Photochemische Reaktionen. 105. Mitteilung [1]. Zur Photochemie optisch aktiver λ, δ‐Epoxy‐enone: Racemisierung und Cyclisierung von (−)‐4‐Methyliden‐5,6‐epoxy‐5,6‐dihydro‐β‐jonon und (−)‐4‐Oxo‐5,6‐epoxy‐5,6‐dihydro‐β‐jonon

The photochemistry of optical active λ, δ‐epoxy‐enones. Racemization and cyclization of (−)‐4‐methylidene‐5,6‐epoxy‐5,6‐dihydro‐β‐ionone and of (−)‐4‐oxo‐5,6‐epoxy‐5,6‐dihydro‐β‐ionone UV.‐irradiation (λ ≥ 347 nm as well as λ = 254 nm) converts the conjugated λ, δ‐epoxy‐enones (−)‐2 and (−)‐4 by cleavage of the C,C‐oxirane bond to an intermediate ketonium ylide f which cyclizes giving the racemic starting materials. The degree of racemization depends on the length of the irradiation time. The formation of the optical active products (−)‐3 and (+)‐5 in these irradiations gives evidence, that the photocyclization of (−)‐2 und (−)‐4, respectively, is a one step reaction of a state g.