The Sensitized Photooxidation of Cycloheptatriene (Tropilidene). Isolation and Thermal Isomerization of (4π+2π) Cycloadduct, 8,9-Dioxabicyclo[3.2.2]-2,6-nonadiene, and Preparation of Tropone

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Abstract
The sensitized photooxidation of cycloheptatriene (tropilidene) in methanol afforded (4π+2π) cycloadduct; 8,9-dioxabicyclo[3.2.2]-2,6-nonadiene (1), 6-hydroxy-2,4-cycloheptadienone and 6-oxoheptadienal presumably derived from (6π+2π) cycloadduct, and small amounts of tropone and benzaldehyde. Mechanism of their formation are discussed. It was found that the treatment of the photooxidation mixture with trie thy lamine afforded tropone in about 50% yield. Thermal isomerization of 1 in refluxing xylene afforded cis-3,9-dioxatricyclo-[6.1.0.02.4]-5-nonene, 8-oxabicyclo[5.1.0]-4-octen-3-one and 4-hydroxy-2,6-cycloheptadienone.