Photosensitized reactions of conjugated dienes
Conjugated dienes are shown to undergo photosensitized dimerization reaction, photosensitized cross addition reaction, and photosensitized inter- or intramolecular addition to olefins. Structures of isoprene, piperylenes, 2, 3dimethylbutadiene dimers, butadiene-1, 3-cyclohexadiene, 1, 3-cyclohexadie...
| Summary: | Conjugated dienes are shown to undergo photosensitized dimerization reaction, photosensitized cross addition reaction, and photosensitized inter- or intramolecular addition to olefins. Structures of isoprene, piperylenes, 2, 3dimethylbutadiene dimers, butadiene-1, 3-cyclohexadiene, 1, 3-cyclohexadiene-cyclopentene cross adducts, and myrcene photoisomers have been assigned (some in parts). The mechanism of the dimerization reaction, which is closely related to the other reactions, has been studied in detail with isoprene as the representative system. It was found that in order to explain the results consistently, several postulates are necessarily invoked. They include the non-interconvertible stereoisomeric triplets of conjugated diene, the unusual stable nuclei configuration of diene triplets, new assignments of the O-O components of singlet-triplet transition of dienes, and "nonvertical" energy transfer from sensitizer to diene molecules. Evidence is presented in support of the mechanism in which only one diene triplet is involved in such a bimolecular reaction. |
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