Ammonium metavanadate as an efficient catalyst for the synthesis of 2,4,5-triaryl-1H-imidazoles

Article abstract of DOI:10.1002/jhet.548

Ammonium metavanadate (NH₄VO₃) is an inexpensive, efficient and mild catalyst for the synthesis of 2,4,5-triaryl-1H-imidazole from the one-pot three-component condensation of benzil/benzoin, an aldehyde and ammonium acetate in excellent yield. This method has the advantages of good yield, green catalyst, simple procedure, much faster reactions.

Full text of DOI:10.1002/jhet.548

742
Ammonium Metavanadate As an Efficient Catalyst for the
Synthesis of 2,4,5-Triaryl-1H-imidazoles
Vol 48
Kirti S. Niralwad, Bapurao B. Shingate, and Murlidhar S. Shingare*
Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad,
Maharashtra 431004, India
*E-mail: prof_msshingare@rediffmail.com
Received October 6, 2009
DOI 10.1002/jhet.548
Published online 7 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
Ammonium metavanadate (NH4VO3) is an inexpensive, efficient and mild catalyst for the synthesis
of 2,4,5-triaryl-1H-imidazole from the one-pot three-component condensation of benzil/benzoin, an alde-
hyde and ammonium acetate in excellent yield. This method has the advantages of good yield, green
catalyst, simple procedure, much faster reactions.
J. Heterocyclic Chem., 48, 742 (2011).
INTRODUCTION
expensive catalysts. So the development of clean, high-
yielding, and environmentally friendly approaches is still
desirable and much in demand. The use of ammonium
metavanadate (NH4VO3) as an inorganic acid [27] that
meets the demand for an economic catalyst. It is
employed similar to vanadium pentoxide [28] and as a
catalyst in oxidation reactions with other cocatalysts
[29]. It is a reagent used in analytical chemistry, the
photographic industry, and the textile industry [28]. Jad-
hav and coworkers [30] reported the synthesis of benz-
imidazole in the presence of ammonium metavanadate.
Very recently, we have reported [31] the synthesis of
a-hydroxyphosphonates using ammonium metavanadate
as a catalyst in good yields. In continuation [32] of our
research work devoted to the development of useful
synthetic methodologies for the synthesis of bioactive
heterocycles, herein, we would like to report the facile
and ecofriendly methodology for the synthesis of 2,4,5-
triaryl-1H-imidazoles.
Imidazole derivatives are a very interesting class of
heterocyclic compounds because they are found in many
natural products and pharmacologically active com-
pounds, such as antiulcerative agent cimetidine [1], the
proton pump inhibitor omeprazole [2], and the benzodia-
zepine antagonist flumazenil [3], are imidazole deriva-
tives. Many of the substituted imidazoles are known as
inhibitors of p38 MAP kinase, fungicides, herbicides,
plant growth regulators, and therapeutic agents.[4–7].
Owing to the wide range of pharmacological and biolog-
ical activities, the synthesis of imidazoles has become
an important target in current years. Methods for the
synthesis of imidazoles include a four-component con-
densation using Wang’s resin in refluxing acetic acid [8]
and condensation of 1,2-diketones, aldehydes, primary
amines, and ammonium acetate in phosphoric acid [9]
and acetic acid [10] using an organocatalyst in acetic
acid [11] and H2SO4 [12] and dimethyl sulfoxide
(DMSO) [13]. A number of synthetic methods were
reported for the synthesis of 2,4,5-triaryl-1H-imidazoles
from the three-component condensation of benzil/ben-
zoin, aldehydes, and ammonium acetate using various
catalysts, such as ionic liquid [14], iodine [15], zeolite
HY/silica gel [16], ZrCl4 [17], acidic Al2O3 [18], AcOH
[19], NH4OAc [20], Yb(OTf)3 [21], Scolecite [22],
PEG-400 [23], L-proline [24], boric acid [25], and CAN
[26]. However, most of these methods have one or more
disadvantages, such as harsh reaction conditions, pro-
longed time period, poor yields, use of hazardous, and
RESULTS AND DISCUSSION
The present method involves a cyclocondensation of
Benzil 1a with aromatic or heteroaromatic aldehydes
2(a–i) and ammonium acetate 3 in ethanol using 10 mol
% NH4VO3 as a catalyst resulted into the corresponding
2,4,5-triaryl-1H-imidazoles 4(a–i) in good to excellent
yield as indicated in Scheme 1.
Initially, we have studied the solvent effect for the
synthesis of 4a as a model reaction by reacting benzil
C
V
2011 HeteroCorporation

May 2011
Ammonium Metavanadate as an Efficient Catalyst for the Synthesis of
2,4,5-Triaryl-1H-imidazoles
743
Scheme 1
1a, benzaldehyde 2a, and ammonium acetate 3 using 10
mol % NH4VO3 as a catalyst in different solvents. From
Table 1, we observed reaction in DMF and water at
90ꢀC afforded the product in low yields even after heat-
ing for 10 and 12 h, respectively (Table 1, entries 1 and
3). The use of THF at reflux temperature does not pro-
ceed the reaction (Table 1, entry 2), but we have
observed that the reaction gives 90% yield in DMSO at
90ꢀC and 91% yield in absolute ethanol at reflux tem-
perature (Table 1, entries 4 and 6). The reaction also
carried out in methanol at reflux temperature, and the
yield was good (90%) but requires more time (Table 1,
entry 5). We have performed the above model reaction
by combination of ethanol and water as a co-solvent
system, but absolute ethanol was observed better solvent
for this reaction (Table 2). It was also observed that
among the tested solvents (Table 2, entries 1), the reac-
tion in absolute alcohol was more facile in terms of
time and yield.
and reaction time, and the results are shown in Table 4.
Under similar reaction conditions, we have carried out
the cyclocondensation of benzoin 1b with aromatic/het-
eroaromatic aldehydes and ammonium acetate in the
presence of ammonium metavanadate that resulted into
the corresponding triaryl imidazoles in good yields.
However, the reaction requires more time when com-
pared with benzil (Table 4). The formation of triaryl
imidazoles have been confirmed by physical and spec-
troscopic data and is in full agreement with reported
data. Also, the present method was found to be effective
for benzil compared with benzoin in terms of time and
yield.
The present study was then extended for the synthesis
of 1,2,4,5-tetraaryl-1H imidazoles via the one-pot, four-
component condensation of benzil (1a), aldehydes 2,
ammonium acetate 3, and aromatic primary amines 4.
To our delight, the 1,2,4,5-tetraaryl-1H-imidazoles were
obtained in high yields. The results were illustrated in
(Table 4, entries 4j and 4k).
By keeping absolute ethanol as a solvent for model
reaction, the concentration of ammonium metavanadate
also been studied. At 5, 7.5, 10, and 12.5 mol % of am-
monium metavanadate gives the corresponding triaryl
imidazole in 68, 87, 91, and 91%, respectively, are
shown in Table 3.
The role of NH4VO3 has been proposed to activate
the aldehyde by binding the oxygen atom of aldehyde
with vacant ‘‘d’’ orbital of transition metal vanadium to
achieve the stable oxidation state. Along with this, we
recovered the catalyst and reused for further reactions.
The catalyst was recovered by filtration and washed
with diethyl ether and dried at 60–70ꢀC, which was then
dissolved in dilute sulphuric acid to transform it from
(V) to (IV) oxidation state. A little bit of zinc powder
was then added with constant swirling and warming to
reduced V (V) to vanadium compounds with lower oxi-
dation state (IV), as evident by the color of the solution
changes to Persian blue reported in the literature [33].
We have carried out the same cyclocondensation reac-
tion with various aromatic/heteroaromatic aldehydes
containing electron-donating or -withdrawing functional
groups at different positions worked well and did not
show remarkable differences in the yields of product
Table 1
Screening of solvents.a
Entry
Solvent
Time
Yield (%)b
Table 2
1
2
3
4
5
6
DMF
THF
H2O
10 (h)
12 (h)
12 (h)
1 (h)
2 (h)
45 (min)
75
No reaction
Solvent effect for model reaction 4a.
Entry
Solvent
Time
Yield (%)a
30
90
90
91
DMSO
MeOH
EtOH
1
2
3
4
EtOH (100%)
45 (min)
1.3 (h)
2 (h)
91
89
85
80
EtOH þ H2O (50:50)
EtOH þ H2O (20:80)
EtOH þ H2O (10:90)
a Reaction conditions: 2a (1 mmol), 1 (1 mmol), NH4VO3 (10 mol %),
solvent (10 mL).
b Isolated yields.
2.3 (h)
a Isolated yields.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

744
K. S. Niralwad, B. B. Shingate, and M. S. Shingare
Vol 48
Table 3
characterized by comparison of their spectral data (IR, mass,
and 1H-NMR) and physical properties with those reported in
the literature.
Effect of catalyst concentration on model reaction 4a.
2,4,5-Triphenyl-1H-imidazole (4a). M.p.: 275–277ꢀC (lit
[25] 276–278ꢀC). IR (KBr, cmꢁ1): 7125, 3040, 1485, 1459,
1130, 695. 1H-NMR (400 MHz, DMSO-d6, d ppm): 12.72
(brs, 1H, NH), 8.12 (d, 2H, J ¼ 7.6 Hz, ArH), 7.40–7.52 (m,
13H, ArH). MS (EI): m/z (%) ¼ 296 (46) [Mþ]. Anal. calcd.
for C21H16N2: C, 85.11; H, 5.44; N, 9.45. Found: C, 85.07; H,
5.41; N, 9.52.
Entry
Catalyst (mol %)
Yield (%)a
1
5
7.5
10
68
87
91
91
2
3
4
12.5
a Isolated yield.
2-(4-Chlorophenyl)-4,5-diphenyl-1H-imidazole (4b). M.p.:
261–263ꢀC (lit [25] 260–262ꢀC). IR (KBr, cmꢁ1): 3062, 1606,
EXPERIMENTAL
1
1453, 1090, 763, 695. H-NMR (400 MHz, DMSO-d6 d ppm):
All the melting points were determined in open capillaries
in a paraffin bath and are uncorrected. 1H-NMR spectra were
recorded on Mercury Plus Varian in DMSO or CDCl3 at 400
MHz using TMS as an internal standard. IR spectra were
recorded on a Perkin-Elmer FTIR using KBr discs. Mass spec-
tra were recorded on Micromass Quattro II using electrospray
ionization technique. The elemental analysis was carried out
on Flash EA 1112, 50/60 Hz, 1400 VA CHNS analyzer. The
progress of the reactions was monitored by TLC.
General procedure for the synthesis of 2,4,5-triaryl-1H-
imidazoles (4a–i). To the stirred mixture of aldehyde 2 (1
mmol), benzil 1a or benzion 1b, (1 mmol), and ammonium ac-
etate 3 (1.5 mmol) in ethanol (10 mL), ammonium metavana-
date (10 mol %) was added. The reaction mixture was refluxed
as time indicated in Table 4.
The progress of the reaction was monitored by TLC (ethyl
acetate: hexane, 7:3). After completion of reaction, dichloro-
methane (25 mL) was added to the reaction mixture, and it
was then washed with water (10 mL) and dried over anhydrous
CaCl2, and the solvent evaporated in vacuum to give the crude
product. Purification of solid products was achieved by crystal-
lization from EtOH. Products are known compounds and were
12.80 (brs, 1H, NH), 8.10 (d, 2H, J ¼ 8.4 Hz, ArH), 7.22–
7.58 (m, 12H, ArH). MS (EI): m/z (%) ¼ 330 (36), 332 (12)
[Mþ]. Anal. calcd. for C21H15ClN2: C, 76.24; H, 4.57; N, 8.47.
Found: C, 76.20; H, 4.55; N, 8.51.
2-(2-Chlorophenyl)-4,5-diphenyl-1H-imidazole (4c). M.p.:
194–196ꢀC (lit [25] 195–196ꢀC). IR (KBr, cmꢁ1): 3432, 3066,
1630, 1506, 1499. 1H-NMR (400 MHz, DMSO-d6 d ppm):
12.48 (brs, 1H, NH), 7.25–7.59 (m, 14H, ArH). MS (EI): m/z
(%) ¼ 330 (36), 332 (12) [Mþ]. Anal. calcd. for C21H15ClN2:
C, 76.24; H, 4.57; N, 8.47. Found: C, 76.20; H, 4.55; N, 8.51.
2-(4-Methoxyphenyl)-4,5-diphenyl-1H-imidazole (4d). M.p.:
227–229ꢀC (lit [25] 227–228ꢀC). IR (KBr, cmꢁ1): 3030, 1612,
1492, 1250, 1032, 695. 1H-NMR (400 MHz, DMSO-d6
d
ppm): 12.53 (brs, 1H, NH), 8.02 (d, 2H, J ¼ 8.0 Hz, ArH),
7.52 (d, 4H, J ¼ 6.8 Hz, ArH), 7.30–7.37 (m, 6H, ArH), 7.05
(d, 2H, J ¼ 7.6 Hz, ArH), 3.82 (s, 3H, CH3). MS (EI): m/z
(%) ¼ 326 (36) [Mþ]. Anal. calcd. for C22H18N2O: C, 80.96;
H, 5.56; N, 8.58. Found: C, 80.94; H, 5.53; N, 8.63.
2-(2-Nitrophenyl)-4,5-diphenyl-1H-imidazole
(4e). M.p.:
230–232ꢀC (lit [25] 232–233ꢀC). IR (KBr, cmꢁ1): 3422, 3088,
1
1590, 1505, 1336, 1105. H-NMR (400 MHz, DMSO-d6 d ppm)
3
12.65 (s, NH), 8.03 (d, J ¼ 7.5 Hz, C6H4NO2), 7.08–7.60 (m,
Table 4
Synthesis of 2,4,5-triaryl-1H-imidazoles 4(a–i) using. NH4VO3 as a catalyst.a
Melting point (ꢀC)
Entry
Compounds
R
1
Time (min)
Yield (%)c
Found
Reported
1
2
4a
4b
4c
4d
4e
4f
4g
4h
4i
H
4-Cl
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzil
Benzoin
Benzoin
Benzoin
Benzoin
Benzoin
45
60
94
92
90
94
89
94
89
92
88
82
80
90
89
87
88
85
275–277
261–263
194–196
227–229
230–232
188–189
261–262
198–200
270–272
175–178
283–285
–
276–278 [25]
260–262 [25]
195–196 [25]
227–228 [25]
232–233 [25]
190 [25]
260–261 [25]
199–201 [25]
268–270 [25]
174–175 [23]
287–289 [23]
–
3
2-Cl
50
55
60
55
45
60
65
2
5
4-OMe
4-NO2
4-F
2-Thienyl
2-Furyl
4-OH
4-OMe
4-OH
H
6
7
8
9
10
11
12
13
14
15
16
4jb
4kb
4a
4b
4h
4d
4g
120
150
100
90
90
85
4-Cl
–
–
–
–
2-Furyl
4-OMe
2-Thienyl
–
–
–
–
120
a Reaction conditions: benzil/benzoin (1 mmol), aldehyde (1 mmol), ammonium acetate (1.5 mmol), NH4VO3 (10 mol %).
b Reaction conditions: benzil(1 mmol), aldehyde (1 mmol), aromatic primary amines (1 mmol), ammonium acetate (1.5 mmol), NH4VO3 (10 mol %).
c Isolated yields.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2011
Ammonium Metavanadate as an Efficient Catalyst for the Synthesis of
2,4,5-Triaryl-1H-imidazoles
745
2C6H5), 6.69 (d, 3J ¼ 7.4 Hz, C6H4NO2). MS (EI): m/z (%) ¼ 297
(60), 269 (20), 165 (100), 105 (25), 77 (50). Anal. calcd. for
C21H15N3O2: C, 73.90; H, 4.39; N, 12.31. Found: C, 73.83; H,
4.32; N, 12.39.
2-(2-Fluorophenyl)-4,5-diphenyl-1H-imidazole (4f). M.p.:
188–189ꢀC (lit [25] 190ꢀC). IR (KBr, cmꢁ1): 3027, 1495,
1234, 837, 765, 695. 1H-NMR (400 MHz, DMSO-d6 d ppm):
12.71 (brs, 1H, NH), 8.13 (d, 2H, J ¼ 4.2 Hz, ArH), 7.57 (d,
4H, J ¼ 5.6 Hz, ArH), 7.25–7.40 (m, 8H, ArH). MS (EI): m/z
(%) ¼ 314 (44) [Mþ]. Anal. calcd. for C21H15FN2: C, 80.24;
H, 4.81; N, 8.91. Found: C, 80.27; H, 4.79; N, 8.86.
2-(2-Furyl)-4,5-diphenyl-1H-imidazole (4h). M.p.: 198–
200ꢀC (lit [25] 199–201ꢀC). IR (KBr, cmꢁ1): 3318, 2989,
2470, 1660, 1212, 1170, 874, 717, 637. 1H-NMR (400 MHz,
DMSO-d6 d ppm): 7.95–8.02 (m, 6H, Ar), 7.60–7.70 (m, 3H,
Ar), 7.46–7.58 (m, 4H, Ar), 7.20 (m, 1H, NH). MS (EI) (m/z,
%) ¼ 286 (29) [Mþ]. Anal. calcd. for C19H14N2O: C, 79.70;
H, 4.93; N,9.78. Found: C, 79.66; H, 4.91; N, 9.74.
[5] Maier, T.; Schmierer, R.; Bauer, K.; Bieringer, H.; Buerstell,
H.; Sachse, B. US Pat. 4,820,335, 1989; Chem Abstr 1989, 111, 19494.
[6] Schmierer, R.; Mildenberger, H.; Buerstell, H. Ger. Pat.
361464, 1987; Chem Abstr 1988, 108, 37838.
[7] Heeres, J.; Backx, L. J. J.; Mostmans, J. H.; Cutsem, J. V.J
Med Chem 1979, 22, 1003.
[8] Zhang, C.; Moran, E. J.; Woiwode, T. F.; Short, K. M.;
Mjalli, A. M. M.Tetrahedron Lett 1996, 37, 751.
[9] Orain, D.; Mattes, H.Tetrahedron Lett 2006, 47, 1253.
[10] Sarshar, S.; Siev, D.; Mjalli, A. M. M.Tetrahedron Lett
1996, 37, 835.
[11] Frantz, D. E.; Morency, L.; Soheili, A.; Murry, J. A.; Gra-
bowski, E. J. J.; Tillyer, R. D.Org Lett 2004, 6, 843.
[12] Weinmann, H.; Harre, M.; Koenig, K.; Merten, E.; Tilstam,
U.Tetrahedron Lett 2002, 43, 593.
[13] Clark, N. G.; Cawkill, E.Tetrahedron Lett 1975, 16, 2717.
[14] (a) Siddiqui, S. A.; Narkhede, U. C.; Palimkar, S. S.; Dan-
iel, T.; Lahoti, R. J.; Srinivasan, K. V.Tetrahedron 2005, 61, 3539;
(b) Shaabani, A.; Rahmati, A.; Aghaaliakbari, B.; Safaei-Ghomi,
J.Synth Commun 2006, 36, 65.
2-(2-Hydroxyphenyl)-4,5-diphenyl-1H-imidazole (4i). M.p.:
270–272ꢀC (lit [25] 268–270ꢀC). IR (KBr, cmꢁ1): 3283, 3057,
[15] Kidwai, M.; Mothsra, P.; Bansal, V.; Goyal, R.Mont Fur
Chem 2006, 137, 1189.
1702, 1608, 1493, 696. 1H-NMR (400 MHz, DMSO-d6
d
[16] Balalaie, S.; Arabanian, A.; Hashtroudi, M. S.Mont Fur
Chem 2000, 131, 945.
ppm): 12.42 (s, 1H, NH), 9.71 (s, 1H, OH), 7.90 (d, 2H, J ¼
8.4 Hz, ArH), 7.54 (d, 2H, J ¼ 7.6 Hz, ArH), 7.49 (d, 2H, J
¼ 7.2 Hz, ArH), 7.42 (t, 2H, J ¼ 7.6 Hz, ArH), 7.35 (t, 1H, J
¼ 7.6 Hz, ArH), 7.29 (t, 2H, J ¼ 7.6 Hz, ArH), 7.21 (t, 1H, J
¼ 7.2 Hz, ArH), 6.85 (d, 2H, J ¼ 8.4 Hz, ArH). MS (EI): m/z
(%) ¼ 312 (40) [Mþ]. Anal. calcd. for C21H16N2O: C, 80.75;
H, 5.16; N, 8.97. Found: C, 80.70; H, 5.18; N, 8.93.
2-(4-Methoxyphenyl)-1,4,5-triphenyl-1H-imidazole (4j). M.p.:
175–178ꢀC (lit [23] 174–175ꢀC) IR (KBr, cmꢁ1): 3061, 2954,
1605, 1570, 1481. 1H-NMR (400 MHz, DMSO-d6 d ppm):
7.62 (d, 2H, J ¼ 8.0 Hz, ArH), 7.01–7.37 (m, 15H, ArH), 6.77
(d, 2H, J ¼ 8.0 Hz, ArH), 3.77 (s, 3H, OCH3). MS (EI): m/z
(%) ¼ 403 [Mþ]. Anal. calcd. for C28H22N2O: C, 83.56; H,
5.51; N, 6.96. Found: C, 83.57; H, 5.53; N, 6.95.
[17] Sharma, G. V. M.; Jyothi, Y.; Lakshmi, P. S.Synth Com-
mun 2006, 36, 2991.
[18] Usyatinsky, A. Y.; Khmelnitsky, Y. L.Tetrahedron Lett
2000, 41, 5031.
[19] Wolkenberg, S. E.; Winoski, D. D.; Leister, W. H.; Wang,
Y.; Zhao, Z.; Lindsley, C. W.Org Lett 2004, 6, 1453.
[20] Kidwai, M.; Saxena, S.; Ruby; Rastogi, S.; Bull Korean
Chem Soc 2005, 26, 2051.
[21] Wang, L. M.; Wang, Y. H.; He, T.; Yao, Y. F.; Shao, J. H.;
Liu, B.J Fluorine Chem 2006, 127, 1570.
[22] Gadekar, L. S.; Mane, S. R.; Katkar, S. S.; Arbad, B. R.;
Lande, M. K.Central Eur J Chem 2009, 7, 550.
[23] Wang, X. C.; Gong, H. P.; Quan, Z. J.; Li, L.; Ye, H.
L.Chin Chem Lett 2009, 20, 44.
4-(1,4,5-Triphenyl-1H-imidazol-2-yl)phenol
(4k). M.p.:
[24] Shitole, N. V.; Shelke, K. F.; Sonar, S. S.; Sadaphal, S. A.;
Shingate, B. B.; Shingare, M. S.Bull Korean Chem Soc 2009, 30, 1963.
[25] Shelke, K. F.; Sapakal, S. B.; Sonar, S. S.; Madje, B. R.;
Shingate, B. B.; Shingare, M. S.Bull Korean Chem Soc 2009, 30, 1057.
[26] Sangshetti, J. N.; Kakare, N. D.; Kotharkar, S. A.; Shinde,
D. B.J Chem Sci 2008, 120, 463.
283–285ꢀC (lit [23] 287–289ꢀC) IR (KBr, cmꢁ1): 3430, 3057,
1610, 1581, 1499. 1H-NMR (400 MHz, DMSO-d6 d ppm):
9.30 (s, 1H, OH), 7.58–7.62 (d, 2H, J ¼ 8.1 Hz, ArH), 7.15–
7.53 (m, 15H, ArH), 6.74 (d, 2H, J ¼ 8.0 Hz, ArH). MS (EI):
m/z (%) ¼ 389 [Mþ]. Anal. calcd. for C27H20N2O: C, 83.48;
H, 5.19; N, 7.21. Found: C, 83.50; H, 5.21; N, 7.25.
[27] Synecek, V.; Hanic, F.Czechoslovak J Phys 1954, 4, 120.
[28] Stellman, J. M. Ed. Encyclopaedia of Occupational Health
and Safety, 4th ed.; Geneva: ILO, 1998; Vol. 3, p 63.
[29] (a) Garcia, T.; Solsona, B.; Murphy, D. M.; Antcliff, K. L.;
Taylor, S. H.J Catal 2005, 229, 1; (b) Reddy, B. M.; Ratnam, K. J.; Sai-
kia, P.J Mol Catal A 2006, 252, 238; (c) Reddy, B. M.; Rao, K. N.;
Reddy, G. K.; Bharali, P.J Mol Catal A 2006, 253, 44; (d) Radhika, T.;
Sugunan, S.Catal Commun 2007, 8, 150; (e) Gomez-Bernal, H.; Cede-
no-Caero, L.; Gutierrez-Alejandre, A.Catal Today 2009, 142, 227.
[30] Jadhav, G. R.; Shaikh, M. U.; Kale, R. P.; Gill, C. H.Chin
Chem Lett 2009, 20, 292.
REFERENCES AND NOTES
[1] (a) Chung, K. H.; Hong, S. Y.; You, H. J.; Park, R. E.; Ryu,
C. K.Bioorg Med Chem 2006, 14, 5795; (b) Wiglenda, T.; Ott, I.;
Kircher, B.; Schumacher, P.; Schuster, D.; Langer, T.; Gust, R.J Med
Chem 2005, 48, 6516; (c) Cescon, L. A.; Coraor, G. R.; Dessauer, R.;
Silversmith, E. F.; Urban, E. J.J Org Chem 1971, 36, 2262; (d) Naka-
mura, T.; Kakinuma, H.; Umemiya, H.; Amada, H.; Miyata, N.; Tanigu-
chi, K.; Bando, K.; Sato, M.Bioorg Med Chem Lett 2004, 14, 333.
[2] Tanigawara, Y.; Aoyama, N.; Kita, T.; Shirakawa, K.;
Komada, F.; Kasuga, M. K.Clin Pharmacol Ther 1999, 66, 528.
[3] Hunkeler, W.; Mohler, H.; Pieri, L.; Polc, P.; Bonetti, E. P.;
Cumin, R.; Schaffner, R. W.Nature 1981, 290, 514.
[31] Sonar, S. S.; Kategaonkar, A. H.; Ware, M. N.; Gill, C. H.;
Shingate, B. B.; Shingare, M. S. Arkivoc 2009, (ii), 138.
[32] (a) Sadaphal, S. A.; Shelke, K. F.; Sonar, S. S.; Shingare M. S.
Central Euro J Chem 2008 6, 622; (b) Sapkal, S. B.; Shelke, K. F.; Shin-
gate B. B.; Shingare M. S.Tetrahedron Lett 2009, 50, 1754; (c) Shelke, K.
F.; Sapkal S. B.; Shingare M. S.Chin Chem Lett 2009, 20, 283.
[33] (a) Basavaiah, K.; Krishnamurthy, G.; Mikrochim Acta 1999,
130, 197; (b) Sing, S.; Shukla, I. C.; Shukla, S.Indian J Pharm Sci 1988,
50, 278; (c) Kanakpura, B.; Javarappa, M.Tur J Chem 2002, 26, 551.
[4] Lee, J. C.; Laydon, J. T.; McDonnell, P. C.; Gallagher, T.
F.; Kumar, S.; Green, D.; McNulty, D.; Blumenthal, M.; Heys, J. R.;
Landvatter, S. W.; Strickler, J. E.; McLaughlin, M. M.; Siemens, I. R.;
Fisher, S. M.; Livi, J. P.; White, J. R.; Adams, J. L.; Young, P. R.Na-
ture 1994, 372, 739.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet