Water → Methyl 2-chloro-3-oxoheptanoate

5.0 g 3-Oxo-heptanoic acid methyl ester were dissolved in 80 ml dry dichloromethane and 2.82 ml sulfurylchloride were added. The reaction mixture was stirred at room temperature for 30 minutes. 20 ml of water were added and the reaction mixture extracted five times with portions of 30 ml of dichloromethane. The combined organic extracts were washed with water and saturated NaHCO3 solution and brine and dried over MgSO4. The solvent was removed under reduced pressure to obtain 6.0 g 2-Chloro-3-oxo-heptanoic acid methyl ester as raw material. This material was used without further purification. 6.0 g 2-Chloro-3-oxo-heptanoic acid methyl ester were dissolved in 50 ml ethanol and 6.4 g 4-(Trifluoromethyl)thiobenzamide were added. The reaction mixture was heated under reflux overnight. The solvent was removed under reduced pressure and the residue purified by chromatography with the eluent n-heptane:ethyl acetate=100:1=>60:1. This gives 7.4 g 4-Butyl-2-(4-trifluoromethyl-phenyl)-thiazol-5-carboxylic acid methyl ester as yellow oil.