Selective synthesis of sulfoxides and sulfones from sulfides using silica bromide as the heterogeneous promoter and hydrogen peroxide as the terminal oxidant

Article abstract of DOI:10.1039/c4ra06132b

Silica bromide as a heterogeneous promoter and reagent is prepared from the reaction of silica gel with PBr₃as a non-hydroscopic, filterable, cheap, and stable yellowish powder that can be stored for months. The results show that silica bromide is a suitable and efficient promoter for the chemoselective oxidation of sulfides to the corresponding sulfoxides or sulfones in the presence of 30% H₂O₂in acetonitrile. The excellent yields, heterogeneous conditions, simplicity, compatibility with a variety of functionalities, and ease of isolation of the products make our procedure a practical alternative.

Full text of DOI:10.1039/c4ra06132b

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Selective synthesis of sulfoxides and sulfones from
sulfides using silica bromide as the heterogeneous
Cite this: RSC Adv., 2014, 4, 40505
promoter and hydrogen peroxide as the terminal
oxidant
a
Behrooz Maleki, Saba Hemmati,b Alireza Sedrpoushan,c Samaneh Sedigh Ashrafia
*
and Hojat Veisid
Silica bromide as a heterogeneous promoter and reagent is prepared from the reaction of silica gel with
PBr3 as a non-hydroscopic, filterable, cheap, and stable yellowish powder that can be stored for months.
The results show that silica bromide is a suitable and efficient promoter for the chemoselective oxidation
of sulfides to the corresponding sulfoxides or sulfones in the presence of 30% H2O2 in acetonitrile. The
excellent yields, heterogeneous conditions, simplicity, compatibility with a variety of functionalities, and
ease of isolation of the products make our procedure a practical alternative.
Received 30th June 2014
Accepted 18th August 2014
DOI: 10.1039/c4ra06132b
www.rsc.org/advances
that excess reagents or by-products remain attached to the
insoluble resin. These unwanted materials are then removed by
ltration and the pure product is isolated from the ltration.5–11
Introduction
In order to perform chemical reactions in heterogeneous media
rather than homogeneous, a number of ideas was deliberately
suggested by R. B. Merrield1 for use in polypeptide synthesis
and by R. L. Letsinger2 for polynucleotide synthesis. It was
demonstrated that the classical idea that chemical reactions
should be performed in a completely homogeneous medium
was not necessarily correct and that reactions can be accom-
plished even if one of the substrates was insoluble in the reac-
tion media. Uncatalyzed reactions of neat reactants are of
elemental importance in chemistry and one of the most
preferred transformations. The methodology of some organic
synthesis has been revolutionized by this idea in that the
normal procedures associated with the workup of a chemical
reaction are obviated and replaced by a simple ltration step.1,2
This general advantage of solid-phase synthesis has been
particularly exploited in polypeptide synthesis3 where a poly-
peptide is synthesized in a repetitive sequential manner on the
solid phase and the nal products are only liberated from the
polymer in a nal cleavage reaction. Another approach to using
polymer supports in organic synthesis was outlined by Fridkin,
Patchornik, and Katchalski,4 who showed that a polymer-bound
reagent could be used in heterogeneous reaction in such a way
Many specic advantages of using insoluble resins as
supports, reagents, or catalysts have been reviewed,12,13 these
include the simulation of high-dilution14,15 or pseudodilution16
conditions, the shhook and concentration principle,17 selec-
tive intrapolymeric reactions,18 bulk and steric effects of the
polymer backbone in asymmetric synthesis,19 the stabilization
of reactive substances,20,21 and the elimination of volatile
malodorous reagents.22,23
Oxidation of suldes is the most straightforward method for
the synthesis of sulfoxides and sulfones. Sulfones are valuable
synthetic intermediates for the construction of various chemi-
cally and biologically signicant molecules in particular.24,25
Sulfones represent an important course group of compounds
due to their properties and reactivity. The direct oxidation of
suldes is an important and widely studied reaction for the
preparation of sulfoxides and sulfones. However, the oxidation
of suldes to sulfones has been much less investigated as
compared to the oxidation of suldes to sulfoxides. For the
selective oxidation of suldes to sulfoxides and sulfones, a range
of oxidants have been studied. In addition, H2O2 was frequently
utilized in combination with different catalysts such as MoO3,26
CH3ReO3,27 dioxo-molybdenum(VI) complex,28 NH4Cl,29 poly-
oxometalate-cored dendrimers,30 silica–vanadia catalyst,31 silica
sulfuric acid,32 heterogeneous TiO2,33 tetra-(tetraalkylammoni-
um)octamolybdate,34 immobilized molybdenum hetero-
polyacid,35 TaC and NbC,36 sodium tungstate/PTC/
phenylphosphonic acid,37 MoO2Cl2,38 Cp0Mo(CO)3Cl,39 cer-
ium(IV) triate,40 cyanuric chloride,41 [SeO4{WO(O2)}2]2,42
composite oxide catalyst LiNbMoO6,43 carbon-based solid acid,44
aDepartment of Chemistry, Hakim Sabzevari University, Sabzevar 96179-76487, Iran.
E-mail: b.maleki@hsu.ac.ir; malekibehrooz@gmail.com; Fax: +98-571-4410300; Tel:
+98-571-4002643
bYoung Researchers and Elite Club, Kermanshah Branch, Islamic Azad University,
Kermanshah, Iran
cInstitute of Industrial Chemistry, Iranian Research Organization for Science and
Technology, Tehran, Iran
dDepartment of Chemistry, Payame Noor University(PNU), 19395-4697 Tehran, Iran
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1,3,4-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-tetrachloride,45 H3BO3,46 room temperature. Aer screening different solvents, it was found
H5IO6,47–49 ozone,50 an aqueous NaOCl,51 HOF$CH3CN,52 oxygen/2- that CH3CN is proved to be the optimum solvent and was used in
methylpropanal,53 NaIO4,54 oxone,55 ZnCl2/DBU,56 [(C18H37)2- subsequent optimization studies. At lower concentration of
(CH3)2N]3[SiO4H(WO5)3],57 TsOH/PhI(OAc)2,58 PyHBr3/TBN,59 hydrogen peroxide (1 mmol), the reaction took a long time (10
(C19H42N)2[MoO(O2)2(C2O4)]$H2O,60
and poly(4-vinylpyridine),61 silica-based tungstate interphase,62 (3 mmol), loading did not signicantly affect the yield and time.
and 30% H2O2.63
The reaction was also monitored with different silica bromide
poly(N-vinylpyrrolidone) min) andlow yield (86%). The increasing ofthe hydrogen peroxide
Besides extended reaction times, some of these processes loading, at a lower silica bromide loading (1 mmol) the reaction
suffer from drawbacks, such as elevated temperatures, unde- took longer time (8min) andlower yield (91%). Further increase in
sired side reactions occurring on other functional groups, the amount of silica bromide (3 mmol) in the mentioned reaction did
use of hazardous peracids, and toxic metallic compounds that not has signicant effect on the product time and yield. It was also
generate waste streams. However, a promoter was still required found that without H2O2, and silica bromide alone cannot oxidize
in those processes. Therefore, simple, convenient and envi- suldes to sulfoxides. Therefore, A ratio of (sulde–H2O2–SB;
ronmentally benign methods for the oxidation of suldes to 2 : 2 : 2) was found to be optimum for the complete conversion of
sulfoxides or to sulfones are still highly desired.
suldes to sulfoxides in CH3CN at room temperature.
In order to generalize the scope of the reaction, a series of
structurally diverse suldes were subjected to oxidation under
the optimized reaction conditions, and the results are pre-
sented in Table 1. Oxidation of allyl phenyl, alkyl aryl, aryl
benzyl, dialkyl, diaryl, cyclic, and heterocyclic suldes produced
excellent yields of the corresponding sulfoxides. It is notable
that the suldes were chemoselectively oxidized in the presence
of oxidation-prone functional groups, such as OH and C]C.
Encouraged by these results, we studied the complete
conversion of suldes (via sulfoxides) into sulfones. Initially, we
optimized amount of silica bromide and hydrogen peroxide for
oxidation of benzyl phenyl sulde (2 mmol) to corresponding
sulfone. The best result was obtained with a ratio of (benzyl
phenyl sulde–H2O2–SB; 2 : 2 : 2) in CH3OH at 40 ꢀC. To
investigate the versatility of the system, the reaction of oxida-
tion suldes (via sulfoxides) into sulfones was carried out in
CH3OH at 40 ꢀC. All reactions proceeded efficiently within
25–100 minutes at 40 ꢀC to provide the corresponding sulfones
derivatives in excellent yields ranging from 84–95% (Table 1).
A possible mechanism for oxidation of the sulde into the
corresponding sulfoxides and sulfones using H2O2 in the pres-
ence of silica bromide is shown in Scheme 2. Nucleophilic attack
of H2O2 on silica bromide leads to intermediate 1 in which the
oxygen atom is more electrophilic. Next, nucleophilic attack of
sulde 2 on this intermediate gives intermediate 3 followed by
the abstraction of hydrogen to yield the corresponding sulfoxide
4. Sulfoxide 4 reacts with the intermediate 1 to form 5, which
follows the abstraction of hydrogen produces sulfone 6.
Result and discussions
In continuation of our research on new synthetic methods in
organic synthesis,64–73 herein, we report the application of silica
bromide as a selective and efficient heterogeneous promoter for
the oxidation of suldes into sulfoxides and sulfones using
H2O2 in acetonitrile at room temperature (Scheme 1).
Heterogeneous reagents have gained signicant attraction
due to economic and environmental considerations. They can
be handled conveniently and removed from the reaction
mixture, thus making experimental procedures simple.74–77
Silica bromide as heterogeneous promoter and reagent is
prepared from reaction of silica gel with PBr3 as a non-hydro-
scopic, lterable, cheap, and stable yellowish powder that can
be stored for months.78
A preliminary study with benzyl phenyl sulde (2 mmol), 30%
H2O2 (2 mmol), and silica bromide (2 mmol Br per g silica) as a
model reaction quickly established that this oxidation protocol
produced the anticipated sulfoxide in excellent yield (98%) and in
a short reaction time (5 min) in CH3CN at room temperature.
Then, the inuence of different reaction parameters (amount of
reagents, temperature and solvent) on the efficiency of the oxida-
tion process was evaluated in this model reaction. The oxidation
was investigated invarious solvents such as toluene, THF, CH3CN,
CH3NO2, CH3OH, C2H5OH, CH3COOH, CH2Cl2 and CCl4 using
30% H2O2 (2 mmol), and silica bromide (2 mmol Br per g silica) at
Experimental
Chemicals were obtained from Merck and Fluka chemical
companies. Nuclear magnetic resonance spectra were recorded
on a Brucker Advanced DPX-250 MHz spectrometer using tetra-
methylsilane as internal standard. Infrared spectra were recor-
ded on a Perkin-Elmer 781 spectrometer. The plate silica gel used
for the preparation of silica bromide was type 60 (15–40 mm).
Procedure for preparation of silica bromide
To silica gel (40 g) and dry toluene (80 mL) in a round bottomed
Scheme 1 Conversion of sulfides into sulfoxides and sulfones.
40506 | RSC Adv., 2014, 4, 40505–40510
ask equipped with a condenser and a drying tube, was added
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Table 1 Conversion of sulfides to sulfoxides or sulfones
Timea (min)
Sulfoxide
10
Yieldb (%)
Timea (min)
Sulfone
75
Yieldb (%)
Entry
1
Substrate
91
94
91
92
2
3
10
10
90
80
92
99
90
95
4
5
3
5
30
25
98
94
6
7
8
9
7
5
7
7
96
92
94
89
30
40
35
45
92
90
94
84
10
11
12
5
7
7
91
94
89
40
95
50
90
89
85
13
14
10
10
92
94
40
60
90
82
15
5
95
70
92
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Table 1 (Contd.)
Timea (min)
Sulfoxide
Yieldb (%)
Timea (min)
Sulfone
Yieldb (%)
Entry
Substrate
16
10
96
100
90
a
b
The course of reaction was checked by TLC or GC. Yield of isolated pure sulde.
washed with Na2CO3 (20%, 10 mL). The organic layer was dried
over anhydrous Na2SO4. The solvent was removed under
reduced pressure to afford the desired product without further
purication (Table 1).
Conclusion
In conclusion, we have shown that silica bromide (SB) as
heterogeneous reagent can promote the selective oxidation of a
variety of suldes into the corresponding sulfoxides and
sulfones in the presence of H2O2 as the terminal oxidant. This
reagent is prepared from reaction of silica gel with PBr3 as a
non-hydroscopic, lterable, cheap, and stable yellowish powder
that can be stored for months. Although the literature reports a
number of procedures for the oxidation of suldes, the excellent
yields, heterogeneous conditions, simplicity, good availability
of starting materials, compatibility with a variety of function-
alities, and ease of isolation of the products make our procedure
a practical alternative.
Scheme 2 Proposed mechanism.
phosphorus tribromide (75 g, 0.21 mol) and reuxed for 18 h.
Aer cooling, the product was ltered and washed, rst, with
dry 1,4-dioxane (2 ꢁ 20 mL) and then with dichloromethane
(2 ꢁ 20 mL). The yellowish product was kept in dessicator. The
amount of bromosilyl group (2.2 mmol of Br per g silica) is
determined by a standard method.78
General procedure for the preparation of sulfoxides
Acknowledgements
To a mixture of sulde (2 mmol) and yellowish silica bromide
(2 mmol) in acetonitrile (5 mL) was added 30% H2O2 (2 mmol).
The mixture was stirred at room temperature for the appro-
priate period of time until complete consumption of the start-
ing material as observed by TLC. Aer completion of the
reaction, the reaction mixture was ltered to separate the white
SiO2. Then, the ltrate was extracted with EtOAc (10 mL) and
washed with Na2CO3 (20%, 10 mL). The organic layer was dried
over anhydrous Na2SO4. The solvent was removed under
reduced pressure to afford the desired product without further
purication (Table 1).
We are thankful to Payame Noor University (PNU), and Hakim
Sabzevari university for partial support of this work.
References
1 R. B. Merrield, J. Am. Chem. Soc., 1963, 85, 2149.
2 R. L. Letsinger and V. V. Mahade, J. Am. Chem. Soc., 1965, 87,
3526.
3 B. W. Erickson and R. B. Merrield, in The proteins, ed.H.
Neurath and R. L. Hill, Academic Press, New York, 1976,
vol. 2, p. 256.
4 M. Fridkin, A. Patchornik and E. Katchalski, J. Am. Chem.
Soc., 1966, 88, 3164.
5 F. Camps, J. Castells, J. Font and F. Vela, Tetrahedron Lett.,
1971, 12, 1715.
General procedure for the preparation of sulfones
To a mixture of sulde (2 mmol) and yellowish silica bromide
(2 mmol) in methanol (5 mL) was added 30% H2O2 (2 mmol) at
40 ꢀC. The mixture was stirred at 40 ꢀC for the appropriate
period of time until complete consumption of the starting
material as observed by TLC. Aer completion of the reaction,
the reaction mixture was ltered to separate the white solid
SiO2. Then, the ltrate was extracted with EtOAc (10 mL) and
6 W. Heitz and R. Michels, Angew Chem., Int. Ed. Engl., 1972,
11, 298.
7 S. McKinley and J. Rakshys Jr, J. Chem. Soc., Chem. Commun.,
1972, 134.
40508 | RSC Adv., 2014, 4, 40505–40510
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
8 C. R. Harrison and P. Hodged, J. Chem. Soc., Chem. Commun., 39 C. A. Gamelas, T. Lourenço, A. Pontes da Costa,
´
˜
1974, 1009.
A. L. Simplıcio, B. Royo and C. C. Romao, Tetrahedron
9 J. M. J. Frechet and K. E. Haque, Macromolecules, 1975, 8,
130.
10 N. M. Weishenker and C. M. Shen, Tetrahedron Lett., 1972,
13, 3281.
11 A. Patchornik and M. A. Kraus, Pure Appl. Chem., 1975, 43,
503.
12 N. K. Mathur and R. E. Williams, J. Macromol. Sci., Rev.
Macromol. Chem., 1976, 15, 117.
13 C. C. Leznoff, Chem. Soc. Rev., 1974, 3, 65.
14 M. Fridkin, A. Patchornik and A. Katchalski, J. Am. Chem.
Soc., 1965, 87, 4646.
15 R. H. Grubbs, C. Gibbons, L. C. Kroll, W. D. Bonds Jr and
C. H. Brubaker Jr, J. Am. Chem. Soc., 1973, 95, 2373.
16 P. Jayalekshmy and S. Mazur, J. Am. Chem. Soc., 1976, 89,
6710.
Lett., 2008, 49, 4708.
40 B. R. Raju, S. Sarkar, U. C. Reddy and A. K. Saikia, J. Mol.
Catal. A: Chem., 2009, 308, 169.
41 K. Bahrami, M. M. Khodaei and S. Sohrabnezhad,
Tetrahedron Lett., 2011, 52, 6420.
42 K. Kamata, T. Hirano and N. Mizuno, Chem. Commun., 2009,
3958.
43 S. Choi, J.-D. Yang, M. Ji, H. Choi, M. Kee, K.-H. Ahn,
S.-H. Byeon, W. Baik and S. Koo, J. Org. Chem., 2001, 66,
8192.
44 A. Zali, A. Shokrolahi, M. H. Keshavarz and M. A. Zarei, Acta
Chim. Slov., 2008, 55, 257.
45 K. Bahrami, M. M. Khodaei and M. S. Arabi, J. Org. Chem.,
2010, 75, 6208.
46 A. Rostami and J. Akradi, Tetrahedron Lett., 2010, 51, 3501.
17 I. T. Harrison and S. Harrison, J. Am. Chem. Soc., 1967, 89, 47 D. H. R. Barton, W. Li and J. A. Smith, Tetrahedron Lett.,
5723. 1998, 39, 7055.
18 M. K. Kraus and A. Patchornik, J. Am. Chem. Soc., 1971, 93, 48 L. Xu, J. Cheng and M. L. Trudell, J. Org. Chem., 2003, 68,
7325. 5388.
19 M. Kawama and S. Emoto, Tetrahedron Lett., 1972, 13, 4855. 49 T. Zweifel, M. Nielsen, J. Overgaard, C. B. Jacobsen and
20 T. M. Fyles and C. C. Leznoff, Can. J. Chem., 1976, 54, 935. K. A. Jørgensen, Eur. J. Org. Chem., 2011, 47.
21 L. Letsinger, L. M. J. Kornet, V. Mahadevan and D. M. Jerina, 50 M. Irfan, T. N. Glasnov and C. O. Kappe, Org. Lett., 2011, 13,
J. Am. Chem. Soc., 1964, 86, 5163. 984.
22 G. A. Crosby, N. M. Weinshenker and H. S. Uh, J. Am. Chem. 51 N. Fukuda and T. Ikemoto, J. Org. Chem., 2010, 75, 4629.
Soc., 1975, 7, 2232. 52 S. Rozen, Eur. J. Org. Chem., 2005, 2433.
23 R. Michels, M. Kato and W. Heitz, Makromol. Chem., 1976, 53 V. Khanna, G. C. Maikap and J. Iqbal, Tetrahedron Lett., 1996,
177, 2311. 37, 3367.
24 S. Patai and Z. Rappoport, Synthesis of Sulfones, Sulfoxides, 54 M. Moghadam, S. Tangestaninejad, V. Mirkhani,
and Cyclic Suldes, J. Wiley, Chichester, 1994.
25 P. Metzner and A. Thuillier, Sulfur Reagents in Organic
Synthesis, Academic Press, London, 1994.
26 M. M. Khodaei, K. Bahrami and M. Khedri, Can. J. Chem.,
2007, 85, 7.
27 S. Yamazaki, Bull. Chem. Soc. Jpn., 1996, 69, 2955.
28 I. Sheikhshoaie, A. Rezaeifard, N. Monadi and S. Kaa,
Polyhedron, 2009, 28, 733.
29 Q. Xue, Z. Mao, Y. Shi, H. Mao, Y. Cheng and C. Zhu,
Tetrahedron Lett., 2012, 53, 1851.
I. Mohammadpoor-Baltork and A. A. Abbasi-Larki, Appl.
Catal., A, 2008, 349, 177.
55 B. Yu, A.-H. Liu, L.-N. He, B. Li, Z.-F. Diao and Y.-N. Li, Green
Chem., 2012, 14, 957.
56 J. B. Feng, J. L. Gonga and X. F. Wu, RSC Adv., 2014, 4, 29273.
57 B. Ma, W. Zhao, F. Zhang, Y. Zhang, S. Wu and Y. Ding, RSC
Adv., 2014, 4, 32054.
58 B. Yu, C. X. Guo, C. L. Zhong, Z. F. Diao and L. N. He,
Tetrahedron Lett., 2014, 55, 1818.
59 H. Zhang and G. Wang, Tetrahedron Lett., 2014, 55, 56.
30 S. Nlate, L. Plault and D. Astruc, Chem.–Eur. J., 2006, 12, 903. 60 R. D. Chakravarthy, V. Ramkumar and D. K. Chand, Green
31 F. Gregori, I. Nobili, F. Bigi, R. Maggi, G. Predieri and
G. Sartori, J. Mol. Catal. A: Chem., 2008, 286, 124.
32 A. Shaabani and A. H. Rezayan, Catal. Commun., 2007, 8,
1112.
33 W. Al-Maksoud, S. Daniele and A. B. Sorokin, Green Chem.,
2008, 10, 447.
Chem., 2014, 16, 2190.
61 G. K. S. Prakash, A. Shakhmin, K. E. Glinton, S. Rao,
T. Mathew and G. A. Olah, Green Chem., 2014, 16, 3616.
62 B. Karimi, M. Ghoreishi-Nezhad and J. H. Clark, Org. Lett.,
2005, 7, 625.
63 M. Jereb, Green Chem., 2012, 14, 3047.
34 C. Yang, Q. Jin, H. Zhang, J. Liao, J. Zhu, B. Yu and J. Deng, 64 H. Veisi, B. Maleki, F. Hosseini Eshbala, H. Veisi, R. Masti,
Green Chem., 2009, 11, 1401. S. Sedigh Ashra and M. Baghayeri, RSC Adv., 2014, 4, 30683.
35 V. Palermo, G. P. Romanelli and P. G. Vazquez, Phosphorus, 65 H. Veisi, A. Aminimanesh, N. Khankhani and R. Ghorbani
Sulfur Silicon Relat. Elem., 2009, 184, 3258. Vaghei, RSC Adv., 2014, 4, 25057.
36 M. Kirihara, A. Itou, T. Noguchi and J. Yamamoto, Synlett, 66 H. Veisi, A. R. Sedrpoushan, P. Mohammadi, A. R. Faraji and
2010, 1557. S. Sajjadifar, RSC Adv., 2014, 4, 25898.
37 K. Sato, M. Hyodo, M. Aoki, X.-Q. Zheng and R. Noyori, 67 B. Maleki, R. Tayebee, M. Kermanian and S. Sedigh Ashra,
Tetrahedron, 2001, 57, 2469. J. Mex. Chem. Soc., 2013, 57, 290.
38 K. Jeyakumar and D. K. Chand, Tetrahedron Lett., 2006, 47, 68 B. Maleki and S. Sedigh Ashra, J. Mex. Chem. Soc., 2014, 58,
´
4573.
76.
This journal is © The Royal Society of Chemistry 2014
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View Article Online
RSC Advances
Paper
69 B. Maleki, S. Hemmati, R. Tayebee, R. S. Salemi, 73 B. Maleki and F. Taimazi, Org. Prep. Proced. Int., 2014, 46,
Y. Farokhzad, M. Baghayeri, F. Mohammadi Zonoz, 252.
E. Akbarzadeh, R. Moradi, A. Entezari, M. R. Abdi, 74 M. J. Climent, A. Corma and S. Iborra, RSC Adv., 2012, 2, 16.
S. Sedigh Ashra, F. Taimazi and M. Hashemi, Helv. Chim. 75 J. Cai, J. Huang, C. M. Li, H. Feng and Z. Liu, RSC Adv., 2013,
Acta, 2013, 96, 2147.
3, 18661.
70 B. Maleki, M. Gholizadeh and Z. Sepehr, Bull. Korean Chem. 76 Y. Qu, W. Zhou, L. Jiang and H. Fu, RSC Adv., 2013, 3, 18305.
Soc., 2011, 32, 1697.
77 S. H. Shuit, K. F. Yee, K. T. Lee, B. Subhash and S. H. Tan,
RSC Adv., 2013, 3, 9070.
78 F. Mohanazadeh, M. A. Zolgol, A. Sedrpushan and H. Veisi,
Lett. Org. Chem., 2012, 9, 598.
71 B. Maleki, S. S. Barzegar, Z. Sepehr, M. Kermanian and
R. Tayebee, J. Iran. Chem. Soc., 2012, 9, 757.
72 B. Maleki, R. Tayebee, Z. Sepehr and M. Kermanian, Acta
Chim. Slov., 2012, 59, 814.
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