General procedure for the synthesis of 6-hydroxy-1,4-benzodioxane from 1,4-benzodioxane-6-carboxaldehyde: To a solution of 2,3-dihydro-benzo[1,4]dioxine-6-carboxaldehyde (30.0 g, 183 mmol) in methylene chloride (500 mL) was added m-chloroperoxybenzoic acid (mCPBA, 37.85 g, 219 mmol). The suspension was heated to 50 °C and the reaction was carried out for 16 hours. Upon completion of the reaction, saturated sodium bicarbonate (NaHCO3) solution was added and the mixture was extracted with dichloromethane (CH2Cl2). The organic phases were combined, concentrated in vacuum, dissolved in methanol (MeOH) and 4 M sodium hydroxide (NaOH, 200 mL) solution was added. After 2 hours of reaction, the mixture was acidified with 4 M hydrochloric acid (HCl) and extracted with ethyl acetate (EtOAc). The organic phases were combined, washed sequentially with saturated sodium bicarbonate (NaHCO3) solution and brine, concentrated in vacuum and dissolved in dichloromethane (CH2Cl2). The solution was filtered to remove the precipitate. The resulting solution was stirred with saturated sodium bicarbonate (NaHCO3) solution for 1 h. The organic phase was separated, dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated in vacuo to give 2,3-dihydro-benzo[1,4]dioxin-6-ol (26.92 g, 94% yield).
