1,3-Dienes, photooxygenation

Mechanism of the Singlet Oxygen Diene Photooxygenation Theoretical Models Experimental Results. .. 25-2... 

Substrates for Diene Photooxygenation Carbocyclic Substrates Heterocyclic Substrates . . 25-3... 

In this case, the benzene dioxide 5 is obtained from a [2,2]paracyclophane diene by photooxygenation and rearrangement of the derived endoperoxide. 

Following a mechanism similar to that described in Scheme 29, electron transfer photooxygenation of 1-tert-bntylcyclohexa-l,3-diene (145) in the presence of Tr BF4 leads, throngh the intermediacy of cation radicals 146,149 and 150, to the dimeric fused tricyclic peroxides 151 (total 40% yield, cisitrans ca 5 4) rather than to the monomeric bridged bicyclic peroxide 148 (5-10%) which derives from cation radical 147 (Scheme 36) ... 

Singlet oxygen reacts with many carbocyclic 1,3-dienes to form the corresponding bridged endoperoxides, which can be further transformed into miscellaneous polyoxy functionalized carbocycles . The rate of photooxygenation of n-cyclic 1,3-dienes is gradually decreasing in the order n = 5) >6>7 8 While the rate... 

The main types of substrates investigated so far are polycyclic aromatic compounds, aryl substituted carbo- and heterocyclic pentadienes, cyclic 1,3-dienes, furans, and olefins. It has turned out that type II photooxygenation of these compounds in solution occurs via the oxygen-activation mechanism. 

From a preparative point of view, type II direct and indirect photooxygenations of diene systems have been compiled in a review Oxygen... 

Until recently, the hypothesis that the termination reaction of type II photooxygenation reactions occurs between the substrate and an excited light absorber-oxygen complex seemed to be well established. The typical products obtained from cyclic 1,3-dienes and olefins (see Fig. 1 and Sect. IV) could only be made by photochemical reactions. 

C. Conjugated Diene Systems as Substrates of Photooxygenation Reactions... 

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