Preparation and characterization of substituted 3-benzothiazol-2- ylcoumarins

Article abstract of DOI:10.1002/jccs.201000033

A series of substituted 3-benzothiazolylcoumarins was prepared from condensation of 2-hydroxybenzaldehyde and 2-cyanomethylbenzothiazole to investigate the effect of the nature and position of substituents on their absorption and fluorescent behavior. Com

Full text of DOI:10.1002/jccs.201000033

Journal of the Chinese Chemical Society, 2010, 57, 213-221
213
Preparation and Characterization of Substituted
3-Benzothiazol-2-ylcoumarins
Richard Y. Chaoa (
), Mei-Fang Dinga (
), Jhao-Yu Chena (
),
Chuan-Chen Leeb (
) and Shaw-Tao Lina,c* (
)
aDepartment of Applied Chemistry, Providence University, Sha-Lu, Taichung 433, Taiwan, R.O.C.
bDepartment of Applied Life Science, Asia University, Wufong, Taichung 431, Taiwan, R.O.C.
cDepartment of Environmental Science and Hygiene, Yuanpei University, Hsin-Chu 300, Taiwan, R.O.C.
A series of substituted 3-benzothiazolylcoumarins was prepared from condensation of 2-hydroxy-
benzaldehyde and 2-cyanomethylbenzothiazole to investigate the effect of the nature and position of sub-
stituents on their absorption and fluorescent behavior. Compounds with a substituent containing a hetero-
atom which attached at the C6 position showed a split broad absorption band. Solutions of these com-
pounds in various solvents exhibited brilliant blue fluorescence. The emission intensity for compounds
with an alkoxy group at the C6 or C7 position in DMF was approximately 7- and 15-fold higher than for
the corresponding precursor and quinine sulfate solution, respectively. These compounds also exhibit
high thermal stability in solid state.
Keywords: Benzothiazolylcoumarins; UV-visible absorption; Fluorescence; Hydrogen bond;
Stokes shift; Quinine sulfate.
1. INTRODUCTION
benzothiazol-2-ylcoumarins to investigate the influence
of the nature and position of substituents on the coumarin
ring on the absorption and emission wavelength and the
emission intensity.
Coumarins are natural products showing a wide
range biological properties, the most prominent of which
are photobiological effects upon irradiation with UV
light. Thus, many coumarins are potent photosensitizers
of human skin, with valuable applications in medicine for
the treatment of skin diseases and as photo-materials.1
Owing to their inherent photochemical characteristics,
reasonable stability, good solubility and relative ease of
synthesis, coumarin derivatives have been extensively in-
vestigated for electronic and photonic applications such
as charge-transfer agents, solar energy collectors and
non-linear optical materials.2-4 The emission wavelength
and intensity of coumarin chromophores strongly depend
on the various functional groups substituents at different
positions.5,6 Appropriately substituted coumarins have
been used as fluorescent dyes for synthetic fibers and as
daylight fluorescent pigments.7,8 The fluorescence of the
coumarin chromophore system is known to vary signifi-
cantly for appropriate substituents at the C3 and C7 posi-
tions. Chromophores with an electron donor at the C3 po-
sition or an electron acceptor at the C7 position exhibit
substantial bathochromicity and strong fluorescence. In
the present study, we prepared a series of substituted 3-
2. RESULTS AND DISCUSSION
2.1. Preparation of 3-benzothiazol-2-ylcoumarins
3-Benzothiazol-2-ylcoumarins were prepared from
the reaction of substituted 2-hydroxybenzaldehyde and 2-
cyanomethylbenzothiazole, as illustrated in Fig. 1. 2-Cy-
anomethylbenzothiazole was obtained from reaction of
2-aminothiophenol and malonitrile in the methanol solu-
tion with HOAc as a catalyst at RT.9 After stirring for 5 h
the product was harvested by filtration in good yield. The
product can be used without further purification. To pre-
pare 3-benzothiazol-2-ylcoumarins, the compound mixture
and substituted 2-hydroxybenzaldehyde in ethanol were
treated with 1 M NaOH for 15 min, yielding a solid adduct
to which aqueous HCl (1:1 vol.) was added and then heated
to 90 °C for 15 min.10 Those products were recrystallized
from DMF for spectral analysis. The corresponding ether
or ester was prepared from the hydroxyl derivatives and
alkyl halide or acyl halide to give the compounds as shown

214 J. Chin. Chem. Soc., Vol. 57, No. 2, 2010
Chao et al.
1
assigned using COSY and HMQC techniques. The H
in Fig. 2.11 3-Benzothiazol-2-yl-6-aminocoumarin (4r)
was obtained by reduction of its nitro-counterpart 4f by us-
ing iron powder and H2SO4 as showing in Fig. 3.12 The
chemical shifts at 9.10-9.20 and 8.10-8.20 ppm are attrib-
uted to the protons on C4 and C5, respectively. The charac-
teristic 13C chemical shifts at ~160 (two signals) and 154
ppm are due to the resonance of C2, C2¢ and C9 atoms in
the skeleton. The skeleton of most of this series of com-
structures of the compounds were confirmed by 1H and 13
C
NMR spectroscopy, mass spectrometry and elemental anal-
ysis. The chemical shifts of all protons and carbons were
Fig. 1. Pathway for the preparation of benzothiazolylcoumarins 4a-4h.
N
O
N
S
S
R -X
2
HO
R2O
K CO
2
/acetone
3
O
O
O
4c or 4g
4
from 4c
R : CH C H (i); C H (j); CH C H Br-p (k);
2
from 4g
2
6
5
3
5
2 6 4
R : CH (l); CH C H (m); CH C H Br-p (n);
2
3
CH C H F-p (o); C(O)C H C H (p);
2
6
5
2 6 4
2
C H (q).
6
5
2 2 6 5
3
5
Fig. 2. Pathway for derivatization of benzothiazolyl-hydroxycoumarine.
N
O
N
H2N
O2N
S
S
Fe/H SO
2
4
O
O
O
4r
4f
Fig. 3. Reduction of nitro group to prepare compound 4r.

Spectral Analysis of 3-Benzothiazol-2-ylcoumarins
J. Chin. Chem. Soc., Vol. 57, No. 2, 2010 215
pounds is stable and retains the molecular ion under EI con-
ditions during MS analysis.
position C6, respectively) and an electron-withdrawing
group has the opposite effects shifts of -4 nm shift for NO2
(4f).
2.2. UV-visible and fluorescence characteristics of
3-benzothiazol-2-ylcoumarins
In general, a substituent (such as OCH3) on position
C6 (4e) or C7 (4l) caused a longer wavelength shift (28 nm)
than on C5 (4b, 11 nm) or C8 (4h, -2 nm). The longer wave-
length shift can probably be attributed to aggregates such
as H-type and J-types due to presence of the hydrogen
bonds shown in Fig. 4a.13-15 A substituent on C5 might pro-
hibit the formation of aggregates via the hydrogen bonding.
On the other hand, a substituent on C8 might create the
steric hindrance that inhibits potential intermolecular hy-
drogen bonding. However, the presence of a heteroatom at
C6 caused the absorption band to broaden, with two max-
ima and consequently weaken absorption coefficients. This
can be rationalized as potential interaction between the
The spectral characteristics of the compounds inves-
tigated, such as the absorption maximum (lmax), emission
maximum (lem), extinction coefficient (emax) and relative
fluorescent intensity (with respected to quinine sulfate)
were measured in DMF (Table 1). Addition of a benzo-
thiazole (5) ring to coumarin (6) at the C3 position caused a
46-nm shift in lmax. The maximum shifts for compounds 4
due to the additional substituent strongly depends upon the
nature and position of the substituents. As a general rule, an
electron donor leads to a shift to longer wavelength shift
(69, 30, and 28 nm for NH2 (4r), OH (4c) and OCH3 (4e) at
Table 1. Spectral properties of the dyes 4a-4r in DMF solution
Emission intensity
Stokes shift relative to quinine
sulfate
l max
(nm)a
l em
(nm)b
e
Dyes
mol-1dm3cm-1
H (4a)
364
368
375
355
392
392
362
349
394
396
283
360
354
433
357
391
357
391
357
391
393
392
392
383
392
433.5
435.0
435.5
460.4
459.7
441.0
433.5
486.6
486.1
447.5
461.9
460.6
477.0
502.1
461.0
460.8
461.0
440.5
461.0
461.0
443.0
440.5
438.5
443.0
439.5
69.5
67.0
5.1
4.7
25200
24320
25600
18829
19671
30800
28240
17471
15200
32400
15416
21200
18734
06442
17122
17600
17368
17600
24088
24800
35200
38800
34800
31600
25200
6-CH3 (4d)
5-OCH3 (4b)
6-OCH3 (4e)
60.5
6.9
105.4
67.7
11.2
7.6
7-OCH3 (4l)
8-OCH3 (4h)
6-OH (4c)
49.0
14.4
5.3
71.5
137.6
92.1
7.5
7.4
7-OH (4g)
6-NO2 (4f)
51.5
15.2
3.7
178.9
100.6
123.0
69.1
4.5
6-NH2 4r
7.1
7.2
6-OCH2C6H5 (4i)
6-OC3H5 (4j)
104.0
69.8
7.0
7.1
104.0
49.5
7.0
7.0
6-OCH2C6H4Br (4k)
104.0
70.0
7.1
7.2
7-OCH2C6H5 (4m)
7-OCH2C6H4Br (4n)
7-OCH2C6H4F (4o)
7-OCOC2H2C6H5 (4p)
7-OC3H5 (4q)
50.0
15.0
15.7
14.6
12.7
14.9
48.5
46.5
60.0
47.5
a Concentration of 2.0 ´ 10-5 M.
b Concentration of 1.0 ´ 10-7 M.

216 J. Chin. Chem. Soc., Vol. 57, No. 2, 2010
Chao et al.
heteroatom and the hydrogen on C8 (Fig. 4b).
The compounds investigated exhibited a remarkable
bathochromic shift depending on the substituent position.
For OCH3 the Stokes shifts was 60, 71, 68, and 49 nm for
substitution at positions C5 (4b), C8 (4h), C6 (4e), and C7
(4l), respectively. The different shifts for 4e and 4l com-
pared to 4b and 4h might again be attributed to more inter-
molecular hydrogen bonding for the former two isomers.
Compound 4e in CH2Cl2 solution exhibited two maxima
that were excited separately resulting in two the identical
emissions shown in Fig. 5. This indicates the formation of
the identical excited states from different ground states. To
obtain the information on the emission efficiency for the
3-benzothiazol-2-ylcoumarins compared to coumarin, the
emission intensity from quinine sulfate (7) was used as a
reference. Table 1 shows that less enhancement was ob-
tained for substituents at C5 and C8 (5-fold), and strong en-
hancement for a substituent at C7 (13-15-fold). Since the
UV absorption band was split into two maxima to reduce
the absorption coefficient for C6-isomer and excitation of
two maxima yield identical emission spectra. If the emis-
sion intensity for two different excited wavelengths is
added, the total intensity is comparable to that obtained for
the C7 counterpart.
Fig. 4. Possible formation of intermolecular hydrogen
bond. (a) without heteroatom at C6 position, (b)
with heteroatom at C6 position, a potential for-
mation of an additional hydrogen bond.
The basic principle for electronic absorption and emis-
sion is an electron transition between the ground state and
Fig. 5. The absorption spectrum and emission spectra of 3-benzothiazol-2-yl-6-methoxycourmarin (4e) obtained from exci-
tation at different wavelength.

Spectral Analysis of 3-Benzothiazol-2-ylcoumarins
J. Chin. Chem. Soc., Vol. 57, No. 2, 2010 217
Table 2. Spectral properties of some selected 3-benzothiazoylcoumarinsa
Chloroform
Stokes
DMF
Dichloromethane
Stokes
Stokes
shift
Subtituent
l max l em
(nm) (nm)
e
l max
l em
e
l max l em
e
shift
(nm)
shift
(nm)
mol-1 dm3cm-1 (nm)
(nm)
mol-1 dm3cm-1 (nm)
(nm)
mol-1 dm3cm-1
(nm)
H (4a)
366.00 447.02 81.02
23386
34816
32587
28856
19884
364.00 433.50 069.50
368.00 435.00 067.00
392.00 458.70 066.70
355.00 460.39 105.39
394.00 489.99 095.99
349.00 486.65 137.65
360.00 460.62 100.62
283.00 461.88 178.88
396.00 447.50 051.50
392.00 441.00 049.00
25200
24320
19671
18829
15200
17471
21200
15416
32400
30800
363.00 448.38 85.38
368.00 446.06 78.06
393.00 453.70 60.70
359.00 455.25 96.25
391.00 452.44 61.44
358.00 450.93 92.93
365.00 451.09 86.09
36787
28997
25815
23269
18288
16734
30809
6-CH3 (4d) 370.00 447.62 77.62
6-OCH3 (4e) 395.00 454.54 59.54
360.00 453.70 93.70
6-OH (4g)
6-NO2 (4f)
7-OH (4g)
392.00 452.01 60.01
366.00 456.96 90.96
377.00 457.80 80.80
40092
05007
30441
30359
377.00 455.00 78.00
392.00 457.50 65.50
381.00 459.52 78.52
27806
36668
36341
7-OCH3 (4q) 394.00 458.69 64.69
380.00 459.70 79.70
a Concentration for absorption and emission determination are 2.0 ´ 10-5 M and 1.0 ´ 10-7 M, respectively.
the excited state. The energies for these states can be al-
tered by hydrogen bonding and the degree of polarization,
depending on the nature of the solvents. The solubility of
3-benzothiazol-2-ylcoumarins is relatively poor in com-
mon solvents, such as alcohols and hydrocarbons. To check
whether the shift is caused by solvatochromism,16 we mea-
sured the UV-vis absorption of compounds with a substi-
tuent on either the C6 or C7 position in CHCl3 (hydrogen
donor), CH2Cl2 (non-polar) and DMF (polar and proton ac-
ceptor) at a concentration of approximately 2 ´ 10-5 M (Ta-
ble 2). Almost no solvatochromism was observed. This can
be explained on the basis that the resonance between two
moieties occurs without involving the carbonyl group of
the lactone. Therefore, interaction between carbonyl groups
and solvent molecules does not significantly influence the
resonance electron flow. Among the solvents used, a more
bathochromic shift and more intense emission were ob-
served for the least polar solvent, dichloromethane.
particular showed good thermal stability up to 300 °C.
3. CONCLUSIONS
3-Benzothiazol-2-ylcoumarins are potential fluores-
cent chromophores with long absorption and emission
maxima. The absorption maxima and relative fluorescent
intensity were affected by the position of substituents. Sub-
stituents at the C6 and C7 positions on the coumarin ring
yielded stronger fluorescence. This series of compounds
did not show any appreciable solvatochromism.
2.3. Thermal properties of 3-benzothiazol-2-ylcou-
marins
Four typical compounds were analyzed by DSC to
determine their thermal stability. Fig. 6 shows thermo-
grams of 4a, 4e, 4f and 4l. The DSC thermal curves show a
clear plateau followed by a sharp peak. The presence of a
plateau before the melting point suggests that no phase
transition occurred before melting. Melting of these com-
pounds occurred on heating at > 210 °C. Compound 4f in
Fig. 6. DSC thermal curve of 3-benzothiazoylcou-
marins 4a (H), 4e (6-OCH3), 4l (7-OCH3), and

218 J. Chin. Chem. Soc., Vol. 57, No. 2, 2010
Chao et al.
4. EXPERIMENTAL
8.10 (d, 8.0 Hz, 1H, C4¢-H), 7.70 (t, 8.0 Hz, 1H, C7-H),
7.57 (td, 8.0, 1.2 Hz, 1H, C5¢-H), 7.47 (td, 8.0, 1.2 Hz, 1H,
C6¢-H), 7.09 (d, 8.0 Hz, 1H, C8-H), 7.05 (d, 8.0 Hz, 1H,
C6-H), 4.04 (s, 3H, CH3); 13C NMR d 160.24, 159.73,
157.51, 154.69, 152.42, 136.46, 136.31, 135.44, 127.17,
125.88, 123.10, 122.6, 118.11, 109.69, 108.94, 107.10,
57.09; Anal. Calcd. for C17H11O3NS: C, 66.01; H, 3.58; N,
4.53. Found: C, 66.07; H, 3.62; N, 4.55; MS: m/z 309 (M+,
100%).
4.1. Materials and Instrumentation
All melting points were recorded on Fargo MP-2D
system and are uncorrected. 1H and 13C NMR spectra were
recorded at 400 and 100 MHz, respectively, on a Bruker
Advance 400 spectrometer at ambient temperature. Chemi-
cal shifts for samples in DMSO-d6 solution are reported in
d units relative to TMS. C, H, and microanalysis was per-
formed at the Analytical Center of National Chung-Hsing
University. EI mass spectra were obtained on a Thermo Fo-
cus GC coupled to a Thermo PolarisQ MS with an ioniza-
tion potential of 70 eV and a directed insert probe for sam-
ple introduction. Electronic absorption spectra were re-
corded on a Varian Cary 300 spectrophotometer. Fluores-
cence spectra were recorded on Perkin Elmer LS-55 fluo-
rimeter. Differential scanning calorimetry analysis was
carried out on DSC Q-10 (TA Instruments) system.
Common reagent-grade chemicals were purchased
from either Aldrich or E. Merck and were used without fur-
ther purification. Spectroscopic grade solvents from E.
Merck were used in determining UV-visible and fluores-
cence spectra.
4.5. Synthesis of 3-benzothiazol-2-yl-6-hydroxy-
coumarin 4c
M.p. 293-294 °C; (2.63 g, 88%); brownish solid; 1H
NMR d 9.95 (s, 1H, OH), 9.15 (s, 1H, C4-H), 8.17 (d, 8.0
Hz, 1H, C7¢-H), 8.07 (d, 8.0 Hz, 1H, C4¢-H), 7.57 (t, 8.0
Hz, 1H, C5¢-H), 7.47 (t, 1H, 8.0 Hz, 1H, C6¢-H), 7.38 (d,
8.8 Hz, 1H, C8-H), 7.36 (d, 2.8 Hz, 1H, C5-H), 7.17 (d, 8.8,
2.8 Hz, 1H, C7-H); 13C NMR d 60.36, 160.10, 154.74,
152.36, 147.35, 142.52, 136.41, 127.19, 125.93, 122.98,
122.71, 122.50, 119.82, 119.72, 117.68, 114.26; Anal.
Calcd. for C16H9O3NS: C, 65.07; H, 3.07; N, 4.74. Found:
C, 65.09; H, 3.05; N, 4.79; MS: m/z 295 (M+·, 100%).
4.6. Synthesis of 3-benzothiazol-2-yl-6-methyl-
coumarin 4d
4.2. Synthesis of 2-cyanomethylbenzothiazole 1
Acetic acid (0.57 mL, 0.01 mol) was slowly added to
a mixture of 2-aminothiophenol (1.1 mL, 0.01 mol) and
malononitrile (0.64 mL, 0.01 mol) in methanol (10 mL).
After stirring at ambient temperature for 5 h, the yellow
solid was harvested by filtration and recrystallized from
ethanol to give 1 (1.47 g, 85%); m.p. 102-103 °C (Lit: 103
°C).11
1
M.p. 223-224 °C; (2.49 g, 85%); yellow solid; H
NMR d 9.13 (s, 1H, C4-H), 8.15 (d, 8.0 Hz, 1H, C7¢-H),
8.07 (d, 8.0 Hz, 1H, C4¢-H), 7.81 (s, 1H, C6-H), 7.53-7.70
(m, 2H, C5¢-, C7-H), 7.46 (t, 8.0 Hz, 1H, C6¢-H), 7.41 (d,
8.0 Hz, 1H, C8-H), 2.38 (s, 3H, CH3); 13C NMR d 159.57,
159.21, 151.85, 151.48, 141.77, 135.85, 134.45, 134.41,
129.42, 126.38, 125.21, 122.40, 121.85, 119.19, 115.78,
19.99; Anal. Calcd. for C17H11O2NS: C, 69.61; H, 3.78; N,
4.78. Found: C, 69.54; H, 3.76; N, 4.86. MS: m/z 293 (M+·,
100%).
4.3. Synthesis of 3-benzothiazol-2-ylcoumarin 4a
An aqueous NaOH solution (1 mL, 1.0 M) was slowly
added to a 50-mL two-necked flask containing 2-hydroxy-
benzaldehyde (1.10 mL, 10 mmol) and 2-cyanomethyl-
benzothiazole (1.74 g, 10 mmol) in ethyl alcohol (10 mL)
heated at 40 °C. The resulting suspension was stirred at am-
bient temperature for 15 min before adding HCl solution
(10 mL, 6 M) to ensure complete precipitation. The solid
product was collected by filtration and was purified by
recrystallization to yield brownish compound 4a (2.28 g,
82%); m.p. 216-217 °C (Lit: 217-218 °C).17
4.7. Synthesis of 3-benzothiazol-2-yl-6-methoxy-
coumarin 4e
M.p. 222-223 °C; (Lit: 215-217 °C);17 (2.47 g, 80%);
yellow solid.
4.8. Synthesis of 3-benzothiazol-2-yl-6-nitrocoumarin
4f
M.p. 306-307 °C; (Lit: 306-307 °C);18 (2.59 g, 80%);
light yellow solid.
4.4. Synthesis of 3-benzothiazol-2-yl-5-methoxy-
coumarin 4b
4.9. Synthesis of 3-benzothiazol-2-yl-7-hydroxy-
coumarin 4g
M.p. 295 °C; (Lit: 295 °C);18 (2.30 g, 78%); orange
solid.
1
M.p. 241-242 °C; (2.62 g, 85%); yellow solid; H
NMR d 9.23 (s, 1H, C4-H), 8.15 (d, 8.0 Hz, 1H, C7¢-H),

Spectral Analysis of 3-Benzothiazol-2-ylcoumarins
J. Chin. Chem. Soc., Vol. 57, No. 2, 2010 219
4.10. Synthesis of 3-benzothiazol-2-yl-8-methoxy-
coumarin 4h
C19H13O3NS: C, 68.04; H, 3.91; N, 4.18. Found: C, 68.01;
H, 3.89; N, 4.22. MS: m/z 335 (M+·, 100%).
4.13. Synthesis of 3-benzothiazol-2-yl-6-(p-bromo-
benzyloxy)coumarin 4k
M.p. 239-240 °C; (2.72 g, 88%); brownish solid; 1H
NMR d 9.21 (s, 1H, C4-H), 8.18 (d, 8.0 Hz, 1H, C7¢-H),
8.08 (d, 8.0 Hz, 1H, C4¢-H), 7.61 (dd, 8.0, 1.6 Hz, 1H,
C7-H), 7.58 (t, 8.0 Hz, 1H, C5¢-H), 7.48 (t, 8.0 Hz, 1H,
C6¢-H), 7.37-7.45 (m, 2H, C5-, C6-H), 3.95 (s, 3H, CH3);
13C NMR d 159.78, 159.18, 152.22, 146.75, 143.16,
142.37, 136.22, 126.76, 125.60, 125.30, 122.77, 122.23,
121.52, 119.81, 119.60, 116.44, 56.67; Anal. Calcd. for
C17H11O3NS: C, 66.01; H, 3.58; N, 4.53. Found: C, 66.09;
H, 3.65; N, 4.45. MS: m/z 309 (M+·, 100%).
1
M.p. 245-246 °C; (2.31 g, 83%), yellow solid; H
NMR d 9.17 (s, 1H, C4-H), 8.17 (d, 8.0 Hz, 1H, C7¢-H),
8.08 (d, 8.0 Hz, 1H, C4¢-H), 7.71 (d, 2.8 Hz, 1H, C5-H),
7.56-7.61 (m, 3H, phenyl proton), 7.44-7.51 (m, 4H, phen-
yl proton), 7.41 (dd, 8.8, 2.8 Hz, 1H, C7-H), 5.18 (s, 2H,
-O-CH2-); 13C NMR d 159.47, 159.10, 154.81, 151.83,
147.97, 141.54, 135.88, 131.14, 129.60, 126.36, 125.21,
122.38, 121.96, 121.83, 120.86, 119.55, 119.09, 117.15,
113.4, 69.51; Anal. Calcd. for C23H14BrO3NS: C, 59.49; H,
3.04; N, 3.02. Found: C, 59.41; H, 3.07; N, 2.93. MS: m/z
463 (M+·, 18%), 169 (100%).
4.11. Synthesis of 3-benzothiazol-2-yl-6-benzyloxy-
coumarin 4i
An acetone solution (50 L) containing a mixture of
3-benzothiazol-2-yl-6-hydroxycoumarin (1.81 g, 6 mmol),
benzyl bromide (0.72 mL, 12 mmol) and K2CO3 (1.0 g, 7.2
mmol) was refluxed in a two-necked reaction flask for 16 h.
After the system cooled to ambient temperature, the prod-
uct was harvested by filtration and washing with H2O and
ethanol. The product was recrystallized from DMF to give
4.14. Synthesis of 3-benzothiazol-2-yl-7-methoxy-
coumarin 4l
M.p. 243-244 °C (Lit: 242-244 °C);17 (1.48 g, 80%),
yellow solid.
4.15. Synthesis of 3-benzothiazol-2-yl-7-benzyloxy-
coumarin 4m
1
dark brown solid 4i (1.73 g, 75%); m.p. 203-204 °C; H
1
M.p. 238-239 °C; (1.85 g, 80%), yellow solid; H
NMR d 9.19 (s, 1H, C4-H), 8.17 (d, 8.0 Hz, 1H, C7¢-H),
8.07 (d, 8.0 Hz, 1H, C4¢-H), 7.74 (d, 2.8 Hz, 1H, C5-H),
7.57 (t, 8.0 Hz, 1H, C6¢-H), 7.45-7.55 (m, 4H, phenyl pro-
ton), 7.39-7.43 (m, 3H, phenyl proton), 7.34 (t, 7.2 Hz, 1H,
phenyl proton), 5.17 (s, 2H, -CH2-); 13C NMR d 160.23,
159.96, 155.48, 152.37, 148.43, 142.22, 136.94, 136.45,
129.72, 128.97, 128.54, 128.49, 127.19, 125.95, 123.02,
122.74, 122.46, 120.07, 119.76, 117.88, 113.62, 70.35;
Anal. Calcd. for C23H15O3NS: C, 71.67; H, 3.92; N, 3.63.
Found: C, 71.66; H, 3.90; N, 3.65. MS: m/z 385 (M+·, 33%),
91 (100%).
NMR d 9.20 (s, 1H, C4-H), 8.16 (d, 8.0 Hz, 1H, C7¢-H),
8.05 (d, 8.0 Hz, 1H, C4¢-H), 8.01 (d, 8.8 Hz, 1H, C5-H),
7.56 (t, 8.0 Hz, 1H, C5¢-H), 7.24-7.50 (m, 6H, phenyl pro-
ton), 7.24 (d, 2.0 Hz, 1H, C8-H), 7.15 (dd, 8.8, 2.0 Hz, 1H,
C6-H), 5.28 (s, 2H); 13C NMR d 169.09, 159.99, 159.39,
151.92, 142.12, 135.93, 135.64, 131.33, 128.2. 127.93,
127.59, 126.31, 124.97, 122.18, 121.81, 115.82, 14.05,
112.55, 101.48, 70.23; Anal. Calcd. for C23H15O3NS: C,
71.67; H, 3.92; N, 3.63. Found: C, 71.61; H, 3.90; N, 3.66.
MS: m/z 385 (M+·, 9%), 91 (100%).
4.16. Synthesis of 3-benzothiazol-2-yl-7-(p-bromoben-
zyloxy)coumarin 4n
4.12. Synthesis of 6-allyloxy-3-(benzothiazol-2-yl)-
coumarin 4j
1
M.p. 268-269 °C; (2.31 g, 83%), yellow solid; H
1
M.p. 179-180 °C; (1.41 g, 70%); brown solid; H
NMR d 9.19 (s, 1H, C4-H), 8.14 (d, 8.0 Hz, 1H, C7¢-H),
8.05 (d, 8.0 Hz, 1H, C4¢-H), 7.99 (d, 8.8 Hz, 1H, C5-H),
7.61 (d, 8.0 Hz, 1H, phenyl proton), 7.56 (t, 8.0 Hz, 1H,
C5¢-H), 7.40-7.48 (m, 3H, phenyl proton), 7.21 (d, 2.0 Hz,
1H, C8-H), 7.14 (dd, 8.8, 2.0 Hz, 1H, C6-H), 5.28 (s, 2H,
-O-CH2-); 13C NMR d 162.71, 159.82, 159.16, 155.24,
151.81, 141.92, 135, 135.30, 131.18, 131.12, 129.51,
126.11, 124.79, 122.04, 121.64, 120.95, 115.85, 113.85,
112.55, 101.45, 69.28; Anal. Calcd. for C23H14BrO3NS: C,
59.49; H, 3.04; N, 3.02. Found: C, 59.44; H, 3.06; N, 2.98.
NMR d 9.21 (s, 1H, C4-H), 8.19 (d, 8.0 Hz, 1H, C7¢-H),
8.08 (d, 8.0 Hz, 1H, C5¢-H), 7.67 (d, 2.8 Hz, 1H, C5-H),
7.58 (t, 7.2 Hz, 1H, C5¢-H), 7.48 (m, 2H, phenyl proton),
7.36 (dd, 8.8, 2.8 Hz, 1H, C7-H), 6.07 (m, 1H, vinyl pro-
ton), 5.46 (dd, 17.2, 1.6 Hz, 1H, vinyl proton), 5.31 (d, 1H,
10.4 Hz, vinyl proton), 4.64 (d, 5.2 Hz, 2H, -O-CH2-); 13
C
NMR d 159.58, 159.23, 154.95, 151.89, 147.89, 141.72,
135.93, 133.10, 126.46, 125.30, 122.45, 121.94, 119.53,
119.13, 117.74, 117.17, 113.22, 68.99; Anal. Calcd. for

220 J. Chin. Chem. Soc., Vol. 57, No. 2, 2010
Chao et al.
MS: m/z 465 (M+·, 15%), 171 (100%).
4.17. Synthesis of 3-benzothiazol-2-yl-7-(p-fluoroben-
zyloxy)coumarin 4o
4.20. Synthesis of 3-benzothiazol-2-yl-6-amino-
coumarin 4r
A mixture of 3-benzothiazol-2-yl-6-nitrocoumarin
(0.5 g, 1.5 mmol), iron powder (0.25 g, 4.4 mmol), conc.
H2SO4 (25 mL) and H2O (0.1 mL) was stirred at ambient
temperature for 96 h and then slowly poured onto ice-water
(100 mL). The aqueous solution was extracted with ethyl
acetate (3 ´ 20 mL). The ethyl acetate extracts were com-
bined, washed with water, dried over anhydrous magne-
sium sulfate, filtered and subjected to vacuum evapora-
tion. The brownish yellow residue was purified by column
chromatography using silica gel with ethyl acetate/hexane
(1:1) as eluent to afford 4r (0.32 g, 72%); m.p. 271-272
1
M.p. 264-265 °C; (2.06 g, 85%), yellow solid; H
NMR d 9.20 (s, 1H, C4-H), 8.16 (d, 8.0 Hz, 1H, C7¢-H),
8.04 (d, 8.0 Hz, 1H, C5-H), 8.00 (d, 8.8 Hz, 1H, phenyl pro-
ton), 7.57-7.53 (m, 3H), 7.45 (t, 8.0 Hz, 1H, C6¢-H), 7.27-
7.22 (m, 3H, phenyl proton), 7.14 (dd, 8.8, 2.0 Hz, 1H,
C6-H), 5.25 (s, 2H, -O-CH2-); 13C NMR d 162.98, 160.15,
159.42, 155.41, 151.94, 142.15, 135.66, 132.21, 131.37,
129.97, 129.89, 126.36, 125.02, 122.22, 121.85, 115.90,
115.27, 115.05, 114.08, 112.63, 101.53, 69.53; Anal.
Calcd. for C23H14FO3NS: C, 70.58; H, 3.55; N, 3.29.
Found: C, 70.66; H, 3.50; N, 3.33. MS: m/z 403 (M+·, 8%),
109 (100%).
1
°C; H NMR d 9.21 (s, 1H, C4-H), 8.18 (d, 8.0 Hz, 1H,
C7¢-H), 8.09 (d, 8.0 Hz, 1H, C4¢-H), 7.68 (d, 2.0 Hz, 1H,
C5-H), 7.58 (t, 8.0 Hz, 1H, C5¢-H), 7.44-7.53 (m, 3H,
phenyl proton); 13C NMR d 159.64, 159.18, 151.91,
148.40, 141.55, 138.61, 135.96, 126.45, 125.28, 124.02,
122.45, 121.93, 119.60, 119.15, 116.91, 116.60; Anal.
Calcd. for C16H10O2N2S: C, 65.29; H, 3.42; N, 9.52.
Found: C, 65.20; H, 3.38; N, 9.59. MS: m/z 294 (M+·,
100%).
4.18. Synthesis of 3-(benzothiazol-2-yl)-2-oxo-2H-
chromen-7-yl cinnamate 4p
M.p. 237-238 °C; (2.17 g, 85%); light yellow solid;
1H NMR d 9.26 (s, 1H, C4-H), 8.18 (d, 8.0 Hz, d, C7¢-H),
8.16 (d, 8.8 Hz, 1H, C4¢-H), 8.09 (d, 8.0 Hz, 1H), 7.93 (d,
16.0 Hz, 1H, C5-H), 7.82-7.84 (m, 2H, phenyl proton),
7.58 (t, 8.0 Hz, 1H, C6¢-H), 7.53 (d, 2.0 Hz, 1H, phenyl
proton), 7.52-7.47 (m, 4H, phenyl proton), 7.38 (dd, 8.8,
ACKNOWLEDGEMENTS
2.0 Hz, 1H, C6-H), 6.91 (d, 16 Hz, 1H, vinyl proton); 13
C
The authors are grateful to the National Science
Council of ROC (NSC-95-2113-M-126-005) for financial
support and the National Center for High-Performance
Computing for computer time and facilities.
NMR d 164.64, 160.17, 159.63, 154.88, 154.61, 152.57,
147.75, 142.22, 136.53, 134.32, 131.65, 131.47, 129.48,
129.13, 127.10, 125.92, 123.08, 122.58, 119.84, 119.36,
117.23, 110.36; Anal. Calcd. for C25H15O4NS: C, 70.58; H,
3.55; N, 3.29. Found: C, 70.66; H, 3.51; N, 3.20. MS: m/z
425 (M+·, 7%), 131 (100%).
Received August 13, 2009.
4.19. Synthesis of 7-allyloxy-3-benzothiazol-2-yl-
coumarin 4q
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M.p. 209-210 °C; (1.63 g, 81%); yellow solid; H
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