One-step synthesis of pyrido[1,2-a]benzimidazole derivatives by a novel multicomponent reaction of chloroacetonitrile, malononitrile, aromatic aldehyde, and pyridine

Article abstract of DOI:10.1021/jo802166t

Polysubstituted pyrido[1,2-a]benzimidazole derivatives are efficiently produced in moderate yields in a novel one-pot, four-component reaction from pyridine or 3-picoline, chloroacetonitrile, malononitrile, and aromatic aldehyde in refluxing acetonitrile.

Full text of DOI:10.1021/jo802166t

One-Step Synthesis of Pyrido[1,2-a]benzimidazole Derivatives by a
Novel Multicomponent Reaction of Chloroacetonitrile,
Malononitrile, Aromatic Aldehyde, and Pyridine
Chao Guo Yan,* Qi Fang Wang, Xiao Kai Song, and Jing Sun
College of Chemistry & Chemical Engineering, Yangzhou UniVersity, Yangzhou 225002, China
cgyan@yzu.edu.cn
ReceiVed September 27, 2008
Polysubstituted pyrido[1,2-a]benzimidazole derivatives are efficiently produced in moderate yields in a
novel one-pot, four-component reaction from pyridine or 3-picoline, chloroacetonitrile, malononitrile,
and aromatic aldehyde in refluxing acetonitrile. The mechanism of this novel reaction was believed
involving the formation of polysubstituted benzenes with subsequent substitution and annulation reaction
of pyridine. All pyrido[1,2-a]benzimidazoles, polysubstituted benzenes, polysubstituted indoles, and some
key reaction intermediates are characterized by 1H and 13C NMR, MS, IR spectra, and elemental analysis
as well as X-ray crystallography.
Introduction
substituents like carbonyl, cyano, or nitro groups increase the
activity, and hence the synthetic utility, of methylene groups.5
The typical Kro¨hnke synthesis of pyridines is readily achieved
by heating pyridinium salt with R,ꢀ-unsaturated ketones.6 On
the other hand, malononitrile is an exceptionally versatile
compound; therefore, it is used extensively as a reactant or
reaction intermediate. It exhibits unique reactivity since the
strongly electron-withdrawing cyano groups activate the me-
thylene groups (pKa ) 11.2), whose polar multiple bond is
suitable for nucleophilic addition and is also a good leaving
group for substitution.7 The methylene group and either one or
both cyano groups can take part in condensation reactions to
give a variety of addition products and heterocyclic compounds.8
This exceptional behavior makes malononitrile an important
Ammonium ylides, which are often generated by deproto-
nation of the corresponding quaternary ammonium salts, are
prone to be potential synthons and undergo versatile reactions,
especially in the enantioselective catalytic cyclopropanation
1,2
process.
As one kind of heterocyclic ammonium salts, the
special nature of pyridinium salts allows them to be used to a
great variety of synthetic reactions.3,4 Due to the aromatic
character and basicity of the pyridine heterocycle, and to the
electron-attracting influence of the nitrogen atom, pyridinium
cations in combination with strongly electron-withdrawing
* To whom correspondence should be addressed. Tel: 86-051487993351.
(1) (a) Papageorgiou, C. D.; Ley, S. V.; Gaunt, M. J. Angew. Chem., Int.
Ed. 2003, 42, 828–831. (b) Bremeyer, N.; Smith, S. C.; Ley, S. V.; Gaunt, M. J.
Angew. Chem., Int. Ed. 2004, 43, 2681–2684. (c) Papageorgiou, C. D.; de Dios,
M. A. C.; Ley, S. V.; Gaunt, M. J. Angew. Chem., Int. Ed. 2004, 43, 4641–
4644.
(2) (a) Kowalkowska, A.; Sucholbiak, D.; Jonczyk, A. Eur. J. Org. Chem.
2005, 925–933. (b) Bremeyer, N.; Smith, S. C.; Ley, S. V.; Gaunt, M. J. Angew.
Chem., Int. Ed. 2004, 43, 2681. (c) Do¨mling, A.; Ugi, I. Angew. Chem., Int. Ed.
2000, 39, 3168–3210. (d) Ramon, D. J.; Miguel, Y. Angew. Chem., Int. Ed.
2005, 44, 1602–1634.
(5) (a) Neve, F.; Crispini, A.; Campagna, S. Inorg. Chem. 1997, 36, 6150–
6156. (b) MacGillivray, L. R.; Diamente, P. R.; Reid, J. L.; Ripmeester, J. A.
Chem. Commun. 2000, 359–360. (c) Barrio, M. C. G.; Barrio, J. R.; Walker, G.;
Novelli, A.; Leonard, N. J. J. Am. Chem. Soc. 1973, 95, 4891–4895.
(6) (a) Kro¨hnke, F. Angew. Chem., Int. Ed. 1963, 2, 225–238. (b) Kro¨hnke,
F.; Zecher, W. Angew. Chem., Int. Ed. 1962, 1, 626–632. (c) Kro¨hnke, F.
Synthesis 1976, 1–37.
(3) Yan, C.-G.; Cai, X.-M.; Wang, Q.-F.; Wang, T.-Y.; Zheng, M. Org.
Biomol. Chem. 2007, 5, 945–951.
(7) (a) Freeman, F. Chem. ReV. 1969, 69, 591–624. (b) Fatiadi, A. J. Synthesis
1978, 241–282. (c) Fatiadi, A. J. Synthesis 1978, 241–282. (d) Saikia, A. Synlett
2004, 2247–2248.
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Synthesis 2006, 2357–2370. (b) Nair, V.; Deepthi, A.; Beneesh, P. B.;
Eringathodi, S. Synthesis 2006, 1443–1446. (c) Balalaie, S.; Bararjanian, M.;
Amani, A. M.; Movassagh, B. Synlett 2006, 263–266. (d) Jin, T.-S.; Wang, A.-
Q.; Wang, X.; Zhang, J.-S.; Li, T.-S. Synlett 2004, 871–873. (e) Fringuelli, F.;
Piermatti, O.; Pizzo, F. Synthesis 2003, 2331–2334.
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Nikishin, G. I.; Struchkov, Y. T. Tetrahedron Lett. 1993, 34, 5195–5198. (b)
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10.1021/jo802166t CCC: $40.75 2009 American Chemical Society
Published on Web 12/11/2008

One-Step Synthesis of Pyrido[1,2-a]benzimidazole DeriVatiVes
TABLE 1. One-Pot Synthesis of Polysubstituted Benzoates
entry
compd
Ar
time (h)
yield (%)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
Ph
p-ClC6H4
p-BrC6H4
p-CH3C6H4
m-BrC6H4
p-FC6H4
p-EtC6H4
m-CH3C6H4
p-CH3OC6H4
18
12
12
24
12
12
24
24
24
37
38
54
27
27
44
38
30
29
candidate for the design of new practical multicomponent
reaction procedures in research and in medicinal, industrial, and
agricultural chemistry. In fact, there are a lot of multicomponent
reaction procedures with malononitrile to prepare carbocyclic
and heterocyclic compounds.9-11 Recently, we found that
polysubstituted benzene derivatives with an unprecedented
substitution pattern could be produced in a one-pot multicom-
ponent cyclization reaction of pyridine, ethyl R-bromoacetate,
malononitrile, and aromatic aldehyde in refluxing acetonitrile.12
In continuation of our efforts to investigate new one-pot
multicomponent reactions, we developed this kind of reaction
to other reactive R-halogenato-substituted carbonyl compounds
and found very intriguing results of a new multicomponent
reaction which involves malononitrile, aromatic aldehydes,
pyridine, and chloroacetonitrile.
FIGURE 1. Molecular structure of 1a in crystal.
TABLE 2. Results of One-Pot, Four-Component Reactions of
Chloroacetonitrile
yield (%)
entry
compd
Ar
time (h)
2a-l
3a-l
4a-l
1
2
3
4
5
6
7
8
9
a
b
c
d
e
f
g
h
i
Ph
12
24
6
12
6
35
20
33
46
28
26
34
32
31
51
40
35
p-CH3C6H4
p-ClC6H4
m-ClC6H4
p-BrC6H4
m-BrC6H4
p-CH3OC6H4
m-CH3C6H4
p-C2H5C6H4
p-i-PrC6H4
p-t-BuC6H4
p-FC6H4
17
15
17
6
24
18
24
24
12
12
10
10
11
12
j
k
l
14
14
Results and Discussion
SCHEME 1. One-Pot, Four-Component Reactions
With the initial success of the one-pot multicomponent
cyclization reaction of ethyl R-bromoacetate, pyridine, malono-
nitrile, and aromatic aldehyde in refluxing acetonitrile to yield
polysubstituted benzene derivatives with an unprecedented
substitution pattern, 12 we tried to screen the reactivity of other
reactive R-halogenato-substituted carbonyl compounds and use
this four-component reaction to prepare cyclopropane deriva-
tives. At first, we used methyl R-chloroacetate to replace ethyl
R-bromoacetate in the reaction, and the respected polysubstituted
methyl benzoates 1a-i were produced as main products in
similar yields (Table 1, entries 1-9). The polysubstituted
Affording Three Kinds of Products 2-4
1
benzoates 1a-i were fully characterized by H and 13C NMR
and IR spectra and elemental analysis, and their structures were
also confirmed by single-crystal X-ray diffraction determination
of 1a (Figure 1). Thus, we could conclude that R-halogenato
esters behave similarly in this component reaction and this
reaction is a convenient synthetic procedure for the preparing
some polysubstituted benzene derivatives.
When a mixture of chloroacetonitrile, malononitrile, benzal-
dehyde, and an excess of pyridine was heated in acetonitrile
for several hours, the unexpected nitrogen-containing hetero-
cyclic compound pyrido[1,2-a]benzimidazole 2a was isolated
in 35% yield after workup. Similarly, various aromatic aldehydes
were screened under the same conditions, and the corresponding
pyrido[1,2-a]benzimidazole 2a-l were produced in moderate
yields (Table 2). Besides affording pyrido[1,2-a]benzimidazole
derivatives (2) as main products, the reactions of p-chloro- and
p-isopropylbenzaldehyde also yield polysubstituted indole prod-
ucts 4c (17%) (Table 2, entry 3) and 4j (14%) (Table 2, entry
10) in lower yields. From the reaction mixture of p-methoxy-
benzaldehyde and p-fluorobenzaldehyde, another byproduct
polysubstituted benzene derivative 3g and 3l could be separated
(9) (a) Xue, D.; Chen, Y.-C.; Wang, Q.-W.; Cun, L.-F.; Zhu, J.; Deng, J.-G.
Org. Lett. 2005, 7, 5293–5296. (b) Xue, D.; Li, J.; Zhang, Z.-T.; Deng, J.-G. J.
Org. Chem. 2007, 72, 5443–5445. (c) Pratap, R.; Ram, V. J. J. Org. Chem.
2007, 72, 7402–7405.
(10) (a) Marchalin, S.; Baumlova, B.; Baran, P.; Oulyadi, H.; Daich, A. J.
Org. Chem. 2006, 71, 9114–9127. (b) Inokuma, T.; Hoashi, Y.; Takemoto, Y.
J. Am. Chem. Soc. 2006, 128, 9413–9419.
(11) Elinson, M. N.; Vereshchagin, A. N.; Feducovich, S. K.; Zaimovskaya,
T. A.; Starikova, Z. A.; Belyakov, P. A.; Nikishin, G. I. Tetrahedron Lett. 2007,
48, 6614–6619.
(12) Yan, C. G.; Song, X. K.; Wang, Q. F.; Sun, J.; Siemeling, U.; Bruhn,
C. Chem. Commun. 2008, 1440–1442.
J. Org. Chem. Vol. 74, No. 2, 2009 711

Yan et al.
FIGURE 2. Molecular structure of 2b in the crystal.
FIGURE 4. Molecular structure of 4b in the crystal.
ates.13 The preparation of them often required lengthy steps and
suffered from some drawbacks as well as lower yields.14-16
The short reaction time and easiness of handling should render
this new multicomponent reaction applicable to the synthesis
of pyrido[1,2-a]benzimidazole derivatives. The special feature
of the structure of 3 is that the two p-methylphenyl substituents
are in the ortho position of the benzene ring, which has not
been observed to date in any of the known cyclization reactions
of malononitrile with formation of carbocyclic and heterocyclic
compounds.8-10 But the formation of 3 is reasonable according
to our recent published work, in which a mixture of malono-
nitrile, benzaldehyde, ethyl R-bromoacetate, and an excess of
pyridine was heated in acetonitrile to give product with similar
structure. By using chloroacetonitirle to replace ethyl R-bro-
moacetate in the reaction, the product is 3 in which the ester
group is substituted by a cyano group. The formation of 4 is
very intriguing. The most unusual feature of the structure of 4
is that there are three p-methylphenyl groups in the molecule,
which means that at least three molecules of p-methylbenzal-
dehyde might take part in the reaction.
As shown in Table 2, benzaldehyde bearing moderate
electronic influence substituents such as bromo, chloro, fluoro,
alkyl, and methoxyl afforded three kinds of the desired products
(Table 2). In some cases, compounds 3 and 4 were not separated
because of low yields. In contrast, benzaldehydes with stronger
electron-donating groups such as hydroxyl and dimethylamino
or with stronger electron-withdrawing groups such as the nitro
group as well as pyridinecarbaldehydes did not give one of the
three kinds of products, affording only gummy materials whose
structure could not be elucidated. To optimize the reaction
conditions for the formation of pyrido[1,2-a]benzimidazole, the
FIGURE 3. Molecular structure of 3b in the crystal.
in 10% and 14% yields, respectively (Table 2, entries 7 and
12). The reaction of p-methylbenzaldehyde give all three
products: 2b (20%), 3b (17%), and 4b (15%). The results of
the reaction are very interesting and show that three different
kinds of products can be formed in the reactions. Theses four-
component reactions of malononitrile, benzaldehyde, R-chlo-
roacetonitrile, and pyridine are much more complicated than
the similar multicomponent reactions of pyridine, ethyl R-bro-
moacetate, malononitrile, and aromatic aldehyde in refluxing
acetonitrile, which were reported by us recently. The structures
of all pyrido[1,2-a]benzimidazoles (2a-2l), polysubstituted
benzenes (3), and polysusbtituted indoles (4) were fully
1
characterized by H and 13C NMR, MS, and IR spectra and
(13) (a) Jordan, A. D.; Vaidya, A. H.; Rosenthal, D. I.; Dubinsky, B.; Kordik,
C. P.; Sanfilippo, P. J.; Wu, W.-N.; Reitz, A. B. Bioorg. Med. Chem. Lett. 2002,
12, 2381–2386. (b) Reitz, A. B.; Gauthier, D. A.; Ho, W.; Maryanoff, B. E.
Tetrahedron 2000, 56, 8809–8812. (c) Alajaro˜, M.; Vidal, A; Tovar, F.
Tetrahedron Lett. 2000, 41, 7029–7032.
(14) (a) Janowski, W. K.; Prager, R. H.; Smith, J. A. J. Chem. Soc., Perkin
Trans. 1 2000, 3212–3216. (b) Hubert, A. J. J. Chem. Soc. C 1969, 1334–1336.
(c) Delgado, F.; Linares, M. L.; Alajarin, R.; Vaquero, J. J.; Alvarez-Builla, J.
Org. Lett. 2003, 5, 4057–4060.
(15) (a) Hranjec, M.; Kralj, M.; Piantanida, I.; Sedic, M.; Sy¨uman, L.; Pavelic,
K.; Karminski-Zamola, G. J. Med. Chem. 2007, 50, 5696–5711. (b) Sundberg,
R. J.; Ellis, J. E. J. Hetercocycl. Chem. 1982, 19, 585–588. (c) Latif, F. M.;
Rady, E. A.; Dopp, D. J. Hetercocycl. Chem. 2003, 40, 57–60.
elemental analysis, and their structures were confirmed by
single-crystal X-ray diffraction studies of 2b, 2c, 3b, 4b, 4c,
and 4j. As examples, the structures of 2b, 3b, and 4b are shown
in Figures 2-4.
Formation of pyrido[1,2-a]benzimidazole (2) is also very
interesting. In the structures of 2a-2l there is one pyridine ring,
which is clearly coming from the reaction of pyridine. Py-
rido[1,2-a]benzimidazole motifs constitute various natural prod-
ucts, biologically active compounds, and synthetic intermedi-
712 J. Org. Chem. Vol. 74, No. 2, 2009

One-Step Synthesis of Pyrido[1,2-a]benzimidazole DeriVatiVes
SCHEME 2. Proposed Mechanism for the Formation of
Pyrido[1,2-a]benzimidazole (2) and Polysubstituted Benzenes
SCHEME 3. Proposed Mechanism for the Formation of
Polysubstituted Indoles (4)
(3)
arylidenemalononitrile (B) to afford a cyclopropane derivative
(D). The third step is initiated by deprotonation and leads to
the ring-opening of the activated cyclopropane (D) to form a
allylic carbanionic intermediate (E), which in turn reacts with
a second equivalent of arylidenemalononitrile (B) to form a new
cyano-stabilized carbanionic intermediate (F). Then this cyano-
stabilized carbanion concomitantly intramolecularly adds to one
of the cyano groups to give a six-membered carbon ring system
(G). This intermediate (G) reacts further according to two
different paths to give different products. By elimination of one
hydrocyanide molecule and aromatization the polysubtitute
benzene derivative (3) was formed. On the other hand, the one
cyano group in intermediate (G) can be substituted by excess
pyridine to form a new pyridinium ion (H). In the resonance
hybrid of this intermediate, an amino group attacks intramo-
lecularly the ortho positive center of pyridine intermolecularly
to yield a cyclic fused pyridine derivative (J) from which one
hydrocyanide and two hydrogen atoms were eliminated to form
pyrido[1,2-a]benzimidazole as the final product (2). This kind
of the concerted substitution and annulation reaction pattern of
pyridine have been encountered in several formation reactions
of pyrido[1,2-a]benzimidazole.14-16 In this proposed reaction
mechanism, the unique properties of the two cyano groups in
malononitrile are a crucial factor in the reaction sequence,
especially in the final steps, where the cyano group acts as a
strongly electron-withdrawing substituent, as a leaving group,
and as a polar triple bond for nucleophilic addition. Pyridine
also plays very important factor. It acts as a tertiary amine to
form pyridinium cations, as a base to deprotonation to yield
carbanium intermediate, and as a stronger nucleophilic reagent
and so on. All these combinations result in this novel multi-
component reaction.
We also tentatively suggest one plausible mechanism for the
formation of the minor polysubstituted indole product (Scheme
3). In the formation process of the products 2 and 3 (Scheme
2), the cyano-stabilized carbanionic intermediate (F) reacts with
some additional aromatic aldehyde in solution to form a adduct
intermediate (K). After a proton immigration from carbon atom
to oxygen atom the new formed carbanion (L) intramolecularly
adds to cyano group to form a cyclohexyl imine intermediate
(M), which in turn adds to another cyano group to form a
nitrogen-containing five-member ring species (N). The final
polysubstituted indole (4) was produced by elimination of one
molecule of water and hydrocyanide and aromatization process.
In order to probe the credibility of our proposed mechanistic
scheme and shed more light on the formation of the pyrido[1,2-
influences of base catalyst, solvent, and the ratio of the
components were investigated using the reaction of p-meth-
oxybenzaldehyde as an example. If triethylamine, diethylamine,
piperidine, morpholine, and potassium carbonate were used to
replace pyridine as base, no anticipated products could be
separated, which also indicate that pyridinium salt displays a
crucial factor in the reaction. The reactions proceeds smoothly
and moderate yields of pyrido[1,2-a]benzimidazole 2g are
produced in acetonitrile (34%), ethanol (29%), DMF (25%),
and pyridine (24%). No pyrido[1,2-a]benzimidazoles can be
separated from the reactions in dioxane and toluene.
To explain the mechanism of this one-pot multicomponent
tandem reaction, we propose a plausible reaction course, which
is illustrated in Scheme 2. The first step is the formation of the
two reaction intermediates, namely the N-cyanomethylpyri-
dinium salt (A) formed from the addition of chloroacetonitrile
to pyridine and the arylidenemalononitrile (B) formed by the
Knoevenagel condensation of the respective aromatic aldehyde
with malononitrile. The second step is a Michael addition of a
pyridinium ylide (C) which is formed by deprotonation of the
N-cyanomethylpyridinium species (A) by excess pyridine to the
(16) (a) Rida, S.; Soliman, F.; Badawey, E.; El-Ghazzawi, E.; Kader, O.;
Kappe, T. J. Hetercocycl. Chem. 1988, 25, 1087–1093. (b) Elwan, N. M.
J. Hetercocycl. Chem. 2004, 41, 281–284. (c) Anderson, D. J.; Taylor, A. J.
J. Hetercocycl. Chem. 1986, 23, 1091–1094.
J. Org. Chem. Vol. 74, No. 2, 2009 713

Yan et al.
FIGURE 5. Molecular structure of intermediate J1 in the crystal.
FIGURE 6. Molecular structure of intermediate 5b in the crystal.
TABLE 3. Results of the One-Pot, Four-Component Reaction with
3-Picoline
two minor products, polysubstituted benzene (6a) and polysub-
stituted indole (7a), are also separated in 6.6% and 8.6% yields
respectively. In the reaction of other aldehydes the yields of
these two minor products are too lower to separate. The
structures of all pyrido[1,2-a]benzimidazoles (5a-i), polysub-
stituted benzene (6a) and polysusbtituted indoles (7a) were
fully characterized by 1H and 13C NMR, MS, and IR spectra,
and their structures were confirmed by single-crystal X-ray
diffraction studies performed for 5a, 5b, 5c, 5g, and 5i. As an
example, the structure of 5b is shown in Figure 6. It is worthy to
mention that the ortho-position of methyl group rather than the
relatively less crowded para-position in 3-picoline was attacked
by imine anion to form a imidazole ring. The reactivities of
2-picoline and 4-picoline were also tested and they give much
complicated results and no any pyrido[1,2-a]benzimidazole deriva-
tives can be separated, which might due to stronger acidity of
methyl group at the 2- and 4-positions of pyridine.
In conclusion, we have developed a new one-pot, four-
component reaction involving pyridine or 3-picoline, chloro-
acetonitrile, malononitrile, and aromatic aldehyde in acetonitrile
for the efficient synthesis of pyrido[1,2-a]benzimidazole deriva-
tives in moderate yields. Even though the yield of product is a
little lower, the short reaction time and easiness of handling
should render this new multicomponent reaction applicable to
the synthesis of pyrido[1,2-a]benzimidazole derivatives. The
mechanism of this tandem reaction was investigated and some
crucial reaction paths as well as some reaction intermediates
have been observed. We are currently investigating the expan-
sion of the scope of the reaction by other R-halogen-substituted
carbonyl compounds and its application to the synthesis of other
heterocyclic compounds.
entry
compd
Ar
yield (%)
1
2
3
4
5
6
7
8
9
5a
5b
5c
5d
5e
5f
5g
5h
5i
Ph
27
48
29
25
29
33
35
30
45
p-CH3C6H4
p-ClC6H4
p-BrC6H4
p-FC6H4
p-CH3OC6H4
p-C2H5C6H4
m-CH3C6H4
p-i-PrC6H4
a]benzimidazole, further experiments were carried out. First,
in the reaction of p-methylbezaldehyde and p-isopropylbenza-
dehyde the cyclic fused pyridine intermediates (J1: Ar )
p-MeC6H4; J2: p-i-PrC6H4) could be isolated for their lower
solubility, from which one hydrogen cyanide and two hydrogen
atoms to be eliminated to give the final pyrido[1,2-a]benzimi-
dazole derivatives. By prolonged heating in a mixture of
acetonitrile and pyridine nearly quantitative conversion of this
compound to final product proved to be possible. Fortunately,
we have been able to obtain the crystal structures of two
representative reaction intermediates (J1, J2). As an example,
the structure of J1 is shown in Figure 5. The mechanism
proposed in Scheme 2 is strongly supported by the isolation of
key intermediates, which were structurally characterized by
X-ray diffraction.
Experimental Section
1. Typical Procedure of One-Pot Four-Component Reac-
tion Involving Pyridine, Methyl Chloroacetate, Malononitrile,
and Aromatic Aldehyde. A mixture of pyridine (20.0 mmol,
1.58 g), methyl R-chloroacetate (2.0 mmol, 0.217 g), aromatic
aldehyde (4.0 mmol), and malononitrile (4.0 mmol, 0.264 g) in
acetonitrile (20 mL) was refluxed for 12 h. The solvent was removed
by evaporation, and the residue was titrated with ethanol (10 mL)
to give the crude product, which was recrystallized in ethanol to
give light yellow solid 1a-i.
Second, the reactivity of some pyridine derivatives such as
picolines was tested in the reaction. The reactions of 3-picoline
with various aromatic benzadehyde also give the corresponding
methyl-substituted pyrido[1,2-a]benzimidazoles (5a-i) in mod-
erate yields (Table 3). In the reaction of benzaldehyde, the other
714 J. Org. Chem. Vol. 74, No. 2, 2009

One-Step Synthesis of Pyrido[1,2-a]benzimidazole DeriVatiVes
Methyl 5-amino-4,6-dicyano-2,3-diphenylbenzoate (1a): mp
) 7.2 Hz, 2H, p-EtC6H4), 6.96 (d, J ) 7.8 Hz, 4H, p-EtC6H4),
6.80 (d, J ) 7.2 Hz, 2H, p-EtC6H4), 5.34 (s, 2H, NH2), 3.61 (s,
3H, OCH3), 2.59 (q, J ) 7.2 Hz, 2H, CH2), 2.55 (q, J ) 7.2 Hz,
2H, CH2), 1.18 (t, J ) 7.2 Hz, 3H, CH3), 1.15 (t, J ) 7.2 Hz, 3H,
CH3); 13C NMR (150 MHz, CDCl3) δ 165.5, 150.4, 150.0, 144.2,
142.9, 140.7, 132.5, 129.2, 129.1, 128.6, 126.8, 126.6, 114.5, 113.6,
99.2, 93.3, 52.2, 27.8,27.7, 14.5, 14.3; IR (KBr) ν 3474 (s), 3366
(s), 3247 (m), 2967 (m), 2219 (m), 1744 (s), 1639 (s), 1566 (m),
1514 (w), 1449 (s), 1370 (w), 1234 (s), 1121 (w), 1027 (w), 852
(w), 792 (w) cm-1. Anal. Calcd for C26H23N3O2: C, 75.57; H, 5.02;
N, 11.02. Found: C, 75.33; H, 4.85; N, 10.75.
1
210-211 °C; H NMR (600 MHz, CDCl3) δ 7.25 (s, 3H, C6H5),
7.14 (s, 3H, C6H5), 7.06 (s, 2H, C6H5), 6.91 (s, 2H, C6H5), 5.38 (s,
2H, NH2), 3.60 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 164.8,
149.7, 140.2, 134.7, 134.6, 128.7, 128.1, 127.7, 127.0, 126.7, 126.5,
113.7, 113.0, 98.7, 93.2, 51.8; IR (KBr) ν 3424 (s), 3353 (vs), 3254
(s), 2225 (m), 1731 (s), 1655 (s), 1565 (m), 1439 (m), 1366 (w),
1236 (s), 1019 (w), 754 (w), 703 (m) cm-1. Anal. Calcd for
C22H15N3O2: C, 74.78; H, 4.28; N, 11.89. Found: C, 75.67; H, 4.66;
N, 11.68.
Methyl 5-amino-4,6-dicyano-2,3-di(p-chlorophenyl)benzoate
(1b): mp 231-232 °C; 1H NMR (600 MHz, CDCl3) δ 7.25 (s, 2H,
p-ClC6H4), 7.15 (d, J ) 7.8 Hz, 2H, p-ClC6H4), 6.99 (d, J ) 7.8
Hz, 2H, p-ClC6H4), 6.85 (d, J ) 7.8 Hz, 2H, p-ClC6H4), 5.41 (s,
2H, NH2), 3.66 (s, 3H, OCH3); 13C NMR (150 MHz, CDCl3) δ
163.9, 149.3, 147.8, 139.9, 133.8, 132.6, 132.4, 132.3, 129.6, 129.0,
127.2, 126.9, 113.0, 112.3, 98.2, 93.3, 51.7; IR (KBr) ν 3241 (m),
2226 (m), 1749 (s), 1642 (s), 1562 (m), 1494 (m), 1444 (s), 1369
(m), 1221 (vs), 1090 (s), 1018 (m), 850 (m), 790 (m) cm-1. Anal.
Calcd for C22H13Cl2N3O2: C, 62.58; H, 3.10; N, 9.95. Found: C,
62.33; H, 3.51; N, 9.73.
Methyl 5-amino-4,6-dicyano-2,3-di(m-methylphenyl)benzoate
1
(1h): mp 174-175 °C; H NMR (600 MHz, CDCl3) δ 7.1-.95
(m, 4H, m-CH3C6H4), 6.85 (t, J ) 7.8 Hz, 2H, m-CH3C6H4),
6.7-.70 (m, 2H, m-CH3C6H4), 5.37 (s, 2H, NH2), 3.63 (s, 3H,
OCH3), 2.23 (s, 3H, CH3), 2.17 (s, 3H, CH3); 13C NMR (150 MHz,
CDCl3) δ 166.1, 151.1, 150.9, 141.3, 137.8, 137.4, 135.9, 135.7,
130.6, 129.9, 129.5, 128.3, 128.0, 127.7, 127.0, 126.4, 115.1, 114.3,
99.7, 94.1, 53.0, 21.3, 21.2; IR (KBr) ν 3465 (s), 3360 (s), 3240
(m), 2956 (w), 2222 (m), 1738 (s), 1634 (s), 1567 (m), 1444 (s),
1370 (w), 1310 (vw), 1239 (s), 1092 (vw), 1031 (w), 786 (w) cm-1
.
Methyl 5-amino-4,6-dicyano-2,3-di(p-bromophenyl)benzoate
(1c): mp 252-253 °C. 1H NMR (600 MHz, CDCl3) δ 7.42 (d, J )
8.4 Hz, 2H, p-BrC6H4), 7.31 (d, J ) 7.8 Hz, 2H, p-BrC6H4), 6.92
(d, J ) 6.6 Hz, 2H, p-BrC6H4), 6.78 (d, J ) 8.4 Hz, 2H, p-BrC6H4),
5.40 (s, 2H, NH2), 3.66 (s, 3H, OCH3); 13C NMR (150 MHz, CDCl3)
δ 165.5, 150.9, 149.3, 141.5, 134.4, 131.8, 131.4, 130.8, 128.4,
123.8, 122.4, 114.6, 113.9, 99.8, 95.0, 93.3, 29.7; IR (KBr) ν 3467
(m), 3345 (s), 3241(m), 2226 (m), 1749 (s), 1641 (s), 1564 (m),
1492 (m), 1443 (s), 1369 (m), 1220 (vs), 1072 (m), 1012 (m), 848
(m), 789 (m), 529 (w) cm-1. Anal. Calcd for C22H13Br2N3O2: C,
51.69; H, 2.56; N, 8.22. Found: C, 51.55; H, 2.89; N, 8.03.
Methyl 5-amino-4,6-dicyano-2,3-di(p-methylphenyl)benzoate
Anal. Calcd for C24H19N3O2: C, 76.26; H, 5.66; N, 10.26. Found:
C, 75.94; H, 5.81; N, 10.61.
Methyl 5-amino-4,6-dicyano-2,3-di(p-methoxyphenyl)ben-
1
zoate (1i): mp 220-222 °C; H NMR (600 MHz, CDCl3) δ 6.99
(s, 2H, p-OCH3C6H4), 6.8-6.9 (m, 6H, p-OCH3C6H4), 5.35 (s, 2H,
NH2), 3.77 (s, 3H, OCH3), 3.74 (s, 3H, OCH3), 3.65 (s, 3H, OCH3);
13C NMR (150 MHz, CDCl3) δ 166.2, 159.8, 158.9, 150.9, 150.7,
141.6, 131.1, 130.8, 129.6, 128.2, 128.0, 115.3, 114.3, 113.7, 113.5,
100.0, 93.9, 55.2, 55.1, 53.1; IR (KBr) ν 3457 (s), 3342 (s), 3240
(m), 2953 (w), 2841 (w), 2223 (m), 1740 (s), 1642 (s), 1612 (s),
1567 (m), 1516 (s), 1446 (s), 1371 (w), 1296 (m), 1247 (vs), 1179
(s), 1116 (w), 1031 (m), 844 (w) cm-1. Anal. Calcd for C24H19N3O4:
C, 69.72; H, 4.64; N, 10.16. Found: C, 79.45; H, 4.99; N, 9.67.
2. Typical Procedure for a One-Pot, Four-Component Reac-
tion Involving Pyridine, Chloroacetonitrile, Malononitrile, and
Aromatic Aldehyde. A mixture of pyridine (20.0 mmol, 1.58 g),
chloroacetonitrile (2.0 mmol, 0.151 g), aromatic aldehyde (4.0
mmol), and malononitrile (4.0 mmol, 0.264 g) in acetonitrile (20
mL) was refluxed for 24 h. The solvent was removed by evapora-
tion, and the residue was titrated with ethanol (10 mL) to give the
crude product, which was purified by TLC thin-layer chromatog-
raphy with chloroform and light petroleum as elute and then
recrystallized from ethanol to give the pure product for analysis.
1
(1d): mp 190-191 °C; H NMR (600 MHz, CDCl3) δ 7.04 (d, J
) 6.6 Hz, 2H, p-CH3C6H4), 6.94 (d, J ) 6.6 Hz, 4H, p-CH3C6H4),
6.79 (d, J ) 6.6 Hz, 2H, p-CH3C6H4), 5.32 (s, 2H, NH2), 3.63 (s,
3H, OCH3), 2.29 (s, 3H, CH3), 2.25 (s, 3H, CH3); 13C NMR (150
MHz, CDCl3) δ 166.2, 151.1, 150.8, 141.5, 138.8, 137.3, 133.1,
132.8, 129.8, 129.7, 129.2, 128.9, 128.7, 115.2, 114.3, 100.0, 94.0,
53.0, 21.3, 21.2; IR (KBr) ν 3465 (m), 3343 (s), 3239 (m), 2228
(m), 1744 (s), 1642 (s), 1562 (m), 1443 (m), 1369 (m), 1224 (vs),
1026 (m), 846 (m), 762 (m) cm-1. Found: C, 75.33; H, 4.85; N,
10.75. C24H19N3O2: C, 75.57; H, 5.02; N, 11.02.
Methyl 5-amino-4,6-dicyano-2,3-di(m-bromophenyl)benzoate
1
1
(1e): mp 187-188 °C; H NMR (CDCl3) δ 7.44 (d, J ) 8.4 Hz,
2a: Ar ) C6H5; mp >300 °C; H NMR (600 MHz, CDCl3) δ
1H, m-BrC6H4), 7.33 (d, J ) 7.8 Hz, 1H, m-BrC6H4), 7.21 (s, 1H,
m-BrC6H4), 7.16 (t, J ) 7.2 Hz, 1H, m-BrC6H4), 7.11 (s, 1H,
m-BrC6H4), 7.05 (t, J ) 7.2 Hz, 1H, m-BrC6H4), 7.04 (d, J ) 7.2
Hz, 1H, m-BrC6H4), 6.84 (s, 1H, m-BrC6H4), 5.44 (s, 2H, NH2),
3.69 (s, 3H, OCH3); 13C NMR (150 MHz, CDCl3) δ 164.6, 150.3,
148.2, 140.6, 136.6, 131.5, 131.3, 130.4, 129.2, 128.8, 127.9, 127.3,
127.1, 121.6, 113.7, 113.1, 99.0, 94.3, 52.5; IR (KBr) ν 3458 (s),
3355 (vs), 2221 (m), 1742 (m), 1633 (s), 1563 (m), 1443 (m), 1384
(m), 1229 (s), 1023 (w), 848 (m), 772 (m) cm-1. Anal. Calcd for
C23H13Br2N3O2: C, 51.69; H, 2.56; N, 8.22. Found: C, 51,48; H,
2.71; N, 8.38.
7.86 (d, J ) 8.4 Hz, 1H, NC5H4), 7.54 (t, J ) 7.8 Hz, 1H, NC5H4),
7.42 (s, 3H, C6H5), 7.34 (d, J ) 6.6 Hz, 1H, NC5H4), 7.27 (s, 3H,
C6H5), 7.20 (t, J ) 6.6 Hz, 2H, C6H5), 7.16 (t, J ) 6.6 Hz, 2H,
C6H5), 6.64 (t, J ) 6.6 Hz, 1H, NC5H4); 13C NMR (150 MHz,
CDCl3) δ 151.9, 144.5, 137.7, 134.9, 132.3, 132.5, 132.0, 129.9,
128.9, 128.8, 127.9, 127.6, 126.9, 118.2, 115.2, 113.6, 111.7, 105.3;
IR (KBr) ν 3433 (m), 3355 (s), 3254 (m), 2986 (w), 2220 (m),
1726 (m), 1647 (m), 1565 (m), 1453 (m), 1374 (m), 1353 (w),
1304 (m), 1230 (s), 1123 (w), 1074 (m), 1034 (m), 865 (w), 790
(m), 755 (m), 702 (m) cm-1. Anal. Calcd for C25H14N4: C, 81.06;
H,3.81; N, 15.13. Found: C, 79.83, H, 4.25; N, 15.80.
2b: Ar ) p-CH3C6H4; mp >300 °C; 1H NMR (600 MHz, CDCl3)
δ 7.85 (d, J ) 7.2 Hz, 1H, NC5H4), 7.55 (t, J ) 7.2 Hz, 1H, NC5H4),
7.37 (d, J ) 7.2 Hz, 1H, p-CH3C6H4), 7.22 (d, J ) 7.2 Hz, 2H,
NC5H4), 7.0-.03 (m, 6H, p-CH3C6H4), 2.41 (s, 3H, CH3), 2.31 (s,
3H, CH3); 13C NMR (150 MHz, CDCl3) δ 151.8, 144.4, 138.7,
137.9, 137.6, 132.7, 132.1, 131.8, 123.0, 129.8, 129.4, 129.2, 128.7,
128.3, 127.0, 118.1, 115.3, 113.8, 113.6, 111.5, 105.1, 20.9, 20.7;
IR (KBr) ν 3425 (m), 3049 (m), 2228 (s), 1642 (s), 1489 (vs),
1444 (m), 1388 (s), 1358 (s), 1249 (s), 1148 (s), 841 (m), 785 (vs),
763 (m) cm-1. Anal. Calcd for C27H18N4: C, 81.39; H, 4.55; N,
14.06. Found: C, 81.24; H, 4.46; N, 13.87.
Methyl 5-amino-4,6-dicyano-2,3-di(p-fluorophenyl)benzoate
1
(1f): mp 206 °C; H NMR (600 MHz, CDCl3) δ 7.03 (br, 2H,
p-FC6H4), 6.97 (t, J ) 7.8 Hz, 2H, p-FC6H4), 6.88 (br, 4H,
p-FC6H4), 5.44 (s, 2H, NH2), 3.65 (s, 3H, OCH3); 13C NMR (150
MHz, CDCl3) δ 165.8, 163.6, 162.9, 162.0, 151.1, 149.9, 141.6,
131.7, 131.6, 131.3, 131.2, 128.6, 115.7, 115.6, 115.3, 115.2, 114.8,
114.1, 99.9, 94.6, 53.2; IR (KBr) ν 3475 (m), 3349 (s), 3245 (m),
2221 (w), 1742 (s), 1641 (s), 1605 (m), 1567 (m), 1513 (s), 1449
(s), 1227 (vs), 1161 (m), 1119 (w), 1023 (w), 849 (m), 806 (w)
cm-1. Anal. Calcd for C23H13F2N3O2: C, 67.87; H, 3.37; N, 10.79.
Found: C, 67.80; H, 3.63; N, 10.45.
1
Methyl 5-amino-4,6-dicyano-2,3-di(p-ethylphenyl)benzoate
2c: Ar ) p-ClC6H4; mp >300 °; H NMR (600 MHz, DMSO-
1
(1g): mp 192-193 °C; H NMR (600 MHz, CDCl3) δ 7.05 (d, J
d6) δ 7.95 (d, J ) 8.4 Hz, 1H, NC5H4), 7.79 (t, J ) 8.4 Hz, 1H,
J. Org. Chem. Vol. 74, No. 2, 2009 715

Yan et al.
NC5H4), 7.55 (d, J ) 8.4 Hz, 2H, NC5H4), 7.4-7.39 (m, 5H,
p-ClC6H4), 7.31 (d, J ) 8.4 Hz, 2H, p-ClC6H4), 7.01 (t, J ) 7.2
Hz, 1H, p-ClC6H4); IR (KBr) ν 3425 (w), 3123 (w), 2229 (m),
1640 (m), 1489 (s), 1444 (m), 1387 (m), 1359 (m), 1329 (m), 1313
(m), 1248 (m), 1199 (w), 1153 (w), 1091 (m), 1015 (m), 883 (w),
824 (m), 764 (m) cm-1. Anal. Calcd for C25H12Cl2N4: C, 68.35; H,
2.76; N, 12.75. Found: C, 68.31, H, 3.10; N, 12.57.
6H, CH3), 1.18 (d, J ) 7.2 Hz, 6H, CH3); 13C NMR (150 MHz,
CDCl3) δ 152.3, 150.2, 148.8, 144.8, 138.6, 133.5, 132.8, 132.6,
130.7, 130.4, 129.6, 129.4, 127.7, 127.1, 125.9, 118.4, 115.9, 114.3,
113.8, 112.1, 105.2, 33.9, 33.1, 23.9, 23.8; IR (KBr) ν 3426 (w),
2960 (s), 2228 (s), 1642 (s), 1487 (vs), 1388 (s), 1360 (m),1310
(s), 1245 (s), 1202 (w), 1129 (m), 1053 (m), 854 (m), 761 (s), 740
(m), 647 (w), 616 (w), 503 (w) cm-1. Anal. Calcd for C31H26N4:
C, 81.91; H, 5.77; N, 12.33. Found: C, 82.02; H, 5.83; N, 12.10.
2k: Ar ) p-t-BuC6H4; mp >300 °C; 1H NMR (600 MHz, CDCl3)
δ 7.84 (d, J ) 8.4 Hz, 1H, NC5H4), 7.53 (d, J ) 7.2 Hz, 2H,
NC5H4), 7.36 (d, J ) 8.4 Hz, 2H, p-t-BuC6H4), 7.18 (d, J ) 8.4
Hz, 2H, p-t-BuC6H4), 7.03 (d, J ) 8.4 Hz, 2H, p-t-BuC6H4), 6.99
(d, J ) 8.4 Hz, 2H, p-t-BuC6H4), 6.64 (t, J ) 7.2 Hz, 1H, NC5H4),
1.28 (s, 9H, CH3), 1.22 (s, 9H, CH3); 13C NMR (150 MHz, CDCl3)
δ 152.9, 132.8, 130.2, 127.7, 125.9, 124.8, 118.5, 117.1, 116.0,
111.9, 114.1, 34.7, 31.2. Anal. Calcd for C33H30N4: C, 82.13; H,
6.27; N, 11.60. Found: C, 82.37, H, 6.48; N, 11.54.
2d: Ar ) m-ClC6H4; mp >300 °C; 1H NMR (600 MHz, DMSO-
d6) δ 7.97 (b, 1H, NC5H4), 7.80 (b, 1H, NC5H4), 7.45-7.35 (m,
8H, m-ClC6H4), 7.01 (b, 2H, NC5H4). Anal. Calcd for C25H12Cl2N4:
C, 68.35; H, 2.76; N, 12.75. Found: C, 68.08, H, 2.81; N, 12.64.
2e: Ar ) p-BrC6H4; mp >300 °C; 1H NMR (600 MHz, DMSO-
d6) δ 7.94 (d, J ) 9.6 Hz, 1H, NC5H4), 7.78 (t, J ) 8.4 Hz, 1H,
p-BrC6H4), 7.68 (d, J ) 8.4 Hz, 2H, p-BrC6H4), 7.54 (d, J ) 8.4
Hz, 2H, p-BrC6H4), 7.38 (d, J ) 7.2 Hz, 1H, p-BrC6H4), 7.33 (d,
J ) 8.4 Hz, 2H, p-BrC6H4), 7.23 (d, J ) 7.2 Hz, 2H, p-BrC6H4),
7.01 (t, J ) 6.6 Hz, 1H, p-BrC6H4); IR (KBr) ν 3425 (w), 2226
(m), 1641 (m), 1488 (s), 1443 (m), 1384 (m), 1357 (m), 1329 (m),
1312 (m), 1247 (m), 1074 (m), 1011 (m), 849 (w), 821 (m), 763
(m) cm-1. Anal. Calcd for C25H12Br2N4: C, 56.85; H, 2.29; N, 10.61.
Found: C, 56.98, H, 2.47; N, 10.49.
1
2l: Ar ) p-FC6H4; mp >300 °C; H NMR (600 MHz, CDCl3)
δ 7.86 (d, J ) 8.4 Hz, 1H, NC5H4), 7.57 (t, J ) 7.2 Hz, 1H, NC5H4),
7.40 (d, J ) 6.6 Hz, 1H, NC5H4), 7.21-7.12 (m, 6H, p-FC6H4),
6.99 (t, J ) 8.4 Hz, 2H, p-FC6H4), 6.71 (t, J ) 6.6 Hz, 1H, NC5H4);
13C NMR (150 MHz, CDCl3) δ 163.3, 161.6, 161.3, 152.0, 144.6,
136.8, 132.3, 131.7, 131.5, 130.9, 130.8, 129.1, 128.8, 128.7, 126.7,
118.4, 116.4, 116.2, 115.1, 114.9, 113.6, 113.4, 112.1, 105.5; IR
(KBr) ν 3484 (m), 3034 (m), 2226 (w), 2197 (m), 1643 (m), 1600
(s), 1514 (s), 1486 (vs), 1388 (m), 1358 (w), 1314 (m), 1238 (s),
1223 (s), 1160 (s), 1097 (m), 1066 (w), 850 (w), 838 (m), 775
(m). Anal. Calcd for C25H12N4F2: C, 73.88; H, 2.98; N, 13.79.
Found: C, 73.76, H, 3.12; N, 13.76.
2f: Ar ) m-BrC6H4; mp >300 °C; 1H NMR (600 MHz, DMSO-
d6) δ 7.97 (d, J ) 9.6 Hz, 1H, m-BrC6H4), 7.83 (t, J ) 8.4 Hz, 1H,
m-BrC6H4), 7.6-.28 (m, 9H, m-BrC6H4), 7.02 (t, J ) 6.6 Hz, 1H,
m-BrC6H4); IR (KBr) ν 3424 (m), 2229 (m), 1641 (m), 1560 (m),
1485 (s), 1387 (m), 1355 (w), 1328 (m), 1312 (m), 1245 (m), 1128
(m), 1065 (m), 900 (w), 841 (m), 783 (s), 758 (m), 740 (m) cm-1
.
Anal. Calcd for C25H12Br2N4: C, 56.85; H, 2.29; N, 10.61. Found:
C, 56.62, H, 2.38; N, 10.27.
1
1
2g: Ar ) p-CH3OC6H4; mp >300 °C; H NMR (600 MHz,
3b: Ar ) p-CH3C6H4; mp 136-137 °C; H NMR (600 MHz,
CDCl3) δ 7.85 (d, J ) 8.4 Hz, 1H, NC5H4), 7.55 (t, J ) 6.6 Hz,
1H, NC5H4), 7.46 (d, J ) 7.2 Hz, 1H, p-CH3OC6H4), 7.08 (q, J )
8.4 Hz, 2H, p-CH3OC6H4), 6.94 (d, J ) 8.4 Hz, 2H, NC5H4), 6.80
(d, J ) 8.4 Hz, 2H, p-CH3OC6H4), 6.66 (t, J ) 7.2 Hz, 1H,
p-CH3OC6H4), 3.86 (s, 3H, OCH3), 3.79(s, 3H, OCH3); 13C NMR
(150 MHz, CDCl3) δ 159.4, 158.8, 151.8, 144.4, 132.6, 131.9,
131.2, 130.2, 129.4, 127.3, 127.0, 118.1, 115.4, 114.2, 113.1, 111.6,
105.0. Anal. Calcd for C27H18N4O2: C, 75.34; H, 4.21; N, 13.02.
Found: C, 75.53; H, 4.67; N,12.75.
CDCl3) δ 7.08 (d, J ) 7.8 Hz, 2H, p-CH3C6H4), 7.04 (d, J ) 7.8
Hz, 2H, p-CH3C6H4), 6.95 (d, J ) 7.8 Hz, 2H, p-CH3C6H4), 6.89
(d, J ) 7.8 Hz, 2H, p-CH3C6H4), 5.50 (s, 2H, NH2), 2.31 (s, 3H,
CH3), 2.29 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 151.4,
150.9, 139.5, 138.6, 135.9, 132.2, 131.5, 129.9, 129.2, 129.1, 112.0,
114.9, 114.6, 113.6, 102.7, 98.3, 21.4, 21.3; IR (KBr) ν 3415 (m),
3347 (vs), 3248 (s), 2923 (w), 2222 (m), 1655 (vs), 1562 (vs), 1560
(w), 1451 (vs), 1268 (vs), 1188 (w), 1120 (w), 1023 (w), 847 (w),
820 (w), 765 (m) cm-1. Anal. Calcd for C23H16N4: C, 79.29; H,
4.63; N, 16.08. Found: C, 78.85; H, 4.48; N, 15.80.
2h: Ar ) m-CH3C6H4; mp >300 °C; 1H NMR (600 MHz,
CDCl3) δ 7.85 (d, J ) 8.4 Hz, 1H, NC5H4), 7.53 (d, J ) 7.8 Hz,
1H, NC5H4), 7.35 (d, J ) 7.2 Hz, 1H, NC5H4), 7.29 (d, J ) 7.8
Hz, 1H, m-CH3C6H4), 7.22 (d, J ) 7.2 Hz, 1H, m-CH3C6H4), 7.14
(t, J ) 7.2 Hz, 1H, m-CH3C6H4), 7.06 (d, J ) 7.8 Hz, 1H,
m-CH3C6H4), 6.9-.96 (m, 4H, m-CH3C6H4), 6.63 (t, J ) 7.2 Hz,
1H, NC5H4), 2.31 (s, 3H, CH3), 2.26 (s, 3H, CH3); IR (KBr) ν
3433 (s), 2921 (w), 2227 (w), 1641 (m), 1488 (vs), 1387 (m), 1323
(m), 1246 (m), 1134 (w), 834 (w), 749 (m), 701 (w) cm-1. Anal.
Calcd for C27H18N4: C, 81.39; H, 4.55; N, 14.06. Found: C, 81.56;
H, 4.71; N, 13.65.
3g: Ar ) p-CH3OC6H4; mp 125-126 °C; 1H NMR (600 MHz,
CDCl3) δ 7.00 (d, J ) 8.4 Hz, 2H, p-CH3OC6H4), 6.93 (d, J ) 8.4
Hz, 2H, p-CH3OC6H4), 6.8-.77 (m, 4H, p-CH3OC6H4), 5.46 (s,
2H, NH2), 3.79 (s, 3H, OCH3), 3.78 (s, 3H, OCH3); IR (KBr) ν
3442 (s), 2922 (w), 2221 (w), 1638 (m), 1609 (s), 1567 (w), 1516
(m), 1453 (m), 1293 (m), 1253 (vs), 1180 (s), 1129 (m), 841 (w).
Anal. Calcd for C23H16N4O2: C, 72.62; H, 4.24; N, 14.73. Found:
C, 72.49, H, 4.57; N, 14.47.
3l: Ar ) p-FC6H4; mp 222-224 °C; 1H NMR (600 MHz, CDCl3)
δ 7.04-6.97 (m, 8H, p-FC6H4), 5.57 (s, 2H, NH2); 13C NMR (150
MHz, CDCl3) δ 163.4, 163.1, 161.8, 161.4, 150.4, 149.6, 134.1,
131.5, 131.4, 130.8, 130.7, 130.4, 129.7, 119.7, 115.6, 115.5, 115.4,
115.3, 113.9, 113.6, 112.7, 102.2, 98.4; IR (KBr) ν 3392 (vs), 3348
(vs), 3248 (vs), 2226 (m), 1661 (s), 1604 (m), 1568 (m), 1513 (s),
1454 (s), 1267 (s), 1229 (vs), 1160 (m), 1199 (w), 834 (m), 799
(w). Anal. Calcd for C21H10N4F2: C, 70.78; H, 2.83; N, 15.72.
Found: C, 70.98, H, 2.95; N, 15.61.
2i: Ar ) p-C2H5C6H4; mp >300 °C; 1H NMR (600 MHz, CDCl3)
δ 7.81 (d, J ) 8.4 Hz, 1H, NC5H4), 7.53 (d, J ) 7.8 Hz, 1H,
NC5H4), 7.39 (d, J ) 7.2 Hz, 1H, NC5H4), 7.23 (d, J ) 7.8 Hz,
2H, p- C2H5C6H4), 7.1-.04 (m, 6H, p-C2H5C6H4), 6.64 (t, J ) 7.2
Hz, 1H, NC5H4), 2.70 (q, J ) 7.8 Hz, 2H, CH2), 2.60 (q, J ) 7.8
Hz, 2H, CH2), 1.26 (t, J ) 7.8 Hz, 3H, CH3), 1.18 (t, J ) 7.8 Hz,
3H, CH3); 13C NMR (150 MHz, CDCl3) δ 152.3, 145.5, 144.8,
144.2, 138.4, 133.4, 132.7, 132.6, 130.5, 130.4, 123.0, 129.3, 128.7,
127.7, 127.5, 118.4, 115.9, 114.3, 114.0, 11.2, 105.2, 28.6, 28.5,
15.3, 15.1; IR (KBr) ν 2970 (m), 2225 (s), 1642 (s), 1486 (vs),
1394 (s), 1332 (vs), 1249 (s), 1146 (m), 1069 (m), 831 (m), 762
(s) cm-1. Anal. Calcd for C29H22N4: C, 81.66; H, 5.20; N, 13.14.
Found: C, 81.53; H, 5.08; N, 12.77.
1
4b: Ar ) p-CH3C6H4; mp 269-270 °C; H NMR (600 MHz,
CDCl3) δ 10.62 (s, 1H, NH), 7.48 (d, J ) 7.8 Hz, 2H, p-CH3C6H4),
7.40 (d, J ) 7.8 Hz, 2H, p-CH3C6H4), 7.03-6.97 (m, 8H,
p-CH3C6H4), 6.70 (s, 2H, NH2), 2.42 (s, 3H, CH3), 2.23 (s, 3H,
CH3), 2.23 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 107.8,
138.7, 138.2, 136.4, 136.1, 136.1, 134.3, 132.1, 131.0, 130.9, 130.8,
130.0, 127.9, 129.2, 128.5, 128.4, 127.0, 119.4, 115.8, 103.0, 65.1,
56.5, 21.4, 21.3, 21.2, 19.0; IR (KBr) ν 3452 (m), 3334 (s), 3026
(w), 2203 (vs), 1639 (vs), 1556 (vs), 1517 (m), 1485 (w), 1396
(m), 1308 (w), 1183 (w), 1115 (w), 1020 (w), 819 (m), 750 (m)
cm-1. Anal. Calcd for C33H30N4O(C31H24N4 ·C2H5OH): C, 79.49;
H, 6.06; N, 11.24. Found: C, 79.36; H, 5.72; N, 11.40.
2j: Ar ) p-i-PrC6H4; mp >300 °C; 1H NMR (CDCl3, 600 MHz)
δ 7.82 (d, J ) 8.4 Hz, 1H, NC5H4), 7.54 (d, J ) 7.2 Hz, 1H,
NC5H4), 7.48 (d, J ) 7.2 Hz, 1H, NC5H4), 7.24 (d, J ) 7.8 Hz,
2H, p-i-PrC6H4), 7.08 (d, J ) 8.4 Hz, 4H, p-i-PrC6H4), 7.03 (d, J
) 7.8 Hz, 2H, p-i-PrC6H4), 6.64 (t, J ) 7.2 Hz, 1H, NC5H4),
2.9-2.92 (m, 1H, CH), 2.8-.82 (m, 1H, CH), 1.25 (d, J ) 6.6 Hz,
716 J. Org. Chem. Vol. 74, No. 2, 2009

One-Step Synthesis of Pyrido[1,2-a]benzimidazole DeriVatiVes
1
4c: Ar ) p-ClC6H4; mp 246-247 °C; H NMR (600 MHz,
p-BrC6H4), 6.62 (t, J ) 6.6 Hz, 1H, NC5H3), 2.75 (s, 3H, CH3);
13C NMR (150 MHz, CDCl3) δ 152.8, 144.5, 135.9, 132.2, 131.7,
131.5, 131.1, 130.5, 130.1, 124.1, 123.4, 122.7, 114.9, 113.5, 112.0,
16.9; MS(APCI+) m/z ) 543.60.
DMSO-d6) δ 10.77 (s, 1H, NH), 7.54-6.71 (m, 12H, p-ClC6H4),
4.20 (s, 2H, NH2); 13C NMR (150 MHz, DMSO-d6) δ 158.1, 137.4,
136.9, 135.6, 134.3, 133.6, 132.9, 132.7, 132.7, 132.5, 132.0, 131.1,
129.5, 128.7, 128.1, 128.0, 126.0, 119.0, 115.7, 102.6, 79.6, 65.0,
56.5, 19.0; IR (KBr) ν 3312 (s), 3187 (s), 2969 (m), 2208 (vs),
1643 (vs), 1554 (vs), 1498 (vs), 1448 (m), 1393 (s), 1315 (m),
1176 (w), 1090 (vs), 1044 (m), 1015 (s), 878 (w), 854 (s), 764 (s),
723 (w) cm-1. Anal. Calcd for C30H21N4OCl3(C28H15N4Cl3 ·
C2H5OH): C, 64.36; H, 3.78; N, 10.01. Found: C, 64.14; H, 3.29;
N, 9.87.
5e: Ar ) p-FC6H4; mp >300 °C; IR (KBr): 3446 (m), 2228
(m), 1637 (m), 1605 (m), 1514 (vs), 1482 (vs), 1388 (s), 1361 (w),
1309 (s), 1237 (s), 1161 (s), 1073 (w), 1018 (w), 844 (m), 805
1
(w), 752 (m) cm-1; H NMR (600 MHz, CDCl3) δ 7.35 (d, J )
6.6 Hz, 1H, NC5H3), 7.24 (s, 1H, NC5H3), 7.17-7.11(m, 6H,
p-FC6H4), 6.98 (t, J ) 8.4 Hz, 2H, p-FC6H4), 6.60 (t, J ) 6.6 Hz,
1H, NC5H3), 2.75 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ
163.2, 161.6, 152.7, 144.5, 136.5, 131.8, 131.7, 130.9, 130.8, 130.0,
128.8, 124.1, 116.2, 116.1, 115.0, 114.9, 113.5, 111.9, 105.8, 16.9;
MS (APCI+) m/z ) 422.13.
4j: Ar ) p-i-PrC6H4; mp >300 °C; 1H NMR (600 MHz, DMSO-
d6) δ 10.51 (s, 1H, NH), 7.54 (d, J ) 8.4 Hz, 2H, p-i-PrC6H4),
7.48 (d, J ) 7.8 Hz, 2H, p-i-PrC6H4), 7.01 (d, J ) 8.4 Hz, 6H,
p-i-PrC6H4), 6.95 (d, J ) 7.8 Hz, 2H, p-i-PrC6H4), 6.65 (s, 2H,
NH2), 2.99-3.06 (m, 1H, CH), 2.77-2.83 (m, 2H, CH), 1.30 (d,
J ) 7.2 Hz, 6H, CH3), 1.12 (d, J ) 6.6 Hz, 12H, CH3); IR (KBr)
ν 3422 (s), 3307 (s), 3187 (s), 2962 (s), 2212 (vs), 1644 (s), 1555
5f: Ar ) p-CH3OC6H4; mp 282-283 °C; IR (KBr) 3426 (w),
2933 (w), 2837 (w), 2225 (m), 1609 (s), 1516 (s), 1481 (m), 1456
(m), 1387 (m), 1291 (m), 1251 (vs), 1179 (s), 1112 (w), 1073 (w),
1
1028 (m), 840 (m), 792 (w), 752 (w) cm-1; H NMR (600 MHz,
(s), 1460 (m), 1399 (m), 1040 (s), 877 (w), 834 (m), 555 (w) cm-1
.
CDCl3) δ 7.32 (d, J ) 6.0 Hz, 2H, NC5H3), 7.06 (d, J ) 6.6 Hz,
4H, p-CH3OC6H4), 6.92 (d, J ) 7.8 Hz, 2H, p-CH3OC6H4), 6.79
(d, J ) 7.8 Hz, 2H, p-CH3OC6H4), 6.56 (t, J ) 6.6 Hz, 1H, NC5H3),
3.86 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 2.74 (s, 3H, CH3); 13C
NMR (150 MHz, CDCl3) δ 159.4, 158.8, 152.5, 144.2, 137.7, 132.6,
131.2, 130.2, 129.9, 128.3, 127.5, 125.0, 124.6, 115.6, 114.1, 113.1,
111.5, 54.8, 54.7, 17.0; MS (APCI-) m/z ) 444.80.
5g: Ar ) p-C2H5C6H4; mp >300 °C; IR (KBr) 3424 (w), 3125
(w), 2967 (m), 2928 (m), 2225 (m), 1634 (m), 1573 (w), 1516 (w),
1481 (vs), 1387 (s), 1313 (s), 1248 (m), 1201 (w), 1161 (w), 1113
(w), 1071 (m), 832 (m), 754 (m) cm-1; 1H NMR (600 MHz, CDCl3)
δ 7.31 (d, J ) 6.6 Hz, 1H, NC5H4), 7.24 (d, J ) 7.2 Hz, 1H,
NC5H4), 7.21 (d, J ) 7.2 Hz, 2H, p-C2H5C6H4), 7.05 (q, J ) 7.2
Hz, 6H, p-C2H5C6H4), 6.54 (t, J ) 7.2 Hz, 1H, NC5H4), 2.73 (s,
3H, CH3), 2.69 (q, J ) 7.2 Hz, 2H, CH2), 2.60 (q, J ) 7.2 Hz, 2H,
CH2), 1.25 (t, J ) 7.8 Hz, 3H, CH3), 1.19 (t, J ) 7.8 Hz, 3H,
CH3); 13C NMR (150 MHz, CDCl3) δ 152.5, 149.5, 148.2, 144.3,
138.0, 132.8, 132.4, 130.4, 129.9,129.8, 129.7, 129.0, 128.3, 128.1,
126.9, 126.5, 125.4, 124.6, 115.5, 114.1, 113.2, 111.4, 105.0, 33.4,
33.2, 23.3, 23.2, 17.0; MS (APCI+) m/z ) 442.33.
Anal. Calcd for C37H36N4: C, 82.80; H, 6.76; N, 10.44. Found: C,
82.45; H, 6.92; N, 9.75.
3. Typical Procedure for a One-Pot, Four-Component Reac-
tion Involving 3-Picoline, Chloroacetonitrile, Malononitrile,
and Aromatic Aldehyde. A mixture of 3-picoline (20.0 mmol,
1.66 g), chloroacetonitrile (2.0 mmol, 0.151 g), aromatic aldehyde
(4.0 mmol), and malononitrile (4.0 mmol, 0.264 g) in acetonitrile
(20 mL) was refluxed for 24 h. The solvent was removed by
evaporation, and the residue was titrated with ethanol (10 mL) to
give the crude product, which was purified by TLC with chloroform
and light petroleum as elute and then recrystallized from ethanol
to give the pure product for analysis.
5a: Ar ) C6H5; mp >300 °C; IR (KBr) 3432 (m), 3058 (w),
2225 (m), 1636 (m), 1575 (w), 1482 (vs), 1391 (s), 1312 (s), 1275
(w), 1250 (m), 1202 (w), 1160 (w), 1113 (vw), 1074 (m), 750 (s),
699 (s) cm-1; 1H NMR (600 MHz, CDCl3) δ 7.40 (d, J ) 6.6 Hz,
3H, NC5H3, C6H5), 7.32 (d, J ) 6.6 Hz, 1H, NC5H3), 7.25 (br, 3H,
C6H5), 7.20-7.15 (m, 5H, C6H5), 6.54 (t, J ) 6.6 Hz, 1H, NC5H3),
2.75 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 152.6, 144.3,
137.5, 135.1, 133.0, 132.4, 130.0, 129.0, 128.7, 128.5, 127.8, 127.6,
124.5, 115.3, 113.9, 113.4, 111.6, 105.4, 17.1; MS (APCI+): m/z
) 386.13.
5h: Ar ) m-CH3C6H4; mp 276-277 °C; IR (KBr) 3435 (s), 3126
(w), 3041 (w), 2921 (w), 2225 (m), 1636 (m), 1482 (vs), 1389 (s),
1328 (s), 1276 (w), 1251 (m), 1164 (w), 1075 (w), 774 (m), 751
5b: Ar ) p-CH3C6H4; mp >300 °C; IR (KBr) 3446 (w), 3123
(w), 2920 (w), 2225 (m), 1635 (m), 1571 (w), 1517 (w), 1482 (vs),
1388 (s), 1358 (w), 1326 (s), 1248 (m), 1192 (w), 1162 (w), 1111
(w), 1071 (m), 815 (s), 757 (w) cm-1; 1H NMR (600 MHz, CDCl3)
δ 7.31 (d, J ) 6.6 Hz, 1H, NC5H4), 7.22 (s, 1H, NC5H4), 7.20 (d,
J ) 7.8 Hz, 2H, p-CH3C6H4), 7.06-7.02 (m, 6H, p-CH3C6H4), 6.54
(t, J ) 7.2 Hz, 1H, NC5H4), 2.74 (s, 3H, CH3), 2.40 (s, 3H, CH3),
2.30 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 152.5, 144.8,
144.3, 143.6, 137.8, 132.8, 132.3, 130.2, 129.9, 129.8, 128.9, 128.3,
128.0, 126.9, 124.6, 115.5, 114.0, 113.4, 111.4, 28.1, 28.0, 17.0,
14.7, 14.6; MS (APCI+) m/z ) 414.27.
1
(s), 695 (w) cm-1; H NMR (600 MHz, CDCl3) δ 7.32 (s, 1H,
NC5H3), 7.20 (br, 2H, NC5H3, m-CH3C6H4), 7.13-6.97(m, 7H,
m-CH3C6H4), 6.55 (br, 1H, NC5H3), 2.74 (s, 3H, CH3), 2.31 (s,
3H, CH3), 2.26 (s, 3H, CH3); 13C NMR (150 MHz, CDCl3) δ 152.5,
144.2, 138.5, 137.7, 137.0, 135.0, 132.9, 132.7, 130.7, 130.0, 129.6,
129.4, 129.3, 128.5, 128.3, 127.3, 127.1, 125.9, 124.6, 115.4, 114.0,
113.2, 111.6, 104.9, 20.9, 20.8, 17.0; MS (APCI-) m/z ) 413.40.
5i: Ar ) p-i-PrC6H4; mp >300 °C; IR (KBr) 3425 (m), 3122
(w), 2960 (s), 2925 (m), 2225 (m), 1635 (m), 1481 (vs), 1388 (vs),
1309 (s), 1272 (w), 1249 (m), 1201 (w), 1161 (w), 1111 (w), 1053
1
(m), 788 (w), 755 (m) cm-1; H NMR (600 MHz, CDCl3) δ 7.32
5c: Ar ) p-ClC6H4; mp >300 °C; IR (KBr) 3449 (w), 2226
(m), 1637 (m), 1486 (vs), 1385 (s), 1308 (s), 1249 (m), 1161 (w),
(t, J ) 7.8 Hz, 2H, NC5H4), 7.21 (d, J ) 7.8 Hz, 2H, p-i-PrC6H4),
7.06 (d, J ) 7.8 Hz, 2H, p-i-PrC6H4), 7.03 (t, J ) 8.4 Hz, 4H,
p-i-PrC6H4), 6.54 (t, J ) 7.2 Hz, 1H, NC5H4), 2.95-2.90 (m, 1H,
CH), 2.85-2.81 (m, 1H, CH), 2.74 (s, 3H, CH3), 1.24 (d, J ) 6.6
Hz, 6H, CH3), 1.18 (d, J ) 6.6 Hz, 6H, CH3); 13C NMR (150 MHz,
CDCl3) δ 152.5, 144.2, 138.5, 137.8, 137.5, 132.6, 132.2, 130.0,
129.8, 129.4, 128.8, 128.3, 124.6, 115.5, 114.0, 113.5, 111.4, 105.1,
20.9, 20.8, 17.0; MS (APCI+) m/z ) 470.33.
1091 (s), 1017 (m), 825 (m), 778 (m), 752 (m) cm-1; H NMR
1
(600 MHz, CDCl3) δ 7.42 (d, J ) 8.4 Hz, 2H, NC5H3, p-ClC6H4),
7.36 (d, J ) 6.6 Hz, 1H, NC5H3), 7.28 (d, J ) 8.4 Hz, 3H,
p-ClC6H4), 7.12 (d, J ) 7.8 Hz, 2H, p-ClC6H4), 7.08 (d, J ) 8.4
Hz, 2H, p-ClC6H4), 6.03 (t, J ) 6.6 Hz, 1H, NC5H3), 2.76 (s, 3H,
CH3); 13C NMR (150 MHz, CDCl3) δ 152.8, 144.5, 136.0, 135.2,
134.4, 133.3, 131.2, 130.9, 130.3, 130.1, 129.2, 128.8, 128.2, 124.1,
114.9, 113.5, 113.3, 112.0, 106.1, 16.9; MS (APCI+) m/z ) 454.27.
5d: Ar ) p-BrC6H4; mp >300 °C; IR (KBr) 3423 (w), 3133
(w), 2226 (m), 1633 (m), 1575 (w), 1484 (vs), 1385 (s), 1310 (s),
1247 (m), 1199 (w), 1161 (w), 1109 (w), 1070 (s), 1009 (s), 822
6a: mp 237 °C; IR (KBr) 3444 (m), 3336 (vs), 3238 (s), 2222
(m), 1651 (vs), 1555 (s), 1445 (s), 1268 (vs), 1075 (w), 1030 (w),
1
921 (vw), 779 (vw), 722 (s), 694 (s) cm-1; H NMR (600 MHz,
CDCl3) δ 7.31 (d, J ) 7.2 Hz, 1H, C6H5), 7.28-7.24 (m, 5H, C6H5),
7.06 (d, J ) 7.8 Hz, 2H, C6H5), 7.01 (d, J ) 7.2 Hz, 2H, C6H5),
5.54 (s, 2H, NH2); 13C NMR (150 MHz, CDCl3) δ 150.7, 150.4,
135.3, 134.6, 133.9, 129.6, 128.9, 128.7, 128.3, 127.9, 119.5, 114.1,
113.8, 113.0, 102.1, 98.1; MS(APCI-): m/z )320.13.
(m), 777 (m), 753 (m) cm-1; H NMR (600 MHz, CDCl3) δ 7.58
(d, J ) 7.8 Hz, 2H, p-BrC6H4), 7.43 (d, J ) 7.2 Hz, 2H, p-BrC6H4),
7.35 (d, J ) 7.2 Hz, 1H, NC5H3), 7.24 (d, J ) 7.8 Hz, 1H, NC5H3),
7.05 (d, J ) 7.8 Hz, 2H, p-BrC6H4), 7.01 (d, J ) 7.8 Hz, 2H,
1
J. Org. Chem. Vol. 74, No. 2, 2009 717

Yan et al.
7a: mp >300 °C; IR (KBr) 3444 (s), 3355 (s), 3230 (s), 2204
(vs), 1638 (vs), 1559 (vs), 1497 (w), 1443 (w), 1404 (m), 1355
(w), 1315 (w), 1123 (w), 1074 (w), 1030 (w), 724 (w), 699 (m)
Supporting Information Available: Single-crystal X-ray
diffraction data have been deposited with the CCDC (deposition
nos.: 1a, 691943; 2b, CCDC 691938; 3b, CCDC 691936; 4b,
CCDC 691937; 2c, CCDC 691941; 4c, CCDC 691940; 2j,
691934; J1, 691939; J2, CCDC 691935; 5a, CCDC 703765;
5b, CCDC703766; 5c, CCDC 703767; 5g, CCDC 703769 and
5i, CCDC 703770). Experimental procedures and spectral data
for all new compounds, including crystallographic data (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
cm-1 1H NMR (600 MHz, DMSO-d6) δ 10.69 (s, 1H, NH),
;
7.63-7.60 (m, 4H, C6H5), 7.57-7.54 (m, 1H, C6H5), 7.20-7.16
(m, 8H, C6H5), 7.11-7.09 (m, 2H, C6H5), 6.75 (s, 2H, NH2); 13C
NMR (150 MHz, DMSO-d6) δ 157.5, 138.3, 137.7, 136.5, 134.5,
130.5, 130.4, 129.6, 129.0, 127.4, 127.3, 118.8, 115.2, 102.2;
MS(APCI-): m/z ) 410.40.
Acknowledgment. This work was financially supported by
the National Natural Science Foundation of China (Grant No.
20672091) and the Jiangsu Provincial Key Program of Physical
Chemistry in Yangzhou University, China.
JO802166T
718 J. Org. Chem. Vol. 74, No. 2, 2009