Reactions of various nucleophiles with d-glucal over keggin-type heteropoly compounds: A simple, rapid, and expedient method for the synthesis of pseudoglycals

Article abstract of DOI:10.1080/07328300903477796

The reaction of benzyl alcohol with 3,4,6-tri-O-acetyl-d-glucal has been investigated with several heteropoly compounds, and the optimal catalyst is 12-tungstophosphoric acid supported on carbon. In the presence of this catalyst, various alcohols gave the corresponding alkyl and aryl 2,3-unsaturated glycopyranosides in excellent yields and good anomeric selectivity under solvent-free condition. 4,6-Di-O-acetyl-2,3-dideoxy - d-erythro-hex-2- enopyranosyl cyanide and ethyl 4,6-di-O-acetyl-2,3-dideoxy-1-thio - d-erythro-hex-2-enopyranoside have also been prepared with trimethylsilyl cyanide and ethanthiol as nucleophiles, respectively. The catalyst could be easily recovered and reused several times with slight loss of activity. The selectivity to give α-anomers predominantly did not show any change in all runs.

Full text of DOI:10.1080/07328300903477796

This article was downloaded by: [McMaster University]
On: 23 October 2014, At: 12:50
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Carbohydrate Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lcar20
Reactions of Various Nucleophiles with
d-Glucal over Keggin-Type Heteropoly
Compounds: A Simple, Rapid, and
Expedient Method for the Synthesis of
Pseudoglycals
Ezzat Rafiee a b , Sara Eavani a & Mohammad Joshaghani a b
a Faculty of Chemistry , Razi University , Kermanshah, 67149, Iran
b Kermanshah Oil Refining Company , Kermanshah, Iran
Published online: 04 Jan 2010.
To cite this article: Ezzat Rafiee , Sara Eavani & Mohammad Joshaghani (2010) Reactions of Various
Nucleophiles with d-Glucal over Keggin-Type Heteropoly Compounds: A Simple, Rapid, and Expedient
Method for the Synthesis of Pseudoglycals, Journal of Carbohydrate Chemistry, 29:1, 20-29, DOI:
10.1080/07328300903477796
To link to this article: http://dx.doi.org/10.1080/07328300903477796
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Carbohydrate Chemistry, 29:20–29, 2010
ꢀ
C
Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328300903477796
Reactions of Various
Nucleophiles with D-Glucal
over Keggin-Type Heteropoly
Compounds: A Simple, Rapid,
and Expedient Method for the
Synthesis of Pseudoglycals
Ezzat Rafiee,2 Sara Eavani,1 and Mohammad Joshaghani2
1Faculty of Chemistry, Razi University, Kermanshah, 67149, Iran
2Faculty of Chemistry, Razi University, Kermanshah, 67149, Iran; and Kermanshah
Oil Refining Company, Kermanshah, Iran
The reaction of benzyl alcohol with 3,4,6-tri-O-acetyl-D-glucal has been investigated
with several heteropoly compounds, and the optimal catalyst is 12-tungstophosphoric
acid supported on carbon. In the presence of this catalyst, various alcohols gave the
corresponding alkyl and aryl 2,3-unsaturated glycopyranosides in excellent yields and
good anomeric selectivity under solvent-free condition. 4,6-Di-O-acetyl-2,3-dideoxy-α-
D-erythro-hex-2-enopyranosyl cyanide and ethyl 4,6-di-O-acetyl-2,3-dideoxy-1-thio-α-D-
erythro-hex-2-enopyranoside have also been prepared with trimethylsilyl cyanide and
ethanthiol as nucleophiles, respectively. The catalyst could be easily recovered and
reused several times with slight loss of activity. The selectivity to give α-anomers pre-
dominantly did not show any change in all runs.
Keywords Ferrier rearrangement; Pseudoglycals; C-Glycosylations; Glycosides; Thio-
glycosides
INTRODUCTION
There are only a limited number of reports on the synthesis of pseudogly-
cals (hex-2-enoglycopyranosides), but it has an important place in the field
of carbohydrate chemistry. These compounds can be further functionalized
Received August 1, 2009; accepted November 4, 2009.
Address correspondence to Ezzat Rafiee, Faculty of Chemistry, Razi University, Ker-
manshah 67149, Iran. E-mail: ezzat rafiee@yahoo.com; e.rafiei@razi.ac.ir
20

Synthesis of Pseudoglycals
21
and serve as chiral intermediate[1,2] in the synthesis of glycopeptide building
blocks,[3] uronic acids,[4] and modified carbohydrates and oligosaccharides.[5]
2,3-Dideoxy sugars, which are easily derived from hex-2-enoglycopyranosides,
are common structural units in many medicinally significant molecules such
as antibiotics.[6,7] For these reasons, preparation of 2,3-unsaturated glycosides
is an interesting goal.
The acid-catalyzed allylic rearrangement of glycals in the presence of al-
cohols, known as Ferrier rearrangement,[8–11] is widely used to obtain 2,3-
unsaturated glycosides. Besides, the synthetic utility of the Ferrier rearrange-
ment is not limited to the preparation of unsaturated O-glycosides, since the
variation of nucleophiles can result in S- and C-glycosides. The catalysts com-
monly employed to form 2,3-unsaturated glycosides are either Lewis acids or
oxidizing agents.[12–21] In addition, the use of protic acid catalysts such as
HClO4/SiO2[22] has also been reported for the preparation of these compounds.
With a few exceptions, many of these procedures have limitations in terms of
yields, selectivities, reaction temperatures, high amounts of reagent or cata-
lyst, expensive reagent, and equipment. In addition, some catalysts are toxic,
which restrict their applications. As a result, most of these methods do not
satisfy the rule of green chemistry. The establishment of “Green Carbohydrate
Chemistry” is of significant importance as a major branch of “Green Chem-
istry.” Therefore, progressive efforts have been done to introduce new environ-
mentally benign catalysts or safe reaction media. This can be achieved by the
development of strong solid acid catalysts that are stable, regenerable, and
active at moderate temperatures.
Heteropoly acids (HPAs) are promising solid acid catalysts for various or-
ganic reactions.[23] Among them, the catalytic function of the Keggin family
has attracted much attention. Keggin-type HPAs have the general formula
L8-xXM12O40, where L is a countercation (proton, group I and II metals, and
transition metals); X is the heteroatom, also called the central atom (P5+, Si4+
etc.); x is its oxidation state; and M is the addenda atom (most commonly Mo6+
,
,
W6+, or V5+).[24] These compounds provide a good basis for the molecular de-
sign of mixed oxide catalysts and possess special characteristics that make
them very useful in catalysis; for instance, their highly acidic nature is very
interesting in industrial reactions.[25] In this context, we investigated glycosy-
lation reaction using environmentally benign HPA-based catalysts.
RESULTS AND DISCUSSION
As a part of our endeavor to develop a mild, rapid, and eco-friendly method
for glycosylation reaction, the we explored the use of heteropoly compounds
(HPCs) for Ferrier rearrangement. Successful uses of K5CoW12O40.3H2O as
an electron transfer catalyst in the reaction of 3,4,6-tri-O-acetyl-D-glucal (1)

E. Rafiee et al.
22
Table 1: Effect of different catalysts in the reaction of 1 with benzyl alcohola
Yield
(%)b
Entry
Catalyst
Time (min)
1
2
H3PW12O40
4
20
20
20
30
30
30
30
30
30
90
41
54
32
5
H5PMo10V2O40
H6PMo9V3O40
H7PMo8V4O40
3
4
5
6
7
K7[PTi2W10O40]
[(n-C4H9)4N]5 PMo2W9O39 (Sn2+.H2O)
[(n-C4H9)4N]3 PMo2W9O39 (Sn4+.H2O)
[(n-C4H9)4N]3 PMo2W9O39 (Ti4+.H2O)
[(t-C4H9)4N]4 PW11CoO39
0
13
0
0
6
8
9
10
Cs2.5H0.5PW12O40
aOnly α-anomer was observed.
bIsolated yield after purification by column chromatography and characterized by 1H NMR.
with various alcohols and aryl amines were previously studied in our labora-
tory.[26,27] However, these reactions were performed in CH3CN as solvent and
have not been extended either with S- or C-nucleophiles. In this report, we
describe our results on the interesting use of other HPCs as a catalyst for α-
selective synthesis of pseudoglycals in a solventless system.
Initially, catalytic performance of different HPAs, their salts, and transi-
tion metal-substituted heteropoly anions was investigated in model reaction
(Sch. 1). The results are summarized in Table 1. H3PW12O40 (PW) gave supe-
rior results in terms of yield and reaction time (Table 1, entry 1) while mixed-
addenda HPAs had low activities (Table 1, entries 2–4). HPA salts and metal-
substituted heteropoly anions showed poor or no catalytic activity in the reac-
tion of 1 with benzyl alcohol (Table 1, entries 5–10).
OAc
OAc
CH2OH
O
O
Solvent-free
r.t.
AcO
AcO
AcO
+
O
Ph
1
Scheme 1: Reaction of 1 with benzyl alcohol.
From environmental and economic considerations, it is desirable to use
HPAs as heterogeneous catalysts. This encouraged us to investigate the ef-
ficiency of PW/support as a catalyst in the reaction of 1 with benzyl alcohol
(Sch. 2). The results are summarized in Table 2. It is assumed that resonance
of the double bond increases the electron density of C3 and exerts its influ-
ence in the selective departure of the OAc group in this position. This reso-
nance makes the allylic oxonium intermediate more stable. [19,21] In all cases,

Synthesis of Pseudoglycals
23
Table 2: Effect of different supported H3PW12O40 (PW) catalysts in glycosylation of
benzyl alcohola
Yield
Entry
Catalyst
Time (min)
(%)b
1
2
3
4
5
6
7
8
PW/γ -Al2O3 (0.05 g)
PW/K10 (0.05 g)
PW/KSF (0.05 g)
PW/TiO2 (0.05 g)
PW/SiO2 (0.05 g)
PW/C (0.05 g)
60
30
30
15
10
5
11
32
41
43
91
96
96
96
PW/C (0.1 g)
3
PW/C (0.2 g)
2
aOnly α-anomer was observed.
bIsolated yield after purification by column chromatography and characterized by 1H NMR.
α-glycosides was exclusively produced. It was found that PW/C is the best
catalyst in comparison with others (Table 2, entries 1–6). Different amounts
of 40 wt.% of PW/C were used in the model reaction (Table 2, entries 6–8). It
was observed that by using 0.2 g of the catalyst, reaction time decreased only
3 min in comparison with 0.05 g of PW/C. Hence, from an economical point of
view, 0.05 g of 40 wt.% PW/C was selected as the best case for more investiga-
tions.
OAc
CH2OH
O
PW/support
AcO
1
+
Solvent-free, r.t.
O
Ph
Scheme 2: Reaction of 1 with benzyl alcohol in the presence of supported PW.
To examine the universality of PW/C in glycosylation reaction, this cat-
alyst was applied to the reaction of various nucleophiles with 1 in solvent-
free condition (Table 3). With alcohols as nucleophile, the reactions were com-
pleted within less than 10 min, except for cyclohexanol (Table 3, entries 1–4).
In the case of p-methoxyphenol (Table 3, entry 5), the reaction proceeded
smoothly to afford p-methoxyphenyl-4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-
hex-2-enopyranoside, whereas in our previous work,[26] K5CoW12O40.3H2O
was not efficient for phenols with different substitutions. Me3SiCN was
rapidly reacted with 1 to obtain 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-
2-enopyranosyl cyanide in excellent yield (Table 3, entry 6). When EtSH was
used as nucleophile (Table 3, entry 7), in addition to Ferrier product (4,6-
di-O-acetyl-2,3-dideoxy-1-thio-D-erythro-hex-2-enopyranoside), an anomeric
mixture of ethyl 2-deoxy-3,4,6-tri-O-acetyl-1-thio-D-hexopyranoside was also

24

Synthesis of Pseudoglycals
25
OAc
O
OAc
O
PW/C
AcO
AcO
1 + EtSH
+
AcO
CH3CN, r.t.
SEt
β = 9:1)
SEt
β = 8:2)
α:
α:
(40%,
(50%,
Scheme 3: Reaction of 1 with ethanethiol.
formed with 40% yield (Sch. 3). Due to the volatility of EtSH (bp. = 35◦C), this
reaction was performed in CH3CN as solvent.
The reusability of the PW/C was studied in the reaction of 1 with benzyl
alcohol. After each run, the reaction mixture was diluted with CH3CN; the
catalyst was removed by filtration, washed with CH3CN, and calcinated at
150◦C for 1 h before reusing. We have found that 40 wt.% of PW/C can be
reused several times with slightly loss of activity. The yield of the product for
model reaction decreased to 85% after the fourth run (Fig. 1). The selectivity to
α-anomer did not show any change and α-glycosides was exclusively produced
in all runs.
EXPERIMENTAL
Materials
PW was purchased from Aldrich and H3PMo12O40 hydrate from Merck.
Activated carbon, KSF, and K10 montmorillonite were purchased from Fluka.
Aerosil silica and titania were used from Degussa. γ-Alumina was obtained
100
80
60
First run
40
Second run
Third run
Fourth run
20
0
0
1
2
3
4
5
Time (min)
Figure 1: Reusability of 40 wt.% of PW/C; only α-anomer was observed in all runs.

E. Rafiee et al.
26
from Aldrich. [(n-C4H9)4N]Br, [(t-C4H9)4N]Br, Cs2CO3, TiCl4, SnCl4, sodium
molybdate, and disodium hydrogen phosphate were obtained from Merck;
sodium metavanadate and SnCl2 were used from Aldrich and Fluka, respec-
tively.
Catalyst Preparation
H3+xPMo12-xVxO40 (x = 2–4), K7PTi2W10O40, and [(t-C4H9)4N]4 PW11CoO39
catalysts were prepared and purified by literature procedures.[33–35] The
acidic salt Cs2.5H0.5PW12O40 was prepared from the Cs2CO3 and PW solu-
tion according to the literature method.[36] The syntheses of [(n-C4H9)4N]5
PMo2W9O39 (Sn2+.H2O), [(n-C4H9)4N]3 PMo2W9O39 (Sn4+.H2O), and [(n-
C4H9)4N]3 PMo2W9O39 (Ti4+.H2O) were started with the preparation of
α-K7PMo2W9O39.19H2O from β-Na8HPW9O34.24H2O and sodium molybdate
according to the procedures that were described in our previously published
papers.[37]
All supported catalysts were prepared by the impregnation method. The
solution of PW was used to impregnate activated carbon, silica, alumina,
titania, KSF, and K10 montmorillonite as supports, followed by drying as
described in our previously published papers.[38,39]
Glycosylation Using Alcohols and Phenol
The D-glucal (1) (1 mmol), an alcohol or phenol (1.5 mmol), and 0.05 g of
catalyst were added to a Pyrex tube fitted with a ground glass joint. These
compounds were ground together using a glass rod at rt (ca. 25◦C). Progress of
the reaction was followed by TLC. The mixture was diluted with CH3CN (2 ×
5 mL) and filtered. The filtrate was quenched with saturated NaHCO3 (10%,
25 mL) and then extracted with CH2Cl2 (3 × 25 mL). The organic layer was
dried over anhydrous sodium sulfate, filtered, and concentrated. The residue
was purified by plate silica gel chromatography to afford the pure product.
Products were characterized from their NMR spectral data.
Glycosidation Using Me3SiCN
A mixture of 1 (1 mmol), Me3SiCN (1 mmol), and 0.05 g of 40 wt.% PW/C
was added to a Pyrex tube fitted with a ground glass joint and crushed using a
glass rod at rt (ca. 25◦C). Progress of the reaction was followed by TLC. The re-
action mixture was diluted by diethyl ether (2 × 5 mL) and poured into mixture
of 1 M HCl (10 mL) and diethyl ether (5 mL). Extractive workup with EtOAc (3
× 15 mL) followed by column chromatography afforded pure glycoside, which
was characterized from its NMR spectral data.

Synthesis of Pseudoglycals
27
Glycosidation Using EtSH
A solution of 1 (1 mmol) and EtSH (5 mmol) in CH3CN (2 mL) was treated
with 0.05 g of 40 wt.% PW/C and stirred at rt (ca. 25◦C). Progress of the re-
action was followed by TLC. The reaction mixture was extracted with EtOAc,
dried, and concentrated. The resulting crude product was subjected to column
chromatography to afford the pure product, which was characterized from its
NMR spectral data.
CONCLUSIONS
In summary, various nucleophiles reacted with 3,4,6-tri-O-acetyl-D-glucal to
yield the corresponding 2,3-unsaturated glycosides in good to excellent yield
and short reaction times with high to excellent α-selectivity. The catalytic ac-
tivity of PW/C is remarkable and the use of inexpensive and reusable catalyst
under solvent-free conditions makes this method a quite simple, environmen-
tally benign, and eco-friendly procedure to prepare various 2,3-unsaturated
glycosides.
ACKNOWLEDGMENTS
The authors thank the Razi University Research Council and Kermanshah Oil
Refining Company for support of this work.
REFERENCES
1. Mallans, N.R. Carbohydrates Chemistry; Clarendon Press: Oxford, 1988, 73–85.
2. Saeeng, R.; Isobe, M. Partial synthesis of ciguatoxin (5R)-ABC segment. Tetrahe-
dron Lett. 1999, 40, 1911–1914.
3. Ramesh, N.G.; Balasubramanian, K.K. 2-C-Formyl glycals: emerging chiral syn-
thons in organic synthesis. Eur. J. Org. Chem. 2003, 4477–4487.
4. Danishefsky, S.J.; Bilodeau, M.T. Glycals in organic synthesis: the evolution of
comprehensive strategies for the assembly of oligosaccharides and glycoconjugates of
biological consequence. Angew Chem. Int. Ed. Engl. 1996, 35, 1380–1419.
5. Schmidt, R.R.; Angerbauer, R. Simple de-novo synthesis of reactive pseudoglycals
(hex-2-enopyranosides)-stereospecific α-glycoside coupling. Angew. Chem. Int. Ed. Engl.
1977, 16, 783–784.
6. Williams, N.R.; Wander, J.D. The Carbohydrates in Chemistry and Biochemistry;
Academic: New York, 1980, 761–798.
7. Descotes, G.; Martin, J.C. Sur l’isome´risation du 1,5-anhydro-3,4,6-tri-O-benzyl-
1,2-dide´soxy-D-arabino-hex-1-e´nitol on pre´sence d’acides de Lewis. Carbohydr. Res.
1977, 56, 168–172.
8. Ferrier, R.J.; Prasad, N. Unsaturated carbohydrates. Part IX. Synthesis of 2,3-
dideoxy-α-D-erythro-hex-2-enopyranosides from tri-O-acetyl-D -glucal. J. Chem. Soc. C
1969, 570–575.

E. Rafiee et al.
28
9. Marzabadi, C.H.; Franck, R.W. The synthesis of 2-deoxyglycosides: 1988–1999.
Tetrahedron 2000, 56, 8385–8417.
10. Ashry, E.S.H. El; Awad, L.F.; Atta, A.I. Synthesis and role of glycosylthio hetero-
cycles in carbohydrate chemistry. Tetrahedron 2006, 62, 2943–2998.
11. Ferrier, R.J.; Zubkov, O.A. Transformation of glycals into 2,3–unsaturated glycosyl
derivatives. Organic reactions 2003, 62, 569–736.
12. Grynkiewicz, G.; Priebe, W.; Zamojski, A. Synthesis of alkyl 4,6-di-o-acetyl-2,3-
dideoxy-α-D-threo-hex-2- enopyranosides from 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-
D-lyxo-hex-1-enitol (3,4,6-tri-O-acetyl-D-galactal). Carbohydr. Res. 1979, 68, 33–41.
13. Tilve, R.D.; Alexander, M.V.; Khandekar, A.C.; Samant, S.D.; Kanetkar, V.R. Syn-
thesis of 2,3-unsatureted glycopyranosides by Ferrier rearrangement in FeCl3 based
ionic liquid. J. Mol. Catal. A Chem. 2004, 223, 237–240.
14. Yadav, J.S.; Reddy, B.V.S.; Murthy, C.V.S.R.; Kumar, G.M. Scandium triflate cat-
alyzed Ferrier rearrangement: an efficient synthesis of 2,3-unsatureted glycopyrano-
sides. Synlett 2000, 1450–1451.
15. Sobhana Babu, B.; Balasubramanian, K.K. Indium trichloride catalyzed glycosi-
dation. An expeditious synthesis of 2,3-unsatureted glycopyranosides. Tetrahedron Lett.
2000, 41, 1271–1274.
16. Ronaldo, N.O.; Filho, J.R.F.; Srivastava, R.M. Microwave-induced synthesis of 2,3-
unsatureted O-glycosides under solvent-free conditions. Tetrahedron Lett. 2002, 43,
2141–2143.
17. Swamy, N.R.; Venkateswarlu, Y. An efficient method for the synthesis of 2,3-
unsatureted glycopyranosides catalyzed by bismuth trichloride in Ferrier rearrange-
ment. Synthesis 2002, 598–600.
18. Yadav, J.S.; Reddy, B.V.S.; Reddy, J.S.S. Dy(OTf)3-immobilized in ionic liquids: a
novel and recyclable reaction media for the synthesis of 2,3-unsaturated glycopyrano-
sides. J. Chem. Soc. Perkin Trans. 1 2002, 2390–2394.
19. Toshima, K.; Ishizuka, T.; Matsuo, G.; Nakata, M.; Konoshita, M. Glycosidation
of glycals by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as a catalytic promoter. J.
Chem. Soc. Chem. Commun. 1993, 704–706.
20. Sobhana Babu, B.; Balasubramanian, K.K. Lithium tetrafluoborate catalyzed Fer-
rier rearrangement—facile synthesis of alkyl 2,3-unsaturated glycopyranosides. Synth.
Commun. 1999, Synth. Commun., 4299–4305.
21. Pachamuthu, K.; Vankar, Y.D. Ceric ammonium nitrate-catalyzed tetrahydropy-
ranylation of alcohols and synthesis of 2-deoxy-O-glycosides. J. Org. Chem. 2001, 66,
7511–7513.
22. Agarwal, A.; Rani, S.; Vankar, Y.D. Protic acid (HClO4 supported on silica gel)-
mediated synthesis of 2,3-unsaturated-O-glucosides and a chiral furan diol from 2,3-
glycals. J. Org. Chem. 2004, 69, 6137–6140.
23. Firouzabadi, H.; Jafari, A.A. Heteropoly acids, their salts and polyoxometalates
as heterogenous, efficient and eco-friendly catalysts in organic reactions: some recent
advances. J. Iran. Chem. Soc. 2005, 2, 85–114.
24. Kozhevnikov, I.V. Catalysis by heteropoly acids and multicomponent polyoxomet-
alates in liquid-phase reactions. Chem. Rev. 1998, 98, 171–198.
25. Mizuno, N.; Misono, M. Heterogeneous catalysis. Chem. Rev. 1998, 98, 199–217.
26. Rafiee, E.; Tangestaninejad, Sh.; Habibi, M.H.; Mirkhani, V. A mild, efficient and
α-selective glycosidation by using potassium dodecatungstocobaltate trihydrate as cat-
alyst. Bioorg. Med. Chem. Lett. 2004, 14, 3611–3614.

Synthesis of Pseudoglycals
29
27. Rafiee, E.; Azad, A. Cobaltpolyoxometalate-cataltzed cyclization of glucal with aryl
amines: synthesis of 2,4-disubstituted tetrahydroquinolines. Bioorg. Med. Chem. Lett.
2007, 17, 2756–2759.
28. Naik, P.U.; Nara, S.J.; Harjani, J.R.; Salunkhe, M.M. Metal nitrates catalysed O-
glycosylation using acetyl glucal in organic solvents and ionic liquides: a comparative
investigation. J. Mol. Catal. A Chem. 2005, 234, 35–43.
29. Takhi, M.; Abdel-Rahman, A.A.H.; Schmidt, R.R. Highly stereoselective synthesis
of pseudoglycals via Yb(OTf)3 catalyzed Ferrier glycosylation. Synlett 2001, 427–429.
30. Yadav, J.S.; Reddy, B.V.S. InBr3-catalyzed Ferrier rearrangement: an efficient syn-
thesis of C-pseudoglycals. Synthesis 2002, 511–514.
31. Hayashi, M.; Kawabata, H.; Inoue, K. Thermal C-glycosylation of D-glucal with
trimethylsilyl cyanide. Carbohydr. Res. 2000, 325, 68–71.
32. Paul, S.; Jayaraman, N. Catalytic ceric ammonium nitrate mediated synthesis of
2-deoxy-1-thioglycosides. Carbohydr. Res. 2004, 339, 2197–2204.
33. Tsigdinos, G.A.; Halada, C.J. Molybdovanadophosphoric acids and their salts. I.
Investigation of methods of preparation and characterization. Inorg. Chem. 1968, 7,
437–441.
34. Johnson, B.J.S.; Stein, A. Surface modification of mesoporous, macroporous, and
amorphous silica with catalytically active polyoxometalate clusters. Inorg. Chem. 2001,
40, 801–808.
7−
5−
35. Domaille, P.J.; Knoth, W.H. Ti2Wl0PO40 and [CpFe(CO)2Sn]2W10PO38 prepa-
ration, properties, and structure determination by tungsten-183 NMR. Inorg. Chem.
1983, 22, 818–822.
36. Okuhara, T.; Watanabe, H.; Nishimura, T.; Inumaru, K.; Misono, M. Microstruc-
ture of cesium hydrogen salts of 12-tungstophosphoric acid relevant to novel acid catal-
ysis. Chem. Mater. 2000, 12, 2230–2238.
37. Rafiee, E.; Baltork, I.; Tangestaninejad, Sh.; Azad, A.; Moinee, S. Tin (II) polyox-
ometalates as an efficient catalyst for selective oxidation of sulfides to sulfoxides. Z.
Naturforsch. 2006, 61b, 601–606.
38. Rafiee, E.; Paknezhad, F.; Shahebrahimi, Sh.; Joshaghani, M.; Eavani, S.;
Rashidzadeh, S. Acid catalysis of different supported heteropoly acids for a one-pot
synthesis of β-acetamido ketones. J. Mol. Catal. A Chem. 2008, 282, 92–98.
39. Rafiee, E.; Eavani, S.; Rashidzadeh, S.; Joshaghani, M. Tungstophosphoric acid
supported on titania as an eco-friendly, green and reusable catalyst for the solvent-free
Hantzsch multi-component condensation. Heterocycles 2008, 75, 2225–2233.