1,3-dibromo-5,5-dimethylhydantoin (DBH) as a mild and efficient catalyst for chemoselective thioacetalization of carbonyl compounds and dethioacetalization under mild conditions

Article abstract of DOI:10.1080/10426500902917669

Hydantoin bromide is an effective catalyst for chemoselective thioacetalization of aldehydes in the presence of ketones under neutral conditions. In addition, a simple and efficient procedure for the deprotection of 1,3-dithianes and 1,3-dithiolanes of ar

Full text of DOI:10.1080/10426500902917669

This article was downloaded by: [University of West Florida]
On: 28 December 2014, At: 01:37
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
Phosphorus, Sulfur, and Silicon and the
Related Elements
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gpss20
1,3-Dibromo-5,5-dimethylhydantoin
(DBH) as a Mild and Efficient Catalyst
for Chemoselective Thioacetalization
of Carbonyl Compounds and
Dethioacetalization Under Mild
Conditions
a
b
c
Hojat Veisi , Mostafa Amiri , Amir Hossein Hamidian , Javad
d
e
b
Malakootikhah , Leila Fatolahi , Alireza Faraji , Alireza
f
g
a
Sedrpoushan , Behrooz Maleki , Shokufe Ghahri Saremi
,
h
i
a
Mohammad Noroozi , Fatemeh Bahadoori & Somayeh Veisi
a
Department of Chemistry , Payame Noor University (PNU) , Iran
Department of Chemistry , Bu-Ali Sina University , Hamedan, Iran
Department of Chemistry , University of Otago , Dunedin, New
b
c
Zealand
d
Research Center for New Technologies in Life Science Engineering ,
University of Tehran , Tehran, Iran
e
Department of Chemistry , Payame Noor University (PNU) ,
Aleshtar, Khoramabad, Iran
f
Chemical Industries Department , Iranian Research Organization for
Science and Technology (IROST) , Tehran, Iran
g
Department of Chemistry , Sabzevar Tarbiat Moallem University ,
Sabzevar, Iran
h
Research Institute of Petroleum Industry (PIPI) , Kermanshah, Iran
i
Science Faculty , Chemistry Department, Organic Chemistry, ITU ,
Istanbul, Turkey
Published online: 23 Mar 2010.
To cite this article: Hojat Veisi , Mostafa Amiri , Amir Hossein Hamidian , Javad Malakootikhah , Leila
Fatolahi , Alireza Faraji , Alireza Sedrpoushan , Behrooz Maleki , Shokufe Ghahri Saremi , Mohammad
Noroozi , Fatemeh Bahadoori & Somayeh Veisi (2010) 1,3-Dibromo-5,5-dimethylhydantoin (DBH)
as a Mild and Efficient Catalyst for Chemoselective Thioacetalization of Carbonyl Compounds and
Dethioacetalization Under Mild Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements,
185:4, 689-696, DOI: 10.1080/10426500902917669

To link to this article: http://dx.doi.org/10.1080/10426500902917669
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

Phosphorus, Sulfur, and Silicon, 185:689–696, 2010
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902917669
1
,3-DIBROMO-5,5-DIMETHYLHYDANTOIN (DBH) AS A
MILD AND EFFICIENT CATALYST FOR CHEMOSELECTIVE
THIOACETALIZATION OF CARBONYL COMPOUNDS AND
DETHIOACETALIZATION UNDER MILD CONDITIONS
1
2
3
Hojat Veisi, Mostafa Amiri, Amir Hossein Hamidian,
4
5
2
Javad Malakootikhah, Leila Fatolahi, Alireza Faraji,
6
7
Alireza Sedrpoushan, Behrooz Maleki, Shokufe Ghahri
1
8
9
Saremi, Mohammad Noroozi, Fatemeh Bahadoori, and
1
Somayeh Veisi
Department of Chemistry, Payame Noor University (PNU), Iran
1
2
Department of Chemistry, Bu-Ali Sina University, Hamedan, Iran
Department of Chemistry, University of Otago, Dunedin, New Zealand
Research Center for New Technologies in Life Science Engineering, University of
3
4
Tehran, Tehran, Iran
5
Department of Chemistry, Payame Noor University (PNU), Aleshtar,
Khoramabad, Iran
6
Chemical Industries Department, Iranian Research Organization for Science
and Technology (IROST), Tehran, Iran
7
Department of Chemistry, Sabzevar Tarbiat Moallem University, Sabzevar, Iran
8
Research Institute of Petroleum Industry (PIPI), Kermanshah, Iran
9
Science Faculty, Chemistry Department, Organic Chemistry, ITU, Istanbul, Turkey
Hydantoin bromide is an effective catalyst for chemoselective thioacetalization of aldehydes
in the presence of ketones under neutral conditions. In addition, a simple and efficient
procedure for the deprotection of 1,3-dithianes and 1,3-dithiolanes of aromatic, aliphatic,
and α,β-unsaturated aldehydes and ketones in solvent-free conditions to the corresponding
parent carbonyl compounds was successfully carried out with hydantoin bromide in excellent
yields.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Carbonyl compounds; DBH; deprotection; thioacetalization
INTRODUCTION
The protection of functional groups and their regeneration constitute important and
essential processes in the synthesis of polyfunctional molecules and complex natural prod-
1,2
ucts. Thioacetals are relatively stable toward a wide variety of reagents and are also useful
3
,4
in organic synthesis as acyl carbanion equivalents in C C bond-forming reactions. They
Received 2 February 2009; accepted 23 March 2009.
Address correspondence to Hojat Veisi, Department of Chemistry, Payame Noor University (PNU), Songhor,
Khoramabad, Iran. E-mail: h organo2005@yahoo.com
6
89

6
90
H. VEISI ET AL.
are usually prepared by the condensation of carbonyl compounds with thiols or dithiols
5
6
7
using a strong protic acid such as HCl or Lewis acids such as BF3.OEt2 or ZnCl2 as cat-
8
3
9
10
11
alysts. Other Lewis acids include AlCl3, WCl6, InCl3, P2O5/SiO2, and [bmim]HSO4.
12
13
A number of milder procedures employing lithium salts, NiCl2, trichloroisocyanuric
acid, NBS, I2, microwave, HBF4-SiO2, Y(OTf)3, VO(OTf)2,20 ScCl3, and
14
15
16
17
18
19
21
22
silica-functionalized sulfonic acid have also been reported for this purpose. The regener-
ation of parent carbonyl compounds is not always a facile and straightforward process, and
therefore development of dethioacetalization protocols has engaged the attention of organic
chemists over the years.2
3–26
Among the various reagents employed for this purpose are
dimethylsulfoxide in the presence of iodine27 or t-butyl chloride, N-halosuccinimide,
28
29
30
dinitrogen tetroxide complexes of iron(III) and copper(II) nitrates, 2,3-dichloro-
,6-dicyanobenzoquinone (DDQ),31 tellurium tetrachloride,
32
dimethylsulfoxide,
33
5
3
4
N-fluoro-2,4,6-trimethylpyridinium
triflate-water,
photosensitized
oxygenation
35
36
SiO2Cl/DMSO,37 N,N -diiodo-N,N -1,2-
ꢁ
ꢁ
reactions,
trichloroisocyanuric acid,
38
39
ethanediyl-bis(p-toluenesulphonamide),
zirconium sulfonyl phosphonate,
m-
ClC6H4CO3H/CF3CO2H,40 SeO2,
41
HgCl2,42 Hg(NO3)2.3H2O,
43
and oxone/KBr.
44
Unfortunately, many of these protocols suffer from the drawbacks such as a requirement
for stoichiometric amounts of catalysts, long reaction times, the use of expensive reagents
and/or chlorinated organic solvents, harsh reaction conditions, difficult workup, and in
some instances, strong acidic reagents.
RESULTS AND DISCUSSION
In this communication, we wish to report a mild and highly chemoselective procedure
for the conversion of aldehydes in the presence of ketones into 1,3-dithiolanes and 1,3-
dithianes using a catalytic amount of 1,3-dibromo-5,5-dimethylhydantoin (DBH) under
almost neutral reaction conditions (Scheme 1).
n
S
O
dithiol, DBH (0.1 mmol)
S
R
R'
CH CN , rt
R
3
R'
(
a)
(b)
R: aryl, alkyl
R: alkyl, H
n: 2, 3
'
O
N
Br
N
O
Br
DBH
Scheme 1
First the reaction of benzaldehyde, with 1,2-ethanedithiol in the presence of 1,3-
dibromo-5,5-dimethylhydantoin (DBH) (0.1 mmol) at room temperature using different
solvents such as CH2Cl2, CHCl3, CCl4, CH3CN, and EtOH were carried out (Table I). The
results show that CH3CN is a better solvent.
To test the generality and versatility of this procedure in the thioacetalization, we ex-
amined a number of aromatic, aliphatic, and α,β-unsaturated aldehydes and ketones using

DBH AS A MILD AND EFFICIENT CATALYST
691
a
Table I Solvent effect on the reaction of benzaldehyde and 1,2-ethanedithiol by DBH at room temperature
Entry
Solvent
Time (min.)
Yield (%)b
1
2
3
4
5
CH2Cl2
CHCl3
CCl4
CH3CN
EtOH
45
65
90
35
35
92
80
85
98
90
a
0
.1 mmol.
b
Isolated yield.
optimized conditions (Table II). As shown in Table II, various types of aromatic aldehydes
with electron-donating and electron-withdrawing groups were cleanly and rapidly con-
verted to the corresponding dithianes and dithiolanes in the presence of catalysts. However,
aromatic and aliphatic ketones were slowly converted to their corresponding S,S-acetals
(Table II, entries 19–22).
The difference in reactivity of the 1,3-dibromo-5,5-dimethylhydantoin (DBH) to-
wards aldehydes and ketones gave us impetus to study chemoselective reactions. Towards
this objective, we carried out initial experiments with equimolar mixtures of an aldehyde
and a ketone (Scheme 2). When an equimolar (1 mmol) mixture of p-methoxybenzaldehyde
and acetophenone was allowed to react with 1.1 mmol of 1,2-ethanedithiol and a catalytic
amount of DBH in acetonitrile at room temperature, a high yield (96%) of I was obtained,
and unchanged acetophenone was recovered (Scheme 2).
S
MeO
(96 %)
MeO
CHO
S
1
, 2-ethanedithiol (1.1 mmol)
DBH (0.1 mmol)
I
1
mmol
CH CN , rt
3
O
S
S
(0 %)
1
mmol
II
Scheme 2
To compare DBH with previously published methods for the thioacetalization of car-
bonyl compounds with benzaldehyde, p-chlorobenzaldehyde, and p-methoxybenzaldehyde,
we carried out the following studies, as shown in Table III. This clearly demonstrates that
DBH is a good catalyst for the thioacetalization of carbonyl compounds.
In continuation of our work in organic synthesis, we decided to study the role of DBH
in the deprotection of thioacetals and thioketals under various conditions (see Scheme S1,
available online in the Supplemental Materials). For this purpose, acetophenone dithioacetal
in methanol was stirred with DBH (0.5 mmol) at room temperature for 5 h, and the smooth
formation of acetophenone was observed in 90% yield. Methanol was found to be the best
solvent. In other solvents, such as carbon tetrachloride and dichloromethane, the reaction
was sluggish and did not go to completion.
In recent years, there has been an increasing interest in reactions that proceed in
the absence of solvents, due to the reduced pollution, low cost, and simplicity in process

6
92
H. VEISI ET AL.
Table II Thioacetalization of carbonyl compounds catalyzed by DBH in CH3CN at ambient conditions
DBH
Entry
1
Substrate
Producta
Time (min)[h]
(35)
Yield (%)
96
Ref.
13
2
3
4
5
6
7
8
9
(35)
(40)
(45)
(15)
(20)
(20)
(25)
(25)
(30)
(45)
90
92
90
97
97
98
98
94
90
90
13
16
16
13
13
16
11
13
13
16
1
1
0
1
1
2
(55)
88
16
1
1
1
1
1
3
4
5
6
7
(50)
(55)
[1.6]
[2]
90
90
86
80
92
18
18
13
13
16
[1.2]
1
8
[1.2]
90
16

DBH AS A MILD AND EFFICIENT CATALYST
693
Table II Thioacetalization of carbonyl compounds catalyzed by DBH in CH3CN at ambient conditions
Continued)
(
DBH
Entry
Substrate
Producta
Time (min)[h]
[4]
Yield (%)
75
Ref.
18
1
2
9
0
[5]
70
65
18
16
2
2
1
2
[4.5]
[5]
60
16
aProducts were characterized from their physical properties, comparison with authentic samples, and by
spectroscopic methods.
and handling of solvent-free reactions. Therefore, we decided to test this reaction under
solvent-free conditions. We found that the reaction was rapid and gave excellent yields of
the products when catalyzed by DBH in the presence of wet-SiO2 (3 min, 98%, see entry
21, Table S1, Supplemental Materials).
To test the generality and versatility of this procedure in the deprotection of thioac-
etals and thioketals, we examined a number of 1,3-dithianes and 1,3-dithiolanes of aro-
matic, aliphatic, and α,β-unsaturated aldehydes and ketones using the optimized conditions
Table III Reaction times and yield for previously published methods
Yield
(%)
Reaction
time
Ref.
—
Conditions
Substrate
96
80
96
89
95
35 min
40 min
165 min
300 min
60 min
DBH, 1,2 propanedithiol, CH3CN, rt
NBS, 1,2 propanedithiol, CH2Cl2, rt
NiCl2, 1,2 propanedithiol, CH2Cl2-MeOH, rt
CoCl2, 1,2 propanedithiol, CH3CN, rt
Trichloroisocyanuric acid, 1,2 propanedithiol,
CHCl3, rt
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
15
13
46
14
—
98
88
78
90
94
20 min
30 min
30 min
40 min
120 min
DBH, 1,3 propanedithiol, CH3CN, rt
CoCl2, 1,3 propanedithiol, CH3CN, rt
NBS, 1,3 propanedithiol, CH2Cl2, rt
Sc(OTf)3, 1,3 propanedithiol, CH2Cl2, rt
Trichloroisocyanuric acid, 1,2 propanedithiol,
CHCl3, rt
p-(Cl)-benzaldehyde
p-(Cl)-benzaldehyde
p-(Cl)-benzaldehyde
p-(Cl)-benzaldehyde
p-(Cl)-benzaldehyde
4
1
4
1
6
5
5
4
—
97
70
89
92
15 min
30 min
75 min
30 min
DBH, 1,3 propanedithiol, CH3CN, rt
NBS, 1,3 propanedithiol, CH2Cl2, rt
NiCl2, 1,3 propanedithiol, CH2Cl2-MeOH, rt
CoCl2, 1,3 propanedithiol, CH3CN, rt
p-(MeO)-benzaldehyde
p-(MeO)-benzaldehyde
p-(MeO)-benzaldehyde
p-(MeO)-benzaldehyde
1
1
4
5
3
6

6
94
H. VEISI ET AL.
(Table S1, Supplemental Materials). As shown in Table S1, various types of 1,3-dithianes
and 1,3-dithiolanes (aromatic, aliphatic, and α,β-unsaturated) with electron-donating and
electron-withdrawing groups were cleanly and rapidly converted to the corresponding par-
ent carbonyl compounds in the solvent-free conditions using DBH at room temperature.
Since DBH contains bromine atoms, which are attached to the nitrogen atoms, it
+
is very probable that they release Br in situ, which would be attacked by the dithiane,
making it a good leaving group with a subsequent attack by a water molecule leading to
44
the carbonyl.
CONCLUSIONS
In conclusion, in this study we have introduced a new and useful catalytic application
of DBH as an efficient catalyst for the thioacetalization of aldehydes and ketones under
mild reaction conditions. The method is highly chemoselective for protection of aldehydes
in the presence of ketones. Moreover, the method has advantages in terms of high yields
of products, short reaction times, operational simplicity, and easy workup of products.
In addition, we have introduced a new and useful solvent-free application of DBH as an
efficient reagent for dethioacetalization under mild reaction conditions at room temperature.
EXPERIMENTAL
General Procedure for Thioacetalization Catalyzed
by 1,3-Dibromo-5,5-dimethylhydantoin (DBH) in CH3CN
To a stirred solution of substrate (1 mmol) and DBH (0.1 mmol) in CH3CN (3 mL),
1,2-ethanedithiol or 1,3-propanedithiol (1.1 mmol) was added at room temperature. The
mixture was stirred for an appropriate time (Table II). After completion of the reaction
as indicated by TLC, the organic solvent was evaporated in vacuum, and then CH2Cl2
(10 mL) was added, and the catalyst was removed by filtration. The filtrate was evaporated
under reduced pressure to achieve crude products. The crude products were purified by
recrystallization from ethanol or column chromatography using n-hexane/acetone (10:1) as
the eluent system.
General Procedure for the Deprotection of 1,3-Dithianes and
1,3-Dithiolanes Using DBH in Solvent-Free Conditions
Substrate (1 mmol), DBH (0.5 mmol), and 0.5g wet-SiO2 were added to a mortar,
and the mixture was pulverized with a pestle. A spontaneous reaction took place (2–5 min,
Table S1, monitored by TLC (9:1, hexane/acetone)]. After completion of the reaction,
CH2Cl2 (10 mL) was added, and insoluble reagent was removed by filtration. The filtrate
was evaporated under reduced pressure, and the resulting crude material was purified by
chromatography column (eluent: CH2Cl2) to give pure carbonyl compounds.
Analytical Data for Compound 11 (Table II). IR (KBr): 3050, 2950, 2900,
−1
1
1
635, 1506, 1457, 1377, 1216, 1173, 1082, 742 cm . H NMR (90 MHz, CDCl3):
δH (ppm) 3.35–3.40 (m, CH2, 2H), 3.42–3.52 (m, CH2, 2H), 5.64 (s, CH, 1H), 7.65–8.15
(
4
m, CH aromatic, 4H). Anal. Calcd for C9H9NO2S2: C, 47.56; H, 3.99; N, 6.16. Found: C,
7.43; H, 4.05; N, 6.12. MS: m/z = 228 (M+H) .
+

DBH AS A MILD AND EFFICIENT CATALYST
695
Analytical Data for Compound 6 (Table II). IR (KBr): 3010, 3000, 2900, 1640,
−1 1
1
510, 1450, 1357, 1170, 740 cm . H NMR (90 MHz, CDCl3): δH (ppm) 1.80–2.15 (m,
CH2, 2H), 2.80–2.91 (m, CH2, 2H), 2.96–3.10 (m, CH2, 2H), 3.75 (s, CH3, 3H), 5.06 (s,
+
CH, 1H), 6.82–7.40 (m, CH aromatic, 4H). MS: m/z = 226 (M+H) .
REFERENCES
1
. T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 3rd ed. (John Wiley
and Sons Inc., New York, 1999), pp. 329–344.
2
3
4
5
6
7
. T. W. Greene, Protective Groups in Organic Synthesis (John Wiley: NewYork, 1981), p. 129.
. H. Yu, D. Dong, Y. Ouyang, and Q. Liu, Can. J. Chem., 83, 1741 (2005).
. L. Battaglia, F. Pinna, and G. Strukul, Can. J. Chem., 79, 621 (2001).
. P. C. Bulman Page, J. C. Prodger, and D. Westwood, Tetrahedron, 49, 10355 (1993).
. T. Nakata, S. Nagao, S. Mori, and T. Oishi, Tetrahedron Lett., 26, 6461 (1985).
. D. V. Evans, L. K. Truesdale, K. G. Grimm, and S. L. Nesbitt, J. Am. Chem. Soc., 99, 5009
(1977).
8
9
. B. C. Ong, Tetrahedron Lett., 21, 4225 (1980).
. S. Muthusamy, S. Arulananda Babu, and C. Gunanathan, Tetrahedron Lett., 42, 359 (2001).
1
0. B. F. Mirjalili, M. A. Zolfigol, A. Bamoniri, M. A. Amrolahi, and A. Hazar, Phosphorus, Sulfur,
and Silicon, 179, 1397 (2004).
1
1
1
1
1
1
1
1
1. N. Gupta, S. L. Goverdhan, and J. Singh, Catal. Commun., 8, 1323 (2007).
2. H. Firouzabadi, N. Iranpoor, and B. Karimi, Synthesis, 58 (1999).
3. T. H. Khan, E. Mondal, D. R. Sahu, and S. Islam, Tetrahedron Lett., 44, 919 (2003).
4. H. Firouzabadi, N. Iranpoor, and H. Hazarkhani, Synlett, 1641 (2001).
5. A. Kamal and G. Chouhan, Synlett, 474 (2002).
6. H. Firouzabadi, N. Iranpoor, and H. Hazarkhani, J. Org. Chem., 66, 7527 (2001).
7. G. Bez and D. Gogoi, Tetrahedron Lett., 47, 5155 (2006).
8. V. T. Kamble, B. P. Bandgar, D. B. Muley, and N. S. Joshi. J. Mol. Catal. A: Chem., 268, 70
(2007).
1
2
2
2
2
9. S. K. De, Tetrahedron Lett., 45, 2339 (2004).
0. S. K. De, J. Mol. Catal. A: Chem., 226, 77 (2005).
1. S. K. De, Synthesis, 828 (2004).
2. B. Karimi and M. Khalkhali, J. Mol. Catal. A: Chem., 271, 76 (2007).
3. J. S. Yadav, B. V. S. Reddy, S. Raghavendra, and M. Satyanarayana, Tetrahedron Lett., 43, 4679
(2002).
24. N. Komatsu, M. Uda, and H. Suzuki, Synlett, 984 (1995).
25. F. M. Moghadam, H. Z. Boeini, D. Zargarani, and G. R. Bardajee, Synth. Commun., 36, 1093
(2006).
2
2
2
2
3
3
3
6. A. R. Hajipour, S. E. Mallakpour, I. M. Baltork, and H. Adibi, Molecules, 7, 674 (2002).
7. J. B. Chattopadhyaya and A. V. Ramarao, Tetrahedron Lett., 58, 3735 (1973).
8. G. A. Olah, A. K. Mehrotra, and S. C. Narang, Synthesis, 151 (1982).
9. E. J. Corey and B. W. Erickson, J. Org. Chem., 36, 3553 (1971).
0. H. Firouzabadi, N. Iranpoor, and M. A. Zolfigol, Bull. Chem. Soc. Jpn., 71, 2169 (1998).
1. L. Mathew and S. Sankararaman, J. Org. Chem., 58, 7576 (1993).
2. H. Tani, T. Inamasu, K. Masumoto, R. Tamura, H. Shimizu, and H. Suzuki, Phosphorus, Sulfur,
and Silicon, 67, 261 (1992).
3
3
3
3
3. C. S. Rao, M. Chandrasekharam, H. Ila, and H. Junjappa, Tetrahedron Lett., 33, 8163, (1992).
4. A. S. Kiselyov and L. Strekowski, Tetrahedron, 49, 2151 (1993).
5. M. Kamata, M. Sato, and E. Hasegawa, Tetrahedron Lett., 33, 5085 (1992).
6. H. Firouzabadi, N. Iranpoor, and H. Hazarkhani, Phosphorus, Sulfur, and Silicon, 177, 2571
(2002).

6
96
H. VEISI ET AL.
3
3
3
4
4
4
4
7. H. Firouzabadi, N. Iranpoor, H. Hazarkhani, and B. Karimi, J. Org. Chem., 67, 2572 (2002).
8. R. Ghorbani-Vaghei and M. A. Zolfigol, J. Chin. Chem. Soc., 52, 327 (2005).
9. M. Curini, M. C. Marcotullio, E. Pisani, and O. Rosati, Synlett, 769 (1997).
0. J. Cossy, Synthesis, 1113 (1987).
1. S. A. Haroutounian, Synthesis, 39 (1995).
2. E. J. Corey and M. G. Bock, Tetrahedron Lett., 16, 2643 (1975).
3. M. H. Habibi, S. Tangestaninejad, M. Montazerzohori, and I. Mohamadpoor-Baltork, Molecules,
8, 663 (2003).
44. U. V. Desai, D. M. Pore, B. V. Tamhankar, S. A. Jadhav, and P. P. Wadgaonkar, Tetrahedron
Lett., 47, 8559 (2006).
4
4
5. A. Kamal and G. Chouhan, Tetrahedron Lett., 43, 1347 (2002).
6. S. K. De, Tetrahedron Lett., 45, 1035 (2004).