Oxidation of Cage Derivatives of Quinopimaric Acid

The oxidation of cage compounds derived from quinopimaric acid, namely γ-diketone, oxa-“bird cage,” 18-chloro-15-oxa-“bird cage,” and 16-sulfanyl-15-oxa-“bird cage,” was studied using a number of oxidating agents, including sodium percarbonate in trifluoroacetic acid at 0°C, 36% hydrogen peroxide in acetone at room temperature, and tert-butyl hydroperoxide in the presence of MoCl₅ in boiling benzene. It was shown for the first time that the oxidation of diterpene oxa-“bird cages” led to the formation of mixtures of keto lactones (Baeyer–Villiger oxidation products), in which 7,10-dioxo-6-oxaheptacyclo[11.8.0.0^3,8.0^4,12.0^5,11.0^9,13.0^16,21]heneicosane was the major component.