Efficient and general synthesis of 3-aryl coumarins using cyanuric chloride 1

Article abstract of DOI:10.1055/s-0031-1290344

An efficient and general protocol for a rapid synthesis of different substituted 3-aryl coumarins is reported. A series of different substituted phenyl acetic acids have been successfully reacted with different substituted 2-hydroxy benzaldehydes in the presence of cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) and N-methyl morpholine to afford 3-aryl coumarins in good to excellent yields. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1290344

LETTER
611
Efficient and General Synthesis of 3-Aryl Coumarins
Using Cyanuric Chloride1
S
ynthesis of 3-Ary
o
l
Coumarinsneni V. Sashidhara,* Gopala Reddy Palnati, Srinivasa Rao Avula, Abdhesh Kumar
Medicinal and Process Chemistry Division, Central Drug Research Institute, CSIR-CDRI, Lucknow 226 001, India
Fax +91(522)2623405; E-mail: sashidhar123@gmail.com; E-mail: kv_sashidhara@cdri.res.in
Received 22 December 2011
ylpyridinium iodide).16,22 Very recently, Matos et al. have
developed a Pd-catalyzed cross-coupling reaction for the
synthesis of substituted 3-aryl coumarins.23
Abstract: An efficient and general protocol for a rapid synthesis of
different substituted 3-aryl coumarins is reported. A series of differ-
ent substituted phenyl acetic acids have been successfully reacted
with different substituted 2-hydroxy benzaldehydes in the presence
of cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) and N-methyl
morpholine to afford 3-aryl coumarins in good to excellent yields.
Most of the methods for the synthesis of the 3-aryl cou-
marins suffer from low yields and/or long reaction times.
Therefore, in spite of the present methodologies, there is
still a need to explore a versatile synthetic methodology
for the construction of a chemical library of 3-substituted
coumarin derivatives.
Key words: synthesis, 3-aryl coumarins, cyanuric chloride, 2-
hydroxy benzaldehyde
Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine or TCT)
has received considerable attention for the preparation of
alkyl chlorides,24 Beckmann rearrangement products,25
isonitriles,26 bis(indolyl)methanes,27 thiiranes,28 dihydro-
pyridines,29 14-aryl and alkyl-14-H-dibenzo[a,j]xan-
thenes,30 alcohols,31 diazocarbonyl,32 acyl azides,33
hydroxamic acids,34 and acyl chlorides.35 Recently, cya-
nuric chloride has also been used in the Friedel–Craft acy-
lation for the formation of carbonyl compounds in
excellent yield.36 In this paper, we wish to report a very
simple and highly efficient method for the synthesis of 3-
aryl coumarin derivatives, using 2-hydroxy benzalde-
hydes and phenylacetic acid derivatives in the presence of
cyanuric chloride. To the best our knowledge, this is the
Coumarins are an important class of compounds, which
occupy a special role in nature.2,3 The diverse biological
and pharmaceutical properties of natural and synthetic
coumarins as anti-HIV,4 anticoagulant,5 antibacterial,6 an-
tioxidant,7 and anticancer agents8 are well known. In the
last few years our research group has been engaged in the
synthesis of new biologically active coumarins.9 In partic-
ular, the 3-phenylcoumarin scaffold has been the focus of
our most recent studies with some compounds exhibiting
significant antidepressant activity10 and coumestrol (3-
phenylcoumarin) being one of the most important known
phytoestrogens. Furthermore, some 3-phenylcoumarins
have been demonstrated to play an important role in
monoamino oxidase inhibition.11
Table 1 Effect of Reaction Conditions on the Cyanuric Chloride
Mediated Reaction of 1a and 1b
Different synthetic strategies are known in the literature
for the synthesis of substituted 3-aryl coumarins deriva-
tives. The well-known Knoevenagel condensation,12,13
Wittig,14 Pechmann,15,16 and Perkin reactions,17–21 are
some of the synthetic routes commonly used to synthesize
3-aryl coumarins derivatives. Besides these routes, 3-aryl
coumarins were also prepared using DCC, DDQ, NaOH,
POCl3, and the Mukaiyama reagent (2-chloro-1-meth-
Entry
Base (mmol)
Solvent
Time
(min)
Temp
(°C)
Yield
(%)a
1
2
pyridine (3.0)
piperidine (3.0)
Et3N (3.0)
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
MeCN
180
180
180
180
180
180
180
30
110
110
110
110
110
110
110
110
r.t.
30
45
40
30
95
95
83
95
0
3
4
K2CO3 (3.0)
NMM (3.0)
NMM (1.5)
NMM (1.0)
NMM (1.5)
NMM (1.5)
NMM (1.5)
NMM (1.5)
NMM (1.5)
OH
5
O
O
OH
O
6
CHO
cyanuric chloride
O
+
7
base, solvent
temp, time
1a
8
O
1b
1c
9
45
Scheme 1 Reaction between 2-hydroxy benzaldehyde (1a) and
4-methoxy phenyl acetic acid (1b) promoted by TCT
10
11
12
45
60
25
75
46
45
90
SYNLETT 2012, 23, 611–621
x
x
.
x
x
.
2
0
1
1
60
100
Advanced online publication: 10.02.2012
DOI: 10.1055/s-0031-1290344; Art ID: D25011ST
© Georg Thieme Verlag Stuttgart · New York
a Yields after purification by column chromatography.

612
K. V. Sashidhara et al.
LETTER
first example of a cyanuric chloride mediated synthesis of diverse 2-hydroxybenzaldehydes and a variety of pheny-
substituted 3-aryl coumarins.
lacetic acids, and representative examples are summa-
rized in Table 2. 2-Hydroxybenzaldehydes bearing either
electron-withdrawing or electron-donating groups were
converted into the corresponding 3-aryl coumarins in very
short reaction times and in excellent yields (90–99%,
Table 2, entries 1–14). To generalize our reagent system
to more complex systems, we examined several chalcone-
substituted 2-hydroxybenzaldehydes 15a–20a (derived
from the reaction of 4a with appropriate acetophe-
nones),9d which readily underwent smooth conversion un-
der the optimized conditions to afford a wide range of 3-
aryl coumarins 15c–22c, Table 2, entries 15–22) in good
to excellent yields, indicating that this reaction is quite
general and has very broad substrate scopes.
Thus, we demonstrated that 3-aryl coumarin derivative 1c
can be easily synthesized from 2-hydroxy benzaldehyde
(1a) and 4-methoxy phenyl acetic acid (1b), by employing
TCT (use of 1.0 mmol molar ratio gave best results,
Scheme 1). Different sets of conditions (reaction times,
temperatures, base molar ratios, and solvents) were tried
to investigate the efficacy and selectivity of cyanuric chlo-
ride (Table 1).
From Table 1, it is clear that N-methylmorpholine at 1.5
mmol promotes the reaction to produce the desired prod-
uct 3-aryl coumarin 1c in 95% yield (Table 1, entry 8) in
30 minutes. In a brief solvent screen, DMF gave best
yields at a temperature of 110 °C.
With the optimized reaction conditions in hand, we ex-
plored the generality and scope of the reaction by using
Table 2 General Synthesis of Substituted 3-Aryl Coumarins
R4
R3
O
OH
O
R2
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
1c–14c
OH
O
R3
O
OH
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
15c–20c
21c–22c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
OH
OH
CHO
O
1
45
95
1a
O
1c
1b
O
O
O
OH
Br
OH
CHO
O
2
60
90
O
Br
2a
1b
2c
Synlett 2012, 23, 611–621
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LETTER
Synthesis of 3-Aryl Coumarins
613
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
21c–22c
15c–20c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
OH
OH
CHO
O
3
40
30
45
97
96
98
3a
O
3c
1b
O
O
O
OH
OH
CHO
O
4
CHO
O
CHO
4a
1b
4c
O
O
O
OH
OH
CHO
O
5
CHO
OH
O
CHO
5a
1b
5c
O
O
O
OH
CHO
O
6
85
90
O
6a
1b
6c
© Thieme Stuttgart · New York
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K. V. Sashidhara et al.
LETTER
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
15c–20c
21c–22c
Entry
7
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
OH
OH
O
CHO
40
93
1a
2b
7c
O
O
OH
O
OH
CHO
O
8
35
95
O
CHO
4a
CHO
3b
8c
O
O
OH
O
OH
CHO
O
9
45
98
O
CHO
5a
CHO
3b
9c
O
O
O
OH
O
OH
CHO
O
10
30
98
O
CHO
O
4a
CHO
4b
10c
Synlett 2012, 23, 611–621
© Thieme Stuttgart · New York

LETTER
Synthesis of 3-Aryl Coumarins
615
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
21c–22c
15c–20c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
OH
O
OH
CHO
O
11
50
98
O
CHO
O
5a
CHO
4b
11c
O
O
O
O
OH
OH
CHO
O
12
90
92
O
O
6a
12c
4b
O
O
O
OH
O
OH
CHO
O
O
13
40
99
O
O
CHO
O
4a
CHO
5b
13c
O
O
O
O
OH
O
OH
O
CHO
O
14
90
93
O
O
6a
5b
14c
© Thieme Stuttgart · New York
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K. V. Sashidhara et al.
LETTER
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
15c–20c
21c–22c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
O
O
O
O
O
O
OH
15
90
87
O
O
O
1b
15c
7a
O
O
O
OH
O
O
CHO
OH
16
80
89
O
O
O
O
4b
7a
16c
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LETTER
Synthesis of 3-Aryl Coumarins
617
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
21c–22c
15c–20c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
OH
O
O
CHO
O
OH
O
17
75
92
O
O
O
O
5b
7a
17c
O
O
OH
O
O
CHO
OH
18
80
90
O
O
O
O
1b
O
8a
18c
© Thieme Stuttgart · New York
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K. V. Sashidhara et al.
LETTER
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
15c–20c
21c–22c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
O
OH
CHO
O
O
OH
19
85
92
O
O
O
O
O
4b
O
O
O
9a
19c
O
O
O
OH
O
O
CHO
O
OH
O
20
90
94
O
O
O
O
O
O
O
O
5b
O
10a
O
20c
Synlett 2012, 23, 611–621
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LETTER
Synthesis of 3-Aryl Coumarins
619
Table 2 General Synthesis of Substituted 3-Aryl Coumarins (continued)
R4
R3
R2
O
OH
O
CHO
a
R1
R4
R1
R4
R3
R2
1a–6a
OH
1c–14c
OH
O
R3
O
CHO
O
O
CHO
O
O
R2
a
OH
CHO
a
c
b
R5
R6
O
CHO
4a
X
R5
R6
O
X
R7
15a–18a
19a–20a
R7
21c–22c
15c–20c
Entry
Substrate a
Substrate b
Product
Time (min) Yield (%)
O
O
OH
O
CHO
O
O
OH
21
85
91
O
O
O
O
O
4b
O
O
11a
21c
O
O
O
OH
O
CHO
OH
22
90
92
O
O
O
O
S
4b
S
12a
22c
a Reaction conditions: Phenylacetic acid 1b–5b, cyanuric chloride, NMM, DMF, 110 °C, 30–90 min.
b Reaction conditions: Appropriate acetophenone, concd HCl, dioxane, reflux, 2–3 h.
c Reaction conditions: 2-Acetylthiofuran/2-acetyl furan, concd HCl, dioxane, reflux, 2–3 h.
As shown in Table 2, all the substrates participated very A plausible mechanism for the formation of 3-aryl cou-
efficiently in the reaction to afford the desired products in marin derivatives is given in Scheme 2. It is postulated
very short times (30–90 min only) and better yields than that an initial reaction of cyanuric chloride33,36 with N-me-
those reported by earlier methods.21 All compounds were thylmorpholine generates adduct (I), which upon the nu-
characterized through 1H, 13C NMR, MS, and IR spectro- cleophilic attack of the carboxyl group of phenyl acetic
scopic studies.37
acid (2b), leads to the formation of ester (II), that subse-
quently reacts with 2-hydroxybenzaldehyde (1a) to form
© Thieme Stuttgart · New York
Synlett 2012, 23, 611–621

620
K. V. Sashidhara et al.
LETTER
O
O
+
N
Cl
OCOBn
N
HO
Me
Cl–
O
N Me
N
N
N
N
N
DMF
r.t.
Cl
N
Cl
Cl
N
Cl
Cl
N
Cl
I
2b
II
OH
CHO
1a
O
O
O
O
CHO
7c
III
Scheme 2 Plausible mechanism of cyanuric chloride mediated reaction of 2-hydroxy benzaldehydes and phenyl acetic acid
(8) Go, M. L.; Wu, X.; Liu, X. L. Curr. Med. Chem. 2005, 12,
483.
ester (III), which, on consequent intramolecular cycliza-
tion–dehydration, furnishes the 3-aryl coumarin 7c.
(9) (a) Sashidhara, K. V.; Kumar, A.; Kumar, M.; Sonkar, R.;
Bhatia, G.; Khanna, A. K. Bioorg. Med. Chem. Lett. 2010,
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Bhatia, G.; Khanna, A. K. Bioorg. Med. Chem. Lett. 2010,
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In summary, we have developed a simple and efficient
method for the synthesis of substituted 3-aryl coumarins
in good to excellent yields using cyanuric chloride. The
important features of this methodology are shorter reac-
tion times and higher yields compared to previously
known methods and simple experimental procedure.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett. They in-
clude spectral data of all the compounds associated with this article.
(10) Sashidhara, K. V.; Kumar, A.; Chatterjee, M.; Rao, K. B.;
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Acknowledgment
The authors thank the SAIF Division for providing the spectrosco-
pic and analytical data. The authors are grateful to Dr Tushar K.
Chakraborty (Director, CDRI) for his constant support and encou-
ragement. G.R.P, A.S.R and A.K are thankful to CSIR, New Delhi,
India for financial support. This is CDRI communication number
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Synlett 2012, 23, 611–621
© Thieme Stuttgart · New York

LETTER
Synthesis of 3-Aryl Coumarins
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(37) Representative Experimental Procedure for the
Synthesis of 3-(4¢-Methoxy Phenyl) Coumarin (1c)
A mixture of cyanuric chloride (377 mg, 1.0 mmol), NMM
(331 mg, 1.5 mmol), and 4-methoxyphenylacetic acid (1b,
340 mg, 1 mmol) in DMF (5 mL) was stirred at r.t. for 10
min. After this time 2-hydroxybenzaldehyde (1a, 250 mg, 1
mmol) was added. Subsequently, the resulting reaction
mixture was refluxed for 45 min. Completion of the reaction
was monitored by TLC. The reaction mixture was diluted
with H2O (10 mL) and extracted 3 times with EtOAc (15
mL). The combined organic layers were dried over Na2SO4,
filtered, and concentrated to dryness under reduced pressure.
The residue was purified by column chromatography
(Al2O3, 70–230 mesh, neutral, hexane–CH2Cl2) to provide
pure 1c [3-(4¢-methoxyphenyl)coumarin] as a colorless
crystalline solid; yield 95%; mp 146–148 °C. IR (KBr):
3033, 1705, 1633, 1020 cm–1. 1H NMR (300 MHz, CDCl3):
d = 7.75 (s, 1 H), 7.68 (d, J = 8.8 Hz, 2 H), 7.53–7.47 (m, 2
H), 7.36–7.28 (m, 2 H), 6.97 (d, J = 8.8 Hz, 2 H), 3.85 (s, 3
H). 13C NMR (75 MHz, CDCl3): d = 160.8, 160.2, 153.3,
138.5, 131.0, 129.9, 127.9, 127.8, 127.1, 124.5, 119.9,
116.4, 113.9, 55.4. ESI-MS: m/z = 252 [M + H]+.
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L.; Uriarte, E. Tetrahedron Lett. 2011, 52, 1225.
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3413.
© Thieme Stuttgart · New York
Synlett 2012, 23, 611–621

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Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not be copied or
emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.
However, users may print, download, or email articles for individual use.