Schiff base transition metal complex catalyzed one-pot synthesis of 2-aryl-1H-phenanthro[9,10-d]imidazoles

Article abstract of DOI:10.1080/15533174.2011.594839

A rapid, efficient, and novel methodology for the synthesis of 2-aryl-1H-phenanthro[9,10-d]imidazole derivatives, catalyzed by bis[N-(3,5-dicumylsalicylidene)-2',6'- fluoroanilinato]zirconium(IV) dichloride under ultrasonic irradiation at room temperature, is reported. A range of substituted imidazoles was synthesized in excellent yields from one-pot reaction of aromatic aldehydes, 9,10-phenanthrenequinone, and ammonium acetate. The remarkable features of this new procedure are introducing a new one-pot method for synthesis of 2-aryl-1H-phenanthro[9,10-d]imidazoles, high conversion, short reaction time, and simple experimental and workup procedure. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2011.594839

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Schiff Base Transition Metal Complex Catalyzed
One-Pot Synthesis of 2-Aryl-1H-phenanthro[9,10-
d]imidazoles
Saman Damavandi a
a Department of Chemistry, Sarvestan Branch , Islamic Azad University , Sarvestan, I. R.
Iran
Published online: 02 Dec 2011.
To cite this article: Saman Damavandi (2011) Schiff Base Transition Metal Complex Catalyzed One-Pot Synthesis of 2-
Aryl-1H-phenanthro[9,10-d]imidazoles, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
41:10, 1274-1277, DOI: 10.1080/15533174.2011.594839
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:1274–1277, 2011
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.594839
Schiff Base Transition Metal Complex Catalyzed One-Pot
Synthesis of 2-Aryl-1H-phenanthro[9,10-d]imidazoles
Saman Damavandi
Department of Chemistry, Sarvestan Branch, Islamic Azad University, Sarvestan, I. R. Iran
a diketone. In the present study, 9,10-phenanthrenequinone
instead of benzil was used as a diketone and one-pot, three-
component reactions of 9,10-phenanthrenequinone, various aro-
matic aldehydes, and ammonium acetate in the presence of
a catalytic amount of bis[N-(3,5-dicumylsalicylidene)-2ꢁ,6ꢁ-
fluoroanilinato]zirconium(IV) dichloride under ultrasonic irra-
diation have been carried out, and the corresponding 2-aryl-1H-
phenanthro[9,10- d]imidazoles were obtained in excellent yields
whithin short time (Scheme 1). To the best of our knowledge, the
one-pot synthesis of 2-aryl-1H-phenanthro[9,10-d]imidazole
and its derivatives has not been reported up to now. This study
provides fast, mild, and efficient method for synthesis of these
compounds in a one-pot, three component condensation.
A rapid, efficient, and novel methodology for the syn-
thesis
tives,
of
2-aryl-1H-phenanthro[9,10-d]imidazole
deriva-
catalyzed
by
bis[N-(3,5-dicumylsalicylidene)-2ꢀ,6ꢀ-
fluoroanilinato]zirconium(IV) dichloride under ultrasonic
irradiation at room temperature, is reported. A range of substi-
tuted imidazoles was synthesized in excellent yields from one-pot
reaction of aromatic aldehydes, 9,10-phenanthrenequinone,
and ammonium acetate. The remarkable features of this new
procedure are introducing a new one-pot method for synthesis of
2-aryl-1H-phenanthro[9,10-d]imidazoles, high conversion, short
reaction time, and simple experimental and workup procedure.
Keywords 2-aryl-1H-phenanthro[9, 10-d]imidazoles, one-pot,
Schiff base
EXPERIMENTAL
INTRODUCTION
Chemicals were either prepared in our laboratories or
purchased from Merck, Fluka, and Aldrich chemical com-
panies. All yields refer to isolated products. The reactions
were monitored by thin-layer chromatography carried out
on silica plates. Infrared (IR) spectra were recorded on a
Shimadzu-IR 470 spectrophotometer. 1H-Nuclear magnetic
resonance (NMR) spectra were recorded on a Bruker 100-MHz
spectrometer in dimethyl sulfoxide (DMSO) as the solvent
with trimethylsilane (TMS) as internal standard. Flash column
chromatography was performed with 300 and 400 meshes
silica gel, and analytical thin-layer chromatography (TLC) was
performed on precoated silica gel plates (60F-254). Elemental
analyses were performed on a Thermo Finnigan EA1112 ele-
mental analyzer. Synthesis of bis[N-(3,5-dicumylsalicylidene)-
2ꢁ,6ꢁ-fluoroanilinato]zirconium(IV) dichloride has been
reported elsewhere.[13] Scheme 2 shows the synthetic route to
the FI Zr-based catalyst.
Multicomponent reactions (MCRs) have attracted consider-
able attention since they are performed without need to isolate
any intermediate during their processes, which reduces time
and saves both energy and raw materials; thus, development
and discovery of new MCRs are still in demand.[1–3]
Imidazole and its derivatives are receiving growing atten-
tion for their pharmacologically properties, such as herbicidal,
fungicidal, analgesic, anti-inflammatory, and antithromobotic
activities.[4] During the course of studies on the development
of new procedures to synthesize 2,4,5-triarylimidazoles, a num-
ber of catalysts, such as copper(II) acetate,[5] Yb(OTf)3,[6] ele-
mental iodine,[7] ZrCl4,[8] HClO4-SiO2,[9] and NiCl2·6H2O,[10]
were screened. Some procedures also involve ionic liquid-
promoted[11] or microwave assisted synthesis.[12]
However, the development of a simple, efficient, and versatile
approach for the preparation of 2,4,5-triarylimidazoles is still an
active area of research for further improvements toward milder
reaction conditions and higher product yields.
All the reported literature in the field of one-pot syn-
thesis of 2,4,5-triaryl-1H-imidazole has examined benzil as
General Procedure for Preparation of
2-Aryl-1H-phenanthro[9,10-d]imidazole Derivatives
A
mixture of aromatic aldehyde (1 mmol), 9,10-
phenanthrenequinone (1 mmol), and ammonium acetate
(3.5 mmol) in CH3CN (10 mL) was stirred at room temperature
in the presence of bis[N-(3,5-dicumylsalicylidene)-2ꢁ,6ꢁ-
fluoroanilinato]zirconium(IV) dichloride (10 mol%) under
ultrasonic irradiation using ultrasonic cleaner with a frequency
of 40 kHz and a nominal power 100 W for the appropriate
Received 9 April 2011; accepted 30 May 2011.
Address correspondence to Saman Damavandi, Department of
Chemistry, Sarvestan Branch, Islamic Azad University, Sarvestan, I. R.
Iran. E-mail: Saman Damavandi@yahoo.com
1274

ONE-POT, 2-ARYL-1H-PHENANTHRO[9,10-d]IMIDAZOLES
1275
F
F
Cl
Cl
N
O
Zr
CHO
R
Ph
NH4OAc
2
O
O
N
Ph
+
+
R
N
H
US irradiation
SCH. 1. Synthetic route to imidazol derivatives.
6.95–7.45 (m, 9H, Ar), 7.75 (d, 2H, J = 7.5 Hz), 8.10 (d, 2H,
J = 5.2 Hz), 12.25 (s, NH). Found for C21H14N2: C, 85.33; H,
4.55; N, 9.44%. Calcd: C, 85.69; H, 4.79; N, 9.52%.
NH2
H
F
F
O
(CH2O)n
OH
OH
2-(4-Nitrophenyl)-1H-phenanthro[9,10-d]imidazole (2): IR
P-TSA
(KBr, cm 1): 3435 (N–H), 1555 (C C), 1585 (C N), 1340
1
(NO2), 1525 (NO2). H-NMR δ 7.10–7.65 (m, 10H, Ar), 8.04
(d, 2H, J = 8 Hz), 11.95 (s, 1H, NH). Found for C21H13N3O2:
C, 74.25; H, 3.90; N, 12.22%. Calcd.: C, 74.33; H, 3.86; N,
12.38%.
F
F
2-(4-Methoxyphenyl)-2H-phenanthro[9,10-d]imidazole (3):
F
F
N
1
N
O
IR (KBr, cm 1): 3405 (N–H), 1552 (C C), 1590 (C N). H-
Cl
Zr
Cl
n-BuLi
0.5 mmol ZrCl4
NMR δ 3.72 (s, 3H), 6.90–7.35 (m, 8H, Ar), 7.88 (d, 2H, J =
7.5 Hz), 8.10 (d, 2H, J = 7.5 Hz), 12.30 (s, NH). Found for
C22H16N2O: C, 80.95; H, 4.90; N, 8.55%. Calcd.: C, 81.46; H,
4.97; N, 8.64%.
OH
2
2-(4-Chlorophenyl)-1H-phenanthro[9,10-d]imidazole (4):
IR (KBr, cm 1): 3420 (N–H), 1425–1540 (C C), 1595 (C N).
1H-NMR 7.05–7.55 (m, 8H, Ar), 7.6–7.95 (m, 2H, Ar), 8.10
(d, 2H, J = 7 Hz), 12.14 (s, NH). Found for C21H13ClN2:
C, 76.61; H, 3.98; N, 8.46%. Calcd.: C, 76.71; H, 3.99; N,
8.52%.
2-p-Tolyl-1H-phenanthro[9,10-d]imidazole (5): IR (KBr,
cm 1): 3405 (N–H), 1425–1525 (C C), 1605 (C N). 1H-NMR
δ 2.20 (s, 3H), 7.10–7.50 (m, 8H, Ar), 7.70–7.90 (m, 2H, Ar),
8.05 (d, 2H, J = 5.2 Hz), 12.10 (s, NH). Found for C22H16N2: C,
85.60; H, 5.20; N, 8.97%. Calcd.: C, 85.69; H, 5.23; N, 9.08%.
SCH. 2. Synthetic route of the FI Zr-based catalyst.
time (Table 1). After completion of the reaction, as indicated
by TLC, the heterogeneous catalyst was filtered out. The
obtained crude product was purified by short column chro-
matography (petroleum ether:ethyl acetate, 9:1) to obtain pure
products. The spectra data of the selected compounds are as
follows:
2-Phenyl-1H-phenanthro[9,10-d]imidazole (1): IR (KBr,
1
cm 1): 3405 (N–H), 1552 (C C), 1590 (C N). H-NMR δ
TABLE 1
Influence of the catalyst amount on FI-Zr/US-catalyzed reaction of 9,10-phenanthrenequinone, ammonium acetate, and
p-nitrobenzaldehyde
CHO
O
O
FI catalyst
N
+ NH4OAc
+
NO2
US irradiation, r.t.
N
H
NO2
Catalyst (mol%)
Yielda,b
5%
82
10%
92
15%
93
20%
93
aReaction conditions: CH3CN (10 ml), p-nitrobenzaldehyde (1 mmol), 9,10-phenanthrenequinone (1 mmol), ammonium acetate (3.5 mmol),
room temperature and under UV irradiation (6 min).
bIsolated yield.

1276
S. DAMAVANDI
2-(Furan-2-yl)-1H-phenanthro[9,10-d]imidazole (8): IR Ar), 11.95 (s, NH). Found for C21H13N2Cl: C, 76.55; H, 3.91;
(KBr, cm 1): 3410 (N–H), 1415–1530 (C C), 1608 (C N). 1H- N, 8.55%. Calcd.: C, 76.71; H, 3.99; N, 8.52%.
NMR (100 MHz, DMSO-d6): 7.07–7.55 (m, 7H, Ar), 7.70–8.05
(m, 2H, Ar), 8.35 (d, 2H, J = 5.2 Hz), 12.12 (s, NH). Found for
RESULTS AND DISCUSSION
C19H12N2O: C, 80.02; H, 4.21; N, 9.79%. Calcd.: C, 80.27; H,
4.25; N, 9.85%.
As a preliminary study, the reaction of p-nitrobenzaldehyde,
9,10-phenanthrenequinone, and ammonium acetate was chosen
as a model, and to evaluate the effect of ultrasound for the model
reaction, first the reaction was examined without ultrasound at
2-(2-Chlorophenyl)-1H-phenanthro[9,10-d]imidazole (10):
IR (KBr, cm 1): IR 3385 (N–H), 1416–1605 (C C), 1635
(C N). 1H-NMR δ 7.05–7.50 (m, 4H, Ar), 7.70–8.10 (m, 8H,
TABLE 2
Results of 2-phenyl-1H-phenanthro[9,10-d]imidazole derivatives synthesis using FI Zr-based catalyst under ultrasonic irradiation
Entry
1
Aldehyde
Product
Time (min)
45
Yield (%)a
90
N
CHO
N
H
CHO
2
3
45
55
92
85
N
NO2
N
H
NO2
CHO
N
OMe
N
H
OMe
CHO
4
45
90
N
Cl
N
H
Cl
5
6
7
8
50
50
55
50
86
84
85
78
CHO
N
Me
OH
N
N
H
Me
CHO
N
N
H
OH
CHO
N
N
H
NMe2
N
O
N
CHO
O
H
9
40
60
90
93
HO
N
CHO
OH
N
H
10
Cl
N
CHO
Cl
N
H
aIsolated yields.

ONE-POT, 2-ARYL-1H-PHENANTHRO[9,10-d]IMIDAZOLES
1277
room temperature. Moderate yield (58%) with prolonged re- which may be catalyzed by the FI catalyst, intramolecular cy-
action time (5 h) was found, while with the usage of ultra- clization, and subsequently [1,5] sigmatropic proton shift to af-
sound at room temperature a surprisingly excellent yield was ford the corresponding 2-aryl-1H-phenanthro[9,10-d]imidazole
found (92%) with a short reaction time (45 min). Therefore, derivatives.
this method was chosen to perform the synthesis of all deriva-
tives of benzochromeno-pyrazoles under ultrasound irradiation.
It should be noted that no reaction was observed in the absence
of catalyst despite prolonged reaction times.
CONCLUSION
An efficient, fast and convenient synthesis of 2-aryl-
1H-phenanthro[9,10-d]imidazole derivatives accomplished via
one-pot, three-component condensations of aryl aldehy-
des, 9,10-phenanthrenequinone, and ammonium acetate
in the presence of bis[N-(3,5-dicumylsalicylidene)-2ꢁ,6ꢁ-
fluoroanilinato]zirconium(IV) dichloride under ultrasonication
at room temperature has been described. Applicability of the
method for the various compounds, high efficiency of the cata-
lyst system, short reaction times, and high yields of the products
prove the merit of this research. Finally, this approach could
make a valuable contribution to the existing processes in the
field of substituted imidazole synthesis.
To optimize the catalyst loading, 5 mol%, 10 mol%, 15 mol%,
and 20 mol% of FI catalyst were employed. The yields of 82, 92,
92, and 93% were obtained, respectively. Therefore, 10 mol%
loading of FI Zr-based catalyst was sufficient to push the reaction
forward.
To generalize the methodology, various starting ma-
terial were examined and different types of 2-aryl-1H-
phenanthro[9,10-d]imidazole were synthesized. Substituted
aldehydes bearing electron-withdrawing or electron-donating
groups, such as 4-methyl- and 4-methoxy-4-nitrobenzaldehyde,
were treated with ammonium acetate in combination with 9,10-
phenanthrenequinone under the same experimental conditions,
and the corresponding desired products were isolated in excel-
lent yields.
In this method the desired imidazole was obtained without
suffering from steric effects; however the reactions took more
time (Table 1, entries 10). In this case, a longer reaction time
was required to achieve better transformation. As it can be seen
in Table 2 (entry 9), salicylaldehyde reacted with ammonium
acetate in combination with 9,10-phenanthrenequinone under
the same experimental conditions and the corresponding prod-
uct was obtained in good yield, but the reaction proceeds more
rapidly than with other aldehydes used, and the isolated im-
idazole compound was afforded in a shorter time, due to the
intramolecular general acid-catalyzed reaction that facilitates
aminal intermediate formation.
The lower chemical yield with heterocyclic aldehyde in com-
parison with other aldehydes used can be explained by low cat-
alytic activation of furfural carbonyl group by acid, because
conjugation with the heterocyclic heteroatom lowers the car-
bonyl carbon’s electrophilicity.
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The probable mechanism involves the formation of an ami-
nal intermediate, condensation with 9,10-phenanthrenequinone,