Potassium Carbonate → 2-(3-Bromobenzyl)-5-methylthiophene

1,3-Dibromobenzene (25 g) and a solution of a Grignard reagent prepared using metal magnesium in ether (50 ml) were added to a solution of 5-ethylthiophene-2-carboxyaldehyde (5.0 g) in tetrahydrofuran (50 ml) at 0° C., and the mixture was stirred for one hour. The reaction mixture was poured into ice-cooled water and extracted with ethyl acetate. The organic layer was washed with saturated saline solution and dried over anhydrous sodium sulfate. After filtration, the solvent was evaporated from the filtrate under reduced pressure to give the residue, and the resulting residue was purified by silica gel column chromatography (n-hexane-ethyl acetate) to obtain (3-bromophenyl) (5-ethyl-2-thienyl)methanol (5.57 g). Borontrifluoride diethyl ether complex (1.57 ml) and triethylsilane (3.83 ml) were added to a solution of (3-bromophenyl) (5-ethyl-2-thienyl)methanol in acetonitrile (20 ml) at −40° C., and the mixture was stirred for two hours. Aqueous solution of saturated potassium carbonate was added to the reaction mixture, and extracted with ethyl acetate. The organic layer was washed with saturated saline solution and dried over anhydrous sodium sulfate. After filtration, the solvent was evaporated from the filtrate under reduced pressure to give the residue, and the residue was purified by silica gel column chromatography (n-hexane-ethyl acetate) to obtain 2-(3-bromobenzyl)-5-methylthiophene (3.77 g).