Cycloreversion of 1-(1-Naphthyl)-5-phenylbicyclo[3.2.0]hept-6-ene to 1-(1-Naphthyl)-4-phenyl-1,3-cycloheptadiene by Triplet Sensitization and Direct Irradiation

Article abstract of DOI:10.1246/bcsj.69.1313

The cycloreversion of 1-(1-naphthyl)-5-phenylbicyclo[3.2.0]hept-6-ene (1b) to 1-(1-naphthyl)-4-phenyl-1,3-cycloheptadiene (2b) upon benzophenone (BP) sensitization and direct irradiation has been investigated. The triplet sensitization of 1b in benzene gave 2b quantitatively up to a stationary state where the quantum yield was 0.96. The triplet state of 2b (λ_max =455 nm, τ=4.6 μs) was formed by the pulse radiolysis of 1b in benzene. It has been found that cycloreversion proceeds by an adiabatic mechanism via a triplet state. The quantum yield for the formation of 2b by the irradiation of 1b at 313 nm was determined to be 0.17 in hexane. The fluorescence spectra of 1b and 2b indicated that diabatic cycloreversion occurred via a singlet state. The singlet and triplet energies of 1b, as well as those of 2b, were estimated to be 88, 60, 72, and 39 kcal mol^-1, respectively. The effect of a substitution of the naphthalene chromophore on bicyclo[3.2.0]hept-6-ene was estimated.