[N:1]([CH2:4][C@@H:5]([OH:14])[C@H:6]([OH:13])[C@H:7]([OH:12])[C@@H:8]([OH:11])[CH:9]=O)=[N+]=[N-].B(F)(F)F.[CH3:19]COCC.CCOC(C)=O.CCCCCC>C(O)C1C=CC=CC=1>[CH3:19][O:11][C@@H:8]1[C@H:7]([OH:12])[C@@H:6]([OH:13])[C@H:5]([OH:14])[CH2:4][NH:1][CH2:9]1A suspension of 6-azido-6-deoxy-D-galactose 14 (1.63 g, 7.9 mmol) obtained as describe above in benzyl alcohol (5 mL) was heated to 80° C. and BF3.OEt2 (984 μL, 8 mmol) was added dropwise. After 20 minutes the suspension became transparent. The solution was allowed to cool down. The reaction mixture was passed through a SiO2 column. Benzyl alcohol came out first using EtOAc:Hexane 1:5, then benzyl 6-azido-6-deoxy-D-galactopyranoside was separated from the furanose byproduct with EtOAc as eluent (1.21 g, 75%, α/β 60:40): 1H-NMR (CD3OD, δ, ppm, α-anomer only): 7.4-7.6 (5H, Benzyl group); 5.3 (H1, overlapped by HDO signal); 4.98 and 4.78 (2H, AB system, J=12 Hz, CH2—OBn); 4.18 (1H, dd, J=4.2 Hz, 8.7 Hz, H5); 4.0 (3H, overlapped, H2, H3, H4); 3.75 (1H, dd, J=13 Hz, 8.7 Hz, H6); 3.49 (1H, dd, J=13 Hz, 4.2 Hz, H6′). 13C-NMR (CD3OD, δ, ppm, α-anomer only): 139.76, 131.64, 130.31, 100.28, 72.54, 72.36, 72.10, 71.36, 70.89, 53.62.
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