After 3-bromopropene (2.1 ml, 24.8 mmol) was added to a solution of the compound 14 (6.79 g, 16.5 mmol), and cesium carbonate (8.09 g, 24.8 mmol) in dimethylformamide (5 ml), the mixture was stirred at room temperature for 4.5 hours. To the reaction solution was added an aqueous ammonium chloride solution, and this was extracted with ethyl acetate, washed with water and an aqueous saturated sodium chloride solution, and dried with anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and the residue was washed with diethyl ether to obtain 1-allyl-3-benzyloxy-5-(4-fluoro-benzylcarbamoyl) 4-oxo-1,4-dihydro-pyridine-2-carboxylic acid methyl ester 15 (6.15 g, 88%) as a colorless crystal.
