Water → 4-Chloro-5-ethyl-2-thiophenecarboxaldehyde

To a solution of 5-ethyl-2-thiophenecarboxaldehyde (6.0 g) in N,N-dimethylformamide (60 ml) was added N-chlorosuccinimide (8.57 g), and the mixture was stirred at room temperature for 2 hours, and subsequently stirred under heating at 60° C. for 2 hours. N-chlorosuccinimide (4.00 g) was further added thereto, and the mixture was further stirred under heating at 60° C. for 2 hours. The reaction mixture was poured into water, and the mixture was extracted with ethyl acetate, washed with brine, and dried over sodium sulfate. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (hexane:ethyl acetate=33:1) to give 4-chloro-5-ethyl-2-thiophenecarboxaldehyde (3.1 g) as colorless oil. (2) The above 4-chloro-5-ethyl-2-thiophenecarboxaldehyde was treated in a manner similar to Reference Example 1 to give 3-bromo-1-(4-chloro-5-ethyl-2-thienylmethyl)benzene as yellow oil. APCI-Mass m/Z 347/349 (M+H+MeOH).