On triplet excitation (1 > 280 nm, acetone), the epoxydiene (E)-5 undergoes initial cleavage of the C(5)-0 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-en01 ether 10 which undergoes a photochemical [2 + 21-cycloaddition to compounds 12 and 13, the main products on triplet excitation of (E)-5. On singlet excitation (A = 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 + Bare formed via the ylide intermediate h. Finally, the cyclobutene 18 is the product of an electrocyclic reaction of the diene side chain.

The synthesis and photolyses of the epoxydiene (E)-5 are described. On triplet excitation (1 > 280 nm, acetone), (E)-5 undergoes initial cleavage of the C(5)-0 bond leading to the intermediate c.Presumably an H-shift (c-+e) followed by the fragmentation of the 1,Cdiradical e leads (via the enol37) to the diketones (E)-6 and (Z)-12. Alternatively, cleavage of the C(6)-C (7)

Die Synthese und Photolyse des Jonon‐Derivates (V) werden beschrieben.

Die Triplett‐Anregung des Epoxydiens (Ia) führt zu ähnlichen Reaktionsprodukten (Umsatz 92%), wie sie früher bereits im Falle des Hydroxy‐Derivates (Ib) nachgewiesen wurden [Hauptprodukte (IIIa)/(IIIb), 5 weitere identifizierte Verbindungen zu jeweils I‐6%], zusätzlich werden die neuen Photoprodukte (IV)‐(VI) erhalten.

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