Efficient route to highly functionalized chalcone-based pyranocoumarins via iodine-promoted michael addition followed by cyclization of 4-hydroxycoumarins

Article abstract of DOI:10.1080/00397911.2012.763099

Molecular iodine is used as an efficient promoter in the regioselective synthesis of highly functionalized chalcone-based pyranocoumarin derivatives using 4-hydroxycoumarin in acetic acid solvent at 100 °C. Under optimized reaction conditions, our protoco

Full text of DOI:10.1080/00397911.2012.763099

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Efficient Route to Highly Functionalized
Chalcone-Based Pyranocoumarins via
Iodine-Promoted Michael Addition
Followed by Cyclization of 4-
Hydroxycoumarins
Naseem Ahmed a & B. Venkata Babu a
a Department of Chemistry , Indian Institute of Technology Roorkee ,
Roorkee , Uttarakhand , India
Accepted author version posted online: 18 Jun 2013.
To cite this article: Naseem Ahmed & B. Venkata Babu (2013) Efficient Route to Highly Functionalized
Chalcone-Based Pyranocoumarins via Iodine-Promoted Michael Addition Followed by Cyclization of 4-
Hydroxycoumarins, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 43:22, 3044-3053, DOI: 10.1080/00397911.2012.763099
To link to this article: http://dx.doi.org/10.1080/00397911.2012.763099
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Synthetic Communications1, 43: 3044–3053, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.763099
EFFICIENT ROUTE TO HIGHLY FUNCTIONALIZED
CHALCONE-BASED PYRANOCOUMARINS VIA
IODINE-PROMOTED MICHAEL ADDITION FOLLOWED
BY CYCLIZATION OF 4-HYDROXYCOUMARINS
Naseem Ahmed and B. Venkata Babu
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee,
Uttarakhand, India
GRAPHICAL ABSTRACT
Abstract Molecular iodine is used as an efficient promoter in the regioselective synthesis of
highly functionalized chalcone-based pyranocoumarin derivatives using 4-hydroxycoumarin
in acetic acid solvent at 100 ꢀC. Under optimized reaction conditions, our protocol (Michael
addition followed by intermolecular cyclization) has tolerance for many functional groups
and gave products in good to excellent yields (75–98%) within 1–2 h.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource: Full
experimental and spectral details.]
Keywords Annulation reaction; chalcones-based pyranocoumarins; 4-hydroxycoumarin;
Michael addition; molecular-iodine promoter
INTRODUCTION
Functionalized pyranocoumarins are an important class of oxygen-containing het-
erocyclics. They have shown various biological and pharmaceutical applications[1–3]
such as antipsoriasis,[1a] anti–mycobacterium tuberculosis,[2a] anti-inflammatory,
antiviral hepatitis,[2b] anticytotoxic,[2b] antifungal,[2c] anticoagulant, insecticidal,
anticancer,[3a] antibacterial,[3b] antitumor,[3d] anti-HIV,[3e] and antiproliferative[3g]
Received October 10, 2012.
Address correspondence to Naseem Ahmed, Department of Chemistry, Indian Institute of
Technology Roorkee, Roorkee 247 667, Uttarkhand, India. E-mail: nasemfcy@iitr.ernet.in
3044

CHALCONE PYRANOCOUMARINS
3045
Figure 1. Biologically active pyranocoumarin derivatives.
applications. Many pyranocoumarins are natural products and widely distributed in
higher plants such as Calophyllumlanigerium, Calophyllumteysmannii, Zanthoxylumchi-
loperone, and Meliaceae trees. These natural products are used as versatile motifs in the
synthesis of useful organic compounds as well as natural products and semisynthetic
derivatives of natural products for better pharmaceutical,[4a] medicinal,[4b] and photo-
chromic[4c] properties. They are found as core structures in many natural products such
as ferprenine,[5a] ethuliacoumarin A,[5b] pterophyllin-III,[5c] cyclocoumarol,[5d] and nor-
bothrioclinin, and bothrioclinin.[5f] These natural products were found to be potent
anticoaglent, anti-HIV, and antiproliferative agents (Fig. 1).
Generally, synthesis of functionalized pyranocoumarin derivatives is difficult.
Therefore, development of facile and convenient methods for synthesis has attracted
great attention from synthetic chemists because of biological importance. During
pyranocoumarin synthesis, typically C–C bond formation followed by cyclization
takes place, where chemists face problems in selecting efficient catalyst for regioselec-
tive products, unavailable precursors, expensive and toxic reagents, poor yield, and
longer reaction time. Recently, Palmisano et al. synthesized regioselective pyrano-
coumarin derivatives via hetero-Diels–Alder reaction (HDA). This method failed
to synthesize pyranocoumarins because of lack of starting materials such as diene
and dienophile derivatives.[5e] Similarly, Lin et al. reported pyranocoumarin syn-
thesis with an I2-H2SO4 system[6] and Berger and Haak used a ruthenium complex
system.[7] However, both protocols have drawbacks as moderate yield and poor sel-
ectivity in the product. Lin et al. further reported a modified method using
2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)–mediated oxidative cross-coupling
reaction, but it yielded poor regioselectivity.[8] Zhiwei et al.[9] and Moreau et al.[10]
reported regioselective synthesis of pyranocoumarins using 4-hydroxycoumarins
and a, b-unsaturated aldehydes, but the catalyst is commercially unavailable. Simi-
larly, other methods are also available for the synthesis of pyranocoumarins using
4-hydroxycoumarins and a, b-unsaturated aldehydes[11] and ketones.[12] However,
the selectivity and toxicity of the reagents are major problems. Majumdar et al.[13]
prepared dihydropyranocoumarin derivatives from 4-prop-2-ynyloxy coumarin via
a thiol-mediated radical reaction in a regioselective manner where reactants are
commercially not available. Yunkui et al.[14] also synthesized functionalized pyrano-
coumarins in a selective approach using a gold(III) catalyst along with silver triflate.

3046
N. AHMED AND B. VENKATA BABU
In this protocol, drawbacks such as expensive catalyst, poor yield, and poor
regioselectivity have been observed.[15] Further, Sarma et al. prepared pyranocou-
marins using cerium(IV) ammonium nitrate (CAN)–mediated oxidative addition
of 4-hydroxycoumarin to 2-methyl-3-buten-2-ol, which gave good selectivity of
Michael addition but poor yield during pyran ring formation.[15b] Therefore, there
is still a need to develop efficient and selective reaction protocols with broader sub-
strate scope in the synthesis of functionalized pyranocoumarins.
Molecular iodine has received considerable attention as an inexpensive, less
toxic, environmentally compatible, selective, cheap, and readily available catalyst
in various organic transformations because of its moderate Lewis acidity and water
tolerance.[16] However, the catalytic action has not been completely investigated
from a mechanistic point of view[17] and compatibility with many substrates is unde-
termined. In recent papers,[18] iodine was proposed as a very efficient catalyst in the
Mukaiyamaaldol reaction of 2-(trimethylsilyloxy)furan with aromatic and aliphatic
aldehydes, selective and efficient conjugate additions of pyrrole to nitro-olefins, or a,
b-unsaturated ketones, novel multicomponent reactions (MCRs), and domino reac-
tion strategy for heterocyclic synthesis; meso-substituted porphyrins synthesis;[19]
air-mediated tandem condensation; imino-Diels–Adler; isomerization; oxidation of
simple and readily available amines, aldehydes, alkynes, and disulfidation reactions;
protection of carbonyl and hydroxyl groups; oxidation of benzylic alcohols; cycload-
dition; and aromatization of a, b-unsaturated ketones.[19b]
Based on these advantages of iodine as a catalyst=promoter and our interest in
Lewis acid catalysis for Michael addition and annulation reactions during hetero-
cycle synthesis,[20] we herein report an efficient and regioselective method for the
synthesis of biologically important and highly functionalized pyranocoumarin deri-
vatives using easily available 4-hydroxycoumarins and chalcones in the presence of
molecular iodine promoter in acetic acid solvent at 100 ꢀC.
Different chalcones were prepared following literature procedure.[21] Initially,
we tried MgO, SnCl4, SnCl2 ꢁ 2H2O, TaCl5, LaCl3, ZnO, CuO, BiNO3, CuO, LaCl3,
and TiCl4 as Lewis acid catalysts varying 10–100 mol% in different solvents (tetrahy-
drofuran [THF], toluene, dimethylosulfoxide (DMSO), dimethylformomide (DMF))
from room temperature to reflux temperature for 30 h. We failed to get the product
(footnotes in Table 1). Use of AcOH as a catalyst in these solvents gave 5% product
yield (entry 1, Table 1). Then, we tried the reaction in neat acetic acid (used as cata-
lyst and solvent) at room temperature as well as reflux temperature and we got
enhanced product yield (12%) at reflux temperature (entry 2, Table 1). However,
on adding iodine (2–50 mol%) in the reaction mixture at 100 ꢀC, we got a better yield
(up to 60%) (entries 3–8, Table 1). Further, when we increased catalyst loading
(100 mol%) at room temperature, we got poor yield (5%) (entry 9, Table 1). How-
ever, we serendipitously got an excellent yield (98%) within 30 min at 100 ꢀC (entry
10, Table 1). Further increase in catalyst loading (120–200 mol%) gave no difference
in the reaction time or product yield (entry 11, Table 1).
In the optimized reaction conditions, we used 4-hydroxycoumarins such as
6-methyl-4-hydroxycoumarin, 6-bromo-4-hydroxycoumarin, and 6-chloro-4-hydro-
xycoumarin derivatives[22] (entries 20–28, Table 2); different A-ring substituted
chalcones as electron-releasing groups such as methyl and halogens, electron-
withdrawing groups such as nitro, B-ring substituted chalcones as 3-position

CHALCONE PYRANOCOUMARINS
3047
Table 1. Optimization condition of compound 2
No.
1
Catalyst
AcOH
Solvent
Moles (%)
10–20
Temperature
Reflux
Time (h)
30
Yield (%)
5
THF=toluene=
DMSO=DMF
AcOH
2
3
—
I2
I2
I2
I2
I2
I2
I2
I2
I2
—
2
rt–100 ꢀC
100 ꢀC
100 ꢀC
100 ꢀC
100 ꢀC
100 ꢀC
100 ꢀC
Rt
30
30
30
30
30
30
30
30
0.5
0.5
12
10
15
20
32
43
60
05
98
98
AcOH
AcOH
4
5
10
5
AcOH
AcOH
6
25
40
7
AcOH
AcOH
8
50
9
AcOH
AcOH
AcOH
100
100
120–200
10
11
100 ꢀC
100 ꢀC
Note. MgO, ZnO, CuO, LaCl3, BiNO3, SnCl4, SnCl2ꢁ2H2O, TaCl5, LaCl3, CuBr2, and TiCl4: no product
obtained.
electron-withdrawing groups; 4-position electron-releasing groups such as methoxy,
methyl, dimethyl, and thiomethyl, and poor releasing group such as halides, which
furnished the respective products in moderate to excellent yields (75–98%)
(Scheme 1, path I). The methoxy group–substituted chalcones gave moderate yield
because of inductive effects on Michael addition, and thiophenechalcone and nitro
group also gave moderate yield; however, other groups have no substitution effects.
In all these cases, entries 1–28 in Table 2, 1,4-Micheal addition followed by annu-
lation reaction (cyclization) and dehydration gave a single product with good regios-
electivity and good to excellent yield. However, the reaction of 4-hydroxycoumarins
with 20-hydroxychalcones gave flavanones instead of pyranocoumarins, even
prolonging the reaction time (Scheme 1, path III). Here, iodine-promoted reaction
in acetic acid at refluxed temperature further enhanced the flavanone formation.[23]In
the case of protected 20-hydroxychalcone, we got the desired product (entry 33,
Table 2). Similarly, 20-aminochalcones gave no product, which might be due to pro-
tonation of amino group that forbade the Michael addition reaction (entry 34,
Table 2). However, protected 20-aminochalcones gave the desired product
(Scheme 1, path II) (entry 34, Table 2).
All products 1–28 were well characterized by infrared (IR), 1H and 13C NMR,
and mass spectrometry (electrospray ionization) [MS (ESI)] and compared with the
literature.[6,15] For example, 4-(4-chlorophenyl)-2-phenylpyrano[3,2-c]chromen-
5(4H)-one (2) had IR peaks at [nmax(KBr, cmꢂ1)] 1720 cmꢂ1, indicating a carbonyl
1
group; and 2979, 2861 cmꢂ1, indicating aromatic C-H stretching. The H NMR
(CDCl3, 500 MHz) spectum at d 5.46 (d, J ¼ 5.0 Hz, 1H) showed C-3 proton of pyran
=
ring (Ar-C CH-CH-Ar), and peak at d 4.59 (d, J ¼ 5.0 Hz, 1H) showed C-4 proton
of pyran ring (Ar-C CH-CH-Ar). The 13C NMR (CDCl3, 125 MHz) spectrum gave
=
peak at d 161.2 ppm for the characteristic carbonyl carbon of coumarin ring and
35.09 ppm for C-4 carbon of pyran ring[6,15] (Ar-C CH-CH-Ar), also confirmed
=
by peak in MS-ESI (m=z): [Mþ þ Na] of C24H15ClO3: 409.0. Similarly,
2-(3,4-dimethylphe-nyl)-9-methyl-4-phenylpyrano[3,2-c]chromen-5(4H)-one
(26)
had IR peaks at [nmax(KBr, cmꢂ1)] 1705 cmꢂ1, indicating a carbonyl group, and

3048
N. AHMED AND B. VENKATA BABU
Table 2. Different derivatives of pyranocoumarins
R
Ar1
Ar2
Pyrano coumarin
Rxn. time (min)
Yield (%)a
H
Ph
Ph
Ph
4-Cl-Ph
4-Br-Ph
4-OMe-Ph
3-NO2-Ph
Ph
1
2
50
45
98
98
H
H
Ph
Ph
3
50
96
90
H
4
100
90
H
Ph
4-Cl-Ph
5
90
95
H
6
50
55
H
4-Cl-Ph
4-Cl-Ph
4-Br-Ph
4-Me-Ph
4-OMe-Ph
Ph
7
94
90
H
8
100
100
60
H
4-Cl-Ph
4-Br-Ph
9
87
95
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
H
4-Br-Ph
4-Br-Ph
4-Br-Ph
4-Cl-Ph
4-Me-Ph
4-OMe-Ph
4-Me-Ph
Ph
55
90
96
92
H
H
95
90
89
90
H
4-NO2-Ph
3,4-(di Me)-Ph
3,4-(di Me)-Ph
3,4-(di Me)-Ph
3,4-(di Me)-Ph
4-(SMe)-Ph
4-(SMe)-Ph
Ph
H
60
70
91
90
H
4-Cl-Ph
4-Me-Ph
3-NO2-Ph
4-Cl-Ph
4-Me-Ph
Ph
H
75
90
89
H
100
100
100
50
H
87
85
H
Br
Br
Br
Br
Me
Me
Me
Cl
H
95
95
Ph
4-Cl-Ph
4-Me-Ph
4-Cl-Ph
4-Cl-Ph
Ph
55
95
4-(SMe)-Ph
3,4-(di Me)-Ph
Ph
86
88
95
60
92
90
3,4-(di Me)-Ph
4-Cl-Ph
Ph
70
80
2-Thiophene
4-Cl-Ph
Ph
80
70
93
2-OH-Ph
2-OH-Ph
2-NH2-Ph
2-NH2-Ph
2-OMe-Ph
2-NHCOCH3-Ph
100
100
100
100
80
NRb
NRb
NRb
NRb
83a
75a
H
4-Br-Ph
Ph
H
H
4-Cl-Ph
4-Br-Ph
4-Cl-Ph
H
H
100
aIsolated yield.
bNo reaction (NR).
2939, 2880 cmꢂ1, indicating aromatic C-H stretching. The 1H NMR (CDCl3,
500 MHz) spectum at d 5.68 (d, J ¼ 5.0 Hz, 1H) showed a C-3 proton of the pyran
=
ring (Ar-C CH-CH-Ar), a peak at d 4.60 (d, J ¼ 5.0 Hz, 1H) of the C-4 proton of
=
pyran ring (Ar-C CH-CH-Ar), and peaks at d 2.49 (s, 3H), 2.26 (s, 3H), and 2.20
(s, 3H) of three methyl groups on aromatic rings. The 13C NMR (CDCl3,
125 MHz) gave a peak at d 161.8 ppm for the characteristic carbonyl carbon of cou-
marin ring, 36.06 ppm for C-4 carbon of the pyran ring[6,15] (Ar-C CH-CH-Ar), and
=

CHALCONE PYRANOCOUMARINS
3049
Scheme 1. Synthesis of pyranocoumarin derivatives.
peaks at 21.1, 20.0, and 19.7 for three methyl carbons, also confirmed by peaks in
ESI-MS (m=z) [Mþ.þNa] of C27H22O3, 417.0. Similarly, other derivatives 1, 3–25,
and 27, 28 were confirmed by their spectral analysis and compared with literature
(see the experimental section), and products 29–33 were confirmed by ESI-MS
molecular ion peak. Finally, the structure of one of the representative compounds,
2,4-diphenylpyrano[3,2-c]chromen-5(4H)-one (1) was confirmed unambiguously
by single-crystal x-ray diffraction analysis (see the supplementary data) (CCDC-
895196) (Fig. 2).
Figure 2. ORTEP diagram of 2,4-diphenylpyrano[3,2-c] chromen-5(4H)-one (1a) (CCDC-895196).
(Figure is provided in color online.)

3050
N. AHMED AND B. VENKATA BABU
Scheme 2. Plausible mechanism.
A plausible mechanism is proposed in Scheme 2, where molecular iodine
ligated with chalcone (II) activates Michael addition with 4-hydroxycoumarin (I)
and forms a 1,5-diketone (III) intermediate. The unstable intermediate is equili-
brated in keto-enol (IV) forms. Further, the intermediate undergoes intramolecular
cyclization by the loss of a water molecule to form the desired product (V).
CONCLUSION
In conclusion, we have developed a molecular iodine–promoted efficient and
regioselective synthetic method for highly functionalized pyranocoumarin deriva-
tives in good to excellent yield from 4-hydroxycoumarin and chalcone derivatives
in AcOH solvent at 100 ꢀC. Our protocol has synthesized functionalized pyranocu-
marins and has advantages over previous methods such as cheap catalyst, nontoxic
and commercially available substrates, economic viability, and environmental
compatibility.
EXPERIMENTAL
Commercially available reagents were used without further purification unless
mentioned. All reactions were monitored by thin-layer chromatography (TLC) using
precoated silica-gel aluminum plates with GF254 silica (Spechrochem, Mumbai).
Visualization of TLC plates was accomplished with an ultraviolet lamp at 254 nm
or in an iodine chamber. Melting points were recorded on a perfit apparatus and
are uncorrected. IR spectra of the compounds were expressed as wavenumbers
1
(cmꢂ1). H and 13C NMR spectra were recorded at 500 and 125 MHz, respectively.
1H NMR spectra were recorded in CDCl3 solvent and an internal standard as
1
tetramethylsilane (TMS). Chemical shifts of H NMR spectra were given in parts
per million (ppm) and the coupling constant J was measured in hertz. Data are
reported as follows: chemical shifts (d), multiplicity (s ¼ singlet, d ¼ doublet,
t ¼ triplet, q ¼ quartet, m ¼ multiplet, dd ¼ double doublet). Mass spectra were
recorded by ESI-MS. The x-ray data collection were performed on a Bruker Kappa
Apex four circle-CCD diffractometer using graphite monochromated MoKa
˚
radiation (k ¼ 0.71073 A) at 100 K. Images were created in the crystal lattice with
Diamond software.
General Procedure: Synthesis of Pyrano[3,2-c]coumarin
A mixture of a selected chalcone (0.5 mmol), 4-hydroxycoumarin (0.5 mmol),
and iodine (0.5 mmol) was dissolved in 2–3 mL acetic acid. Then, the mixture was

CHALCONE PYRANOCOUMARINS
3051
stirred under reflux at 100 ꢀC for the time indicated in Table 1. The reaction mixture
was cooled to room temperature and diluted with water, followed by Na2S2O3ꢁH2O
solution to quench excess iodine. The reaction mixture was filtered invacuo, and the
residue was purified by column chromatography on silica gel (100–200mesh) using
hexane=EtOAc (10:2 to 10:1, v=v) as eluent to give the pure product.
Selected Spectral Data
2,4-Diphenylpyrano[3,2-c]chromen-5(4H)-one(1) (Table 2). White solid;
)
yield: 0.172 g (98%); mp ¼ 168–170 ꢀC (lit.[14] mp 173–175 ꢀC); IR nmax (KBr, cmꢂ1
1
=
2949, 2860 (aromatic C-H str), 1709 (C O str); H NMR (500 MHz, CDCl3) d
(ppm): 8.01 (d, J ¼ 8.0 Hz, 1H), 7.73–7.70 (m, 2H), 7.59–7.55 (m, 1H), 7.46–7.40
(m, 6H), 7.35–7.28 (m, 4H), 5.83 (d, J ¼ 5.0 Hz, 1H), 4.72 (d, J ¼ 4.5 Hz, 1H); 13C
NMR (125 MHz, CDCl3) d (ppm): 161.4, 155.8, 152.8, 147.0, 143.6, 132.7,
132.0,129.3, 128.7 (2C), 128.6 (2C), 128.5 (2C), 127.2, 124.7 (2C), 124.2, 122.7,
116.8, 114.6, 103.8, 103.7, 36.7; ESI-MS m=z (%) C24H16O3: 375 (100) [M þ Na].
2-(4-Nitrophenyl)-4-p-tolylpyrano[3,2-c]chromen-5(4H)-one (14) (Table 2).
Light yellow solid; yield: 0.184 g (90%); mp ¼ 235–237 ꢀC; IR nmax (KBr, cmꢂ1) 2983,
1
2891 (aromatic C-H str), 1724 (C O str), 1545 (-NO2str); H NMR (500 MHz, CDCl3)
=
d (ppm): 8.32 (d, J¼ 7.0 Hz, 2H), 8.0 (d, J ¼ 7.0 Hz, 1H), 7.90–7.88 (m, 2H), 7.60 (m,
1H), 7.42 (m, 2H), 7.35 (m, 2H), 7.14 (d, J ¼ 7.0 Hz, 2H), 6.05 (d, J ¼ 5.0 Hz, 1H),
4.72 (d, J ¼ 5.0 Hz, 1H), 2.31 (s, 3H); 13C NMR (125 MHz, CDCl3) d (ppm):
161.1, 155.3, 152.8, 147.8, 144.9, 139.8, 138.6, 137.4, 132.3, 129.5, 128.3 (2C),
127.3 (2C), 125.3 (2C), 124.4 (2C),124.2, 124.1, 122.5, 117.2, 117.0, 114.2, 107.2,
103.6, 36.4, 21.1; ESI-MS m=z (%) C25H17NO5: 412(100) [M þ H].
9-Bromo-2,4-diphenylpyrano[3,2-c]chromen-5(4H)-one(21)(Table2). Light
yellow solid; yield: 0.204 g (95%); mp ¼ 220–222 ꢀC; IR nmax (KBr, cmꢂ1) 2992, 2851
1
=
(aromatic C-H str), 1719 (C O str); H NMR (500 MHz, CDCl3) d (ppm): 8.10 (d,
J ¼ 6.0 Hz, 1H), 7.71 (m, 2H), 7.65 (dd, J ¼ 2.0, 7.0 Hz, 1H), 7.49–744 (m, 3H), 7.32
(m, 3H), 7.28 (m, 2H), 7.23 (m, 2H), 5.84 (d, J ¼ 5.0 Hz, 1H), 4.70 (d, J ¼ 5.0 Hz,
1H); 13C NMR (125 MHz, CDCl3) d (ppm): 161.1, 155.7, 152.7, 147.2, 143.5,
132.6, 132.2, 129.5, 128.8 (2C), 128.6 (2C), 127.6 (2C), 126.5, 124.3 (2C), 124.1,
121.9, 116.3, 113.9, 102.8, 102.4, 36.2; ESI-MS m=z (%) C24H15BrO3: 453 (100)
[M þ Na].
9-Chloro-4-(4-chlorophenyl)-2-phenylpyrano[3,2-c]chromen-5(4H)-one (28)
(Table 2). Light yellow solid; yield: 0.195 g (93%); mp ¼ 194–196 ꢀC; IR nmax (KBr,
1
cmꢂ1) 2920, 2870 (aromatic C-H str), 1714 (C O str); H NMR (500 MHz, CDCl3) d
=
(ppm): 7.90 (d, J ¼ 7.0 Hz, 1H), 7.64 (m, 2H), 7.39–734 (m, 5H), 7.27 (m, 2H), 7.22
(m, 1H), 5.74 (d, J ¼ 5.0 Hz, 1H), 4.66 (d, J ¼ 5.0 Hz, 1H); 13C NMR (125 MHz,
CDCl3) d (ppm): 160.6, 154.5, 151.3, 147.2, 142.2, 134.5, 134.0, 133.1, 129.8, 129.4
(2C), 128.5 (2C), 125.1(2C), 124.6 (2C), 122.8, 118.5, 116.9, 116.3, 104.0, 103.5,
36.5; ESI-MS m=z (%) C24H14Cl2O3: 443(100) [M þ Na].

3052
N. AHMED AND B. VENKATA BABU
ACKNOWLEDGMENTS
We thank the Department of Science and Technology, New Delhi, for financial
support and the Department of Chemistry, Indian Institute of Technology Roorkee
for the Ministry of Human Resource Development fellowship to B. V. B.
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