REACTION OF BENZYNE WITH [70]FULLERENE GIVES 4 MONOADDUCTS - FORMATION OF A TRIPTYCENE HOMOLOG BY 1,4-CYCLOADDITION OF A FULLERENE

Mono-, di-, tri- and tetra-benzyne adducts have been isolated by colum n chromatography of the products of the reaction of benzyne with [70]f ullerene. H-1 NMR spectroscopy shows the monoadduct to consist of four isomers, the [1,2]-, [5,6]-, [7,21]- and [7,23]-benzeno [70]fullerene s in yields of 42, 12, 12 and 34%, respectively. The 7,23-isomer has C -2 symmetry and is produced by novel equator-spanning 1,4-addition ([2 + 4] cycloaddition) and is a fullerene homologue of triptycene; molec ular orbital calculations predict this 1,4-addition. Strain may also r ender unfavourable the [2 + 2] cycloaddition of benzyne, whereas the a typical Diels-Alder[2 + 4] cycloaddition may be facilitated by the low er elechophilicity of [70]fullerene, especially in the equatorial regi on. The addition patterns account for the previously observed ability of [70]fullerene to accommodate 10 benzyne addends.