1. Weigh (2,3-dihydrobenzo[b][1,4]dioxohexen-2-yl)methanol (compound b) and dissolve in 0.3 N aqueous KOH (1.3 equiv).
2. KMnO4 (2.0 eq.) was slowly added at 0 °C.
3. The reaction mixture was stirred at low temperature for about 10 minutes, followed by stirring at room temperature overnight.
4. After completion of the reaction, the organic phase was extracted with dichloromethane.
5. The organic phase was washed with water and subsequently dried with anhydrous sodium sulfate and concentrated to give a white solid, the crude product of 4-benzodioxane-2-carboxylic acid (compound c).
6. The crude product was purified by rapid chromatography on silica gel in 92.5% yield.
