Photochemical reactions. 144th Communication. Photochemistry of 5,6-epoxy-1,3-dienes in the ionone series: Influence of a methoxy group in position 7

✍ Scribed by Urs Goldener; Bruno Frei; Oskar Jeger

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 802 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680414

✦ Synopsis

Abstract

On triplet excitation (λ > 280 nm, acetone), the epoxydiene (E)‐5 undergoes initial cleavage of the C(5)O bond of the oxirane and subsequent cleavage of the C(6)C(7) bond leading to the diradical intermediate e which reacts by recombination furnishing the cyclic compounds (E/Z)‐6, (E/Z)‐7,8, and 9. Alternatively, a H‐shift leads to the aliphatic methyl‐enol ether 10 which undergoes a photochemical [2+2]‐cycloaddition to compounds 12 and 13, the main products on triplet excitation of (E)‐5. On singlet excitation (λ = 254 nm, MeCN), (E)‐5 undergoes cleavage to the carbene intermediates f and g. The vinyl carbene f reacts with the adjacent double bond furnishing the cyclopropene 14 as the main product. From the carbene intermediate g, the methyl‐enol ether 15 arises by carbene insertion into the neighboring CH bond. Furthermore, the diastereomer of the starting material, the epoxydiene (E)‐16, and compounds 17A+B are formed via the ylide intermediate h. Finally, the cyclobutene 18 is the product of an electrocyclic reaction of the diene side chain.