To a solution of 1H-benzotriazole (2.38 g) in methanol (20 mL) were added ethyl N-benzyl-β-alaninate (4.14 g) and aqueous formaldehyde solution (37%, 2 mL) at room temperature. The reaction mixture was stirred overnight at room temperature, and concentrated under reduced pressure. The residue was purified by silica gel chromatography (ethyl acetate/petroleum ether) to give ethyl N-(1H-benzotriazol-1-ylmethyl)-N-benzyl-β-alaninate (5.60 g). To a mixture of zinc powder (1.74 g) in anhydrous THF (16 mL) was added chlorotrimethylsilane (1.58 g) under nitrogen atmosphere, and the mixture was stirred at room temperature for 10 min. To the reaction mixture was added ethyl bromodifluoroacetate (2.97 g) at room temperature, and then a solution of ethyl N-(1H-benzotriazol-1-ylmethyl)-N-benzyl-β-alaninate (4.50 g) in THF (8 mL) was added thereto at room temperature. The reaction mixture was stirred at room temperature for 18 hr, and added to water. The insoluble substance was removed by the filtration, and the filtrate was extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel chromatography (ethyl acetate/petroleum ether) to give the title compound (3.23 g).
