π-aryl/heteroaryl conjugated coumarin-thiazoles: Synthesis, optical spectral and nonlinear optic properties

Article abstract of DOI:10.1002/jhet.5570430416

A series of π-aryl/heteroaryl conjugated coumarin-thiazole systems 8a-f has been synthesized by using Hantzsch thiazole protocol and Wittig olefination as the keys. In the UV-Visible spectra of 8a-f, a main absorption band associated with a dominant π-π*

Full text of DOI:10.1002/jhet.5570430416

Jul-Aug 2006
917
ꢀ-Aryl/Heteroaryl Conjugated Coumarin-Thiazoles: Synthesis,
Optical Spectral and Nonlinear Optic Properties
Sabir H Mashraqui*, Hitesh Mistry and Subramanain Sundaram
Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai 400098, India.
E-mail: sh_mashraqui@yahoo.com
Received September 11, 2005
S
O
N
+
-
+
PPh3Cl
Ar
H
O
O
S
KtOBu / DMF
N
Ar
O
O
Ar = Donor/ acceptor aryl or heteroaryl groups.
A series of ꢀ-aryl/heteroaryl conjugated coumarin-thiazole systems 8a-f has been synthesized by using
Hantzsch thiazole protocol and Wittig olefination as the keys. In the UV-Visible spectra of 8a-f, a main
absorption band associated with a dominant ꢀ-ꢀ* transition is observed in the region of 338 to 390 nm.
Qualitatively, the values of ꢁmax have been found to correlate satisfactory with the donor/acceptor
characteristics of the ꢀ-attached chromophores. Marked changes observed in the absorption maxima of 8a
under acidic conditions are rationalized on the basis of mono-or bis-protonation and modification of the
donor/acceptor properties of chromophores undergoing protonation. The emission spectra of 8a-f, obtained
by exciting the molecules at their main absorption bands showed emission maxima in the region of 429 nm
to 537 nm, with relatively high Stokes shifts of 145 and 171 nm being observed for 8a and 8e, carrying a
ꢀ-donor, dimethylaminophenyl and a ꢀ-acceptor, p-nitrophenyl chromophore, respectively. Although, the
first hyperpolarisability ꢂ, measured by the hyper-Reileigh scattering (HRS) technique are modest (12 to
23 ꢃ 10-30 esu), all the compounds exhibited complete transparency in the frequency doubling region at 532
nm and showed high thermal stability (Td from 330 to 365 °C).
J. Heterocyclic Chem., 43, 917 (2006).
S
S
Introduction.
R1
N
N
R1
R
R
Natural and synthetic coumarins continue to
engage interest for their wide ranging applications
e.g., in the areas of biological activities [1-4], laser
dyes [5-10], fluorescence brighteners [11-14] and
fluorochromophores [15-18]. Among a class of 3-
(heteroaryl) coumarins, a variety of 3-(thiazolyl)
O
O
O
O
Type B
Type A
Chart 1
coumarins containing
a
biologically significant
We became interested in the study of these molecules on
heterocycle, thiazole has been synthesized and
evaluated as pharmaceutically active agents,
fluorescence probes and laser dyes [19-22]. In
addition, ꢀ-conjugated polymers consisting of
recurring thiazole rings are known to display
interesting electronic, optical and electric properties
[23,24]. Despite the popularity of coumarin-thiazole
systems (type A structures, Chart 1), there appears to
be no report on the design of ꢀ-aryl/heteroaryl
conjugated coumarin-thiazole systems, represented
by type B structures shown in Chart 1.
consideration that the presence of a ꢀ-polarised framework
might impart these systems with potentially useful
electronic, photo-physical and nonlinear optic properties. In
pursuit of our interest in the electronic properties of novel
heterocyclic systems [25-27], we herein describe synthesis,
optical spectral studies and nonlinear optic properties of
one of the type B systems, exemplified by structures 8a-f
depicted in Scheme 1. These compounds are characterized
by the linkages of ꢀ-aryl/heteroaryl chromophore and the
coumarin motif at the C4 and C2 positions of the thiazole
nucleus, respectively.

918
S. H Mashraqui, H. Mistry and S. Sundaram
Vol 43
Scheme 1
S
S
O
O
H2N
H2SO4 / AcOH
H2O
O
Br
DMF
N
+
O
O
O
O
O
O
3
2
1
S
S
PPh3
PCl5
N
N
OH
Cl
Toluene
O
O
O
O
4
5
S
S
O
KtOBu / DMF
N
+
N
-
+
PPh3Cl
Ar
H
O
O
Ar
O
O
6
7a-f
8a-f
a:
d:
Ar =
Ar =
Ar =
b:
c:
Ar =
OMe
NO2
N
HO
Ar =
f: Ar =
e:
N
S
Synthetic route for the preparation of compounds 8a-f
Table 1
1H-nmr data (500MHz, CDCl3) of 8a-f
Compounds
8a
1H-nmr (ꢀ)
3.01 (6H, s), 6.71 (1H, d, J= 8 Hz), 7.13 (1H, d, J=14 Hz, olefinic H), 7.32 (1H, t, J=8Hz), 7.37 (1H, d, J=8 Hz), 7.38 (1H,
d, J=14 Hz, olefinic H), 7.45 (1H, d, J=8 Hz), 7.54 (1H, t, J=8Hz), 7.64 (1H, d, J=8 Hz), 8.30 (1H, s, thiazole H), 8.78 (1H,
s, coumarin H).
8b
8c
3.8 (6H, s), 6.93 (1H, d, J=8 Hz),7.20 (d, J=16 Hz, olefinic H), 7.32 (1H, t, J=8Hz), 7.38 (1H, d, J=8 Hz), 7.42 (1H, d, J=16
Hz, olefinic H), 7.52 (1H, d, J=8 Hz), 7.55 (1H, t, J=8Hz), 7.65 (1H, d, J=8 Hz), 8.38 (1H, s, thiazole H), 8.79 (1H, s,
coumarin H).
6.85, (1H, t, J=8Hz), 6.92 (1H, d, J=8 Hz), 7.18 (1H, t, J=8Hz), 7.4 (1H, t, J=8Hz), 7.45 (1H, d, J=8 Hz), 7.54 (d, J=18 Hz,
olefinic H), 7.64 (1H, d, J=8 Hz), 7.65 (1H, t, J=8Hz), s7.71 (1H, d, J=18 Hz, olefinic H), 7.95 (1H, d, J=8 Hz), 8.38 (1H, s,
thiazole H), 8.89 (1H, s, coumarin H), 10.15 (1H, s, OH).
8d
8e
7.11-7.42 (4H, m, ArH & thiophene H), 7.18 (1H d, J=16 Hz, olefinic H), 7.4 (1H, d, J=8 Hz), 7.6 (1H, t, J=8Hz), 7.61-
7.71 (m, 2H, Ar H & olefinic H), 8.45 (1H, s, thiazole H), 8.84 (1H, s, coumarin H).
7.34 (1H, t, J=8Hz), 7.39 (1H, d, J=8 Hz),7.48 (1H, d, J=18 Hz, olefinic H), 7.53 (1H, d, J=18 Hz, olefinic H), 7.55 (1H, t,
J=8Hz), 7.66 (1H, d, J=8 Hz), 7.71 (1H, d, J=8 Hz), 8.26 (1H, d, J=8 Hz), 8.51 (1H, s, thiazole H), 8.81 (1H, s, coumarin
H).
8f
7.34 (1H, t, J=8Hz), 7.39 (1H, d, J=8 Hz), 7.41(1H, d, J=15 Hz, olefinic H), 7.49(1H, d, J=16.5 Hz, olefinic H), 7.55 (1H, t,
J=8Hz), 7.66 (1H, d, J=8 Hz), 7.71 (2H, d, J=6 Hz, pyridine H), 8.49 (1H, s, thiazole H), 8.65 (2H, d, J=6 Hz, pyridine H),
8.81 (1H, s, coumarin H).

Jul-Aug 2006
ꢀ-Aryl/Heteroaryl Conjugated Coumarin-Thiazoles
919
Results and Discussion.
DMF at room temperature using freshly prepared
potassium t-butoxide. Extractive work-up of the reaction
gave a dark-red crude showing a single major spot on
TLC. Purification of the crude by flash column
chromatography on silica gel led to the isolation of pure
8a in 60 % yield as a deep yellow solid, mp 187-189 °C.
The compound analyzed correctly for its molecular
formula C22H18N2O2S and showed in the IR spectrum
strong bands at 1720 and 1622 cm-1 due to the
presence of a lactone carbonyl and olefinic group,
respectively. In the 1H NMR spectrum, a sharp
singlet at ꢂ 3.0 (6H) is seen for the -NMe2 group,
whereas singlets located at ꢂ 8.3 and 8.78 could be
assigned to C4 coumarin and C5 thiazole protons,
respectively. The olefinic protons are discernible as
doublets each at ꢂ 7.13 and 7.38 with high J of 14
Hz, thereby indicating "E" olefinic geometry. These
data fully endorse the structural assignment to 8a.
After having established the viability of the synthetic
protocol, we submitted several ꢀ-rich (7b-d) and ꢀ-
The coumarin-thiazole ꢀ-conjugated systems 8a-f were
readily synthesized (Scheme 1) by employing the well-
known Hantzsch thiazole protocol and the Wittig
olefination as the key steps. To start with, 3-ꢁ-bromo-
acetyl coumarin 1 was subjected to the Hantzsch conden-
sation with benzoyloxy thioacetamide 2 in dry DMF to
obtain the desired coumarin-thiazole benzoyl ester 3 in
good yield. The structure 3 is fully supported by analysis
and spectral data as given in the experimental. Hydrolysis
of 3 was accomplished by heating (100 °C, 6 h) in a
mixture of acetic acid, water and sulphuric acid (v/v/v
5:5:1). Hydrolyzed product 4, thus obtained was
converted into the chloro derivative 5 by heating with
PCl5 in refluxing toluene for 2hr under N2 atmosphere.
Fusion of an intimate mixture of 5 with an equivalent
quantity of PPh3 (100 °C, 6hr) provided the phosphonium
salt 6. The Wittig condensation of 6 with 4-N,N-
dimethylaminobenzaldehyde 7a was performed in dry
Table 2
UV- Vis., Emission, NLO and TG-DTA data of compounds 8a-f
ꢄmaxx104
CHCl3
ꢃem nm
Stokes shift
ꢅꢃ nm
ꢆ-value
10-30esua
TG-DTA
(Td)
Compounds
CHCl3
ꢃab nm
S
N
O
390
2.82
537
147
23.2
350 °C
N
O
8a
S
N
O
354
356
1.85
2.60
463
453
109
97
12.2
17.2
330 °C
348 °C
OMe
O
8b
S
N
O
O
HO
8c
S
N
363
346
338
1.52
1.90
1.95
452
517
429
89
171
91
14.3
21.05
17.03
362 °C
349 °C
365 °C
O
S
O
8d
S
N
NO2
O
O
8e
S
N
N
O
O
8f
a
First hyperpolarisability ꢆ was measured with respect to the reference p-nitroaniline in CHCl3 (17.8ꢇ 10-30 esu).

920
S. H Mashraqui, H. Mistry and S. Sundaram
Vol 43
deficient aldehydes (7e-f) to the Wittig reaction with
6 to access the corresponding thiazole-coumarin ꢀ-
conjugated products 8b-f as the pure trans isomers (J
= 15 to 18 Hz) either by crystallization or silica gel
purification in 40-60 % yield. The products showed
expected elemental analysis and spectral features and
minor changes in the ꢁmax (ꢂ ꢁmax ± 2-7 nm). Judging from
the absence of significant solvatochromism, we propose
that no appreciable charge redistribution occurs upon
excitation in more polar solvents [28]. Accordingly, the
coumarin local ꢀ-ꢀ* excitation appears to be the dominant
mode of electronic transition with rather weak charge
transfer character in the excited state.
1
their H NMR data are collected in Table 1.
Scheme 2
S
S
S
N
+
..
N
H+
N
..
N
N
+
H
O
N
H
O
O
O
O
O
= 390 nm
= 501 nm
max
= 365 nm
max
λ
λ
λ
max
8a
S
N
+
+
N
H
H
O
O
= 336 nm
λ
max
Although, not studied in detail, we have also
investigated the affect of addition of acid on the ꢁmax of
8a. Since, this compound carries two potential protonation
sites, one on the acceptor i.e. thiazole and another on the
donor i.e. dimethylamino- chromophore, it was of interest
to see how the protonation on either one or both sites
would affect the UV-Visible spectral behaviour. As
expected, the UV-Visible spectra of 8a recorded in CHCl3
containing ca. 1% trifluoroacetic acid (TFA) produced
marked changes in the positions of ꢁmax (Figure 1),
depending upon the site and degree of protonation. As
shown in Figure 1, in the presence of TFA, three new
absorption bands, one at a longer ꢁmax at 501 nm and two
Optical Spectral Studies
The UV-Visible spectral analysis 8a-f was carried out
in CHCl3 solvent and the data are collected in Table 2.
The absorption spectra of 8a-f are characterized by a
single broad absorption band in the region of 338 to 390
nm, the ꢁmax being dependent upon the donor/acceptor
nature of the ꢀ-attached aryl/ heteroaryl chromophores.
Consistent with very powerful donor ability of the
dimethylaminophenyl donor, the compound 8a showed
ꢁmax at 390 nm, which is the most bathochromically
shifted absorption in the series. For the cases of 8b-d, the
ꢁmax appeared in the order 8d>8c>8b, an observation
which is in keeping with the increasing ꢀ-donor properties
of the ꢀ-attached p-anisyl, 2-hydroxyphenyl and
thiophene chromophores, respectively [27]. For the cases
of 8e and 8f carrying ꢀ-acceptor, p-nitrophenyl group and
pyridyl rings, the ꢁmax appeared much blue shifted (346
and 338 nm, respectively) relative to those recorded for ꢀ-
attached donor chromophoric systems 8a-d (ꢁmax 354 to
390 nm). The blue shifts are in agreement with the
reduced ꢀ-electronic delocalization in ꢀ-acceptor
substituted 8e and 8f. Furthermore, the appearance of ꢁmax
at slightly lower energy at 346 nm for the case of p-
nitrophenyl analog 8e compared to 338 nm observed for
pyridyl analog 8f probably indicates relatively greater
polarisation in the former system. Upon changing the
solvent from CHCl3 to the more polar CH3CN and
CH3OH, the UV-Visible spectra for 8a-f suffered only
0.7
0.6
8a
0.5
0.4
8a+H+
0.3
0.2
0.1
0.0
250
300
350
400
450
500
550
600
Wavelength (nm)
Figure 1. UV-Vis of 8a in CHCl3 and in CHCl3 + 1% TFA.

Jul-Aug 2006
ꢀ-Aryl/Heteroaryl Conjugated Coumarin-Thiazoles
921
at shorter ꢁmax at 365 and 336 nm are seen at the
expense of the original 390 nm absorption band
recorded in plain CHCl3. The appearance of one red and
two blue shifted bands suggests the formation of three
distinct protonated species, depending upon whether the
dimethylamino group or the basic thiazole nitrogen or
both are undergoing protonation. Various protonation
equilibria involved in the protonation of 8a are
illustrated in Scheme 2. The appearance of the red
shifted 501 nm absorption is most likely the
consequence of protonation occurring at the thiazole
nitrogen since, the resulting thiazolium ring in 8a+H+,
being a stronger ꢀ-acceptor compared to the thiazole
ring in 8a, would induce greater charge transfer from
the donor, dimethylamino group and hence the t red
shift. On the other hand, the origin of the band at 365
nm is likely a consequence of the protonation of donor,
dimethylamino group. The protonated dimethylamino
group, being a weak electron donor would diminish the
charge transfer interaction compared to that prevalent in
neutral 8a, thereby causing the blue shift. Finally, the
most blue shifted 336 nm band probably has its origin
in the bis-protonated species, wherein the charge
transfer is expected to be virtually inhibited. Similar
observations have been reported by Mitewa et al for the
case of 2-(4-N,N-dimethylaminophenyl)benzothiazole
and analogs under acidic conditions [29,30].
The emission spectra for 8a-f in CHCl3 were obtained
by exciting these molecules at their main absorption
bands (Table 2). The emission maxima, ꢁem are observed
from a low of 429 nm to a high of 537 nm. However, no
clear trend based on ꢀ-donor or acceptor ability of the ꢀ-
conjugated aryl/heteroaryl groups is discernible in the
series. In particular, high Stokes shifts of 145 and 171 nm
are observed for systems 8a and 8e carrying a ꢀ-attached
donor, dimethylaminophenyl and an acceptor, p-
nitrophenyl chromophore, respectively. The relatively
higher values of Stokes shifts for these molecules indicate
that the dominant local excitations reach the vibrationally
relaxed states (i.e. the Franck-Condon states) prior to the
emission. In comparison to 8a and 8f, the lower values of
Stokes shifts for 8b-d and 8f (89 to 108 nm) are indicative
of relatively destabilized emitting states.
17.8ꢃ 10-30 esu) as the reference standard [33]. The results
are summarized in Table 2. The first hyperpolarisabilities
were found to range from 12 to 23 ꢃ 10-30 esu. For reasons
not yet known, curiously both 8a (ꢂ= 23 ꢃ10-30 esu) and
8e (ꢂ of 21 ꢃ10-30 esu), carrying respectively a strong
donor, dimethylaminophenyl group and
a strong
acceptor p-nitrophenyl group exhibited comparable ꢂ
values. For the remaining systems, the first hyper-
polarisability varied from a low of 12 ꢃ 10-30 esu for 8b
to a high of 17 ꢃ 10-30 esu for 8c and 8f. Unfortunately,
no clear correlation of ꢂ with the nature of ꢀ-attached
aryl/heteroaryl chromophores is available from these
data. Although, the ꢂ values for 8a-f compare favorably
with p-nitroaniline (17.8ꢃ 10-30 esu), however, they are
sizeably lower than the value of 73ꢃ10-30 esu reported for
the well-known NLO benchmark, 4-dimethylamino-4'-
nitrostilbene (DANS) [34]. Nevertheless, it is noteworthy
that systems 8a-f showed complete optical transparency
beyond 465 nm. Hence, despite the moderate ꢂ, these
systems fully conform to the transparency-nonlinearity
trade-off condition required for the design of the NLO
materials. Further, we have also evaluated the thermal
stability of 8a-f using TG-DTA method. The compounds
exhibited the decomposition temperatures (Td) in the
range 330 to 366 °C (Table 2). Thus, the thermal stability
of this class of compounds is superior to that reported for
DANS (Td = 290 °C) [35], a feature which is significant
for NLO applications.
Conclusion.
Hantzsch thiazole protocol and the Wittig olefination
have been used to append thiazole and ꢀ-aryl/heteroaryl
chromophores onto the coumarin motif to construct a
series of ꢀ-conjugated aryl/heteroaryl coumarin-thiazole
systems 8a-f. The UV-Visible data could be correlated
satisfactorily with respect to the characteristic of ꢀ-
attached donor or acceptor chromophores. The UV-
Visible spectral data of molecules 8a under acidic
conditions have been interpreted in terms of modification
of donor/acceptor properties of the chromophores
undergoing protonation. Although, the first hyper-
polarisability for this class of compounds were found to
be rather modest, nevertheless the molecules showed
complete transparency in the frequency doubling region at
564 nm. In addition, compounds were found to be
thermally robust at least up to 330°C These latter
properties are critical for ultimate device fabrications. In
light of these encouraging results, it would be worthwhile
to study other aryl/heteroaryl coumarin-thiazole
frameworks represented by the type B structures (Chart
1), as well as to introduce appropriate substituent(s) on
one or more rings to fine-tune the electronic and other
properties.
Nonlinear Optical Properties and Thermal Stability.
Since, ꢀ-conjugated chromophoric systems are widely
known to display high molecular first hyperpolarisability ꢂ
[31,32], coumarin-thiazoles mofits 8a-f, being ꢀ-
conjugated chromophoric systems are also expected to
exhibit NLO properties. Accordingly, 8a-f were evaluated
for their first hyperpolarisability ꢂ by using the HRS
technique with the laser of frequency of 1064 nm. External
reference method was applied using p-nitroaniline (ꢂ =

922
S. H Mashraqui, H. Mistry and S. Sundaram
Vol 43
EXPERIMENTAL.
Anal. Calcd. for C13H8NO2SCl: C, 56.31; H, 2.88; Cl, 12.8; N,
5.05; S, 11.55. Found: C, 56.15; H, 2.74; Cl, 12.71; N, 5.13; S,
11.33%.
The chemicals, solvents for synthesis and spectral grade
solvents were purchased from SD Fine Chemicals (India) and
used as received. Melting points (uncorrected) were determined
on a Gallenkamp apparatus. Ir spectra were recorded on a
Shimadzu FTIR-420 spectrophotometer. 1H nmr spectra were
recorded on a Bruker-AMX-500 spectrometer with TMS as an
internal standard. UV-Visible spectra were taken on Shimadzu
UV-visible spectrophotometer UV-2100 and Fluorescence
spectra were recorded on a Shimadzu spectrofluoremeter RF-
5301 PC.
Preparation of Phosphonium Salt 6.
A
powdered mixture of 5 (9.69 g, 35 mmole) and
triphenylphosphine (10.48 g, 40 mmole) was heated in an oil
bath for 1 hr at 100-110 °C. The reaction mixture was cooled
and repeatedly triturated with benzene to remove unreacted
starting materials. Finally, the solid was washed with
isopropanol and dried in vacuum dessicator to give
phosphonium salt 6 in 77 % yield (14.52 g), mp 240-245 °C.
Anal. Calcd. for C31H23Cl PNO2S: C, 69.01; H, 4.26, Cl, 6.58;
N, 2.59; S, 5.93. Found: C, 68.89; H, 4.02; Cl, 6.42; N, 2.31; S,
5.78%.
Coumarin-3-(2-benzoyloxy methyl thiazol-4yl) (3).
A mixture of bromoacetyl coumarin 1 (24.03 g, 90 mmole)
and benzoyloxy thioamide 2 (17.55 g, 90 mmole) in dry DMF
(150 ml) was stirred and heated to 90 °C for 24 hr. The reaction
mixture was cooled to room temperature, poured in cooled water
and neutralized with sodium hydrogen carbonate. The solid that
precipitated out was collected by filtration, washed with water
and dried. The crude product was purified using SiO2 column
chromatography (elution CHCl3) to give pure 3, mp 172-175 °C
in 68 % yield. ir (KBr, ꢀ cm-1): 3010, 1720, 1730, 1600, 1460,
Typical Procedure for the Wittig Reaction.
3-{2-[2-(4-Dimethylamino-phenyl)-vinyl]-thiazol-4-yl}-chromen-
2-one (8a).
Phosphonium salt
6 (1.08 g, 2 mmole) and p-N,N-
dimethylamino benzaldehyde 7a (0.298 g, 2 mmole) were
dissolved in dry DMF (15 ml) to which an excess of freshly
prepared potassium t-butoxide (1 g) was added. The reaction
mixture was stirred at room temperature for 2 hr and then
decomposed in cold 5 % HCl. A red colored solid precipitated
which was collected by filtration, washed with water and air
dried. The crude solid was purified by SiO2 column
chromatography (elution; CHCl3 + 2% methanol) to afford 8a as
a yellow solid, mp 187-189 °C in 60 % yield (0.45 g). ir (KBr ꢀ
cm-1): 3010, 1720, 1620, 1540, 1360, 1240, 1090, 760, 780; 1H-
nmr, see Table 1.
1
1360, 1120, 720; H-nmr (CDCl3, 500 MHz): ꢁ 5.7 (s, CH2
proton), 7.31 (t, Ar H), 7.38 (d, J=8 Hz, Ar H), 7.49 (d, J=8 Hz,
Ar 2H), 7.55 (t, Ar H), 7.61 (d, J=8 Hz, Ar H), 8.13 (d, J= 8Hz,
Ar 2H) 8.51 (s, thiazole H), 8.8 (s, coumarin H).
Anal. Calcd. for C20H13NO4S: C, 66.11; H, 3.58; N, 3.85; S,
8.81. Found: C, 66.21; H, 3.34; N, 3.69; S, 8.52%.
Coumarin-3-(2-hydroxylmethylthiazolyl) (4).
Coumarin derivative 3 (21.78 g, 60 mmole) was added to a
solution made up of acetic acid (50 ml), water (50 ml) and conc.
sulphuric acid (10 ml). The reaction mixture was heated to
reflux until a clear solution was obtained (ca. 6 hr). The reaction
mixture was cooled and poured over crushed ice. The
precipitated solid was collected by filtration, washed thoroughly
with water and air dried. The crude product was purified by SiO2
column chromatography (elution; CHCl3 + 2% CH3OH) to give
13.2 g (85 %) of pure 4, mp 185-190 °C. ir (KBr ꢀ cm-1): 3400,
1720, 1620, 1020, 1060, 1080, 760; 1H-nmr (CDCl3, 500MHz): ꢁ
5.01 (s, CH2 proton), 5.03 (s, OH proton), 7.32 (t, Ar H), 7.38 (d,
J=8 Hz, Ar H), 7.58 (t, Ar H), 7.61 (d, J=8 Hz, Ar H) , 8.45 (s,
thiazole H), 8.71 (s, coumarin H),
Anal. Calcd. for C22H18N2O2S: C, 70.58; H, 4.8; N, 7.48; S,
8.55. Found: C, 70.35; H, 4.55; N, 7.32; S, 8.35%.
3-{2-[2-(4-Methoxy-phenyl)-vinyl]-thiazol-4-yl}-chromen-2-
one (8b).
This compound was prepared from phosphonium salt 6 (1.08
g, 2 mmole) and p-methoxy benzaldehyde 7b (2 mmol) in dry
DMF following the typical procedure described for 8a; mp 184-
187 °C, yield 58 %; ir (KBr ꢀ cm-1): 3010, 1720, 1620, 1520,
1260, 1180, 1100, 760, 780; 1H-nmr, see Table 1.
Anal. Calcd. for C21H15NO3S: C, 69.80; H, 4.15; N, 3.87; S,
8.86. Found: C, 69.67; H, 4.05; N, 3.73; S, 8.93%.
3-{2-[2-(2-Hydroxy-phenyl)-vinyl]-thiazol-4-yl}-chromen-2-
one (8c).
Anal. Calcd. for C13H9NO3S: C, 65.25; H, 3.47; N, 5.40; S,
12.35. Found: C, 65.02; H, 3.29; N, 5.13; S, 12.09%.
This compound was prepared from phosphonium salt 6 (1.08
g, 2 mmole) and salicaldehyde 7c (2 mmol) in dry DMF
following the typical procedure; mp 225 °C, yield 50 %; ir (KBr,
Coumarin-3-(2-chloromethyl thiazol-4-yl) (5).
Coumarin derivative 4 (12.95 g, 50 mmole) and PCl5 (10.4 g,
50 mmole) were taken in dry toluene (200 ml) and the reaction
was refluxed and stirred for 2 hr. Most of the toluene was
removed by distillation under vacuum and residue neutralized
with saturated aqueous sodium carbonate. The crude solid
product (13 g) thus obtained was purified by SiO2 column
chromatography (elution; CHCl3) to afford the desired product
5, mp 155 °C in 75 % yield (10.4 g). ir (KBr ꢀ cm-1): 3010,
1
ꢀ cm-1): 3400, 1720, 1600, 1460, 1100, 960, 760; H-nmr, see
Table 1.
Anal. Calcd. for C20H13NO3S: C, 69.16; H, 3.74; N, 4.03; S,
9.22. Found: C, 69.05; H, 3.59; N, 3.89; S, 9.13%.
3-[2-(2-Thiophen-2-yl-vinyl)-thiazol-4-yl]-chromen-2-one (8d).
This compound was prepared from phosphonium salt 6 (1.08
g, 2 mmole) and thiophene-2-carboxaldehyde 7d (2 mmol) in
dry DMF following the typical procedure; mp 162-165 °C, yield
60 %; ir (KBr, ꢀ cm-1): 3010, 1720, 1620, 1480, 1245, 1180,
940, 760, 780, 700. 1H-nmr, see Table 1.
1
1720, 1620, 1480, 1180, 1000, 760; H-nmr (CDCl3, 500MHz):
ꢁ 5.01 (s, CH2 proton), 5.03 (s, OH proton), 7.33 (t, Ar H), 7.38
(d, J=8 Hz, Ar H), 7.56 (t, Ar H), 7.63 (d, J=8 Hz, Ar H) , 8.5 (s,
thiazole 1H), 8.74 (s, coumarin 1H).

Jul-Aug 2006
ꢀ-Aryl/Heteroaryl Conjugated Coumarin-Thiazoles
923
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Anal. Calcd. for C18H11NO2S2: C, 64.09; H, 3.26; N, 4.15; S,
18.99. Found: C, 63.79; H, 3.18; N, 3.87; S, 18.74%.
3-{2-[2-(4-Nitro-phenyl)-vinyl]-thiazol-4-yl}-chromen-2-one
(8e).
This compound was prepared from phosphonium salt 6 (1.08
g, 2 mmole) and p-nitro benzaldehyde 7e (2 mmol) in dry DMF
following the typical procedure; mp 252- 255 °C, yield 40 %; ir
(KBr, ꢁ cm-1): 3010, 1720, 1600, 1520, 1340, 940, 760, 780; 1H-
nmr, see Table 1.
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(1995).
Anal. Calcd. for C20H12N2O4S: C, 63.82; H, 3.19; N, 7.44; S,
8.51. Found: C, 63.64; H, 3.04; N, 7.14; S, 8.24%.
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Photochem. Photobiol. A., 162, 599 (2004).
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Kawamoto, J. Antibiotics, 42, 1768 (1989).
3-{2-[2-(4-Pyridyl)-vinyl]-thiazol-4-yl}-chromen-2-one (8f).
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This compound was prepared from phosphonium salt 6 (1.08
g, 2 mmole) and pyridine-4-carboxaldehyde 7f (2 mmol) in dry
DMF following the typical procedure; mp 224-226 °C, yield 40
%; ir (KBr, ꢁ cm-1): 3010, 1720, 1620, 1480, 1410, 1180, 1100,
760, 780. 1H-nmr, see Table 1.
Anal. Calcd. for C19H12N2O2S: C, 68.67; H, 3.61; N, 8.43; S,
9.63. Found: C, 68.46; H, 3.75; N, 8.34; S, 9.49%.
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