5,6,7,7a-Tetrahydro-4H-thieno[3,2-c]pyridin-2-one (2.0 g) was added to dichloromethane (10 mL) and stirred for 10 minutes at 10° C. Triethylamine (1.22 g) was then added and the mixture was stirred for 15 minutes to form a reaction mixture. Tert-butyldimethylsilyl chloride (1.81 g) dissolved in dichloromethane was added to the mixture at 10° C. The mixture was stirred at 10° C. and the reaction was monitored by Thin Layer Chromatography (TLC) (methanol/ethyl acetate=3/7) until the reaction was completed. Triethylamine (2.12 g), sodium iodide (0.02 g) and 2-bromo-2-(2-fluorophenyl)-1-cyclopropyl-ethanone (1.5 molar eq.) were added slowly to the reaction mixture at 10° C. The reaction mixture was stirred at 25° C. and the reaction was monitored by Thin Layer Chromatography (TLC) (methanol/ethyl acetate=3/7). After the reaction was completed, the organic phase was then washed with phosphate buffer (pH 6-7), and concentrated under reduced pressure at 30° C. to obtain 2-(tert-butyldimethylsilyloxy)-5-(α-cyclopropylformyl-2-fluorobenzyl)-4,5,6,7-tetrahydrothieno[3,2-c]pyridine as a crude product. The crude product (1 g) was recrystallized using acetone/water (1:1 v/v) (acetone volume=10 ml) at −5° C. for 3 hours for the crystallization method. Crystal precipitate was collected by filtration and dried under vacuum at 50° C. for 24 hours to obtain (tert-butyldimethylsilyloxy)-5-(α-cyclopropylformyl-2-fluorobenzyl)-4,5,6,7-tetrahydro-thieno[3,2-c]pyridine with the HPLC purity of 96%. The yield was 90%.
