-70, which is encapsulated in two different nanocapsules to achieve the Bingel bis-cyclopropanation at alpha-bonds of opposite poles. Based on the tetragonal prismatic geometry imposed by the smaller supramolecular mask tested, the obtained major bis-adduct is completely reversed (major 5 o'clock) compared to bare C-70 functionalization (major 2 o'clock). Moreover, by further restricting the accessibility of C-70 using a three-shell Matryoshka mask and dibenzyl-bromomalonate, a single regiospecific 2 o'clock bis-isomer is obtained, owing to the perfect complementarity of the mask and the addend steric properties. The outcome of the reactions is fully explained at the molecular level by means of a thorough molecular dynamics (MD) study of the accessibility of the alpha-bonds to produce the different bis-adducts.