Synthesis of alkyl and aryl C-pyranosides using organozinc reagents via a Ferrier-type rearrangement

Article abstract of DOI:10.1016/j.carres.2004.11.012

The reaction of 1,2-dihydropyranyl acetates with dimethylzinc, diethylzinc and diphenylzinc in the presence of CF₃COOH gave the corresponding alky and aryl C-pyranosides via a Ferrier rearrangement in excellent yields. Use of the organozinc species, CF₃CO₂ZnPh, reacted with high stereoselectivity to give the phenyl C-glycosides. Arylzinc chlorides could also be successfully applied to this reaction in the presence of BF ₃?OEt₂.

Full text of DOI:10.1016/j.carres.2004.11.012

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 303–307
Note
Synthesis of alkyl and aryl C-pyranosides using organozinc
reagents via a Ferrier-type rearrangement
Song Xue,* Lin He, Kai-Zhen Han, Xiao-Qi Zheng and Qing-Xiang Guo
Department of Chemistry, University of Science and Technology of China, Hefei 230026, PR China
Received 29 June 2004; accepted 13 November 2004
Available online 18 December 2004
Abstract—The reaction of 1,2-dihydropyranyl acetates with dimethylzinc, diethylzinc and diphenylzinc in the presence of
CF3COOH gave the corresponding alky and aryl C-pyranosides via a Ferrier rearrangement in excellent yields. Use of the organo-
zinc species, CF3CO2ZnPh, reacted with high stereoselectivity to give the phenyl C-glycosides. Arylzinc chlorides could also be suc-
cessfully applied to this reaction in the presence of BF3ÆOEt2.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Organozinc reagents; Alkyl and aryl C-pyranosides; Ferrier rearrangement
Alkyl and aryl C-pyranosides are valuable synthetic
intermediates that can be further functionalized for the
preparation of structural units present in many natural
biologically active products.1 Lewis acid-mediated Fer-
rier rearrangement of glycals with carbon nucleophiles,
such as allyltrimethylsilane,2 olefins,3 or silyl enol
ethers,4 is widely employed to obtain 2,3-unsaturated
C-glycosides in good to excellent yields. Organozinc re-
agents, which can tolerate a broad range of functional-
ities,5 can be made to react with per-O-acetyl-D-glucal
in the presence of BF3ÆOEt2,6 TMSOTf7 and ZnCl2.8
These reactions afford moderate to good yields of C-gly-
cosides preferring a-anomeric selectivity (2–10:1). Here-
in, we wish to report our preliminary results regarding
the addition of organozinc reagents to 1,2-dihydropyran-
yl acetates for the synthesis of alkyl and aryl C-
pyranosides.
The organozinc reagent, CF3CO2ZnEt, can be readily
prepared by stirring ZnEt2 with CF3COOH in CH2Cl2
at 0 ꢁC for 30 min. Treatment of 3,4,6-tri-O-acetyl-D-glu-
cal (1) with the in situ generated CF3CO2ZnEt in
CH2Cl2 at room temperature for 5 h afforded the desired
product with a 2.5:1 ratio of a and b anomers in com-
bined 90% yield (entry 1 in Table 1). The ratio of a
1
and b isomers was established by the H NMR spectra
of the crude products. In the presence of Lewis acids
such as ZnCl2, ZnBr2, or BF3ÆOEt2 as activators the
reaction of (1) with CF3CO2ZnEt gave the product 2a
with high yield in shorter reaction times. But these Lewis
acids showed little effect on the ratio of a and b ano-
mers. The choice of Et2O as solvent afforded a 34% yield
of 2a after stirring 10 h (entry 6 in Table 1). Reactions
performed in THF gave only small amounts of the cor-
responding product after lengthy reaction times (21 h).
The organozinc species, CF3CF2CF2CO2ZnEt, afforded
a slightly lower 82% yield under similar reaction condi-
tions. However, CF3SO3ZnEt gave only a 61% yield of
the desired product after stirring for 7 h at room
temperature.
More recently, the organozinc reagent, CF3CO2ZnEt,
has been exploited in the nucleophilic ring-opening reac-
tion of epoxides with stereoselectivity.9 Our continued
interest in developing the organozinc reagent,
CF3CO2ZnR, has prompted us to verify their possibility
in the Ferrier rearrangement reaction.
Glycosidation of 1 with dimethylzinc in the presence
of CF3COOH proceeded smoothly to give the corre-
sponding glycoside 2b in 97% yield (entry 1 in Table
2). Interestingly, the reaction of 1 with diphenylzinc in
the presence of CF3COOH afforded the phenyl glycoside
*
Corresponding author. Fax: +86 551 360 7864; e-mail: xuesong@
ustc.edu.cn
0008-6215/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2004.11.012

304
S. Xue et al. / Carbohydrate Research 340 (2005) 303–307
Table 1. Addition of ZnEt2 to 3,4,6-tri-O-acetyl-D-glucal (1)
with 10:1 a:b selectivity in 90% yield (entry 2 in Table 2).
Extension of the organozinc species CF3CO2ZnR to
other substrates furnished the corresponding products
in excellent yields. Treatment of compound 3a with
the organozinc reagent, CF3CO2ZnMe, gave the desired
product 4a with a 5:1 ratio of a and b anomers in com-
bined 89% yield (entry 3 in Table 2). The addition of
CF3CO2ZnPh to 3a provided in 4b 88% yield with high
selectivity (a:b = 19:1). The stereoselectivity difference
between the reaction of glycals and with the organozinc
species, CF3CO2ZnR, seems to indicate that substitu-
ents at C-6 and nucleophiles exert a significant influence
on the ratio of a and b anomers. Substituent factors
contributing to the stereoselectivity in the reaction of
tetrahydropyran acetals with allyltrimethylsilane have
been explored by Woerpel and co-workers.10 Further-
more, 1,2-dihydropyranyl acetate 3b when submitted
to this reaction gave the corresponding products in
excellent yields and high a selectivity (a:b P 10:1) (en-
tries 5–7 in Table 2). These results suggest that organo-
zinc species, CF3CO2ZnR, which can be easily formed,
provide a simple and practical method for the synthesis
of alkyl and aryl C-pyranosides.
O
O
AcO
AcO
ZnEt2, HX
CH2Cl2, r.t.
AcO
AcO
OAc
2a
1
Entry Solvent HX
Activator Time, Yielda, a:bb
(1.0 equiv)
CH2Cl2 CF3CO2H None
CH2Cl2 CF3CO2H ZnCl2
h
%
%
1
2c
3
4
5
6
7
8
9
4
90
70
87
95
96
34
91
82
61
2.5:1
3.0:1
2.5:1
2.1:1
2.5:1
2.7:1
2.8:1
2.0:1
2.4:1
10
2
CH2Cl2 CF3CO2H ZnCl2
CH2Cl2 CF3CO2H ZnBr2
CH2Cl2 CF3CO2H BF3ÆOEt2
3
2
10
Et2O
Et2O
CF3CO2H None
CF3CO2H BF3ÆOEt2 10
CH2Cl2 C4F9CO2H None
CH2Cl2 CF3SO3H None
5
7
a Isolated yields.
b The a:b ratios were determined by 1H NMR spectroscopy of the
crude products.
c The reaction was carried out at 0 ꢁC.
Table 2. Addition of ZnR2 to 1 and 3a, b in the presence of CF3COOH
O
R1
R1
O
R
Encouraged by the initial results using ZnPh2 in the
presence of CF3CO2H with good stereocontrol, we wish
to extend further the organozinc species ArZnX, which
can be easily prepared from ArLi and ZnCl2, as nucleo-
philes to this reaction. Although per-O-acetyl-D-glucals
have been frequently used as suitable donors in the car-
bon–Ferrier rearrangement, to our knowledge, few
examples of the aryl glycosidations of 3,4,6-tri-O-ace-
ZnR2, CF3CO2H
CH2Cl2, r.t.
R2
R2
OAc
3a: R1 = TBSO; R2 = AcO
4
3b: R1 = PhCH2; R2 = H
Entry ZnR2
Product
Time, h Yielda, % a:bb
Me
Ph
O
AcO
1
2
3
4
5
6
7
ZnMe2
3
97
90
89
88
89
98
87
2.3:1
10:1
5:1
AcO
AcO
tyl-D-glucal
1 with arylzinc reagents have been
2b
described.11–13 The results of glycosidation of 1 with
ArZnCl are summarized in Table 3. The reaction of gly-
cal with o-CH3C6H4ZnCl in CH2Cl2 at room tempera-
ture for 12 h gave only a small amount of 2d.
Interestingly, moderate yields were obtained in the pres-
ence of BF3ÆOEt2 as activator (entries 1–2 in Table 3).
Notably, the solvents have an important influence on
the reaction efficiencies. The reaction mixture stirring
in Et2O solvent led to rapid consumption (1 h, rt) of
starting materials afforded the corresponding product
2d with 7:1 a:b selectivity in 97% yield (entry 3 in Table
3). However, no desired product was obtained when the
reaction was carried out in Et2O solvent in the absence
of BF3ÆOEt2. Mixing of 1 with an Et2O solution of
PhZnCl in the presence of BF3ÆOEt2 gave 2c in 98% yield
with a slightly lower a:b selectivity (6:1) in compari-
son with the CH2Cl2 solution of ZnPh2 in the presence
of CF3 CO2H (entry 4 in Table 3 vs entry 2 in Table
2). Similarly, the reaction of 1 with p-BrC6H4ZnCl and
p-ClC6H4ZnCl also furnished the corresponding glyco-
sides 2e and 2f in 94% (a:b 7:1) and 86% (a:b 8:1) yields,
respectively.
O
AcO
ZnPh2
ZnMe2
ZnPh2
ZnEt2
ZnMe2
ZnPh2
2
2c
Me
O
TBSO
3
AcO
AcO
4a
O
Ph
TBSO
Ph
3
19:1
10:1
10:1
20:1
4b
O
Et
1.5
1.5
1.5
4c
Ph
Ph
Me
O
4d
O
Ph
4e
a Isolated yields after purification by column chromatography.
b The a:b ratios were determined by 1H NMR spectroscopy of the
crude products.
In conclusion, we have demonstrated a new and sim-
ple method for the synthesis of 2,3-unsaturated alkyl

S. Xue et al. / Carbohydrate Research 340 (2005) 303–307
Table 3. Addition of ArZnCl to 1 in the presence of BF3ÆOEt2
305
Entry
ArBr
Product
Time, h
Yielda, %
a:bb
Br
O
Me
AcO
AcO
1c
2d
3
8
5
1
42
56
97
7:1
7:1
7:1
Me
2d
Br
Br
O
AcO
AcO
4
5
2
2
98
94
6:1
7:1
2c
Br
O
AcO
AcO
2e
Br
Br
CI
O
AcO
AcO
6
1
86
8:1
2f
Cl
a Isolated yields after purification by column chromatography.
b The a:b ratios were determined by 1H NMR spectroscopy of the crude products.
c The reaction was performed in CH2Cl2 using 1.0 equiv of BF3ÆOEt2.
d Performed in CH2Cl2 using 2.0 equiv of BF3ÆOEt2.
and aryl C-pyranosides using organozinc reagents. Di-
methylzinc and diethylzinc afforded the corresponding
products in high yields with 2–10:1 a:b selectivity in
the presence of CF3CO2H, whereas diphenylzinc pro-
vided an efficient and high stereoselectivity route to
the synthesis of phenyl pyranosides. Arylzinc chlorides
can also be successfully applied to the synthesis of aryl
C-glycosides from 3,4,6-tri-O-acetyl-D-glucal in the pres-
ence of BF3ÆOEt2.
C-(4,6-Di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-eno-
pyranosyl)ethane (2a),6a C-[4,6-Di-O-acetyl-2,3-dide-
oxy-a-D-erythro-hex-2-enopyranosyl]methane (2b),14 C-
[4,6-Di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-enopyra-
nosyl]benzene (2c),11 1-C-[4,6-Di-O-acetyl-2,3-dideoxy-
a-D-erythro-hex-2-enopyranosyl]-2-methylbenzene (2d),11
1-C-[4,6-Di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-eno-
pyranosyl]-4-chlorobenzene (2f),11 and trans-5,6-Dihy-
dro-6-phenethyl-2-phenyl-2H-pyran (4e).8
1.1.1. Standard procedure for preparation of alkyl and
aryl C-pyranosides with ZnR2 in the presence of
1. Experimental
CF3COOH. To
a solution of ZnR2 (0.6 mmol,
1.1. General methods
2.0 equiv) in 1.0 mL of CH2Cl2 at 0 ꢁC was added drop-
wise CF3COOH (46 lL, 0.6 mmol, 2.0 equiv) slowly via
syringe under N2. After stirring for 30 min at 0 ꢁC, a
solution of 1,2-dihydropyranyl acetates (0.3 mmol,
1.0 equiv) in 1.0 mL of CH2Cl2 was added. The mixture
was stirred at room temperature until TLC indicated
complete consumption of the starting glucal. The reac-
tion was quenched by addition of 1.0 mL satd aq NH4Cl
and extracted with Et2O (3 · 10 mL). The combined or-
ganic extracts was washed with brine, dried over MgSO4
and concentrated under reduced pressure to an oily
residue. The desired product was purified by silica gel
chromatography using 20:1–15:1 petroleum ether–
EtOAc.
IR spectra were recorded on a Perkin–Elmer FT210 spec-
trophotometer. 1H NMR (300 MHz) and 13C NMR
(75 MHz) spectra were measured with a Bruker AC 300
spectrometer using Me4S as the internal standard. Col-
umn chromatography was performed on silica gel (100–
200 mesh), and analytical TLC was carried out on silica
gel 60-F254 plates (Qindao) with detection by fluores-
cence and then charring with a 10% ethanolic solution
of sulfuric acid. High-resolution mass spectra were ob-
tained with a Micromass GCT TOF mass spectrometer.
The following compounds were prepared essentially
as described in the literature:

306
S. Xue et al. / Carbohydrate Research 340 (2005) 303–307
1.1.1.1. C-4-O-Acetyl-[6-O-(tert-butyldimethylsilyl)-
2,3-dideoxy-a-D-erythro-hex-2-enopyranosyl]methane (4a).
n-BuLi (240 lL, 0.6 mmol, 2.0 equiv). The mixture was
stirred at room temperature for 30 min, then a solution
of ZnCl2 (82 mg, 0.6 mmol, 2.0 equiv) in 1.0 mL of
Et2O was added via syringe at 0 ꢁC. Transfer of the ZnCl2
was made quantitative with an additional 0.5 mL of
Et2O. After the white suspension was stirred at room
temperature for 1 h, a solution of 3,4,6-tri-O-acetyl-D-
glucal (81.6 mg, 0.3 mmol) in 1.5 mL of Et2O was added
at À78 ꢁC, followed by addition of BF3ÆEt2O (159 lL,
0.6 mmol, 2.0 equiv). Then the reaction flask was moved
from the cold bath and stirred for 1–2 h at room temper-
ature. The reaction was quenched by addition of 2.5 mL
of satd aq NH4Cl and extracted with Et2O (3 · 10 mL).
The combined organic extracts was washed with brine,
dried over MgSO4 and concentrated under reduced pres-
sure. The desired product was isolated by silica gel chro-
matography with 15:1 petroleum ether–EtOAc.
IR (neat, cmÀ1) 2956, 1743, 1466, 1237, 1192, 1049, 970,
1
839, 779; H NMR (CDCl3, 300 MHz) (a-anomer): d
5.87 (td, J 1.4, 10.1 Hz, 1H), 5.78 (td, J 2.2, 10.1 Hz,
1H), 5.11 (m, 1H), 4.38–4.35 (m, 1H), 3.82–3.71 (m,
3H), 2.08 (s, 3H), 1.29 (d, J 6.8 Hz, 3H), 0.90 (s, 9H),
0.08 (s, 3H), 0.07 (s, 3H); 13C NMR (CDCl3, 75 MHz)
(a-anomer): d 170.7, 135.2, 122.9, 73.2, 67.6, 65.5, 62.9,
1
29.9, 26.0, 21.4, 19.6, À5.2, À5.3; H NMR (CDCl3,
300 MHz) (b-anomer): d 5.78 (m, 1 H), 5.71 (m, 1H),
5.21 (m, 1H), 4.23 (m, 1H), 3.82–3.71 (m, 2H), 3.57 (m,
1H), 2.06 (s, 3H), 1.23 (d, J 6.7 Hz, 3H), 0.90 (s, 9H),
0.08 (s, 3H), 0.07 (s, 3H); HRCIMS: Calcd for
C15H29O4Si, m/z 301.1835 [MH]+. Found: m/z 301.1840.
1.1.1.2. C-4-O-Acetyl-[6-O-(tert-butyldimethylsilyl)-
2,3-dideoxy-a-D-erythro-hex-2-enopyranosyl]benzene (4b).
IR (neat, cmÀ1) 2931, 1740, 1494, 1095, 973, 838, 779,
700; 1H NMR (CDCl3, 300 MHz) for a-anomer: d
7.44–7.33 (m, 5H), 6.16 (br d, J 10.3 Hz, 1H), 5.99 (br
d, J 10.3 Hz, 1H), 5.29 (m, 2H), 3.74 (m, 3H), 2.08 (s,
3H), 0.87 (s, 9H), 0.07 (s, 3H), 0.04 (s, 3H); 13C NMR
(CDCl3, 75 MHz): d 170.6, 139.5, 131.9, 128.5, 128.0,
127.8, 124.9, 73.5, 72.4, 65.5, 63.1, 25.9, 21.3, 18.4,
À5.4, À5.3; HRCIMS: Calcd for C20H31O4Si, m/z
363.1992 [MH]+. Found: m/z 363.1986.
1.1.2.1. 1-C-[4,6-Di-O-acetyl-2,3-dideoxy-a-D-erythro-
hex-2-enopyranosyl]-4-bromobenzene (2e). IR (neat,
cmÀ1) 2953, 1740, 1370, 1233, 1047, 801; 1H NMR
(CDCl3, 300 MHz): d 7.45 (d, J 8.1 Hz, 2H), 7.23 (d, J
8.1 Hz, 2H), 6.08 (d, J 9.8 Hz, 1H), 5.94 (d, J 9.8 Hz,
1H), 5.22–5.11 (m, 2H), 4.20 (dd, J 6.0, 11.7 Hz, 1H),
4.03 (dd, J 2.4, 11.7 Hz, 1H), 3.76–3.75 (m, 1H), 2.05
(s, 3H), 2.03 (s, 3H); 13C NMR (CDCl3, 75 MHz): d
170.7, 170.3, 130.0, 131.7, 130.9, 129.6, 125.4, 122.3,
73.0, 69.5, 64.9, 62.8, 21.0, 20.8. HRCIMS: Calcd for
C16H18BrO5, m/z 369.0337 [MH]+. Found: m/z
369.0338.
1.1.1.3. trans-5,6-Dihydro-2-ethyl-6-phenethyl-2-phen-
yl-H-pyran (4c). IR (neat, cmÀ1) 3030, 2963, 1602,
1454, 1261, 1023, 801, 699; 1H NMR (CDCl3,
300 MHz): d 7.27–7.15 (m, 5H), 5.75–5.70 (m, 2H),
4.05 (m, 1H), 3.65 (m, 1H), 2.84 (m, 1H), 2.66 (m,
1H), 1.96–1.87 (m, 3H), 1.73 (m, 1H), 1.58 (m, 1H),
1.48 (m, 1H), 1.00 (t, J 7.3 Hz, 3H); 13C NMR
(CDCl3, 75 MHz): d 142.5, 129.9, 128.6, 128.4, 125.8,
123.9, 74.1, 67.1, 37.3, 32.2, 30.1, 27.3, 10.7; HREIMS:
Calcd for C15H20O, m/z 216.1514 [M]+. Found: m/z
216.1518.
Acknowledgements
We thank the National Natural Science Foundation of
China (20202009) for financial support.
Supplementarydata
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2004.11.012.
1.1.1.4. trans-5,6-Dihydro-2-methyl-6-phenethyl-2H-
pyran (4d). IR (neat, cmÀ1) 3029, 2926, 1604, 1495,
1454, 1365, 1240, 1051, 952, 750, 700; 1H NMR (CDCl3,
300 MHz): d 7.22–7.09 (m, 5H), 5.69–5.66 (m, 2H),
4.30 (m, 1H), 3.60 (m, 1H), 2.72 (m, 1H), 2.61 (m,
1H), 1.90–1.66 (m, 4H), 1.17 (d, J 6.8 Hz, 3H); 13C
NMR (CDCl3, 75 MHz): d 142.3, 131.0, 128.6, 128.3,
125.8, 123.5, 68.5, 66.6, 37.0, 31.9, 30.7, 20.1; HREIMS:
Calcd for C14H18O, m/z 203.1436 [M]+. Found: m/z
203.1439.
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