Solvent-dependent fluorescence emission in heterocyclic compounds having isoquinoline backbone

Article abstract of DOI:10.1002/jhet.310

(Chemical Equation Presented) Few amino derivatives of benzo[de]benzo[4,5] imidazo[2,1-a]isoquinolin-7-one having amino groups at different positions of the rings are prepared and characterized. Solvent-dependent emission and changes in emission properties on protonation of amine group are observed.

Full text of DOI:10.1002/jhet.310

January 2010
Solvent-Dependent Fluorescence Emission in Heterocyclic
Compounds Having Isoquinoline Backbone
199
Devendra Singh, Subrata Kumar Ghosh, and Jubaraj B. Baruah*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039,
Assam, India
*E-mail: juba@iitg.ernet.in
Additional Supporting Information may be found in the online version of this article.
Received July 20, 2009
DOI 10.1002/jhet.310
Published online 8 January 2010 in Wiley InterScience (www.interscience.wiley.com).
Few amino derivatives of benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one having amino groups
at different positions of the rings are prepared and characterized. Solvent-dependent emission and
changes in emission properties on protonation of amine group are observed.
J. Heterocyclic Chem., 47, 199 (2010).
INTRODUCTION
RESULTS AND DISCUSSION
The organic compounds having fluorophores that are
sensitive to environment are of great importance [1–5] in
chemistry and biology. The fluorescence emission spectra
of some heterocyclic compounds such as benzo [de]ben-
zo[4,5]imidazo[2,1-a]isoquinoline (Fig. 1) are sensitive to
environment [6–8], and some of such heterocyclic com-
pounds are used as organic photoconductive materials [9].
Therefore, the functionalization of such heterocyclic com-
pounds is expected to form derivatives that may possess
interesting optical properties [10]. Heterocyclic com-
pounds having more numbers of delocalized aromatic
rings in conjugation to each other would lead to better as
well as novel optical properties [9]. With an interest to
identify and characterize and also to understand optical
properties of compounds bearing fluorophores that are sen-
sitive to environment, we have synthesized few heterocy-
clic compounds as shown in Figure 1. We have studied
fluorescence emission of these compounds and compared
with some of their derivatives.
Synthesis of the heterocycles. The compounds 2 and
4 were prepared by the reactions as depicted in Schemes
1 and 2. The condensation of 1,8-naphthalic anhydride
with 4-nitro 1,2-diaminobenzene in acetic acid gave 11-
nitro-benzo[de] benzo[4,5] imidazo[2,1-a] isoquinolin-7-
one (1). Although this reaction is expected to give two
isomeric products, we obtained a single isomeric prod-
uct. This is due to the fact that such cyclization process
passes through imide intermediates. It is recently shown
that only one imide isomer is formed in this reaction
before cyclization. This was shown by trapping the in-
termediate imide derivative in dimethylformamide
(DMF) as a solvent. The formation of specific imide in
this reaction, between the two possible isomers, may be
attributed to the ease of attack of the less sterically
crowded [11] amino group at p-position to the nitro
group of 4-nitro 1,2-diaminobenzene. The reduction of
the nitro group of the compound 1 resulted in the forma-
tion of the corresponding amine 2. Acetic acid is found
C
V
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D. Singh, S. K. Ghosh, and J. B. Baruah
Vol 47
1
the assumption that the simulated H-NMR of other iso-
mer namely 5-nitro-benzo[de]benzo[4,5]imidazo[2,1-
a]isoquinolin-7-one shows proton signals at relatively
high chemical shift than the 2-nitro-benzo[de]ben-
zo[4,5]imidazo[2,1-a]one methane. As the optical prop-
erties of these two isomers and derivatives are indistin-
guishable, we proceeded to take the mixture of isomers
for optical study described in the Experimental section.
The reduction of the nitro groups of these isomers (3)
was carried out by hydrogen gas with a catalytic amount
of palladized carbon to prepare two isomeric amine
derivatives 4 (Scheme 2). In the case of 1, we have
obtained only one isomer because of the presence of
nitro-group on diamino benzene ring, which could dif-
ferentiate the two amino groups on the ring in terms of
reactivity. The nitro group on the compound 1 was
reduced to amino group, and the amino group was fur-
ther functionalized to various derivatives 5–8 as illus-
trated in Scheme 3. Methyl and acyl derivatives (9–12)
of compound 4 were also synthesized by similar proce-
dure (Scheme 4).
Figure 1. Structure of the heterocycles.
to be appropriate solvent for the synthesis of 2.
Recently, we have discussed about the role of solvent in
the formation of similar heterocycles [11] and also men-
tioned about the usefulness of acetic acid in the synthe-
sis of such heterocycles. Similarly, the condensation
reaction of 3-nitro-1,8-naphthalic anhydride with 1,2-
diaminobenzene gave a mixture of isomeric products,
namely 2-nitro-benzo[de]benzo[4,5]imidazo[2,1-a]one-
methane and 5-nitro-benzo[de]benzo[4,5]imidazo[2,1-
a]isoquinolin-7-one (3). We could not separate the two
isomers by conventional chromatographic techniques
such as preparative thin layer (TLC) or column chroma-
Optical properties. The compounds 2 and 4 show
solvatochromic properties, and the absorption features of
2 and 4 differ in different solvents, which are listed in
Table 1. The compounds 2 and 4 are derived from a
planar aromatic ring system, which is derived from 1,8-
naphthalic anhydride [6]. The imides derived from naph-
thalic anhydride are useful as fluorescence probes, and
their applications are decided by the presence of tether
connecting two similar or dissimilar molecules [12]. The
compounds 2 and 4 have reasonable fluorescence emis-
sion properties on excitation at appropriate wavelengths.
The UV–visible absorption spectra as well as fluores-
cence emission spectra of several derivatives of 11-
amino benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-
one (2) are recorded and listed in Table 2. Among the
nitro and amino group (compounds 1 and 2), the later
shifts the fluorescence emission towards higher wave-
length. In the case of substituted amines, it is observed
that the substituent attached on nitrogen also leads to
emission to higher wavelength. Among the N-substituent
compounds 5–8, the highest shift is observed in N-ben-
zoylated derivative (7). It is attributed to the fact that
benzoate group participates in delocalization of electrons
with the aromatic ring of the heterocycle. The fluores-
cence emission of 2 in dichloromethane solution is
1
tography. The H-NMR chemical shift and the integra-
tion values of the mixture of isomers suggest formation
of almost an equimolar mixture of the two isomers. In
an earlier report, it was suggested that similar reaction
under microwave irradiation in the presence of alumina
resulted only one isomer [12], but in our case we have
failed to obtain pure isomer through the reaction condi-
tion described herein, and the isomeric product separa-
tion of 3 was not successful. However, the condensation
reaction of 3-nitro-1,8-naphthalic anhydride with 1,2-
diaminobenzene under solvothermal condition in acetic
acid at 150ꢀC in an autoclave gave only one isomer.
1
The H-NMR spectra of this isomer obtained from this
reaction is given as Supporting Information. It has eight
peaks in aromatic region and tallies the structure of 2-
nitro-benzo[de]benzo[4,5]imidazo[2,1-a]one methane.
1
The assignment of the H-NMR of this compound is on
Scheme 1
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Solvent-Dependent Fluorescence Emission in Heterocyclic Compounds Having
Isoquinoline Backbone
201
Scheme 2
observed at 508 nm upon excitation at 410 nm. The
compound 2 is found to be fluorescence inactive in
methanol. Accordingly, the fluorescence emission of the
2 observed from dichloromethane solution also gets
quenched on addition of methanol (Fig. 2). The fluores-
cence emission spectra of various derivatives of 11-
amino-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-
one (2) and mixture of 2-amino-benzo[de]benzo[4,5]-
imidazo[2,1-a]isoquinolin-7-one and 5-amino-benzo[de]-
benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (4) were also
recorded, and the emission wavelengths and quantum
yields are listed in Table 2. Although the compound 4 is
a mixture of two isomers, in none of the cases, we could
obtain any distinguishable fluorescence emission features
of the two isomers. The wavelength shifts and intensity
changes in various derivatives of 2 and 4 predominantly
occur from the electronic effect caused to the overall
electronic environment by the presence of the substitu-
ents. It is important to note that the emission spectra of
naphthalimide fluorophores having amine groups are pro-
ton responsive [13], and such compounds have relevance
in recognition of anions [14].
emits at 514 nm, and the shifts to 508 and 498 nm,
respectively, on addition of 1 and 2 equiv of hydrochlo-
ric acid (HCl).
The emission spectra of 4 are highly solvent depend-
ent. A solution of 4 on excitation at 410 nm in dichloro-
methane, acetonitrile, and methanol shows fluorescence
emission at 491 (U ¼ 0.458), 527, and 562 nm, respec-
tively [Fig. 3(a)]. Such large characteristic shifts in
emission spectra make it possible to distinguish these
three solvents. From Table 1, it is clear that the com-
pound 4 shows very small solvatochromicity in visible
spectra, whereas it shows a large shift in emission spec-
tra on change of solvents. This suggests that a polar
excited state capable of forming exciplex with different
solvents is involved in the fluorescence emission.
Addition of methanol to dichloromethane solution of
4 changes its fluorescence emission; initially, the emis-
sion occurring due to excitation at 410 nm decreases,
but the emission shifts to a higher wavelength and on
gradual addition of methanol it once again increases and
reaches the emission wavelength that corresponds to the
observed emission wavelength from a methanolic solu-
tion of 4 [Fig. 3(b)]. Similarly, the addition of methanol
to an acetonitrile solution of 4 shifts the fluorescence
emission to higher wavelength [Fig. 3(c)]. The com-
pound 4 also shows proton responsive fluorescence
In the case of compound 2, the protonation causes
shift in the fluorescence emission to a lower wavelength
from the parent compound. For example, the parent
compound 2 in dichloromethane on excitation at 410 nm
Scheme 3
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D. Singh, S. K. Ghosh, and J. B. Baruah
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Scheme 4
emission, which is dependent on the hydrogen ion con-
centrations. For example, treatment of a solution of 4
with HCl (1 equiv) causes a change of fluorescence
emission from 491 to 501 nm, and on addition of 2
equiv of the acid, the emission occurs at 510 nm [Fig.
3(d)]. These results suggest that the protonation effects
the delocalization of electrons of the amino group,
which in turn contributes to the changes in the emission
spectra of these compounds. The solvato-emissive prop-
erties can be attributed to the stabilization of polar
exited state by polar solvent, whereas the proton respon-
sive nature is attributed to the hydrogen bonding by
protic solvent and protonation by mineral acid. Similar
properties are seen in receptors of carboxylic acids [15].
from the emission wavelengths of the 4 in these sol-
vents. Depending on the position of an amino group on
the rings and protonation of the amino groups at differ-
ent positions, the fluorescence emissions shifts to higher
or lower wavelength.
EXPERIMENTAL
UV–visible spectra were recorded on Perkin Elmer Lamda
25 UV–visible spectrometer, and the fluorescence spectra were
recorded on Perkin Elmer LS-55 fluorescence spectrometer.
Table 2
The visible spectra and fluorescence emission (kex ¼ 410 nm) of
derivatives of 2 and 4.
CONCLUSIONS
Dichloromethane
A large shift in fluorescence emission wavelength is
observed on introduction of amino group at different
positions of benzo[de]benzo[4,5]imidazo[2,1-a]isoquino-
lin-7-one. Different organic solvents such as dichloro-
methane, acetonitrile, and methanol can be distinguished
kmax
(nm)
e (Mꢁ1
cmꢁ1
kem
(nm)
)
U
R ¼ NO2 (1)
390
430
395
397
401
393
19,772
12,727
6818
6136
8409
463
508
515
545
546
518
0.134
0.252
0.060
0.350
0.452
0.343
R ¼ NH2 (2)
R ¼ NHCH3 (5)
R ¼ NHCOCH3 (6)
R ¼ NHCOC6H5 (7)
R¼NHCOCH2Br (8)
Table 1
Effect of solvent on the visible spectra of 2 and 4.
10,909
kmax e (Mꢁ1
Solvent
(nm) cmꢁ1
)
R ¼ NH2, R1, R2 ¼ H (2)
R ¼ NH2, R1, R2 ¼ H (2)
R ¼ NH2, R1, R2 ¼ H (2)
Dichloromethane 430 12,727
437 10,227
444 9545
Methanol
Acetonitrile
R¼NH2 (4)
427
375
401
401
395
11,212
18,909
10,303
19,181
10,393
491
538
493
493
495
0.288
0.156
0.290
0.324
0.215
R¼NHCH3 (9)
R ¼ H, R1, R2 ¼ H/NH2 (4) Dichloromethane 427 11,212
R¼NHCOCH3 (10)
R¼NHCOC6H5 (11)
R¼NHCOCH2Br (12)
R ¼ H, R1, R2 ¼ H/NH2 (4) Acetonitrile
R ¼ H, R1, R2 ¼ H/NH2 (4) Methanol
432 10,000
438 9696
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Solvent-Dependent Fluorescence Emission in Heterocyclic Compounds Having
Isoquinoline Backbone
203
Figure 2. (a) Fluorescence emission (kex ¼ 410 nm) spectra of (i) 2 in dichloromethane: (ii) on addition of 1 mol equiv of HCl and (iii) on addi-
tion of 2 mol equiv of HCl (in each cases 3 mL of 1.1 ꢂ 10ꢁ5M solution). (b) Effect of the addition of methanol (100 lL aliquots) to a solution
of 2 in dichloromethane.
The NMR spectra were recorded on a 400 MHz Varian FT-
NMR instrument with TMS as an internal standard. Mass spec-
tra were recorded in a Water LC-MS. The melting points of
the compounds were determined in a Buchi B-540 melting
point apparatus. All the optical measurements were carried out
by dissolving calculated amount of the compounds in spectro-
scopic grade solvents. The fluorescence titrations were carried
out in quartz cuvette by adding different aliquots of titrant/s
by micropipette to a parent solution (3 mL).
Determination of fluorescence quantum yield. Fluo-
rescence quantum yields were determined by calibrating with
perylene (U ¼ 0.94) by fluorescence excitation at 410 nm as
standard. The fluorescence quantum yield was calculated by
using the following formula [16]:
ðQuantum yieldÞsample
ðQuantum yieldÞstandard
Absorption of standard ðArea under the graph of emission spectraÞSample
Absorption of sample ðArea under the graph of emissio spectraÞStandard
¼
:
For calculation of the quantum yield of the other samples,
the identical procedures were used.
mixture and filtered. The solid product obtained was washed
with water and the product was purified by preparative TLC.
Yield: 55%. Elemental Anal Calcd. for C18H11N3O; C, 75.78;
H, 3.89; Found C, 75.80, H, 3.90. 1H-NMR (400 MHz,
CDCl3) 8.76 (m, 2H), 8.26 (d, 1H, J ¼ 8.4 Hz), 8.1 (d, 1H,
J ¼ 8 Hz), 7.9 (d,1H, J ¼ 2.4 Hz), 7.8 (m, 2H), 7.66 (d, 1H,
J ¼ 8.4 Hz), 6.85 (d, 1H, J ¼ 8.4 Hz), 5.0 (s, 2H).13C-NMR
(CDCl3): 158.9, 145.8, 137.4, 134.3, 134.2, 131.6, 130.8,
129.7, 129.5, 129.3, 127.4, 125.9, 125.7, 123.1, 120.2, 120.1,
118.5, 115.3. IR (KBr, cmꢁ1): 3232 (w), 3363 (s), 1589 (m),
1621 (s), 1697 (s). ESI-MS ¼ 286.1864 (M þ Hþ). m.p.
406ꢀC.
Synthesis and characterization of various compounds.
Compound 1. A mixture of 1,8-naphthalic anhydride (0.99
g, 5 mmol) and 4-nitro 1,2 diaminobenzene (0.77 g, 5 mmol)
was refluxed in acetic acid (10 mL) for 4 h. The reaction mix-
ture was cooled and water (20 mL ) was added to the reaction
mixture and stirred for 20 min. The precipitate was filtered
and washed several times with water to remove acetic acid.
The product was air dried to obtain 11-nitro-benzo[de]ben-
zo[4,5]imidazo[2,1-a]isoquinolin-7-one in 77% yield. Elemen-
tal Anal. Calcd. for C19H9N3O3; C, 68.57; H, 2.88; Found C,
1
68.60, H, 2.86. H-NMR (400 MHz, CDCl3): 9.17 (d, 1H, J ¼
Compound 3. A mixture of 3-nitro-1,8-naphthalic anhydride
(1.22 g, 5 mmol) and 1,2 diaminobenzene (0.54 g, 5 mmol)
was refluxed in acetic acid (20 mL) at 90ꢀC for 4 h. The reac-
tion mixture was cooled and then water (20 mL) was added to
the reaction mixture and stirred for 20 min. The precipitate
was filtered and washed several times with water to remove
acetic acid, and the product was air dried to obtain a mixture
of 2-nitro-benzo[de]benzo[4,5]imidazo[2,1-a]onemethane and
5-nitro-benzo[de]benzo[4,5]imidazo [2,1-a]isoquinolin-7-one in
2.4), 8.75 (m, 4H), 8.51 (dm, 1H, J ¼ 7.2), 8.19 (s, 1H), 7.87
(m, 2H). IR (KBr, cmþꢁ1): 1699 (s), 1517 (s), 1335 (s). ESI-
MS: 316.1757 (M þ H ) m.p. 415ꢀC.
Compound 2. To
a solution of 11-nitro-benzo[de]ben-
zo[4,5]imidazo[2,1-a]isoquinolin-7-one (0.32 g, 1 mmol) in
ethanol/water (2:1, 20 mL), iron powder (35 mmol) and aque-
ous HCl (10%, 5 mL) were added. The mixture was kept at
90ꢀC for 2 h. The reaction mixture was brought to room tem-
perature and then water (10 mL) was added to the reaction
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Figure 3. The fluorescence emission of (kex ¼ 410 nm): (a) 4 in (i) dichloromethane, (ii) acetonitrile, and (iii) methanol (in each cases 3 mL of 1.1 ꢂ 10ꢁ5M so-
lution 4); (b) 4 on addition of different aliquots of methanol (50 lL each from 2–6) to a dichloromethane solution of 4; (c) 4 on addition of different aliquots of
methanol (50 lL each from 2–6) to an acetonitrile solution of 4; (d) 4 (1) in dichloromethane and on addition of (2) 1 equiv of HCl or (3) 2 equiv of HCl.
86% yield. 1H-NMR (400 MHz, CDCl3): 9.55 (d, J ¼ 4 Hz,
1H) 9.48 (d, J ¼ 4 Hz, 1H), 9.18 (d, J ¼ 4 Hz, 1H), 9.0 (d,
J ¼ 4 Hz, 1H), 8.98 (d, 1H, J ¼ 8 Hz), 8.95 (d, 1H, J ¼ 8
Hz), 8.54 (m, 2H), 8.48 (d, 1H, J ¼ 8 Hz), 8.35 (d, J ¼ 8 Hz,
1H), 7.99 (t, J ¼ 8 Hz, 2H), 7.91–7.94 (m, 2H), 7.50–7.53 (m,
4H). IR (KBr, cmꢁ1): 3444 (m), 3067 (m), 1696 (s), 1596 (m),
1531 (m), 1443 (w), 1343 (s), 1234 (m), 115þ2 (w), 1039 (w),
751 (m), 557 (w). ESI-MS: 316.1814 (M þ H ). m.p. 410ꢀC.
Compound 4. To a solution of mixture of 2-nitro-benzo[de]-
benzo[4,5]imidazo[2,1-a]onemethane and 5-nitro-benzo[de]-
benzo[4,5]imidazo [2,1-a]isoquinolin-7-one (1.58 g, 5 mmol)
in tetrahydrofuran (20 mL), palladized carbon (10%, 0.1 g)
was added. The mixture was stirred under hydrogen atmos-
phere (50 psi) for 24 h, filtered, and the solvent was removed
from filtrate under reduced pressure to get the desired product.
The yield after purification was 85%. 1H-NMR (400 MHz,
CDCl3): 8.48–8.56 (m, 4H), 8.25 (d, J ¼ 3 Hz, 1H), 8.18 (d,
1H, J ¼ 3 Hz), 7.96 (d, J ¼ 8 Hz, 1H), 7.83–7.85 (m, 2H),
7.62–7.67 (m, 2H), 7.43–7.48 (m, 4H), 7.35 (d, J ¼ 3 Hz, 1H)
4.2 (broad s, 2H). 13C-NMR (CDCl3): 158.1, 145.4, 134.2,
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Solvent-Dependent Fluorescence Emission in Heterocyclic Compounds Having
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205
Compound 9. Yield: 28%. 1H-NMR (400 MHz, CDCl3):
8.53 (m,4H), 8.43 (d, 1H, J ¼ 6.4 Hz), 8.39 (d, 1H, J ¼ 2.8
Hz), 8.32 (d, 1H, J ¼ 2.8 Hz), 8.00 (d, 1H, J ¼ 8.0 Hz), 7.85
(m, 4H), 7.62 (m, 2H), 7.45 (m, 4H), 7.21 (d, 1H, J ¼ 2.4
Hz), 7.10 (d, 1H, J ¼ 2.4 Hz), 3.07 (d, 6H, J ¼ 6.8 Hz). IR
(KBr, cmꢁ1): 3445 (s), 2924 (m), 2852 (w), 2357 (w), 1622
(s), 1430 (m), 1327 (s), 1231 (m), 1159 (w), 927 (w), 842 (w),
763 (m). ESI-MS: 300.1147 (M þ Hþ). m.p. 367ꢀC.
133.3, 130.0, 128.2, 127.8, 127.4, 125.9, 125.6, 125.4, 123.9,
122.4, 120.1, 118.0, 116.1, 115.7, 112.5. IR (KBr, cmꢁ1):
3448 (w), 3362 (s), 2924 (m), 2851 (m), 1690 (s), 1627 (s),
1550 (w), 1448 (w), 1352 (s), 1330 (s), 1166 (w), 1050 (w),
872 (w), 764 (w). ESI-MS: 286.1957 (M þ Hþ). m.p. 405ꢀC.
Compounds 5–8. The 11-amino-benzo[de]benzo[4,5]imi-
dazo[2,1-a]isoquinolin-7-one (2) was converted to corresponding
N-methyl (5), N-acetyl (6), N-benzoyl (7), and N-bromoacetyl
derivatives (8) by reactions with suitable reagents as follows:
Compound 5. A mixture of compound 1 (0.1 g, 0.35 mmol)
and anhydrous potassium carbonate was refluxed in dry ace-
tone with methyl iodide (0.08 g, 0.53 mmol) for 24 h. The
reaction mixture was evaporated, water (15 mL) and dichloro-
methane (15 mL) were added, the organic layer was separated,
and the product was extracted from the dichloromethane by
evaporation. The compound was further purified by TLC.
Yield: 25 %. 1H-NMR (400 MHz, DMSO-d6): 8.65 (d, 1H,
J ¼ 7.2 Hz), 8.16 (d, 1H, J ¼ 8.4 Hz), 7.98 (d, 1H, J ¼ 8.4
Hz), 7.82 (d, 1H, J ¼ 2.8 Hz), 7.7 (m, 4H), 6.86 (dd, 1H, J ¼
2.8 Hz), 3.0 (s, 3H). IR (KBr, cmꢁ1): 3390 (s), 2924 (s), 2853
(m), 169þ3 (s), 1621 (s), 1502 (s), 1318 (m). ESI-MS: 300.1132
(M þ H ). m.p. 386ꢀC.
Compound 10. Yield: 82%. 1H-NMR (400 MHz, CDCl3):
9.92 (s,1H), 9.85 (s,1H), 8.43 (s,1H), 8.28 (d, 2H, J ¼ 4.0
Hz), 8.26 (s,1H), 8.15 (d, 1H, J ¼ 4.0 Hz), 8.08 (d, 1H, J ¼
7.2 Hz), 8.00 (t, 2H, J ¼ 5.6 Hz), 7.73 (d, 1H, J ¼ 8.4 Hz),
7.60 (d, 1H, J ¼ 7.2 Hz), 7.34 (m, 2H), 7.28 (t, 2H, J ¼ 8.0
Hz), 6.98 (dd, 4H, J ¼ 3.6 Hz), 2.08 (s, 4H). 13C-NMR (100
MHz, DMSO-d6): 169.1, 160.0, 148.6, 143.2, 138.3, 134.7,
132.4, 131.3, 129.2, 127.2, 125.4, 125.0, 122.8, 122.2, 120.2,
119.7, 119.5, 118.4, 115.1, 45.3. IR (KBr, cmꢁ1): 3433 (s),
2983 (m), 2738 (w), 2678 (w), 1657 (s), 1558 (m), 1347 (m),
1262 (m), 1161 (þw), 1035 (m), 878 (w), 767 (m). ESI-MS:
328.1239 (M þ H ). m.p. 356ꢀC.
Compound 11. Yield: 84%. 1H-NMR (400 MHz, CDCl3):
10.24 (s, 1H), 10.18 (s, 1H), 8.72 (s, 1H), 8.58 (s, 1H), 8.22
(d, 1H, J ¼ 7.2 Hz), 8.10 (dd, 2H, J ¼ 3.6 Hz), 7.87 (d, 1H, J
¼ 8.4 Hz), 7.70 (t, 4H, J ¼ 8.0 Hz), 7.59 (d, 4H, J ¼ 6.4 Hz),
7.40 (dd, 2H, J ¼ 6.0 Hz), 7.31 (t, 2H, J ¼ 7.6 Hz), 7.15 (m,
5H), 7.04 (m,5H). 13C-NMR (100 MHz, DMSO-d6): 168.2,
166.6, 163.1, 143.5, 138.3, 135.8, 134.6, 133.6, 132.6, 131.5,
131.1, 130.8, 129.91, 129.8, 129.2, 128.4, 128.3, 125.6, 120.0,
115.0. IR (KBr, cmꢁ1): 3394 (s), 3054 (w), 2923 (w), 1788
(m), 1705 (s), 1657 (m), 1543 (s), 1351 (m), 1243 (s), 1174
(m), 1040 (m), 877 (w), 750 (w), 705 (m). ESI-MS: 390.1074
(M þ Hþ). m.p. 362ꢀC
Compounds 6–8. The compound 2 (0.06 g, 0.2 mmol) was
mixed with RCOX (for 6, 7 R ¼ CH3, Ph and X ¼ Cl, respec-
tively, whereas for 8 R ¼ BrCH2CO- and X ¼ Br) and trie-
thylamine (0.4 mL) in dry dichloromethane (10 mL). The mix-
ture was stirred overnight at room temperature. On adding 40
mL water to the reaction mixture, the solid products in pure
form were obtained from dichloromethane in quantitative
yield.
1
Compound 6. H-NMR (400 MHz, DMSO-d6): 10.26
(s,1H), 8.9 (s,1H), 8.72 (d, 2H, J ¼ 8 Hz ), 8.54 (d, 1H, J ¼
8.4 Hz), 8.38 (d, 1H, J ¼ 8.4 Hz), 7.94 (m, 2H), 7.8 (d, 1H, J
¼ 8.8 Hz ), 7.64 (d, 1H, J ¼ 8.4 Hz), 2.1 (s, 3H). 13C-NMR
(100 MHz, DMSO-d6): 168.4, 159.8, 149.9, 143.7, 139.2,
137.2, 135.5, 132.1, 131.7, 131.1, 127.4, 127.1, 126.7, 122.5,
119.92, 117.5, 116.9, 115.0, 109.6, 105.9, 24.1. IR (KBr,
cmꢁ1): 3302 (s), 2923 (s), 2852þ(m), 1702 (s), 1662 (s), 1597
(m). ESI-MS: 328.1220 (M þ H ). m.p. 395ꢀC.
Compound 12. Yield: 80%. 1H-NMR (400 MHz, CDCl3):
10.44 (s, 1H), 10.38 (s, 1H), 8.46 (s, 1H), 8.37 (s, 1H), 8.31
(s, 2H), 8.22 (d, 1H, J ¼ 7.6 Hz), 8.16 (d, 1H, J ¼ 7.2 Hz),
8.03 (t, 1H, J ¼ 6.8 Hz), 7.79 (d, 1H, J ¼ 8.4 Hz), 7.66 (d,
1H, J ¼ 8.0 Hz), 7.35 (m, 3H), 7.14 (m, 2H), 7.05 (dd, 4H, J
¼ 3.2 Hz), 3.64 (s, 4H). 13C-NMR (100 MHz, DMSO-d6):
172.4, 160.5, 149.4, 143.8, 138.2, 135.6, 133.1, 132.0, 130.2,
128.1, 126.2, 125.8, 123.8, 123.0, 120.8, 120.2, 119.9, 115.9,
62.7. IR (KBr, cmꢁ1): 3437 (s), 3274 (s), 1697 (s), 1673 (s),
1599 (m), 1552 (m), 1492 (w), 1431 (m), 1347 (m), 1050 (w),
868 (w), 766 (m), 677 (w). ESI-MS: 405.9780 and 407.9749
(M þ Hþ). m.p. 360ꢀC.
1
Compound 7. H-NMR (400 MHz, DMSO-d6) 10.57 (s, 1H),
8.7 (d, 1H, J ¼ 3.6 Hz), 8.52 (d, 1H, J ¼ 7.6 Hz), 8.36 (d, 1H,
J ¼ 7.2 Hz), 8.15 (d,1H, J ¼ 4.8 Hz), 8.04 (d,1H, J ¼ 4.8 Hz),
7.94 (d, 2H, J ¼ 4.8 Hz), 7.9 (s, 1H), 7.83 (d, 1H, J ¼ 7.2 Hz),
7.63 (d, 2H, J ¼ 4.8 Hz), 7.57 (s, 1H), 7.51 (d, 2H, J ¼ 4.8
Hz). 13C-NMR (100 MHz, DMSO-d6): 165.5, 160.0, 148.63,
139.5, 136.7, 135.3, 135.0, 131.7, 131.4, 131.0, 129.3, 128.4,
127.8, 127.3, 127.0, 126.1, 122.5, 120.0, 119.2, 118.7, 115.0,
111.1, 107.2. IR (KBr, cmꢁ1): 3301 (m), 307þ1 (m), 1703 (s),
1601 (m), 1699 (s). ESI-MS: 390.1217 (M þ H ). m.p. 385ꢀC.
Acknowledgments. The authors thank the Department of Sci-
ence and Technology, New-Delhi, India, for financial support.
The authors are thankful to Prof. Lyle W. Castle for valuable sug-
gestions on the manuscript.
1
Compound 8. H-NMR (400 MHz, DMSO-d6): 10.72 (s,
1H), 8.90 (s, 1H), 8.70 (d, 2H, J ¼ 8.4 Hz), 8.53 (d, 1H, J ¼
8.4 Hz), 8.37 (d, 1H, J ¼ 8.4 Hz), 7.9 (m, 2H), 7.8 (m, 1H),
7.65 (d, 1H, J ¼ 8.4 Hz), 4.1 (s, 2H). 13C-NMR (100 MHz,
DMSO-d6): 170.9, 160.0, 148.5, 136.5, 136.1, 135.5, 132.4,
131.8, 131.3, 127.4, 127.1, 126.2, 122.5, 119.8, 119.47, 119.2,
118.3, 117.6, 106.5, 62.0. IR (KBr, cmꢁ1): 3253 (s), 2959 (s),
1698 (m), 1654 (s), 1737 (s), 1591 (m), 1233 (m). ESI-MS:
405.9840 and 407.9832 (M þ Hþ). m.p. 378ꢀC.
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