Theoretical analysis of the Cope rearrangement of 1,5-hexadiene and phenyl derivatives

摘要

The mechanism of the Cope rearrangement in the reaction of 1,5-hexadiene and its monophenyl and diphenyl derivatives was studied at the CASSCF/6-31G(d,p) and (U)B3LYP/6-31G(d) levels. CiLC (configuration interaction/localized molecular orbital/CASSCF) analysis was performed for the potential energy surface of the C_(2h) cut in the reaction of 1,5-hexadiene, giving the typical electronic character for the aromatic transition state, diradical intermediate, and the transition state between them. It was also clarified that the electronic transition state between the aromatic transition state and bis-allyl does not exist. The regions of aromatic transition state and diradical intermediate were defined based on the results of the CiLC analysis, and the phenyl-substituted reaction systems were classified into two reaction pathways; via the aromatic transition state, and via the diradical intermediate in the vicinity of the C_(2h) cut. These findings are supported by close agreement between the calculated and the experimental values of the activation enthalpy for phenyl-substituted 1,5-hexadiene.