A solution of sodium phosphate monobasic (0.039 g) in water (1 mL) was added to a solution of tert-butyl 6-(benzenesulfonylmethyl)-3-(2-formylfuran-3-yl)-2-hydroxybenzoate (Intermediate 27, 0.105 g) in acetonitrile (2 mL) at 0° C. Hydrogen peroxide (50% wt. in water, 0.078 mL) and sodium chlorite (0.029 g) were added and the reaction mixture was warmed to room temperature and stirred for 18 hours. The mixture was cooled to 0° C. and further sodium phosphate monobasic (0.028 g) in water (0.5 mL), hydrogen peroxide (50% wt. in water, 0.038 mL) and sodium chlorite (0.052 g) were added and the mixture was warmed to room temperature and stirred for 18 hours. The mixture was poured onto sodium sulfite (10% in water) at 0° C., extracted into ethyl acetate, washed with water, dried (MgSO4) and filtered. The filtrate was evaporated to dryness and the residue was purified by chromatography on silica, eluting with a mixture of methanol and 1% acetic acid in methanol with a gradient of O-100%. The resultant product was triturated in cyclohexane and ethyl acetate and the solid was collected by filtration and dried in vacuo to give 3-[4-(benzenesulfonylmethyl)-3-tert-butoxycarbonyl-2-hydroxy-phenyl]-furan-2-carboxylic acid (0.028 g) as a white solid.
