Theoretical Predictions of Substituent Effects on the Thermal Electrocyclic Ring Openings of Cyclobutenones

The transition structures for the electrocyclic ring openings of a variety of substituted cyclobutenones were located with ab initio molecular orbital theory. The effects of substituents on the stereochemistries and activation energies of the electrocyclic ring openings are predicted to be similar to those in cyclobutene.