A reactor was charged with 325 mg (1.0 mmol) of tert-butyl 2-(3-oxo-3-phenylpropyl)phenylcarbamate (an11) obtained in Synthesis Example 5, 36.9 mg (0.10 mmol) of tetrabutylammonium iodide (Bu4N+I−), and 50 mL of ethyl acetate as a solvent to prepare a solution. Subsequently, 364 μL of 5.5 M decane solution (manufactured by Aldrich) containing 2.0 mmol of tert-butyl hydroperoxide (TBHP) as an oxidizing agent was added to the solution in an amount corresponding to 2 equivalents based on the aniline derivative (an1). After adjusting the temperature of the reaction system to 50° C., the mixture was reacted for 10 hours with stirring. After cooling the reaction mixture including the reaction product to room temperature, the reaction mixture was added to 20 mL of water, and extracted twice with ethyl acetate. The resulting organic layer was sequentially washed with a saturated sodium sulfite (Na2SO3) aqueous solution, an NaCl aqueous solution, and water, followed by the addition of anhydrous sodium sulfate (Na2SO4). The solvent was then evaporated under reduced pressure to obtain a concentrate including a crude product. The concentrate was subjected to silica gel flash column chromatography (eluant: hexane/ethyl acetate=6/1) to obtain 246 mg (0.76 mmol) of tert-butyl 2-benzoylindoline-1-carboxylate represented by the formula (as1) (white solid). The yield was 76% (see Table 1-1). The analysis data for the resulting compound (as1) is shown below.
