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A Grignard reagent was prepared from 3.63 g (0.016 mol) of 3,7-dimethyloctyl bromide, 0.363 g (0.015 mol) of metallic magnesium, 40 ml of tetrahydrofuran and 3 droplets of ethylene dibromide as a reaction initiator. 2.09 g (0.015 mol) of anhydrous zinc chloride was added to the tetrahydrofuran solution of 3,7-dimethyloctylmagnesium bromide, while keeping the solution at 20° C. The obtained mixture was stirred at that temperature for one hour to give a cloudy tetrahydrofuran solution of 3,7-dimethyloctylzinc chloride. 0.3 g (0.0007 mol) of CuI·(C6H5)3P was added to this solution, followed by stirring for 5 minutes. 20 ml of a solution of 1.0 g (0.0024 mol) of 2,5,7,8-tetramethyl-2-(3'-chloro-4'-methylenepentyl)-6-yl benzyl ether having a purity of 98% in tetrahydrofuran was dropped into the obtained mixture at 20° C. over a period of 5 minutes. After the completion of the dropping, the obtained mixture was stirred at that temperature for 2 hours and subjected to TLC and HPLC to confirm the disappearance of the chlorine-containing raw material. The ratio of the γ-adduct to the α-adduct (γ:α) was 98:2 (conversion: 95%).

1. customat 20° C