Origins of Periselectivity and Regioselectivity in Ambimodal Tripericyclic [8+6]/[6+4]/[4+2] Intramolecular Cycloadditions of a Heptafulvenyl-Fulvene

Quantum mechanical calculations and molecular dynamics simulations have elucidated the reaction mechanism for intramolecular cycloadditions of a heptafulvenyl-fulvene tethered by a trimethylene chain. Prior experiments by Liu and Houk reported the formation of only an endo-[8+6] cycloadduct at 185 degrees C. Liu et al. later reported an exo-[4+2] Diels-Alder cycloadduct as the major product at 140 degrees C (Tetrahedron, 1999, 55, 9171). Cycloadditions involve Diels-Alder and an ambimodal intramolecular tripericyclic [8+6]/[6+4]/[4+2] cycloaddition. The mechanistic details explain the experimental reports of temperature dependence on the periselectivity of intramolecular cycloadditions. Additional calculations with multireference-based methods CASSCF and NEVPT2 highlight the artifacts of DFT methods and single-reference wavefunction-based CCSD(T) in the description of complete potential energy surface involving various cycloadditions of the heptafulvenyl-fulvene.

Automated summary

This study investigates the reaction mechanism for intramolecular cycloadditions of a heptafulvenyl-fulvene tethered by a trimethylene chain using quantum mechanical calculations and molecular dynamics simulations. The experimental reports of temperature dependence on the periselectivity of intramolecular cycloadditions are explained by the mechanistic details. Furthermore, additional calculations with multireference-based methods highlight the limitations of DFT methods and single-reference wavefunction-based CCSD(T) in describing the complete potential energy surface involving various cycloadditions of the heptafulvenyl-fulvene.