Electron-transfer photooxygenation. 6. Indirect sensitized photooxygenation of aryl olefins

Photoinduced electron transfer oxygenations

“…At the same time, they confirmed that, with the exception of benzophenone, all of the rearranged products derived directly from the decomposition of the initial endoperoxide 89. Surprisingly, the same authors [135] also observed that the DCA-sensitized photooxygenation of the same substrate afforded a product mixture similar to that formed on RB sensitization. The only difference was that significant amounts of benzophenone (5-50%) were formed along with the other products.…”

“…In fact, as we have already pointed out in a previous section, the efficiency of separation of the geminate pair is strictly dependent on the redox potentials (see also indirect photooxygenation processes) [43,50,[80][81][82][83]135]. Anyway, although in the present case the subsequent electron-transfer from epoxide to biphenyl radical cation BP +, is endothermic enough, in the absence of very fast competing reactions this primary radical cation may still undergo an endothermic electron-transfer process with epoxides.…”

“…The DCA-sensitized reaction on 37, showing a different stereochemical course and requiring the presence of trans-silbene as a cosensitizer, renewed the interest in the indirect DCA-sensitized photo-stilbeneoxygenations of organic substrates, formerly described by Foote, Schaap, and co-workers [50, 94,135]. Since TS is present in high concentrations, the photooxygenation of 37 proceeds via initial formation of the radical cation (TS+.…”

“…The only difference was that significant amounts of benzophenone (5-50%) were formed along with the other products. However, when TS was present in high concentrations, such that the photooxygenation of DPME could proceed by way of an indirect mechanism [135], benzophenone formation was greatly enhanced (95%).…”

Synthetic Aspects of Photochemical Electron Transfer Reactions

“…Foote (205) PhzC -CHOCH I 278 cient (<1>=0.15) production of benzil and benzoic acid. In this study, firm evidence was gathered in support of a mechanism involving dioxetene 280 formation by coupling of the superoxide anion rather than triplet oxygen with the diphenylacetylene cation radical.…”