Circumambulatory Migrations of Phenylchalcogeno Groups in Pentamethoxycarbonyl- and Pentamethylcyclopentadiene Systems. A Quantum-Chemical Study

According to the data of quantum-chemical calculations CAM-B3LYP/Def2TZVP in 5-phenylchalcogeno-1,2,3,4,5-pentamethoxycarbonylcyclopentadienes, intramolecular migrations of phenylchalcogeno groups (PhX) along the perimeter of the five-membered ring occur by the mechanism of 1,5-sigmatropic shifts in conformers with endo arrangement of PhX groups relative to the Cp ring with energy barriers: ΔE≠ZPE = 33.5 (X = O), 17.5 (X = S), 13.8 (X = Se), 10.2 (X = Te) kcal/mol in the gas phase. In 5-phenylchalcogeno-1,2,3,4,5-pentamethylcyclopentadienes, the calculated activation barriers of 1,5-shifts of PhX groups in the cyclopentadiene ring have significantly higher values: ΔE≠ZPE = 38.8 (X = O), 27.2 (X = S), 22.1 (X = Se), 15.4 (X = Te) kcal/mol.