SINTHESIS OF THE COVALENT BENZENE-CARBON MONOXIDE CYCLOADDUCT, NORBORNA-2,5-DIEN-7-ONE CORRELATION OF KINETIC AND THERMODINAMIC STABILITIES IN CYCLOREVERSION REACTIONS

Article abstract of DOI:10.1016/S0040-4020(01)87571-2

endo-Tricyclo<4.2.1.0^2,5>non-7-ene-3,4,9-trione (14) is prepared from the 5,5-diethoxy-cyclopentadiene-diethyl maleate Diels-Alder adduct.Photolysis of the trione in CD2Cl2 solution at 192 K forms norborna-2,5-dien-7-one (2).The latter substance is thermally unstable and decomposes to benzene and CO with ΔG<*>= 15 kcal mol^-1.This appears to be the lowest activation energy for a cycloreversion yet measured.A correlation is found for the kinetic and thermodynamic stabilities in a series of 18 orbital symmetry allowed cycloreversions by plotting ΔG<*> vs ΔH_r.