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Synlett 2009(20): 3267-3270  
DOI: 10.1055/s-0029-1218361
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Efficient Stereoselective Glycosylations of Alcohols by Sugar Perpivalates: The First Use of 1-O-Pivaloylated Glycosyl Donors

Aliaksei V. Pukin, Han Zuilhof*
Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB, Wageningen, The Netherlands
Fax: +31(317)484914; e-Mail: han.zuilhof@wur.nl;
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Publication History

Received 2 September 2009
Publication Date:
11 November 2009 (online)

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Abstract

1-O-Pivaloyl glycosides were shown to be efficient glycosyl donors by using the perpivaloylated derivatives of lactose, galactose and glucose in the direct ZnCl2-promoted glycosylations of various alcohols. The corresponding glycosides were isolated in good yields and β-selectivity.

Key words

carbohydrates - glycolipids - glycosyl donors - glycosylations - stereoselective synthesis

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Data for 2b: ¹H NMR (400 MHz, C6D6): δ = 6.52 (d, J = 3.8 Hz, 1 H), 5.82 (t, J = 9.8 Hz, 1 H), 5.28 (t, J = 9.9 Hz, 1 H), 5.23 (dd, J = 10.0, 3.8 Hz, 1 H), 4.21-4.28 (m, 2 H), 4.08-4.14 (m, 1 H), 1.16 (s, 9 H), 1.12 (s, 9 H), 1.12 (s, 9 H), 1.09 (s, 9 H), 1.08 (s, 9 H); ¹³C NMR (100 MHz, C6D6): δ = 177.8, 177.2, 176.9, 176.8, 175.9, 89.5, 71.4, 70.5, 70.3, 68.5, 62.4, 39.4, 39.3, 39.2 (2 C, peaks overlap), 39.1, 27.7, 27.6, 27.5, 27.5, 27.4.

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Typical glycosylation procedure: To a solution of lactose octapivalate 1 (1 g, 0.99 mmol) and 8-chlorooctan-1-ol (4b; 243 µL, 1.48 mmol) in anhydrous toluene (10 mL), was added ZnCl2 (0.2 g, 1.48 mmol, which was dried in vacuo at 120 ˚C for at least 1 h prior to use) and the resulting suspension was stirred at 70 ˚C for 5 h. After cooling, the reaction mixture was diluted with EtOAc (10 mL), and solid NaHCO3 (2 g) and H2O (0.5 mL) were added portion-wise with stirring. After the formation of gas stopped (˜20 min), the solution was filtered over Hyflo. The precipitate was washed thoroughly with EtOAc. The combined organic phase was evaporated in vacuo and the residue was purified by silica gel column chromatography (EtOAc-petroleum ether, 1:7) to give 8-chlorooctyl lactoside 5b (0.97 g, 0.9 mmol, 91%) as a white foam. ¹H NMR (400 MHz, CDCl3): δ = 5.36 (d, J = 2.3 Hz, 1 H), 5.18 (t, J = 9.5 Hz, 1 H), 5.09 (dd, J = 10.5, 8.0 Hz, 1 H), 4.96 (dd, J = 10.5, 3.5 Hz, 1 H), 4.79 (dd, J = 9.7, 7.9 Hz, 1 H), 4.50 (d, J = 7.8 Hz, 1 H), 4.47-4.56 (m, 1 H), 4.44 (d, J = 8.0 Hz, 1 H), 4.18 (dd, J = 12.0, 5.0 Hz, 1 H), 4.04-4.11 (m, 1 H), 3.95-4.03 (m, 1 H), 3.88-3.94 (m, 1 H), 3.85 (t, J = 9.5 Hz, 1 H), 3.67-3.75 (m, 1 H), 3.47 (t, J = 6.8 Hz, 2 H), 3.44-3.53 (m, 1 H), 3.33-3.41 (m, 1 H), 1.65-1.75 (m, 2 H), 1.48 (t, J = 6.4 Hz, 2 H), 1.32-1.42 (m, 2 H), 1.22-1.28 (m, 6 H), 1.21 (s, 9 H), 1.19 (s, 9 H), 1.17 (s, 9 H), 1.15 (s, 9 H), 1.11 (s, 9 H), 1.11 (s, 9 H), 1.05 (s, 9 H); ¹³C NMR (101 MHz, CDCl3): δ = 177.7, 177.5, 177.2, 177.0, 176.7, 176.5, 175.9, 100.7, 100.0, 73.7, 73.3, 71.7, 71.6, 71.4, 71.3, 69.6, 68.8, 66.8, 61.7, 61.3, 44.9, 38.9-38.6 (7 C, peaks overlap), 32.5, 29.4, 29.0, 28.7, 27.3, 27.2, 27.1, 27.0 (3 C, peaks overlap), 26.9, 26.7, 25.8.