An efficient ultrasound promoted catalyst-free protocol for the synthesis of chromeno[4,3-b]quinolin-6-ones

Article abstract of DOI:10.1007/s12039-011-0134-z

A convenient, catalyst-free protocol for the quantitative synthesis of fused chromeno[4,3-b]quinolin-6-ones has been developed by simple one-pot reaction of substituted anilines with 4-chloro-3-formylcoumarin using ultrasound irradiation. The protocol offers the advantages of mild reaction conditions, short reaction times and high yields. Indian Academy of Sciences.

Full text of DOI:10.1007/s12039-011-0134-z

c
J. Chem. Sci. Vol. 123, No. 5, September 2011, pp. 673–679. ꢀ Indian Academy of Sciences.
An efficient ultrasound promoted catalyst-free protocol for the synthesis
of chromeno[4,3-b]quinolin-6-ones
J VENKATA PRASAD, J SATYANARAYANA REDDY, N RAVI KUMAR,
K ANAND SOLOMON and G GOPIKRISHNA∗
Sankar Foundation Research Institute, Visakhapatnam 530047, India
e-mail: gkrishnagps@gmail.com
MS received 31 December 2010; revised 24 May 2011; accepted 30 May 2011
Abstract. A convenient, catalyst-free protocol for the quantitative synthesis of fused chromeno[4,3-
b]quinolin-6-ones has been developed by simple one-pot reaction of substituted anilines with 4-chloro-3-
formylcoumarin using ultrasound irradiation. The protocol offers the advantages of mild reaction conditions,
short reaction times and high yields.
Keywords. Ultrasound; 4-chloro-3-formylcoumarin; anilines; chromeno-quinoline.
1. Introduction
2. Experimental
Functionalized quinoline derivatives are integral com- 2.1 General remarks
ponent of several natural products which are used
1HNMR spectra were recorded at 400 MHz with a
as antibacterial,1 antiasthmatic,2 antifungal,3 anti-
inflammatory4 and anticancer5 agents. Further, they are
qualified as valuable starting materials for the synthesis
of nano and mesostructures with improved electronic
and photonic properties.6 The synthesis of quinoline
derivatives thus continues to be an active area of hete-
rocyclic chemistry research, and the synthesis of vari-
ous substituted quinolines has been largely explored.7
On the other hand, coumarin derivatives are known
to be equally important molecules endowed with wide
spectrum of medicinal properties including antibacte-
rial,8 antiinflammatory,9 antitumor10 and anti-HIV11
activities. They are also used as perfumes,12 dyes13
and fluorescent indicators.14 Chromeno-quinolines are
fused poly heterocyclic systems comprising both
coumarin and quinoline motifs which are known to pos-
sess interesting biological properties like bacteriostatic
activity,15 glucocorticoid modulators,16 antiinflamma-
tory effects17 and selective progesterone receptor
modulators.18 Thus the structural features and the bio-
logical applications prompt intense research by the
organic chemists for the development of novel method-
ologies for their synthesis.
Varian Gemini FT-NMR spectrometer. The chemical
shifts are reported in δppm relative to tetramethylsi-
lane (TMS). The Fourier transform FT–IR spectra were
recorded using a Perkin-Elmer 16650 FT-IR spectrome-
ter. The solvents and reagents were used without further
purification.
2.2 Synthesis of chromeno[4,3-b]quinolin-6-one
(3a–n)
A mixture of 4-Chloro-3-formylcoumarin (1) (1.0 mmol)
and anilines 2a–n (1.0 mmol) in 5 ml of ethanol were
subjected to ultrasound irradiation (33 KHz) for 15 min
resulting in precipitation of white solids which were
filtered and washed with methanol to yield 3a–n in
94–97% yield.
2.2a 6H-Chromeno[4,3-b]quinolin-6-one (3a): White
1
solid. H NMR (400 MHz, CDCl3): δ 9.24 (s, 1H),
8.85 (m, 1H), 8.25 (d, 1H), 8.04 (m, 1H), 7.91 (m, 1H),
7.62 (m, 2H), 7.49 (m, 2H); 13C NMR (400 MHz,
CDCl3): 160.3, 158.4, 152.7, 146.7, 134.5, 132.4,
128.6, 128.1, 127.0, 126.6, 124.2, 122.5, 119.6, 118.6,
118.7, 114.4; IR (KBr, νmax/cm−1): 1735, 1732, 2965;
EI-MS: m/z = 247.06.
∗For correspondence
673

674
J Venkata Prasad et al.
2.2b 9-Methyl-6H-chromeno[4,3-b]quinolin-6-one (3b): (m, 1H), 7.63 (m, 1H), 7.45 (m, 1H), 7.24 (s, 1H);
White solid. 1H NMR (400 MHz, CDCl3): δ 9.12 13C NMR (400 MHz, CDCl3): 161.3, 158.4, 154.3,
(s, 1H), 8.77 (m, 1H), 8.13 (d, 1H), 7.76 (s, 1H), 7.74 141.1, 131.6, 130.7, 129.1, 126.9, 126.5, 124.9, 122.3,
(d, 1H), 7.60 (d, 1H), 7.58 (m, 1H), 7.40 (m, 1H), 2.59 123.1, 122.3, 119.8, 117.8, 113.7; IR (KBr, νmax/c−1):
(s, 3H). 13C NMR (400 MHz, CDCl3): 161.4, 152.5, 1735, 1737, 1172; EI-MS: m/z = 326.17.
149.7, 148.8, 139.9, 137.5, 135.7, 131.9, 129.2, 127.8,
127.3, 125.1, 124.8, 119.7, 117.3, 115.7, 21.5; IR (KBr,
2.2h 9,10-Difluoro-6H-chromeno[4,3-b]quinolin-6-
one (3h): White solid. H NMR (400 MHz, CDCl3):
νmax/cm−1): 1735, 1734, 2923, 1188; EI-MS: m/z =
1
261.27
δ 9.46 (s, 1H), 8.63 (m, 1H), 8.25 (m, 1H), 7.89 (m, 2H),
7.70 (m, 1H), 7.52 (m, 1H); 13C NMR (400 MHz,
CDCl3): 162.7, 158.2, 155.3, 152.8, 148.4, 134.2,
128.2, 125.5, 124.2, 120.1, 119.2, 118.7, 118.2, 116.5,
115.4, 115.7; IR (KBr, νmax/cm−1): 1735, 1739, 1176;
EI-MS: m/z = 283.14.
2.2c 9-Chloro-6H-chromeno[4,3-b]quinolin-6-one (3c):
White solid. 1H NMR (400 MHz, CDCl3): δ 9.15
(s, 1H), 8.77 (m, 1H), 8.19 (d, 1H), 8.01 (d, 1H), 7.86
(m, 1H), 7.61 (m, 1H), 7.44 (m, 1H), 7.26 (s, 1H);
13C NMR (400 MHz, CDCl3): 160.9, 152.8, 149.9,
149.5, 139.9, 134.3, 133.4, 132.6, 131.2, 127.8, 127.7,
125.3, 125.1, 119.4, 117.5, 116.6; IR (KBr, νmax/cm−1):
3061, 1744, 1176; EI-MS: m/z = 281.44
2.2i 10,11-Difluoro-6H-chromeno[4,3-b]quinolin-6-
1
one (3i): White solid. H NMR (400 MHz, CDCl3):
δ 9.47 (s, 1H), 8.65 (m, 1H), 8.28 (m, 1H), 7.88 (m, 2H),
7.75 (m, 1H), 7.53 (m, 1H). 13C NMR (400 MHz,
CDCl3): 161.7, 156.2, 153.2, 151.3, 145.3, 136.7,
131.8, 127.4, 127.1, 126.4, 125.6, 124.4, 121.5, 120.3,
119.3, 118.1; IR (KBr, νmax/cm−1): 3046, 1734, 1737,
1178; EI-MS: m/z = 283.24.
2.2d 9-Nitro-6H-chromeno[4,3-b]quinolin-6-one (3d):
1
Yellow solid. H NMR (400 MHz, CDCl3): δ 9.18
(s, 1H), 8.73 (m, 1H), 8.16 (d, 1H), 8.01 (d, 1H), 7.82
(m, 1H), 7.60 (m, 1H), 7.44 (m, 1H), 7.24 (s, 1H);
13C NMR (400 MHz, CDCl3): 159.8, 155.6, 152.2,
143.4, 135.7, 130.6, 126.9, 126.7, 126.3, 125.2, 125.1, 2.2j 10-Fluoro-6H-chromeno[4,3-b]quinolin-6-one (3j):
120.4, 118.9, 117.9, 117.7, 112.4; IR (KBr, νmax/cm−1): White solid. 1H NMR (400 MHz, CDCl3): δ 9.21
1735, 1743, 1179; EI-MS: m/z = 292.25
(s, 1H), 8.77 (m, 1H), 8.05 (m, 1H), 7.85 (m, 1H),
7.62 (m, 1H), 7.42 (m, 1H), 7.39 (d, 1H), 7.26 (s, 1H);
13C NMR (400 MHz, CDCl3): 166.9, 161.1, 152.6,
150.7, 140.9, 132.7, 131.9, 125.4, 125.1, 119.4, 118.7,
118.4, 117.4, 115.3, 113.3, 113.1; IR (KBr, νmax/c−1):
3070, 1739, 1743, 1181; EI-MS: m/z = 265.05.
2.2e 9-Bromo-6H-chromeno[4,3-b]quinolin-6-one (3e):
White solid. 1H NMR (400 MHz, CDCl3): δ 9.20
(s, 1H), 8.76 (m, 1H), 8.45 (s, 1H), 7.89 (d, 1H), 7.73
(m, 1H), 7.63 (m, 1H), 7.45 (m, 1H), 7.26 (s, 1H);
13C NMR (400 MHz, CDCl3): 162.5, 159.4, 150.3,
146.2, 133.3, 132.3, 130.1, 128.1, 127.4, 126.9, 125.5,
125.1, 122.3, 121.3, 118.8, 113.2; IR (KBr, νmax/c−1):
1737, 1734, 1174; EI-MS: m/z = 326.14.
2.2k 9-Methoxy-6H-chromeno[4,3-b]quinolin-6-one (3k):
White solid. 1H NMR (400 MHz, CDCl3): δ 9.10
(s, 1H), 8.75 (m, 1H), 8.15 (d, 1H), 7.56 (m, 2H),
7.41 (m, 2H), 7.26 (s, 1H), 3.99 (s, 3H); 13C NMR
(400 MHz, CDCl3): 161.5, 158.4, 152.4, 147.7, 147.5,
138.8, 132.2, 131.7, 131.1, 128.5, 126.9, 124.8, 119.8,
117.3, 115.9, 105.6, 55.7; IR (KBr, νmax/cm−1): 2990,
1735, 1737, 1237; EI-MS: m/z = 277.07.
2.2f 9-Fluoro-6H-chromeno[4,3-b]quinolin-6-one (3f):
White solid. 1H NMR (400 MHz, CDCl3): δ 9.25
(s, 1H), 8.77 (m, 1H), 8.26 (m, 1H), 8.27 (m, 1H), 7.67
(m, 1H), 7.58 (m, 1H), 7.45 (m, 1H), 7.26 (s, 1H);
13C NMR (400 MHz, CDCl3): 162.6, 160.1, 158.7,
154.4, 145.3, 136.6, 132.9, 127.1, 126.4, 122.9, 122.4,
118.2, 116.9, 116.1, 115.9, 113.9; IR (KBr, νmax/cm−1):
1735, 1740, 1218. EI-MS: m/z = 265.4
2.2l 10-Methoxy-6H-chromeno[4,3-b]quinolin-6-one (3l):
White solid. 1H NMR (400 MHz, CDCl3): δ 9.20
(s, 1H), 8.86 (m, 1H), 7.39-7.62 (m, 5H), 7.26 (s,
1H), 3.99 (s, 3H); 13C NMR (400 MHz, CDCl3): 162.7,
159.4, 153.4, 148.7, 147.4, 138.4, 132.7, 130.7, 129.1,
2.2g 10-Bromo-6H-chromeno[4,3-b]quinolin-6-one (3g): 128.2, 126.4, 123.5, 118.9, 117.7, 116.1, 104.6, 54.6;
White solid. 1H NMR (400 MHz, CDCl3): δ 9.17 IR (KBr, νmax/cm−1): 3063,1734, 1735, 1181; EI-MS:
(s, 1H), 8.75 (m, 1H), 8.46 (s, 1H), 7.90 (d, 1H), 7.73 m/z = 277.07.

Catalyst-free synthesis of chromeno[4,3-b]quinolin-6-ones
675
2.2m 10-Methyl-6H-chromeno[4,3-b]quinolin-6-one where the reaction conditions have been either modi-
(3m): White solid. 1H NMR (400 MHz, CDCl3): fied and/or improved using the ultrasound irradiation.25
δ 9.14 (s, 1H), 8.77 (m, 1H), 8.10 (d, 1H), 7.72 We have earlier reported L-proline catalysed three com-
(s, 1H), 7.70 (d, 1H), 7.60 (d, 1H), 7.57 (m, 1H), 7.40 ponent asymmetric Mannich reaction where ultrasoni-
(m, 1H), 2.56 (s, 3H); 13C NMR (400 MHz, CDCl3): cation conditions have efficiently enhanced the rate of
161.3, 152.6, 151.2, 149.5, 144.4, 140.3, 132.1, 129.7, the reaction along with improvement in the yields and
128.9, 128.4, 125.2, 124.8, 119.7, 117.2, 114.9, 22.2; enantioselectivities.26 In view of the enormous potential
IR (KBr, νmax/cm−1): 1735,1737, 2923, 1178; EI-MS: of chromeno[4,3-b]quinolin-6-ones for various biolog-
m/z = 261.26.
ical applications, we have envisaged an operationally
benign catalyst-free protocol for their synthesis under
ultrasound irradiation (scheme 1).
2.2n 10-Methoxy-6H-chromeno[4,3-b]quinolin-6-one
(3n): White solid. 1H NMR (400 MHz, CDCl3):
δ 9.65 (s, 1H), 8.75 (m, 1H), 7.89 (d, 1H), 7.81 (d, 1H),
7.60–7.30 (m, 3H), 7.2 (m, 1H), 4.05 (s, 3H); 13C NMR
(400 MHz, CDCl3): 161.8, 159.4, 153.4, 148.7, 147.4,
138.4, 132.7, 130.7, 129.1, 128.2, 126.4, 123.5, 118.9,
117.7, 116.1, 104.6, 54.6; IR (KBr, νmax/c−1): 1735,
1737, 1178; EI-MS: m/z = 277.27.
First,
4-chloro-3-formylcoumarin
and
p-
methylaniline were subjected to ultrasound irradiation
in various solvents. As shown in table 1 (entries 1–6),
ultrasonication promotes the formation of the fused
chromeno-quinolines 3b in different solvents with
varying reaction rates and yields. The results show that
choice of solvent has profound effect on both the rates
of reaction and yields. While the reaction did not pro-
ceed in water, solvents like dichloromethane and chlo-
roform gave comparatively lower yields (∼30%) after
30 min of ultrasound irradiation. Acetonitrile afforded
60% while methanol afforded 85% of the required
product in 20 and 15 minutes respectively. Ethanol
proved to be the solvent of choice which afforded 95%
of the required product as a white precipitate in 15 min
without the requirement for column purification.
The optimized reaction conditions were further
extended to the reaction of various aniline substrates
possessing diverse electronic features making the pro-
tocol rather general and the results are listed in table 2.
For example, the electron-rich anilines having p-Me,
p-OMe, o-OMe, m-Me, m-OMe functional groups
afforded the respective products in 15 minutes with
yield between 94 and 97% (entries 2, 11–14, table 2).
Similarly, the electron withdrawing p-nitroaniline
afforded the required product in 96% yield (entry 4,
3. Results and discussions
Chromeno[4,3-b]quinolin-6-one derivatives (3a–n) are
important class of chromeno-quinolines and the most
conventional approach for their synthesis involves
the reaction of 4-hydroxycoumarins with anilines
and paraformaldehyde at 220–240◦C under vacuum.19
Tabakovic et al. have reported their synthesis starting
from 4-hydroxycoumarin under Vilsmeier-Haack con-
ditions.20 Asherson et al. have reported their synthe-
sis from 3-((dimethylamino)methyl)-4-hydroxy- 2H-
chromen-2-one and anilines but with lower yields.21
Haber et al. have demonstrated stoichiometric AlCl3
catalysed synthesis of the compounds by using
4-chloro-3-formylcoumarin and aniline in refluxing
tetrahydrofuran.22 Bandyopadhyay et al.23 and Wu
et al.24 have used 4-oxo-4H-chromene-3-carbaldehyde
and 4-chloro-3- formylcoumarin respectively for the
synthesis of the chromeno[4,3-b]quinolin-6-ones. All
the above methods require either Lewis acid catalysts
or high temperatures for their synthesis.
Table 1. Effect of solvents for the synthesis of coumarino-
quinolines from 4-chloro-3-formylcoumarin and aniline.a
Entry
Solvent
Time (min)
Yieldb(%)
NH2
O
O
O
O
N
O
Ethanol
1
2
3
4
5
6
C2H5OH
CH3OH
CH3CN
CH2CL2
CHCl3
15
15
20
30
30
45
95
85
60
+
H
Ultrasound
rt, 15 min
R
Cl
1
30
R
3a-n
2a-n
30
Water
NRc
Scheme 1. Synthesis of fused chromeno-quinolines.
aAll the reactions were carried out using 1 (1.0 mmol), 2b
(1.0 mmol) at room temperature under ultrasound conditions,
bdetermined by 1H NMR.
Recently, ultrasonication methods have gained wide
applicability in several organic synthetic protocols
cNo reaction.

676
J Venkata Prasad et al.
Table 2. Synthesis of chromeno[4,3-b]quinolin-6-ones.
Entry
Anilines
Chromeno-quinoline
Yield (%)a
3a-n
O
O
NH2
1
95
N
2a
3a
O
O
NH2
2
3
97
96
N
2b
3b
O
O
Cl
NH2
N
2c
3c
Cl
O
O
O2N
NH2
4
5
96
95
2d
N
3d
NO2
O
O
Br
NH2
2e
N
3e
Br
O
O
F
NH2
6
7
2f
96
95
N
3f
F
O
O
NH2
Br
2g
N
3g
Br
O
N
O
F
NH2
8
F
2h
96
3h
F
F
table 2). Anilines having various mono- and di- ones within 15 minutes under ultrasonication conditions
substituted halogens also gave satisfactory yields (94– (entries 3, 5–10, table 2). All the products were charac-
96%) for the respective chromeno[4,3-b]quinolin-6- terized by 1HNMR, IR, and EI-Mass analysis and were

Catalyst-free synthesis of chromeno[4,3-b]quinolin-6-ones
Table 2. (continued).
677
Entry
Anilines
Chromeno-quinoline
Yield (%)
3a−n
F
F
O
O
9
NH2
94
N
F
2i
3i
F
F
O
O
NH2
10
11
97
96
N
2j
3j
F
O
O
MeO
NH2
N
2k
3k
OMe
OMe
NH2
O
N
O
12
13
14
95
2l
MeO
O
3l
O
NH2
2m
N
94
95
3m
O
O
NH2
MeO
2n
N
3n
OMe
aYields refer to the precipitated products.
found to be in good agreement with those reported in promoting the cyclization of the aromatic ring to gener-
the literature.22
ate intermediate III. Elimination of the water molecule
A plausible mechanism for the synthesis of 3a–3n in the final step affords fused quinoline products
is proposed in scheme 2. The first step of the reaction 3a–3n. The ultrasound energy in the present protocol
involves nucleophilic attack of aniline on 1 resulting efficiently causes acoustic cavitation, which results in
in the N-alkylation intermediate I. The second step extreme temperatures and pressures on microsecond
involves the activation of the aldehyde group by the time scale causing dramatic influence on the rates of the
in situ generated HCl, which acts as a protic acid reaction.25d

678
J Venkata Prasad et al.
NH2
O
O
O
O
O
O
H+
O
OH
R
-HCl
CHO
II
R
Cl
2a-2n
1
R
I
O
N
O
O
N
O
O
O
-H2O
HCl
OH2
H
OH
R
N
Cl
R
H
R
Cl
3a-3n
IV
III
Scheme 2. Plausible mechanism for the synthesis of chromeno[4, 3-b]quinolin-6-ones.
4. Conclusion
Puschmann H and Howard J A K 2004 J. Fluorine
Chem. 125 661; (e) Bonnet V, Mongin F, Trecourt
F, Queguiner G and Knochel P 2002 Tetrahedron. 58
4429
In conclusion, we have reported an efficient, fast,
catalyst-free ultrasonication methodology for the syn-
thesis of fused chromeno[4,3-b]quinolin-6-one deriva-
tives. The present methodology offers the advantages
of mild reaction conditions, short reaction times; high
yields and avoids the requirement of Lewis acid cat-
alysts. Further, the protocol does not require column
chromatography purification.
8. Al-Haiza M A, Mostafa M S and El-Kady M Y
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The authors thank Mr. A Sankar Rao and Mrs. A
Yesodha, Founder Trustees of Sankar Foundation, for
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