PPA-mediated C-C bond formation: A synthetic route to substituted indeno[2,1-c]quinolin-6(7 H)-ones

Article abstract of DOI:10.1021/ol303423f

A facile and efficient synthesis of substituted indeno[2,1-c]quinolin-6(7H) -ones from a variety of α-acyl N-arylcinnamamides mediated by polyphosphoric acid (PPA) is described, and a mechanism involving the formation of a dicationic superelectrophile and

Full text of DOI:10.1021/ol303423f

ORGANIC
LETTERS
2013
Vol. 15, No. 4
776–779
PPA-Mediated CꢀC Bond Formation:
A Synthetic Route to Substituted
Indeno[2,1‑c]quinolin-6(7H)‑ones
Xu Liu,† Qian Zhang,† Dingyuan Zhang,† Xiaoqing Xin,† Rui Zhang,*,†,‡ Fenguo Zhou,†
and Dewen Dong*,†,‡
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, China, Changzhou Institute of Energy Storage Materials & Devices,
Changzhou 213000, China
ariel@ciac.jl.cn; dwdong@ciac.jl.cn
Received December 14, 2012
ABSTRACT
A facile and efficient synthesis of substituted indeno[2,1-c]quinolin-6(7H)-ones from a variety of R-acyl N-arylcinnamamides mediated by
polyphosphoric acid (PPA) is described, and a mechanism involving the formation of a dicationic superelectrophile and subsequent double
intramolecular nucleophilic cyclization reactions is proposed.
The vast number of bioactive natural products and
pharmaceutical drugs based on the indeno[2,1-c]quinoline
ring system exhibit a diverse range of biological proper-
ties,1 such as 5-HT-receptor binding activity2 and anti-
inflammatory activity,3 and also act as antitumor agents,4
antimalarials,1a,5 acetylcholinesterase inhibitors,6 potential
topo I/II inhibitors,7 and steroid reductase inhibitors.8 In
addition, functionalized indeno[2,1-c]quinolines have been
used as versatile intermediates in the synthesis of a series of
other biologically important compounds.9 The develop-
ment of efficient synthetic approaches for indeno[2,1-c]-
quinolines has been the focus of intense research for
decades and continues to be an active area of research
today.10 These compounds are frequently synthesized via
the aza-Bergman cyclization,11 FriedelꢀCrafts-type reac-
tion,12 or the imino DielsꢀAlder reaction.13 Recently, Lee
and co-workers developed an efficient synthetic method
for 7H-indeno[2,1-c]quinolines from BaylisꢀHillman
† Changchun Institute of Applied Chemistry.
‡ Changzhou Institute of Energy Storage Materials & Devices.
(1) (a) Venugopalan, B.; Bapat, C. P.; Desouza, E. P.; Desouza, N. J.
Indian J. Chem., Sect. B: Org. Chem. Inclusion Med. Chem. 1992, 31, 35.
(b) Deady, L. W.; Desneves, J.; Kaye, A. J.; Finlay, G. J.; Baguley, B. C.;
Denny, W. A. Bioorg. Med. Chem. 2000, 8, 977.
(2) Anzini, M.; Cappelli, A.; Vomero, S.; Cagnotto, A.; Skorupska,
M. Med. Chem. Res. 1993, 3, 44.
(3) Quraishi, M. A.; Thakur, V. R.; Dhawan, S. N. Indian J. Chem.,
Sect. B: Org. Chem. Inclusion Med. Chem. 1989, 28, 891.
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Takeuchi, K.; Matsushima, M.; Tsuruo, T.; Tashiro, T.; Tsukagoshi, S.;
Yamashita, Y.; Nakano, H. J. Med. Chem. 1989, 32, 1295.
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Garofalo, A. W.; Phuan, P.-W.; Fort, D. M.; Litvak, J.; Gerber, R. E.;
Sloan, B.; Luo, J.; Cooper, R.; Reaven, G. M. J. Med. Chem. 1998, 41,
2754.
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Cavrini, V.; Cavalli, A.; Recanatini, M. Bioorg. Med. Chem. 2000, 8, 497.
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Denny, W. A. J. Med. Chem. 1997, 40, 2040. (b) Deady, L. W.; Desneves,
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B.; Houssin, R.; Bailly, C.; Henichart, J.-P. J. Med. Chem. 2008, 51, 3617.
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1035. (b) Koyama, J.; Toyokuni, I.; Tagahara, K. Chem. Pharm. Bull.
1998, 46, 332. (c) Bu, X.; Deady, L. W. Synth. Commun. 1999, 29, 4223.
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R. S.; Shinde, P. D.; Kadam, S. A.; Bawane, A. N.; Sayyed, A. Y.;
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r
10.1021/ol303423f
Published on Web 02/07/2013
2013 American Chemical Society

adducts in polyphosphoric acid (PPA).14 Nevertheless, to
match the increasing scientific and practical demands, it
is still of continued interest and great importance to ex-
plore novel, efficient synthetic approaches for indeno-
[2,1-c]quinolines.
The results encouraged us to investigate the reaction
conditions with the aim of optimizing the yield of 2a. It was
observed that the reaction temperature had a dramatic
effect on the reaction of 1a in concentrated H2SO4. When
the reaction temperature was increased to 50 °C, 2a and 3a
were obtained in 55% and 25% yields (Table 1, entry 2),
respectively, whereas further increase of the reaction tem-
perature to 90 °C, the yield of 3a reached 38% (Table 1,
entry 3). Similarly, treatment of 1awithPPA at90°C could
only afford 2a in 37% yield along with the recovery of 1a
(Table 1, entry 4). To our delight, when the reaction of 1a
was performed in PPA at 130 °C, 2a was isolated in 92%
yield (Table 1, entry 5). It seemed that further increase of
the reaction temperature had no significant influence on
the conversion, although the reaction rate could be accel-
erated (Table 1, entry 6). The reaction of 1a could take
place in CF3SO3H, but the conversion was very low within
a short reaction time, and a complex mixture containing
2a was formed when the reaction time was prolonged
(Table 1, entries 7 and 8). No reaction was observed when
1a was subjected to CF3COOH at room temperature, and
a complex mixture was formed at high temperature and the
desired 2awas noteven detected (Table 1, entries 9 and 10).
During the course of our studies on the synthesis of
carbo- and heterocycles based on β-oxo amide derivatives,15
we successfully achieved efficient synthesis of pyrano[2,3-b]-
quinolines from enaminones mediated by trifluorometha-
nesulfonic acid16 and substituted quinolin-2(1H)-ones from
penta-2,4-dienamides mediated by concentrated H2SO4.17
In connection with this previous work and our continued
efforts for the synthesis of highly valuable heterocycles
through acid-mediated processes, we synthesized a series
of R-acyl-N-arylcinnamamides from β-oxo amides and
examined their reactivity toward acidic conditions. As a
result of these studies, we have developed a facile and
efficient synthesis of substituted indeno[2,1-c]quinolin-
6(7H)-ones. Herein we report our preliminary results and
a proposed mechanism.
The substrates, R-acylcinnamamides, were prepared by
Knoevenagel condensation of commercially available
β-oxo amides with aryl aldehydes in the presence of piper-
idine in acetic acid according to a reported procedure.18 It
should be mentioned that the obtained R-acylcinnamamides
were pure E-isomers for tertiary amides or a mixture of a
pair of E- and Z-isomers for secondary amides based on
their 1H NMR and NOE analytical data (see the Supporting
Information). Then, 2-benzylidene-3-oxo-N-phenylbutana-
mide 1a was selected as the model compound and subjected
to H2SO4 (98%) at room temperature. As indicated by
TLC, the reaction occurred and furnished two products
after workup and purification by column chromatography
of the resulting mixture. The main product was character-
ized as 7-methyl-5H-indeno[2,1-c]quinolin-6(7H)-one 2a,
and the by-product was characterized as 3-acetylquinolin-
2(1H)-one 3a on the basis of its spectroscopic and analytical
data (Table 1, entry 1). Actually, we have revealed that the
same compound 3a could be synthesized from penta-2,4-
dienamide in the presence of concentrated H2SO4 in high
yield.17
Table 1. Reactions of 1a under Different Acidic Conditionsa
yieldb (%)
entry
acids
temp (°C) time (h)
2a
3a
1
2
3
4
5
6
7
8
9
10
H2SO4(98%)
H2SO4(98%)
H2SO4(98%)
PPA
rt
5.0
3.0
79
55
6
25
38
<5
<5
<5
<5
50
90
1.0
<5
37c
92
90
12.0
12.0
3.0
PPA
130
150
rt
PPA
89
34d
CF3SO3H
CF3SO3H
CF3COOH
CF3COOH
3.0
rt
5.0
complex mixture
no reaction
rt
10.0
10.0
(12) (a) Curran, D. P.; Liu, H.; Josien, H.; Ko, S.-B. Tetrahedron
1996, 52, 11385. (b) Angibaud, P. R.; Venet, M. G.; Filliers, W.; Broeckx,
R.; Ligny, Y. A.; Muller, P.; Poncelet, V. S.; End, D. W. Eur. J. Org.
Chem. 2004, 479. (c) Kraus, J. M.; Tatipaka, H. B.; McGuffin, S. A.;
Chennamaneni, N. K.; Karimi, M.; Arif, J.; Verlinde, C. L. M. J.;
Buckner, F. S.; Gelb, M. H. J. Med. Chem. 2010, 53, 3887.
(13) (a) Babu, G.; Perumal, P. T. Tetrahedron Lett. 1998, 39, 3225.
(b) Yadav, J. S.; Subba Reddy, B. V.; Srinivas, R.; Madhuri, Ch.;
Ramalingam, T. Synlett 2001, 240.
reflux
complex mixture
a Reaction conditions: 1a (2.0 mmol), acid (5.0 mL). b Isolated yield.
c 46% of 1a was recovered. d 53% of 1a was recovered.
Under the optimal conditions for 2a in entry 5, Table 1, a
range of reactions of substrates 1 were carried out to
determine the scope of the indeno[2,1-c]quinolin-6(7H)-
one synthesis, and some of the results are summarized in
Table 2. It was found that the reactions of 1bꢀj bearing
variable aryl amide groups with both electron-donating
(e.g., Me, MeO) and electron-withdrawing (e.g., Cl) sub-
stituents R1 on the benzene ring in the presence of PPA at
130 °C proceeded smoothly to afford the correspond-
ing substituted indeno[2,1-c]quinolin-6(7H)-ones 2bꢀj in
high yields (Table 2, entries 2ꢀ10). In the case of 1f,
(14) Lee, C. G.; Lee, K. Y.; Sankar, S. G.; Kim, J. N. Tetrahedron
Lett. 2004, 45, 7409.
(15) For our recent work, see: (a) Pan, W.; Dong, D.; Wang, K.;
Zhang, J.; Wu, R.; Xiang, D.; Liu, Q. Org. Lett. 2007, 9, 2421. (b) Xiang,
D.; Wang, K.; Liang, Y.; Zhou, G.; Dong, D. Org. Lett. 2008, 10, 345.
(c) Zhang, R.; Liang, Y.; Zhou, G.; Wang, K.; Dong, D. J. Org. Chem.
2008, 73, 8089. (d) Xiang, D.; Xin, X.; Liu, X.; Zhang, R.; Yang, J.;
Dong, D. Org. Lett. 2012, 14, 644. (e) Liu, X.; Xin, X.; Xiang, D.; Liang,
Y.; Xin, X.; Li, W.; Dong, D. RSC Adv. 2013, 3, 1346.
(16) Xiang, D.; Xin, X.; Liu, X.; Kumar, S.; Dong, D. Synlett. 2011,
2187.
(17) Liu, X.; Xin, X.; Xiang, D.; Zhang, R.; Kumar, S.; Zhou, F.;
Dong, D. Org. Biomol. Chem. 2012, 10, 5643.
(18) Zarif, A. K.; Amal, S. Y. J. Indian Chem. Soc. 1981, 58, 168.
Org. Lett., Vol. 15, No. 4, 2013
777

indeno[2,1-c]quinolin-6(7H)-one 2f was exclusively ob-
tained in 86% yield, which indicated that the cyclization
reaction of 1f occurred in a regioselective manner (Table 2,
entry 6). In the same fashion, the corresponding indeno-
[2,1-c]quinolin-6(7H)-one 2k was obtained in good yield
when substrate 1k containing a propyl group (R3) was
employed (Table 2, entry 11). The versatility of this
cyclization protocol was further evaluated by performing
the reaction of R-acyl N-arylcinnamamides 1iꢀ1o bearing
variable aromatic groups (R4) under identical conditions
(Table 2, entries 12ꢀ15).
efficient, and metal-free synthetic method for a highly
substituted indeno[2,1-c]quinolin-6(7H)-one of type 2.
Scheme 1. Reactions of N-Arylcinnamamides 1p and 1q
with PPA
Table 2. Reactions of R-Acyl N-Arylcinnamamides 1 with PPAa
To extend the scope of this indeno[2,1-c]quinolin-6(7H)-
one synthesis, we prepared N-arylcinnamamides 1p and 1q
with benzyl and ester groups, respectively, as shown in
Scheme 1 and subjected them to PPA at 130 °C. In these
cases, 3-benzoyl-4-phenyl-3,4-dihydroquinolin-2(1H)-one
4p and ethyl 2-oxo-4-phenyl-1,2,3,4-tetrahydroquinoline-
3-carboxylate 4q were obtained in excellent yields
(Scheme 1). The results revealed that 1p and 1q could only
undergo a single nucleophilic cyclization to form the
dihydro quinolin-2(1H)-one ring, and probably the further
nucleophilic cyclization reaction was prohibited by the
electronic and steric effect from benzyl and ester groups.
entry
1
R1
R2
R3
R4
2
yieldb (%)
1
1a
1b
1c
1d
1e
1f
H
H
H
H
Me
Et
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Pr
H
2a
2b
2c
2d
2e
2f
92
87
89
91
78
86
81
75
77
82
84
67
71
69
72
2
H
3
H
4
4-Me
2-Me
3-Me
2,4-Me2
4-Cl
H
5
H
6
H
7
1g
1h
1i
H
2g
2h
2i
8
H
9
4-MeO
2-MeO
H
H
Scheme 2. Stepwise experiment with 1b and PPA
10
11
12
13
14
15
1j
H
2j
1k
1l
H
2k
2l
H
Me
Me
Me
Me
4-Me
2-Me
2-Me
2-Me
1m
1n
1o
H
2m
2n
2o
4-Me
2-Me
a Reagents and conditions: 1 (1.0 mmol), PPA (2.0 mL), 130 °C,
10.0ꢀ15.0 h. b Isolated yield.
To gain insight into the mechanism of the indeno[2,1-
c]quinolin-6(7H)-one synthesis, a controlled experiment
was carried out. As shown in Scheme 2, (E)-2-benzylidene-
3-oxobutanamide 1b was subjected into PPA at 130 °C for
0.3 h, the reaction was then quenched. Two products,
3-acetyl-1-methyl-4-phenyl-3,4-dihydroquinolin-2(1H)-
one 4b and 1-hydroxy-N,1-dimethyl-N-phenyl-1H-indene-
2-carboxamide 5b, were obtained as an inseparable mix-
ture with a ratio of 5:2 by silica gel column chromatogra-
phy (determined by NMR spectra). The mixture was then
investigated by means of GCꢀMS. From one mass spec-
trum, the peaks appeared at 279 and 236 were assigned to
the molecular ion [M]þ of 4b and its molecular fragment
ion [M ꢀ CH3CO]þ, respectively. Similarly, the peaks
displayed at 279, 202, and 184 on another mass spectrum
could be easily assigned to the molecular ion [M]þ of 5b,
and its molecular fragment ions [M ꢀ Ph]þ and [M ꢀ
Ph ꢀ OH þ 1]þ, respectively. It is worth noting that the
Figure 1. ORTEP drawing of 2j.
It is worth mentioning that the structure of 2j was
elucidated by means of NMR (1H, 13C) spectra and further
confirmed by the X-ray single-crystal analysis (Figure 1).
The results shown above demonstrated the efficiency and
synthetic value of the cyclization with respect to R-acyl
N-arylcinnamamides 1. Therefore, we provide a facile,
778
Org. Lett., Vol. 15, No. 4, 2013

obtained mixture of 4b and 5b could be converted into 2b
in 94% yield when treated with PPA at 130 °C within
2.0 h. These results indicate that 4b and 5b are generated
simultaneously, and both of them are the intermediates in
the transformation.
B and C upon treatment with water, and quinolin-2(1H)-
one 3 is derived from B through the elimination of an arene.17
Scheme 3. Possible Mechanism for the PPA-Mediated Cycliza-
tion of R-Acyl-N-arylcinnamamides
The formation of 4b demonstrated that the nucleophilic
addition site of aryl amide was on the CꢀC double bond of
1b instead of the R-acyl group and also clearly showed that
the intramolecular cyclization proceeded in a chemoselec-
tive manner, which was different from the conventional
acid-catalyzed Knorr quinolin-2(1H)-one synthesis.19 During
the investigation of the Knorr cyclization at 1960s and
1970s, a number of cationic electrophilic reagents were
noted to show greatly enhanced reactivities in the pre-
sence of superacids, which led to the concept of super-
electrophilic activation.20 At the time of that study, there
was a considerable amount of uncertainty regarding the
protonation site on amides. This problem has been re-
solved over the years and in most cases oxygen is pre-
ferred over nitrogen as the protonation site.21 Recently,
Sai et al. studied the acid-catalyzed Knorr cyclization by
both experimental and computational methods, and re-
vealed that β-oxo amides underwent deprotonation at the
two carbonyl oxygen atoms to form distonic superelec-
trophiles, which gave rise to Knorr products.22
On the basis of the results obtained above and the
reported literature,23 a plausible mechanism for the synth-
esis of indeno[2,1-c]quinolin-6(7H)-ones 2 is presented
in Scheme 3. Mediated by PPA, R-acylcinnamamide 1 is
protonated to form a dicationic superelectrophile A,20
which undergoes double-intramolecular cyclization reac-
tions in two different pathways, path I and path II, to give
the same intermediate D.24 The elimination of water from
D and the subsequent isomerization of intermediate E via
1,3-H shift under acidic conditions25 led to the formation
of the final product indeno [2,1-c]quinolin-6(7H)-one of
type 2. It is most likely that dihydroquinolinone 4 and 1H-
indene-2-carboxamide 5 are generated from intermediates
In summary, a facile and efficient synthesis of indeno
[2,1-c]quinolin-6(7H)-ones 2 is developed from R-acyl N-
arylcinnamamides, which involves the formation of dica-
tionic superelectrophile, and subsequent double intramo-
lecular nucleophilic cyclization reactions in the presence of
polyphosphoric acid (PPA). This protocol is associated
with readily available starting materials, mild conditions,
good yields, a wide range of substrate scope, dense and
flexible substituted patterns, and important synthetic
potential of the products.
Acknowledgment. Financial support of this research
by the National Natural Science Foundation of China
(51073150 and 21172211), the Department of Science and
Technology of Jilin Province (20111802), and “Hundred
Talents Program” of the Chinese Academy of Sciences is
greatly acknowledged.
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B. A.; Ganesan, A. Chem. Commun. 1998, 785. (d) Li, K.; Foresee, L. N.;
Tunge, J. A. J. Org. Chem. 2005, 70, 2881.
Supporting Information Available. Experimental de-
tails, spectral and analytical data, and copies of 1H NMR
and 13C NMR spectra for new compounds 1, 2, 4, and 5;
crystallographic data for compound 2j (CIF). This mate-
rial is available free of charge via the Internet at http://
pubs.acs.org
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The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 4, 2013
779