CF₃SO₃H-catalyzed reaction of 5-alkyl-(R)-substituted diphenylhomobenzoquinone epoxides (R = Me, iPr, tBu) provided indenoquinones, a cyclopenta[b]chromene-2-carbaldehyde, and furan-3(2H)-ones through novel cationic domino rearrangements depending on the R substituents. The mechanisms of these reactions were described by a combination of various key steps involving (i) transannular cyclization of the endo-phenyl group, (ii) epoxide and cyclopropane ring opening, (iii) ring contraction of the original quinone frame, (iv) dehydration and intramolecular S_E2/S_N2-Ar cyclization, as well as (v) possible pseudopericyclic cheletropic decarbonylation.

A kinetic study of Diels–Alder (DA) reactions of some fullerene dienophiles, i.e. C₆₀, [R¹, R²]-substituted fulleroids 1 (a: [H, H], b: [H, CN], c: [H, CO₂Et]; d: [H, Ph], e: [Ph, Ph]) and [H, H]-substituted methanofullerene (2), with various dienes [cyclopentadiene (3a), 9-methylanthracene (3b), 1,3-cyclohexadiene (3c), 2,3-dimethylbutadiene (3d) and 2-methylbutadiene (3e)] has been carried out in toluene at 30 °C. Notably, the relative rate ratio k/k₀ for each dienophile (vs. C₆₀) was remarkably dependent on the diene used; the less hindered H/CN fulleroids 1a and 1b became 25–104 times more reactive than C₆₀ 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, slightly hindered 1c exhibited a three to seven times reduced rate of reaction for 3d–e, and more hindered 1d–e and the 58-π-conjugated 2 displayed reduced reactivity with almost all the dienes. Based on product analysis, the enhanced reactivity was ascribed to the exclusive addition at the highly strained bridgehead double bond of the transannular [5,6] open ring orifice. It was concluded that the twisted anti-Bredt double bond can perform a topologically suitable [_π2_s + _π4_s] orbital interaction with the less congested, labile dienes. Such an orbital interaction is inhibited for both the congested fulleroids and the rigid dienes, which displayed alternative addition at a less twisted double bond.