Photochemistry of 8,8,9,9‐tetramethyl‐1,3,4,6,7,8‐hexahydro‐1,4‐ethanonaphthalene‐2,5‐dione, a δ‐oxo‐β,γ‐unsaturated ketone

Abstract
The oxa‐di‐π‐methane rearrangement product 4,4,9,9‐tetramethyltetracyclo [6.4.0.01,5.02,8]dodecane‐7,12‐dione (2) is formed selectively in a variety of solvents on either direct (λLD = 254, 300, 350 nm) or sensitized (xanthone, acetone, benzene) irradiation of the title compound 1. The efficiency for this rearrangement is higher on So–S1 excitation (Φ−1 = 0.67) than on either So–S2 or So–S3 excitation (Φ−1 = 0.58).