To a mixture of 4,6-difluoro-5-[4-(3-hydroxypropoxy)phenyl]-1H-indole-3-carbaldehyde (30 mg, 0.1 mmol) in ACN/t-butanol=1/1(2 mL) was added 2-methyl-2-butene (0.5 mL) and cooled to 0° C. and added the aqueous solution of sodium chlorite (180 mg, 0.5 mL) and sodium dihydrogen phosphate (270 mg, 2 mmol) in water (0.5 mL) dropwise via additional funnel. The reaction was stirred at room temperature for 10 h. The reaction was quenched with sodium sulfite. The mixture was partioned between dichloromethane and water. The combined organics were concentrated to give a residue, which was purified by reverse phase HPLC to give the title compound (15 mg, 43%) as a white solid. MS (AP+) 348.1 (M+H)+. 1H NMR (400 MHz, CD3OD) δ 7.74 (s, 1H), 7.36 (d, 2H), 7.03-6.98 (m, 3H), 4.14 (t, 2H), 3.77 (t, 2H), 2.04-2.01 (m, 2H).
