Magnetic core-shell Fe3O4@C-SO3H as an efficient and renewable 'Green catalyst' for the synthesis of O-2,3-unsaturated Glycopyra-nosides

Article abstract of DOI:10.1055/s-0036-1588891

A magnetic core-shell solid-acid catalyst Fe₃O₄@C-SO₃H was studied for synthesis of O-2,3-unsaturated glycosides through Ferrier rearrangement. The donors include 3,4,6-tri-O-acetyl-D-glucal and 3,4-di-O-acetyl-L-rhamnal. The acceptors consist of primary alcohols, secondary alcohols, tert-butanol, unsaturated alcohols, halogenated alcohol, sterol, sugars, and phenols. O-2,3-Unsaturated glycosides were obtained rapidly (<3 h) and efficiently (up to 98%) in good α selectivity (α/β >5:1 to 19:1). Moreover, the catalyst can be easily separated from the reaction with an external magnetic force and reused for a minimum of five times without any significant decrease in the yields of the products after every recycle, suggesting it a promising green catalyst in 2,3-unsaturated glycosides syntheses.

Full text of DOI:10.1055/s-0036-1588891

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© Georg Thieme Verlag Stuttgart · New York
2016, 27, A–F
letter
A
G. Sun et al.
Letter
Synlett
Magnetic Core-Shell Fe3O4@C-SO3H as an Efficient and Renewable
‘Green Catalyst’ for the Synthesis of O-2,3-Unsaturated Glycopyra-
nosides
Guosheng Suna
Saifeng Qiua
Zekun Dinga
Heshan Chena
Jiafen Zhoua
Zhongfu Wangb
Jianbo Zhang*a
a School of Chemistry and Molecular Engineering, East China
Normal University, Shanghai, 200241, P. R. of China
Jbzhang@chem.ecnu.edu.cn
b School of Life Sciences, Northwest University, Xi’an, 710069,
P. R. of China
Received: 23.07.2016
Accepted after revision: 06.09.2016
Published online: 06.10.2016
heterogeneous acid catalysts for Ferrier rearrangement
have been reported during the past few years, such as
HClO4·SiO2, HBF4·SiO2, PMA·SiO2, H3PW12O40/C, ZnCl2/Al2O3,
and Amberlyst-15.5 In our previous research for diverse
syntheses of glycosides, we have successfully used H2SO4·-
SiO2 and FeCl3·6H2O/C as immobilized catalysts for Ferrier
rearrangement.6 Unfortunately, shortcomings of the above-
mentioned heterogeneous catalysts, such as low specific
surface area, easy deactivation, inconvenient separation,
and recovery, are difficult to overcome. Thus, new econom-
ical and efficient catalysts to replace the aforementioned
catalysts are still needed.
Recently, carbon-coated Fe3O4 core-shell materials have
been attracted attention as potential supports in heteroge-
neous catalysis.7,8 Sulfonation of carbon would be expected
to generate a stable solid with a high density of catalytic ac-
tive sites and have been proposed as low-cost renewable
‘green catalysts’ able to be prepared from either biomass or
from household waste.9
Zhang et al. reported hydrolysis of cellulose in 2013 us-
ing Fe3O4@C-SO3H as a catalyst.10 Thombal et al. reported
the synthesis of new Glu-Fe3O4-SO3H catalyst and showed
its application for tetrahydropyran protection of alcohols
and glycosylation of protected glycals in the synthesis of 2-
deoxy-O-glycosides in 2016.11 In this study, we prepared a
magnetic sulfonated carbon material with core-shell struc-
ture (Fe3O4@C-SO3H) as an efficient and recyclable catalyst
and first used it in the synthesis of O-2,3-unsaturated glu-
cosides (Scheme 1).8
In our initial attempts, a model study was conducted to
optimize the desired solvent and temperature using 3,4,6-
tri-O-acetyl-D-glucal as the glycosyl donor and benzyl alco-
hol as the acceptor with Fe3O4@C-SO3H as the catalyst. The
preliminary results, which were summed up in Table 1,
showed that the reaction did not proceed at all at 20 °C, nei-
DOI: 10.1055/s-0036-1588891; Art ID: st-2016-w0480-l
Abstract A magnetic core-shell solid-acid catalyst Fe3O4@C-SO3H was
studied for synthesis of O-2,3-unsaturated glycosides through Ferrier
rearrangement. The donors include 3,4,6-tri-O-acetyl-D-glucal and 3,4-
di-O-acetyl-L-rhamnal. The acceptors consist of primary alcohols, sec-
ondary alcohols, tert-butanol, unsaturated alcohols, halogenated alco-
hol, sterol, sugars, and phenols. O-2,3-Unsaturated glycosides were ob-
tained rapidly (<3 h) and efficiently (up to 98%) in good α selectivity
(α/β >5:1 to 19:1). Moreover, the catalyst can be easily separated from
the reaction with an external magnetic force and reused for a minimum
of five times without any significant decrease in the yields of the prod-
ucts after every recycle, suggesting it a promising green catalyst in 2,3-
unsaturated glycosides syntheses.
Key words Fe3O4@C-SO3H, magnetic core shell, recyclable catalyst,
O-2,3-unsaturated glycosides, Ferrier rearrangement
Alkyl and aryl O-2,3-unsaturated glycosides are import-
ant chiral intermediates in organic chemistry to synthesize
new functional materials and compounds with wide range
of biological activities.1 As we know, one of the most useful
procedures to achieve O-2,3-unsaturated glycosides direct-
ly and efficiently is a famous name reaction, Ferrier rear-
rangement.2 A diversity of homogeneous catalysts have
been reported for the synthesis of O-2,3-unsaturated glyco-
pyranosides, such as p-toluenesulfonic acid, trifluoroacetic
acid (TFA), trichloroacetic acid, sulfuric acid, SnCl4, ZnCl2,
AuCl3, and Y(OTf)3.3,4 However, the uses of these homoge-
neous acid catalysts are limited in a practical application
due to corrosion, environmental pollution, side reactions,
sensitivity to water, and so on. Such catalysts are difficult to
separate from the reaction and they cannot be reused. Het-
erogeneous catalysts have advantages over homogeneous
catalysts that they are environmental-friendly, more effi-
cient, stable, easily separable, and reusable. A number of
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F

B
G. Sun et al.
Letter
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Table 1 Optimization of the Glycosylation Reaction Conditions
OAc
OAc
O
OAc
O
Fe3O4@C-SO3H
DCE, 80 °C
+ Nucleophile
AcO
AcO
AcO
Nu
O
Nucleophile = primary alcohols, unsaturated alcohols,
halogenated alcohol, tert-butyl alcohol,
sterol, sugars and phenols
19 examples
AcO
AcO
up to 98% yield
OAc
O
1a
(1 equiv)
Scheme 1 Fe3O4@C-SO3H as an efficient and recyclable catalyst for the
synthesis of O-2,3-unsaturated glycopyranosides
Fe3O4@C-SO3H
AcO
O
+
HO
3a
ther in CH2Cl2, DCE, nor MeCN after 120 minutes (Table 1,
entries 1–3). Poor yield was obtained when the reaction
was carried out in CH2Cl2 even at 40 °C (Table 1, entry 4). To
our delight, the yield was improved significantly when DCE
was used at 60 °C and a reaction time of 30 minutes (Table
1, entry 6). The shortest reaction time and highest yield
were obtained at 80 °C in DCE (Table 1, entry 8). Hence, the
optimum temperature for the reaction was found to be
80 °C. It was found that when MeCN was used as the sol-
vent, the result was similar but a little inferior to that ob-
tained using DCE (Table 1, entry 9). Therefore, DCE was the
best solvent for this reaction. The stoichiometric amount of
catalyst was further studied, and we found that 0.3 equiva-
lents were sufficient to promote the reaction and gave an
excellent yield (96%) in ten minutes at 80 °C using DCE as
the solvent. When a smaller amount of catalyst was used,
the reaction preceded much slower, while the reaction rate
and yield were not improved with a larger amount of cata-
lyst (Table 1, entries 10 and 11). At the same time, the reac-
tion did not proceed at all when Fe3O4@C was used as the
catalyst, which demonstrated the necessity of the acid sites
on the core-shell materials (Table 1, entry 12).
2a
(1.2 equiv)
Entry Solvent
Cat. (equiv)a Temp (°C)
Time (min)
Yield (%)b
1
2
CH2Cl2
DCE
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.1
0.5
0.3
20
20
20
40
40
60
60
80
80
80
80
80
120
120
120
60
NRc
NR
NR
34
58
75
70
96
92
41
97
NR
3
MeCN
CH2Cl2
DCE
4
5
60
6
DCE
30
7
MeCN
DCE
30
8
10
9
MeCN
DCE
10
10
11
12d
15
DCE
10
DCE
120
a The acid sites of Fe3O4@C-SO3H were calculated by an acid–base titration
method.10
b Isolated yields.
c NR = no reaction.
d Fe3O4@C as the catalyst.
With the optimal conditions established, we investigat-
ed the reaction scope using a variety of acceptors. As sum-
marized in Table 2, it could be seen that various alcohols
(including primary, secondary, benzyl, allyl, propargyl, and
halogenated alcohols) gave products 3a–f in high yields
with good anomeric selectivities (Table 2, entries 1–6). The
complex sterol such as menthol and cholesterol were able
to give high yields with pure α selectivities (Table 2, entries
6 and 7). When tert-butanol was used as nucleophile, the
expected product 3h was obtained in low yield, because of
a larger steric hindrance (Table 2, entry 8). Moreover, we
could obtain various disaccharides smoothly while using
monosaccharides as the acceptors, which gave the desirable
2,3-unsaturated glycoside products 3i–l in high yields (90–
93%) with moderate selectivities (Table 2, entries 9–12). It
should be noted that the reaction could be successfully car-
ried out with phenols, which are usually poor acceptors in
Ferrier rearrangement. There was a report mentioned that
when tri-O-acetyl-D-glucal was treated with p-methoxy-
phenol using BF3·OEt2 as the catalyst, C-glycoside was ob-
tained exclusively.12 However, in our case, no such phenom-
enon occurred. Phenol, p-methoxyphenol, and tert-butyl-
phenol gave the normal O-glycosides as the sole products
3m–o in good yields and sole α selectivities (Table 2, en-
tries 13–15). When p-bromophenol was used as nucleo-
phile, the expected product 3p was obtained in acceptable
yield (52%), due to the electron-withdrawing group of bro-
mine in the para position of the phenyl ring (Table 2, entry
16). Similarly, we failed to get the product when p-nitro-
phenol was used as the acceptor.
Ferrier reactions on 3,4-di-O-acetyl-L-rhamnal were
also studied with representative nucleophiles.13 The reac-
tions proceeded smoothly, and the yields were good to ex-
cellent with very high anomeric selectivities (Table 2, en-
tries 17–19). The structure and stereochemistry of all glyco-
sidation products were determined through spectroscopic
analysis and also by comparison with the reported data.4,13–15
Then, the recycling and reuse of the catalyst were inves-
tigated. After the Ferrier reaction, the Fe3O4@C-SO3H cata-
lyst could be separated from solution by using the external-
ly applied magnetic field due to its Fe3O4 core (Figure 1).
The recycling experiments were performed to test the sta-
bility of the catalyst in our reaction system. Beyond our ex-
pectation, though the catalyst reused for the next runs
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F

C
G. Sun et al.
Letter
Synlett
Table 2 (continued)
without any activation, it was observed that reuse of the
catalyst gave no significant decrease in yield of product (Ta-
ble 3).
In summary, we have described Fe3O4@C-SO3H as a
highly efficient and easily recyclable catalyst for Ferrier re-
arrangement. Under our reaction conditions, 3,4,6-tri-O-
acetyl-D-glucal and 3,4-di-O-acetyl-L-rhamnal afforded
products with a range of nucleophiles in high to good yields
and dominant α selectivity.16,17 Moreover, the catalyst could
also be recovered by external magnetic force and reused for
a minimum of five times without any loss of activity. Thus,
we expect that this simple, green, and efficient methodolo-
gy will find widespread use in 2,3-unsaturated glycosides
syntheses.
Table 2 Fe3O4@C-SO3H-Catalyzed Ferrier Rearrangement of 3,4,6-Tri-O-acetyl-D-Glucal and 3,4-Di-O-acetyl-L-Rhamnal in DCE
Entry
Nucleophile
Product
Time (min)
Yield (%)a
OAc
O
96
1
10
α/β = 7:1b
AcO
OH
O
3a
OAc
O
98
OH
2
3
4
10
30
50
AcO
α/β = 10:1
O
3b
OAc
O
94
OH
AcO
α/β = 10:1
O
3c
OAc
O
91
OH
AcO
α/β = 12:1
O
3d
OAc
O
Cl
Cl
90
α/β >19:1
Cl
Cl
Cl
Cl
AcO
5
6
60
90
OH
O
O
3e
OAc
O
AcO
HO
88
α/β >19:1
3f
OAc
O
85
α/β >19:1
AcO
7
8
cholesterol
90
O
3g
OAc
O
AcO
54
α/β >19:1
OH
180
O
3h
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F

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Table 2 (continued)
Entry
Nucleophile
Product
Time (min)
Yield (%)a
OAc
O
HO
AcO
O
92
α/β = 7:1
BnO
O
9
30
O
BnO
BnO
BnO
BnO
OMe
BnO
OMe
3i
OAc
O
HO
AcO
O
BzO
BzO
93
α/β = 5:1
O
10
30
O
BzO
BzO
BzO
OMe
BzO
OMe
3j
OAc
O
OBz
O
HO
BzO
BzO
AcO
OBz
O
92
α/β = 5:1
O
11
30
BzO
OMe
BzO
OMe
3k
OAc
O
HO
O
AcO
O
O
90
α/β = 5:1
O
O
O
12
30
O
O
O
O
O
3l
OAc
O
AcO
88
α/β >19:1
13
120
OH
O
3m
OAc
O
AcO
79
α/β >19:1
14
30
MeO
OH
O
OMe
3n
OAc
O
AcO
85
α/β >19:1
15
O
60
OH
3o
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F

E
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Table 2 (continued)
Entry
Nucleophile
Product
Time (min)
Yield (%)a
OAc
O
AcO
52
α/β >19:1
16
120
Br
OH
O
Br
3p
O
90
α/β >19:1
O
17
18
20
30
AcO
3q
OH
HO
82
α/β >19:1
O
O
AcO
3r
83
α/β >19:1
19
cholesterol
O
60
O
AcO
3s
a Isolated yields.
b The anomeric ratio was determined by integration of the anomeric hydrogen in the 1H NMR spectra.
Table 3 Reusability of Fe3O4@C-SO3H Catalyst in O-2,3-Unsaturated
Glycosides Synthesesa,b
Entry
Reuse
Yield (%)c
1
2
3
4
5
1st recycle
2nd recycle
3rd recycle
4th recycle
5th recycle
95
95
94
93
90
Figure 1 Magnetic property and the separation of Fe3O4@C-SO3H acid
a Reaction performed between 3,4,6-tri-O-acetyl-D-glucal and benzyl alco-
catalyst: a) without magnet; b) with magnet.
hol.
b All reaction time was 10 min.
c Isolated yield.
Acknowledgment
Supporting Information
We thank the analytic center of East China Normal University for data
measurement. This project was financially supported by Natural Sci-
ence Foundation of Shanghai (11ZR1410400), National Students In-
novative Experimental Projects (No. 1310269021 & 201610269070),
and large instruments Open Foundation of East China Normal Univer-
sity (2014-03 & 20151043).
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588891.
S
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p
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F

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(16) Typical Experimental Procedure
To a mixture of tri-O-acetyl-D-glucal (0.2 mmol, 54.4 mg),
benzyl alcohol (26 μL, 0.24 mmol), and Fe3O4@C-SO3H (30 mol%,
25 mg) in a round-bottom flask (10 mL), DCE (2 mL) was added,
and the reaction mixture was stirred for 10 min at 80 °C. After
completion of the reaction (monitored by TLC), the catalyst is
separated from the reaction with an external magnetic force,
and the catalyst was washed with CH2Cl2. The organic phase
was combined and condensed under vacuum to get the crude
product, which was purified by silica gel column chromatogra-
phy PE–EtOAc = 6:1) to get 3a in 96% yield. All compounds were
fully characterized by NMR spectroscopy and MS. Spectral and
analytical data were in good agreement with the desired struc-
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(17) Selected Spectral Data
Benzyl 4,6-Di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-eno-
pyranoside (3a)
Colorless oil. 1H NMR (500 MHz, CDCl3): δ = 7.40–7.33 (m, 5 H),
5.90 (d, J = 10.4 Hz, 1 H), 5.85 (dt, J = 10.2, 2.3 Hz, 1 H), 5.33 (dd,
J = 9.4, 1.2 Hz, 1 H), 5.14 (s, 1 H), 4.81 (d, J = 11.7 Hz, 1 H), 4.69
(s, 1 H), 4.60 (d, J = 11.7 Hz, 1 H), 4.25 (dd, J = 11.6, 5.0 Hz, 1 H),
4.14–4.10 (m, 1 H), 2.08 (s, 3 H), 2.07 (s, 3 H) ppm. ESI-MS: m/z
calcd for C17H20O6Na [M + Na]+: 343.12; found: 343.15.
Trichloroethyl 4,6-Di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-
2-enopyran-oside (3e)
Colorless oil. 1H NMR (500 MHz, CDCl3): δ = 6.00 (d, J = 10.3 Hz,
1 H), 5.97–5.92 (m, 1 H), 5.36 (d, J = 9.2 Hz, 1 H), 5.30 (s, 1 H),
4.35 (d, J = 11.3 Hz, 1 H), 4.26–4.19 (m, 4 H), 2.11 (s, 3 H), 2.11
(s, 3 H) ppm. ESI-MS: m/z calcd for C12H15Cl3O6Na [M + Na]+:
382.98; found: 382.94.
tert-Butyl
4,6-Di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-
enopyranoside (3h)
Colorless oil. 1H NMR (500 MHz, CDCl3): δ = 5.85 (d, J = 10.1 Hz,
1 H), 5.78–5.71 (m, 1 H), 5.32 (s, 1 H), 5.30–5.24 (m, 1 H), 4.26–
4.18 (m, 2 H), 4.17–4.12 (m, 1 H), 2.08 (s, 3 H), 2.08 (s, 3 H),1.29
(d, J = 2.6 Hz, 9 H) ppm. ESI-MS: m/z calcd for C14H22O6Na [M +
Na]+: 309.13; found: 309.17.
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H.; Hayashi, S.; Hara, M. J. Am. Chem. Soc. 2008, 130, 12787.
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Phenoxyl
enopyranoside (3m)
4,6-Di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-
Colorless oil. 1H NMR (500 MHz, CDCl3): δ = 7.05–7.34 (m, 5 H),
6.02–6.07 (m, 2 H), 5.73 (s, 1 H), 5.41–5.43 (dd, J = 9.5, 1.5 Hz, 1
H), 4.16–4.33 (m, 3 H), 2.14 (s, 3 H), 2.01 (s, 3 H) ppm. ESI-MS:
m/z calcd for C16H18O6Na [M + Na]+: 329.10; found: 329.17.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F