Fulleroids, obtained from the 1,3-dipolar cycloaddition of fullerene with a diazoalkane, have a [5,6]-open methylene bridge and two highly twisted bridgehead double bonds. The [H,H]- and [H,CN]-substituted fulleroids were found to display significantly enhanced and regioselective Diels-Alder addition as compared with the [6,6] closed methanofullerene and C(60) with 2,3-dimethyl-1,3-butadiene, but reduced and nonregioselective addition with cyclopentadiene. NMR analysis of the 1:1 adduct and quantum calculations indicated that the high reactivity and the regioselective addition are due to pi-orbital misalignment at the bridgehead double bond.
(3d) and 2-methylbutadiene (3e)] has been carried out in toluene at 30°C. Notably, the relative rate ratio k/k 0 for each dienophile (vs. C 60 ) was remarkably dependent on the diene used; the less hindered H/CN fulleroids 1a and 1b became 25-104 times more reactive than C 60 with conformationally flexible dienes such as 3d and 3e. These fulleroids, however, showed similar or rather diminished reactivity with rigid 3a and 3b. In contrast,
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