The general procedure for the synthesis of 4-benzodioxane-2-carboxylic acid from (2,3-dihydrobenzo[b][1,4]dioxohexen-2-yl)methanol was carried out as follows: (2,3-dihydrobenzo[b][1,4]dioxohexen-2-yl)methanol was accurately weighed and dissolved in 0.3 N aqueous KOH (1.3 equiv). Potassium permanganate (KMnO4, 2.0 eq.) was slowly added under ice bath conditions at 0 °C. The reaction mixture was stirred at low temperature for about 10 minutes and then transferred to room temperature to continue stirring overnight. Upon completion of the reaction, the organic phase was extracted with dichloromethane and subsequently washed with water. The organic phase was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give a white solid as the crude product of 4-benzodioxane-2-carboxylic acid. The crude product was purified by silica gel fast column chromatography, and the final pure product was obtained in 92.5% yield.
