Abstract
| - The starting materials, transition states, and products of the concerted retro [2 + 2 + 2] ring-opening reactions of several tricyclobutabenzene derivatives substituted by double-bonded substituents were calculated at the B3LYP/6-31G* theoretical level. It was found that the geometriesof the products (cyclododecatriyne derivatives) are governed by the electronegativity of thesubstituents and hyperconjugation effects. The transition-state geometries of all the derivativesare similar. It was found that the retro [2 + 2 + 2] ring-opening reactions are endothermic (ca.30−85 kcal mol-1, depending on the substituents) with high barriers, ranging between ca. 95 and115 kcal mol-1. It is predicted that the tricyclobutabenzene derivatives under study will be stablewhen prepared and that they can be made by [2 + 2 + 2] intramolecular ring closure of the respectivecyclododecatriyne derivative, especially with the use of transition metals as mediators or catalysts.
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