Photoinduced electron transfer reaction. Part 3. 9,10-Dicyanoanthracene-sensitized photo-oxidation of electron-rich stilbene oxides

Abstract

The 9,10-dicyanoanthracene (DCA)-sensitized photo-oxygenation of the electron-rich stilbene oxides (1) gives the ozonides (2) almost quantitatively. The fluorescence of DCA is quenched by (1) at a diffusion-controlled rate and the above reaction is quenched by polymethoxybenzenes which indicates that an electron transfer mechanism is involved. The quantum yield for ozonide formation varies from 0.5 for trans-2-(4-methoxyphenyl)-3-phenyloxirane (1d) to 2.4 for trans-2,3-bis(4-methoxyphenyl)-2,3-diethyloxirane (1h), suggesting a duplex reaction mechanism such as photo-oxygenation by superoxide and a Barton mechanism after the initial electron transfer from the epoxides (1) to the excited singlet state of DCA.