Room temperature synthesis of benzimidazole derivatives using reusable cobalt hydroxide (II) and cobalt oxide (II) as efficient solid catalysts

Article abstract of DOI:10.1016/j.tetlet.2011.08.047

Here we demonstrate the synthesis of benzimidazoles through the coupling of 1,2-phenylenediamine with aldehydes by using Co(OH)₂ and similarly CoO(II) as efficient solid catalysts in ethanol at room temperature. The Co(OH)₂ solid catalyst gave better yields (82-98%) in short reaction times (4-7 h) than CoO(II) catalyst (80-94%, 6-9 h). These commercially available cheap catalysts are more active than many reported expensive heterogeneous catalysts.

Full text of DOI:10.1016/j.tetlet.2011.08.047

Tetrahedron Letters 52 (2011) 5575–5580
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Room temperature synthesis of benzimidazole derivatives using reusable
cobalt hydroxide (II) and cobalt oxide (II) as efficient solid catalysts
⇑
Murugulla Adharvana Chari, Donthabhakthuni Shobha, Takehiko Sasaki
Department of Complexity Science and Engineering, School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Here we demonstrate the synthesis of benzimidazoles through the coupling of 1,2-phenylenediamine
Received 4 June 2011
Revised 5 August 2011
Accepted 8 August 2011
Available online 24 August 2011
with aldehydes by using Co(OH)
2
and similarly CoO(II) as efficient solid catalysts in ethanol at room tem-
perature. The Co(OH) solid catalyst gave better yields (82–98%) in short reaction times (4–7 h) than
2
CoO(II) catalyst (80–94%, 6–9 h). These commercially available cheap catalysts are more active than many
reported expensive heterogeneous catalysts.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
1
,2-Phenylenediamine
Aldehyde
Solid catalyst
Heterogeneous
Benzimidazoles
Introduction
hypervalent iodine,42 TsOH/graphite and N,N-dimethylaniline/
4
3
44
graphite, cobalt(III) salen complex on activated carbon, cobalt(II)
4
5
46
Among the various nitrogen containing heterocycles, benzimid-
azole derivatives exhibit antiviral, antiulcer, antihypertension, and
anticancer properties. The benzimidazoles are biologically potent
chloride hexahydrate, VO(acac)
2
-CeCl
3
combo catalyst, gold/
4
7
48
49
CeO
2
,
AlKIT-5,
and copper iodide catalysts
have been
1
2
employed as the reagents or catalysts for the synthesis of benzimi-
dazoles. Although the reaction was efficiently promoted by the
above conditions they are often homogeneous catalysts and some
of these methods suffer from one or more disadvantages, such as
usage of stoichiometric or more quantity of reagent, high cost of
the catalysts, prolonged reaction times, occurrence of several side
reactions, severe reaction conditions, difficulty in separation of the
products from the reaction mixture and strong oxidizing nature of
the reagents. Therefore, the discovery of mild and practicable, stable,
cheap, recyclable, and ecofriendly heterogeneous catalysts for the
synthesis of 2-substituted benzimidazoles continues to attract the
3
a,b
and this moiety is an important pharmacophore
in drug discov-
ery and also good intermediate3 for synthesis of many important
organic compounds. Generally, the synthesis of 2-substituted benz-
imidazoles involves the treatment of 1,2-phenylenediamines either
c,d
4
with carboxylic acids or their derivatives (nitriles, imidates, or
5
orthoesters), under strongly acidic conditions and some times com-
bined with very high temperatures (i.e., PPA, 180 °C) or the use of
microwave irradiation. These derivatives also often generated from
the condensation of phenylenediamines with aldehydes under
oxidative conditions
6
7
8
,9
using various oxidative and catalytic re-
1
0
agents, such as nitrobenzene (high-boiling point oxidant/solvent),
attention of researchers.
1
1
12
13
14
38–51
1
,4-benzoquinone, PhI(OAc)
2
,
Zn-proline, heteropoly acids,
2,3-dichloro-5,6-dicyanobenzoqui-
Recently the use of heterogeneous catalysts
including zeo-
1
5
40,41,50
51
thionyl chloride-treatment,
lites
and nanoporous materials has received considerable
1
6
9b
17
none (DDQ),
MnO
,18 Pb(OAc)
hypervalent iodine (iodobenzene diacetate (IBD),
electron-deficient olefins,
benzofuroxan,
importance in organic synthesis because of ease of handling,
enhanced reaction rates, greater selectivity, and simple workup.
Since we have published the preparation of nanocrystals of cobalt
9a
19
20
21
2
4
,
oxone, NaHSO
3
,
H
2
O
2
/HCl, iodine and
22
23
28
Na
2
2
S O
5
,
,
2
4
25
26
27
52
air,
Sc(OTf)
sulfamic acid,
FeCl
3
Á6H
2
31
O,
In(OTf)
3
,
Yb(OTf)
3
oxides and hydroxides, we have sought the application as cata-
2
9
,30 KHSO
IL,32 (bromo dimethyl)
3
,
Cu(OTf)
2
4
,
lysts for organic reactions. Along this process, we have found that
Co(OH) or CoO(II) which are as-purchased solid catalysts exhibit
2
3
3
34
35
,36 HfCl
36
39
sulfoniumbromide,
p-TSA,
ZrOCl
2
Á8H
2
O,
ZrCl
4
4
,
borontrifluoride etherate,37 copper complex, polyaniline salt,
38
catalytic activity for benzimidazole derivative synthesis. These
solid catalysts are commercially available, nonhazardous, clean,
cost effective than other heterogeneous catalysts. In continuation
of our interest on catalytic applications of various heterogeneous
catalysts, herein we report for the first time a simple, convenient,
Heuland natural zeolite,40 NaYzeolite,
41
polymer-supported
⇑
Corresponding author. Fax: +81 4 7136 3910.
E-mail address: takehiko@k.u-tokyo.ac.jp (T. Sasaki).
0
040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.08.047

5
576
M. Adharvana Chari et al. / Tetrahedron Letters 52 (2011) 5575–5580
and efficient method for the synthesis of benzimidazole and its
derivatives by condensation of 1,2-phenylenediamines with alde-
hydes under open oxygen atmospheric conditions at room temper-
H
N
NH2
NH2
Co(OH)2 / CoO(II)
O
H
N
N
+
R
R +
R
ature in ethanol using Co(OH)
2
or CoO(II) as reusable solid
Ethanol, air, R.T
N
catalysts. However, to the best of our knowledge, there has been
no report available on the synthesis of benzimidazoles using these
solid catalysts in the open literature so far.
1
2
4
3
2
Scheme 1. Room temperature synthesis of benzimidazoles using Co(OH) and
similarly CoO(II) solid catalysts. Side-product 4 is only formed in the absence of
Results and discussion
cobalt catalysts.
Initially, we have attempted the condensation of 1,2-phenyl-
enediamine 1 (1.0 mmol) with benzaldehyde 2 (R=Ph) (1.2 mmol)
at room temperature in ethanol condition for 6 h at open oxygen
atmosphere, in the absence of catalyst and we observed 27.6% of
product 3 and 0.1% of product 4 at 6 h and on long reaction time
(
12 h) resulted in the formation of a mixture like 2-phenyl benz-
imidazole 3 (29.1%) and 1-benzyl-2-phenyl-1H-benzimidazole 4
2%) as side-products. The detailed mechanistic study on oxygen-
(
catalyzed coupling of 1,2-phenylenediamine and benzaldehyde
was carried out by Smith and Ho.5 We have performed control
3
experiments in the absence of air under N
Co (II,III), CoO, and Co(OH) catalysts, but the reaction was not
proceeding much, these gave very low yields of 3 (7%, 9%, and
7%) at 6 h under optimized conditions. This indicates that the
2
atmosphere using
3
O
4
2
2
Figure 2. The crystal structures of Co(OH) (ICSD-88940) (a), CoO(II) (ICSD-9865)
(b) and Co O (II,III) (ICSD-69367) (c).
3
4
1
presence of oxygen is important for the reaction.
We have carried out the reaction using different amounts of the
various catalysts (Fig. 1 and Table 1). It was observed that the
amount of catalyst plays a significant role in controlling the activ-
ity of the catalyst. Among the various amounts of catalyst studied,
1
2
0 mol % of the Co(OH) and similarly 10 mol % of CoO(II) solid cat-
alysts were found to be the best at room temperature in ethanol
condition and only 2-phenyl benzimidazole 3 was isolated in high
yield within short time (Scheme 1).
2
In the case of Co(OH) catalyst, the yields of the final product
increases from 75% to 96% and whereas in the case of CoO(II)
Figure 1. Time course of the various catalysts in the synthesis of benzimidazole 3a
using G.C.
Table 1
Effect of the amount and catalytic activity of the various catalysts in the synthesis of
benzimidazole 3a
Figure 3. Solvent effect for synthesis of benzimidazole 3a using 10 mol % Co(OH)
catalyst by G.C.
2
Entry Catalyst
Amount of the catalyst (mol %) Time (h) Yielda (%)
1
No catalyst
—
6
1
4
4
4
6
6
6
6
27.6, 0.1b
29.1, 2.0b
75.5
2
2
3
4
5
6
7
8
Co(OH)
Co(OH)
Co(OH)
CoO(II)
CoO(II)
CoO(II)
2
2
2
2
5
85.0
Co(OH)2/CoO(II)
10
2
96.4
71.8
NH2 H
H
N
NH2
NH2
O
Co(OH) /CoO(II)
2
O
R
R
5
81.3
H
R
-H2O
R
N
H
N
10
93.0
H
Co
3
O
4
(II,III) 10
78.9
-H2O
Air
Reaction and conditions: Substrates: 1,2-phenylenediamine (108 mg, 1.0 mmol),
benzaldehyde (127 mg, 1.2 mmol), amount of catalyst = 10 mol %, amount of
tetradecane:20 mg as internal standard, reaction was conducted at room temper-
ature in ethanol as solvent.
H
N
N
a
Yields of the product calculated by G.C. using Tetradecane as internal standard.
Yield of the side product 4 (1-benzyl-2-phenyl-1H-benzimidazole).
b
Scheme 2. A plausible mechanism for the synthesis of benzimidazoles.

M. Adharvana Chari et al. / Tetrahedron Letters 52 (2011) 5575–5580
5577
Table 2
Co(OH)
2
and CoO catalyzed synthesis of benzimidazole derivatives
Entry
Aldehyde
Product (3)a
CoO(II)
Co(OH)
2
Time (h)
6
Yield (%)b
93c
Time (h)
4
Yield (%)b
H
N
CHO
a
b
c
96c
87
86
98
N
3a
O2N
H
N
CHO
CHO
CHO
8
8
6
84
83
94
6
6
4
3
b
N
H3C
Cl
H
N
3c
N
H
N
d
3d
N
NO2
CHO
O2N
H
N
e
8
86
6
88
3e
N
H
N
Cl
CHO
f
Cl
6
8
8
94
89
88
4
6
6
98
92
89
N
3f
H
N
H3CO
HO
CHO
g
h
OCH3
3
g
N
H
N
OH
3h
CHO
N
OH
H HO
N
i
j
8
8
86
88
6
6
88
89
HO
CHO
OH
N
3i
OCH3
OCH3
H3CO
H
N
H3CO
CHO
CHO
N
3j
H
N
k
N
H
9
80
7
85
N
N
H
3k
CHO
H
N
l
8
8
8
86
82
86
6
6
6
90
90
92
N
3l
CHO
H
N
m
n
3
m
N
O
H
CHO
N
O
3
n
N
H3C
H
CHO
N
o
3o
CH3
9
80
7
82
N
CHO
H
N
H3C
p
q
CH3
9
9
82
86
7
7
85
85
3
p
N
CHO
H
H3C
H3C
H3C
H3C
N
CH3
N
3q
3r
CH3
H
N
CH3
CH3
CHO
r
6
6
86
85
5
5
94
90
N
H3C
H3C
H
CH CHO
N
CH3
3s CH3
s
N
a
All products were characterized by IR, NMR, and mass spectroscopy.
Yield refers to pure products after purification by column chromatography.
Yields of the product calculated by G.C.
b
c
catalyst, the product yield increases from 71% to 93% with increas-
ing the catalyst weight from 2 to 10 mol %. We also investigated
was found that the present reaction readily proceeds, whereas no
simple oxidation of aldehyde was observed.
the 10 mol % Co
9% was lower than that by Co(OH)
The order of activity was found as Co(OH)
3
O
4
(II,III) activity on this synthesis, but the yield
and CoO(II) solid catalysts.
> CoO(II) > Co . It
2 3 4
The crystal structures of Co(OH) , CoO(II), and Co O (II,III) are
given below (Fig. 2) based on Inorganic Crystal Structures Database
(ICSD, FIZ Karlsruhe) .
7
2
2
3 4
O

5
578
M. Adharvana Chari et al. / Tetrahedron Letters 52 (2011) 5575–5580
Co(OH)
Co(OH) showed better activity than CoO(II) and Co
may be due to the layer structure of Co(OH) and/or that all cobalt
atoms are attached with hydroxyl groups influencing the reaction
rates.
2
geometry is a layered structure. In the present study
present commercially available solid catalysts, such as CoO,
Co(OH) are recyclable catalysts for benzimidazole synthesis as
2
3
O
4
(II,III). This
2
2
mentioned below. The present catalysts are simple, less expensive,
and more convenient than many catalysts presented in the above
introduction. These catalysts were also found to be very active in
the synthesis of benzimidazoles using bulky naphthaldehyde
(3m), an acid sensitive furfuraldehyde (3n), and sterically hindered
aldehydes, such as pivaldehyde (3r) and isobutyraldehyde (3s). In-
dole-3-carboxaldehyde (3k) also worked well. Various substituted
aldehydes have been used with similar success to provide the cor-
responding benzimidazoles in high yields (82–98%). Interestingly
the products 3d and f were obtained at a high yield of 98% and dur-
ing the reaction time within 1 h, the entire reactant (1) was con-
sumed as found by TLC observation.
The effect of the solvents affecting the catalytic activity of the
Co(OH) was also investigated under the optimized reaction condi-
2
tions (Fig. 3). Among various solvents like dichloro methane, meth-
anol, acetonitrile, and ethanol used for this transformation, ethanol
showed the highest yield (96%) in 4 h and was found to be the best
solvent. Acetonitrile (78%) and methanol (75%) exhibited almost
the same activity and dichloro methane showed poor activity
(
23%). A compromise between polarity and a little hydrophobicity
might result in the best performance for ethanol.
As per a plausible mechanism, the reaction proceeds via the
Finally, recycling experiments were conducted to find out the
stability and reusability of the catalysts after the reaction. The cat-
alyst was easily separated by centrifuge and reused after drying at
100 °C for 4 h. The efficiency of the recovered catalyst was verified
activation of aldehyde by Co(OH)
2
or CoO(II) followed by imine for-
mation and this resulting imine further reacts with another –NH
2
group of 1,2-phenylenediamine resulting in the formation of dihy-
droimidazole which subsequently undergoes aromatization under
the oxidative conditions to give the benzimidazole as shown in
Scheme 2.
2
with Entry a, Table 2. Using Co(OH) as a fresh catalyst, the yield of
product 3a was 96%, while the recovered catalyst in the three sub-
sequent cycles gave the yield of 93%, 88%, and 86%, respectively.
Similarly using CoO(II) fresh catalyst, the yield of product 3a was
93%, while the recovered catalyst gave the yield of 90%, 85%, and
83%, respectively (Fig. 4).
Encouraged by these results, we examined several substituted
aldehydes including aromatic, heteroaromatic and aliphatic
groups, which underwent smooth conversion to afford a wide
range of benzimidazoles (Table 2). Aromatic aldehydes containing
both electron-donating and -withdrawing groups worked well in
this reaction. Unfortunately metal oxides are not explored much
in the synthesis of various benzimidazoles. As per our survey
In addition we have also carried out scale up experiments with
1.08 g of 1,2-phenylenediamine and 1.06 g of benzaldehyde using
10 mol % of Co(OH)
2
catalyst at room temperature in ethanol. The
Co(OH) catalyst gave 96% of product 3a, that is almost similar to
2
1
8
MnO
2
is used as a catalyst for oxidation in the synthesis of benz-
the yield obtained in Table 2 Entry a, indicates that the catalyst
imidazoles from p- and m-nitrobenzylidene-o-phenylenediamines
and gave 15% and 25% yield of p-and m-nitrophenylbenzimidaz-
oles. It was found that transition metal oxide is more effective
for oxidation than the corresponding zero-valent metal powders.
Open air and cobalt oxides both may be sources for the oxidation
process. Here, it seems that cobalt catalysts are acting as bifunc-
tional like Lewis acid as well as oxidative reagent. Expensive Co(III)
salen complexes are used in the synthesis of benzimidazoles, but
they have not achieved the products using aliphatic aldehydes. In
the present study we obtained the products using aliphatic alde-
hydes as shown in Table 2 (entries o, p, and q). Although a homo-
could be easily used on a large scale. In the present work, the cat-
alytic activity of the Co(OH) or CoO(II) has been studied for the
2
synthesis of various benzimidazole derivatives at room tempera-
ture. It has been found that these commercially available catalysts
are very cheap, recyclable, and showed superior activity at room
4
4
48
temperature than Co(III) salen, AlKIT-5, and cheaper than many
3
8–49
other expensive heterogeneous catalysts.
4
4
Conclusion
In summary, benzimidazole and its derivatives were synthe-
sized by the coupling of 1,2-phenylenediamine with aldehydes
using commercially available Co(OH) or CoO(II) as an efficient
2
geneous CoCl
benzimidazoles, CoCl
2 2
.6H O catalyst has been used for this synthesis of
4
5
2
2
in the presence of O and water gets oxi-
dized to give a black residue of a mixture of cobalt oxide and
hydroxide which cannot be reused again. It is contrasted that the
recyclable catalyst under open oxygen atmosphere at room tem-
perature using ethanol as solvent. Benzimidazoles could success-
fully be synthesized using these catalysts with acid sensitive,
sterically hindered, and substituted aromatic and aliphatic alde-
hydes. The reactions were performed in ethanol and the catalyst
could be reused for several cycles without much decrease in activ-
ity. The salient features of the present method include mild condi-
tions, short reaction times, high yields, recyclable catalyst, large
scale synthesis, and simple procedure. These catalysts could
replace the existing homogeneous and expensive heterogeneous
catalysts which are currently being used in the synthesis of various
industrially important and biologically active benzimidazoles.
Experimental section
All chemicals and solvents were obtained from Aldrich and
Wako and used without further purification. Column chromato-
graphic separations were carried out on silica gel 60–120 mesh
1
size. The H NMR spectra of samples were recorded on a JEOL
4
00-MHz NMR spectrometer using TMS as an internal standard
in DMSO-d . Mass spectra were recorded on a MALDI-MS (Shima-
6
dzu Axima Resonance) with 2,5-DHB as matrix. GC studies were
carried out using Shimadzu GC-17A and GC-Mass (QP-5050).
Figure 4. Recycle performances in the synthesis of benzimidazole 3a using Co(OH)
and CoO(II) solid catalysts.
2

M. Adharvana Chari et al. / Tetrahedron Letters 52 (2011) 5575–5580
5579
General procedure
7. (a) Kawashita, Y.; Nakamichi, N.; Kawabata, H.; Hayashi, M. Org. Lett. 2003, 5,
713; (b) Sharghi, H.; Asemani, O.; Khalifeh, R. Synth. Commun. 2008, 38, 1128.
3
8
9
.
.
(a) Middleton, R. W.; Wibberley, D. G. J. Heterocycl. Chem. 1980, 17, 1757.
(a) Stephens, F. F.; Bower, J. D. J. Chem. Soc. 1949, 2971; (b) Chikashita, H.;
Nishida, S.; Miyazaki, M.; Morita, Y.; Itoh, K. Bull. Chem. Soc. Jpn. 1987, 60, 737;
To a mixture of 1,2-phenylenediamine (1.0 mmol) and aldehyde
1.2 mmol) in ethanol (3 mL) under open oxygen atmosphere,
0 mol % of the catalysts were added. The resulting mixture was
stirred at room temperature for appropriate time (Table 2). After
completion of the reaction, as monitored by TLC, the reaction mix-
ture was diluted with ethanol (20 mL) and the catalyst was sepa-
rated by filtration. The organic layer was concentrated under
reduced pressure and the crude product was purified by silicagel
column chromatography using ethyl acetate-n-hexane (1:9) as elu-
(
1
(
c) Kumar, S.; Kansal, V.; Bhaduri, A. Ind. J. Chem. 1991, 20B, 254; (d) Patzold, F.;
Zeuner, F.; Heyer, T. H.; Niclas, H. J. Synth. Commun. 1992, 22, 281; (e)
Lombardy, R. L.; Tanious, F. A.; Ramachandran, K.; Tidwell, R. R.; Wilson, W. D. J.
Med. Chem. 1996, 39, 1452; (f) Beaulieu, P. L.; Hache, B.; Moos, E. V. Synthesis
2003, 1683.
1
0. (a) Dubey, P. K.; Ratnam, C. V. Indian J. Chem. B 1979, 18, 428; (b) Yadagiri, B.;
Lown, J. W. Synth. Commun. 1990, 20, 955; (c) Bathini, Y.; Rao, K. E.; Shea, R. G.;
Lown, J. W. Chem. Res. Toxicol. 1990, 3, 268; (d) Singh, M. P.; Joseph, T.; Kumar,
S.; Bathini, Y.; Lown, J. W. Chem. Res. Toxicol. 1992, 5, 597; (e) Harapanhalli, R.
S.; McLaughlin, L. W.; Howell, R. W.; Rao, D. V.; Adelstein, S. J.; Kassis, A. I. J.
Med. Chem. 1996, 39, 4804.
ent to afford pure benzimidazole product. The spectral data are in
full agreement with the data reported in literature.4
the compounds’ spectral data are given below.
8,54,55
Some of
11. (a) Verner, E.; Katz, B. A.; Spencer, J. R.; Allen, D.; Hataye, J.; Hruzewicz, W.; Hui,
H. C.; Kolesnikov, A.; Li, Y.; Luong, C.; Martelli, A.; Radika, K.; Rai, R.; She, M.;
Shrader, W.; Sprengeler, P. A.; Trapp, S.; Wang, J.; Young, W. B.; Mackman, R. L.
J. Med. Chem. 2001, 44, 2753; (b) Kumar, S.; Kansal, V. K.; Bhaduri, A. P. Indian J.
Chem. B 1981, 20, 254.
3
a: 2-Phenyl-1H-benzimidazole (Table 2): Solid, mp 295–
2
7
8
7
1
1
97 °C, IR (KBr):
m
max 3047, 2966, 1462, 1411, 1276, 970, 744,
): d 12.91 (br s, 1H, NH),
.20–8.18 (m, 2H), 7.61–7.56 (m, 2H), 7.53–7.43 (m, 3H), 7.21–
À1
1
03 cm
;
H NMR (400 MHz, DMSO-d
6
12. Du, L.-H.; Wang, Y.-G. Synthesis 2007, 675.
1
1
3. Ravl, V.; Ramu, E.; Vijay, K.; Srinivas Rao, A. Chem. Pharm. Bull. 2007, 55,
254.
4. Heravi, M. M.; Sadjadi, S.; Oskooie, H. A.; Shoar, R. H.; Bamoharram, F. F. Catal.
Commun. 2008, 9, 504.
1
1
3
6
.18 (m, 2H); C NMR (DMSO-d , 100 MHz): d 150.80, 137.92,
37.90, 131.80, 129.40, 127.80, 125.73, 123.10, 122.80, 121.30,
+
15. Allouma, A. B.; Bougrinb, K.; Soufiaoui, M. Tetrahedron Lett. 2003, 44,
935.
21.13, 116.80, 111.21. MALDI-MS: m/z 195 (M+H) .
5
3
k: 2-(3-Indolyl)-1H-benzimidazole (Table 2): Solid, mp 196–
1
1
1
6. (a) Vanden Eynde, J. J.; Delfosse, F.; Lor, P.; Van Haverbeke, Y. Tetrahedron 1995,
51, 5813; (b) Lee, K. J.; Janda, K. D. Can. J. Chem. 2001, 79, 1556.
7. PQtzold, F.; Zeuner, F.; Heyer, T. H.; Niclas, H. J. Synth. Commun. 1992, 22,
À1
1
1
d
1
98 °C; IR (KBr):
m
max 3147, 2976, 1635 cm
; H NMR (DMSO-
6
, 400 MHz): d 11.20 (br s, 1H, NH), 10.65 (br s, 1H, NH), 8.31 (s,
281.
1
3
H), 7.79-7.74 (m, 1H), 7.56–7.29 (m, 3H), 7.26–6.85 (m, 4H);
, 100 MHz): d 149.64, 137.22, 137.20, 136.39,
28.01, 125.90, 123.37, 123.31, 122.10, 121.27, 120.14, 113.10,
C
8. Bhatnagar, I.; George, M. V. Tetrahedron 1968, 24, 1293.
NMR (DMSO-d
6
19. Beaulieu, P. L.; Hache, B.; Von Moos, E. Synthesis 2003, 1683.
2
0. (a) Weidner-Wells, M. A.; Ohemeng, K. A.; Nguyen, V. N.; Fraga-Spano, S.;
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1
1
+
13.07, 111.79, 106.50; MALDI-MS: m/z 234 (M+H) .
2
2
1. Bahrami, K.; Khodaei, M. M.; Kavianinia, I. Synthesis 2007, 4, 547.
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Acknowledgments
This work was supported by the Special Coordination Fund for
Promoting Science and Technology of the Ministry of Education,
Culture, Sports, Science and Technology (MEXT), Japan and KAKEN-
HI (22350005).
23. Navarrete-VRzquez, G.; Moreno-Diaz, H.; Aguirre-Crespo, F.; LeSn-Rivera, I.;
Villalobos-Molina, R.; MuCoz-MuCiz, O.; Estrada-Soto, S. Bioorg. Med. Chem.Lett.
2006, 16, 4169.
2
2
4. Lin, S.; Yang, L. Tetrahedron Lett. 2005, 46, 4315.
5. Chakrabarty, M.; Karmakar, S.; Mukherji, A.; Arima, S.; Harigaya, Y. Heterocycles
2006, 68, 967.
2
2
2
2
6. Singh, M. P.; Sasmal, S.; Lu, W.; Chatterjee, M. N. Synthesis 2000, 1380.
7. Trivedi, R.; De, S. K.; Gibbs, R. A. J. Mol. Cat. A: Chem. 2005, 245, 8.
8. Massimo, C.; Francesco, E.; Francesca, M. Synlett 2004, 1832.
9. (a) Itoh, T.; Nagata, K.; Ishikawa, H.; Ohsawa, A. Heterocycles 2004, 63, 2769; (b)
Nagata, K.; Itoh, T.; Ishikawa, H.; Ohsawa, A. Heterocycles 2003, 61, 93.
0. Chari, M. A.; Sadanandam, P.; Shobha, D.; Mukkanti, K. J. Heterocycl. Chem.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.08.047.
3
2010, 47, 153.
3
3
3
3
3
3
3
3
3
1. Ma, H. Q.; Wang, Y. L.; Wang, J. Y. Heterocycles 2006, 68, 1669.
2. Ma, H. Q.; Wang, Y. L.; Li, J. P.; Wang, J. Y. Heterocycles 2007, 71, 135.
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