Oxidation of mesitol (8) with lead tetraacetate in acrylic acid followed by gentle heating gives 6-hydroxy-4,6,7-trimethyl-5-oxobicyclo[2.2.2]oct-7-ene-2-carboxylic acid lactone (13), which is considered to be formed via intramolecular cycloaddition of 6-acryloxy-2,4,6-trimethyl-2,4-cyclohexadienone (11). Similar treatment of 4-methylxanthen-3-o1 (7) gives the corresponding bridged xanthene keto lactone 5. Ketalization of this with ethylene glycol, followed by treatment with methylmagnesium iodide, hydrolysis, and pyrolysis gives the bridged xanthene keto ether 4, which possesses many of the structural features of the nucleus of the naturally occurring coloring matters morellin and gambogic acid.