Singlet and Triplet Excited State Photochemistry of Tricyclo-[5. 2. 2. 02, 6] undeca-3, 10-dien-9-one Derivatives

The photochemical behavior of tricyclo [5. 2. 2. 02, 6] undeca-3, 10-dien-9-one ring system (4), which was prepared by Diels-Alder reaction of cyclohexadienone derivatives and cyclopentadiene, has been studied under triplet sensitization and direct irradiation. In the triplet state, this ring system undergoes the oxa-di-π-methane (ODPM) rearrangement, while the 1, 3-acyl migration occurs from the singlet state. The triplet energy was estimated to be between 70 and 72 kcal/mol on the basis of sensitization by various sensitizers.