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

✍ Scribed by Bruno Frei; Hans Richard Wolf; Oskar Jeger

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: German
• Weight: 542 KB
• Volume: 62
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19790620533

✦ Synopsis

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.