Farbstoffsensibilisierte Photoreaktionen von vinylogen Epoxycarbonylverbindungen

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Abstract
On irradiation in the presence of dye sensitizers, vinylogous epoxy carbonyl compounds undergo a novel photofragmentation reaction, to give furyl ketones in good yields. The fragmentation process is probably preceded by trans‐cis isomerization of the double bond; in one case the cis‐isomer could be isolated. In a side reaction epoxyenone 10 gives the cyclopentanone derivatives 13 and 14 by a [1, 2] shift of a methyl group.Similar dye sensitized photolysis of the endo‐peroxide 2 also gives the corresponding furyl ketone 4, and the corresponding vinylogous epoxyketone C is probably an intermediate in this transformation.The finding that dyes of relatively low triplet energies (∼ 30 kcal/mol) efficiently sensitize these reactions, and a certain wave length dependence suggest that the usual triplet mechanism cannot be involved.

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