An efficient facile and one-pot synthesis of benzodiazepines and chemoselective 1,2-disubstituted benzimidazoles using a magnetically retrievable Fe3O4 nanocatalyst under solvent free conditions

Article abstract of DOI:10.1039/c3ra47860b

Benzodiazepine and chemoselective 1,2-disubstituted benzimidazole derivatives were synthesized by the condensation reaction of o-phenylenediamine with ketones and aryl aldehydes using Fe₃O₄ nanoparticles as a recyclable catalyst unde

Full text of DOI:10.1039/c3ra47860b

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An efficient facile and one-pot synthesis of
benzodiazepines and chemoselective 1,2-
Cite this: RSC Adv., 2014, 4, 12826
disubstituted benzimidazoles using a magnetically
retrievable Fe O nanocatalyst under solvent free
conditions†
Received 21st December 2013
Accepted 18th February 2014
3 4
DOI: 10.1039/c3ra47860b
Ramen Jamatia, Mithu Saha and Amarta Kumar Pal*
www.rsc.org/advances
Benzodiazepine and chemoselective 1,2-disubstituted benzimidazole
derivatives were synthesized by the condensation reaction of o- benzodiazepine and benzimidazole derivatives are important
phenylenediamine with ketones and aryl aldehydes using Fe class of heterocyclic compounds having interesting pharmaco-
nanoparticles as a recyclable catalyst under solvent free conditions. logical and biological properties (Fig. 1).
Nitrogen containing [6, 7] and [6, 5] fused heterocycles like
3 4
O
4,5,30–32
These
This synthetic approach eliminates the use of toxic organic solvents compounds have also been known for their analgesic, anti-
with the added benefit of easy separation and reusability of the catalyst anxiety, hypnotic, anti-inammatory, anticonvulsant, muscle-
without compromising the yield or purity which makes the procedure relaxant, antitumor, antiulcer, antimicrobial, antiviral, anti-HIV
6–9
green.
and amnesic properties. Benzimidazole has also been found
to be effective against human cytomegalovirus (HCMV) and as
10,11
efficient selective neuropeptide YY1 receptor antagonists.
Green chemistry is the development of reaction processes that
reduce or eliminate the use or generation of hazardous
substances. In the last decade emphasis has been given to
Because of these medicinal and industrial applications, these
compounds have been of wide interest. These compounds can
also be used for the preparation of other important heterocyclic
compounds and are important intermediates in many organic
1
developing more environmentally benign synthetic organic
processes. Organic solvents pose the biggest challenge in this
regard due to their hazardous impact on the environment and
the human health. The design of a reaction process without
the use of hazardous organic solvent would be an important
step towards green chemistry. The present approach offers the
advantage of eliminating the use of hazardous organic
solvents.
12–15
reactions.
Benzodiazepines and benzimidazole derivatives have been
prepared by the condensation or cyclization of o-phenylenedi-
amine with a variety of carbonyl compounds. Various catalyst
16
17
18
19
such as BF
3
$Et
2
20
O, NBS, NaBH
4
,
,
LaCl
Sc(OTf)
3
$7H
2
O, poly-
21
22
23
24
phosphoric acid, AgNO
3
,
Yb(OTf)
3
3
,
3
Ga(OTf) ,
25
26
ZnCl
2
,
and ionic liquids, have been employed for the
Recently, metal nanoparticles have received much attention
in the eld of organic synthesis. Metal nanoparticles are much
more reactive than the bulk because of their higher surface to
volume ratio. Further, the reusability of the catalyst has
become an important trend in chemistry due to growing envi-
synthesis of benzodiazepine. Benzimidazole have also been
27
28
29
reported with amberlite, Fe(ClO ) , In O . However these
4
3
2 3
methods suffer from drawbacks such as the use of hazardous
organic solvents, longer reaction time, low yield, harsher reac-
tion condition and high cost. In our present approach, we have
synthesized benzodiazepine and benzimidazole derivatives
under solvent free condition using Fe O NPs which eliminates
3 4
the use of toxic solvents with the added advantage of reusability
of the catalyst.
2
ronmental and economic concern. Of the nanoparticles, Fe O
3
4
NPs are important because of their potential uses such as in
3
magnetic drug targeting, clinical diagnosis and as catalyst.
3 4
Fe O NPs, are also of interest due to its easy synthesis and
magnetic property which makes it easily separable by an
external magnetic eld and being comparatively cheap.
Department of Chemistry, North Eastern Hill University, Mawlai Campus, Shillong
7
3
93022, India. E-mail: amartya_pal22@yahoo.com; Fax: +91 364 2550076; Tel: +91
64 2307930 ext. 2636
†
Electronic supplementary information (ESI) available. CCDC 933681. For ESI
and crystallographic data in CIF or other electronic format see DOI:
1
0.1039/c3ra47860b
Fig. 1 Some biologically important compounds.
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The characterization of the Fe
3
O
4
NPs was also studied using UV
Results and discussion
and IR. The UV spectra show a characteristic absorption bands
NPs (Fig. 6), which
solution containing Fe and Fe in a molar ratio of 2 : 1, originate primarily from the absorption and scattering of UV
3 4
Fe O
3 4
NPs was prepared by the addition of a base to an aqueous at 370 nm which corresponds to the Fe O
3
+
2+
3
3
according to the procedure given by Karami et al. The resulting radiation by magnetic nanoparticles. The results was found to
ꢀ
34
solution was heated at 50–60 C with stirring. A dark black be in good agreement with those reported in the literature.
precipitate was formed. Then the precipitate was ltered, dried The particles size were found to be 10–20 nm before used. The
and characterized by TEM, SEM, XRD, EDAX, UV and IR. The distributions of Fe NPs are shown in Fig. 7. The IR spectrum
equation can be expressed as
shows bands at 599 cm and 3430 cm which indicates Fe–O
3 4
O
ꢁ
1
ꢁ1
35
structure and OH group for spinel Fe O (Fig. S.I-1†).
3
4
2
+
3+
ꢁ
Fe + 2Fe + 8HO / Fe
3
O
4
+ 4H
2
O
The synthesized Fe O NPs was then applied as a reusable
3 4
catalyst in a condensation reaction which intern will produce
biologically important heterocyclic compounds such as benzo-
diazepine and their derivatives. The model condensation reac-
XRD patterns of Fe O NPs are shown in Fig. 2. The XRD
patterns shows a number of prominent Bragg reections by
their indices (220), (311), (400), (422), (511) and (440) which
3 4
indicates that the resultant nanoparticles were Fe O with a
spinel structure. The broad peak is an indication that the
particles were of nanoscale size. The size of the particles was
examined by transmission electron microscope (TEM) and the
TEM image (Fig. 3a) clearly shows a monodispersed spherical
3
4
tion between o-phenylenediamine (1,
acetophenone (2, 2.2 mmol) in presence of Fe
1
mmol) and
NPs was
3 4
O
carried out under solvent free condition (Scheme 1). The reac-
tion was carried out in various solvents, like water, THF,
acetonitrile, ethanol and toluene. Signicant improvement was
achieved in ethanol and acetonitrile, but the best result was
observed under solvent free condition (Fig. 8). However, the
shaped Fe O4 NPs. The morphology and particle size of the
3
Fe O NPs was studied using SEM. The SEM image (Fig. 4a)
3
4
indicates that the Fe O NPs are spherical in shape and in the
3
4
nanometer range. Characterization of Fe
3 4
O NPs was also done
using EDAX. The EDAX spectra show a strong peak of Fe (Fig. 5).
3 4
Fig. 5 EDAX spectra of Fe O NPs.
3 4
Fig. 2 Powder XRD of Fe O NPs.
Fig. 3 TEM image of Fe
O
3 4
NPs before and after use.
Fig. 6 UV visible spectra of Fe
3
O
4
NPs.
Fig. 4 SEM image of Fe
O
3 4
NPs before and after use.
3 4
Fig. 7 Histogram diagram of Fe O NPs.
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product in high yield (89%). The structure of the compound was
established by analytical and spectroscopic methods. The
1
presence of peaks in H NMR at 3.4 (brs, 1H), 3.08 (d, J ¼ 13.2
Hz, 1H) and 2.92 (d, J ¼ 13.2 Hz, 1H) due to NH and methylene
ꢁ
1
protons and peak at 3281 cm due to NH stretching in IR
spectra clearly indicates the formation of 3a. The effect of
temperature on the product yield was also studied. The reaction
was carried out at room temperature but no desired product was
obtained only starting materials were recovered aer 1 h. With
increase in the temperature, yield of the desired product
ꢀ
increases and maximum yield was achieved at 80 C (Table 1).
To make the process more general, the model reaction was
carried out with different substituted ketones. In all the cases, the
reactions were completed within very short period and furnished
the corresponding products (3a–h) in higher yield (Table 1).
Encouraged by the initial success, next we decided to explore
the synthesis of biologically important benzimidazole and their
derivatives using the present protocol. To our delight, it was
observed that the reaction worked well and furnished chemo-
selectively the 1,2-disubstituted benzimidazoles (5a–f) instead
of a mixture of monosubstituted and disubstituted product
Scheme 1
36
irrespective of the molar ratio used (Scheme 1). We also
carried out the reaction using various aryl aldehydes having
electron donating or electron withdrawing groups. In all the
cases, desired product was achieved in good yields (Table 1).
The plausible mechanism for the formation of compounds
Fig. 8 Chart for the optimization of solvent effect.
3
a–h and 5a–f is given below (Scheme 2). Initially the Fe O NPs
3 4
facilitated the reaction between diamine 1 and ketones 2 or
aldehyde 4, which generates the common intermediate 9. The
intermediate 9 undergoes tautomerism to form intermediate
reaction did not proceed in water medium which might be due
to poor solubility of the starting materials.
The amount of catalyst concentration for the model reaction
was scanned. Firstly, the condensation reaction of o-phenyl-
enediamine (1, 1 mmol) and acetophenone (2, 2.2 mmol) was
carried out in absence of catalyst, very less conversion was
observed (22%). The reaction was then studied with various
mol% of the catalyst (2–10 mol%). It was found that the product
yield proportionally increased with catalyst concentration.
Maximum yield was obtained by using 6 mol% of the catalyst.
Further increase in the catalyst concentration (8 mol% and 10
mol%), the yield of the product did not improve. So 6 mol% is
the optimum catalyst concentration is this reaction (Fig. 9).
Rationalising the above results, we carried out the said
condensation reaction of o-phenylenediamine (1, 1 mmol) and
10. The intermediate 10 then undergoes intramolecular cycli-
zation followed by hydride shi to furnish the nal benzodi-
37
azepine products 3a–h. In case of aryl aldehydes, intermediate
9
undergoes cyclization (12) followed by 1,3-hydride shi to
38
produce the disubstituted benzimidazole products 5a–f.
Reusability is one of the most important properties of a good
catalyst. So, we checked the reusability of the catalyst in our
present protocol. Aer the completion of the reaction, the
reaction mixture was dissolved in 10 mL of ethyl acetate and the
catalyst was separated using external magnetic eld. The sepa-
rated catalyst was then dried and reused for another set of
reaction. To our excitement, it was found that the Fe O NPs can
3
4
be reused for four consecutive runs without any appreciable
decrease in its catalytic activity (Fig. 10).
Structure of the compound 3b was further conrmed by X-
ray crystallography. The compound 3b was carefully recrystal-
lized from ethanol. Fig. 11 shows the ORTEP diagram of
compound 3b.†
acetophenone (2, 2.2 mmol) in presence of Fe
under solvent free condition at 80 C (Scheme 1). The reaction
went to completion within 15 min yielding a solid pale white
3
O
4
NPs (6 mol%)
ꢀ
Conclusions
In conclusion, we have developed a new efficient and simple
method for the synthesis of benzodiazepine and chemoselective
1,2-disubstituted benzimidazole derivatives. This method will
be very useful in industrial point of view because it is high
yielding, solvent free and catalyst can be separated by external
magnetic eld and reused for several runs.
Fig. 9 Effect of catalyst loading on the reaction yield.
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Table 1 Synthesis of compounds 3a–h and 5a–f
a
ꢀ
ꢀ
Carbonyl compound
Product
Time (min)
Yield (%)
Mp ( C) [found]
Mp ( C) [lit.]
22
1
15
89
150–152
[151–152]
24
2
12
93
137–139
[147–149]
24
3
10
90
154–156
[164–166]
19
4
14
91
135–137
[145–146]
24
5
10
95
152–154
[154–155]
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Table 1 (Contd.)
a
ꢀ
ꢀ
Carbonyl compound
Product
Time (min)
Yield (%)
Mp ( C) [found]
Mp ( C) [lit.]
24
6
15
88
97–100
[99–101]
24
7
15
89
113–116
[115–116]
22
8
13
89
133–135
[137–139]
28
9
15
87
129–130
[134]
28
1
0
10
91
131–135
[137]
28
1
1
10
89
125–127
[125]
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Table 1 (Contd.)
a
ꢀ
ꢀ
Carbonyl compound
Product
Time (min)
Yield (%)
Mp ( C) [found]
Mp ( C) [lit.]
27
1
2
15
92
157–159
[157–158]
b
1
3
15
86
116–119
NF
28
1
4
10
90
149–150
[150]
a
b
Isolated yields. NF ¼ not found.
Fig. 10 Reusability chart.
Scheme 2
3
CDCl (chemical shis in d with TMS as internal standard).
Mass spectra were recorded on Waters ZQ-4000. Transmission
Electron Microscope (TEM) was recorded on JEOL JSM 100CX.
Scanning electron microscope (SEM) was recorded on JSM-6360
Experimental
(JEOL). XRD was recorded on Bruker D8 XRD instrument
Melting points were determined in open capillaries and are SWAX.CHN were recorded on CHN-OS analyzer (Perkin Elmer
uncorrected. IR spectra were recorded on Spectrum BX FT-IR, 2400, Series II). Silica gel G (E-mark, India) was used for TLC.
ꢁ
1
1
13
ꢀ
ꢀ
Perkin Elmer (ymax in cm ) on KBr disks. H NMR and C NMR Hexane refers to the fraction boiling between 60 C and 80 C.
400/300 MHz and 100/75 MHz respectively) spectra were Absorption spectra were recorded in Lambda25 (Perkin Elmer
(
recorded on Bruker Avance II-400 and 300 spectrometer in Inc.) spectrometers.
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Spectral data for selected compounds
Compound 3b: (entry 2): yellow solid. IR (KBr): 3496, 3025, 1686,
ꢁ
1 1
1
4
6
493, 751 cm . H NMR (CDCl
3
, 300 MHz): d ¼ 7.51–7.45 (m,
H), 7.30–7.25 (m, 1H), 7.20–7.17 (m, 4H), 7.07–7.01 (m, 2H),
.82–6.76 (m, 1H), 3.41 (s, 1H), 3.07 (d, J ¼ 13.3 Hz, 1H), 2.88 (d,
1
3
J ¼ 13.5, 1H), 1.71 (s, 3H). C NMR (CDCl
3
, 100 MHz): d ¼ 166.1,
1
1
45.7, 139.8, 137.6, 136.1, 133.0, 128.5, 128.38, 128.31, 127.0,
26.6, 122.0, 121.5, 73.5, 42.9, 29.7. ESI-MS: m/z 381, 383 [M +
+
H] . Anal. calcd for C H Cl N : C, 69.30; H, 4.76; N, 7.35.
2
2
18
2 2
Found: C, 69.53; H, 4.64; N, 7.44%.
Compound 3c: (entry 3): orange solid. IR (KBr): 3278, 3088,
ꢁ
1 1
1
1
7
1
1
604, 1473, 1349 cm . H NMR (CDCl
3
, 300 MHz): d ¼ 8.47 (s,
Fig. 11 ORTEP diagram of 3b (CCDC 933681).†
H), 8.16 (s, 1H), 8.12 (d, J ¼ 8.1 Hz, 1H), 7.99–7.96 (m, 3H),
.42–7.32 (m, 3H), 7.18–7.08 (m, 2H), 6.93–6.91 (dd, J ¼ 7.5 Hz,
.2 Hz, 1H), 3.55 (s, 1H), 3.28 (d, J ¼ 13.5 Hz, 1H), 3.02 (d, J ¼
X-ray crystallography
13
3.5, 1H), 1.87 (s, 3H). C NMR (CDCl , 100 MHz): d ¼ 164.1,
3
The X-ray diffraction data were collected at 293 K with Mo Ka 149.0, 148.1, 148.0, 140.4, 139.2, 137.1, 132.5, 131.9, 129.5,
˚
129.2, 128.9, 127.4, 124.4, 122.4, 122.2, 121.6, 120.8, 74.1, 42.8,
radiation (l ¼ 0.71073 A) using Agilent Xcalibur (Eos, Gemini)
diffractometer equipped with a graphite monochromator. The 29.9. ESI-MS: m/z 403 [M + H] . Anal. calcd for C22
soware used for data collection CrysAlis PRO (Agilent, 2011), 65.66; H, 4.51; N, 13.92. Found: C, 65.61; H, 4.62; N, 13.80%.
data reduction CrysAlis PRO and cell renement CrysAlis PRO.
Compound 3d: (entry 4): pale brown solid. IR (KBr): 3370,
The structure were solved by direct methods and rened by full- 2979 cm . H NMR (CDCl
+
18 4 4
H N O : C,
ꢁ
1 1
3
, 300 MHz): d ¼ 7.46–7.27 (m, 9H),
39
matrix least-squares calculation using SHELXS-97
and 7.11–7.01 (m, 2H), 6.83–6.80 (m, 1H), 3.42 (s, 1H), 3.07 (d, J ¼
1
3
40
SHELXL-97. †
13.2 Hz, 1H), 2.89 (d, J ¼ 13.2 Hz, 1H), 1.72 (s, 3H). C NMR
CDCl , 100 MHz): d ¼ 166.2, 146.5, 140.0, 138.3, 137.7, 131.5,
(
1
3
31.4, 128.8, 128.7, 127.6, 126.8, 124.7, 122.2, 121.7, 121.4, 73.7,
+
General procedure for the synthesis of 3a–h
43.0, 29.9. ESI-MS: m/z 469, 471 [M + H] . Anal. calcd for
: C, 56.20; H, 3.86; N, 5.96. Found: C, 56.12; H, 3.88;
22 2 2
C H18Br N
Fe O (6 mol%) was added to a mixture of o-phenylenediamine
(1 mmol) and acetophenone 2a–h (2.2 mmol) and heated at
C under solvent free condition. Aer completion of the
reaction, monitored by TLC, the reaction mixture was cooled to
room temperature and dissolved in 10 mL ethyl acetate. The
3
4
N, 5.77%.
Compound 5b: (entry 10): pale white solid. IR (KBr): 3075,
1
ꢀ
80
ꢁ
1 1
2
¼
928, 2852, 1611, 1250, 744 cm . H NMR (CDCl
7.81 (d, J ¼ 7.6 Hz, 1H), 7.53 (d, J ¼ 8.4 Hz, 2H), 7.38 (d, J ¼ 8.4
Hz, 2H), 7.29–7.19 (m, 4H), 7.14 (d, J ¼ 8 Hz, 1H), 6.96 (d, J ¼ 8
3
, 400 MHz): d
Fe
3
O
4
NPs was then separated by external magnetic eld. The
NPs was washed with ethyl acetate and dried.
1
3
Hz, 2H), 5.33 (s, 2H). C NMR (CDCl , 100 MHz): d ¼ 152.8,
3
separated Fe
3 4
O
1
1
42.9, 136.3, 135.8, 134.6, 133.8, 130.4, 129.3, 129.1, 128.2,
Then it was used for another set of reaction under similar
condition. The reaction mixture was then washed with water (3
ꢂ 5 mL), brine (1 ꢂ 5 mL) and dried over anhydrous Na SO .
27.2, 123.5, 123.1, 120.1, 110.3, 47.8. ESI-MS: m/z 353, 355 [M +
+
H] . Anal. calcd for C20
H
14 Cl
2
N
2
: C, 68.00; H, 3.99; N, 7.93.
2
4
Found: C, 68.21; H, 4.03; N, 7.82%.
The reaction mass was concentrated under vacuum and the
pure product was obtained by purication through column
chromatography using ethyl acetate–hexane as eluent.
Acknowledgements
We thank the Department of Chemistry, Sophisticated Analyt-
ical and Instrumentation Facility (SAIF) of North-Eastern Hill
University, SAIF-CDRI Lucknow, UGC for supporting this work
under Special Assistance Programme (SAP) and DST-Purse
programme of NEHU Shillong. We are also thankful to DST for
General procedure for the synthesis of 5a–f
In a round bottom ask, o-phenylenediamine 1 (1 mmol) and
aldehyde 4a–f (2.2 mmol), was taken and Fe O NPs (6 mol%)
was added. The reaction was carried out at 80 C under solvent
free condition. Aer completion (TLC), the reaction mixture was
cooled to room temperature and dissolved in 10 mL ethyl
3
4
ꢀ

nancial support (sanctioned no: SERC/F/0293/2012-13),
Dr S. Khatua and Dr S. L. Nongbri.
acetate. The Fe
3 4
O NPs was then separated by external magnetic

eld and washed with ethyl acetate and dried. The separated
Notes and references
3 4
Fe O NPs was then used for another set of reaction under
similar condition. The reaction mixture was then washed with
water (3 ꢂ 5 mL), brine (1 ꢂ 5 mL) and dried over anhydrous
Na SO . The reaction mass was concentrated under vacuum.
1 P. T. Anastas, L. G. Heine and T. C. Williamson, Green
Chemical Syntheses and Processes: Introduction, 2000, vol. 1,
p. 1.
2
4
The crude mixture was puried by column chromatography
using ethyl acetate–hexane as eluent.
2 C. Burda, X. Chen, R. Narayana and M. A. E. Sayed, Chem.
Rev., 2005, 105, 1025.
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3
(a) S. Lian, E. Wang, Z. Kang, Y. Bai, L. Gao, M. Jiang, C. Hu 20 D. I. Jung, T. W. Choi, Y. Y. Kim, I. S. Kim, Y. M. Park,
and L. Xu, Solid State Commun., 2004, 129, 485; (b) Y. G. Lee and D. H. Jung, Synth. Commun., 1999, 29, 1941.
V. S. Zaitsev, D. S. Filimonov, I. A. Presnyakov, 21 R. Kumar, P. Chaudhary, S. Nimesh, A. K. Verma and
R. J. Gambino and B. Chu, J. Colloid Interface Sci., 1999,
12, 49.
H. Schutz, Benzodiazepines, Springer, Heidelberg, 1982, vol.
R. Chandra, Green Chem., 2006, 8, 519.
22 M. Curini, F. Epifano, M. C. Marcotullio and O. Rosati,
Tetrahedron Lett., 2001, 42, 3193.
2
4
5
6
2
, p. 240; J. K. Landquist, in Comprehensive Heterocyclic 23 S. K. De and R. A. Gibbs, Tetrahedron Lett., 2005, 46, 1811.
Chemistry, ed. A. R. Katritzky and C. W. Rees, Pergamon 24 X.-Q. Pan, J.-P. Zou, Z.-H. Huang and W. Zhang, Tetrahedron
Press, Oxford, U.K., 1984, vol. 1, p. 166. Lett., 2008, 49, 5302.
(a) H. Nakano, T. Inoue, N. Kawasaki, H. Miyataka, 25 M. A. Pasha and V. P. Jayashankara, Heterocycles, 2006, 68,
H. Matsumoto, T. Taguchi, N. Inagaki, H. Nagai and 1017.
T. Satoh, Bioorg. Med. Chem., 2000, 8, 373; (b) D. A. Horton, 26 D. V. Jarikote, S. A. Siddiqui, R. Rajagopal, D. Thomas,
G. T. Bourne and M. L. Smythe, Chem. Rev., 2003, 103, 893.
L. O. Randall and B. Kappel, Benzodiazepines, ed. S. Garattini,
R. J. Lahoti and K. V. Srinivasan, Tetrahedron Lett., 2003,
44, 1835.
E. Mussini and L.O. Randall, Raven Press, New York, 1973, 27 S. D. Sharma and D. Konwar, Synth. Commun., 2009, 39, 980.
p. 27.
28 H. A. Oskooie, M. M. Heravi, A. Sadnia, F. K. Behbahani and
F. Jannati, Chin. Chem. Lett., 2007, 18, 1357.
29 S. Santra, A. Majee and A. Hajra, Tetrahedron Lett., 2012, 53,
1974.
7
8
9
J. R. De Baun, F. M. Pallos and D. R. Baker, US Pat. 3, 1976,
vol. 978, p. 227, Chem. Abstr., 1977, 86, 5498.
W. A. Denny, G. W. Rewcastle and B. C. Bagley, J. Med. Chem.,
1
990, 33, 814.
T. Fonseca, B. Gigante and T. L. Gilchrist, Tetrahedron, 2001,
7, 1793.
30 M. E. Tranquillini, P. G. Cassara, M. Corsi, G. Curotto,
D. Donati, G. Finizia, G. Pentassuglia, S. Polinelli,
G. Tarzia, A. Ursini and F. T. M. V. Amsterdam, Arch.
Pharm., 1997, 330, 353.
31 D. A. Claremon, N. Liverton, H. G. Selnick and G. R. Smith,
PCT Int. Appl. WO 9640653, 2003.
5
10 Z. Zhu, B. Lippa, J. C. Drach and L. B. Townsend, J. Med.
Chem., 2000, 43, 2430.
11 H. Zarrinmayeh, D. M. Zimmerman, B. E. Cantrell,
D. A. Schober and R. F. Bruns, Bioorg. Med. Chem. Lett., 32 M. D. Rosen, Z. M. Simon, K. T. Tarantino, X. L. Zhao and
999, 9, 647. M. H. Rabinowitz, Tetrahedron Lett., 2009, 50, 1219.
2 M. Essaber, A. Baouid, A. Hasnaoui, A. Benharref and 33 B. Karami, S. J. Hoseini, K. Eskandari, A. Ghasemib and
J. P. Lavergne, Synth. Commun., 1998, 28, 4097. H. Nasrabadia, Catal. Sci. Technol., 2012, 2, 331.
3 (a) J. X. Xu, H. T. Wu and S. Jin, Chin. J. Chem., 1999, 17, 84; 34 O. U. Rahman, S. C. Mohapatra and S. Ahmad, Mater. Chem.
1
1
1
(
4
b) X. Y. Zhang, J. X. Xu and S. Jin, Chin. J. Chem., 1999, 17,
04.
4 K. V. V. Reddy, P. S. Rao and D. Ashok, Synth. Commun.,
000, 30, 1825.
5 Y. Bai, J. Lu, Z. Shi and B. Yang, Synlett, 2001, 4, 544.
Phys., 2012, 32, 196.
35 Y.-P. Chang, C.-L. Ren, J.-L. Qu and X.-G. Chen, Appl. Surf.
Sci., 2012, 61, 504.
36 V. Kumar, D. G. Khandare, A. Chatterjee and M. Banerjee,
Tetrahedron Lett., 2013, 54, 5505.
1
2
1
1
6 J. A. L. Herbert and H. Suschitzky, J. Chem. Soc., Perkin Trans. 37 (a) S. K. De and R. A. Gibbs, Tetrahedron Lett., 2005, 46, 1811;
, 1974, 1, 2657. (b) M. Saha, A. K. Pal and S. Nandi, RSC Adv., 2012, 2, 6397.
7 C.-K. Kuo, S. V. More and C.-F. Yao, Tetrahedron Lett., 2006, 38 J.-P. Wan, S.-F. Gan, J.-M. Wu and Y. Pan, Green Chem., 2009,
7, 8523. 11, 1633.
8 H. R. Morales, A. Bulbarela and R. Contreras, Heterocycles, 39 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
986, 24, 135. 1990, 96, 467.
9 S. S. Pandit, B. D. Vikhe and G. D. Shelke, J. Chem. Sci., 2007, 40 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
19, 295. 2008, 645, 112.
1
1
1
1
4
1
1
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