NaHSO4 supported on silica gel: An alternative catalyst for Ferrier rearrangement of glycals

Article abstract of DOI:10.1016/j.carres.2011.08.023

NaHSO₄ supported on silica gel catalyses the Ferrier rearrangement reaction of 3,4,6-tri-O-acetyl-d-glucal with alcohols and thiols to give the corresponding 2,3-unsaturated glycosides in high anomeric selectivity and good to excellent yield in short reaction time.

Full text of DOI:10.1016/j.carres.2011.08.023

Carbohydrate Research 346 (2011) 2528–2532
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
NaHSO4 supported on silica gel: an alternative catalyst for Ferrier
rearrangement of glycals
⇑
Henok H. Kinfe , Fanuel M. Mebrahtu, Khuphukile Sithole
Research Centre in Synthesis and Catalysis, Department of Chemistry, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 June 2011
Received in revised form 2 August 2011
Accepted 24 August 2011
Available online 5 September 2011
NaHSO4 supported on silica gel catalyses the Ferrier rearrangement reaction of 3,4,6-tri-O-acetyl-D-glucal
with alcohols and thiols to give the corresponding 2,3-unsaturated glycosides in high anomeric selectiv-
ity and good to excellent yield in short reaction time.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
NaHSO4
Silica gel
Ferrier rearrangement
Glucal
Glycoside
1. Introduction
and cost of catalyst. The use of basic23 and weak acid catalysts has
received little attention as alternatives in alleviating some of the
Ferrier rearrangement is a Lewis acid catalyzed allylic rear-
rangement of glycals in the presence of alcohols to yield 2,3-unsat-
urated glycosides.1 As shown in Scheme 1 the reaction proceeds via
a cyclic oxocarbonium intermediate 2 and can be intercepted by
nucleophiles other than an alcohol such as halides and carbanion
to give the corresponding products.2 Even though the reaction is
efficient, the requirement for a Lewis acid as a catalyst causes
restriction to the glycals and glycosyl acceptors to be used and
its wider synthetic applications.2a This called for the development
of non-acidic catalyzed allylic rearrangement as an alternative to
the original Ferrier rearrangement reaction. Since the report of
the reaction by Ferrier in 1969,1 several promoters have been re-
ported and can be broadly categorized into three, namely: Lewis
acids (such as BF3ÁOEt2,1,3 Bi(OTf)3 with and without SiO2,4 FeCl3,5
acidic Montmorillonite K-10,6 I2,7 InCl3,8 CeCl3Á7H2O,9 Sc(OTf)3,2b
Al(OTf)3,10 ZnCl2/Al2O3,11 TMSOTf,12 Pd(OAc)2,13 K5CoW12O44Á3H2O,14
limitations. Thus, the search for an inexpensive, readily available,
and convenient catalyst is desirable.
Recently, NaHSO4 supported on silica gel has attracted consider-
able attention due to its low cost, ease of preparation, mildness,
recoverability, reusability, and insensitivity to moisture. It has been
applied as a catalyst in the opening of epoxides into b-hydroperoxy
alcohols,24 synthesis of trisubstitutedquinolines,25 b-enaminones,26
N-acylsulfonamides,27 aryl-14-H-dibenzo[a.j]xanthenes,28 amid-
oalkyl naphthols,29 coumarins,30 and selective monoacetylation of
unsymmetrical diols.31 In a continuation of our work to develop
new synthetic methodologies for the transformation of glycals,10,32
we report herein the ability of NaHSO4–SiO2 to promote Ferrier
rearrangement of glycals.
2. Result and discussion
Fe2(SO4)3ÁxH2O,15 zeolites,16 and SiO2 by microwave irradiation at
In our first attempts a solution of acetylated glucal 4 and benzyl
alcohol in acetonitrile was treated with catalytic amounts of NaH-
SO4–SiO2 at room temperature. However, TLC analysis showed no
formation of a product. Addition of stoichiometric amount of the
catalyst failed to show any change and the starting material was
recovered intact after work up. Reactions at different temperatures
were then carried out using benzyl alcohol as a model to investi-
gate the optimum conditions to effect Ferrier rearrangement and
it was found that the minimum temperature required to favor
formation of the product was at 80 °C. This was in accordance
with the literature report where H2SO4–SiO2 was employed as a
650 W17), protic acids (H2SO4–SiO2
and HClO4–SiO2,19 and
18
H3PO420) and oxidative promoters (NIS,2a DDQ,21 CAN,22 iodonium
dicollidinium perchlorate2a).
Although a number of catalysts have been reported in the liter-
ature as stated above, none of the methods reported is superior in
terms of yield, anomeric selectivity, reaction time, temperature,
amount of catalyst, catalyst reusability, environmental benignness,
⇑
Corresponding author. Tel.: +27 115593918; fax: +27 115592819.
E-mail address: hhkinfe@uj.ac.za (H.H. Kinfe).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.08.023

H. H. Kinfe et al. / Carbohydrate Research 346 (2011) 2528–2532
2529
Scheme 1. General reaction of Ferrier rearrangement.
and provided excellent yield of the rearranged compounds. The
low yield with longer reaction time could be attributed to the
decomposition of the starting/product material at high tempera-
ture in acidic medium.18
Since SiO2 alone has been reported to catalyze Ferrier rear-
rangement reaction under 650 W microwave irradiation,17 it was
imperative to investigate whether the activity of the NaHSO4–
SiO2 was the result of SiO2 alone or a combination of the two. Thus,
a reaction was set up at 80 °C using SiO2 as a catalyst to provide a
Ferrier product at no avail. The importance of SiO2 was then tested
by trying to effect Ferrier rearrangement of acetylated glucal 1
with benzyl alcohol in the presence of unsupported NaHSO4
(10 mol %). To our surprise the reaction gave the desired Ferrier
product but the rate of the reaction was very sluggish (45 min vs
5 min) proving it was the combination of NaHSO4 and SiO2 that
contributed to the efficiency of the catalyst.
Under the optimum conditions 1.2 equiv of several alcohols,
including primary, secondary, allylic and propargyl alcohols, and
thiols reacted with acetylated glucal 4 according to Scheme 2 using
2 mol % NaHSO4–SiO2 (3.0 mmol NaHSO4/g)31 at 80 °C to give the
corresponding 2,3-unsaturated-O and S-glycosides in good to
Scheme 2. Ferrier rearrangement of acetylated glucal 4 with different nucleophiles.
promoter.18 Temperatures less than 80 °C were not sufficient en-
ough to provide the needed activation energy while higher than
80 °C resulted in the formation of many by-products as judged
by TLC analysis. After finding the right temperature, investigation
was carried out to determine the minimum amount of catalyst re-
quired to effect complete conversion of the starting glucal into a
product. Thus, catalyst loadings of 1 and 2 mol % were investigated
to provide a guide. Reactions that were carried out at 80 °C using
1 mol % catalyst loadings went to completion in 60 min providing
low yield of the product while reactions carried out at the same
temperature but with 2 mol % were completed in less than 5 min
excellent yields and in very short reaction time with
a-anomer
as a major product. The results are shown in Table 1 and the selec-
tivities and yields compare favorably with reported methods
Table 1
NaHSO4–SiO2 catalyzed synthesis of 2,3-unsaturated glycosides 3,4,6-tri-O-acetyl-D-glucal and 3,4,6-tri-O-benzyl-D-glucala
Entry
Nucleophile
Product
Reaction time (min)
Yieldb (%)
a
:b ratioc
Ref.
OAc
OH
15
O
1
5
91
4:1
9:1
6:1
AcO
OBn
OAc
HO
HO
O
33
2
3
5
5
72
90
AcO
AcO
O
OAc
O
33
O
OAc
HO
20
4
5
40
60
85
80
8:1
7:1
O
AcO
AcO
O
O
OAc
OH
33
O
(continued on next page)

2530
H. H. Kinfe et al. / Carbohydrate Research 346 (2011) 2528–2532
Table 1 (continued)
Entry
Nucleophile
SH
Product
Reaction time (min)
Yieldb (%)
a
:b ratioc
Ref.
OAc
16
6
5
8
96
4:1
5:1
O
AcO
SPh
SH
OAc
HS
HS
HS
7
55
—
O
SH
10
AcO
S
OAc
10
8
9
5
8
65
50
>99:1
>99
—
O
AcO
AcO
S
OAc
SH
—
O
S
SH
OBn
22a
10
MeOH
180d
20
5:1
O
BnO
OMe
OBn
O
OH
34
11
12
13
180d
90
64
75
4:1
2:1
7:1
BnO
BnO
BnO
OBn
S
SH
OBn
O
HS
HS
45d
—
—
SH
10
OBn
O
10
60d
S
a
b
c
Substrate (1.8 mmol), 1.2 equiv alcohol/thiol, 1 mL CH3CN, 2 mol % NaHSO4–SiO2, 80 °C.
Isolated yields.
The anomeric ratios were based on the integration of the corresponding anomeric protons in the 1H NMR spectrum.
Performed at room temperature.
d
(Table 2). Products were identified by 1H and 13C NMR
spectroscopy.
3,4-6-tri-O-acetyl-
D
-glucal and 3,4-6-tri-O-benzyl-
D
-glucal with
alcohols and thiols. The short reaction time, high anomeric selec-
tivity, low catalyst loading, low cost, and stability of the catalyst
make the method attractive in organic synthesis. To the best of
our knowledge, this is the second report where a weak protic acid
(the first being H3PO4) has been used as a catalyst for the Ferrier
rearrangement reaction of glycals.
The notion that the group at position C-3 of the glucal has to be
a good leaving group (3-OAc or 3-SR) has been over ruled since 3-
O-unprotected8c and 3-O-benzyl protected10,15,16 glucals have re-
sulted in the formation of 2,3-unsaturated glycosides on treatment
with different Lewis acids. In agreement with our recent report
using Al(OTf)3,10 NaHSO4–SiO2 catalyzed the Ferrier rearrangement
reaction of perbenzylated glucal 6 with alcohols and resulted in a
mixture of the desired 2,3-unsaturated product and a significant
amount of the competitive product, benzyl glycoside 5k, due to
the strong nucleophilicity of the benzyloxy group eliminated from
position C-3 of the starting glucal (Scheme 3). However, when
stronger nucleophiles such as thiols were employed, the formation
the competitive product, glycoside 5k, was suppressed resulting in
2,3-unsaturated thioglycosides (entries 12 and 13 in Table 1) as
major products.
4. Experimental
The NaHSO4–SiO2 catalyst was prepared according to the proto-
col reported by Breton.31
4.1. General procedure for the Ferrier rearrangement of glycals
To a solution of a glycal (1.8 mmol) in CH3CN (1 mL) NaHSO4–
SiO2 (12 mg, 3.0 mmolNaHSO4/g)31 was added. The resulting
mixture was stirred at 80 °C (room temperature for 3,4,6-tri-O-
3. Conclusion
benzyl-D-glucal) till TLC analysis showed disappearance of the
starting material. After adding silica gel to the reaction mixture
at room temperature, the solvent was evaporated in vacuo without
heating until a free-flowing solid was obtained. The resulting solid
In conclusion, we have demonstrated that NaHSO4 sup-
ported on silica gel can catalyze the Ferrier rearrangement of

H. H. Kinfe et al. / Carbohydrate Research 346 (2011) 2528–2532
2531
Table 2
Comparison of NaHSO4–SiO2 with literature reported catalysts for the Ferrier rearrangement of 3,4,6-tri-O-acetyl-D-glucal with different alcohols4,11,17
Entry
Alcohol
Catalyst
Time
Yield %
a:b ratio
Amount of catalyst (mol %)
Ref.
4
4
CAN
Sc(OTf)3
Yb(OTf)3
BiCl3
InCl3
Bi(OTf)3–SiO2
Bi(OTf)3
SiO2 MW
NaHSO4–SiO2
3 h
3.5 h
3 h
1 h
10 min
15 min
3 min
10 min
5 min
90
85
7:1
5:1
9:1
10:1
6.3:1
2.2:1
4:1
10
5
10
5
20
OH
4
94
94
86
90
69
92
91
4
4
1
4
2
2
4
17
5:1
4:1
100 mg/mol glucal
2
—
4
4
CAN
Sc(OTf)3
Yb(OTf)3
BiCl3
Bi(OTf)3–SiO2
Bi(OTf)3
ZnCl2/Al2O3
NaHSO4–SiO2
6 h
1.5 h
4 h
1.5 h
2.5 h
5 min
10 min
5 min
80
93
4:1
10:1
10:1
10:1
7.8:1
a
10
5
10
5
2
HO
4
91
95
76
73
88
90
4
2
3
4
4
4
2
11
a
6:1
250 mg/0.37 mmol glucal
2
—
4
4
CAN
Sc(OTf)3
BiCl3
Bi(OTf)3–SiO2
Bi(OTf)3
3 h
1.5 h
1.5 h
2 h
3 min
1 h
90
95
4:1
7:1
11:1
a
a
7:1
10
5
5
2
2
HO
HO
4
95
51
75
88
83
72
4
4
4
I2
20
11
ZnCl2/Al2O3
NaHSO4–SiO2
20 min
5 min
a
9:1
250 mg/0.37 mmol glucal
2
—
4
4
CAN
Sc(OTf)3
Yb(OTf)3
InCl3
Bi(OTf)3–SiO2
Bi(OTf)3
ZnCl2/Al2O3
NaHSO4–SiO2
4.5 h
3 h
18 h
30 min
2 h
30 min
10
5
80
83
14:1
7:1
11:1
9:1
3:1
a
10
5
10
20
2
4
89
90
80
82
85
85
4
4
4
2
11
a
8:1
250 mg/0.37 mmol glucal
2
—
Scheme 3. Ferrier rearrangement of benzylated glucal 6 with MeOH and thiols.
was column chromatographed using 1:9 ethyl acetate/hexane elu-
ent to afford pure 2,3-unsaturated glycosides. Analytical data for
known compounds 5a–5f, 5j, and 5k were consistent with pub-
lished data (see Table 1 for references). Data for new compounds
are as follows.
3H), 1.69–1.59 (m, 4H), 1.49–1.40 (m, 2H), 1.31 (t, 1H, J = 7.8 Hz); 13
C
NMR (CDCl3, 100 MHz): d 170.7, 170.3, 129.0, 126.8, 80.3, 66.8, 65.0,
62.9, 33.4, 31.8, 29.4, 27.5, 24.4, 21.0, 20.8; MS (ESI) m/z (M+Na)⁄:
calcd 371.1; found 371.1.
4.1.3. Dodecanyl-4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-1-
thio-hex-2-enopyranoside (5h)
4.1.1. 2-Mercaptoethyl-4,6-di-O-acetyl-2,3-dideoxy-
a-
D-erythro-
1-thio-hex-2-enopyranoside (5g)
Yellowish oil; 1H NMR (CDCl3, 400 MHz): d 5.91 (d, 1H,
J = 10.4 Hz), 5.75 (d, 1H, J = 10.4 Hz), 5.52 (s, 1H), 4.35–4.20 (m,
2H), 4.14 (d, 1H, J = 11.2 Hz), 2.75–2.65 (m, 1H), 2.64–2.50 (m,
1H), 2.07 (s, 3H), 2.06 (s, 3H), 1.70–1.50 (m, 2H), 1.40–1.10 (m,
17H), 0.90–0.70 (m, 4H); 13C NMR (CDCl3, 100 MHz): 170.8,
170.3, 129.1, 126.7, 80.4, 66.8, 65.1, 63.0, 32.0, 31.9, 30.0, 29.6
(Â3), 29.5, 29.3, 29.2, 28.9, 22.7, 21.0, 20.8, 14.1; HRMS (ESI) m/z
(M+Na)⁄: calcd 437.2338; found 437.2328
Colorlessoil; 1HNMR (CDCl3, 400 MHz): d 5.91 (dd, 1H, J = 2.0 and
9.6 Hz), 5.89 (d, 1H, J = 10.0 Hz), 5.59 (s, 1H), 5.34 (dd, 1H, J = 6.6 and
10.8 Hz), 4.20–4.10 (m, 3H), 2.90–2.68 (m, 4H), 2.08 (s, 3H), 2.05 (s,
3H), 1.65 (t, 1H, J = 16.0 Hz); 13C NMR (CDCl3, 100 MHz): d 171.1,
170.6, 128.9, 127.6, 81.3, 67.3, 65.4, 63.4, 36.9, 25.6, 21.3, 21.2;
HRMS (ESI) m/z (M+H)⁄: calcd 307.0674; found 307.0665.
4.1.2. 5-Mercaptopentyl-4,6-di-O-acetyl-2,3-dideoxy-
a-D-
erythro-1-thio-hex-2-enopyranoside (5i)
4.1.4. 2-Mercaptoethyl-4,6-di-O-benzyl-2,3-dideoxy-
a-D-
Colorlessoil;1H NMR(CDCl3, 400 MHz):d 5.95(ddd, 1H, J = 2.0, 3.2
and 10.0 Hz), 5.75(td, 1H, J = 1.6 and10.4 Hz), 5.58–5.50 (m, 1H), 5.34
(dd, 1H, J = 2.0 and 9.2 Hz), 4.30–4.20(m, 2H), 4.13 (d, 1H, J = 10.0 Hz),
2.80–2.55(m, 2H), 2.50(q,2H, J = 7.2and14.4 Hz), 2.07(s, 3H), 2.06 (s,
erythro-1-thio-hex-2-enopyranoside (5l)
Colorless oil; 1H NMR (CDCl3, 400 MHz): d 7.35–7.26 (m, 10H),
6.00 (d, 1H, J = 10.0 Hz), 5.85 (td, 1H, J = 5.8 and 12.4 Hz), 5.60 (s,
1H), 4.65 (d, 1H, J = 12.0 Hz), 4.60 (d, 1H, J = 11.2 Hz), 4.50 (d, 1H,

2532
H. H. Kinfe et al. / Carbohydrate Research 346 (2011) 2528–2532
9. Yadav, J. S.; Reddy, V. S.; Reddy, K. B.; Satyanarayana, M. Tetrahedron Lett. 2002,
43, 7009–7012.
10. Simelane, S. B. Aluminium Triflate Mediated Reactions of Cyclic Enol Ethers.
Unpublished Thesis (M.Sc.), University of Johannesburg, 2010.
11. Gorityala, B. K.; Lorpitthaya, R.; Bai, Y.; Liu, X.-W. Tetrahedron 2009, 65, 5844–
5848.
J = 12.0 Hz), 4.40 (d, 1H, J = 11.6 Hz), 4.20 (dd, 1H, J = 1.2 and
9.2 Hz), 4.10 (dd, 1H, J = 1.6 and 9.2 Hz), 3.78 (dd, 1H, J = 4.0 and
10.4 Hz), 3.70 (dd, 1H, J = 1.2 and 10.8 Hz), 3.00–2.70 (m, 4H),
1.66 (t, 1H, J = 8.0 Hz); Anal. Calcd for C22H26S2O3: C, 65.64; H,
6.51; S, 15.93. Found: C, 65.44; H, 6.54; S, 13.87.
12. Abdel-Rahman, A. A.-H.; Winterfeld, G. A.; Takhi, M’.; Schmidt, R. R. Eur. J. Org.
Chem. 2002, 713–717.
13. (a) Kim, H.; Men, H.; Lee, C. J. Am. Chem. Soc. 2004, 126, 1336–1337; (b) de la
Figuera, N.; Forns, P.; Fernàndez, J.-C.; Fiol, S.; Fernández-Forner, D.; Albericio,
F. Tetrahedron Lett. 2005, 46, 7271–7274.
14. Rafiee, E.; Tangestaninejad, S.; Habibi, M. H.; Mirkhani, V. Bioorg. Med. Chem.
Lett. 2004, 14, 3611–3614.
15. Zhang, G.; Liu, Q.; Shi, L.; Wang, J. Tetrahedron 2008, 64, 339–344.
16. Levecque, P.; Gammon, D. W.; Jacobs, P.; De Vos, D.; Sels, B. Green Chem. 2010,
12, 828–835.
17. Du, W.; Hu, Y. Synth. Commun. 2006, 36, 2035–2046.
18. Zhou, J. F. et al Chin. Chem. Lett. 2010, 21, 922–926.
19. Agarwal, A.; Rani, S.; Vankar, Y. D. J. Org. Chem. 2004, 69, 6137–6140.
20. Gorityala, B. K.; Cai, S.; Lorpitthaya, R.; Ma, J.; Pasunooti, K. K.; Liu, X.-W.
Tetrahedron Lett. 2009, 50, 676–679.
4.1.5. Dodecanyl-4,6-di-O-benzyl-2,3-dideoxy-a-D-erythro-1-
thio-hex-2-enopyranoside (5m)
Yellowish oil; 1H NMR (CDCl3, 400 MHz):d7.40–7.10 (m, 10H), 5.93
(d, 1H, J = 10.0 Hz), 5.84 (d, 1H, J = 11.2 Hz), 5.53 (s, 1H), 4.70–4.37 (m,
4H), 4.23 (d, 1H, J = 9.2 Hz), 4.15 (d, 1H, J = 9.2 Hz), 3.80–3.60 (m, 2H),
2.75–2.50 (m, 2H), 1.70–1.50 (m, 2H), 1.40–1.10 (m, 17H), 0.90–0.70
(m, 4H); 13C NMR (CDCl3, 100 MHz): d 138.2, 138.1, 128.4, 128.3,
128.2, 127.9, 127.8, 127.7, 127.6, 80.6, 73.4, 73.3, 71.1, 70.2, 69.0,
68.9, 32.0, 31.9, 30.1, 29.7, 29.6, 29.5, 29.3, 29.2, 28.9, 22.7; HRMS
(ESI) m/z (M+Na)⁄: calcd 533.3065; found 533.3063.
21. Toshima, K.; Ishizuka, T.; Matsuo, G.; Nakata, M.; Kinoshito, M. J. Chem. Soc.,
Chem. Commun. 1993, 704–706.
22. (a) Pachamuthu, K.; Vankar, D. J. Org. Chem. 2001, 66, 7511–7513; (b) Yadav, J.
S.; Reddy, B. V. S.; Pandey, S. K. New J. Chem. 2001, 25, 538–540; (c) Paul, S.;
Jayaraman, N. Carbohydr. Res. 2004, 339, 2197–2204.
23. Watanabe, Y.; Itoh, T.; Sakakibara, T. Carbohydr. Res. 2009, 344, 516–520.
24. Liu, Y.-H.; Zhang, Z.-H.; Li, T.-S. Synthesis 2008, 3314–3318.
25. Desai, U. V.; Mitragotri, S. D.; Thopate, T. S.; Pore, D. M.; Wadgaonkar, P. P.
Arkivoc 2006, 15, 198–204.
26. Sapkal, S. B.; Shelke, K. F.; Shingate, B. B.; Shingare, M. S. J. Korean Chem. Soc.
2010, 54, 723–726.
27. Wu, L.; Yang, C.; Zhang, C.; Yang, L. Lett. Org. Chem. 2009, 6, 234–236.
28. Rostamizadeh, S.; Shadjou, N.; Amani, A. M.; Balalaie, S. Chin. Chem. Lett. 2008,
19, 1151–1155.
29. Shaterian, H. R.; Yarahmadi, H.; Ghashang, M. Turk. J. Chem. 2009, 33,
449–457.
30. Chavan, F.; Madje, B.; Bharad, J.; Ubale, M.; Ware, M.; Shingare, M.; Shinde, N.
Bull. Catal. Soc. India 2008, 7, 41–45.
31. Breton, G. W. J. Org. Chem. 1997, 62, 8952–8954.
32. (a) Gammon, D. W.; Kinfe, H. H.; De Vos, D. E.; Jacobs, P. A.; Sels, B. F.
Tetrahedron Lett. 2004, 45, 9533–9536; (b) Sels, B.; Levecque, P.; Brosius, R.; De
Vos, D.; Jacobs, P.; Gammon, D. W.; Kinfe, H. H. Adv. Synth. Catal. 2005, 347, 93–
104; (c) Levecque, P.; Gammon, D. W.; Kinfe, H. H.; Jacobs, P.; De Vos, D.; Sels,
B. Org. Biomol. Chem. 2007, 5, 1800–1806; (d) Gammon, D. W.; Kinfe, H. H.; De
Vos, D. E.; Jacobs, P. A.; Sels, B. F. J. Carbohydr. Chem. 2007, 26, 141–157; (e)
Levecque, P.; Gammon, D. W.; Kinfe, H. H.; Jacobs, P.; De Vos, D.; Sels, B. Adv.
Synth. Catal. 2008, 350, 1557–1568.
Acknowledgment
Research funds of the University of Johannesburg and the Research
Center for Synthesis and Catalysis are gratefully acknowledged.
References
1. Ferrier, R. J.; Prasad, N. J. J. Chem. Soc. 1969, 570–575.
2. (a) López, J. C.; Gómez, A. M.; Valverde, S.; Fraser-Reid, B. J. Org. Chem. 1995, 60,
3851–3858; (b) Yadav, J. S.; Reddy, B. V. S.; Chand, P. K. Tetrahedron Lett. 2001,
42, 4057–4059.
3. (a) Dunkerton, L. V.; Adair, N. K.; Euske, J. M.; Brady, K. T.; Robinson, P. D. J. Org.
Chem. 1988, 53, 845–850; (b) Wieczorek, E.; Thiem, J. Carbohydr. Res. 1998, 307,
263–270.
4. Babu, J. L.; Khare, A.; Vankar, Y. D. Molecules 2005, 10, 884–892.
5. Tilve, R. D.; Alexander, M. V.; Khandekar, A. C.; Samant, S. D.; Kanetkar, V. R. J.
Mol. Catal. A: Chem. 2004, 223, 237–240.
6. (a) Toshima, K.; Miyamoto, N.; Matsuo, G.; Nakata, M.; Matsumura, S. Chem.
Commun. 1996, 1379–1380;; (b) de Oliveira, R. N.; Filho, J. R. d. F.; Srivastava, R.
M. Tetrahedron Lett. 2002, 43, 2141–2143; (c) Shanmugasundaram, B.; Bose, A.
K.; Balasubramanian, K. K. Tetrahedron Lett. 2002, 43, 6795–6798.
7. Koreeda, M.; Houston, T. D.; Shull, B. K.; Klemke, E.; Tuinman, J. Synlett 1995,
90–92.
8. (a) Babu, B. S.; Balasubramanian, K. K. Tetrahedron Lett. 2000, 41, 1271–1274;
(b) Das, S. K.; Reddy, K. A.; Roy, J. Synlett 2003, 1607–1610; (c) Nagaraj, P.;
Ramesh, N. G. Tetrahedron Lett. 2009, 50, 3970–3973.
33. Balamurugan, R.; Koppolu, S. R. Tetrahedron 2009, 65, 8139–8142.
34. Kashyap, S.; Hotha, S. Tetrahedron Lett. 2006, 47, 2021–2023.