Synthesis and study of fluorescent properties of benzothiazolylthieno- thiophene derivatives

Article abstract of DOI:10.1007/s10593-012-0932-3

A number of benzothiazolylthienothiophenes have been synthesized. Spectral studies have revealed that all these compounds have fluorescent properties that depend on their structure. Dependence of absorption and fluorescence bands positions on the nature of substituents have been established. Increase of the electron-withdrawing nature of substituents led to bathochromic shift of the absorption and fluorescence bands as well as to decrease of the fluorescence intensity.

Full text of DOI:10.1007/s10593-012-0932-3

Chemistry of Heterocyclic Compounds, Vol. 47, No. 11, February, 2012 (Russian Original Vol. 47, No. 11, November, 2011)
SYNTHESIS AND STUDY OF FLUORESCENT
PROPERTIES OF BENZOTHIAZOLYLTHIENO-
THIOPHENE DERIVATIVES*
I. V. Zavarzin1, L. K. Karabaeva1, N. G. Shimkina1, S. V. Shorunov1,
V. N. Yarovenko1, I. V. Platonova1, O. I. Kobeleva2, T. M. Valova2,
V. A. Barachevskii2, and M. M. Krayushkin1*
A number of benzothiazolylthienothiophenes have been synthesized. Spectral studies have revealed that
all these compounds have fluorescent properties that depend on their structure. Dependence of
absorption and fluorescence bands positions on the nature of substituents have been established.
Increase of the electron-withdrawing nature of substituents led to bathochromic shift of the absorption
and fluorescence bands as well as to decrease of the fluorescence intensity.
Keywords: benzothiazolylthienothiophenes, Schiff bases, stilbenes, absorption spectra, fluorescence
properties.
The idea of creating photochromic recording media with nondestructive fluorescent reading of optical
information [1, 2] has recently been implemented by the development of photochromic recording media for
three-dimensional optical memory [3]. In particular, this concept can be realized by synthesis of hybrid
photochromic compounds containing a photochromic fluorescent fragment [4-9]. Earlier we have proposed to
use the strongly luminescenting benzothiazolylthieno[3,2-b]thiophene derivatives as such a fragment. Thus, the
reaction of 5-(1,3-benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophene-2-carbaldehyde (1) with aniline derivatives
of fulgimides led to photochromes containing fulgimide and fluorescing benzothiazolylthienothiophene
fragments. The absorption and fluorescence spectral properties of these compounds were studied [10]. In the
present work, thiophene 1 obtained from (3-pentylthieno[3,2-b]thiophen-2-yl)-1,3-benzothiazole (2) [10] was
used as a starting material to prepare hydrazones 3a,b, azomethine derivatives 3c-e, as well as stilbenes 4a-d.
The spectral parameters of these compounds were studied.
Schiff bases 3a-e were synthesized in 60-70% yield according to Scheme 1.
_______
*To our dear colleague, Prof. M. G. Voronkov on the occasion of his 90th birthday.
**To whom correspondence should be addressed, e-mail: mkray@mail.ioc.ac.ru.
1N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninskii Ave., Moscow
119991, Russia.
2Photochemistry Center, Russian Academy of Sciences, 7a Novatorov St., Moscow 119421, Russia; e-mail:
barva@photonics.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 47, pp. 1735-1743, November, 2011.
Original article submitted September 29, 2011.
0009-3122/12/4711-1445©2012 Springer Science+Business Media, Inc.
1445

Stilbenes 4a-d were obtained by the Wittig reaction of aldehyde 1 with phosphonium chlorides 5a-d,
which, in turn, were prepared by the reaction of triphenylphosphine with chlorides 6a-d* in toluene (Scheme 2).
Scheme 1
LDA
DMF
THF
N
N
N
S
S
S
RNH2
EtOH
S
S
S
–78°C
S
S
S
C5H11
C5H11
N
R
C5H11
O
2
1
3a–e
3 a R = NHPh, b R = NHC(O)(C6H4NO2-p), c R = Bu, d R = (CH2)2NEt2, e R = (CH2)3NHEt
Scheme 2
R
Cl
6a–d
N
PPh3
PhMe
S
S
LiN(SiMe3)2
THF, DMF
+
3 Cl–
R
PPh
1
+
S
C5H11
5a–d
R
4a–d
OMe
OMe
Me
OMe
O
N
S
CH
2 , c R =
, d R =
4–6 a R = Ph, b R =
N
2-(Chloromethyl)-6-methoxy-1,3-benzothiazole (6c) was synthesized by the reduction of methyl ester 7
[11] using sodium borohydride in methanol with subsequent chlorination of the resultant (6-methoxy-1,3-benzo-
thiazol-2-yl)methanol (8) (Scheme 3).
Scheme 3
CCl4
PPh3
NaBH4
MeOH
Cl
N
S
OMe
O
OH
N
S
N
S
MeO
MeO
MeO
7
8
6c
The reaction of aldehyde 1 with phosphonium chlorides 5a-d in THF in the presence of LiN(SiMe3)2
with the intermediate generation of phosphoric ylides led to (E)-isomers of stilbenes 4a-d in 63-68% yield. The
1
trans geometry of the double bond in products 4a-d was assigned by the H NMR spectra where coupling
constants were in the range of 14.3-16.0 Hz, which is a characteristic value for the trans orientation.
_______
*The authors express their gratitude to D. S. Khachatryan of IREA, Institute of High-Purity Chemical Reagents
for supplying chloride 6d.
1446

The results of the study of the absorption spectra of these compounds along with their fluorescence
properties are given in Table 1 and Figs. 1-3. All these compounds appeared to be fluorescent. We note that
benzothiazole 2 obtained in our previous work [10] displays coinciding absorption and fluorescence excitation
bands with maximum at 353 nm as well as a fluorescence band with maximum at 413 nm, which is shifted
toward longer wavelengths by 60 nm relative to the absorption band (Fig. 1, Table 1).
Introduction of the electron-withdrawing carbonyl group into benzothiazole 2 lead to the bathochromic
shift of the absorption and fluorescence bands by 25 nm for the thienothienylbenzothiazole aldehyde 1 (Table 1).
Schiff bases 3a-e give a hypsochromic shift of both the absorption and the fluorescence bands. This shift
also depends on the nature of the substituents. Table 1 shows that the bathochromic spectral shift for compounds
3a and 3c-e increases in the order 3e < 3d < 3c < 3a.
Fig. 1. Absorption (1), fluorescence excitation (2), and fluorescence spectra (3) for
benzothiazole 2 in toluene.
TABLE 1. Spectral Properties of Benzothiazolylthienothiophenes 1, 2, 3a-e
and Stilbenes 4a-d in Toluene*
max 10–4,
I fl,
rel. units
max
abs
max
exc
max
fl
max
fl
max
exc
Com-
pound
ε

,

,

,

–

,
l·mol–1·cm–1
nm
nm
nm
nm
378
353
377
398
376
374
362
415
403
430
410
5.0
4.2
5.2
2.4
8.4
5.6
3.6
9.0
3.4
6.6
6.2
377
353
375
420
376
362
360
415
403
430
408
438
413
436
506
436
425
420
457
474
505
482
60
60
61
109
60
51
58
71
71
75
72
145
1140
130
1
2
3a
3b
3c
3d
3e
4a
4b
4c
4d
0.12
405
225
1230
2660
1840
1615
990
_______
* max  and  fml ax are the maxima of the long-wavelength absorption
max
exc
abs
band, fluorescence excitation band and fluorescence band, respectively, max
is the molar extinction coefficient at the absorption band maximum, Ifl is the
fluorescence intensity at the fluorescence band maximum.
1447

Diamine 3e has the shortest-wavelength absorption (362 nm) and fluorescence bands (420 nm) (Fig. 2)
as well as the strongest fluorescence in comparison with other compounds described (Table 1). The Stokes shift
max
( - emxacx ) for this compound is 61 nm. The fluorescence intensity for the diamine 3e is much higher than for
fl
derivatives 3a, 3c, and 3d. Introduction of the strong electron-withdrawing 4-nitrophenylhydrazone fragment into
3b, as in the case of compound 1, leads to a bathochromic shift of the absorption bands (from 377 to 398 nm) and a
max
fl
rather significant shift of 
from 436 to 506 nm (Table 1). In this case, the fluorescence intensity also drops
sharply, while the Stokes shift increases to 109 nm.
Dependence of the fluorescence band shift on the electron-withdrawing capacity of substituents is also
found for stilbenes 4a-d. Table 1 shows that the maxima of fluorescence bands are shifted toward longer
wavelengths with increasing electron-withdrawing capacity of substituents (4a < 4b < 4d < 4c). The Stokes shift
for all these compounds is about 70 nm. No clear tendencies are found in the behavior of the absorption bands
although a trend for the bathochromic spectral shift is noted. As in the case of compounds examined above, the
fluorescence intensity decreases with increasing electron-donor capacity of the substituents. A typical change in
the spectral parameters in the case of the spectrum of compound 4d is shown in Fig. 3.
Fig. 2. Spectra for the absorption (1), fluorescence excitation (2), and fluorescence (3)
of compound 3c in toluene.
Fig. 3. Spectra for the absorption (1), fluorescence excitation (2), and fluorescence
(3) of compound 4d in toluene.
1448

We should note that stilbenes 4a-d stand out among the other products due to their high fluorescence
intensity, which is independent on the substituents nature (Table 1). A characteristic feature of these compounds
is the fine structure in the absorption and, especially, the fluorescence spectra (Fig. 3).
Thus, we have prepared a series of new benzothiazolylthienothiophenes possessing fluorescent
properties. The spectral studies have shown that the fluorescent properties of these products depend on the
substituent at the second position of the thieno[3,2-b]thiophene fragment. The best fluorescence properties were
found for the stilbene derivatives. Dependence was found between the position of the absorption and
fluorescence bands and the nature of the substituents. A bathochromic shift of the absorption and fluorescence
bands was noted with increase of the electron-withdrawing nature of the substituents, which led us to assume the
feasibility of controlling the spectral characteristics of benzothiazolylthienothiophenes by means of the fine
chemical modification of these compounds.
EXPERIMENTAL
The spectrophotometric measurements (photostationary spectra) of the studied compounds were
recorded on a Varian Carey 50 Bio spectrophotometer in toluene solution. The spectrofluorimetric
measurements were carried out on a Varian Carey Eclipse spectrofluorimeter under identical experimental
conditions (spectrofluorimeter slit width, sample position, and concentration). The spectrofluorimetric
measurements were recorded using cells with 10 mm path length. A solution with concentration 5·10-6 mol/l was
taken as the working concentration for taking the absorption, excitation, and emission spectra. The concentration
for compound 4b was 1·10-5 mol/l.
1
The H NMR spectra were recorded on a Bruker AC-300 spectrometer at 300 MHz with the residual
solvent protons as internal standard (DMSO-d6,  2.51 ppm; CDCl3,  7.27 ppm). The electron impact mass
spectra were taken on a Kratos spectrometer with direct sample inlet into the radiation source with ionization
energy 70 eV and control voltage 1.75 kV. The melting points were determined on a Boethius heating block and
were not corrected.
Commercial substances 6a and 6b were obtained from Acros. Commercially available reagents from
Acros and Sigma-Aldrich were used in this work.
5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophene-2-carbaldehyde
Phenylhydrazone
(3a).
Phenylhydrazine hydrochloride (0.047 g, 0.323 mmol) was added to a solution of compound 1 (0.100 g, 0.269
mmol) in ethanol (15 ml). The reaction mixture was stirred for 4 h at 60°C. The dark-brown precipitate formed
was filtered off, washed with petroleum ether, and dried in vacuum to give compound 3a. Yield 65%; mp
1
155-157°C (ethanol). H NMR spectrum (DMSO-d6), , ppm (J, Hz): 0.87 (3H, t, J = 6.9, CH3); 1.40 (4H, m,
CH2CH2); 1.77 (2H, m, CH2); 3.17 (2H, t, J = 7.6, CH2); 6.80 (1H, t, J = 7.3, H Ar); 7.05-7.30 (4H, m, H Ar);
7.40-7.60 (2H, m, H Ar); 7.55 (1H, s, H-3); 8.00 (2H, m, H Ar); 8.15 (1H, s, N=CH); 8.20 (1H, s, NH). Mass
spectrum, m/z (Irel, %): 462 (19), 461 [M]+ (55), 418 [M-C3H7]+ (3), 93 (100). Found, %: C 64.68; H 5.44;
N 9.45, S 20.43. C25H23N3S3. Calculated, %: C 65.04; H 5.02; N 9.10; S 20.84.
N'-{[5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophen-2-yl]methylidene}-4-trobenzohydrazide
(3b). 4-Nitrobenzohydrazide (0.058 g, 0.323 mmol) was added to a solution of compound 1 (0.100 g, 0.269
mmol) in ethanol (15 ml). The reaction mixture was stirred for 3.0-3.5 h at 60°C. The yellow precipitate formed
was filtered off, washed with petroleum ether, and dried in vacuum to give compound 3b. Yield 70%; mp
1
162-163°C (ethanol). H NMR spectrum (DMSO-d6), , ppm (J, Hz): 0.90 (3H, t, J = 6.6, CH3); 1.40 (4H, m,
CH2CH2); 1.80 (2H, m, CH2); 3.17 (2H, t, J = 7.3, CH2); 7.40-7.60 (2H, m, H Ar); 7.87 (1H, s, H-3); 7.90-8.10
(2H, m, H Ar); 8.15 (2H, d, J = 7.7, H Ar); 8.35 (2H, d, J = 7.7, H Ar); 8.70 (1H, s, N=CH); 12.20 (1H, s, NH).
Mass spectrum, m/z (Irel, %): 534 [M]+ (35), 418 [M-C3H7]+ (5), 120 (100). Found, %: C 58.73; H 4.56; N 10.10;
S 17.51. C26H22N4O3S3. Calculated, %: C 58.41; H 4.15; N 10.48; S 17.99.
1449

N-{[5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophen-2-yl]methylidene}butane-1-amine
(3c).
Butyl-amine (0.060 ml, 0.646 mmol) was added to a solution of compound 1 (0.100 g, 0.269 mmol) in
ethanol(15 ml). The reaction mixture was stirred for 6 h at 60°C. The precipitate formed was filtered off, washed
with petroleum ether, and dried in vacuum to give compound 3c. Yield 60%; mp 145-147°C (ethanol). 1H NMR
spectrum (DMSO-d6), , ppm (J, Hz): 0.85-0.95 (6H, m, 2CH3); 1.27-1.50 (6H, m, 3CH2); 1.60 (2H, m, CH2);
1.75 (2H, m, CH2); 3.15 (2H, t, J = 7.8, CH2); 3.55 (2H, t, J = 6.8, CH2); 7.40-7.60 (2H, m, H Ar); 7.80 (1H, s,
H-3); 8.05 (1H, d, J = 8.0, H Ar); 8.15 (1H, d, J = 7.9, H Ar); 8.50 (1H, s, N=CH). Mass spectrum, m/z (Irel, %):
427 (17), 426 [M]+ (100). Found, %: C 64.32; H 6.39; N 6.39; S 22.90. C23H26N2S3. Calculated, %: C 64.75;
H 6.14; N 6.57; S 22.55.
N-{[5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophen-2-yl]methylidene}-N',N'-diethylethane-
1,2-diamine (3d). N,N-Diethylethylidenediamine (0.045 ml, 0.323 mmol) was added to a solution of compound
1 (0.100 g, 0.269 mmol) in ethanol (15 ml). The reaction mixture was stirred for 4.0-4.5 h at 60°C. The yellow
precipitate was filtered off, washed with petroleum ether, and dried in vacuum to give compound 3d. Yield 70%;
mp 150-152°C (ethanol). 1H NMR spectrum (CDCl3), , ppm (J, Hz): 0.95 (3H, t, J = 7.0, CH3); 1.00-1.11 (6H,
m, 2CH3); 1.45 (4H, m, CH2CH2); 1.85 (2H, m, CH2); 2.68 (4H, m, CH2CH2); 2.85 (2H, t, J = 6.9, CH2); 3.20
(2H, t, J = 7.9, CH2); 3.75 (2H, t, J = 6.9, CH2); 7.35-7.50 (3H, m, H Ar, H-3); 7.90 (1H, d, J = 8.0, H Ar); 8.05
(1H, d, J = 8.1, H Ar); 8.45 (1H, s, N=CH). Mass spectrum, m/z (Irel, %): 469 [M]+ (7), 87 (100). Found, %:
C 63.86; H 6.88; N 8.72; S 20.64. C25H31N3S3. Calculated, %: C 63.92; H 6.65; N 8.95; S 20.48.
N-{[5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophen-2-yl]methylidene}-N'-ethylpropane-
1,3-diamine (3e). N-Ethyl-1,3-propanediamine (0.033 g, 0.323 mmol) was added to a solution of compound 1
(0.100 g, 0.269 mmol) in ethanol (15 ml). The reaction mixture was stirred for 5 h at 60°C. The yellow
precipitate was filtered off, washed with petroleum ether, and dried in vacuum to give compound 3e. Yield
70%; mp 153-154°C (ethanol). 1H NMR spectrum (CDCl3), , ppm (J, Hz): 0.90 (3H, t, J = 7.0, CH3); 1.15 (3H,
t, J = 5.9, CH3); 1.50 (4H, m, 2CH2); 1.85-1.90 (4H, m, 2CH2); 2.68 (2H, m, CH2); 3.10 (2H, t, J = 7.0, CH2);
3.25 (2H, t, J = 7.6, CH2); 3.85 (2H, t, J = 7.7, CH2); 7.30-7.40 (3H, m, H Ar, H-3); 8.05 (1H, d, J = 8.0, H Ar);
8.15 (1H, d, J = 8.0, H Ar); 8.55 (1H, s, N=CH). Mass spectrum, m/z (Irel, %): 456 (9), 455 [M]+ (43), 82 (100).
Found, %: C 63.44; H 6.02; N 9.04; S 21.50. C24H29N3S3. Calculated, %: C 63.26; H 6.41; N 9.22; S 21.11.
(6-Methoxy-1,3-benzothiazol-2-yl)methanol (8). NaBH4 (0.42 g, 11.052 mmol) was added in portions
with stirring to a solution of ester 7 (1.10 g, 4.933 mmol) in methanol (30 ml). After 2 h stirring at room
temperature, the solvent was evaporated in vacuum. The reaction mixture was then brought to pH 7 by adding
2% hydrochloric acid. The precipitate formed was filtered off, washed with water, and dried in vacuum to give
compound 8. Yield 83%; mp 160-162°C (ethanol). 1H NMR spectrum, , ppm (J, Hz): 3.85 (3H, s, OCH3); 4.85
(2H, s, CH2); 6.25 (1H, s, OH); 7.10 (1H, d, J = 8.0, H Ar); 7.65 (1H, s, H Ar); 7.80 (1H, d, J = 8.1, H Ar). Mass
spectrum, m/z (Irel, %): 195 [M]+ (47), 166 [M-CH2OH]+ (100). Found, %: C 55.59; H 4.21; N 7.42; S 16.03.
C9H9NO2S. Calculated, %: C 55.37; H 4.65; N 7.17; S 16.42.
2-Chloromethyl-6-methoxy-1,3-benzothiazole (6c). Triphenylphosphine (1.6 g, 6.1 mmol) was added
to a solution of compound 8 (0.8 g, 4.1 mmol) in CCl4 (15 ml). The reaction mixture was heated at reflux for 2 h.
After cooling, the solvent was evaporated in vacuum. The residue was separated by thin-layer chromatography
1
using 1:1 ethyl acetate–hexane to give compound 6c. Yield 45%; mp 145-147°C (ethanol). H NMR spectrum
(CDCl3), , ppm (J, Hz): 3.90 (3H, s, CH3); 4.90 (2H, s, CH2); 7.10 (1H, d, J = 8.1, H Ar); 7.35 (1H, s, H Ar);
7.95 (1H, d, J = 7.9, H Ar). Mass spectrum, m/z (Irel, %): 214 [M]+ (54). Found, %: C 50.88; H 3.98; Cl 16.23; N
6.87; S 14.72. C9H8ClNOS. Calculated, %: C 50.59; H 3.77; Cl 16.59; N 6.55; S 15.01.
Phosphonium chlorides 5a-d (General Method). Triphenylphosphine (8.0 mmol) was added to a
solution of benzyl chloride (6a), 4-vinylbenzyl chloride (6b), 2-chloromethyl-6-methoxy-1,3-benzothiazole (6c),
or 4-chloromethyl-2-(3,4-dimethoxyphenyl)-5-methyl-1,3-oxazole (6d) in toluene. The reaction mixture was
heated at reflux for 12 h in an argon atmosphere. The precipitate formed was filtered off, washed with petroleum
ether, and dried in vacuum.
1450

1
Benzyl(triphenyl)phosphonium Chloride (5a). Yield 75%; mp 118-120°C (ethanol). H NMR
spectrum (DMSO-d6), , ppm (J, Hz): 5.15-5.25 (2H, s, CH2); 7.00 (2H, m, H Ar); 7.20-7.35 (3H, m, H Ar);
7.60-7.80 (9H, m, H Ar); 7.85-8.00 (6H, m, H Ar). Mass spectrum, m/z (Irel, %): 352 [M-Cl-H]+ (45), 351[M-Cl-
2H]+ (51), 183 (100). Found, %: C 77.50; H 5.36; Cl 9.35; P 7.79. C25H22ClP. Calculated, %: C 77.22; H 5.70;
Cl 9.12; P 7.97.
4-Vinylbenzyl(triphenyl)phosphonium Chloride (5b). Yield 69%; mp 135-137°C (ethanol). 1H NMR
spectrum, , ppm (J, Hz): 5.15 (1H, d, J = 7.7) and 5.70 (1H, d, J = 7.5, =CH2); 5.40 (2H, s, CH2); 6.50-6.65
(1H, m, =CH–); 7.00-7.20 (4H, m, H Ar); 7.50-7.85 (15H, m, H Ar). Mass spectrum, m/z (Irel, %): 277 (1), 276
[M-Cl-CH2=CHC6H4] (9), 183 (100). Found, %: C 78.52; H 5.44; Cl 8.06; P 7.98. C27H24ClP. Calculated, %:
C 78.16; H 5.83; Cl 8.54; P 7.47.
[(6-Methoxy-1,3-benzothiazol-2-yl)methyl]triphenylphosphonium Chloride (5c). Yield 73%; mp
1
130-132°C (ethanol). H NMR spectrum, , ppm (J, Hz): 3.80 (3H, s, OCH3); 6.00 (2H, s, CH2); 7.05 (1H, d,
J = 7.5, H Ar); 7.60-7.95 (17H, m, H Ar). Mass spectrum, m/z (Irel, %): 440 [M-Cl]+ (9). Found, %: C 68.41;
H 5.04; Cl 7.13; N 2.68; P 6.83; S 6.45. C27H23ClNOPS. Calculated, %: C 68.13; H 4.87; Cl 7.45; N 2.94;
P 6.51; S 6.74.
{[2-(3,4-Dimethoxyphenyl)-5-methyl-1,3-oxazol-2-yl]methyl}triphenylphosphonium Chloride (5d).
1
Yield 69%; mp 135-137°C (ethanol). H NMR spectrum, , ppm (J, Hz): 2.05 (3H, s, CH3); 3.80 (6H, s,
2OCH3); 5.15 (2H, s, CH2); 7.05 (1H, d, J = 7.7, H Ar); 7.12 (1H, s, H Ar); 7.30 (1H, d, J = 7.5, H Ar);
7.70-7.95 (15H, m, H Ar). Mass spectrum, m/z (Irel, %): 494 [M-Cl]+ (6), 493 [M-H-Cl]+ (19), 262 (100). Found,
%: C 70.58; H 5.23; Cl 6.37; N 2.96; P 5.49. C31H29ClNO3P. Calculated, %: C 70.25; H 5.52; Cl 6.69; N 2.64;
P 5.84.
3-Alkyl-5-arylvinyl-2-(1,3-benzothiazol-2-yl)thieno[3,2-b]thiophenes 4a-d (General Method). A
solution of LiN(SiMe3)2 (5.30 ml, 1.0 mol/l) in THF was added to a suspension of compound 5a-d (4.8 mmol) in
dry THF (40 ml) and stirred for 30 min. Then, a solution of compound 1 (1.79 g, 4.8 mmol) in THF (40 ml) and
DMF (2 ml) was added. The reaction mixture was stirred at room temperature for 1 h. The reaction mixture was
then poured into water and extracted with methylene chloride. The extract was washed with water, and dried
over magnesium sulfate, and evaporated. The residue was subjected to chromatography on silica gel using 4:1
hexane–ethyl acetate as the eluent.
2-{3-Pentyl-5-[(E)-2-phenylvinyl]thieno[3,2-b]thiophen-2-yl)-1,3-benzothiazole (4a). Yield 63%; mp
145-147°C (ethanol). 1H NMR spectrum, , ppm (J, Hz): 0.98 (3H, t, J = 6.9, CH3); 1.50 (4H, m, CH2CH2); 1.89
(2H, m, CH2); 3.21 (2H, t, J = 7.8, CH2); 7.00 (1H, d, J = 16.0, CH vinyl); 7.20-7.70 (9H, m, CH vinyl, H-6, H Ar);
7.90 (1H, d, J = 7.8, H Ar); 8.18 (1H, d, J = 8.1, H Ar). Mass spectrum, m/z (Irel, %): 446 (12), 445 [M]+ (50),
402 [M-CH2CH2CH3]+ (72), 41 (100). Found, %: C 70.42; H 5.53; N 2.88; S 21.17. C26H23NS3. Calculated, %:
C 70.07; H 5.20; N 3.14; S 21.59.
2-{5-[(E)-2-(4-Vinylphenyl)vinyl]-6-pentylthieno[3,2-b]thiophen-2-yl}-1,3-benzothiazole (4b). Yield
1
65%; mp 158-160°C (ethanol). H NMR spectrum, , ppm (J, Hz): 0.98 (3H, t, J = 7.0, CH3); 1.50 (4H, m,
CH2CH2); 1.89 (2H, m, CH2); 3.20 (2H, t, J = 7.9, CH2); 5.20 (1H, d, J = 8.0) and 5.70 (1H, d, J = 7.7, =CH2);
6.60-6.70 (1H, m, =CH–); 7.09 (1H, d, J = 16.0, H vinyl); 7.20-7.60 (8H, m, CH vinyl, H-6, H Ar); 7.90 (1H, d,
J = 8.2, H Ar); 8.18 (1H, d, J = 8.4, H Ar). Mass spectrum, m/z (Irel, %): 472 [M]+ (9), 54 (100). Found, %:
C 71.46; H 5.17; N 2.72; S 20.65. C28H25NS3. Calculated, %: C71.30; H 5.34; N 2.97; S 20.39.
2-{(E)-2-[5-(1,3-Benzothiazol-2-yl)-6-pentylthieno[3,2-b]thiophen-2-yl]vinyl}-6-methoxy-1,3-benzo-
1
thiazole (4c). Yield 68%; mp 158-160°C (ethanol). H NMR spectrum, , ppm (J, Hz): 0.95 (3H, t, J = 7.0,
CH3); 1.50 (4H, m, 2CH2); 1.90 (2H, m, CH2); 3.20 (2H, t, J = 8.0, CH2); 3.90 (3H, s, OCH3); 7.05 (1H, d,
J = 14.3, CH vinyl); 7.20-7.70 (7H, m, CH vinyl), H-6, H Ar); 7.90 (1H, d, J = 8.2, H Ar); 8.10 (1H, d, J = 8.2,
H Ar). Mass spectrum, m/z (Irel, %): 532 [M]+ (7). Found, %: C 63.51; H 4.33; N 5.56; S 23.87. C28H24N2OS4.
Calculated, %: C 63.12; H 4.54; N 5.26; S 24.08.
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2-(5-{(E)-[4-(3,4-Dimethoxyphenyl)-5-methyl-1,3-oxazol-4-yl]vinyl}-3-pentylthieno[3,2-b]thiophen-
1
2-yl]-1,3-benzothiazole (4d). Yield 68%; mp 158-160°C (ethanol). H NMR spectrum, , ppm (J, Hz): 0.98
(3H, t, J = 7.0, CH3); 1.50 (4H, m, CH2CH2); 1.85 (2H, m, CH2); 2.50 (3H, s, CH3); 3.20 (2H, t, J = 7.9, CH2);
3.95 (3H, s, OCH3); 4.05 (3H, s, OCH3); 6.85 (1H, d, J = 14.3, CH vinyl); 6.95 (1H, s, H Ar); 7.20-7.70 (6H, m,
CH vinyl, H-6, H Ar); 7.90 (1H, d, J = 8.2, H Ar); 8.10 (1H, d, J = 8.4, H Ar). Mass spectrum, m/z (Irel, %): 586
[M]+ (16). Found, %: C 65.43; H 5.22; N 4.58; S 16.57. C32H30N2O3S3. Calculated, %: C 65.50; H 5.15; N 4.77;
S 16.39.
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