To a 3 L reactor was added 1- (4-amino-2-methylbenzoyl) -7-chloro-5-oxo-2,3,4,5-tetrahydro- 1 H- 1 -benzazepine (70. 0 g, 212.90 mmol), dichloromethane (560 ml) and distilled water (140 ml), and the mixture was stirred for 1 hour. Magnesium hydroxide (14.90 g, 14.90 mmol) was added to the reaction mixture at 10 ° C. or lower, and the mixture was stirred for 30 minutes. 2-Methylbenzoyl chloride (30.42 ml) was gradually added to the reaction mixture, stirring for 3 hours. The reaction mixture was filtered to remove magnesium hydroxide, and the pH of the reaction mixture was adjusted to pH 8 to 9 using an aqueous sodium hydroxide solution, and then the organic layer was separated. The obtained organic layer was dried with sodium sulfate (Na 2 SO 4), filtered, and concentrated under reduced pressure to give 5-Dehydro Tolvaptan (yield: 96 percent).
