Bromine adds cis to the double bond in the addend of the [60]fullerene
-cydopentadiene adduct, so that both bromines are directed away from t
he cage. The epoxide,formed by peracetic acid oxidation of the double
bond of the addend, also points away from the cage. These results are
attributed to a combination of steric hindrance and polar repulsion by
the fullerene cage, the first time such effects have been reported to
control addition. The epoxide appears to extrude CO during mass spect
rometry to give a cyclobutane derivative of [60]fullerene.