Photochemische Reaktionen. 97 Mitteilung [1]. Zur Photochemie konjugierter Epoxy‐diene II . Versuche mit ( E )‐β‐Jonyliden‐epoxiden

Photolysis of Conjugated Epoxy‐dienes Direct and sensitized excitation of the ( E )‐β‐ionylidene‐epoxides 1 and 4 leads to different types of isomerizations. Thus photocycloelimination to the cyclopropene‐ketones 2 and 6 is only achieved by 1 (π, π*)‐excitation (λ=254 nm), whereas 3 (π, π*)‐excitation (λ > 280 nm, acetone) gives selective C(1′), O‐cleavage of the oxirane ( 1 → 7 – 10 and 4 → 11 – 13 ). In contrast to 1 the twofold methylsubstituted epoxy‐diene 4 shows mainly ( E / Z )‐isomerization ( 4 → 5 ) on both 1 (π, π*)‐ and 3 (π, π*)‐excitation while the isomerizations 4 → 6 and 4 → 11 – 13 are minor processes, only.