[CH3:1][Mg]Cl.[CH3:4][O:5][C:6](=[O:20])[C:7](=[C:12]([C:14]1[O:15][C:16]([CH3:19])=[CH:17][CH:18]=1)[CH3:13])[C:8]([O:10][CH3:11])=[O:9].[NH4+].[Cl-]>O1CCCC1.[Cu]I>[CH3:11][O:10][C:8](=[O:9])[CH:7]([C:12]([CH3:1])([C:14]1[O:15][C:16]([CH3:19])=[CH:17][CH:18]=1)[CH3:13])[C:6]([O:5][CH3:4])=[O:20]Step B To a suspension of CuI (7.61 g, 40 mmol) in anhydrous tetrahydrofuran (100 mL) at −50° C. was added methylmagnesium chloride (3 M, 27 mL, 80 mmol) during a period of 15 min. After the addition was finished, the reaction mixture was gradually warmed room temperature and stirred for 20 min. Then the temperature of the mixture was lowered to −50° C., a tetrahydrofuran solution (50 mL) of 2-[1-(5-methyl-furan-2-yl)-ethylidene]-malonic acid dimethyl ester (3.7 g, 15.5 mmol) was added. The reaction mixture was allowed to slowly warmed to room temperature and stirred for 3 h. Aqueous saturated NH4Cl solution was added to quench the reaction. The mixture was filtered, and the filtrate was concentrated to remove most of tetrahydrofuran. The residue was extracted with ethyl acetate twice. The organic layers were combined, concentrated. The residue was purified by chromatography (EtOAc:hexanes=1:20, 1:10) to give 2-[1-methyl-1-(5-methyl-furan-2-yl)-ethyl]-malonic acid dimethyl ester as a colorless oil (2.5 g, 63%).
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