Acid-catalyzed rearrangement of 3-(β-2-aminostyryl)quinoxalin-2(1H) ones-a new and efficient method for the synthesis of 2-benzimidazol-2- ylquinolines

Article abstract of DOI:10.1016/j.tetlet.2010.10.007

A highly efficient, one-step, versatile method for the synthesis of 2-benzimidazol-2-ylquinolines has been developed on the basis of an acid-catalyzed rearrangement proceeding via a novel ring contraction of 3-( β-2-aminostyryl )quinoxalin-2( 1 H)ones.

Full text of DOI:10.1016/j.tetlet.2010.10.007

Tetrahedron Letters 51 (2010) 6503–6506
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Tetrahedron Letters
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Acid-catalyzed rearrangement of 3-(b-2-aminostyryl)quinoxalin-2(1H)ones—a
new and efficient method for the synthesis of 2-benzimidazol-2-ylquinolines
Vakhid A. Mamedov a,b, , Dina F. Saifina a, Aidar T. Gubaidullin a, Venera R. Ganieva a, Saniya F. Kadyrova a,
⇑
Dimitry V. Rakov b, Il’dar Kh. Rizvanov a, Oleg G. Sinyashin a,b
a A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center of the Russian Academy of Sciences, Arbuzov str. 8, 420088 Kazan, Russian Federation
b Kazan State Technological University, Karl Marx str. 68, 420015 Kazan, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient, one-step, versatile method for the synthesis of 2-benzimidazol-2-ylquinolines has been
developed on the basis of an acid-catalyzed rearrangement proceeding via a novel ring contraction of
3-(b-2-aminostyryl)quinoxalin-2(1H)ones.
Received 19 June 2010
Revised 20 September 2010
Accepted 1 October 2010
Available online 12 October 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Quinoxalin-2(1H)ones
Benzimidazoles
Ring contraction
Acid-catalyzed rearrangement
2-Benzimidazol-2-ylquinolines
1H NMR data
X-ray diffraction analysis
The benzimidazole1 moiety is an important pharmacophore
that has proved to be useful for a number of biologically relevant
targets. Compounds possessing a benzimidazole moiety exhibit
significant activity towards several viruses, such as HIV,1d,e Herpes
(HSV-1),1d,f human cytomegalovirus (HCMV),1b,d,f and influenza.1g
On the other hand, nitrogen-containing heterocyclic systems, in
which nitrogen atoms are intimately related to the bond connect-
ing the nuclei, are of interest due to their ability to form complexes
with metal ions. Since the report on organic light emitting diodes
(OLED) by Tang and VanSlyke,2 LEDs based on organic or polymeric
materials have generated considerable interest and have enabled
the development of low-cost, full-color, flat-panel displays along
with other emissive products.3–6 Organic electronic devices (OEDs)
have made excellent progress over the past few years and investi-
gations into synthesizing new active organic materials for applica-
tions in organic thin film transistors have recently attracted much
attention.7 The best-known electroluminescent (EL) metal chelate
is Alq3, where q is the 8-hydroxyquinolinato ligand, which is not
only a good emitter, but is also a highly efficient electron-trans-
porting material.8,9 Attachment of a benzimidazole group at the
2-position would allow this ligand to form stable complexes with
metal ions in a way similar to 8-hydroxyquinoline.
The preparation of benzimidazole derivatives in general, and
2-benzimidazol-2-ylquinolines in particular, is usually straightfor-
ward and a number of synthetic methods are available.10,11
However, these methods have disadvantages, such as low yields,
harsh reaction conditions, for example, high reaction temperatures
(ꢀ200 °C), use toxic reagents, such as POCl3, TMS-Cl, and polyphos-
phoric acid, and the following catalyst/oxidizing agents: Pb(OAc)4,
Py(Cr2O7)2, and Cu(OAc)2, and continuous O2 bubbling over the
course of the reaction.
In the present work, we report a direct, efficient, and convenient
approach to the synthesis of 2-benzimidazol-2-ylquinolines. The
method12 is based on a new acid-catalyzed quinoxaline-benzimid-
azole rearrangement of 3-(b-2-aminostyryl)quinoxalin-2(1H)ones
which occurs via reduction of the corresponding, easily available,
3-(b-2-nitrostyryl)quinoxalin-2(1H)ones 1a–i when exposed to
Na2S2O4. As is evident from the structures of products 2, the
C(2)–C(3) fragment and the b-2-nitrostyryl group at position 3 of
the starting quinoxalin-2(1H)one system, are involved in con-
structing two new heterocyclic systems (Scheme 1).
This reaction also proceeded with a compound possessing two
3-(b-2-nitrostyryl)quinoxalin-2(1H)one fragments, with the for-
mation of a benzimidazole-monopodand with terminal quinoline
fragments at the 2 and 20 positions of the benzimidazole ring sys-
tem (Scheme 2).
The structures of compounds 2a–i were deduced from their ele-
⇑
Corresponding author. Tel.: +7 843 2727304; fax: +7 843 2732253.
E-mail address: mamedov@iopc.ru (V.A. Mamedov).
mental analyses and 1H NMR data.12 The mass spectra of these
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.10.007

6504
V. A. Mamedov et al. / Tetrahedron Letters 51 (2010) 6503–6506
R3
1) EtOH, H2O, Δ
2) HCl, H2O, Δ
3) Na2CO3
R1
R1
R1
N
N
N
+
Na2S2O4
NO2
R3
R1
N
N
R2
O
R2
2a-i
1a-i
R1
H
H
H
H
H
H
H
Me
H
R2
H
Me
Et
R3
H
H
H
H
H
H
H
H
Cl
Product (yield) M.p., oC Rfa
2a (80%)
2b (76%)
2c (74%)
2d (53%)
2e (69%)
2f (70%)
2g (54%)
2h (79%)
2i (59%)
93-95
108-110
86-88
< 70
–
–
–
n-Pr
n-Bu
(CH2)4CH3
–
–
–
–
0.39
0.49
0.50
–
(CH2)5CH3
H
H
225-227
168-170
–
aEluent: hexane – EtOAc (3:1)
Scheme 1. An efficient method for the synthesis of 2-benzimidazol-2-ylquinolines from 3-(b-2-nitrostyryl)quinoxalin-2(1H)ones (2a–i).
N
N
N
N
NO2
NO2
1) EtOH, H2O, Δ
2) HCl, H2O, Δ
3) Na2CO3
N
N
O
O
+
Na2S2O4
N
N
N
N
4 (56%)
3
Scheme 2. Synthesis of 1,4-bis-[2-(quinolin-2-yl)benzimidazol-1-yl]butane (4).
compounds displayed molecular ion peaks at appropriate m/z val-
ues. Initial fragmentation involved scission of the benzimidazole
and quinoline ring systems.12
In the 1H NMR spectra of compounds 2b–i, along with signals
due to the two aromatic fragments, in the region of d 7.70–8.61
and d 7.32–7.83, two doublet signals for the AB-system were seen.
The chemical shift of this AB system was not only shifted down-
field (d 8.55–8.61 and d 8.48–8.54) compared with the chemical
shifts of the signals of the AB protons of the styryl fragment (d
8.30–8.36 and d 7.61–7.66, 3J ꢁ 16.0 Hz) of the starting compounds
1, but also had a small 3J ꢁ 8.6 Hz coupling constant, characteristic
of the cis-configuration of the vinyl protons. This indicated that
closure of the pyridine ring had occurred with formation of the
quinoline system of the 2-benzimidazol-2-ylquinolines 2b–i. The
chemical shifts of the protons of the N–CH2 fragments of the sub-
stituent at position 1 of the 2-benzimidazol-2-ylquinolines 2c–g
moved downfield by about ꢀ0.7 ppm compared with the chemical
shifts of the same protons of the starting compounds 1c–g. It
should be pointed out that the protons of the benzimidazole frag-
ment in compounds 2b–g resonate as two doublets and two trip-
lets, whereas in compound 2a they resonate as AA0BB0-system
multiplets.
Figure 1. ORTEP plot of compound 2c. Displacement ellipsoids are drawn at the
30% probability level. H atoms are represented by spheres of arbitrary radii.
one (1h) with hydrogen using 10 mol % Pd/CaCO3 as the catalyst
in methanol and obtained the corresponding 3-(b-2-aminosty-
ryl)-6,7-dimethylquinoxalin-2(1H)-one (5h).14 When boiled in
AcOH for 3 h the latter was transformed into 2-benzimidazol-2-
ylquinoline 2h (Scheme 3).15
The molecular structure of compound 2c was established
unambiguously by single crystal X-ray analysis (Fig. 1).13
To investigate the reaction mechanism, we performed the
reduction of 3-(b-2-nitrostyryl)-6,7-dimethylquinoxalin-2(1H)-
On the basis of the known chemistry of aniline,16 azadienes,17
and quinoxalinones,18 it is reasonable to assume that the first stage
of this reaction involves the nucleophilic attack of the amine group

V. A. Mamedov et al. / Tetrahedron Letters 51 (2010) 6503–6506
6505
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H2
N
AcOH
-H2O
Pd/CaCO3
1h
2h
NH2
MeOH
N
H
O
5h
6. Nakada, H.; Tohma, T. In Inorganic and Organic Electroluminescence;
Wissenschaft-und-Technik: Berlin, 1996; p 385.
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Scheme 3. The formation of 2-benzimidazol-2-ylquinoline (2h) from 3-(b-2-
aminostyryl)quinoxalin-2(1H)one (5h).
8. Liu, S. F.; Seward, C.; Aziz, H.; Hu, N. X.; Popovic, Z.; Wang, S. Organometallics
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Naturforschung 1991, 46B, 901.
H
H
N
+
N
H+
N
+
H
5a
2a
10. (a) Preston, P. N. Chem. Rev. 1974, 74, 279–314; (b) Singh, M. P.; Sasmal, S.; Lu,
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Heterocycl. Chem. 1990, 27, 563–566; (d) Mederski, W. W. K. R.; Pachler, K. G. R.
Tetrahedron 1992, 48, 10549–10558; (e) Middleton, R. W.; Wibberley, D. G. J.
Heterocycl. Chem. 1980, 17, 1757–1760; (f) Garmaise, D. L.; Komlossy, J. J. Org.
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Smith, G.; Kennard, C. H. L. Ind. J. Chem. 2004, 43B, 952–956; (i) Robertson, D.
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Ryabukhin, S. V.; Plaskon, A. S.; Volochnyuk, D. M.; Tolmachev, A. A. Synthesis
2006, 3715–3726; (l) Schiffmann, R.; Neugebauer, A.; Klein, C. D. J. Med. Chem.
2006, 49, 511–522.
NH2
H
N
H
B
N
H
A
O
O
NH2
+
..
H
H
OH
+
N
-H2O
N
H
N
H
+
-
H
N
N
H
O
11. (a) Alimohammadi, F.; Abedifard, S.; Shafiee, A. J. Heterocycl. Chem. 1994, 31,
1037; (b) Hisano, T.; Ichikawa, M.; Tsumoto, K.; Tasaki, M. Chem. Pharm. Bull.
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Heterocycl. Compd. 1973, 775; (h) Case, F. H. J. Heterocycl. Chem. 1967, 4, 157.
12. Typical procedure for the preparation of 2. A solution of 0.30 g (0.9 mmol) of 1-
ethyl-3-(b-2-nitrostyryl)-quinoxalin-2(1H)-one (1c) and 0.77 g (3.7 mmol) of
85% Na2S2O4 in 5 mL of EtOH and 5 mL of H2O was heated under reflux for 3 h.
Next, 5 mL of HCl and 5 mL of H2O were added, and the mixture was heated
under reflux for 2 h. After cooling to room temperature, the reaction mixture
was neutralized by addition of aqueous Na2CO3. The product was extracted
with CHCl3 (3 ꢂ 20 ml), and the organic extracts dried over MgSO4 and
concentrated. The residue was purified by column chromatography on silica
gel with hexane–EtOAc (15:1) as eluent to give 0.19 g (74%) of an analytically
D
C
Scheme 4. A plausible mechanism for the formation of 2-benzimidazol-2-
ylquinolines.
at C(3) of the quinoxalin-2(1H)-one of A to form the spiro-quinox-
aline derivative B. Rearrangement of the spiro-quinoxaline is then
assumed to occur according to Scheme 4 by cascade reactions
involving: (a) acid-catalyzed ring-opening with cleavage of the
C(3)–N(4) bond in the spiro-compound C leading to formation of
the quinoline derivative D, and (b) intramolecular nucleophilic at-
tack by the amino group on the carbamoyl carbonyl group with
formation of the final product 2 following elimination of water
(Scheme 4).
In conclusion, we have developed a synthetic strategy for the
preparation of substituted 2-benzimidazol-2-ylquinolines 2 that
have not as yet been described in the literature. This protocol in-
cludes a novel acid-catalyzed rearrangement of 3-(b-2-aminosty-
ryl)quinoxalin-2(1H)ones. The simplicity of the reaction design
and the possibility of introducing a variety of substituents at any
position of both the benzimidazole and quinoline ring systems
makes this method a useful tool for constructing these medicinally
and technically (organic emitting materials) relevant compounds.
The reaction is readily applicable to large-scale synthesis. Applica-
tion of this method to the synthesis of other heterocyclic ring
systems is currently under investigation and the results will be
published in due course.
pure sample of 2-(1-ethylbenzimidazol-2-yl)quinoline (2c): IR (KBr)
2955, 2925, 2854, 1615, 1599, 1563, 1496, 1466, 1437, 1398, 1375, 1329, 1258,
1190, 1117, 1067, 828, 761, 740 cmꢃ1 1H NMR (400 MHz, DMSO-d6) d 1.56
m 3046,
;
(3H, t, J = 7.0 Hz); 5.07 (2H, q, J = 7.0 Hz); 7.34 (1H, dd, J = 8.2; 6.8 Hz); 7.42 (1H,
dd, J = 7.9; 7.2 Hz); 7.70–7.80 (2H, m); 7.83 (1H, d, J = 8.2 Hz); 7.91 (1H, dd,
J = 7.9; 7.2 Hz); 8.11 (1H, d, J = 8.2 Hz); 8.18 (1H, d, J = 8.2 Hz); 8.54 (1H, d,
*
J = 8.5 Hz); 8.59 (1H, d, J = 8.5 Hz). MS (EI ), m/z I (%): 274 (17), 273 (87) M+Å
,
272 (42), 259 (20), 258 (100), 246 (37), 245 (32), 136 (13), 129 (11), 128 (24),
*
77 (10). (The peaks of ions with relative intensity less than 10% are not
specified.) MALDI mass spectrum m/z: 274 MH+.
1,4-Bis-[2-(quinolin-2-yl)benzimidazol-1-yl]butane (4). Mp 264–267 °C. IR (KBr)
m
3077, 3048, 2954, 2925, 2855, 1673, 1597, 1496, 1461, 1437, 1427, 1397,
1367, 1329, 1284, 1259, 1159, 1121, 1074, 842, 758, 736, 719 cmꢃ1 1H NMR
;
(400 MHz, DMSO-d6) d 2.20 (4H, br s); 5.09 (4H, br s); 7.29–7.40 (4H, m);
7.56–7.68 (4H, m); 7.74 (2H, d, J = 7.6 Hz); 7.75–7.81 (4H, m); 8.05 (2H, d,
*
J = 7.9 Hz); 8.49 (2H, d, J = 8.6 Hz); 8.53 (2H, d, J = 8.6 Hz). MS (EI ), m/z I (%):
545 (28), 544 (75) M+Å, 416 (19), 415 (19), 412 (14), 300 (14), 299 (65), 298
*
(11), 286 (22), 272 (100), 258 (66), 246 (34), 171 (46). (The peaks of ions
with relative intensity less than 10% are not specified.) MALDI mass spectrum
m/z: 545 MH+.
13. The X-ray diffraction data for crystals of 2c were collected on a Bruker AXS
Smart Apex II CCD diffractometer at 296 K. Crystallographic data for 2c.
Acknowledgment
C
18H15N3, pink prisms, formula weight 273.33, orthorhombic, Pca21,
a = 21.506(2), b = 4.9627(5), c = 13.1575(13) Å, V = 1404.3(3) Å3, Z = 4, qcalc
=
The authors thank the Russian Foundation for Basic Research
(Grant No. 10-03-00413-a) for financial support.
1.293 g cmꢃ3 (kMoK ) = 0.78 cmꢃ1
, l . F(0 0 0) = 576, reflections collected =
a
8128, unique = 2940, R(int) = 0.0885, full-matrix least-squares on F2,
parameters = 191, restraints = 1. Final indices R1 = 0.0546, wR2 = 0.0766 for
References and notes
1952 reflections with I > 2
of-fit on
r
(I); R1 = 0.0922, wR2 = 0.0851 for all data, goodness-
F
2 = 0.974, largest difference in peak and hole (0.149 and
ꢃ0.177 eÅꢃ3). Crystallographic data (excluding structure factors) for the
structure 2c in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication number CCDC
778693. Copies of the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44-(0)1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
1. (a) Fellenius, E.; Berglindh, T.; Sachs, G.; Olbe, L.; Elander, B.; Sjostrand, S. E.;
Wallmark, B. Nature 1981, 290, 159–161; (b) Emery, V. C.; Hassan-Walker, A. F.
Drugs 2002, 62, 1853–1858; (c) Sondhi, S. M.; Singhal, N.; Johar, M.; Narayan
Reddy, B. S. N.; Lown, J. W. Curr. Med. Chem. 2002, 9, 1045–1074; (d) Porcari, A.
R.; Devivar, R. V.; Kucera, L. S.; Drach, J. C.; Townsend, L. B. J. Med. Chem. 1998,
41, 1252–1262; (e) Roth, T.; Morningstar, M. L.; Boyer, P. L.; Hughes, S. M.;
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Migawa, M. T.; Girardet, J. L.; Walker, J. A.; Koszalska, G. W.; Chamberlain, S. D.;
14. 3-(b-2-Aminostyryl)-6,7-dimethylquinoxalin-2(1H)one (5h).
A suspension of
0.50 g (1.6 mmol) of 3-(b-2-nitrostyryl)-6,7-dimethylquinoxalin-2(1H)-one

6506
V. A. Mamedov et al. / Tetrahedron Letters 51 (2010) 6503–6506
(1h) and 0.05 g of Pd/CaCO3 in 20 mL of MeOH was stirred under a H2 atmos-
(1H, dd, J = 8.2; 7.0 Hz); 8.09 (1H, d, J = 8.0 Hz); 8.19 (1H, d, J = 8.2 Hz); 8.48
*
phere for 3 d. The precipitated crystals were collected by filtration and washed
with 40 ml of DMF. The DMF layer was diluted with 70 ml of H2O, and the
precipitated crystals were collected by filtration to afford 0.30 g (67%) of an
analytically pure sample of 3-(b-2-aminostyryl)-6,7-dimethylquinoxalin-
(1H, d, J = 8.6 Hz); 8.55 (1H, d, J = 8.6 Hz). MS (EI ), m/z I (%): 274 (21), 273
*
(100) M+, 272 (45), 258 (27), 128 (15), 60 (11). (The peaks of ions with
relative intensity less than 10% are not specified.) MALDI mass spectrum m/z:
274 MH+.
2(1H)-one (5h): IR (KBr)
m
3444, 3229, 3063, 2918, 1659, 1614, 1508, 1489,
16. (a) Parvatkar, P. T.; Parameswaran, P. S.; Tilve, S. G. J. Org. Chem. 2009, 74, 8369;
(b) Zhu, L.; Zhang, M. J. Org. Chem. 2004, 69, 7371; (c) Ham, G. E. J. Org. Chem.
1964, 29, 3052; (d) Byun, E.; Hong, B.; De Castro, K. A.; Lim, M.; Rhee, H. J. Org.
Chem. 2007, 72, 9815; (e) Marco-Contelles, J.; Pérez-Mayoral, E.; Samadi, A.;
Carmo Carreiras, M.; Soriano, E. Chem. Rev. 2009, 109, 2652; (f) Bian, M.; Yao,
W.; Ding, H.; Ma, Ch. J. Org. Chem. 2010, 75, 269; (g) Newhouse, T.; Lewis, C. A.;
Eastman, K. J.; Baran, P. S. J. Am. Chem. Soc. 2010, 132, 7119.
17. (a) Bandini, E.; Corda, G.; D’Aurizio, A.; Panunzio, M. Tetrahedron Lett. 2010, 51,
933; (b) Gouverneur, V.; Ghosez, L. Tetrahedron 1996, 52, 7585; (c) Bouaziz, Z.;
Nebois, P.; Fillion, H. Tetrahedron 1995, 51, 4057; (d) Berry, C. R.; Hsung, R. P.
Tetrahedron 2004, 60, 7629; (e) Palacios, F.; Rubiales, G. Tetrahedron Lett. 1996,
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Cuellar, M. A.; Alegria, L. K.; Prieto, Y. A.; Cortes, M. J.; Tapia, R. A.; Preite, M. D.
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1456, 1438, 1390, 1255, 1154, 741, 595 cmꢃ1
;
1H NMR (400 MHz, DMSO-d6) d
2.30 (3H, s); 2.31 (3H, s); 5.39 (2H, br s); 6.61 (1H, dd, J = 7.6; 7.3 Hz); 6.74 (1H,
d, J = 7.9 Hz); 7.06 (1H, dd, J = 7.9; 7.3 Hz); 7.06 (1H, s); 7.43 (1H, d, J = 15.9 Hz);
7.47 (1H, d, J = 7.6 Hz); 7.55 (1H, s); 8.12 (1H, d, J = 15.9 Hz); 12.27 (1H, br s).
*
MS (EI ), m/z I (%): 292 (10), 291 (55) M+Å, 290 (32), 289 (11), 274 (19), 273 (25),
272 (18), 264 (12), 263 (61), 262 (27), 248 (23), 247 (100), 246 (10), 147 (10),
145 (25), 135 (13), 131 (33), 129 (24), 128 (14), 123 (10), 118 (12), 117 (16).
*
(The peaks of ions with relative intensity less than 10% are not specified.)
MALDI mass spectrum m/z: 292 MH+.
15. 2-(5,6-Dimethylbenzimidazole-2-yl)quinoline (2h).
A
solution of 0.30 g
(1.0 mmol) of 3-(b-2-aminostyryl)-6,7-dimethylquinoxalin-2(1H)-one (5h) in
8 mL of AcOH was heated under reflux for 3 h. After cooling to room
temperature, the precipitated crystals were collected by filtration and 0.21 g
(75%) of an analytically pure sample of 2-(5,6-dimethylbenzimidazol-2-
yl)quinoline (2h) was obtained: IR (KBr)
1717, 1701, 1652, 1618, 1600, 1563, 1506, 1448, 1413, 1324, 1277, 1261,
1234, 1111, 1003, 865, 856, 834, 757 cmꢃ1 1H NMR (400 MHz, DMSO-d6) d
2.38 (6H, s); 7.42 (1H, br s); 7.56 (1H, br s); 7.70 (1H, dd, J = 7.6; 7.0 Hz); 7.89
18. (a) Cheeseman, G. W. H.; Cookson, R. F. In Condensed Pyrazines; Weissberger, A.,
Taylor, E. C., Eds.; Wiley-Interscience: New York, 1979; Vol. 35, (b) Mamedov,
V. A.; Kalinin, A. A.; Yanilkin, V. V.; Gubaidullin, A. T.; Latypov, Sh. K.; Balandina,
A. A.; Isaikina, O. G.; Toropchina, A. V.; Nastapova, N. V.; Iglamova, N. A.;
Litvinov, I. A. Russ. Chem. Bull. Int. Ed. 2005, 54, 2616.
m 3501, 3052, 2964, 2939, 2317,
;