Efficient and highly selective method for the synthesis of benzo(naphtho)quinoline derivatives catalyzed by iodine

Article abstract of DOI:10.1021/cc900165j

A mild, efficient, and highly selective method for the synthesis of pyranoquinoline and furoquinoline derivatives via a three-component reaction of aromatic aldehyde, naphthalen-2-amine or anthracen-2-amine and 2,3-dihydrofuran, or 3,4-dihydro-2H-pyran catalyzed by iodine is described. It should be noted that exo-isomer was obtained with high selectivity in good yields, which was confirmed by X-ray diffraction analysis. The 3-arylbenzo(naphtha)[f]quinolines were isolated in high yields when the chain n-butylvinyl ether was used as reactant, with the unexpected loss of the butoxy group.

Full text of DOI:10.1021/cc900165j

266
J. Comb. Chem. 2010, 12, 266–269
Efficient and Highly Selective Method for the Synthesis of
Benzo(naphtho)quinoline Derivatives Catalyzed by Iodine
Xiang-Shan Wang,* Jie Zhou, Ming-Yue Yin, Ke Yang, and Shu-Jiang Tu
School of Chemistry and Chemical Engineering, Xuzhou Normal UniVersity, The Key Laboratory of
Biotechnology on Medical Plant, Xuzhou Jiangsu 221116, P.R. China
ReceiVed October 23, 2009
A mild, efficient, and highly selective method for the synthesis of pyranoquinoline and furoquinoline
derivatives via a three-component reaction of aromatic aldehyde, naphthalen-2-amine or anthracen-2-amine
and 2,3-dihydrofuran, or 3,4-dihydro-2H-pyran catalyzed by iodine is described. It should be noted that
exo-isomer was obtained with high selectivity in good yields, which was confirmed by X-ray diffraction
analysis. The 3-arylbenzo(naphtha)[f]quinolines were isolated in high yields when the chain n-butylvinyl
ether was used as reactant, with the unexpected loss of the butoxy group.
1. Introduction
Therefore, the development of a system with reagent
economy, metal free, one-pot, and good stereoselectivity is
desirable.
Control of selectivity, for example, chemo-, stereo, and
regioselectivity, is among the most important objectives in
organic chemistry. Many different process parameters such
as temperature, pressure, solvent, as well as catalyst type,
and other factors can be utilized to modulate the selectivity
of synthetic transformations.1 Multicomponent reactions
(MCRs) play an important role in modern synthetic organic
chemistry since they generally occur in a single pot and
exhibit a high atom-economy and selectivity. They also
deliver fewer byproducts compared to classical stepwise
synthetic routes.2 They provide a powerful tool toward the
one-pot synthesis of diverse and complex compounds as well
as small and drug-like heterocycles.3 Owing to their con-
vergence and productivity, the MCRs have attracted con-
siderable attention from the point of view of combinatorial
chemistry.4 For multicomponent reactions involving the
simultaneous molecular interaction of three or more com-
ponents, the issue of selectivity is of particular significance
because of the high probability of several potential parallel
reaction pathways leading to different product classes.5
Pyranoquinoline derivatives are found to possess a wide
spectrum of biological activities, such as psychotropic,
antiallergenic, anti-inflammatory and estrogenic activity.6 The
imino-Diels-Alder reaction provides easy access to the
preparation of pyrano and furoquinolines. The imines derived
from aromatic amines act as heterodienes and undergo imino-
Diels-Alder reaction with various dienophiles in the pres-
ence of acid catalysts.7-10 However, many of these synthetic
protocols reported so far suffer from disadvantages, such as
harsh reaction conditions, multistep reaction, use of metals
and expensive reagents, poor stereoselectivity, and so forth.
Especially for the latter, most of the reported procedures
always give a mixture of endo and exo-isomers11 using 2,3-
dihydrofuran or 3,4-dihydro-2H-pyran as starting materials.
In our previous paper, we have synthesized series of
benzo[f]quinoline derivatives through three-component reac-
tions of aromatic aldehyde, various ketones, and naphthalen-
2-amine.12 It was found that naphthalen-2-amine involved-
reaction always gave the desired products in high yields and
good stereoselectivity for its higher activity. In connection
with our previous research on this iodine-catalyzed reaction
and for the challenge of stereoselectivity of above-mentioned
imino-Diels-Alder reaction, naphthalen-2-amine or anthra-
cen-2-amine was selected as similar aromatic amine to react
with aromatic aldehyde and 2,3-dihydrofuran or 3,4-dihydro-
2H-pyran. It was noteworthy that exo-4-arylbenzo[f]furo [3,2-
c]quinoline, pyrano[3,2-c]quinoline, naphtho[2,3-f]furo[3,2-
c]quinoline or naphtho[2,3-f] pyrano[3,2-c]quinoline derivatives
were obtained with high selectivity in good yields. 3-Aryl-
benzo[f]quinolines or 3-arylnaphtho[2,3-f]quinolines were
obtained in high yields when the chain n-butylvinyl ether
was selected as dienophile, with the unexpected loss of the
butoxy group.
2. Results and Discussion
Treatment of aromatic aldehyde 1, naphthalen-2-amine 2,
and 2,3-dihydrofuran 3 in tetrahydrofuran (THF) in the
presence of 10 mol % iodine at reflux condition afforded
the corresponding exo-4-arylbenzo[f]furo[3,2-c]quinoline
derivatives 4 in good yields with high stereoselectivity
(Scheme 1). Obviously, these results were different from
endo- and exo-isomers catalyzed by PMA, SbCl3-HAP,
Scheme 1. Reaction of 1, 2 and 2,3-Dihydrofuran
* To whom correspondence should be addressed. E-mail: xswang1974@
yahoo.com. Phone: +86 516 83500065. Fax: +86 516 83500065.
10.1021/cc900165j  2010 American Chemical Society
Published on Web 01/12/2010

Synthesis of Benzo(naphtho)quinoline Derivatives
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 2 267
Table 1. Synthetic Results of 4a under Different Reaction
Table 2. Synthetic Results of 4a-o Catalyzed by Iodine in
Conditionsa
THFa
entry
temp. (°C)
catalyst (mol %)
solvent
yields (%)b
entry
Ar
products
time (h)
yields (%)b
1
2
3
4
5
6
7
8
r.t.
reflux
r.t.
0
0
I2(5)
I2(5)
THF
THF
THF
THF
THF
THF
THF
CH3CN
benzene
DMF
CHCl3
CH2Cl2
none
0
0
trace
68
84
83
83
72
1
2
3
4
5
6
7
8
4-NO2C6H4
4-ClC6H4
3-NO2C6H4
3,4-(MeO)2C6H3
2-thienyl
C6H5
4-BrC6H4
3-ClC6H4
3,4-Cl2C6H3
4-FC6H4
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
10
10
11
15
14
14
14
15
12
10
12
14
18
13
18
84
92
88
90
78
89
90
82
84
88
83
90
93
83
79
50
reflux
reflux
reflux
reflux
reflux
80
reflux
r.t.
r.t.
I2(5)
I2(10)
I2(20)
I2(5)
I2(5)
I2(5)
9
82
75
76
9
10
11
12
13
14
10
11
12
13
14
15
I2(5)
3-FC6H4
I2(15)
H3PMO12O40(1)
SbCl3(10)
72(68:32)c
92(8:12)d
90(28:72)e
2-MeOC6H4
4-MeOC6H4
3-BrC6H4
r.t.
CH3CN
3,4-(MeO)2C6H3
a Reagents and conditions: 4-nitrobenzaldehyde 1a (0.302 g, 2 mmol),
2 (0.286 g, 2 mmol), 3 2,3-dihydrofuran (0.210 g, 3 mmol), solvent (10
mL). b Isolated yields. c Reference 11e, benzaldehyde (1 mmol), aniline
(1 mmol), 2,3-dihydrofuran (2 mmol), CH2Cl2, r.t. the 68:32 is the ratio
of exo/endo. d Reference 11a, benzaldehyde (1.5 mmol), aniline (1.5
mmol), 2,3-dihydrofuran (2 mmol), solvent free, r.t. the 8:12 is the ratio
of exo/endo. e Reference 11c, benzaldehyde (2 mmol), aniline (2.2
mmol), 2,3-dihydrofuran (2.6 mmol), CH3CN, r.t. the 28:72 is the ratio
of exo/endo.
a Reagents and conditions: 1 (2 mmol), 2 (0.286 g, 2 mmol), 3 (0.210
g, 3 mmol), I2 (0.1 mmol, 0.026 g), THF (10 mL). b Isolated yields.
SbCl3 or iodine using simple aromatic amines as reactants
(Table 1, Entries 12-14).11
In our initial study, the reaction of 4-nitrobenzaldehyde
1a, naphthalen-2-amine 2, and 2,3-dihydrofuran 3 was used
as a model reaction to optimize the reaction conditions. The
reaction was first carried out in THF in the absence of I2. It
was found that no reaction occurred at room temperature or
reflux condition (Table 1, entries 1 and 2). Similar reactions
were attempted in the presence of 5, 10, and 20 mol % of
I2. The results from Table 1 (entries 5-7) show that 5 mol
% I2 at reflux in THF is sufficient to initiate the reaction.
Higher loading of the catalyst had no significant influence
on the reaction yield. To find the optimum reaction temper-
ature, the reaction was carried out with 5 mol % of I2 at
room temperature, 50 °C and reflux temperature, resulting
in the isolation of 4a in trace amount, 68%, and 84% yields
(Table 1, entries 3-5), respectively. Thus, 5 mol % of I2
and a reaction temperature at reflux were optimal conditions.
In addition, CH3CN, benzene, N,N-dimethylformamide (DMF),
and CHCl3 (Table 1, entries 8-11) were also tested as the
solvents. In these cases, product 4a was formed in slightly
lower yields (Table 1, entries 8-11).
According to the optimized conditions, various aromatic
aldehydes 1 were then subjected to react with 2 and 2,3-
dihydrofuran 3 to generate a library of exo-benzo[f]furo[3,2-
c]quinoline derivatives 4 (Table 2). For aldehyde 1, the yields
of 4 were not sensitive to the electronic properties of the
aromatic ring in the presence of electron-withdrawing groups
(such as halide and nitro) or electron-donating groups (such
as alkoxyl group) (Table 2). The sole product was observed
in the solution of the reaction system monitored by TLC.
Subsequently it was separated by filtration before crystal-
lization, and was also confirmed to be the exo-isomer by 1H
NMR. Furthermore, the naphthalen-2-amine 2 also gives high
regioselectivity in position 1 rather than position 3 for its
high activity, because the position 1 is not only the ortho
position of the amino group, but also the R-position or benzyl
position of another benzene ring in the naphthalene ring
Figure 1. Crystal structure of product 4b indicating the exo-
structure.
Scheme 2. Reaction of 1, 2 and 3,4-Dihydro-2H-pyran
moiety. The exo-structure of 4b was further confirmed by
X-ray diffraction analysis. Figure 1.
As expected, the substrate of 2,3-dihydrofuran could be
extended to 3,4-dihydro-2H-pyran, which was also chosen
to react with the aromatic aldehyde, naphthalen-2-amine
(Scheme 2), and were found to generate the corresponding
exo-5-arylbenzo[f]pyrano[3,2-c]quinoline derivatives (5a-l).
The results are summarized in Table 3.
These three-component reactions with good stereoselec-
tivity inspire us to choose other similar moieties to expand
their application, especially for chain vinyl ethers. As a
representative, n-butylvinyl ether was chosen as reactant to
react with aromatic aldehyde, and naphthalen-2-amine to
obtain trans-1-butoxy-1,2,3,4-tetrahydro-3- arylbenzo[f]quin-
oline derivatives 6′. To our surprise, the desired reaction
proceeded smoothly, but the butoxy group was not found in
the 1 H NMR with aromatized 3-arylbenzo[f]quinolines 6a-i
being obtained in high yields (Scheme 3). The results are
summarized in Table 4.

268 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 2
Wang et al.
Scheme 5. Reaction of 1, 3 and Anthracen-2-amine
Table 3. Synthetic Results of 5a-l Catalyzed by Iodine in
THFa
entry
Ar
products
time (h)
yields (%)b
1
2
3
4
5
6
7
8
4-NO2C6H4
4-MeOC6H4
4-ClC6H4
3,4-(MeO)2C6H3
2-Thienyl
C6H5
4-BrC6H4
3-ClC6H4
3,4-Cl2C6H3
4-FC6H4
5a
5b
5c
5d
5e
5f
5g
5h
5i
12
18
16
19
16
14
16
14
13
16
18
18
82
84
82
76
74
86
86
80
89
80
78
81
Table 5. Synthetic Results of 7a-o Catalyzed by Iodine in
9
THFa
10
11
12
5j
5k
5l
4-MeC6H4
3,4-(MeO)2C6H3
entry
Ar
n
products
time (h)
yields (%)b
1
2
3
4
5
6
7
8
4-BrC6H4
4-ClC6H4
4-MeC6H4
4-MeOC6H4
4-FC6H4
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
7o
12
11
13
13
10
10
14
14
14
12
8
82
84
78
80
87
86
83
84
79
78
80
82
80
83
84
a Reagents and conditions:
1 (2 mmol), 2 (0.286 g, 2 mmol),
3,4-dihydro-2H-pyran (0.252 g, 3 mmol), I2 (0.1 mmol, 0.026 g), THF
(10 mL). b Isolated yields.
2-thienyl
Scheme 3. Reaction of 1, 2 and n-Butylvinyl Ether
3,4-(MeO)2C6H3
3,5-(MeO)2C6H3
3,4-OCH2OC6H3
4-BrC6H4
4-FC6H4
4-MeC6H4
4-MeOC6H4
3,4-(MeO)2C6H3
3,4-OCH2OC6H3
9
10
11
12
13
14
15
12
10
10
14
a Reagents and conditions: 1 (2 mmol), anthracen-2-amine (0.386 g, 2
mmol), 2,3-dihydrofuran or 3,4-dihydro-2H-pyran (3 mmol), I2 (0.1
mmol, 0.026 g), THF (10 mL). b Isolated yields.
Table 4. Synthetic Results of 6a-i Catalyzed by Iodine in
THFa
entry
Ar
products
time (h)
yields (%)b
1
2
3
4
5
6
7
8
9
C6H5
4-FC6H4
4-MeOC6H4
4-NO2C6H4
4-BrC6H4
6a
6b
6c
6d
6e
6f
6g
6h
6i
10
12
12
8
12
11
10
12
12
92
88
92
93
90
87
84
86
82
3-BrC6H4
3,4-Cl2C6H3
3,4-OCH2OC6H3
3,4-(MeO)2C6H3
a Reagents and conditions:
1 (2 mmol), 2 (0.286 g, 2 mmol),
n-butylvinyl ether (0.300 g, 3 mmol), I2 (0.1 mmol, 0.026 g), THF (10
mL). b Isolated yields.
Figure 2. Crystal Structure of Product 7e Indicating the exo-
Structure.
Scheme 4. Possible Mechanism for the Formation of
Products 6
product III. The unexpected loss of BuOH induced by iodine
results in dihydroquinoline IV, which is further oxidized by
air to afford aromatized 3-arylbenzo[f]quinolines 6.
This sequence is also extended from naphthalen-2-amine
to other amine, such as anthracen-2-amine (Scheme 5). The
desired three-component reactions of aromatic aldehyde,
anthracen-2-amine and 2,3-dihydrofuran, 3,4-dihydro-2H-
pyran took place successfully and also selectively afforded
exo-naphtho[2,3-f]furo(pyrano) [3,2-c]quinoline derivatives
(7a-o) in good yields at reflux in THF (Table 5). The exo-
structure of 7e is also confirmed by X-ray diffraction analysis,
and its crystal structure is shown in Figure 2.
As expected, the formation of aromatized arylbenzo[f]quin-
olines lacking the butoxy fragment is also applied to
anthracen-2-amine (Scheme 6). The aromatized 3-arylnaph-
tho[2,3-f]quinoline derivatives 8a-j were obtained in high
yields at reflux in THF (Table 6), when the 2,3-dihydrofuran
was replaced by n-butylvinyl ether in above-mentioned
reaction.
On the basis of the literature,12c,13 we think that iodine
catalyzes the reaction as a mild Lewis acid. The mechanism
was tentatively proposed as shown in Scheme 4. The Schiff
base I may be formed by the reaction of aromatic aldehyde
and naphthalen-2-amine first. And then the vinyl ether attacks
iodine-activated Schiff base to form intermediate II, followed
by an intramolecular Friedel-Crafts cyclization to give the

Synthesis of Benzo(naphtho)quinoline Derivatives
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 2 269
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Scheme 6. Reaction of 1, n-Butylvinyl Ether, and
Anthracen-2-amine
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Table 6. Synthetic Results of 8a-j Catalyzed by Iodine in
THFa
entry
Ar
products
time (h)
yields (%)b
1
2
3
4
5
6
7
8
9
10
4-MeC6H4
8a
8b
8c
8d
8e
8f
8g
8h
8i
9
6
7
10
10
8
7
7
10
8
87
89
93
92
83
84
88
87
89
89
4-NO2C6H4
2,4-Cl2C6H3
3,4-OCH2OC6H3
3,4-(MeO)2C6H3
4-MeOC6H4
3,4-Cl2C6H3
4-FC6H4
3,4-(MeO)2C6H3
4-ClC6H4
8j
a Reagents and conditions: 1 (2 mmol), anthracen-2-amine (0.386 g, 2
mmol), n-butylvinyl ether (0.300 g, 3 mmol), I2 (0.1 mmol, 0.026 g),
THF (10 mL). b Isolated yields.
3. Conclusion
In conclusion, we found a mild and efficient method for
the synthesis of exo-pyranoquinoline and exo-furoquinoline
derivatives via three-component reactions of aromatic alde-
hyde, naphthalen-2-amine or anthracen-2-amine and 2,3-
dihydrofuran, or 3,4-dihydro-2H-pyran catalyzed by iodine.
The 3-arylbenzo(naphtha)[f]quinolines were obtained in high
yields when the chain n-butylvinyl ether was used as reactant,
with the unexpected loss of the butoxy group. The features
of this procedure are mild reaction conditions, good to high
yields, operational simplicity, and high stereoselectivity.
Acknowledgment. We are grateful to the National Natural
Science foundation of China (20802061), the Natural Science
foundation (08KJD150019), and the Qing Lan Project
(08QLT001) of Jiangsu Education Committee for financial
support.
Supporting Information Available. Representative ex-
perimental procedures, spectral data of compounds 4a-o,
5a-l, 6a-i, 7a-o, and 8a-j, crystallographic information
files (CIF) of 4b and 7e. This material is available free of
charge via the Internet at http://pubs.acs.org.
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