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M. K. Gurjar, A. Talukdar / Tetrahedron 60 (2004) 3267–3271
(m, 6H), 4.82 (d, 1H, J¼10.8 Hz), 6.76 (d, 2H, J¼8.8 Hz),
7.21 (m, 12H); 13C NMR (50 MHz, CDCl3): d 25.4, 18.1,
25.7, 54.1, 54.6, 62.6, 71.8, 71.9, 72.9, 74.4, 74.7, 76.7,
80.0, 98.6, 113.4, 127.2, 127.3, 127.6, 128.0, 129.0, 130.4,
138.5, 138.7. Anal. calcd for C35H48O7Si: C, 69.04; H, 7.95.
Found: C, 68.91; H, 7.66.
CDCl3) data: d 1.20 and 1.30 (2s, 6H), 3.18 (s, 3H), 3.56 (m,
5H), 3.65 (s, 3H), 3.85 (t, 1H, J¼7.9 Hz), 4.18 (m, 1H), 4.47
(m, 6H), 4.83 (d, 1H, J¼11.0 Hz), 6.67 (d, 2H, J¼8.7 Hz),
7.17 (m, 12H); 13C NMR (50 MHz, CDCl3): d 27.2, 54.9,
55.6, 65.1, 69.5, 72.3, 72.6, 73.0, 74.5, 74.8, 75.2, 80.2,
99.7, 127.6, 127.7, 127.8, 128.0, 128.4, 128.6, 129.8, 138.5.
Anal. calcd for C33H40O8: C, 70.19; H, 7.14. Found: C,
69.92; H, 7.18. Further elution gave 8b (0.078 g, 5.2%) as a
colourless oil; [a]D¼þ19.4 (c 1.05, CHCl3); 1H NMR
(200 MHz, CDCl3) data: d 1.38 and 1.44 (2s, 6H), 3.32 (s,
3H), 3.80 (s, 3H), 3.83 (m, 3H), 4.01 (m, 3H), 4.41 (dd, 1H,
J¼2.3, 6.1 Hz), 4.62 (m, 6H), 4.98 (d, 1H, J¼8.3 Hz), 6.83
(d, 2H, J¼7.2 Hz), 7.29 (m, 12H). Anal. Calcd for
C33H40O8: C, 70.19; H, 7.14. Found: C, 70.04; H, 7.26.
3.1.3. Methyl 3,4-di-O-benzyl-2-O-(p-methoxybenzyl)-a-
D-mannopyranoside (5).
A solution of 4 (10.0 g,
16.4 mmol) and n-Bu4NF (33.0 mL, 33.0 mmol, 1 M) was
stirred for 1 h and concentrated. The residue was partitioned
between EtOAc–water, dried (Na2SO4), concentrated and
purified on silica gel using EtOAc and light petroleum ether
(1:4) to give 5 (6.0 g, 74%) as colourless oil; [a]D¼þ28.6 (c
0.7, CHCl3); IR (cm21): 3359, 3032, 2868, 1602, 1211,
1
1155; H NMR (200 MHz, CDCl3) data: d 2.05 (brs, 1H),
3.1.6. Methyl 2,3,4,6,7-penta-O-benzyl-L-glycero-a-D-
mannoheptopyranoside (9). A solution of 8b (1.0 g,
1.8 mmol) and DDQ (0.47 g, 2.1 mmol) in CH2Cl2:H2O
(9:1, 7 mL) was stirred for 3 h, concentrated and purified on
silica gel using EtOAc–light petroleum (1:4). The resulting
product (0.5 g) and NaH (0.2 g, 4.9 mmol, 60% dispersion
in oil) in dry DMF (5 mL) were stirred for 30 min followed
by addition of BnBr (0.45 mL, 3.7 mmol). After 12 h, the
reaction was worked up as usual to afford a residue which
was purified on silica gel using EtOAc–light petroleum
(1:10) to give 9 (0.68 g, 57%) as a colourless syrup; [a]D¼
þ22.4 (c 0.98, CHCl3); IR (cm21): 3012, 2866, 1611, 1219,
1131; 1H NMR (200 MHz, CDCl3) d 3.26 (s, 3H), 3.81 (m,
7H), 4.55 (m, 11H), 7.25 (m, 25H); 13C NMR (50 MHz,
CDCl3): d 54.7, 70.9, 72.1, 72.4, 72.6, 73.2, 74.8, 75.0, 75.2,
78.5, 80.5, 98.8, 127.2, 127.3, 127.5, 127.6, 128.2, 138.5,
138.6. Anal. calcd for C43H46O7: C, 76.53; H, 6.87. Found:
C, 76.30; H, 6.78.
3.21 (s, 3H), 3.55 (m, 1H), 3.77 (s, 3H), 3.81 (m, 5H), 4.57
(m, 7H), 6.76 (d, 2H, J¼8.7 Hz), 7.23 (m, 12H); 13C NMR
(50 MHz, CDCl3): d 54.7, 55.1, 62.4, 72.2, 72.6, 74.4, 74.9,
75.1, 80.2, 99.5, 113.8, 127.5, 128.0, 128.3, 129.4, 130.3,
138.6. Anal. calcd for C29H34O7: C, 70.43; H, 6.93. Found:
C, 70.59; H, 7.11.
3.1.4. Methyl 3,4-di-O-benzyl-6-eno-2-O-(p-methoxyben-
A solution of
zyl)-a-D-mannoheptopyranoside (6).
DMSO (2.8 mL, 32.4 mmol) and oxalyl chloride (1.4 mL,
16.2 mmol) in CH2Cl2 (50 mL) at 278 8C was stirred for
30 min and then 5 (4.0 g, 8.1 mmol) was added. After
45 min, Et3N (6.8 mL, 48.6 mmol) was added and the
reaction slowly brought to RT. The CH2Cl2 layer was
washed with water, dried (Na2SO4) and concentrated to
obtain the aldehyde (3.4 g), which was dissolved in dry
ether (30 mL), cooled to 240 8C and Ph3PvCH2 {gener-
ated from PPh3CH3I (11.2 g, 27.6 mmol) and sodamide
(1.0 g, 25.6 mmol)} was added. After 30 min, reaction
mixture was concentrated and the residue purified on silica
gel using EtOAc–light petroleum (0.07:0.93) to give 6
(1.3 g, 32%) as a colourless syrup; [a]D¼þ24.4 (c 1,
CHCl3); IR (cm21): 3025, 2890, 1638, 1604, 1205, 1137; 1H
NMR (200 MHz, CDCl3) data: d 3.29 (s, 3H), 3.71 (m, 3H),
3.78 (s, 3H), 3.91 (t, 1H, J¼6.9 Hz), 4.64 (m, 7H), 5.25 (d,
1H, J¼8.8 Hz), 5.43 (d, 1H, J¼14.4 Hz), 5.96 (m, 1H), 6.80
(d, 2H, J¼8.4 Hz), 7.28 (m, 12H); 13C NMR (50 MHz,
CDCl3): d 54.7, 55.2, 72.5, 72.5, 72.9, 74.7, 75.1, 79.0, 80.1,
99.4, 113.9, 117.7, 127.6, 128.0, 128.3, 128.4, 129.5, 130.6,
135.8. Anal. calcd for C30H34O6: C, 73.45; H, 6.98. Found:
C, 73.68; H, 6.92.
3.1.7. Methyl 3,4,6,7-tetra-O-benzyl-2-O-(p-methoxy-
benzyl)-D-glycero-a-D-mannoheptopyranoside (11). A
solution of 8a (0.68 g, 1.2 mmol) and PPTS (0.33 g,
1.3 mmol) in MeOH (10 mL) was stirred for 6 h, neutralized
by Et3N and concentrated. The resulting compound 7a
(0.5 g, 1.0 mmol) was dissolved in dry THF (7 mL) and
NaH (0.15 g, 3.8 mmol, 60% dispersion in oil) was added.
After 30 min, BnBr (0.3 mL, 2.4 mmol) was introduced,
stirred for another 12 h and worked up as usual to afford a
residue which was purified on silica gel using EtOAc–light
petroleum (1:10) to give 11 (0.55 g, 65%) as a colourless
syrup; [a]D¼þ29.2 (c 1.07, CHCl3); IR (cm21): 3022,
1
2875, 1612, 1216, 1140; H NMR (200 MHz, CDCl3): d
3.31 (s, 3H), 3.70 (m, 5H), 3.77 (m, 3H), 3.96 (s, 2H), 4.65
(m, 11H), 6.76 (d, 2H, J¼7.3 Hz), 7.26 (m, 22H); 13C NMR
(50 MHz, CDCl3) data: d 54.6, 55.1, 63.2, 72.0, 72.3, 73.2,
74.7, 74.9, 75.0, 80.5, 99.7, 113.6, 127.4, 127.5, 127.9,
128.3, 129.5, 138.7, 138.9. Anal. calcd for C44H48O8: C,
74.98; H, 6.86. Found: C, 74.69; H, 7.08.
3.1.5. Methyl 3,4-di-O-benzyl-6,7-O-isopropylidine-2-O-
(p-methoxybenzyl)-D-glycero-a-D-mannopyranoside
(8a) and methyl 3,4-di-O-benzyl-6,7-O-isopropylidine-2-
O-(p-methoxybenzyl)-L-glycero-a-D-mannopyranoside
(8b). A solution of K2CO3 (1.1 g, 8.0 mmol), K3Fe(CN)6
(2.6 g, 8.0 mmol), OsO4 (27 mg, 0.1 mmol) and (DHQ)2
PYR (23 mg, 0.026 mmol) in t-BuOH–H2O (16.0 mL, 1:1)
was added to 6 (1.3 g, 2.65 mmol). After 6 h at 0 8C, the
reaction was quenched with solid sodium sulphite and
extracted with EtOAc, dried (Na2SO4) and concentrated to
give 7a/7b (1.0 g), which was treated with DMP (5 mL) and
PPTS (0.53 g) for 4 h. The reaction mixture was neutralized
with Et3N, concentrated and chromatograph on silica gel
using EtOAc–light petroleum (1:9) to give 8a (0.71 g,
3.1.8. Methyl 3,4,6,7-tetra-O-benzyl-D-glycero-a-D-man-
noheptopyranoside (12).
A solution of 11 (1.3 g,
1.8 mmol) and DDQ (0.46 g, 2.0 mmol) in CH2Cl2–H2O
(9:1) was stirred for 3 h, concentrated and the residue
purified on silica gel using EtOAc–light petroleum (1:4) to
give 12 (0.76 g, 70%) as a colourless oil; [a]D¼þ17.3 (c
0.9, CHCl3); IR (cm21): 3376, 3035, 2892, 1615, 1210,
1190; 1H NMR (200 MHz, CDCl3) data: d 3.35 (s, 3H), 3.85
(m, 7H), 4.65 (m, 9H), 7.31 (m, 20H); 13C NMR (50 MHz,
1
47%); [a]D¼þ30.8 (c 0.8, CHCl3); H NMR (200 MHz,