The [4+2] cycloaddition of anthracene with C60F18;: anthracene goes ring walking

From the [4+2] cycloaddition of anthracene at the curved face of C60F18 we have isolated two main isomers of C-s and C-1 symmetry (isomers 1 and 2, respectively) in ca. 3:2 relative yields; isomer 2 contained traces of a third isomer, also of C-s symmetry. Of the four mono adducts that can, in principle, be formed by this cycloaddition, the yields of the three obtained reflect differences in steric hindrance between the fluorine and aromatic addends. The major C-s isomer (1) is reasonably stable, but the more crowded C-1 isomer (2) reverts readily to C60F18 and anthracene on standing, and also undergoes rearrangement to isomer (1). This is the first example of spontaneous migration of a cycloaddend from one 6:6-bond to another on the same fullerene cage surface. The UV/VIS spectrum of 1 is significantly different from that for C60F18, suggesting that some electronic interaction may exist between the addend and the cage. Anthraquinone is produced as a by-product of the reaction (and also from that between either C-60 or C60Cl6 and anthracene) showing the fullerene cage acts here as an oxidant.