To prepare 6-ethyl-4-oxo-4a,8a-dihydro-4H-chromene-3-carboxylic acid, 6-ethyl-3-formyl chromone (0.25 g) was dissolved in DMF (10 mL), and OXONE (0.76 g) was added and stirred at room temperature for 3 hours with the reaction having a final volume (12 mL). The reaction was monitored by TLC or GC analysis. EtOAc was added to extract the products and 1N HCl was used to dissolve the salts. The organic extract was washed with 1N HCl (30 mL×3) and brine (30 mL), dried over Na2SO4, and the solvent was removed under reduced pressure to obtain 6-ethyl-4-oxo-4a,8a-dihydro-4H-chromene-3-carboxylic acid in 52% yield and 6-ethyl-3-hydroxy-4a,8a-dihydro-chromene-4-one in 34% yield after purification by silica gel column chromatography.
