Stereoselectivity of reactions at the glycoside center of carbohydrates: VII. Synthesis of aryl α- and -β-D-glucopyranosides by Helferich, catalyzed by boron trifluoride etherate

Article abstract of DOI:10.1023/A:1019532924135

¹³C NMR spectroscopy was used to study the stereoselectivity of glycosylation of phenols with the α and β anomers of penta-O-acetyl-D-glucopyranose, penta-O-trifluoroacetyl-D-glucopyranose, and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-D-glucopyranose in the presence of boron trifluoride etherate at varied temperature, time, and catalyst amount. The boron trifluoride etherate-catalyzed reaction of penta-O-acetyl-β -D-glucopyranose and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-β -D-glucopyranose with phenols occurs with a high stereocontrol to give, depending on conditions, predominantly 1,2-cis- or 1,2-trans-aryl-glycosides. This reaction can be used for preparative synthesis of the α- and β-anomeric forms of glycosides of a wide range of phenols.

Full text of DOI:10.1023/A:1019532924135

Russian Journal of General Chemistry, Vol. 72, No. 5, 2002, pp. 806 811. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 5, 2002,
pp. 863 868.
Original Russian Text Copyright
2002 by Sokolov, Zakharov, Studentsov.
Stereoselectivity of Reactions
at the Glycoside Center of Carbohydrates:
VII.1 Synthesis of Aryl - and - -D-Glucopyranosides
by Helferich, Catalyzed by Boron Trifluoride Etherate
V. M. Sokolov, V. I. Zakharov, and E. P. Studentsov
St. Petersburg State Institute of Technology, St. Petersburg, Russia
Received May 22, 2000
Abstract 13C NMR spectroscopy was used to study the stereoselectivity of glycosylation of phenols with
the
and
anomers of penta-O-acetyl-D-glucopyranose, penta-O-trifluoroacetyl-D-glucopyranose, and
2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-D-glucopyranose in the presence of boron trifluoride etherate at
varied temperature, time, and catalyst amount. The boron trifluoride etherate catalyzed reaction of penta-O-
acetyl- -D-glucopyranose and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl- -D-glucopyranose with phenols
occurs with a high stereocontrol to give, depending on conditions, predominantly 1,2-cis- or 1,2-trans-aryl-
glycosides. This reaction can be used for preparative synthesis of the - and -anomeric forms of glycosides
of a wide range of phenols.
Phenol glycosides are conveniently prepared by
the Helferich method that involves the acid-catalyzed
orthophosphoric acid [7], etc. The excess of phenols
can be much cut down by boiling the reagents in an
reaction of full saccharide acetates with phenols [2], inert solvent in the presence of phosphorus oxy-
yielding a mixture of 1,2-trans- and 1,2-cis-glycosides
and anomers), which is separated by fractional
chloride [8], anisole boron trifluoride complex [9], or
tin chloride [10] as catalysts.
(
crystallization or chromatographic methods.
We earlier studied the stereoselectivity of glycosyla-
tion of phenols with full D-glucopyranoside acetates
in various conditions [11]. By spectral data we deter-
mined the contents and ratios of the and anomers
of arylglycosides in the reaction products and for-
mulated principal regularities. In the present work we
studied the boron trifluoride etherate catalyzed glyco-
AcO
R1
O
AcO
+ ArOH
R2
AcO
AcO
, -I
sylation of phenols with the
and
anomers of
AcO
AcO
AcO
penta-O-acetyl-D-glucopyranose - and -I, penta-O-
trifluoroacetyl-D-glucopyranose - and -III, and
2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-D-gluco-
pyranose - and -IV.
OAr
O
AcO
O
Cat
AcOH
AcO
and/or
OAr
AcO
-II
AcO
AcO
-II
The conversions of starting materials and the com-
positions of arylglycosides were determined by the
intensities of signals of anomeric carbon atoms in the
13C NMR spectra as described in [11].
R1 = H, R2 = OAc ( -I); R1 = OAc, R2 = H ( -I).
Preliminary experiments with varied reagent con-
centrations and ratios, catalysts, and reaction tempera-
tures and times showed that phenol is easily glyco-
sylated with acetate -I in an inert organic solvent,
such as benzene or methylene chloride, even at room
temperature in the presence of a small excess of
phenol and a catalyst (0.1 0.2 mol) to give predo-
minantly phenyl tetra-O-acetyl- -D-glucopyranoside
The reaction can be accomplished by melting the
reagents in a 4 6-fold excess of phenols at 110 140 C
using as catalysts p-toluenesulfonic acid or zinc
chloride [3], sulfuric acid [4], aluminum chloride [5],
polyphosphoric acid or its ethyl ester [6], anhydrous
1
For communication VI, see [1].
1070-3632/02/7205-0806$27.00 2002 MAIK Nauka/Interperiodica

STEREOSELECTIVITY OF REACTIONS AT THE GLYCOSIDE CENTER OF CARBOHYDRATES: VII. 807
Table 1. Stereoisomeric composition of products of boron trifluoride etherate-catalyzed glycosylation of phenols with
1,2,3,4,6-penta-O-acetyl- -D-glucopyranose ( -I)a
Total
content
of - and cosides (II) in
-glycosides
Ratio of
and -gly-
-
Conversion
of acetate
( -I),
Content of
other
components,
%
Catalyst
amount,
mol
Reaction
time,
h
Exp.
no.
Compound
reaction
products, %
%
(II), %
1
2
3
4
5
6
7
8
9
Phenol
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.5
0.5
0.5
0.1
0.2
0.2
1
1
1
1
1
1
1
1
1
1
1
1
1
2
24
48
25
46
53
86
89
92
93
92
98
100
68
100
92
96
96
87
0
68
97
25
46
53
86
89
92
93
82
82
82
68
100
92
76
76
87
0
0/100
0/100
0/100
0/100
0/100
5/95
8/92
8/92
15/85
22/78
0/100
8/92
-I, 75
-I, 54
-I, 47
-I, 14
-I, 11
-I, 8
-I, 7
-I, 14; -I, 4
-I, 16; -I, 2
-I, 18
70
115
144b
190
48
96
120
48
48
48
48
96
48
48
48
48
96
190
48
4-Methylphenol
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
2-Methoxyphenol
4-Methoxyphenol
4-Hexyloxyphenol
3-Methylphenol
-I, 32
9/91
-I, 8
15/85
24/76
13/87
-I, 20; -I, 4
-I, 20; -I, 4
-I, 13
-I, 100
-I, 32
-I, 24; -I, 3
-I, 27; -I, 3
-I, 17
-I, 24; -I, 3
-I, 29; -I, 7
-I, 30; -I, 4
6c
3,4-Dimethylphenol
3-Diethylaminophenol
3-Chlorophenol
68
71
74
83
3
0/100
16/84
32/68
42/58
0/100
0/100
0/100
75/25
89/11
88/12
54/46
85/15
83/17
85/15
83/17
88/12
86/14
29/71
63/37
100/0
97
100
27
33
36
4-Nitrophenol
Phenol
190b
285
0.167
0.5
1
4
6
100
100
100
100
100
100
100
100
100
100
100
100
100
94
100
93
75
92
94
100
74
81
84
66
95
18
7c
-I, 12; 13c
-I, 8
4-Methoxyphenol
0.25
0.5
1
1.5
0.5
1
1.5
0.5
1
-I, 6
4-Methylphenol
-I, 26
-I, 6; 13c
-I, 4; 12c
-I, 34
3-Chlorophenol
4-Nitrophenol
-I, 5
-I, 82
1
a
Exp. nos. 1 24 were performed at room temperature and with excess phenol (0.1 mol); exp. nos. 25 37 were performed by boiling
b
c
reactants in benzene with excess phenol (2 mol).
Additional amount of catalyst was added.
Unidentified admixtures.
( -II). According to spectral data, the conversion of
-I increases with increasing reaction time and
reaches 86% after 70 h (Table 1, exp. nos. 1 4). The
an yield of 70% by fractional crystallization from
ethanol. Longer reaction times (115, 144, and 190 h)
and double catalyst concetration increased the con-
reaction occurs stereoselectively with exclusive forma- version of acetate -I by only 3 6% (exp. nos. 5 7).
tion of -II. The product was isolated individual in The above reagent:catalyst ratio appears to be close to
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 5 2002

808
SOKOLOV et al.
Table 2. Ratios of the and forms of acetylated aryl
glucopyranosides - and -II in products of anomerization
of aryl tetra-O-acetyl- -D-glucopyranosides -II in the
presence of boron trifluoride etherate at various reaction
times (%/%)
sides II is as low as 6% even after 285 h, while most
pentaacetate -I undergoes anomerization to -I
(exp. nos. 22 24).
If glycosylation of phenols with pentaacetate -I is
performed with an equimolar catalyst amount under
reflux in benzene, the starting acetate almost com-
pletely converts into glycosides -II and -II already
within 15 30 min (exp. nos. 25 37). Therewith, the
fraction of -II increases with increasing reaction
/
Ratio
Initial
glycoside
5 min 15 min 0.5 h 1 h 1.5 h
12/88 29/71 30/70 72/28 89/11
time. Table 2 lists the the ratios of the
and
Phenyl tetra-O-
acetyl- -D-glu-
copyranoside
anomers obtained by anomerization of phenyl 2,3,4,6-
tetra-O-acetyl- -D-glucopyranoside, 4-methylphenyl
2,3,4,6-tetra-O-acetyl- -D-glucopyranoside, and
4-chlorophenyl 2,3,4,6-tetra-O-acetyl- -D-gluco-
pyranoside under reflux in benzene at a glycoside
phenol etherate ratio of 1:1.1:1. These data provide
evidence showing that boron trifluoride etherate
induces anomerization, and this property can be used
for preparative synthesis of aryl tetra-O-acetyl- -D-
4-Methylphenyl- 25/75
tetra-O-acetyl-
-D-gluco-
45/55
30/70
75/25
64/36
pyranoside
4-Chlorophenyl-
tetra-O-acetyl- -
D-glucopyrano-
side
6/94
glucopyranosides from corresponding
isomers.
As known, the stereisomeric composition of glyco-
sylation products is much dependent on the type of
protective groups in the carbohydrate moiety of the
molecule. Therewith, protective groups that take no
part in the reaction are considered to favor 1,2-cis-
glycoside formation [12]. We studied the stereoiso-
optimum, since using 0.5 mol of boron trifluoride
etherate per 1 mol of acetate -I increases the fraction
of glycoside -II, apparently because of anomeriza-
tion of the primarily formed -arylglycoside -II
(exp. nos. 6 and 7). Increased reaction temperature meric composition of products of phenol glycosyla-
and time produce the same effect.
tion with 1-O-trifluoroacetyl-2,3,4,6-tetra-O-acetyl- -
D-glucopyranose ( -IV) and of 4-metoxyphenol with
1,2,3,4,6-penta-O-trifluoroacetyl- -D-glucopyranose
( -III). At room temperature in the presence of
catalytic amounts of boron trifluoride etherate, the
conversions of -IV and -III into and glycosides
after 48 h were as low as 11 and 8%, respectively
(Table 3, exp. nos. 1 2), while the most part of the
starting acetates converted into the poorly reactive
anomers ( -IV and -III) which, according to our
experimental findings, fail to enter the phenol glyco-
Unlike acetate
-I, penta-O-acetyl- -D-gluco-
pyranose ( -I) failed to react with phenol under these
conditions and was almost completely recovered from
the reaction mixture.
Analysis of the 13C NMR spectra of the reaction
mixtures obtained by glycosylation of substituted
phenols with pentaacetate -I showed that electron-
donor substituents in the aromatic ring accelerate the
reaction, and the conversion of the starting acetate -I
reaches 76 100% already within 48 h (exp. nos. 8 16). sylation reaction.
Unlike the other phenols with electron-donor sub-
If the reaction of trifluoroacetate -IV with phenol
stituents, 3-diethylaminophenol fails to enter the
glycosylation reaction, and from the reaction mixture
we quantitatively recovered the starting pentaacetate
-I (exp. no. 17).
is performed at the boiling point of the solvent with a
stoichiometric amount of the catalyst, complete con-
version of -IV into - and -glycosides occurs
within 5 min; therewith, the fraction of -II increases
with increasing reaction time (exp. nos. 3 8). Under
these conditions, both -IV and -III fail to react
with phenol.
The example of the reaction of 2-methoxyphenol
with acetate -I was used to show that ortho substi-
tuents in the aromatic ring decrease the conversion of
acetate -I, probably, by steric reasons (exp. no. 11).
Pentaacetate -I and its 1-O-trifluroacetyl deri-
vative -IV similarly react with phenols containing
electron-donor substituents. The major products of
these reactions are 1,2-cis-arylglycosides whose frac-
tions in the reaction mixtures attain 85% and more
(Table 1, exp. nos. 28 34, Table 3, exp. nos. 9 11).
Electron-acceptor substituents in the aromatic ring
adversely affect the activity of phenols in the glyco-
sylation reaction and increase the fractions of glyco-
side -II and acetate -I. 4-Nitrophenol is poorly
reactive, the conversion of pentaacetate -I into glyco-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 5 2002

STEREOSELECTIVITY OF REACTIONS AT THE GLYCOSIDE CENTER OF CARBOHYDRATES: VII. 809
Table 3. Stereoisomeric composition of products of boron trifluoride etherate catalyzed glycosylation of phenols with
1-O-trifluoroacetyl-2,3,4,6-tetra-O-acetyl- -D-glucopyranose ( -IV) and 1,2,3,4,6-penta-O-trifluoroacetyl- -D-gluco-
pyranose ( -III)a
Total
Ratio of
- and -
glycosides
Content of
other
components,
%
Starting
trifluoro-
acetate
Catalyst
amount,
mol
Reaction
time,
h
Conversion content of
Exp.
no.
Compound
of acetate
- and
-I, %
-glycosides, in reaction
%
products, %
1
2
3
4
5
6
7
8
9
10
11
12
13
-IV
-III
-IV
-IV
-IV
-IV
-IV
-IV
-IV
-IV
-IV
-IV
-IV
Phenol
4-Methoxyphenol
Phenol
0.1
0.1
0.2
1
1
1
1
1
1
1
48
48
1
0.08
0.25
0.5
1
1.5
1
1
86
66
11
8
63
100/0
100/0
12/88
26/74
47/53
59/41
93/7
100/0
85/15
89/11
89/11
75/25
65/35
-IV, 75
-III, 58
37b
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
4-Methylphenol
3-Methylphenol
4-Methoxyphenol
4-Chlorophenol
4-Nitrophenol
1
1
1
1
1
1
a
Exp. nos. 1 and 2 were performed at room temperature and with excess phenol (0.1 mol); exp. nos. 3 13 were performed by boiling
b
reactants in benzene with excess phenol (2 mol).
Unidentified admixtures.
With 4-chlorophenol, the fraction of a 1,2-cis-aryl-
glycoside in the reaction products is much reduced
(Table 1, exp. nos. 35 36, Table 3, exp. no. 12). The
greatest difference in the reactivity of pentaacetate -I
and trifluoroacetate -IV is observed in the glycosyla-
tion of 4-nitrophenol. Unlike pentaacetate -I, tri-
fluoroacetate -IV readily reacts with 4-nitrophenol
in similar conditions, and the fraction of a 1,2-cis-
glycoside in the reaction mixture attains 65%
(Table 3, exp. no. 13).
The results obtained for phenol glycosylation with
compounds -I and -IV were used to prepare a series
of aryl tetra-O-acetyl- - and - -glucopyranosides in
good yields (Table 4). The purity and structure of the
resulting compounds were confirmed by their
elemental analyses, optical rotations, and 13C NMR
spectra (Tables 4, 5).
Table 4. Aryl tetra-O-acetyl- - and - -D-glucopyranosides - and -II
Method of
Found, %
Calculated, %
mp,
C
[ ]2D0,
deg (c 1,
synthesisa, Yield,
Compound
Formula
reaction
time, h
%
(ethanol) CHCl3)
C
H
C
H
Phenyl tetra-O-acetyl- -
D-glucopyranoside ( -IIa)
3-Methylphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIb)
A, 115
A, 48
70
62
125 126
136 136
22
20
56.40
57.80
5.59 C20H24O10
5.75 C21H26O10
56.60
57.53
5.70
5.97
4-Methylphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIc)
4-Methoxyphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IId)
A, 48
A, 48
54
68
95 97
90 92
10
14
57.40
55.38
5.77 C21H26O10
5.54 C21H26O11
57.53
55.50
5.97
5.76
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 5 2002

810
SOKOLOV et al.
Table 4. (Contd.)
Method of
Found, %
Calculated, %
mp,
C
[ ]2D0,
deg (c 1,
synthesisa, Yield,
Compound
Formula
reaction
time, h
%
58
58
(ethanol) CHCl3)
C
H
C
H
2-Methoxyphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIe)
3-Chlorophenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIf)
A, 48
A, 48
154 155
133 134
21
25
55.20
5.59 C21H26O11
55.50
5.76
51.92
5.15 C20H23ClO10 52.35
5.05
Phenyl tetra-O-acetyl- -
D-glucopyranoside ( -IIa)
3-Methylphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIb)
B, 1
C, 1
C, 1
70
76
63
112 114
158 160
+170
+178
55.70
58.00
5.00 C20H24O10
6.10 C21H26O10
56.60
57.53
5.70
5.97
4-Methylphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIc)
4-Methoxyphenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IId)
4-Chlorophenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIg)
4-Nitrophenyl tetra-O-
acetyl- -D-glucopyrano-
side ( -IIh)
C, 1
60
188 190
144 145
100 102
108 110
+182
+159
+169
+170
57.60
55.90
53.18
52.18
6.00 C21H26O10
5.90 C21H26O11
57.53
55.50
5.97
5.76
5.05
4.93
B, 1
C, 1
68
64
C, 1
C, 1
50
43
5.86 C20H23ClO10 52.35
4.94 C20H23NO12
51.17
a
(A) Reaction of pentaacetate -I with phenols at room temperature; (B) boiling of pentaacetate -I with phenols in a benzene
solution; and (C) boiling of 1-O-trifluoroacetate -IV with phenols in a benzene solution.
Table 5. 13C NMR spectra of aryl tetra-O-acetyl- - and - -D-glucopyranosides, C, ppm
Com-
pound
no.
Carbohydrate component
Other carbon atoms
C1
C2
C3
C4
C5
C6
-IIa
-IIb
-IIc
98.9 71.0 71.8
99.0 71.1 71.8
99.5 71.2 71.9
68.2
68.3
68.3
68.4
67.9
72.5
72.7
72.7
72.6
70.0
61.8 156.7, 116.8, 129.3, 123.1, 129.3, 116.8 (Ara); 20.3 (CH3CO);
168.9, 169.1, 169.8, 170.1 (CO)
62.0 156.8, 117.7, 139.3, 124.0, 129.5, 113.7 (Ar); 21.3 (CH3); 20.4
(CH3CO); 169.2, 169.3, 170.1, 170.4 (CO)
61.9 154.8, 117.0, 129.9, 132.8, 129.9, 117.0 (Ar); 20.4 (CH3); 20.4
(CH3CO); 169.2, 170.1, 170.5 (CO)
61.9 146.1, 150.6, 112.9, 124.5, 120.7, 120.1 (Ar); 55.9 (CH3O);
20.4 (CH3CO); 169.1, 169.2, 169.8, 170.1, 170.3 (CO)
61.5 156.0, 116.6, 129.5, 123.0, 129.5, 116.6 (Ar); 20.4 (CH3CO);
169.4, 169.9, 170.3 (CO)
-IIe 100.6 71.2 71.8
-IIa 94.2 68.3 70.4
a
1
2
3
4
5
6
Signals of phenyl C , C , C , C , C , and C , respectively.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 5 2002

STEREOSELECTIVITY OF REACTIONS AT THE GLYCOSIDE CENTER OF CARBOHYDRATES: VII. 811
EXPERIMENTAL
responding phenol, and 1.3 ml of boron trifluoride
etherate in 25 ml of dry benzene in moisture-proof
conditions. After a time, the solution was cooled,
diluted with benzene, treated as described above, and
the residue was analyzed by 13C NMR spectroscopy.
The 13C NMR spectra of acetylated and trifluoro-
acetylated derivatives were recorded for 50% solutions
in CDCl3 on a Varian CFT-20 spectrometer against
internal TMS. The rotation angles of arylglycosides
in chloroform were measured on an SU-3 universal
saccharimeter at 20 C.
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penta-O-trifluoroacetates - or -III in 100 ml of dry
benzene we added 33 mmol of corresponding phenol,
0.4 ml of boron trifluoride etherate ( 3 mmol), and
the reaction mixture was left to stand at room tempera-
ture. After a time, the reaction was terminated by dilu-
tion of the reaction mixture with 100 ml of benzene.
The benzene solution was washed with water (1
100 ml), 1 N sodium hydroxide (2 50 ml), and water
to neutral washings, dried with sodium sulfate, and
evaporated in a vacuum at a bath temperature not
higher than 50 C. The syrup-like residue was
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In a preparative experiment, aryl tetra-O-acetyl- -
D-glucopyranosides -II were isolated by crystalliza-
tion of the syrup-like residue from hot ethanol and
dried in a vacuum at 75 80 C.
8. Bembry, T.H. and Powell, G., J. Am. Chem. Soc.,
1942, vol. 64, no. 10, p. 2418.
9. Bretschneider, H. and Beran, K., Monatsh. Chem.,
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b. To a solution of 30 mol of penta-O-acetyl- - or
- -D-glucopyranosides - or -I, 1-O-trifluoroacetate
- or -IV, or penta-O-trifluoroacetate - or -III in
70 ml of dry benzene we added 33 ml ( 30 mmol) of
corresponding phenol. The reaction mixture was
refluxed for 1 h in moisture-proof conditions and then
treated as described above.
10. Audichya, T.D., Ingle, T.R., and Bose, J.L., Indian J.
Chem., 1971, vol. 9, no. 4, p. 315.
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nov, M.A., Zakharov, V.I., and Sochilin, E.G., Zh.
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Obrazovanie i rasshcheplenie glikozidnykh svyazei
(Formation and Cleavage of Glycoside Bonds),
Moscow: Nauka, 1978.
Anomerization of acetylated aryl -D-gluco-
pyranosides. A solution of 10 mmol of aryl tetra-O-
acetyl- -D-glucopyranoside -II, 1.1 mmol of cor-
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