Ytterbium(III) tris[bis(perfluorobutylsulfonyl)amide] as a Lewis acid for glycosidations

Article abstract of DOI:10.1081/SCC-100103325

The reaction of 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl acetate with alcohols in the presence of 5 mol% ytterbium(III) tris[bis(perfluorobutylsulfonyl)amide] as an activator afforded the corresponding glucopyranosides in good yields. This ytterbium complex also activated the benzylated glucosyl donors having trichloroacetoimidate, fluoride, and methoxyacetate as the leaving groups.

Full text of DOI:10.1081/SCC-100103325

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YTTERBIUM(III)
TRIS[BIS(PERFLUORO-
BUTYLSULFONYL)AMIDE]
AS A LEWIS ACID FOR
GLYCOSIDATIONS
Takashi Yamanoi a , Sonoe Nagayama a , Hide-ki
Ishida a , Joji Nishikido a & Toshiyuki Inazu b
a The Noguchi Institute , 1-8-1, Kaga, Itabashi-ku,
Tokyo, 173-0003, Japan
b The Noguchi Institute , 1-8-1, Kaga, Itabashi-ku,
Tokyo, 173-0003, Japan
Published online: 09 Nov 2006.
To cite this article: Takashi Yamanoi , Sonoe Nagayama , Hide-ki Ishida ,
Joji Nishikido & Toshiyuki Inazu (2001) YTTERBIUM(III) TRIS[BIS(PERFLUORO-
BUTYLSULFONYL)AMIDE] AS A LEWIS ACID FOR GLYCOSIDATIONS, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 31:6, 899-903, DOI: 10.1081/SCC-100103325
To link to this article: http://dx.doi.org/10.1081/SCC-100103325
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SYNTHETIC COMMUNICATIONS, 31(6), 899–903 (2001)
YTTERBIUM(III) TRIS[BIS(PERFLUORO-
BUTYLSULFONYL)AMIDE] AS A LEWIS
ACID FOR GLYCOSIDATIONS
Takashi Yamanoi,* Sonoe Nagayama, Hide-ki Ishida,
Joji Nishikido, and Toshiyuki Inazu*
The Noguchi Institute, 1-8-1, Kaga, Itabashi-ku,
Tokyo 173-0003, Japan
ABSTRACT
The reaction of 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl
acetate with alcohols in the presence of 5 mol% ytterbium(III)
tris[bis(perfluorobutylsulfonyl)amide] as an activator afforded
the corresponding glucopyranosides in good yields. This ytter-
bium complex also activated the benzylated glucosyl donors
having trichloroacetoimidate, fluoride, and methoxyacetate as
the leaving groups.
Glycosidation is a significant method for synthesizing glycosides and
oligosaccharides related to natural products and their analogs for the inves-
tigation of their biological functions.1 Most of the known glycosidation
methods are based on the activation of a leaving group of a glycosyl
donor.2 Lewis acids are widely used as an activator of a leaving group,
and in synthetic carbohydrate chemistry, it is very important to develop a
new Lewis acid for glycosidation methods.
* Corresponding author.
899
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

900
YAMANOI ET AL.
Trifluoromethanesulfonic acid (TfOH) shows strong Brꢀnstead
acidity due to the effect of the powerful electron-withdrawing trifluoro-
methanesulfonyl (Tf ) group, and their metal complexes [M(OTf )n)], whose
bonds between metals and OTf are very weak, indicate high Lewis
acidity. They are used as efficient Lewis acids for organic reactions in
many research studies.3 More interest has been concentrated on the
stronger Lewis acids provided by the perfluoroalkylsulfonyl (Rf ) groups
having long alkyl chains and/or by amine replaced by two Rf groups.
The metal complexes, M(ORf )n and M[N(ORf )2]n, have been employed
as versatile catalysts in organic reactions such as the Diels-Alder
reaction, Friedel-Craft acylation, and esterification.4–7 Mikami et al.
have reported that ytterbium(III) tris[bis(perfluorobutylsulfonyl)amide]
{Yb[N(O2SC4F9)2]3} (YTA) catalyzed these reactions more efficiently
than Yb(OTf )3.8,9
The recent studies by us and other groups showed that 1-O-acyl
sugars as glycosyl donors are useful because they are stable and easy to
prepare.10–13 However, some of them are difficult to activate, and it was
reported that 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl acetate (1) was not
easily activated by lanthanide trifluoromethanesulfonates.14 As part of our
continuous study of glycosidation, we utilized YTA as the Lewis acid for the
glycosidation of 1 and other glycosyl donors.
First of all, based on the property of the strong affinity of YTA for
carbonyl groups, we investigated the reaction between 1 and n-octanol in
CH2Cl2. The effect of amounts of YTA was examined. This glycosidation
proceeded in the presence of a catalytic amount of YTA. The reaction con-
ditions using only 5 mol% YTA afforded the corresponding glucoside in
71% yield with the stereoselectivity of an ꢁ/ꢂ ratio of 33/67. However, the
reaction condition using less than 5 mol% YTA reduced the yields of the
glucoside.
Secondly, the effect of solvents was examined using CH2Cl2,
CH3CN, PhH, hexafluorobenzene, and Et2O. Although the reaction using
CH2Cl2 gave the glucoside in good yield, the other solvents, except for
CH2Cl2 were not suitable for this glycosidation. YTA was relatively
soluble in CH2Cl2 but was almost insoluble in the other solvents. The
solubilities of YTA were apparently important for the process of this
glycosidation.
Thirdly, the effect of drying agents was examined using molecular
sieves (MS) 4A, CaSO4, Na2SO4, and MgSO4. The reaction using MS 4A
gave no glucoside at all because the basic component of MS 4A could reduce
the acidity of YTA. The corresponding glucoside was obtained in 81%
yield with an ꢁ/ꢂ ratio of 72/28 by the reaction using CaSO4.
Interestingly, the addition of CaSO4 changed the stereoselectivity of this

LEWIS ACID FOR GLYCOSIDATIONS
901
Table 1. Glycosidation Using 5 mol% Yb[N(O2SC4F9)2]3
Entrya
X
ROH
Drying Agent
Yield/%
ꢀ/ꢁ
1b
2c
3
4OAc
5
6
7
8
9
10
11
12
13
OAc
OAc
OAc
n-Octanol
n-Octanol
n-Octanol
n-Octanol
n-Octanol
n-Octanol
n-Octanol
5
none
none
none
MS 4A
CaSO4
Na2SO4
MgSO4
none
none
none
none
none
none
12
58
29/71
27/73
7431/69
no reaction
—
OAc
OAc
OAc
81
22
79
68
72/28
18/82
32/68
49/51
54/46
OAc
OC(O)CH2OCH3
F
5
69
n-Octanol
5
n-Octanol
5
6468/32
69
69
F
63/37
31/69
44/56
OC(NH)CCl3
OC(NH)CCl3
50
aMolar ratio Donor: ROH¼1:1.
b3 mol% Yb[N(O2SC4F9)2]3 was used.
c4mol% Yb[N(O SC4F9)2]3 was used.
2
glycosidation compared with the additions of other metal sulfates or none.
In this glycosidation system, it seemed that the complex between ca2þ and
the glycosyl intermediate played an important role in the appearance of the
ꢁ-stereoselectivity.
Finally, we used YTA in the glycosidations using several glycosyl
donors. As the glycosyl donors, 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl
methoxyacetate (2), 2,3,4,6-tetra-O-benzyl-ꢁ-D-glucopyranosyl trichloroace-
toimidate (3), and 2,3,4,6-tetra-O-benzyl-ꢂ-D-glucopyranosyl fluoride (4)
were used. The reactions of these glycosyl donors with n-octanol or
methyl 2,3,4-tri-O-benzyl-ꢂ-D-glucopyranoside (5) afforded the correspond-
ing glucosides in satisfactory yields. The reaction using 2 and 4 gave the ꢁ-
glucosides predominantly,15,16 and on the other hand, the ꢂ-glucosides were
obtained by the reactions using 1 and 3. We found that the stereoselectivities
of glucosides were also interestingly changed by the species of the leaving
groups of the glycosyl donors.

902
YAMANOI ET AL.
As mentioned above, we found that YTA is useful as an activator of
the benzylated glycosyl donors having acetate, methoxyacetate, fluoride,
and trichloroacetoimidate as the leaving groups and that, in some cases,
the stereoselectivities of the glycosidation were influenced by the species of
the leaving group of the glycosyl donor and the effect of the metal ion of the
drying agent.
EXPERIMENTAL
1H NMR and 13C NMR spectra were recorded on JEOL EX-400
spectrometers with tetramethylsilane as the internal standard in CDCl3.
General Procedure
To a solution of glycosyl acetate (0.2 mmol) and alcohol (0.2 mmol) in
CH2Cl2 (4mL) was added YTA (0.01 mmol). The resulting mixture was
stirred overnight. The reaction was then quenched with sat. NaHCO3
solution (5 mL). The mixture was extracted with CHCl3, and the organic
layer was washed with water and sat. NaCl solution. After the organic layer
was dried over Na2SO4, the solvent was evaporated under reduced pressure.
The crude product was purified by a preparative silica gel TLC to give the
corresponding glucoside.
n-Octyl 2,3,4,6-tetra-O-benzyl-ꢁ and ꢂ-D-glucopyranoside
13C NMR ꢃ ¼ 103.54(C-1 ꢂ), 96.78 (C-1ꢁ); 1H NMR ꢃ ¼ 4.75 (d, H-1ꢁ,
J ¼ 3.2 Hz), 4.39 (d, H-1ꢂ, J ¼ 8.0 Hz).
Methyl 6-O-(2,3,4,6-tri-O-benzyl-D-glucopyranosyl)-2,3,4,-tri-O-ben-
zyl-ꢁ and ꢂ-D-glucopyranoside
13C NMR ꢃ ¼ 103.70 (C-10ꢂ), 97.94(C-1 ꢂ), 97.85 (C-1ꢁ), 97.15 (C-10ꢁ);
1H NMR ꢃ ¼ 3.35 (s, OMeꢁ), 3.33 (s, OMeꢂ).
ACKNOWLEDGMENTS
We are deeply indebted to Professor Teruaki Mukaiyama, Science
University of Tokyo, for his helpful discussions.

LEWIS ACID FOR GLYCOSIDATIONS
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Received in Japan April 19, 2000