A partial suspension of 5-[4-(1-hydroxycyclobutyl)phenyl]-6-methyl-1H-indole-3-carbaldehyde (130 mg, 0.426 mmol) in tetrahydrofuran (3 mL) and tert-butanol (3 mL) was treated with 2-methyl-2-butene (2.27 mL, 21.4 mmol) followed by a solution of sodium chlorite (538 mg, 6.4 mmol) and sodium phosphate monobasic hydrate (904 mg, 6.5 mmol) in water (2 mL) via glass pipet at room temperature. The reaction mixture was stirred vigorously at room temperature for 62 hours, and was poured into half-diluted saturated aqueous ammonium chloride solution (50 mL). The product was extracted with ethyl acetate (3×60 mL), and the combined organic layers were dried over sodium sulfate, filtered and evaporated. The crude product was purified using reverse-phase chromatography to give the title compound.
