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Synlett 2010(8): 1193-1196  
DOI: 10.1055/s-0029-1219798
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Regioselective Reductive Ring Opening of Benzylidene Acetals Using Triethylsilane and Iodine

Rajib Panchadhayee, Anup Kumar Misra*
Division of Molecular Medicine, Bose Institute, P-1/12, C. I. T. Scheme VII M, Kolkata 700054, India
Fax: +91(33)23553886; e-Mail: akmisra69@gmail.com;
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Publication History

Received 22 January 2010
Publication Date:
23 March 2010 (online)

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Regioselective Reductive Ring Opening of Benzylidene Acetals Using Triethylsilane and IodineSynlett 2010; 2010(09): 1430-1430
DOI: 10.1055/s-0029-1219941

Abstract

Novel reaction conditions have been developed for the regioselective reductive ring opening of benzylidene acetals in carbohydrate derivatives using triethylsilane and molecular iodine. The reaction is fast, compatible with most of the functional groups encountered in the oligosaccharide synthesis, and yields were excellent. The reaction conditions are equally effective in thioglycosides.

Key words

carbohydrate - benzylidene acetal - regioselective - ­iodine - triethylsilane

23

Spectroscopic data for novel products are presented below. To aid assignments, data were taken after acetylation of the products.
4-Methoxyphenyl 2,3,4-Tri- O -acetyl-6- O -benzyl-β- d -galactopyranoside (Acetylated 22)
¹H NMR (500 MHz, CDCl3): δ = 7.25-7.17 (m, 5 H, ArH), 6.87 (d, J = 9.0 Hz, 2 H, ArH), 6.70 (d, J = 9.0 Hz, 2 H, ArH), 5.40 (d, J = 3.3 Hz, 1 H, H-4), 5.31 (dd, J = 7.9 Hz each, 1 H, H-2), 4.99 (dd, J = 10.4, 3.4 Hz, 1 H, H-3), 4.83 (d, J = 7.9 Hz, 1 H, H-1), 4.48 (d, J = 11.9 Hz, 1 H, PhCH2a), 4.36 (d, J = 11.9 Hz, 1 H, PhCH2b), 3.87-3.84 (m, 1 H, H-5), 3.68 (s, 3 H, OCH3), 3.52-3.44 (m, 2 H, H-6a,b), 2.01, 1.99, 1.93 (3 s, 9 H, 3 COCH3). ¹³C NMR (125 MHz, CDCl3): δ = 170.3, 170.1, 169.5 (3 COCH3), 156.0-114.9 (ArC), 101.1 (C-1), 73.9, 72.9, 71.5, 69.4, 67.9, 67.8, 55.8, 21.1, 21.0, 20.9 (3 COCH3). ESI-MS (C26H30O10): m/z = 525.1 [M + Na]+.
Phenyl 2,3,4-Tri- O -acetyl-6- O -benzyl-1-seleno-β-d-glucopyranoside (Acetylated 25) ¹H NMR (500 MHz, CDCl3): δ = 7.59-7.21 (m, 10 H, ArH), 5.15 (t, J = 9.2 Hz, 1 H, H-3), 5.01 (t, J = 9.8 Hz, 1 H, H-2), 4.97 (t, J = 9.2 Hz, 1 H, H-4), 4.88 (d, J = 9.9 Hz, 1 H, H-1), 4.53-4.46 (2 d, J = 11.8 Hz, 2 H, PhCH2), 3.67-3.63 (m, 1 H, H-5), 3.56-3.54 (m, 2 H, H-6a,b), 2.14, 2.05, 1.96 (3 s, 9 H, 3 COCH3). ¹³C NMR (125 MHz, CDCl3): δ = 170.4, 169.6, 169.4 (3 COCH3), 138.2-127.6 (ArC), 81.4 (C-1), 78.9, 74.4, 73.9, 71.3, 69.4 (2 C), 21.1, 20.9 (2 C) (3 COCH3). ESI-MS (C25H28O8Se): m/z = 559.1 [M + Na]+.
Methyl (2,3,4-Tri- O -acetyl-6- O -benzyl-β-d-glucopyranosyl)-(1→6)-2,3,4-tri- O -acetyl-α-d-glucopyranoside (Acetylated 26)
¹H NMR (500 MHz, CDCl3): δ = 7.33-7.24 (m, 5 H, ArH), 5.43 (t, J = 10.0 Hz each, 1 H, H-3A), 5.16 (t, J = 9.4 Hz each, 1 H, H-4A), 5.03 (t, J = 9.5 Hz each, 1 H, H-3B), 4.96 (dd, J = 7.9 Hz each, 1 H, H-2B), 4.90 (t, J = 9.4 Hz each, 1 H, H-4B), 4.88 (d, J = 3.6 Hz, 1 H, H-1A), 4.82 (dd, J = 10.1, 3.6 Hz, 1 H, H-2A), 4.55 (d, J = 11.9 Hz, 1 H, PhCH2a), 4.52 (d, J = 7.9 Hz, 1 H, H-1B), 4.48 (d, J = 11.9 Hz, 1 H, PhCH2b), 3.94-3.89 (m, 2 H, H-6abA), 3.65-3.61 (m, 1 H, H-5B), 3.55-3.51 (m, 3 H, H-5A, H-6a,bB), 3.37 (s, 3 H, OCH3), 2.06, 2.03, 1.98, 1.89 (4 s, 18 H, 6 COCH3). ¹³C NMR (125 MHz, CDCl3): δ = 170.4, 170.1, 170.0, 169.7, 169.6, 169.4 (6 COCH3), 137.9-128.1 (ArC), 101.2 (C-1B), 96.8 (C-1A), 73.9, 73.7, 73.3, 71.6, 71.2, 70.6, 69.7, 69.4, 69.2, 68.5, 68.3, 55.5 (OCH3), 21.1 (2 C), 21.0 (2 C), 20.9 (2 C). ESI-MS (C30H40O16): m/z = 679.2 [M + Na]+.