Efficient Acetylation of Carbohydrates Promoted by Imidazole
SHORT COMMUNICATION
(1.0 mmol) and acetic anhydride (1.2 equiv. per OH) in acetonitrile
(2.0 mL) was added imidazole (0.6 mmol) at room temperature and
the reaction mixture was stirred at ambient temperature for the
appropriate time as mentioned in Table 1. After completion of the
reaction (TLC; hexane/EtOAc, 1:1), the reaction mixture was
poured in water and extracted with CH2Cl2. The organic layer was
washed with aq. NaHCO3 and water, dried (Na2SO4) and concen-
trated under reduced pressure. Column chromatography of the
crude product on SiO2 using hexane/EtOAc (4:1) as an eluent fur-
nished pure acetylated carbohydrate derivatives (Table 1). In some
cases, direct evaporation of the solvent under reduced pressure avo-
iding two-phase partition of the reaction mixture followed by col-
umn chromatography furnished pure acetylated products. Spectral
data for compounds, which were not reported earlier follow below.
20.9 ppm. IR (KBr): ν = 2934, 2829, 2367, 1715, 1595, 1366, 1228,
˜
1105, 1030, 966, 719 cm–1. ESI-MS: m/z = 554 [M + Na].
C29H25NO7S (531): C 65.52, H 4.74; found C 65.68, H 5.0.
Methyl 2,3,4-Tetra-O-acetyl-6-O-di-tert-butyldiphenylsilyl-α-D-gluc-
opyranoside: Syrup. [α]2D5 = +124 (c = 1.5, CHCl3). 1H NMR
(CDCl3): δ = 7.65–7.64 (m, 4 H, aromatic H), 7.42–7.32 (m, 6 H,
aromatic H), 5.38 (t, J = 9.6 and 9.9 Hz, 1 H, 2-H), 5.03 (t, J =
9.9 and 9.3 Hz, 1 H, 3-H), 4.92 (d, J = 3.0 Hz, 1 H, 1ϪH), 4.82
(dd, J = 10.2 and 2.4 Hz, 1 H, 4-H), 3.85–3.80 (m, 1 H, 5-H), 3.71–
3.63 (m, 2 H, 6-Hab), 3.39 (s, 3 H, OCH3), 2.07, 1.98, 1.86 (3 s, 9
H, 3 COCH3), 1.05 [s, 9 H, C(CH3)3] ppm. 13C NMR (CDCl3,
75 Hz): δ = 169.8, 169.7, 169.0, 135.7–127.7 (aromatic C), 96.5,
71.0, 70.6, 69.9, 68.9, 62.6, 55.0, 26.8 (3 C), 20.7 (2 C), 20.5,
19.3 ppm. IR (neat): ν = 2390, 1715, 1580, 1366, 719 cm–1. ESI-
˜
5,6,7,9-Tetra-O-acetyl-4,8-anhydro-1,3-dideoxy-D-glycero-L-
MS: m/z = 581 [M + Na]. C29H38O9Si (558): C 62.34, H 6.86; found
glucononulose [1-(2,3,4,6-Tetra-O-acetyl-β-D-galactopyranosyl)ace-
C 62.10, H 7.05.
tone]: Yield: 96%; white solid; m.p. 91–92 °C. [α]2D5 = +5.6 (c = 1.5,
1
CHCl3). H NMR (CDCl3, 300 MHz): δ = 5.34 (br. s, 1 H, 7-H),
Acknowledgments
5.01–4.98 (m, 2 H, 5-H and 6-H), 4.05–3.98 (m, 2 H, 9-Hab), 3.96–
3.85 (m, 2 H, 4-H and 8-H), 2.74 (dd, J = 16.3 and 8.5 Hz, 1 H,
3-Ha), 2.45 (dd, J = 16.4 and 3.4 Hz, 1 H, 3-Hb), 2.16, 2.15, 2.02,
2.01, 1.96 (5 s, 15 H, 5 COCH3) ppm. 13C NMR (CDCl3, 75 Hz):
δ = 204.5, 169.9 (2 C), 169.7, 169.6, 74.4, 74.3, 71.9, 69.3, 67.9,
Instrumentation facilities from SAIF, CDRI is gratefully acknowl-
edged. P. T. and R. K. thank CSIR and DOD New Delhi for pro-
viding fellowships. This project was partly funded by the Depart-
ment of Science and Technology (DST), New Delhi (Project no.
SR/FTP/CSA-10/2002), India.
61.6, 45.6, 30.9, 20.7, 20.6 (2 C), 20.5 ppm. IR (KBr): ν = 2960,
˜
1741, 1713, 1598, 1439, 1386, 1220, 1030, 726 cm–1. ESI-MS: m/z
= 411 [M + Na]. C17H24O10 (388): calcd. C 52.57, H 6.23; found
C 52.30, H 6.50.
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2,3-Di-O-acetyl-5-O-tert-butyldimethylsilyluridine: Yield: 92%;
white solid; m.p. 84 °C. [α]2D5 = –2.5 (c = 1.5, CHCl3). 1H NMR
(CDCl3, 300 MHz): δ = 10.18 (br. s, 1 H, NH), 7.72 (d, J = 9.0 Hz,
1 H), 6.15 (d, J = 6.0 Hz, 1 H), 5.62 (d, J = 9.0 Hz, 1 H), 5.20–
5.18 (m, 2 H), 4.09 (br. s, 1 H), 3.85–3.73 (m, 2 H), 2.04, 1.98 (2 s,
6 H, 2 COCH3), 0.85 [s, 9 H, C(CH3)3], 0.06 (s, 6 H, 2 CH3Si)
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139.0, 103.0, 85.0, 83.4, 73.1, 71.4, 63.0, 25.7 (2 C), 25.4, 20.4, 20.1,
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18.1, –5.8 (2 C) ppm. IR (KBr): ν = 3202, 3072, 2929, 2858, 1749,
˜
1715, 1460, 1380, 1241, 1125, 1101, 1046, 834, 813, 778, 757 cm–1.
ESI-MS: m/z = 465 [M + Na]. C19H30N2O8Si (442): calcd. C 51.57,
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D
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[α]2D5 = +5.5 (c = 1.5, CHCl3). 1H NMR (CDCl3, 300 MHz): δ =
7.52–7.20 (m, 5 H, aromatic H), 5.23 (dd, J = 10.8 and 8.1 Hz, 1
H, 2-H), 4.92 (t, J = 9.5 Hz each, 1 H, 2Ј-H), 4.87–4.80 (m, 1 H),
4.67 (d, J = 9.8 Hz, 1 H, H-1), 4.47 (d, J = 11.2 Hz, 1 H, 1-H),
4.35–4.20 (m, 3 H), 4.19–4.02 (m, 3 H), 3.95–3.90 (m, 1 H), 3.80–
3.55 (m, 2 H), 2.08, 2.04 (2 s, 15 H, 5 COCH3), 1.52, 1.31 [2 s, 6
H, C(CH3)2] ppm. 13C NMR (CDCl3, 75 Hz): δ = 170.5, 170.4,
170.0, 169.4, 169.3, 133.2–128.4 (aromatic C), 111.0, 100.6 (C-1Ј),
85.7 (C-1), 78.1, 77.2, 76.2, 73.8, 73.4, 72.9, 71.2, 70.6, 63.4, 62.7,
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27.7, 26.5, 21.0 (3 C), 20.9 (2 C) ppm. IR (neat): ν = 2923, 2855,
˜
2363, 1730, 1461, 1218, 769 cm–1. ESI-MS: m/z = 707 [M + Na].
C31H40O15S (684): C 54.38, H 5.89; found C 54.75, H 6.12.
Phenyl 3-O-Acetyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-1-thio-
β-D
-glucopyranoside: White solid; m.p. 115 °C. [α]2D5 = +18.3 (c =
1.5, CHCl3). 1H NMR (CDCl3, 300 MHz): δ = 7.85–7.71 (m, 4 H,
aromatic H), 7.42–7.25 (m, 10 H, aromatic H), 5.85 (t, J = 9.5 and
9.0 Hz, 1 H, 3-H), 5.80 (d, J = 10.6 Hz, 1 H, 1-H), 5.50 (s, 1 H,
PhCH), 4.41 (d, J = 5.9 Hz, 1 H, 4-H), 4.30 (t, J = 10.2 and 10.1
Hz, 1 H, 2-H), 3.82–3.70 (m, 3 H, 5-H and 6-Hab), 1.87 (s, 3 H,
COCH3) ppm. 13C NMR (CDCl3, 75 Hz): δ = 170.5, 168.2, 167.6,
137.3–124.1 (aromatic C), 102.1, 84.3, 79.4, 70.9, 69.0, 54.7,
Eur. J. Org. Chem. 2005, 4265–4270
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