Example 025 (4π conrotation)

Thermal electrocyclic ring-opening of cyclobutene

Thermal electrocyclic ring-opening of cyclobutene
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Reaction:  R. W. Carr and W. D. Walters, J. Phys. Chem., 1965, 69, 1073–1075
DOI: 10.1021/j100887a510

MO Theory:  R. B. Woodward and R. Hoffmann, Angew. Chem., Int. Ed., 1969, 8, 781–932
DOI: 10.1002/anie.196907811