Photochemical Reactions of 1,3,3‐Trimethylbicyclo[2.2.2]octa‐5,7‐dien‐2‐ones

The photochemistry of 1,3,3‐trimethylbicyclo[2.2.2]octa‐5,7‐dien‐2‐ones 1a – f containing multiple chromophoric moieties under various conditions is described. Upon direct irradiation, dienones 1a – f in benzene, acetonitrile, and methanol were found to aromatize through photoelimination of dimethylketene, which was trapped with 3‐phenylprop‐2‐en‐1‐ol ( 12 ). Triplet sensitization of dienone 1a in acetone and in acetone/acetophenone mixed solvents afforded aromatic compound 2a , whilst bicyclic systems 1b – c were found to be unreactive on sensitization. In the cases of dienones 1d – f in acetone, aromatic compounds 2d – f and di‐π‐methane (DPM) photoproducts 3d – f and 4f were observed, but in the acetone/acetophenone mixed solvent system only DPM photoproducts were detected. Plausible mechanisms for these photochemical reactions are described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)