[Mg].[CH2:2]([C:4]1[CH:9]=[C:8]([CH3:10])[CH:7]=[C:6]([CH2:11][CH3:12])[C:5]=1Br)[CH3:3].[C:14](OCC)(=[O:20])[C:15]([O:17][CH2:18][CH3:19])=[O:16].Cl>C1(C)C=CC=CC=1.BrC(Br)C.O1CCCC1>[CH2:2]([C:4]1[CH:9]=[C:8]([CH3:10])[CH:7]=[C:6]([CH2:11][CH3:12])[C:5]=1[C:14](=[O:20])[C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH3:3]To a 2 L volume four-necked flask, magnesium (cutting chip) (66.2 g), tetrahydrofuran (anhydrous) (494 g), and toluene (549 g) were added under a nitrogen atmosphere at room temperature. After starting to stir the mixture, dibromoethane (26.9 g) was added dropwise over 10 minutes at about 20° C., and then the internal temperature was raised to 33° C. The resulting mixture was stirred at 30° C. for 20 minutes. 2,6-diethyl-4-methylbromobenzene (10-a) (549.0 g) was added dropwise thereto at 40° C. over 1 hour. The resulting mixture was stirred at 50° C. for 51 hours, and diethyl oxalate (389.1 g) dissolved in toluene (550.1 g) was added dropwise thereto at about 0° C. over 1 hour. The resulting mixture was stirred at about 5° C. for 1 hour. Then, to the mixture, 3.5 w/w % of hydrochloric acid (832 g) was added dropwise at the same temperature. Then the mixture was warmed to room temperature, and the organic layer was separated. The aqueous layer was extracted with toluene (548.3 g). The organic layers were combined, washed with water (1098 g) and concentrated under reduced pressure to give 710.8 g of ethyl 2-(2,6-diethyl-4-methylphenyl)-2-oxoacetate (9-a).
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