Br[Zn][CH2:3][C:4]([O:6][CH2:7][CH3:8])=[O:5].[CH3:9][C:10]1[C:11](=[O:20])[C:12]([CH3:19])=[C:13]([CH3:18])[C:14](=[O:17])[C:15]=1[CH3:16].Cl.C(OCC)(=O)C>C1COCC1>[OH:20][C:11]1([CH2:3][C:4]([O:6][CH2:7][CH3:8])=[O:5])[C:10]([CH3:9])=[C:15]([CH3:16])[C:14](=[O:17])[C:13]([CH3:18])=[C:12]1[CH3:19]Under nitrogen atmosphere, 6 mL of THF was added to 1.22 g (2 mmol, 0.6 equivalent) of (BrZnCH2COOEt.THF)2. Under argon atmosphere, a solution of 0.45 g (3.33 mmol) of 2,3,5,6-tetramethyl-1,4-benzoquinone in 4 mL of THF was added dropwise while stirring at 0˜5° C. The mixture was stirred at 20˜25° C. for 1 hour. 5 mL of 1N hydrochloric acid was added dropwise at 20° C. or lower, followed by dilution with 25 mL of ethyl acetate. Then, the layers were separated. The organic layer was washed successively with 5 mL (×2) of 1N hydrochloric acid, 5 mL of water, 5 mL (×2) of an aqueous saturated sodium bicarbonate solution, and 5 mL (×2) of an aqueous saturated sodium chloride solution. After cooling, the organic layer was dried with anhydrous magnesium sulfate. Concentration under reduced pressure afforded 0.79 g of the desired product (yield 94%).
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