Mechanistic studies on the photooxygenation of 1,1-diphenyl-2-vinylcyclopropane

Abstract

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer induced photooxygenation of 1,1-diphenyl-2-vinylcyclopropane (VCP-DPh) in oxygen saturated acetonitrile to form 3,3-diphenyl-5-vinyl-1,2-dioxolane. These photoreactions are greatly accelerated by the addition of aromatic hydrocarbon such as biphenyl (BP) as a catalyst or cosensitizer. VCP-DPh and BP with oxidation potentials lower than 2V vs SCE quench the fluorescence of DCA at almost a diffusion controlled rate. When solvent polarity was increased the fluorescence of DCA was more efficiently quenched by both VCP-DPh and BP without any shift in emission maximum. No photooxygenation takes place in nonpolar solvents. In addition, this photooxygenation in protic solvents affords 3,3-diphenyl-5- vinylcyclopropane-1,2-dioxolane in low yield due to giving the organic hydroperoxides, 1,3-butadiene, and benzophenone as by-products. the cosensitization with dCA and BP was accelerated by the addition of metal salts such as $Mg(ClO_4)_2$ and the slat effects in thsi reaction were more efficient than those in the DCA sensitized photooxygenation of VCP-DPh. Moreover, in a given temperature, pressure, solvent, and ionic charge of salt cation, VCP-DPh photooxygenation increased in the order of $LiClO_4<(NaClO_4<(n-Bu)_4NClO_4$. However, the fluorescence of DCA was not quenched by $Mg(ClO_4)_2$ and the rate constant of this fluorescence quenching was not affected by the addition of these metal salts.