To 1-methyl-2-oxo-2-tetrahydro-1-H-1-pyrrolylethyl 2,6-dibromohexanoate (295 mg, 0.75 mmol), NaI (225 mg, 1.5 mmol) and tetrahydrofuran (4 mL) were added. The mixture was stirred at 40° C. for 1.5 hours. Next, triethylamine (84 mg, 0.83 mmol), benzylamine (97 mg, 0.90 mmol) and tetrahydrofuran (4 mL) were added thereto. The mixture was stirred at 20° C. for 15 hours. It was confirmed with NMR analysis of the reaction solution that the conversion ration was 83% and the diastereo ratio calculated from the NMR analysis was 79:21.
