Photochemical transformations of tropolones. Part V. The photo-oxidation of tropolone methyl ether

When tropolone methyl ether is photo-oxidised in the presence of sensitizers, the products formed depend upon the solvent. A mechanistic rationalisation of the reaction is supported by the isolation and characterisation of an unstable intermediate peroxide. Kinetic and spectroscopic studies show that the peroxide decomposes thermally to a keten, which reacts further, to form esters in the presence of alcohols, and a lactone in aprotic solvents. Comparison is made with the photo-oxidation of benztropolone methyl ethers.