After dissolving 100 mg of (E)-4-[2-(2-fluorophenyl)vinyl]piperidine in 3 ml of tetrahydrofuran, 116 mg of 2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxaldehyde, 0.05 ml of acetic acid and 198 mg of sodium triacetoxyborohydride were added while stirring, and the stirring was continued for 20 hours at room temperature. An additional 200 mg of sodium triacetoxyborohydride was then added and the mixture was stirred overnight at room temperature. Aqueous sodium carbonate solution was added to the reaction mixture and extraction was performed with ethyl acetate. The organic layer was washed with brine and dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. The residue was purified by NH silica gel column chromatography (solvent: tetrahydrofuran/methanol). Ethyl acetate was added and the mixture was filtered to obtain the title compound (90 mg, 38% yield).
