Molecular iodine catalysed one-pot synthesis of chromeno[4,3-b]quinolin-6-ones under microwave irradiation

Article abstract of DOI:10.1039/c5gc00756a

We demonstrate a facile one pot approach for the regioselective synthesis of chromeno[4,3-b]quinolin-6-one derivatives in excellent yields under microwave (MW) irradiation. This transformation presumably proceeds via a three-component tandem annulation of

Full text of DOI:10.1039/c5gc00756a

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Cite this: DOI: 10.1039/x0xx00000x
Molecular Iodine Catalysed One-Pot Synthesis of
Chromeno[4,3-b]quinolin-6-ones under Microwave
Irradiation*
Received 00th January 20xx,
Accepted 00th January 20xx
Koneni V. Sashidhara,*a Gopala Reddy Palnati a†
,
L. Ravithej Singh a†
, Amit
Upadhyay,c Srinivasa Rao Avula,a Abdhesh Kumar,a Ruchir Kantb
DOI: 10.1039/x0xx00000x
www.rsc.org/
ABSTRACT: We demonstrate a facile one pot approach for santiagonamine 26 and pheofungin A 37 contain this core
the regioselective synthesis of chromeno[4,3- ]quinolin-6-one structure as shown in figure 1.
derivatives in excellent yields under microwave (MW) A major challenge often encountered in the synthesis of
irradiation. This transformation presumably proceeds via these enticing hybrids is the design of highly efficient
b
a
three-component tandem annulation of 4-hydroxycoumarin chemical reaction sequences in a minimum number of
with aromatic aldehydes and aromatic amines, involving a synthetic steps. One such protocol to realize these goals
Povarov type reaction.
involves the use of multi-component reactions, that enable
the creation of several bonds in a single operation and offers
remarkable advantages such as convergence, operational
simplicity, facile automation, reduction in the number of
work-ups, thus rendering the transformations more
environmentally friendly.8
An emerging strategy in the design and synthesis of new
drugs is the combination of two distinct pharmacophores
into a single molecule, well documented as pharmacophore
hybridization.1,2 Since natural products have been the most
consistent source of drug leads, they have become attractive
pharmacophoric components in hybrid molecules.3 The
hybrid approach is a promising path to drug molecules that
are able to modulate multiple targets.4
General strategies for the synthesis of coumarin-quinoline
hybrids rely on lengthy multistep protocols consisting of
unfriendly procedures, resulting in very low overall yields.5,6
Recently, Iaroshenka et al. used 4-chloro-3-(trifluoroacetyl)
coumarin as a novel building block for the synthesis of 7-
(trifluoromethyl)-6H-chromeno[4,3-
two step method.9a While, Jie Wu et al 9b
synthesized -chromeno-[4,3- ]quinolines by using 4-
chloro-2-oxo-2 -chromene-3-carbaldehyde and anilines.
Martinez et al.,10a Weike Su et al 10b and Khan et al 10c
described
b
]quinolin-6-ones in
a
.
and Tabakovic et al.9c
6
H
b
H
.
.
the synthesis of fused coumarin-quinoline hybrids in a two
step sequence. However, some of these are typically
associated with low to no yields with electron withdrawing
groups (26%)10, multiple step reaction sequences, use of toxic
reagents, and complicated by-products. In terms of one pot
synthesis protocol, Khan et al. have reported a one pot
Figure 1. Examples of biologically active coumarin-quinoline
synthesis of chromeno[3,4-b]quinoline derivatives through
hybrids and our synthesized prototype.
Michael initiated ring closure by employing three-component
condensation of aromatic aldehydes, 3-aminocoumarins and
cyclic 1,3 diketones.11 Thus there is great scope to develop a
convenient and general approach towards the synthesis of
Chromeno-quinoline derivatives represent one such unique
class of hybrids found in the framework of several
pharmacologically active compounds and natural products.
For example, these structural frameworks form the integral
part of the non steroidal progesterone receptor modulators
coumarin fused quinoline hybrids (Figure 1,
4) from
inexpensive, non-toxic and readily available reagents with
improved yields in an eco-friendly fashion. As a part of our
such as 1 5
. In addition, many natural products including
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ongoing efforts to develop cost effective and simpler new delight, we observed that only iodine can efficiently catalyse
methodologies for the synthesis of hybrid the reaction to furnish 7-(4-chlorophenyl)-9-methyl-6H-
pharmacophores,12,13 we wish to report herein a simple and chromeno[4,3-
]quinolin-6-one 8abh
In an VaietwteArmticlpetOnlitnoe
convenient synthesis of coumarin fused quinoline hybrids via evaluate the catalytic efficiency of iodine, we carried out the
one-pot three-component tandem annulation of 4- reaction with -toluidine 5b, 4-hydroxycoumarin 6a and 4-
b
.
DOI: 10.1039/C5GC00756A
a
p
hydroxycoumarin with aromatic aldehydes and aromatic chlorobenzaldehyde 7h in acetic acid in the presence of
amines using molecular iodine as an efficient catalyst various equivalents of iodine. The reaction occurred most
(Scheme 1). To the best of our knowledge, this is the first one efficiently with 10mol% iodine under MW conditions at 165
pot report for the synthesis of chromeno[4,3-
ones.
b
]quinolin-6- °C (Table 2, entry 16). However, in the absence of iodine
(Table 2, entry 18), poor yields were observed even after
prolonged heating, clearly indicating that molecular iodine is
Molecular iodine has recently received much attention due to essential to facilitate the reaction (Scheme 2).
its low-cost, nontoxic, ready availability, easy handling, and
Table 2. Optimization of MW reaction conditions.a
for affording the corresponding products in excellent yields
with high selectivity.14 In an attempt to carry out the union of
S.No
Solvent
Catalyst (eq)a Time
(mins)
Yield
(%)b
65
85
45
18
55
85
78
p
-toluidine
(5b), 4-hydroxycoumarin
(
6a
)
and 4-
chlorobenzaldehyde (7h), molecular iodine in acetic acid
15
16
17
18
19
20
21
CH3COOH
CH3COOH I2 (10mol%)
I2 (5mol%)
30
30
15
15
15
30
30
under microwave irradiation was investigated (scheme 1).
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
I2 (10mol%)
No catalyst
I2 (20mol%)
I2 (20mol%)
I2 (0.5)
Scheme 1. Synthesis of chromeno[4,3-b]quinolin-6-one.
aReaction conditions:
p
-toluidine
(
5b)
(1 mmol), 4-
hydroxycoumarin (6a) (1 mmol), 4-chlorobenzaldehyde (7h) (1
mmol), catalyst, in 1mL solvent, MW irradiation, 165 °C.
b Isolated yields.
After determining the amount of catalyst, we further
evaluated the reaction with various solvents (Table 1, entry
10-12) but the yields were found to be better in acetic acid
only. With a set of optimized conditions in hand, we next
examined the scope of this cyclization process (Scheme 1).
Table 1. Optimization of reaction conditions.a
S.No
Solvent
Catalyst (eq)a Time
(hrs)
Yield
(%)b
75
0
10
12
10
10
79
18
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
DMF
I2 (0.5)
BF3.OEt2(0.5)
SnCl2(0.5)
Bi(NO2)3(0.5)
AlCl3(0.5)
CuI(0.5)
I2(20mol%)
AuCl3(0.5)
Ag(OTf)(0.5)
I2 (0.5)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Dioxane
TFA
CH3COOH
CH3COOH
I2 (0.5)
I2 (0.5)
I2 (10mol%)
I2 (5mol%)
10
0
85
62
aReaction conditions: p-toluidine (5b) (1 mmol), 4-hydroxycoumarin
(6a) (1 mmol), 4-chlorobenzaldehyde (7h) (1 mmol), catalyst in
5mL solvent at 110 °C. b Isolated yields.
The compound 8abh having
a
skeleton of 7-(4-
]quinolin-6-one,
chlorophenyl)-9-methyl-6H-chromeno[4,3-
b
was formed as the sole product in albeit moderate yield. This
interesting result prompted us to further investigate the
reaction. To find the optimal reaction conditions, we
screened a large number of Lewis acid catalysts (Table 1,
entry 1-9) but left out without much success. Much to our
2 | J. Name., 2012, 00, 1-3
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Reaction conditions: aromatic amine (5) (1 mmol), 4-
hydroxycoumarin (6a) (1 mmol), aromatic aldehyde (7) (1 mmol),
catalyst, in 1mL solvent, MW irradiation, 16D5O°IC: 1.0.1039/C5GC00756A
Scheme 2. Controlled experiments.
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The effect of substituents on the arene of aldehyde undergoing
the cyclization reaction was first examined. This aromatic ring was
found to be tolerant to both electron-rich groups, such as methyl
(8abe), isopropyl (8abd), methoxy (8ahc), dimethoxy (8abb) and
trimetoxy (8aba) and electron deficient groups, such as cyano
(8abj), nitro (8abk) and trifluoromethyl (8abl) (scheme 3). Notably,
the halogen containing motifs, such as fluro (8abg), chloro (8abh),
and bromo (8abi) worked well in this transformation. It is
noteworthy that even heteroaromatic aldehyde, such as 3-
thiophene (scheme 5, 8abm), could also be employed to give the
chromeno[4,3-b]quinolin-6-one product in good yield. Also, the
presence or absence of the methyl substituent on the coumarin
moiety had no effect on the yield and reaction time (scheme 5,
8bbe and 8cbe). Similarly, a variety of aromatic amines (scheme 4)
were also successfully reacted under the same reaction conditions.
However, aliphatic amines and aliphatic aldehydes failed to
undergo the rearrangement. The structure of chromeno[4,3-
b]quinolin-6-ones was assigned on the basis of 1D (1H, 13C), 2D
NMR, IR and mass spectrometry analysis. In addition, the structure
was unambiguously confirmed by X-ray diffraction analysis of
compound 8abh (Figure 2). The most plausible mechanism
pathway for chromeno[4,3-b]quinolin-6-one is depicted in Scheme
6. The first step is the condensation of aldehyde 7h and aromatic
amine 5b which gave Schiff base a. The nucleophilic attack of
coumarin 6a on imine a resulted in unstable adduct b. The adduct
b then underwent rearrangement via transition states (c, d, and e)
to give adduct f, which on 1,3-H shift give thermodynamically
stable g,10c which on subsequent oxidation in presence of iodine
furnished the desired final product 8abh. This hypothesis was
supported by controlled experiments (scheme 2), as it was found
that the isolated Schiff base a and intermediate g were readily
converted into the desired final product 8abh under the
optimized reaction conditions (scheme-2a and 2c).
Reaction conditions:
hydroxycoumarin (6a) (1 mmol), 4-chlorobenzaldehyde (7h) (1
mmol), catalyst, in 1mL solvent, MW irradiation, 165 °C.
p
-toluidine
(
5b
)
(1 mmol), 4-
Scheme 3. Scope of different aldehydes under optimized
reaction conditions.
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Scheme 4. Scope of different amines under optimized
Scheme 6. Mechanistic proposal for the formation of
chromeno[4,3-b]quinolin-6-one 8abh.
reaction conditions.
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R1
DOI: 10.1039/C5GC00756A
O
NH2
CHO
O
CHO
O
R2
I2 / CH3COOH
O
or
OH
165 oC, MW, 30 min.
S
R1
7b,c,e,g
N
R2
6a-6
c
R3
5a-j = F,Br,Cl,NO2,H,
8
C2 H5 ,CH(CH3
CH3,C(CH3)3 ,OCH3,
)
2
R3
7m
6a-c= H,6-CH3
8-CH3
CH3
F
OCH3
OCH3
O
O
O
O
Br
Cl
F
O2
N
O
O
O
O
N
N
N
N
8 ajc 84%
8 ahg 82%
8 aic 88%
8 age 88%
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
O
O
O
O
(H3C)3
C
C2H5
H3
C
O
O
O
O
N
N
8 afc 91%
CH3
N
N
8 aeb 94%
8 abc 85%
8 acb 92%
OCH3
OCH3
O
O
H3CO
(H3C)2HC
O
O
N
8 aae 88%
N
8 adb 91%
Reaction conditions: aromatic amine (5) (1 mmol), 4-
hydroxycoumarin (6a) (1 mmol), aromatic aldehyde (7) (1 mmol),
catalyst, in 1mL solvent, MW irradiation, 165 °C.
In conclusion, we have established a novel protocol for the
construction of a series of chromeno[4,3- ]quinolin-6-ones
b
from aryl amines, aryl aldehydes, and 4-hydroxy coumarin
under MW conditions by using molecular iodine as the sole
catalyst. The developed process may find application in the
synthesis of diverse libraries of hybrid drug like scaffolds. This
strategy is an effective method to construct a complex core in
Scheme
5.
Diversified
CH3
chromeno[4,3-b]quinolin-6-ones.
CH3
OCH3
S
O
O
O
O
H3
C
H3C
H3C
Br
O
O
O
O
CH3
N
a single operation from simple starting materials and
N
N
N
8 agc 86%
8 abm 85%
environmentally benign oxidant in an eco-friendly fashion.
8 cbe 90%
8 bbe 92%
CH3
Acknowledgement
Authors are grateful to Director, CSIR-CDRI for his constant
support and encouragement, Dr. S. P. Singh for technical
support, SAIF for NMR, IR, and Mass spectral data. The CSIR,
New Delhi, is thanked for the award of Senior Research
Fellowship to G.R.P, L.R.S, A.S.R. and A.U is thankful to the
Department of Pharmaceuticals, Ministry of Chemicals and
Fertilizers, Government of India. We acknowledge the
financial support of CSIR network project BSC00102
(THUNDER). We thank Dr. Tejender S. Thakur of Molecular and
Structural Biology Division, CSIR-Central Drug Research
Institute for supervising the X-ray Data collection and
structure determination of our compound reported in this
paper. This is CDRI communication number 8989.
Notes and references
b
aMedicinal and Process Chemistry Division and Molecular and Structural
Biology Division, CSIR-Central Drug Research Institute, BS-10/1, Sector 10,
Jankipuram extension, Sitapur Road, P.O. Box 173, Lucknow 226031, India.
cMedicinal Chemistry, National Institute of Pharmaceutical Education and
Research (NIPER), Raebareli 229 010, India.
Figure 2. ORTEP diagram of compound 8abh.
†These authors contributed equally.
4 | J. Name., 2012, 00, 1-3
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*Part XIV in the series, “Studies on Novel Synthetic Methodologies”.
*Tel: +91 9919317940; fax: +91 522 2771942;
M. N. Khan, S. Pal, S. Karamthulla and L. H. Choudhury, New
J. Chem., 2014, 38, 4722-4729.
E-mail: sashidhar123@gmail.com, kv_sashidhara@cdri.res.in.
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DOI: 10.1039/C5GC00756A
$Electronic
Supplementary
DOI: 10.1039/b000000x/
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DOI: 10.1039/C5GC00756A
Table of contents:
A one pot protocol for the generation of diverse libraries of medicinally important chromeno[4,3-
b]quinolin-6-one hybrids is presented.