Singlet oxygen, photooxidation reactions

Figure 4.15 Dye sensitised singlet oxygen photooxidation reactions.

Clennan, E.L. and Sram, J.P. (1999). Photooxidation in zeolites. Part 2 a new mechanistic model for reaction selectivity in singlet oxygen ene reactions in zeolitic medsia. 

Photooxidation of Dienes Investigated in Micro Reactors Cas/liquid reaction 24 [CL 24] Oxidation of cyclopentadiene by singlet oxygen to 2-cyclopentene-1,4-diol... 

Oxidation photooxidation t,/2 = 0.32-3.2 h estimated, based on estimated rate constant for the reaction with hydroxyl radicals in air (Atkinson 1987 quoted, Howard et al. 1991) photooxidation t,/2(aq.) = 1,57 - 157 yr estimated, based on measured rate constant for the reaction with singlet oxygen in benzene (Stevens et al. 1974 quoted, Howard et al. 1991). 

Besides these external processes, formation of ROS may also take place intrac-ellularly. Photooxidative stress, including UVB, stimulates various cellular processes leading to the production of superoxide radicals and hydrogen peroxide, as well as singlet-oxygen and hydroxyl radicals. The sources and production sites of ROS are mainly related to photosynthetic activities such as the pseudocyclic photophosphorylation and the Mehler reaction, which stimulate the accumulation of hydrogen peroxide (Asada 1994 Elstner 1990). 

Figure 4. Methanolic photooxidation of methoprene (reaction with singlet oxygen (40)...

A photooxidative reaction in which molecular oxygen is incorporated into the reaction products(s). Three mechanisms appear to be common for such processes (a) reaction of triplet O2 with free radicals that have been generated photochemically (b) reaction of photochemically produced singlet oxygen with a molecular species and (c) the production of superoxide anion which then acts as the reactive species. See also Photooxidation... 

The reaction of singlet oxygen with conjugated double bonds usually is a 1,4-cycloaddition leading to formation of derivatives of the 1,2-diox -ene ring system. This can be achieved either by photooxidation or by reaction in the presence of triphenyl phosphite-ozone adduct (Section Vin.D.2), shown in equations 85 and 86 . ... 

Singlet oxygen affords a variety of regio and diastereoselective reactions with chiral allylic alcohols amines - (e.g. substrate 161, Scheme 58) and chiral cyclohexadienes - that are useful for synthetic transformations. For example, the photooxygenation of a chiral allylic alcohol was used recently as the key step in the total syntheses of plakorin 162 and ewawfio-chondrilin (Scheme 58). If the photooxidation... 

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