Photochemische Reaktionen. 121. Mitteilung. Zur Photochemie von ε,ζ‐Methano‐α,γ‐dienonen und 7,8‐Methano‐1,3,5‐trienen

Photochemistry of ε,ζ‐Methano‐α,γ‐dienones and 7,8‐Methano‐1,3,5‐trienes Irradiation of the δ‐cyclopropyl‐dienone ( E )‐ 6 (λ ≥ 347 nm) gives ( Z )‐ 6, 10 (1,5‐sigmatropic H‐shift), ( E/Z )‐ 9 (electrocyclic process involving C(ε), C(ζ)‐cleavage) and 11 (ring opening). The corresponding 6‐cyclopropyl‐triene ( E )‐ 7 gives on singlet excitation (δ > 280 nm) 14 (1,5‐sigmatropic H‐shift) and, to a smaller extent, the bicyclo [3.2.0] heptenyl‐dienes ( E/Z )‐ 13 . However, on triplet excitation (λ ≥ 347 nm, benzophenone) ( E )‐ 7 gives ( E/Z )‐ 13 as the main products. On both 1 π,π*‐ and 3 π,π*‐excitation, ( Z )‐ 7 and 15 are formed in small amounts.