Cycloreversion of the CO2 trimer: a paradigmatic pseudopericyclic [2 + 2 + 2] cycloaddition reaction
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Updated: Mar 10, 2026

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
Published on: November 9, 2019
Roberto Villar López1, Olalla Nieto Faza1, Eduard Matito2
1Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario, Ourense, Spain.
Abstract:
Very recently, the CO2 trimer has been experimentally synthesized, isolated and characterized. This process opens new ways for the withdrawal and storage of this greenhouse gas. The trimer is reported to be stable up to -40 °C, with a lifetime of about 40 min at this temperature. At these or under harsher thermal conditions it reverts to the three monomers. The mechanism of this reaction has been theoretically studied and the electronic character of the associated transition state has been analyzed from a variety of perspectives (energetic, magnetic, electron localization and delocalization functions) which indicate that it has paradigmatic pseudopericyclic character. To allow for a comparative study, the isoelectronic fragmentations of cyclohexane into three units of ethylene and of benzene into three units of acetylene have been included in this work. The study of a similar series of formally forbidden-four-centered [2 + 2] cycloreversions confirmed the pseudopericyclic nature of these reactions when the CO2 dimer or trimer is involved.
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