Why Do Cycloaddition Reactions Involving C60 Prefer [6,6] over [5,6] Bonds?

The origin of the experimentally known preference for [6,6] over [5,6] bonds in cycloaddition reactions involving C₆₀ has been computationally explored. To this end, the Diels–Alder reaction between cyclopentadiene and C₆₀ has been analysed by means of the recently introduced activation strain model of reactivity in combination with the energy decomposition analysis method. Other issues, such as the aromaticity of the corresponding transition states, have also been considered. These results indicate that the major factor controlling the observed regioselectivity is the more stabilising interaction between the deformed reactants in the [6,6] reaction pathway along the entire reaction coordinate.     

Thiadiazolo-Azaacenes

This work reports the synthesis and characterization of bis- and tetrakis(thiadiazolo)-appended di- and tetraazaacenes, displaying up to seven catenated benzene/pyrazine rings. The targets are obtained by condensation of benzo-bis(thiadiazole)-4,5-dione with aromatic di- and tetraamines. The condensation products—up to a heptacene-like species—are stable but can be insoluble. Soluble derivatives are readily processible, but do not show enhanced electron affinities, as the two or four attached benzothiadiazole units are effectively resonance-separated from the acene body, maximizing the number of Clar-sextets.