Photo Valence Isomerization of 8,9-Bis(N-cyclohexylcarbamoyloxymethyl)-[6]paracyclophane

Irradiation in the wavelength range of λ = 270 ‐ 320 nm of 8,9‐bis(N‐cyclohexylcarbamoyloxymethyl)‐[6]paracyclophane(1b) in dilute fluid solutions produces the 1,4‐Dewar isomer 2b in a quantum yield of 2.8% while the quantum yield of the rearomatization is 19% in heptane at room temperature. A photostationary equilibrium may be attained which depends strongly on the wavelength of irradiation. At λ = 290 nm 76% of the [6]paracyclophane isomer 1b is obtained whereas at λ = 310 nm 83% of the Dewar isomer 2b is formed in ethanol. The thermal back reaction 2b → 1b follows the Arrhenius law (Ea = 95.9 ± 4.0 kJ/mol, lg A = 10.6 ± 0.4 in heptane). By irradiating 1b with λ < 270 nm the prismane isomer 3b is formed via the Dewar isomer 2b.