Reaction of benzyne with [70]fullerene gives four monoadducts: formation of a triptycene homologue by 1,4-cycloaddition of a fullerene

Abstract

Mono-, di-, tri- and tetra-benzyne adducts have been isolated by column chromatography of the products of the reaction of benzyne with [70]fullerene. ¹H NMR spectroscopy shows the monoadduct to consist of four isomers, the [1,2]-, [5,6]-, [7,21]- and [7,23]-benzeno[70]fullerenes in yields of 42,12,12 and 34%, respectively. The 7,23-isomer has C₂ symmetry and is produced by novel equator-spanning 1,4-addition ([2 + 4] cycloaddition) and is a fullerene homologue of triptycene; molecular orbital calculations predict this 1,4-addition. Strain may also render unfavourable the [2 + 2] cycloaddition of benzyne, whereas the atypical Diels–Alder[2 + 4] cycloaddition may be facilitated by the lower electrophilicity of [70]fullerene, especially in the equatorial region. The addition patterns account for the previously observed ability of [70]fullerene to accommodate 10 benzyne addends.