[Br:1][C:2]1[CH:3]=[CH:4][C:5]([O:12][CH3:13])=[C:6]([C:8]([CH3:11])(O)[CH3:9])[CH:7]=1.[CH2:14]([O:16][C:17](=[O:25])[C:18]([O:20][Si](C)(C)C)=[CH2:19])[CH3:15].[Sn](Cl)(Cl)(Cl)Cl.C(=O)([O-])[O-].[K+].[K+]>ClCCl>[CH2:14]([O:16][C:17](=[O:25])[C:18](=[O:19])[CH2:20][C:8]([C:6]1[CH:7]=[C:2]([Br:1])[CH:3]=[CH:4][C:5]=1[O:12][CH3:13])([CH3:11])[CH3:9])[CH3:15]
9.8 g of 1-(5-bromo-2-methoxyphenyl)-1-methylethanol and 15.24 g of 2-(trimethylsilyloxy)-acrylic acid ethyl ester in 150 ml of dichloromethane are mixed at −70° C. with 5.6 ml of tin tetrachloride. After 20 minutes at −70° C., the solution is poured onto a semi-saturated potassium carbonate solution and mixed with dichloromethane. The dichloromethane phase is washed with potassium carbonate solution, 1 M hydrochloric acid and water, dried (Na2SO4) and concentrated by evaporation. After bulb tube distillation, 5.2 g of 4-(5-bromo-2-methoxyphenyl)-4-methyl-2-oxopentanoic acid-ethyl ester is obtained. Boiling point: 160° C./0.04 hPa
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