Boron tribromide → N-{2-Hydroxy-5-[2-(3-propyl-[1,2,4]oxadiazol-5-yl)-vinyl]-phenyl}-methanesulfonamide

N-{2-Methoxy-5-[2-(3-propyl-[1,2,4]oxadiazol-5-yl)-vinyl]-phenyl}-methane sulfonamide (compound of Example 9; 0.08 g, 0.23 mmol) was dissolved in dichloromethane (7 mL) and cooled to −78° C. A solution of boron tribromide in dichloromethane (0.15 mL, 1.61 mmol) was cooled to −78° C. and slowly added to the reaction mixture. After 1.5 h, the reaction mixture was warmed to room temperature and stirred for 3 h. At the end of 3 h, the mixture was quenched by dropwise addition of methanol (5 mL) at 0° C. and stirred for 20 min at room temperature. The solvent was evaporated, and the residue was redissolved in a mixture of 10% methanol in chloroform at 0° C. Solid sodium carbonate was added to this solution to adjust pH to 8. The solvent was evaporated and the crude product obtained was purified by column chromatography (silica gel, 0.5% methanol in chloroform) to afford the title compound.