Photochemical Reactions. 126th Communication. Photochemistry of an α, β: δ, ε-unsaturated ketone: 4-(2′, 7′, 7′-Trimethylbicyclo [3.2.0]hept-2′-en-1′-yl)-3-buten-2-one

On ¹n,π*-excitation, the title compound 2 undergoes a photoinduced intramolecular 4 + 2]-cycloaddition affording the tetracyclic enol ether 3 as the only product in 79% yield. The assigned structure of 3 was confirmed by its conversion to the p-nitrobenzoate 6 whose structure was determined by X-ray analysis.