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

Abstract

AbstractThe 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)