Dihydro-3 H -chromeno-[3,4- b ][4,7]phenanthrolin-3-one and Chromeno[4,3- b ]pyrano[3,2- f ]quinolin-3(13 H)-one derivatives by aza-Diels-Alder reaction

Article abstract of DOI:10.1055/s-0030-1258380

Dihydro-3H-chromeno[3,4-b][4,7]phenanthrolin-3-one and chromeno[4,3-b] pyrano[3,2-f]quinolin-3(13H)-one derivatives have been synthesized by aza-Diels-Alder reaction of O-propargylated salicylaldehyde with 6-aminoquinolone and 6-aminocoumarin respectively

Full text of DOI:10.1055/s-0030-1258380

PAPER
463
Dihydro-3H-chromeno[3,4-b][4,7]phenanthrolin-3-one and Chromeno-
[4,3-b]pyrano[3,2-f]quinolin-3(13H)-one Derivatives by Aza-Diels–Alder
Reaction
A
za-Diels–Alde
r
R
.
eaction C. Majumdar,* Sudipta Ponra, Abu Taher
Department of Chemistry, University of Kalyani, Kalyani 741235, W.B., India
E-mail: kcm_ku@yahoo.co.in
Received 15 November 2010; revised 24 November 2010
thermore, there is no report on the synthesis of chromene-
annulated pyranoquinoline and 4-alkyl-4,7-phenanthro-
lin-3(4H)-one derivatives. In continuation of our work on
the synthesis of quinoline-annulated heterocyclic com-
Abstract: Dihydro-3H-chromeno[3,4-b][4,7]phenanthrolin-3-one
and chromeno[4,3-b]pyrano[3,2-f]quinolin-3(13H)-one derivatives
have been synthesized by aza-Diels–Alder reaction of O-propargy-
lated salicylaldehyde with 6-aminoquinolone and 6-aminocoumarin
respectively. The reaction occurs in a single-step operation and pro- pounds,10,11 we became interested to undertake a study on
vides potentially bioactive polycyclic heterocycles in high yields.
the synthesis of chromene-annulated pyranoquinoline and
4-alkyl-4,7-phenanthrolin-3(4H)-one derivatives. Herein,
we report our results.
Key words: aza-Diels–Alder reaction, dihydro-3H-chromeno[3,4-
b][4,7]phenanthrolin-3-one, chromeno[4,3-b]pyrano[3,2-f]quino-
lin-3(13H)-one, Lewis acid catalysis, annulated quinoline
The required precursors 2a–e were prepared in high yields
by the reaction of various substituted salicylaldehydes
1a–e with propargyl bromide in the presence of anhydrous
potassium carbonate in anhydrous DMF at room
temperature12 (Scheme 1).
Quinoline and its annulated-derivatives are important due
to their interesting diverse applications.1 Compounds con-
taining quinoline moiety have wide application in medic-
inal chemistry.2 They possess a broad spectrum of
biological activities like antimalarial, anti-inflammatory,
antiasthmatic, antihypertensive, antibacterial, anticancer,
and tyrosine kinase inhibiting agents.3 On the other hand,
2H-chromene nucleus is found in many naturally occur-
ring biologically active compounds. They have been
shown to possess antihypertensive and anti-ischemic ac-
tivities and exhibit anti-HIV activity.4 Chromenoquino-
line derivatives have been used as drugs that modulate the
transcriptional activity of human progesterone receptor,
which play an important role in medicine, and have been
used therapeutically.5 Some chromenoquinolines have
shown antagonists activity and androgen receptor antago-
nist activity.6 Alkaloids containing the pyranoquinoline
core constitute a significant group of the quinoline alka-
loids and these compounds have been shown to exhibit a
range of biological activities.7 Some examples of natural
products containing the pyranoquinoline core structure in-
clude helietidine, dutadrupine, and geibalansine.8 There-
fore, chromene-annulated pyranoquinoline and 4-alkyl-
4,7-phenanthrolin-3(4H)-one derivatives are expected to
possess bioactivity. With this end in view we became in-
terested to synthesize chromene-annulated pyranoquino-
line and phenanthrolinone derivatives.
OH
O
a R1 = H
CHO
CHO
(i)
b R1 = Me
c R1 = t-Bu
d R1 = OMe
e R1 = Br
R1
1a–e
R1
2a–e
Scheme 1 Reagents and conditions: (i) propargyl bromide, anhyd
K2CO3, anhyd DMF, r.t.
To examine the aza-Diels–Alder reaction of 6-aminoqui-
nolones 3a,b and 6-aminocoumarin (3c) with various O-
propargylsalicylaldehydes 2, the parent O-propargylsali-
cylaldehyde (2a) was first used as a precursor of the het-
erodiene. We chose 6-amino-1-ethylquinolin-2(1H)-one
(3a) and O-propargylsalicylaldehyde (2a) as model sub-
strates to optimize the reaction conditions (Scheme 2).
The results are summarized in Table 1.
NH2
O
O
N
Et
3a
catalyst
+
N
There are reports on the synthesis of chromenoquinolines9
and pyranoquinolines.10 However, most of them are of
limited synthetic scope due to low yields, long reaction
time, multiple steps, and harsh reaction conditions. Fur-
solvent
reflux
O
O
N
Et
CHO
4a
2a
Scheme 2 Aza-Diels–Alder reaction
SYNTHESIS 2011, No. 3, pp 0463–0468
x
x
.
x
x
.2
0
1
1
Advanced online publication: 22.12.2010
DOI: 10.1055/s-0030-1258380; Art ID: Z27610SS
© Georg Thieme Verlag Stuttgart · New York

464
K. C. Majumdar et al.
PAPER
the product was obtained (entry 5). Among the various
solvents (toluene, MeCN, THF, DMF, DMSO, EtOH)
used, toluene was found to be superior to others when
BF3·OEt2 (10 mol%) was used as the catalyst (entries 1, 6–
10). We then varied the amount of catalyst loading. A
yield of 69% of the product was obtained when the reac-
tion was carried out with 5 mol% BF3·OEt2 for four hours
in refluxing toluene (entry 11). Increasing the amount of
catalyst loading (15 mol%) did not improve the yield of
the product (entry 12). The reaction failed in the absence
of BF3·OEt2 catalyst, perhaps imine formation is inhibited
in the absence of the catalyst. Among the various condi-
tions employed, the reaction in refluxing toluene in the
presence of 10 mol% BF3·OEt2 catalyst was found to give
the best results (Table 1).
Table 1 Effect of Catalyst and Solvent on the Aza-Diels–Alder Re-
action of 3a with 2a
Entry
1
Catalyst (mol%)
BF3·OEt2 (10)
Yb(OTf)3 (10)
CuBr (10)
Solvent
toluene
toluene
toluene
toluene
toluene
MeCN
THF
Time (h) Yield (%)
4
4
8
6
5
4
4
4
4
4
4
4
78
73
53
60
50
60
62
65
57
48
69
77
2
3
4
CuI (10)
5
CF3CO2H
6
BF3·OEt2 (10)
BF3·OEt2 (10)
BF3·OEt2 (10)
BF3·OEt2 (10)
BF3·OEt2 (10)
BF3·OEt2 (5)
BF3·OEt2 (15)
7
8
DMF
To extend the utility of this methodology, the aza-Diels–
Alder reaction of other O-propargylated salicylaldehydes
2b–e with 6-aminoquinolones 3a,b and 6-aminocoumarin
(3c) was then carried out using the optimized conditions.
The results are listed in Table 2. The reaction of 3a with
one equivalent of 2b in refluxing toluene and in the pres-
ence of BF3·OEt2 (10 mol%) gave the product 4b in 72%
yield (Table 2, entry 2). When the same reaction was car-
ried out with 2c the desired products 4c was obtained in
75% yield (entry 3). The aza-Diels–Alder reaction of 6-
amino-1-methylquinolin-2(1H)-one (3b) with O-propar-
gylsalicylaldehyde (2a) in refluxing toluene in the pres-
ence of BF3·OEt2 (10 mol%) gave 77% yield of the
product 4d (entry 4). When the same reaction was carried
out with 2d and 2e, 74 and 70% yield of the products 4e
and 4f were obtained, respectively (entries 5 and 6). Un-
der the same conditions, the reaction of 6-aminocoumarin
(3c) with 2a and 2e afforded the products 4g and 4h in 64
and 60% yield, respectively (entries 7 and 8). All the reac-
tions were carried out in refluxing toluene for four hours
and the structures of the products were determined from
their spectroscopic data.
9
DMSO
EtOH
10
11
12
toluene
toluene
We have examined the influence of catalysts and solvents
in the reaction. When the reaction of 3a and 2a was car-
ried out in toluene at reflux for four hours in the presence
of BF3·OEt2 (10 mol%) the product 4a was obtained in
78% yield (Table 1, entry 1). However, when Yb(OTf)3
(10 mol%) was employed as a catalyst, the desired prod-
uct 4a was obtained in 73% yield after refluxing for four
hours in toluene (entry 2). When the same reaction was
carried out in the presence of copper(I) bromide (10
mol%) for eight hours, 53% yield of the product was ob-
tained (entry 3). The yield of the product was slightly in-
creased when the reaction was carried out in the presence
of copper(I) chloride (10 mol%) for six hours in refluxing
toluene, but did not exceed than that of BF3·OEt2 (10
mol%) (entry 4). When the same reaction was carried out
in the presence of CF3CO2H for five hours a 50% yield of
A probable mechanism of the aza-Diels–Alder reaction is
depicted in Scheme 3. The intermediates 6 were not isol-
O
R1
NH2
O
N
BF3•OEt2
BF3
+
R1
CHO
O
X
O
X
3
2
6
O
N
O
R1
R1
NH
+
O
X
O
X
4a–h
5 X = O, R1 = H
Scheme 3 Probable mechanism of aza-Diels–Alder reaction
Synthesis 2011, No. 3, 463–468 © Thieme Stuttgart · New York

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Aza-Diels–Alder Reaction
465
able. Even then we can reasonably assume that initially induced intramolecular hetero-Diels–Alder reaction to
imine formation occurs between 3 and 2 to give the give the cyclized products 4. In some case we have isolat-
hetero-diene intermediate, which then undergo Lewis acid ed some uncyclized reduction product 5.
Table 2 Aza-Diels–Alder Reaction of 3a–c with 2a–e in Refluxing Toluenea
O
R1
O
N
NH2
BF3•OEt2
+
toluene
reflux
R1
CHO
O
X
O
X
3a X = NEt
3b X = NMe
3c X = O
2a–e
4a–h
Entry
Aromatic aldehyde 2
Substrate 3 Product 4a–h
Yield (%)b
O
N
O
1
2
3
4
5
6
2a
2b
2c
2a
2d
2e
3a
3a
3a
3b
3b
3b
4a
4b
4c
4d
4e
4f
78
CHO
O
O
O
O
O
O
N
Et
O
N
O
72
75
77
74
70
CHO
N
Et
O
N
O
CHO
N
Et
O
N
O
CHO
N
Me
O
N
O
OMe
MeO
CHO
N
Me
O
N
Br
O
Br
CHO
N
Me
Synthesis 2011, No. 3, 463–468 © Thieme Stuttgart · New York

466
K. C. Majumdar et al.
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Table 2 Aza-Diels–Alder Reaction of 3a–c with 2a–e in Refluxing Toluenea (continued)
O
N
R1
O
NH2
BF3•OEt2
+
toluene
reflux
R1
CHO
2a–e
O
X
O
X
3a X = NEt
3b X = NMe
3c X = O
4a–h
Entry
7
Aromatic aldehyde 2
Substrate 3 Product 4a–h
Yield (%)b
O
N
O
N
O
2a
2e
3c
3c
4g
4h
64
CHO
O
O
O
Br
8
60
Br
CHO
O
O
a All the reactions were carried out in refluxing toluene for 4 h.
b Isolated yields.
The hetero-Diels–Alder reaction represents one of the Melting points were determined in open capillaries and are uncor-
rected. IR spectra were recorded on a Perkin-Elmer L 120-000A
most powerful and efficient synthetic tools for the synthe-
spectrometer on KBr disks. 1H NMR and 13C NMR spectra were re-
sis of heterocyclic compounds, including natural prod-
corded on a Bruker DPX-400 spectrometer in CDCl3 with TMS as
ucts.13 There are several examples of intramolecular
internal standard (chemical shift in d). C,H,N-analyses were record-
domino Knoevenagel–hetero-Diels–Alder reactions with
ed on 2400 series II CHN Perkin-Elmer analyzer. MS were recorded
alkenes and alkynes.14 Despite the proven synthetic utility
of the domino Knoevenagel– hetero-Diels–Alder reac-
tion, the aza-analogue has been much less investigated.15
Various heterocyclic moieties that constitute the structur-
al skeletons of a large number of natural products and
pharmacologically active compounds were synthesized
by aza-Diels–Alder reaction.16 Recently, Ramesh et al.
have reported the synthesis of chromenoquinolines by
copper/Lewis acid catalyzed aza-Diels–Alder reaction of
unactivated alkynes.17 In our laboratory, we have synthe-
sized indole- and thiochromen-annulated [6,6]-fused
thiopyrano chromene derivatives using domino
Knoevenagel–hetero-Diels–Alder reaction of unactivated
alkynes in the absence of copper(I) catalyst.14b,c However,
our approach is solely copper(I) catalyst-free aza-Diels–
Alder reaction.
on a Q-TOF microTM instrument at the Indian Institute of Chemical
Biology, Kolkata. Silica gel [(60–120, 230–400 mesh), Rankem,
India] was used for chromatographic separation. Silica gel G
[CDH (India)] was used for TLC.
Compounds 4a–h; General Procedure
A mixture of 6-aminocoumarin (3c; 0.621 mmol, 1 equiv) or 6-ami-
noquinolone 3a,b (0.530 or 0.574 mmol, 1 equiv) and O-propargy-
lated salicylaldehyde 2a–e (0.530–0.621 mmol, 1 equiv) was stirred
in toluene at r.t. for 30 min. Then, BF3·OEt2 (10 mol%) was added
and the reaction mixture was refluxed for 4 h. After completion of
the reaction as monitored by TLC, the mixture was cooled, diluted
with sat. aq NaHCO3 (50 mL), and extracted with EtOAc (3 × 25
mL). The combined organic extracts were washed with brine (50
mL) and dried (Na2SO4). The solvent was removed by distillation.
The resulting crude product was purified by column chromatogra-
phy over silica gel (60–120 mesh) using hexane–EtOAc mixture as
eluent to give the respective compounds 4a–h.
In conclusion, we have developed a novel and efficient
protocol for the synthesis of dihydro-3H-chromeno[3,4-
b][4,7]phenanthrolin-3-one and chromeno[4,3-b]pyra-
no[3,2-f]quinolin-3(13H)-one derivatives by aza-Diels–
Alder reaction of 6-aminoquinolones and 6-aminocou-
marin with the unactivated alkynes. The copper(I)-cata-
lyst-free reaction occurs in a single-step operation with
the use of commercially available BF3·OEt2 which makes
the protocol simple, convenient, and practical.
4a
Yield: 78%; colorless solid; mp 224–226 °C.
IR (KBr): 1106, 1501, 1646, 2951 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.45 (t, J = 7.2 Hz, 3 H), 4.49 (q,
J = 7.2 Hz, 2 H), 5.42 (s, 2 H), 6.89 (d, J = 10.0 Hz, 1 H), 7.03 (d,
J = 8.0 Hz, 1 H), 7.18 (t, J = 7.2 Hz, 1 H), 7.39 (t, J = 7.6 Hz, 1 H),
7.79 (d, J = 9.6 Hz, 1 H), 8.26 (d, J = 9.6 Hz, 1 H), 8.32 (s, 1 H),
8.39 (d, J = 10.0 Hz, 1 H), 8.44 (d, J = 7.6 Hz, 1 H).
Synthesis 2011, No. 3, 463–468 © Thieme Stuttgart · New York

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Aza-Diels–Alder Reaction
467
13C NMR (100 MHz, CDCl3): d = 13.3, 38.0, 68.5, 114.4, 117.4,
117.9, 121.5, 122.6, 122.7, 124.3, 124.8, 125.2, 126.5, 132.0, 132.9,
137.9, 144.2, 148.1, 157.1, 161.6, 162.5.
Anal. Calcd for C21H16N2O3: C, 73.24; H, 4.68; N, 8.13. Found: C,
73.35; H, 4.71; N, 8.10.
4f
MS: m/z = 351.31 (M+ + Na).
Yield: 70%; colorless solid; mp >250 °C.
IR(KBr): 1076, 1496, 1655, 2851 cm–1.
Anal. Calcd for C21H16N2O2: C, 76.81; H, 4.91; N, 8.53. Found: C,
76.72; H, 4.99; N, 8.46.
1H NMR (400 MHz, CDCl3): d = 3.90 (s, 3 H), 5.44 (s, 2 H), 6.91
(d, J = 8.4 Hz, 1 H), 6.92 (d, J = 9.6 Hz, 1 H), 7.45 (dd, J = 2.4, 8.8
Hz, 1 H), 7.82 (d, J = 9.2 Hz, 1 H), 8.28 (d, J = 9.6 Hz, 1 H), 8.36
(s, 1 H), 8.40 (d, J = 9.6 Hz, 1 H), 8.56 (d, J = 2.4 Hz, 1 H).
4b
Yield: 72%; colorless solid; mp 234–236 °C.
IR (KBr): 1083, 1496, 1658, 2970 cm–1.
Anal. Calcd for C20H13BrN2O2: C, 61.09; H, 3.33; N, 7.12. Found:
C, 61.29; H, 3.26; N, 7.13.
1H NMR (400 MHz, CDCl3): d = 1.46 (t, J = 7.2 Hz, 3 H), 2.43 (s,
3 H), 4.50 (dd, J = 7.2, 14.0 Hz, 2 H), 5.40 (s, 2 H), 6.90 (d, J = 10.0
Hz, 1 H), 6.94 (d, J = 8.0 Hz, 1 H), 7.19 (dd, J = 2.0, 8.4 Hz, 1 H),
7.80 (d, J = 9.6 Hz, 1 H), 8.26 (br s, 1 H), 8.29 (d, J = 9.6 Hz, 1 H),
8.35 (s, 1 H), 8.42 (d, J = 9.6 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 13.3, 20.8, 38.0, 68.5, 114.4,
117.1, 117.8, 121.5, 122.3, 124.3, 124.8, 125.1, 126.7, 132.0, 132.8,
132.9, 132.9, 137.8, 144.1, 148.3, 155.1, 161.6.
4g
Yield: 64%; colorless solid; mp >250 °C.
IR (KBr): 1113, 1504, 1717, 2923 cm–1.
1H NMR (400 MHz, CDCl3): d = 5.43 (s, 2 H), 6.62 (d, J = 9.6 Hz,
1 H), 7.03 (d, J = 8.0 Hz, 1 H), 7.19 (t, J = 7.2 Hz, 1 H), 7.41 (dt,
J = 1.6, 7.6 Hz, 1 H), 7.67 (d, J = 9.2 Hz, 1 H), 8.23 (s, 1 H), 8.27
(d, J = 9.2 Hz, 1 H), 8.37 (d, J = 10.0 Hz, 1 H), 8.45 (dd, J = 1.2, 7.6
Hz, 1 H).
Anal. Calcd for C22H18N2O2: C, 77.17; H, 5.30; N, 8.18. Found: C,
77.01; H, 5.37; N, 8.15.
4c
13C NMR (100 MHz, CDCl3): d = 68.4, 107.9, 112.7, 116.4, 117.4,
120.5, 122.5, 122.8, 123.4, 124.8, 125.4, 126.8, 132.3, 134.3, 138.1,
148.6, 154.5, 157.3, 162.1.
Yield: 75%; colorless solid; mp >250 °C.
IR (KBr): 1106, 1501, 1647, 2951 cm–1.
Anal. Calcd for C19H11NO3: C, 75.74; H, 3.68; N, 4.65. Found: C,
75.53; H, 3.67; N, 4.69.
1H NMR (400 MHz, CDCl3): d = 1.43 (s, 9 H), 1.46 (t, J = 7.2 Hz,
3 H), 4.52 (d, J = 6.8 Hz, 2 H), 5.40 (s, 2 H), 6.90 (d, J = 9.6 Hz, 1
H), 6.98 (d, J = 8.8 Hz, 1 H), 7.44 (d, J = 8.4 Hz, 1 H), 7.80 (d,
J = 9.6 Hz, 1 H), 8.32 (d, J = 8.4 Hz, 2 H), 8.41 (d, J = 10.0 Hz, 1
H), 8.48 (s, 1 H).
13C NMR (100 MHz, CDCl3): d = 13.3, 31.5, 34.6, 38.0, 68.5, 114.5,
116.9, 117.8, 121.5, 121.6, 121.9, 124.3, 124.8, 126.8, 129.4, 133.0,
133.1, 137.9, 144.2, 145.5, 148.6, 155.0, 161.6.
4h
Yield: 60%; colorless solid; mp >250 °C.
IR (KBr): 1114, 1497, 1720, 2921 cm–1.
1H NMR (400 MHz, CDCl3): d = 5.44 (s, 2 H), 6.62 (d, J = 9.6 Hz,
1 H), 6.92 (d, J = 8.4 Hz, 1 H), 7.47 (dd, J = 2.0, 8.4 Hz, 1 H), 7.69
(d, J = 9.2 Hz, 1 H), 8.25 (s, 1 H), 8.27 (d, J = 9.2 Hz, 1 H), 8.36 (d,
J = 10.0 Hz, 1 H), 8.57 (d, J = 2.8 Hz, 1 H).
Anal. Calcd for C25H24N2O2: C, 78.10; H, 6.29; N, 7.29. Found: C,
78.25; H, 6.23; N, 7.30.
Anal. Calcd for C19H10BrNO3: C, 60.02; H, 2.65; N, 3.68. Found: C,
60.15; H, 2.71; N, 3.56.
4d
Yield: 77%; colorless solid; mp >250 °C.
5
IR (KBr): 1118, 1498, 1654, 2847 cm–1.
Yield: 30%; yellow colored solid; mp 74–76 °C.
IR (KBr): 1138, 1702, 2131, 3277 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.88 (s, 3 H), 5.40 (s, 2 H), 6.91
(d, J = 10.0 Hz, 1 H), 7.03 (d, J = 8.0 Hz, 1 H), 7.18 (t, J = 7.2 Hz,
1 H), 7.39 (t, J = 7.6 Hz, 1 H), 7.79 (d, J = 9.6 Hz, 1 H), 8.27 (d,
J = 9.6 Hz, 1 H), 8.33 (s, 1 H), 8.39 (d, J = 9.6 Hz, 1 H), 8.44 (d,
J = 7.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 29.7, 68.5, 114.4, 117.3, 117.9,
121.6, 122.6, 122.7, 124.3, 124.8, 125.2, 126.5, 132.0, 132.9, 132.9,
137.9, 144.2, 148.1, 157.1, 161.6.
1H NMR (400 MHz, CDCl3): d = 2.53 (d, J = 2.4 Hz, 1 H), 4.25 (s,
1 H), 4.37 (s, 2 H), 4.77 (d, J = 2.0 Hz, 2 H), 6.34 (d, J = 9.2 Hz, 1
H), 6.61 (d, J = 2.8 Hz, 1 H), 6.84 (dd, J = 2.8, 8.8 Hz, 1 H), 6.97 (t,
J = 7.6 Hz, 1 H), 7.01 (d, J = 8.4 Hz, 1 H), 7.13 (d, J = 8.8 Hz, 1 H),
7.29 (t, J = 8.4 Hz, 2 H), 7.56 (d, J = 9.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 43.7, 56.0, 75.7, 78.5, 108.6,
112.0, 116.6, 117.4, 118.5, 119.3, 121.6, 127.3, 128.5, 128.9, 143.5,
145.0, 146.7, 155.3, 161.4.
Anal. Calcd for C20H14N2O2: C, 76.42; H, 4.49; N, 8.91. Found: C,
76.65; H, 4.45; N, 8.85.
MS: m/z = 306.0 (M + H)+.
4e
Anal. Calcd for C19H15NO3: C, 74.74; H, 4.95; N, 4.59. Found: C,
74.95; H, 4.83; N, 4.66.
Yield: 74%; colorless solid; mp >250 °C.
IR (KBr): 1047, 1498, 1645, 2834 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.88 (s, 3 H), 3.94 (s, 3 H), 5.37
(s, 2 H), 6.90 (d, J = 9.6 Hz, 1 H), 6.97 (s, 2 H), 7.78 (d, J = 9.2 Hz,
1 H), 7.94 (s, 1 H), 8.28 (d, J = 9.2 Hz, 1 H), 8.32 (s, 1 H), 8.39 (d,
J = 9.6 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 30.2, 55.9, 68.6, 107.8, 114.2,
118.0, 118.4, 119.5, 121.6, 123.1, 124.2, 124.9, 127.0, 133.0, 133.0,
138.8, 144.2, 148,3, 151.4, 155.2, 162.1.
Acknowledgment
We thank CSIR (New Delhi) and DST (New Delhi) for financial
assistance. Two of us (A.T. and S.P.) are grateful to CSIR (New
Delhi) for a Senior and a Junior Research Fellowship, respectively.
We also thank DST (New Delhi) for providing Perkin-Elmer FT-IR
spectrometer, Bruker NMR Spectrometer (400 MHz), and Perkin-
Elmer CHN Analyzer under its FIST programme.
Synthesis 2011, No. 3, 463–468 © Thieme Stuttgart · New York

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K. C. Majumdar et al.
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Synthesis 2011, No. 3, 463–468 © Thieme Stuttgart · New York