Water-mediated synthesis of 2-substituted benzimidazoles by boric acid and glycerol

Article abstract of DOI:10.1071/CH08309

A very simple, mild, and highly efficient green catalyst has been developed for the synthesis of 2-substituted benzimidazoles by treatment of substituted ortho-phenylenediamines and aldehydes in water at 80C in the presence of boric acid (5 mol-%) and glycerol (0.05 mL). This methodology has been standardized on 55 substrates, and nine new compounds have been synthesized.

Full text of DOI:10.1071/CH08309

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 140–144
www.publish.csiro.au/journals/ajc
Water-Mediated Synthesis of 2-Substituted Benzimidazoles
by Boric Acid and Glycerol
Chhanda Mukhopadhyay,A,C Pradip Kumar Tapaswi,A and Ray J. ButcherB
ADepartment of Chemistry, University of Calcutta, 92, APC Road, Kolkata-700009, India.
BDepartment of Chemistry, Howard University, Washington, DC 20059, USA.
CCorresponding author. Email: csm@vsnl.net; cmukhop@yahoo.co.in
Averysimple, mild, andhighlyefficientgreencatalysthasbeendevelopedforthesynthesisof2-substitutedbenzimidazoles
by treatment of substituted ortho-phenylenediamines and aldehydes in water at 80◦C in the presence of boric acid (5 mol-%)
and glycerol (0.05 mL). This methodology has been standardized on 55 substrates, and nine new compounds have been
synthesized.
Manuscript received: 19 July 2008.
Final version: 29 November 2008.
R1
R1
Introduction
B(OH)3 (5 mol-%) and
glycerol (0.05 mL)
R2
R3
R2
R3
N
NH2
NH2
The development of simple, efficient, and eco-friendly processes
from easily available starting materials is a major challenge
to the present day organic chemist. In this category, water-
mediated[1] organic reactions are very useful for the synthesis
of important heterocycles such as benzimidazoles, which posses
anti-hypertension, anti-viral, and anti-cancer properties.[2]
Compounds that contain the benzimidazole skeleton exhibit
significant activity against several viruses such as HIV,[3] her-
pes simplex virus type-1 (HSV-1),[4] RNA,[5] influenza,[6]
and human cytomegalovirus (HCMV).[3] Bis-benzimidazoles
have emerged as DNA-minor groove binding agents, possess
anti-tumour activity,[7] and exhibit themselves as ligands to
transition metals for modelling biological systems.[8] A rapid,
straightforward, and high yielding green synthesis of substituted
benzimidazoles in aqueous media employing green catalytic
methodologies is always a great challenge to the organic chemist.
R4-CHO
R4
ϩ
Water, 80°C
N
H
1
2a/2b
R4 ϭ R-C6H4 (2a, 3a)
R4 ϭ alkyl (2b, 3b)
3a/3b
Scheme 1.
high temperature. Moreover, the use of an oxidizing agent
like molecular O2,[16] H2O2,[11] Fe3+ [15] Yb3+ [26] Sc3+ [24]
,
,
,
or In3+ [23] was absolutely necessary. In a continuation of our
earlier strategies for the establishment of water-mediated proto-
cols for the construction of important heterocycles,[28] we have
developed a highly efficient and straightforward green catal-
ysis for the synthesis of the 2-substituted benzimidazoles 3a
and 3b by direct condensation of equivalent amounts of ortho-
phenylenediamines (substituted or unsubstituted) 1, a variety of
aldehydes2a and 2bwithonly5 mol-%ofboricacidandglycerol
(0.05 mL) in 4 mL of water at 80◦C (Scheme 1).The most impor-
tant advantages of our method are: (a) it is a totally green pro-
cedure that involves homogeneous catalysis; (b) only 5 mol-%
of the catalyst is sufficient to complete the reaction; (c) the
very simple work-up does not require the involvement of any
organic solvents; (d) the products, which in general possess a
very high melting point, solidify readily, and hence can be very
easily removed from the aqueous medium and crystallized from
methanol without the need for further purification; (e) the cata-
lyst is very cheap and readily available; (f) the yields of all the
products are extremely high; and (g) the procedure is a highly
general one with 100% conversion in all the cases (no starting
materials were apparent by TLC).
Results and Discussion
Although many methods are available for benzimidazole
synthesis,[9–16] only two general procedures are available for
the construction of the 2-substituted benzimidazoles. The first
is the condensation between phenylenediamines and carboxylic
acids or their derivatives[17,18] (nitriles, orthoesters, or imi-
dates), which often demands strong acidic conditions or the
use of very high temperatures. The second process involves
a two-step synthesis that displays the oxidative cyclodehy-
dration of Schiff bases generated from the condensation of
ortho-phenylenediamines and aldehydes. The synthesis was
acheived using the reagents H2O2/HCl,[11] p-TsOH,[12] Me2S+
BrBr− [(bromodimethyl)sulfonium bromide],[13] KHSO4,[19]
ionic liquid,[20] I2,[21] 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ),[22] FeBr3, or Fe(NO3)3·9H2O,[15] In(OTf)3,[23]
Sc(OTf)3,[24,25] Yb(OTf)3,[26] sulfamic acid,[27] etc. Some of
these methods suffer from serious drawbacks such as the use
of toxic and hazardous solvents, maintenance of anhydrous
reaction conditions, prolonged reaction times, and sometimes
In order to ascertain the necessity of boric acid, glycerol, or
both, the correct solvent, and the required temperature, the reac-
tion of 4-chlorobenzaldehyde with ortho-phenylenediamine was
carried out separately in water alone (entry 1), in water that con-
tained only glycerol (entry 2), only 2–20% boric acid (entries
© CSIRO 2009
10.1071/CH08309
0004-9425/09/020140

Water-Mediated Synthesis of Benzimidazoles
141
Table 1. Synthesis of 2-(4-chlorophenyl) benzimidazole under various
conditions
Table 2. Synthesis of 2-substituted benzimidazoles with the homo-
geneous catalyst boric acid (5 mol-%) and glycerol (0.05 mL) in water
(4 mL) at 80◦C
Entries 1–49: product 3a; entries 50–55: product 3b; entries 1–16, 50, 51:
R1 = R2 = R3 = H; entries 17–27: R1 = Me, R2 = R3 = H; entries 28–34,
52, 53: R1 = R3 = H, R2 = Me; entries 35–43, 54, 55: R1 = H, R2 =
R3 = Me; entries 44–49: R1 = H, R2 = R3 = Cl
Reactions were carried out in a water bath/oil bath at 80◦C, 25◦C (entry 8),
120◦C (entry 9), or under solvent-free conditions (entry 17)
Entry Boric acid GlycerolA used (+) Solvent Time
Isolated
yield [%]
[mol-%]
not used (−)
(4 mL)
[h]
1
2
3
4
5
6
7
8
–
–
2
−
+
−
−
−
−
+
+
+
+
+
+
+
+
+
+
+
Water
Water
Water
Water
Water
Water
Water
Water
Water
THF
EtOAc
MeOH
EtOH
DMF
DMSO
CH3CN
—
06
0
5
Entry
Product 3a/3b
Time
[h]
YieldA
[%]
Reference
07
06
07
07
10
06
20
[R or R4 (alkyl)]
40
70
50
55
90
20
40
30
30
20
20
25
28
33
30
1
2
3
4
5
6
7
8
H
05
07
05
05
06
08
03
08
10
08
07
11
10
06
10
10
08
09
05
06
07
10
08
10
06
12
10
09
12
11
12
10
10
08
07
11
10
07
08
09
06
04
10
11
12
11
12
12
11
15
18
23
16
22
25
88
84
81
90
85
86
87
89
80
81
82
84
88
82
84
86
84
91
84
90
91
88
87
85
83
85
81
85
84
82
88
86
85
84
87
82
86
84
85
85
86
82
83
60
67
75
73
71
66
65
68
69
72
67
68
[13]
[13]
[13]
[13]
[13]
[13]
[13]
[15]
[15]
[11]
[11]
[27]
[29]
—
[30]
[31]
[14]
[32]
—
[32]
[32]
[33]
[27]
[34]
—
5
4-OMe
3,4-(OMe)2
4-Cl
3-NO2
4-NO2
10
20
5
5
5
5
5
5
5
5
5
5
5
9
0.3
R-C6H4 = 2-furanyl
10
11
12
13
14
15
16
17
07
07
06
06
06
07
08
08
2-OH
9
R-C6H4 = cinnamyl
4-NMe2
2-Cl
2-NO2
4-Br
2,5-(OMe)2
3-Br
3-OMe-4-OH
H
4-Cl
4-Br
4-OMe
4-OH
4-NO2
4-NMe2
2-NO2
3-Br
3,4-(OMe)2
2-Cl
H
3-Br
2-NO2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
AOne drop (0.05 mL) of glycerol was used.
3–6), or both boric acid (5 mol-%) and glycerol (0.05 mL) in
water (entries 7–9) or in other solvents (entries 10–16) at vari-
ous temperatures and even in a solvent-free manner (entry 17;
Table 1).
It was found that only 5 mol-% of boric acid and a drop
(0.05 mL) of glycerol in water at 80◦C (Table 1, entry 7) pro-
vided the best conditions for the synthesis of the benzimidazoles
in moderate to excellent yields.
—
[34]
[11]
—
We have envisaged a wide variety of the substituted
ortho-phenylenediamines, in particular, the 4,5-dichloro-ortho-
phenylenediamine (Table 2).[11,13–15,27,29–48] A wide variety
of aromatic aldehydes were also used, which possessed both
electron donating and electron-withdrawing substituents. The
method is further suitable for heteroaromatic aldehydes like
furfural and α,β-unsaturated aldehydes like cinnamaldehyde.
When the same catalysis mentioned above was applied to
aliphatic aldehydes 2b, the yields of the corresponding substi-
tuted 3b were comparatively lower (Scheme 1, Table 2). The
reasons for this could be possibly: (i) the lower stability of the
imine formed in the first step (see the mechanism) because of
the absence of conjugation and (ii) the acidity of the benzylic
proton, which is absent in aliphatic aldehydes, which might be
an important factor in the last step of the dehydration.
Both boric acid and glycerol, being highly water-soluble,
maintain the optimum acidity of the reaction medium and at
the same time can be easily removed from the medium after
the reaction. The water solution obtained as the filtrate can be
lyophilized to reclaim the boric acid (tested by the usual way
of obtaining the green flame of ethyl borate with ethanol with-
out adding concentrated sulfuric acid) which when dried could
be further reused as the catalyst. This operation could be per-
formed several times with only a 1% decrease in the yields
of the products after each cycle. Therefore, the catalyst could
be reused. To apply the feasibility of our methodology on a
preparative scale, the coupling of 4-chlorobenzaldehyde with
ortho-phenylenediamine (entry 4, Table 2) was carried out on a
—
4-NO2
4-Br
4-Cl
4-OMe
H
[11]
[35]
[11]
[11]
[36,37]
[33]
[38]
—
[38]
[39]
—
[40]
[39]
[14]
[33]
—
[41]
[39]
[42,43]
[44]
[45]
[46]
[47]
[48]
[48]
4-NO2
3-OH
4-NMe2
3-OMe-4-OH
2-Cl
4-OMe
R-C6H4 = 2-furanyl
2-NO2
H
4-NO2
4-Br
2-NO2
2-Cl
4-OH
CH3–CH2–
CH3–CH2–CH2–
CH3–CH2–
CH3–CH2–CH2–
CH3–CH2–
CH3–CH2–CH2–
AIsolated yields.

142
C. Mukhopadhyay, P. K. Tapaswi, and R. J. Butcher
O
R1
R1
B(OH)3 (5 mol-%) and
glycerol (0.05 mL)
R2
R3
R2
R3
NH2
NH2
NH2
H
ϩ
Water, 80°C
R
N
R
2a
1
H
H
R1
R1
R2
R2
R3
N
(aerial O2)
OH
N
R3
N
H
N
H
R
R
ϩHϩ (from boric acid and glycerol)
ϪH2O
R1
R1
R2
R3
R2
H
N
N
ϩ Hϩ
N
H
R3
N
R
R
(minor tautomer)
(major tautomer)
Scheme 2.
50 mmol scale. The reaction proceeded very smoothly, and the
desired 2-(4-chlorophenyl)-1H-benzimidazole was obtained in
90% isolated yield. A probable mechanism of the reaction is
given below (Scheme 2) (shown with aromatic aldehydes):
That the reaction proceeds by the formation of imine is evi-
dent from the 1H NMR and 13C NMR spectra of the crude
mixture after 1 h of heating (entry 19, Table 2), where the imine
proton appears at δ 8.48 and the imine carbon at δ 155.8.
With 2,3-diaminotoluene, a mixture of tautomers were gen-
erally obtained (except entry 25, Table 2 which yielded only
the one tautomer) whose structures were assigned by analogy
with the earlier references[14,32] and the ratios from the 1H NMR
integration studies. However, with 3,4-diaminotoluene, only one
tautomer was obtained as observed earlier.[11]
Br
C12
C9
C13
C8
C11
C10
N2
C2
C1
N1
C3
Cl1
C4
C7
C5
C6
C1S
O1S
Cl2
S
An additional structural confirmation of 2-(4ꢀ-bromophenyl)-
5,6-dichloro-1H-benzimidazole (entry 46;Table 2) was obtained
by X-ray crystal analysis, and the ORTEP diagram of a single
crystal of this molecule is shown below (Fig. 1). The single crys-
tal crystallizes with a molecule of dimethyl sulfoxide (DMSO),
the compound being crystallized from this solvent, with a strong
hydrogenbondbetweentheN–HimidazoleandtheOoftheS=O
bond.
C2S
Fig. 1. ORTEP diagram of 2-(4ꢀ-bromophenyl)-5,6-dichloro-1H-
benzimidazole (entry 46; Table 2) showing the crystallographic numbering
(CCDC 695339).
Experimental
Conclusions
General
We have highlighted the potential of boric acid (5 mol-%) and
glycerol (0.05 mL) for the first time as a cheap, mild, highly
efficient, non-toxic, recyclable catalyst for the high yielding syn-
thesis of 2-substituted benzimidazoles in water at 80◦C with
wide variations both in the aldehyde and also in the diamine.
Thus, this green catalysis opens an important alternative to the
use of volatile organic solvents and, therefore, should be highly
beneficial to both academics and industry.
Methanol was distilled before use. All the chemicals including
CDCl3 and (D6)DMSO were purchased from Aldrich Chemi-
cal Co. Silica Gel G with binder from Spectrochem, Pvt. Ltd
1
Mumbai, India was used for TLC. H and 13C NMR spectra
were obtained on a Bruker 300 MHz instrument at 300 and
75 MHz, respectively. Melting points were determined on an
electrical melting point apparatus with an open capillary and are
uncorrected. IR (KBr) spectra were recorded on a Perkin–Elmer

Water-Mediated Synthesis of Benzimidazoles
143
Spectrophotometer RX/FT-IR system.All theelemental analyses
were carried out on a C–H–N analyzer by courtesy of the Indian
Association for the Cultivation of Science, Jadavpur-700032,
India.
2-(3ꢀ,4ꢀ-Dimethoxyphenyl)-4-methyl-1H-benzimidazole
(Entry 26, Table 2)
Mp 243–245◦C (MeOH). νmax/cm−1 2947, 1498, 1438, 1262,
1223, 1135, 1027, 740. δH ((D6)DMSO) 12.62 and 12.34 (br s,
1H, two tautomers in the ratio 5:4), 7.79 (d, J 8.1) and 7.71 (d, J
6.3) (2H, C5-H and C7-H, both tautomers), 7.33 (dd, J 7.8, 1H,
General Procedure for Benzimidazole Formation
ꢀ
ꢀ
C6-H), 7.13–6.97 (m, 2H, C2 -H and C6 -H), 6.92 (d, J 6.9, 1H,
A mixture of an aldehyde (4 mmol), substituted ortho-
phenylenediamine (4.5 mmol), and water (4 mL) were placed in
a round bottomed flask (25 mL) fitted with a condenser. To the
reaction mixture boric acid (5 mol-%) and glycerol (0.05 mL)
were added and the flask was placed either in a water-bath or an
oil-bath at 80◦C and stirred for a specific time (Table 2).After 1–
2 h, some solid product started separating out. The reaction was
monitored by TLC for the disappearance of the starting alde-
hyde. The products, on cooling, were poured over ice-cold water
in a beaker and stirred for a further 10 min for complete pre-
cipitation. The product was filtered under suction and directly
recrystallized from hot methanol without the need for further
purification to obtain the pure benzimidazoles.
ꢀ
C5 -H), 3.85 (s, 3H, –OMe), 3.79 (s, 3H, –OMe), 2.54 and 2.53
(two merged singlets, 3H, C4-CH3, both tautomers). (Found:
C 71.51, H 5.83, N 10.62. Calcd. for C16H16N2O2: C 71.62,
H 6.01, N 10.44%.)
2-(3ꢀ-Bromophenyl)-5-methyl-1H-benzimidazole
(Entry 29, Table 2)
Mp 172–174◦C (EtOAc). νmax/cm−1 2909, 2371, 1563, 1440,
1380, 1113, 793, 717. δH (CDCl3) 11.48 (br s, 1H, NH), 8.31
(br s, 1H, C2 -H), 8.08 (d, J 7.9, 1H, C6 -H), 7.52 (d, J 8.2, 1H,
ꢀ
ꢀ
ꢀ
C4 -H), 7.44 (br d, J 8.0, 0.7, 1H, C7-H), 7.38 (s, 1H, C4-H),
ꢀ
7.19 (dd, J 7.9, 7.9, 1H, C5 -H), 7.06 (d, J 7.9, 1H, C6-H), 2.44
1
The melting points, spectroscopic data (IR, H NMR, 13C
(s, 3H, C5-CH3). δC 150.2, 138.9, 137.9, 132.5, 132.2, 130.1,
129.5, 125.1, 124.2, 122.6, 115.2, 114.3, 21.5. (Found: C 58.47,
H 3.73, N 9.82. Calcd. for C14H11N2Br: C 58.56, H 3.86,
N 9.75%.)
NMR), and elemental analysis data of all the new compounds
are represented below:
2-(2ꢀ,5ꢀ-Dimethoxyphenyl)-1H-benzimidazole
(Entry 14, Table 2)
Mp 218–220◦C (MeOH). νmax/cm−1 2935, 2376, 1492, 1432,
1210, 1040, 745. δH ((D6)DMSO) 12.09 (s, 1H, NH), 7.85 (d, J
5-Methyl-2-(2ꢀ-nitrophenyl)-1H-benzimidazole
(Entry 30, Table 2)
Mp 224–226◦C (MeOH). νmax/cm−1 2922, 2665, 2373, 1526,
1344, 974, 793. δH ((D6)DMSO) 12.89 (br s, 1H, NH), 7.96 (ddt,
ꢀ
3.2, 1H, C6 -H), 7.65–7.55 (m, 2H, C4-H and C7-H), 7.19–7.10
ꢀ
ꢀ
J 8.1, 7.9, 3.0, 2H, C3 -H and C6 -H), 7.81 (dd, J 7.5, 7.6, 1H,
ꢀ
ꢀ
(m, 3H, C3 -H, C5-H, and C6-H), 7.01 (dd, J 9.0, 3.2, 1H, C4 -H),
3.93 (s, 3H, OMe), 3.76 (s, 3H, OMe). δC 153.3, 151.2, 148.8,
142.7, 134.8, 122.2, 121.7, 118.6, 118.5, 117.2, 113.7, 113.5,
112.1, 56.2, 55.6. (Found: C 70.62, H 5.61, N 11.24. Calcd. for
C15H14N2O2: C 70.85, H 5.55, N 11.02%.)
ꢀ
ꢀ
C5 -H), 7.69 (dd, J 7.7, 7.7, 1H, C4 -H), 7.47 (br d, J 7.8, 1H,
C7-H), 7.36 (br s, 1H, C4-H), 7.03 (br d, J 8.1, 1H, C6-H), 2.39
(s, 3H, C5-CH3). δC 149.0, 146.9, 141.8, 134.9, 132.6, 132.3,
130.9, 130.8, 124.4, 124.3, 123.9, 118.9, 111.5, 21.4. (Found:
C 66.28, H 4.41, N 16.39. Calcd. for C14H11N3O2: C 66.40,
H 4.38, N 16.59%.)
2-(4ꢀ-Bromophenyl)-4-methyl-1H-benzimidazole
(Entry 19, Table 2)
Mp 194–196◦C (MeOH). νmax/cm−1 3112, 3055, 1434, 1316,
1072, 959, 827, 742. δH ((D6)DMSO) 12.88 and 12.62 (br s, 1H,
two tautomeric NH in the ratio 5:4), 8.15 (d, J 8.4) and 8.08 (d,
5,6-Dimethyl-2-(4ꢀ-N,N-dimethylaminophenyl)-
1H-benzimidazole (Entry 38, Table 2)
Mp 266–268◦C (MeOH). νmax/cm−1 2920, 2374, 1612, 1441,
1309, 1205, 823, 691. δH ((D6)DMSO) 12.26 (s, 1H, NH), 7.92
ꢀ
ꢀ
J 8.4) (2H, C2 -H and C6 -H, for major and minor tautomers),
ꢀ
ꢀ
(d, J 8.7, 2H, C2 -H and C6 -H), 7.23 (s, 2H, C4-H and C7-H),
ꢀ
ꢀ
7.72 (d, J 6.6, 2H, C3 -H and C5 -H), 7.37 (dd, J 7.8 and 7.7, 1H,
C6-H), 7.09 (d, J 7.2) and 7.04 (d, J 7.2) (1H, C7-H, for both
major and minor tautomers), 7.01–6.92 (m, 1H, C5-H), 2.46 (s,
3H, –CH3). δC 150.6 and 149.9 (minor and major), 143.9 and
143.6 (minor and major), 135.1, 132.3, 129.9, 129.1, and 128.8
(minor and major), 123.8 and 123.5 (minor and major), 123.2
and 122.4 (minor and major), 121.9, 116.8, 109.3, 17.6, and 17.1
(minor and major). (Found: C 58.42, H 3.94, N 9.61. Calcd. for
C14H11N2Br: C 58.56, H 3.86, N 9.75%.)
ꢀ
ꢀ
6.77 (d, J 9.0, 2H, C3 -H and C5 -H), 2.93 (s, 6H, –N(CH3)2),
2.26 (s, 6H, 2 × –CH3). δC 151.5, 151.1, 129.6, 127.4, 117.9,
111.9, 39.9, 20.1. (Found: C 76.77, H 7.31, N 15.92. Calcd. for
C17H19N3: C 76.95, H 7.22, N 15.83%.)
5,6-Dimethyl-2-(4ꢀ-methoxyphenyl)-1H-benzimidazole
(Entry 41, Table 2)
Mp 198–200◦C (MeOH). νmax/cm−1 2925, 1611, 1497, 1449,
1253, 1179, 1027, 836. δH ((D6)DMSO) 12.46 (s, 1H, –NH),
ꢀ
ꢀ
8.05 (d, J 8.7, 2H, C2 -H and C6 -H), 7.35 and 7.23 (two singlets
2-(3ꢀ-Bromophenyl)-4-methyl-1H-benzimidazole
(Entry 25, Table 2)
Mp 172◦C (EtOAc). νmax/cm−1 3437, 3194, 2922, 2140, 1686,
1445, 964, 751, 707. δH (CDCl3) 9.62 (br s, 1H, NH), 8.17 (dd,
ꢀ
merged together, 2H, C4-H and C7-H), 7.04 (d, J 8.7, 2H, C3 -H
ꢀ
and C5 -H), 3.78 (s, 3H, –OMe), 2.27 (s, 6H, 2 × –CH3). δC
160.8, 151.0, 143.0, 133.9, 131.0, 130.1, 128.3, 123.5, 119.1,
114.7, 111.6, 55.7, 20.4. (Found: C 76.23, H 6.52, N 11.27.
Calcd. for C16H16N2O: C 76.16, H 6.39, N 11.10%.)
ꢀ
ꢀ
J 1.5, 1.5, 1H, C2 -H), 7.96 (d, J 7.9, 1H, C6 -H), 7.44 (d, J 8.0,
ꢀ
1H, C4 -H), 7.39 (dd, J 8.3, 0.7, 1H, C7-H), 7.20–7.02 (m, 3H,
2-(4ꢀ-Bromophenyl)-5,6-dichloro-1H-benzimidazole
(Entry 46, Table 2)
Mp 285◦C (MeOH). νmax/cm−1 3035, 2950, 2296, 1591, 1442,
1407, 1292, 1099, 1017, 836, 723. δH ((D6)DMSO) 13.29 (br s,
ꢀ
C5-H, C6-H, and C5 -H), 2.55 (s, 3H, –CH3). δC 150.4, 139.0,
138.4, 132.7, 131.8, 130.3, 129.9, 125.3, 125.2, 123.8, 123.3,
122.9, 112.9, 17.3. (Found: C 58.49, H 3.93, N 9.66. Calcd. for
C14H11N2Br: C 58.56, H 3.86, N 9.75%.)

144
C. Mukhopadhyay, P. K. Tapaswi, and R. J. Butcher
ꢀ
ꢀ
1H, NH), 8.05 (d, J 8.4, 2H, C2 -H and C6 -H), 7.81 (s, 2H, C4-H
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CJC-79-11-1556
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8. doi:10.1016/J.MOLCATA.2005.09.025
[24] T. Itoh, K. Nagata, H. Ishikawa, A. Ohsawa, Heterocycles 2004, 63,
2769.
[25] K. Nagata,T. Itoh, H. Ishikawa,A. Ohsawa, Heterocycles 2003, 61, 93.
[26] C. Massimo, E. Francesco, M. Francesca, Synlett 2004, 1832.
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ꢀ
ꢀ
and C7-H), 7.74 (d, J 8.7, 2H, C3 -H and C5 -H). δC 152.9, 132.2,
128.7, 128.6, 124.8, 124.1. (Found: C 45.49, H 2.23, N 8.06.
Calc. for C13H7N2Cl2Br: C 45.65, H 2.06, N 8.19%.)
Acknowledgement
The authors thank the CAS Instrumentation Facility, University of Calcutta,
for spectroscopic data. P.K.T. thanks UGC (New Delhi) for his fellowship
(JRF).
[28] C. Mukhopadhyay,A. Datta, B. K. Banik, Heterocycles 2007, 71, 181.
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[30] B. H. Kim, R. Han, J. S. Kim, Y. M. Jun, W. Baik, B. M. Lee,
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