Sequential Ketene Generation from Dioxane-4,6-dione-keto-dioxinones for the Synthesis of Terpenoid Resorcylates

Trapping
of the ketene generated from the thermolysis of 2-methyl-2-phenyl-1,3-dioxane-4,6-dione-keto-dioxinone
at 50 °C with primary, secondary, or tertiary alcohols gave the
corresponding dioxinone β-keto-esters in good yield under neutral
conditions. These intermediates were converted by palladium(0)-catalyzed
decarboxylative allyl migration and aromatization into the corresponding
β-resorcylates. These transformations were applied to the syntheses
of the natural products (±)-cannabiorci­chromenic and (±)-dauri­chromenic
acid.