5-(2-Aminopyridin-4-yloxy)-2,3-dihydro-1H-indole-1-carboxylic acid methylamide (40 mg, 0.14 mmol) was dissolved in acetic acid (0.9 ml), manganese (III) acetate (29 mg, 0.17 mmol) was added thereto and the reaction mixture was stirred at 70° C. for 3.5 hours. Manganese (III) acetate (29 mg, 0.17 mmol) was further added, and the reaction mixture was further stirred at 70° C. for 0.5 hours. After naturally cooled to room temperature, the reaction mixture was partitioned between ethyl acetate and saturated aqueous solution of sodium hydrogencarbonate. The organic layer was washed with brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The obtained crystals were suspended in diethyl ether:acetone=3:1, filtered off, washed with diethyl ether, and dried under aeration to yield the title compound (24 mg, 0.085 mmol, 61%) as colorless crystals.
