Reaction Steps
Boron trifluoride diethyl etherate (80 μl, 0.70 mmol) was added to a stirred solution of 6-azido-6-deoxy-1,2,3,4-tetra-O-acetyl-D-galactopyranose 36 (α:β, 1:1) (52 mg, 0.139 mmol) in DCM (5 mL). The solution was stirred under argon at RT. After 20 min a solution of p-nitrophenol (19 mg, 0.14 mmol) in DCM (5 mL) was added to the reaction mixture and stirring under argon maintained. After 65 min, t.1.c. (DCM:ether, 60:1) indicated formation of two products (Rf 0.1, 0.4) with some remaining starting material (Rf 0.3). The DCM was removed in vacuo. The residue was diluted with chloroform (30 mL), washed with brine (3×30 mL), dried (MgSO4), filtered and concentrated in vacuo. The residue was purified by flash column chromatography (DCM:ether, 60:1) to afford p-nitrophenyl 2,3,4-tri-β-acetyl-6-azido-6-deoxy-α-D-galactopyranoside 40 (9.7 mg, 14%) as a colourless oil; partial data [α]D25 +18.3 (c, 0.5 in CHCl3); νmax (thin film) 3430 (br, OH), 2101 (sh, N3), 1637 (st, C═O)cm−1; δH (500 Mz, CDCl3) 2.05, 2.09, 2.21 (9H, 3 x s, 3 x CH3), 3.13 (1H, dd, J5,6 4.2 Hz, J6,6′ 13.1 Hz, H-6), 3.46 (1H, dd, J5,6′ 8.2 Hz, H-6′), 4.18 (1H, dd, H-5), 5.34 (1H, dd, J2,3 3.7 Hz, J2,3 10.9 Hz, H-2), 5.49 (1H, d, J3,4 3.0 Hz, H-4), 5.57 (1H, dd, H-3), 5.94 (1H, d, H-1) 7.21 (2H, J=9.3 Hz, 2 x CHCHCNO2), 8.26 (2H, 2 x CHCNO2); 5c (125.7 MHz, CDCl3) 19.9, 20.0, 21.0 (3 x q, 3 x CH3), 51.9 (t, C-6), 53.3 (d, C-2), 66.6 (d, C-3), 67.6 (d, C-4), 69.0 (d, C-5), 95.2 (d, C-1), 115.6, 115.7, 125.3 (3 x s, 3 x C═O), 116.9, 117.0 (2 x d, CHCHCNO2), 126.5, 126.6 (2 x d, CHCNO2), 140.8 (s, CNO2), 167.2, 169.9, 170.2, 171.8 (4 x s, 3 x C═O, 1x CCHCHCNO2); m/z (CI+) 470 (M+NH4+, 10%).
