Intramolecular photocycloaddition reactions of phenyl–vinyl bichromophoric systems

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Abstract
The Intramolecular photocycloaddition reactions of several phenyl–vinyl bichromophoric systems are reported. 5-Phenylpent-1-ene and allyl benzyl ether both yielded meta-cycloadducts derived from 1,3- and 2,6-attack of the vinyl group on to the phenyl moiety, whereas 3-phenylpropyl vinyl ether and 2-phenoxybut-1-ene gave products which reflected 1,3- and 2,4-, and 2,4-attack, respectively. In contrast, the major mode of reaction from phenethyl vinyl ether involved 2,5-cycloaddition and the 1,4-intramolecular cycloadduct structure was assigned to the sole photoisomer of 2-phenoxyethyl vinyl ether. Quantum efficiencies were very variable ranging from 0.005 to 0.11; polymeric materials were formed in all cases and were the major products from the two phenoxy-compounds. The reactions are discussed in terms of previous mechanistic proposals for benzene–ethylene photocycloaddition processes and conformation of the excited-state molecules.

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