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To a −78° C. solution of [(2-Benzyloxy-phenyl)-tert-butoxycarbonylmethyl-amino]-acetic acid tert-butyl ester (6.3 g, 14.7 mmol) in CH2Cl2 (100 mL) was added pyridine (1.8 mL, 22.1 mmol) followed by bromine (0.91 mL, 17.6 mmol) under an Ar atmosphere. After 30 min, the mixture was allowed to warm to room temperature and then washed with water, 5% sodium bicarbonate, and brine. The organic layer was dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash column chromatography, eluting with CH2Cl2/hexane/EtOAc=1:4:0.2 to yield 5.9 g (79%) of 13 as a white solid. Rf=0.43 (in CH2Cl2/hexane/EtOAc=1:4:0.2); 1H NMR (300 MHz, CDCl3) δ 7.45-7.26 (m, 5H), 6.99 (m, 2H), 6.73 (m, 1H), 5.09 (s, 2H), 4.04 (s, 4H), 1.41 (s, 18H); 13C NMR (75 MHz, CDCl3) δ 170.1, 151.1, 138.7, 136.6, 128.6, 127.9, 127.4, 124.1, 120.5, 117.6, 113.7, 81.2, 71.2, 54.5, 28.0; mass spectrum, calculated for C25H32BrNO5 (MH+) 506.2, Found 505.8.

1. washwashed with water, 5% sodium bicarbonate, and brine
2. dry with materialThe organic layer was dried over Na2SO4
3. concentrationconcentrated in vacuo
4. customThe crude product was purified by flash column chromatography
5. washeluting with CH2Cl2/hexane/EtOAc=1:4:0.2