A new recyclable 1,4-bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB]·(Br3)2 ionic liquid reagent for selective bromination of anilines or phenols and α-bromination of alkanones under mild conditions

Article abstract of DOI:10.1039/c4ra03006k

1,4-Bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB] ·(Br₃)₂ has been synthesized and explored as a new efficient brominating agent. The crystalline ditribromide reagent is stable for months and acts as a safe source of bromine requiring just 0.5 equiv. for complete bromination. It has a high active bromine content per molecule and shows a remarkable reactivity toward various substrates in acetonitrile at room temperature. The prepared reagents were used as a green recyclable reaction media for the selective bromination of anilines, phenols and α-bromination of alkanones in excellent yields. The product can easily be isolated by just washing the highly water soluble 1,4-bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB]·(Br₃)₂ from the brominated product. The spent reagent can be recovered, regenerated, and reused without any significant loss. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra03006k

RSC Advances
View Article Online
View Journal | View Issue
PAPER
A new recyclable 1,4-bis(3-methylimidazolium-1-
yl)butane ditribromide [bMImB]$(Br3)2 ionic liquid
reagent for selective bromination of anilines or
phenols and a-bromination of alkanones under
mild conditions†
Cite this: RSC Adv., 2014, 4, 25898
a
b
Hojat Veisi, Alireza Sedrpoushan, Pourya Mohammadi,a Ali Reza Farajic
*
*
and Sami Sajjadifara
1,4-Bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB]$(Br3)2 has been synthesized and explored
as a new efficient brominating agent. The crystalline ditribromide reagent is stable for months and acts as
a safe source of bromine requiring just 0.5 equiv. for complete bromination. It has a high active bromine
content per molecule and shows a remarkable reactivity toward various substrates in acetonitrile at room
temperature. The prepared reagents were used as a green recyclable reaction media for the selective
bromination of anilines, phenols and a-bromination of alkanones in excellent yields. The product can
easily be isolated by just washing the highly water soluble 1,4-bis(3-methylimidazolium-1-yl)butane
ditribromide [bMImB]$(Br3)2 from the brominated product. The spent reagent can be recovered,
regenerated, and reused without any significant loss.
Received 4th April 2014
Accepted 2nd June 2014
DOI: 10.1039/c4ra03006k
www.rsc.org/advances
Bromination of aromatic compounds and a-bromination of tribromide [BBIm]Br3,16 ethylenebis(N-methylimidazolium)
alkanones have attracted much attention in recent years1 for the ditribromide (EBMIDTB),17 1-butyl-3-methylpyridinium tri-
synthesis of biologically active compounds such as potent bromide ([BMPy]Br3)18 and BBIm]Br3.19 Recently some ionic
antitumor, antibacterial, antifungal, antiviral, and antioxidizing liquid tribromides (IL-Br3À) for the preparation of bromoesters
agents. Numerous industrially valuable products such as from aromatic aldehydes20 and bromination of aromatic
pesticides, insecticides, herbicides, re retardants, and other substrates21 were reported. It would be extremely useful to
new materials carry the bromo functionality.2 These halides also develop further synthetic protocols for the synthesis of organic
undergo carbon–carbon bond formation3–5 or carbon–hetero- tribromide reagents.22
atom bond formation via aromatic functionalization protocols.6
Development of environmentally benign and efficient
Organic tribromide reagents (OTBs) are preferable as processes with simple work-up and high purity of the products
oxidants to molecular bromine, owing to the hazards associated with high yields is currently receiving considerable attention. In
with elemental bromine. Several tribromides have been repor- this context, tribromide ionic liquid plays an important role in
ted, that is, tetramethylammonium tribromide,7 phenyl- the process of obtaining monobromo derivatives with the ulti-
trimethylammonium tribromide,8 cetyltrimethylammonium mate goal of hazard-free, waste-free and solvent-free efficient
tribromide, tetrabutylammonium tribromide,9 1,8-diazabicyclo- synthesis of biologically active compounds that can be used as
[5,4,0]-tetrabutylammonium tribromide,10 1,2-dipyridiniumdi- precursors of natural products.23,24
tribromide-ethane (DPTBE),11 pyridine hydrobromide per-
In recent years, there has been considerable interest in
bromide,12 hexamethylenetetramine-bromine,13 and DABCO– developing green chemistry25 for organic synthesis due to
bromine.14 {[K.18-crown-6]Br3}n,15 1,3-di-n-butylimidazolium environmental demand and sustainability. There are various
kinds of alkyl imidazolium salts which are commercially
aDepartment of Chemistry, Payame Noor University(PNU), 19395-4697 Tehran, Iran.
E-mail: hojatveisi@yahoo.com; Fax: +98 831 8380709
bInstitute of Industrial Chemistry, Iranian research Organization for Science and
Technology, Tehran, Iran
available as room temperature ionic liquids (RTILs). The
combination of alkylimidazolium cation with the tribromide
anion should therefore lead to RTIL bromine analog. Ionic
liquids were introduced as alternative green reaction media
because of their unique chemical and physical properties of
non-volatility, noninammability, thermal stability, and ease
of recyclability.
cFaculty of chemistry, Pharmaceutical Sciences Branch, Islamic Azad University,
Tehran, Iran
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra03006k
25898 | RSC Adv., 2014, 4, 25898–25903
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Tribromides are more suitable than the liquid bromine
RSC Advances
because of their crystalline nature, hence easy for their storage,
transport, and maintenance of desired stoichiometry. Prepara-
tions of these reagents involve organic ammonium bromide
and molecular bromine in most cases, thus an indirect use of
toxic molecular bromine. So, in continuation of our interest in
organohalogen chemistry,26 herein, we have synthesized a novel
ditribromide reagent. The new reagent has higher bromine
content per molecule, better bromination efficiency and selec-
tivity and is devoid of phase transfer property, and the spent
reagent can be recovered and regenerated easily. In this paper
we wished to report the preparation of a new ditribromide
reagent (Scheme 1), development of a metal and ionic-liquid
free bromination protocol, and recovery of the reagent. The
reagent was prepared by treating 1-methylimidazole (2 equiv.)
with 1,4-dibromobutane (1 equiv.) at room temperature. The
resultant 1,4-bis(3-methylimidazolium-1-yl)butane di(bromide)
[bMImB]$(Br)2 as light brown crystals was treated with molec-
ular bromine. The orange precipitate of 1,4-bis(3-methyl-
imidazolium-1-yl)butane ditribromide [bMImB]$(Br3)2 was
ltered (96% yield) and was recrystallized in acetonitrile to
obtain large crystals as shown in Fig. 1. The compound has been
characterized by spectral and analytical data. This crystalline
compound (Fig. 1) is stable for several months at room
temperature without loss of its activity.
Fig.
1
Crystals of 1,4-bis(3-methylimidazolium-1-yl)butane ditri-
bromide [bMImB]$(Br3)2.
The [bMImB]$(Br3)2 showed an intense UV absorption at
267 nm (Fig. 2), typical for tribromide ion (Br3À).27
Fig. 2 The UV absorption of [bMImB]$(Br3)2.
[bMImB]$(Br3)2 was used as an alternative brominating
agent for bromination of activated aromatic compounds and
a-bromination of alkanones (Scheme 2). It is worthy to be noted
that bromination of organic compounds is usually effected by
using equimolar ratios of bromine or tribromide with the
substrate. To test the bromination efficiency of this new
reagent, 0.5 equiv. of the reagent 1,4-bis(3-methylimidazolium-
1-yl)butane ditribromide [bMImB]$(Br3)2 was added to
1.0 equiv. of phenol in acetonitrile (3 mL). The reaction was
completed within 10 minutes in 96% yield. Thus,
[bMImB]$(Br3)2 efficiently delivers the bromine to the reaction
medium and itself gets recovered quantitatively with adding
water, thereby acting as the perfect bromine carrier.
Various anilines and phenols were monobrominated with
complete selectivity in excellent yields at room temperature,
Scheme 1
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 25898–25903 | 25899

View Article Online
RSC Advances
Paper
an aromatic electrophilic substitution reaction para-orientation
is favored over ortho-orientation due to stereoelectronic effects.
Similarly, a variety of substituted anilines and pheols under-
went regioselective monobromination (entries 3–6). a-Naphthol
and b-naphthol, being a bulky molecule, took 40–50 min for
monobromination (entries 7, 8).
All the reactions were quenched by adding water. This
caused precipitation of the products as solids or oils, which
were readily extracted with ethyl acetate and then dried (either
with sodium sulfate or in vacuo). The aqueous phase containing
Scheme 2
and the results are summarized in Table 1. Phenol and aniline highly water-soluble IL was easily concentrated in vacuo to
were cleanly monobrominated, affording exclusively p-bromo- recycle [bMImB]$(Br)2, which then could be used to regenerate
phenol and p-bromoaniline (entries 1, 2). Regioselective [bMImB]$(Br3)2 with bromine (Scheme 3). Regeneration and
bromination of phenol and aniline is an important protocol in reusability are two signicant features of ionic liquids.28 The
organic synthesis because of their versatile synthetic interme- effectiveness of ionic liquid, their recyclability and regeneration
diates for a considerable number of useful transformations. In
Table 1 Monobromination of various anilines and phenols with [bMImB]$(Br3)2 at room temperaturea
Entry
Substrate
Product
Time (min)
Yield (%)
96
Ref.
11
1
10
2
3
4
5
6
15
10
15
10
15
95
96
90
98
88
11
30
30
31
11
7
50
40
90
90
30
11
8
a
All reactions were carried out with 0.5 equiv. of [bMImB]$(Br3)2 at room temperature.
25900 | RSC Adv., 2014, 4, 25898–25903
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Scheme 3
alkanones, we conducted the experiments with [bMImB]$(Br3)2
to ethyl 3-oxo-3-phenylpropanoate and ethyl acetoacetate, which
were also effective and gave the corresponding mono-
bromination products in excellent yields (Table 2, entries 4, 5).
To investigate the selectivity of this reagent, ethyl methyl ketone
as dissymmetric dialkyl ketone was chosen, but we could not
nd any selectivity under this system.
In conclusion, we have reported a novel ditribromide ionic
liquid reagent with high active bromine content per molecule,
which acts as a good brominating agent for brominating 1
equiv. of the substrate with just 0.5 equiv. of the reagent. The
prepared reagent were used as a green recyclable reaction media
for the selective bromination of anilines, phenols and
a-bromination of alkanones in excellent yields under mild
conditions. The signicant characteristics of the method which
are worth mentioning include high conversions, short process
time, mild reaction conditions, environmentally friendly
process, simple workup with good to quantitative yields and re-
usable ionic liquid.
Fig. 3 Reusability of ionic liquid [bMImB]$(Br3)2 in the bromination of
phenol.
processes were observed for the bromination of phenol and
found to be effective up to 5 cycles (Fig. 3).
The plausible mechanism is shown in Scheme 4.
[bMImB]$(Br3)2 exists in a rapid equilibrium with imidazolium
bromide and bromine in solution.
The ionic liquid under investigation was also effective for the
selective bromination of alkanones (Scheme 2). We found that
the reaction of acetophenone with [bMImB]$(Br3)2, could occur
rapidly in acetonitrile at room temperature and completed
within 30 min to give a-bromoacetophenone (Table 2, entry 1).
In similar fashion, the reaction of [bMImB]$(Br3)2 with a variety
of alkanones was investigated, we found that the reaction is
general and applicable to several substituted acetophenone
containing different substitutes, such as methyl and methoxy
(Table 2, entries 2,3). In order to explore the generality of the
method developed for the synthesis of monobromination of
Experimental section
Preparation of 1,4-bis(3-methylimidazolium-1-yl)butane
dibromide [bMImB]$(Br)2
1,4-Dibromobutane (10.79 g, 50.0 mmol) was mixed with 1-
methylimidazole (8.16 g, 99.5 mmol) and the reaction mixture
was kept at room temperature for 48 h. The resulting dark solid
was crushed under acetone, ltered, washed with small
portions of acetone and dried under reduced pressure, leaving
the desired 1,4-bis(3-methylimidazolium-1-yl)butane di(bro-
mide) [bMImB]$(Br)2 as light brown crystals (14.62 g, 77%
yield). Melting point: 126–128 ꢀC. IR (KBr) 3146, 3093, 3088,
Scheme 4 Plausible mechanism.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 25898–25903 | 25901

View Article Online
RSC Advances
Paper
Table 2 Monobromination of various alkanones with [bMImB]$(Br3)2 at room temperaturea
Entry
Substrate
Product
Time (min)
30
Yield (%)
96
Ref.
11
1
2
25
25
92
96
29
29
3
4
20
20
95
90
29
29
5
a
All reactions were carried out with 0.5 equiv. of [bMImB]$(Br3)2 at room temperature.
2966, 2856, 1635, 1575, 1456, 1427, 1168, 856, 788, 758, 624
General procedure for bromination of anilines or phenols
1
cmÀ1. H NMR (D2O) (ppm) d: 8.59 (s, 2H, CH imidazolium);
To a mixture of anilines or phenols (2.0 mmol) in 2 mL aceto-
nitrile, was added 1,4-bis(3-methylimidazolium-1-yl)butane
ditribromide (1.0 mmol) and stirred at room temperature. Aer
disappearance of the starting material (monitored by TLC;
n-hexane–acetone 5 : 1), water was added into the reaction
mixture to quench the IL. The resulting reaction mixture was
extracted with ethyl acetate, separated from the organic layer,
dried over sodium sulfate, and concentrated to afford pure
monobromo anilines or monobromo phenols.
7.33 (t, 2H, CH imidazolium); 7.29 (s, 2H, CH imidazolium);
4.10 (t, 4H, NCH2); 3.74 (s, 6H, NCH3); 1.76 (m, 4H, CH2CH2).
13C NMR (CDCl3) (ppm) d: 136.8, 129.1 and 118.6 (CH imida-
zolium); 46.6 (NCH2); 30.6 (NCH3); 25.8 (CH2).
Preparation of 1,4-bis(3-methylimidazolium-1-yl)butane
ditribromide [bMImB]$(Br3)2
In a fume cupboard, molecular bromine (1.0 mL, 2.0 mmol) was
added dropwise over 10 min to 1,4-bis(3-methylimidazolium-1-
yl)butane dibromide (0.380 g, 1.0 mmol) under stirring and
General procedure for bromination of alkanones
To a mixture of alkanone (2.0 mmol) in 2 mL acetonitrile, was
added 1,4-bis(3-methylimidazolium-1-yl)butane ditribromide
(1.0 mmol) and stirred at room temperature. Aer disappear-
ance of the starting material (monitored by TLC; n-hexane–
acetone 7 : 1), water was added into the reaction mixture to
quench the IL. The resulting reaction mixture was extracted
with diethyl ether, separated from the organic layer, dried over
sodium sulfate, and puried by ash column chromatography
over silica gel (hexane–EtOAc 10/2).
cooling in an ice-bath affording
a deep orange solid
[bMImB]$(Br3)2 ionic liquid, and stirring was continued for 2 h.
The orange precipitate was recrystallized from acetonitrile to
yield 1.77 g (96% yield) of 1,4-bis(3-methylimidazolium-1-yl)-
butane ditribromide [bMImB]$(Br3)2. Melting point: 132 ꢀC. UV
(CH3CN) 267 nm. IR (KBr) 3158, 3136, 3086, 2966, 2856, 1635,
1595, 1570, 1556, 1464, 1400, 1162, 1103, 837, 742, 617 cmÀ1.1H
NMR (D2O) (ppm) d: 8.83 (s, 2H, CH imidazolium); 7.55 (m, 4H,
CH imidazolium); 4.33 (t, 4H, NCH2); 3.96 (s, 6H, NCH3); 1.99
(m, 4H, CH2CH2). 13C NMR (CDCl3) (ppm) d: 123.7, 123.6 and
122.0 (CH imidazolium); 48.6 (NCH2); 35.8 (NCH3); 26.0 (CH2).
Regeneration of ionic liquid
Anal. calcd for C12H20Br6N4: C, 20.60; H, 2.88; N, 8.01; Br, 68.51. Aer the addition of water into the reaction mixture, the water
Found: C, 20.10; H, 2.19; N, 7.65; Br, 67.87%.
soluble ionic liquid 1,4-bis(3-methylimidazolium-1-yl)butane
25902 | RSC Adv., 2014, 4, 25898–25903
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
dibromide [bMImB]$(Br)2 was recovered by evaporation of the
aqueous solution and washing with diethyl ether in each case.
The recovered ionic liquid [bMImB]$(Br)2 was dried at 40 ꢀC for
12 h, and treated with molecular bromine (2 mmol) under
stirring and cooling in an ice-bath for 2 h to regenerate 1,4-bis-
(3-methylimidazolium-1-yl)butane ditribromide [bMImB]$(Br3)2
ionic liquid and reused for the subsequent reaction without loss
of activity.
5752; (f) J. Cheng, Y. Sun, F. Wang, M. Guo, J.-H. Xu,
Y. Pan and Z. Zhang, J. Org. Chem., 2004, 69, 5428.
6 (a) J. F. Hartwig, Angew. Chem., Int. Ed., 1998, 37, 2046; (b)
J. P. Wolfe, S. Wagaw, J.-F. Marcoux and S. L. Buchwald,
Acc. Chem. Res., 1998, 31, 805; (c) J. F. Hartwig, Acc. Chem.
Res., 1998, 31, 852.
7 (a) F. D. Cattaway and G. Hoyle, J. Chem. Soc., 1923, 654; (b)
M. Avramoff, J. Weiss and O. Schaechter, J. Org. Chem., 1963,
28, 3256.
8 S. Kajigneshi, T. Kakinami, H. Tokiyama, T. Hirakawa and
T. Okamoto, Chem. Lett., 1987, 627.
References
9 R. E. Buckles, A. I. Popov, W. F. Zelezny and R. J. Smith, J. Am.
Chem. Soc., 1951, 73, 4525.
1 R. C. Larock, Comprehensive Organic Transformations, Wiley-
VCH, New York, 2nd edn, 1999.
10 H. A. Muathen, J. Org. Chem., 1992, 57, 2740.
11 V. Kavala, S. Naik and B. K. Patel, J. Org. Chem., 2005, 70,
4267.
2 (a) G. W. Gribble, Chem. Soc. Rev., 1999, 28, 335; (b) A. Butler
and J. V. Walker, Chem. Rev., 1993, 93, 1937; (c) R. H. Seevers
and R. E. Counsell, Chem. Rev., 1982, 82, 575.
12 L. F. Fieser and M. Fieser, Reagents for Organic Synthesis,
Wiley, 1967, p. 967.
3 (a) J. K. Stille, Pure Appl. Chem., 1985, 57, 1771; (b) N. Miyaura
and A. Suzuki, Chem. Rev., 1995, 95, 2457; (c)
W. A. Herrmann, C.-P. Reisinger and P. Haerter, Aqueous-
PhaseOrganometallic Catalysis, ed. B. Cornils and W. A.
Herrmann, Wiley-VCH, Weinheim, Germany, 2004, pp.
511–523; (d) D. Zhao, Z. Fei, T. J. Geldbach, R. Scopelliti
and P. J. Dyson, J. Am. Chem. Soc., 2004, 126, 15876; (e)
A. C. Spivey, C. J. G. Gripton and J. P. Hannah, Curr. Org.
Synth., 2004, 1, 211; (f) R. B. Bedford, S. L. Hazelwood,
M. E. Limmert, D. A. Albisson, S. M. Draper, P. N. Scully,
S. J. Coles and M. B. Hursthouse, Chem.–Eur. J., 2003, 9,
3216; (g) B. M. Choudary, M. S. Chowdari, S. Naidu,
M. L. Kantam and B. J. Sreedhar, J. Am. Chem. Soc., 2002,
124, 14127.
13 I. Yavari and A. Shaabani, J. Chem. Res. (S), 1994, 7, 274.
14 M. M. Heravi, F. Derikvand, M. Ghassemzadeh and
B. Neumuller, Tetrahedron Lett., 2005, 46, 6243.
15 M. A. Zolgol, G. Chehardoli, S. Salehzadeh, H. Adams and
M. D. Word, Tetrahedron Lett., 2007, 48, 7969.
16 S. P. Borikar and T. Daniel, J. Iran. Chem. Soc., 2011, 8, 531.
17 R. Hosseinzadeh, M. Tajbakhsh, M. Mohadjerani and
Z. Lasemi, Synth. Commun., 2010, 40, 868.
18 S. P. Borikar, T. Daniel and V. Paul, Tetrahedron Lett., 2009,
50, 1007.
19 S. P. Borikar, T. Daniel and V. Paul, Synth. Commun., 2010,
40, 647.
20 W. Bao and Z. Wang, Green Chem., 2006, 8, 1028.
21 C. Chiappe, E. Leandri and D. Pieraccini, Chem. Commun.,
2004, 253.
22 M. K. Chaudhuri, A. T. Khan and B. K. Patel, Tetrahedron
Lett., 1998, 39, 8163.
4 (a) I. P. Beletskaya and A. V. Cheprakov, Chem. Rev., 2000,
100, 3009; (b) W. Cabri and I. Candiani, Acc. Chem. Res.,
1995, 28, 2; (c) A. Meijere and F. E. Meyer, Angew. Chem.,
Int. Ed. Engl., 1995, 33, 2379; (d) M. R. Eberhard, Org. Lett.,
2004, 6, 2125; (e) M. Oestreich, F. Sempere-Culler and
A. B. Machotta, Angew. Chem., Int. Ed., 2004, 44, 149; (f)
´
23 P.-M. Leo, C. Morin and C. Philouze, Org. Lett., 2002, 4, 2711.
¨
24 (a) K. Tatsuta, H. Ozeki, M. Yamaguchi, M. Tanaka and
T. Okui, Tetrahedron Lett., 1990, 31, 5495; (b) A. L. Willem,
V. Otterlo, J. P. Michael, M. A. Fernandes and
C. B. Koning, Tetrahedron Lett., 2004, 45, 5091.
25 I. T. Horvath and P. T. Anastas, Chem. Rev., 2007, 107, 2169.
26 H. Veisi and R. Ghorbani-Vaghei, Tetrahedron, 2010, 66,
7445.
27 M. K. Chaudhuri, A. T. Khan, B. K. Patel, D. Dey,
W. Kharmawophlang, T. R. Lakshmiparbha and
G. C. Mandal, Tetrahedron Lett., 1998, 39, 8163.
28 M. P. Kaushik and V. Polshettiwar, Indian J. Chem., 2006,
45B, 2542.
C. J. Kressierer and T. J. J. Muller, Angew. Chem., Int. Ed.,
2004, 43, 5997; (g) J.-C. Xiao, B. Twamley and J. M. Shreeve,
Org. Lett., 2004, 6, 3845; (h) Q. Yao, E. P. Kinney and
C. Zheng, Org. Lett., 2004, 6, 2997; (i) L. A. Arnold, W. Luo
and R. K. Guy, Org. Lett., 2004, 6, 3005; (j) S. Braese and
A. de Meijere, Metal-Catalyzed Cross-Coupling Reactions, ed.
A. DeMeijere and F. Diederich, Wiley-VCH, Weinheim,
Germany, 2004, pp. 217–315.
5 (a) K. Sonogashira, Comprehensive Organic Synthesis, ed. B.
M. Trost and I. Fleming, Pergamon Press, New York, 1991,
vol. 3, p. 521; (b) K. Sonogashira, Metal-Catalyzed Cross-
Coupling Reactions, ed. F. Diederich and P. J. Stang, Wiley-
´
29 S. J. Zhang and Z. G. Le, Chin. Chem. Lett., 2005, 16, 1590.
30 Z. G. Le, Z. C. Chen, Y. Hu and Q. G. Zheng, Chin. Chem. Lett.,
2005, 16, 1007.
VCH, Weinheim, Germany, 1998, p. 203; (c) D. Garcıa,
A. M. Cuadro, J. Alvarez-Builla and J. J. Vaquero, Org. Lett.,
2004, 6, 4175; (d) R. B. DeVashre, L. R. Moore and
K. H. Shaughnessy, J. Org. Chem., 2004, 69, 7919; (e)
S. Urgaonkar and J. G. Verkade, J. Org. Chem., 2004, 69,
31 S. A. Pourmousavi and P. Salehi, Acta Chim. Slov., 2009, 56,
734.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 25898–25903 | 25903