Efficient synthesis and photochromic properties of 2,3-position hybrid diarylethene derivatives

Article abstract of DOI:10.1016/S0040-4020(03)01141-4

An efficient synthetic method was proposed to synthesize some 2,3-position hybrid diarylethene derivatives. In these compounds, one of thiophene rings was attached to the ethylene moiety at 2-position, the other at 3-position. These asymmetric diarylethenes are sensitive at wavelengths in the region of 400 and 500 nm. They can undergo thermally irreversible and fatigue-resistant photochromic reactions in solution, some of them even in the solid state. Substituent effects on their photochromism were examined.

Full text of DOI:10.1016/S0040-4020(03)01141-4

Tetrahedron 59 (2003) 7615–7621
Efficient synthesis and photochromic properties of 2,3-position
hybrid diarylethene derivatives
*
Fan Sun, Fushi Zhang, Haobo Guo, Xinhong Zhou, Ruji Wang and Fuqun Zhao
Department of Chemistry, Tsinghua University, Beijing 100084, People’s Republic of China
Received 9 April 2003; revised 19 June 2003; accepted 14 July 2003
Abstract—An efficient synthetic method was proposed to synthesize some 2,3-position hybrid diarylethene derivatives. In these compounds,
one of thiophene rings was attached to the ethylene moiety at 2-position, the other at 3-position. These asymmetric diarylethenes are sensitive
at wavelengths in the region of 400 and 500 nm. They can undergo thermally irreversible and fatigue-resistant photochromic reactions in
solution, some of them even in the solid state. Substituent effects on their photochromism were examined.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
have a hybrid structure with one of the thiophene rings
attached to the ethylene moiety at 2-position, the other at 3-
position. An efficient synthetic method has been proposed
based on the experimental results, and the photochromic
properties of these compounds both in solution and in solid
state have also been investigated.
To increase the storage density in the region offar field optical
recording, one of the practical approaches to minimize the
mark length is to decrease writing and reading laser
wavelength. Research interests in short wavelength optical
storage have been growing considerably in recent years.1,2
Photochromic diarylethenes have attracted considerable atten-
tion in the field of optical data storage and switches due to their
thermal stability of both isomers and high fatigue resistance.3
However, most diarylethenes reported have absorptionat 550–
750 nm wavelength regions. Developing diarylethene deriva-
tives sensitive at a wavelength around 500 nm or even shorter
for short-wavelength recording is very important.
As well known, the absorption spectrum is dependent on the
substituent effects and the p-conjugation length in a
diarylethene molecule.4–7 In bis(2-thienyl)ethane, the p-
conjugation in closed-ring form is localized in a cyclohex-
adiene structure, shifting the absorption to shorter wave-
length, as compared with the closed-ring form of bis(3-
thienyl)ethane where the p-conjugation extends throughout
the whole molecule.5 Diarylethene with a hybrid structure
of bis(2-thienyl)ethane and bis(3-thienyl)ethane has a
spectrum matching with the short-wavelength laser (400–
500 nm).6 However, these compounds have not been paid
much attention. It is feasible to develop 2,3-position hybrid
diarylethene derivatives for short-wavelength recording.
Scheme 1.
2. Results and discussion
In this paper, we have prepared several asymmetric
diarylethene derivatives (Scheme 1). These compounds
2.1. Synthesis of asymmetric
diarylperfluorocyclopentene derivatives
Keywords: 2,3-position hybrid diarylethene; photochromic; crystal; short-
wavelength recording.
1-(2,5-Dimethyl-3-thienyl)-2-(3-methyl-5-phenyl-2-thienyl)
perfluorocyclopentene (1a), 1-[3-methyl-5-(p-methoxyphenyl)-
2-thienyl]-2-[2-methyl-5-(p-methoxyphenyl)-3-thienyl]
*
Corresponding author. Tel.: þ86-10-62782596; fax: þ86-10-62771149;
e-mail: zhangfs@mail.tsinghua.edu.cn
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)01141-4

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F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
Table 1. The yields of Methods A and B (%)
perfluorocyclopentene (2a), 1-(2,5-dimethyl-3-thienyl)-2-
[3-methyl-5-(p-methoxyphenyl)-2-thienyl]perfluorocyclo-
pentene (3a), and 1-(2,5-dimethylthien-3-yl)-2-(3-methyl-
benzo[b]thien-2-yl)perfluorocyclopentene (4a) were
synthesized by the elimination reaction of mono-substituted
perfluorocyclopentene with organolithium compounds
according to the literature.8 Two methods could be applied
to synthesize the asymmetric diarylethene derivatives as
shown in Scheme 2.
Methods
1a
2a
3a
4a
A
B
75/44.3
45/19.1
85/21.8
43/6.8
78/34.0
40/9.7
84/43.4
49/31.3
The last step yield/total yield.
hydrogen by lithium in Method A created few by-
products.
R–Li þ R1 –X ! R–R þ R1 –R1 þ R–R1
ð1Þ
2.2. Photochromic properties of the asymmetric
diarylethenes in solution
The spectral changes of 1a, 2a, 3a, and 4a in hexane
exposed to UV light are shown in Figures 1–4. Upon
irradiation with 365 nm light the colorless hexane solutions
of 1a, 3a, 4a turned to orange. The photogenerated orange
closed-ring isomers have their absorption maxima at 468,
468, 466 nm, respectively. Upon visible light irradiation
(l.420 nm) the orange color disappeared and the absorp-
tion bands of the open-ring forms were restored. On the
other hand, the colorless hexane solution of 2a turned to red
when irradiated with 365 nm light. A new band appeared at
506 nm which is ascribable to the closed-ring form 2b. This
band disappeared upon irradiation with light of wavelength
.450 nm and the absorption band of open-ring form were
restored. The absorption maxima of the open-ring and
closed-ring forms of 1–4 and their absorption coefficients in
hexane are summarized in Table 2.
Scheme 2.
Method A synthesized the target compounds by using
mono-substituted (3-thienyl)perfluorocyclopentenes while
Method B using mono-substituted (2-thienyl)perfluoro-
cyclopentenes. All the compounds were prepared by these
methods to make a comparison. It was experimentally
found that Method A is more effective than B. By
analyzing the experimental results, we found the total
yields were mainly determined by the metal–hydrogen
exchange or metal–halogen exchange in the last reaction
step. The total yields and the last step yields of them are
summarized in Table 1. The total yields in Method A
were based on starting materials 2-methylthiophene or
2,5-dimethyl-thiophene while in Method B based on 3-
methylthiophene or 3-methylbenzo[b]thiophene. In
Method B, lithiated thiophene derivatives are formed by
the replacement of combined halogen by lithium. In a
metal–halogen exchange reaction of an organolithium
reagent and an alkyl halide, Wurtz coupling is a major
side reaction,9 as shown in reaction Eq. (1). It can give
direct coupling product R–R and R1 –R1 or a cross-
coupling product R–R1. It was found that reactive
heterocyclic aryl halides also followed by a Wurtz
coupling during lithium–halogen exchange, leading to
low concentration of lithiated thiophene derivatives. As a
result, the yields of target compounds were remarkably
decreased. On the other hand, lithiated thiophene
derivatives formed by the replacement of combined
Figure 1. Absorption spectra of 1 in hexane (4.37£1025 mol L21): (—)
before photoirradiation and (- - -) after irradiation with 365 nm at room
temperature.
Figure 2. Absorption spectra of 2 in hexane (5.52£1025 mol L21): (—)
before photoirradiation and (- - -) after irradiation with 365 nm at room
temperature.

F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
Table 2. Absorption maxima and coefficients of 1, 2, 3, and 4; and the
quantum yields in hexane
7617
2.3. Quantum yield
The quantum yields of cyclization and cycloreversion
reactions of 1–4 were measured at room temperature. The
quantum yields were determined by comparing the reaction
yield of the 2,3-position hybrid diarylethenes against
Aberchrome540 in hexane. The intensity of monochromatic
radiation in measuring quantum yields of photoreaction
A!B and B!A was about 4.05£1028 Ein s21 cm21
(365 nm) and 6.16£1029 Ein s21 cm21 (450 nm), respec-
tively. The results are also summarized in Table 2.
a
lmax (nm
b
lmax (nm
Fa!b
365 nm
wb!a
450 nm
(1/L mol21 cm21
)
(1/L mol21 cm21
)
1
2
3
4
224 (2.6£104)
296 (2.2£104)
352 (1.7£104)
228 (3.3£104)
0.28
0.40
0.71
0.57
468 (6.6£103)
506 (5.3£103)
468 (5.3£103)
466 (7.3£103)
0.013
0.024
0.065
0.15
a
Open-ring form.
Closed-ring form.
b
2.4. Thermal stability and fatigue-resistant property
Thermal stability and fatigue-resistant are indispensable
properties for practical applications. The thermal stability of
the open-ring forms and the closed-ring forms of 1–4 were
investigated by storing hexane solutions at 408C in the dark
at the presence of air for more than 3 months. In all cases no
change was observed in the UV/Vis spectra. Also, no
decomposition was detected when the compounds were
exposed in air for more than half a year.
The fatigue resistant properties of 1a, 3a, and 4a were
measured in hexane in the present of air by irradiated with 254
and 365 nm wavelength light, respectively. Upon irradiation
with 365 nm light the absorbance of the closed-ring forms of
the compounds did not change after 1000 cyclization/
cycloreversion cycles. However, upon irradiation with
254 nm light the photochromic performance of 1a, 3a, and
4a decreased to about 89, 81, and 99%, respectively after 200
cycles. It is considered that the degradation is due to the
formation of epoxide which is presumed to be the origin of the
by-product.10,11 Thephotonof254 nmhasahigherenergyand
can easily generate singlet oxygen in the presence of oxygen.
The photo-generated singlet oxygen could react with the 2-
thienyl group of closed-ring form to produce a thiophene-
endoperoxide. Benzothiophene has a much lower reactivity to
singlet oxygen.12 Therefore compound 4a with a benzo
[b]thiophene-2-yl group has a better fatigue resistant. In
addition, other decomposition products could be easily
induced by higher energy light. And further study on
photolysis is currently in progress.
Figure 3. Absorption spectra of 3 in hexane (1.81£1025 mol L21): (—)
before photoirradiation and (- - -) after irradiation with 365 nm at room
temperature.
Figure 4. Absorption spectra of 4 in hexane (3.32£1025 mol L21): (—)
before photoirradiation and (- - -) after irradiation with 365 nm at room
temperature.
2.5. Photochromism in single crystals
As shown in Table 2, the closed-ring isomers 1b, 3b, and
4b have the same absorption maximum at around 468 nm
although their 2-thienyl groups are different. On the other
hand, 2b and 3b have the same 2-thienyl groups, but the
absorption maximum of 2b shows red shift in comparison
with 3b, owing to the introduction of electron-donating
substituent to its 3-thienyl group. It indicates that the
absorption characteristics of the closed isomers of 2,3-
position hybrid diarylethenes derivatives are determined
by the properties of 3-thienyl groups. The closed-ring
form of 2,3-position hybrid diarylethene has a hexatriene
conjugation structure in which the p-conjugation extends
from cyclohexadiene to 3-thienyl moieties. The 2-thienyl
moieties cut off the extending of p-conjugation and thus
do not affect the absorption spectra of the closed-ring
isomer at longer wavelength. Absorption characteristic of
closed-ring form of 2,3-position hybrid diarylethene is
expected to be adjusted by altering the properties of 3-
thienyl group.
The single crystals of 1a–4a† 13 were obtained by
recrystallization from hexane. The ORTEP drawings and
†
Selected crystals data for 1a, 2a, 4a. Compound 1a. C22H16F6S2,
˚
˚
¯
MW¼458.47, triclinic, P1 (No. 2), a¼8.640(5) A, b¼11.444(5) A,
˚
˚
c¼11.945(3) A, a¼103.79(3)8, b¼96.08(3)8, g¼111.55(3)8,
3
V¼1042.1(8) A ,
Z¼2,
F(000)¼468,
Dc¼1.461 g/cm3,
m(Mo Ka)¼0.314 mm21, R[I$2s(I)]¼0.0438, wR2 (all data)¼0.1054,
3029 data, 3617 unique. CCDC reference number 204278. Compound 2a:
C29H22F6O2S2, MW¼580.59, monoclinic, P21/n (No. 14),
˚
˚
˚
a¼17.983(8) A,
b¼12.475(2) A,
c¼24.095(4) A,
a¼90.008,
3
˚
b¼91.676(19)8, g¼908, V¼5403(3) A , Z¼8, F(000)¼2384,
Dc¼1.427 g/cm3, m(Mo Ka)¼0.264 mm21, R[I$2s(I)]¼0.0595, wR2
(all data)¼0.1266, 5265 data, 9506 unique. CCDC reference number
195030. Compound 4a: C20H14F6S2, MW¼432.43, monoclinic, P21/c
˚
˚
˚
(No. 14), a¼19.168(6) A, b¼9.0086(17) A, c¼11.495(4) A, a¼90.008,
3
˚
b¼106.10(3)8, g¼908, V¼1907.0(9) A , Z¼4, F(000)¼880, Dc¼1.506 g/
cm3, m(Mo Ka)¼0.338 mm21
,
R[I$2s(I)]¼0.0725, wR2 (all
data)¼0.1442, 2411 data, 3368 unique. CCDC reference number 204279.

7618
F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
Figure 6. ORTEP drawing (with 35% probability ellipsoids) and packing
view (along the b direction) of 1a.
packed in photoactive antiparallel conformation, as well as
3a.13 The distances between two reactive carbons of them
(C7 and C17 for 1a, C7 and C15 for 4a) were 3.567 and
˚
3.59 A, respectively. Although distances of photoactive
atoms of 1a, 3a, and 4a are close enough for cyclization
reaction,15 only 4a shows photochromic reactivity in the
crystalline state. Upon irradiation with 365 nm light, the
pale yellow crystals of 4a turned orange, and the orange
color faded after irradiation with visible light. It was
observed that the shape of the crystals of 4a showed great
morphological change in the course of photochromic
reaction. Upon exposure to UV light, the surface of the
crystal turned rough. After few minutes, the colored crystal
was broken and separated into several parts. Owing to the
different substituent positions of two thiophene rings, the
closed-ring form of 2,3-position hybrid diarylethene has a
twisted conformation. The crystal disintegration of 4a is
attributed to the large molecular structure change and large
atomic and molecular motion during the photoisomeriza-
tion. It demonstrates that the photochromic reaction is
largely topochemically dominated and strictly controlled by
Figure 5. ORTEP drawing (with 35% probability ellipsoids) and packing
view (along the b direction) of 2a.
packing arrangements of 1a, 2a, and 4a are displayed in
Figures 5–7. The X-ray crystallographic study of 2a shows
that there are two independent molecules in an asymmetric
unit cell. Both of them are packed in non-reactive parallel
conformation.14 The distances between the reactive carbons
˚
of the two independent molecules were 5.884 A (C8, C18)
˚
and 5.534 A (C35, C49), respectively, which are above the
upper limit of the critical distance for photocyclization in
the solid state.15 As a result, the crystals of 2a did not show
any photochromic effect upon irradiation with UV light. On
the other hand, it was observed that both 1a and 4a were

F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
7619
application in rewritable short-wavelength optical data
storage.
4. Experimental
4.1. Materials and apparatus
4-Methyl-2-phenythiophene, 4-methyl-2-(p-methoxy-
phenyl)thiophene and 3-bromo-2-methyl-5-(p-methoxy-
phenyl)thiophene were prepared by using palladium-
catalyzed Suzuki coupling of thiopheneboronic acid and
bromobenzene (or bromoanisole) according to literature
method.5,8 The necessary chemicals were purchased from
commercial sources. Solvents were purified by standard
methods.
The contents of carbon, hydrogen and nitrogen were carried
1
out on an elemental analyzer (Carbo Erba 1106). H NMR
spectra were performed on a NMR spectrometer (Bruker
AM500, 500.13 MHz) in CDCl3 solution using TMS as
internal standard. IR spectra were recorded on Nicolet (PE
2000) FT-IR spectrophotometer using KBr discs in the
range 4000–400 cm21. MS spectra were recorded on a
ZAB-HS apparatus. Melting points were determined on an
XT-4 melting point apparatus. X-ray crystallographic
analysis was measured with a Bruker P4 diffractometer
equipped with graphite monochromatized Mo Ka radiation
at 295 K. Steady absorption spectra were measured with a
HP8452A diode array spectrophotometer. Photo-irradiation
was carried out using an UV lamp (SHG-200) and 150 W
xenon arc lamp. Light of appropriate wavelength was
isolated by a monochromator. The light intensity was
determined by Aberchrome540 actinometry.
Figure 7. ORTEP drawing (with 35% probability ellipsoids) and packing
view (along the b direction) of 4a.
4.1.1. (2,5-Dimethyl-3-thienyl)perfluorocyclopentene (5).
To a stirred THF solution (50 mL) containing 3-iodo-2,5-
dimethylthiophene (3.0 g, 12.5 mmol) was slowly added
7.8 mL of BuLi hexane solution (1.6 M, 12.5 mmol) under
nitrogen atmosphere at 2708C, and the solution was stirred
for 1 h. Then perfluorocyclopentene (2.64 g, 12.5 mmol)
was added. And the mixture was stirred for 3 h at this
temperature. A dilute HCl aqueous solution was added to
the reaction mixture. The mixture was extracted with ether
three times. The combined organic layer was dried with
MgSO4, filtered and evaporated in vacuo. The residue was
purified by column chromatography on silica gel (hexane) to
give 3.08 g of 5 in 81% yield.
the packing arrangement of molecules. When the open-ring
form converts to the closed-ring form, the disrotatory
cyclization of the two thiophene rings requires atomic or
molecular movement and favorable arrangement. Molecules
with elongated shape like those phenyl and 4-anisole-
containing ones (1a, 2a, 3a, but not 4a) would not be
favored to have molecular motions. And more atomic
motions would be needed in these molecules during
isomerization, which would be strongly prohibited by the
packing in densely packed crystalline solid-phase.
3. Conclusion
Pale yellow oil, 1H NMR (500 MHz, CDCl3): 2.39 (s, 3H);
2.43 (s, 3H); 6.73 (s, 1H, Ar). Calcd for C11H7SF7: C, 43.43;
H, 2.32%. Found: C, 43.37; H, 2.13%.
Four kinds of 2,3-position hybrid diarylethene derivatives
were prepared by two methods. It was experimentally found
that a higher yield could be obtained from the method using
mono-substituted (3-thienyl)perfluorocyclopentene. The
absorption spectra of the closed-ring forms of the com-
pounds were located at wavelengths in the region of 400 and
500 nm. They exhibited thermally irreversible and fatigue-
resistant photochromic effects in solution, some of them
even in the solid state. The study on the photochromic
reactivity of the compounds in crystalline state showed that
photochromic reactions were topochemically dominated
and controlled by the packing arrangement of molecules.
These 2,3-position hybrid diarylethenes have potential
4.1.2. [2-Methyl-5-(p-methoxyphenyl)-3-thienyl]per-
fluorocyclopentene (6). The coupling reaction of 3-bromo-
2-methyl-5-(p-methoxyphenyl)thiophene (3.5 g, 12.3 mmol)
and perfluorocyclopentene (2.6 g, 12.3 mmol) was performed
by the procedure as described for compound 5. The crude
product was purified by silica gel chromatography (hexane/
chloroform¼3/1) to give 3.56 g of 6 in 73% yield.
1
Pale blue solid, H NMR (500 MHz, CDCl3): 2.46 (s, 3H);
3.84 (s, 3H); 6.91 (d, J¼8.6 Hz, 2H, Ar); 7.12 (s, 1H, Ar);

7620
F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
7.46 (d, 2H, J¼9.5 Hz, Ar). Calcd for C17H11SOF7: C,
added 0.36 mL of BuLi hexane solution (1.6 M, 0.58 mol)
under nitrogen atmosphere at 2788C. The mixture was
stirred for 15 min. Then, compound 7 (0.21 g, 0.58 mmol)
was added. The reaction mixture was stirred for 3 h at that
temperature. Methanol was added to stop the reaction. The
reaction mixture was extracted with ether and evaporated in
vacuo, then purified by column chromatography (hexane) to
give 0.12 g of 1a in 45% yield.
51.53; H, 2.80%. Found: C, 51.48; H, 2.73%.
4.1.3. (3-Methyl-5-phenyl-2-thienyl)perfluorocyclopen-
tene (7). To a stirred THF solution (50 mL) containing 4-
methyl-2-phenylthiophene (3.0 g, 17.2 mmol) was slowly
added 10.7 mL of BuLi hexane solution (1.6 M, 17.2 mmol)
under nitrogen atmosphere at 08C. 30 min later, perfluoro-
cyclopentene (3.64 g, 17.2 mmol) was added gradually. The
mixture was stirred for 2 h at this temperature. Then the
reaction was stopped by the addition of a dilute HCl aqueous
solution. The reaction mixture was extracted with ether
three times. The combined organic layer was dried with
MgSO4, filtered and evaporated in vacuo. The residue was
purified by column chromatography on silica gel (hexane) to
give 3.65 g of 7 in 58% yield.
1
Yellow prism, mp 82–838C; H NMR (500 MHz, CDCl3):
1.74 (s, 3H), 1.91 (s, 3H); 2.43 (s, 3H); 6.73 (s, 1H); 7.06 (s,
1H); 7.32 (t, J¼7.5 Hz, 1H, Ar); 7.37 (t, J¼7.5 Hz, 2H, Ar);
7.57 (d, J¼7.0 Hz, 2H, Ar). IR (KBr): 2962, 1616, 1492,
1263 cm21; MS (m/z) 426 (Mþ); Calcd for C22H16S2F6: C,
57.63; H, 3.52%. Found: C, 57.88; H, 3.42%.
4.1.7. 1-[3-Methyl-5-(p-methoxyphenyl)-2-thienyl]-2-[2-
methyl-5-(p-methoxyphenyl)-3-thienyl]perfluorocyclo-
pentene (2a). 1-[3-Methyl-5-(p-methoxyphenyl)-2-thienyl]-
2-[2-methyl-5-(p-methoxyphenyl)-3-thienyl]perfluorocyclo-
pentene (2a) was prepared by the same procedure as that used
for 1a. Method A gave 2a in 85% yield, and Method B gave
2a in 43% yield.
Yellow oil, 1H NMR (500 MHz, CDCl3): 2.29 (s, 3H); 7.13 (s,
1H); 7.35–7.37(m, 3H), 7.57(d, 2H, J¼7.7 Hz, Ar). Calcd for
C16H9SF7: C, 52.46; H, 2.48%. Found: C, 52.55; H, 2.35%.
4.1.4. [3-Methyl-5-(p-methoxyphenyl)-2-thienyl]per-
fluorocyclopentene (8). The coupling reaction of 4-
methyl-2-(p-methoxyphenyl)thiophene (3.5 g, 17.2 mmol)
and perfluorocyclopentene (3.64 g, 17.2 mmol) was per-
formed by the procedure as described for compound 7. The
crude product was purified by silica gel chromatography
(hexane/chloroform¼3/1) to give 3.05 g of 8 in 45% yield.
Pale yellow prism, mp 61–628C. 1H NMR (500 MHz,
CDCl3): 2.29 (s, 3H); 3.85 (s, 3H); 6.29 (d, J¼8.0 Hz, 2H,
Ar); 7.08 (s, 1H); 7.52 (d, J¼8.0 Hz, 2H, Ar). Calcd for
C17H11SOF7: C, 51.52; H, 2.80%. Found: C, 51.66; H,
2.92%.
Yellow prism, mp 103–1048C; 1H NMR (500 MHz,
CDCl3): d¼1.72 (s, 3H), 2.32 (s, 3H), 3.85 (s, 3H), 3.86
(s, 3H), 6.90 (s, 1H), 6.91–6.97 (m, 4H, Ar), 6.99 (s, 1H,
Ar), 7.33–7.50 (m, 4H, Ar). IR (KBr): 2958, 1608, 1514,
1251 cm21; MS (m/z) 580 (Mþ); calcd for C29H22S2O2F6:
C, 59.99; H, 3.82%. Found: C, 60.14; H, 3.75%.
4.1.8. 1-(2,5-Dimethyl-3-thienyl)-2-[3-methyl-5-(p-meth-
oxyphenyl)-2-thienyl]perfluorocyclopentene (3a). 1-(2,5-
Dimethyl-3-thienyl)-2-[3-methyl-5-(p-methoxyphenyl)-2-
thienyl]perfluorocyclopentene (3a) was prepared by the
same procedure as that used for 1a. Method A gave 3a in
78% yield, and Method B gave 3a in 40% yield.
4.1.5. (3-Methylbenzo[b]thiophene-2-yl)perfluorocyclo-
pentene (9). The coupling reaction of 3-methylbenzo[b]thio-
phene (2.0 g, 13.5 mmol) and perfluorocyclopentene (2.85 g,
13.5 mmol) was performed by the procedure as described for
compound 7. The crude product was purified by silica gel
chromatography (hexane/chloroform¼4/1) to give 3.53 g of 9
in 77% yield.
1
Yellow prism, mp 73–748C H NMR (500 MHz, CDCl3):
d¼1.73 (s, 3H), 1.91 (s, 3H), 2.43 (s, 3H), 3.84 (s, 3H), 6.90
(d, J¼8.6 Hz, 2H), 6.73 (s, 1H), 6.94 (s, 1H), 7.49 (d,
J¼8.6 Hz, 2H). IR (KBr): 2957, 1608, 1512, 1257 cm21
;
MS (m/z) 456 (Mþ); calcd for C23H18S2OF6: C, 56.55; H,
3.71%. Found: C, 56.44; H, 3.92%.
Pale yellow oil, 1H NMR (500 MHz, CDCl3): 2.44 (s, 3H);
7.34–7.38 (m, 2H); 7.70–7.80 (m, 2H). Calcd for
C14H7SF7: C, 49.42; H, 2.07%. Found: C, 49.24; H, 1.97%.
4.1.9. 1-(2,5-Dimethylthien-3-yl)-2-(3-methylBenzo
[b]thien-2-yl)perfluorocyclopentene (4a). 1-(2,5-Dimethyl-
thien-3-yl)-2-(3-methylBenzo[b]thien-2-yl)perfluorocyclo-
pentene (4a) was prepared by the same procedure as that
used for 1a. Method A gave 4a in 84% yield, and Method B
gave 4a in 49% yield.
4.1.6. 1-(2,5-Dimethyl-3-thienyl)-2-(3-methyl-5-phenyl-
2-thienyl)perfluorocyclopentene (1a). Method A. To a
stirred THF solution (10 mL) containing 4-methyl-2-
phenylthiophene (0.1 g, 0.57 mmol) was slowly added
0.36 mL of BuLi hexane solution (1.6 M, 0.57 mmol)
under nitrogen atmosphere at 08C. 30 min later, compound
5 (0.17 g, 0.56 mmol) was added and the mixture was stirred
for 2 h at this temperature. Methanol was added to stop the
reaction. The reaction mixture was extracted with ether and
evaporated in vacuo, then purified by column chromato-
graphy (hexane) to give 0.2 g of 1-(2,5-dimethylthiophene-
3-yl)-2-(3-methyl-5-phenyl-2-thienyl)perfluorocyclopentene
(1a) in 75% yield.
1
Yellow plate, mp 73–748C; H NMR (500 MHz, CDCl3):
1.84 (s, 3H); 1.95 (s, 3H); 2.42 (s, 3H); 6.76 (1H, Ar); 7.40–
7.42 (m, 2H, Ar); 7.66 (t, J¼4.0 Hz, 1H, Ar); 7.82–7.84 (m,
1H, Ar). IR (KBr): 2954, 1618, 1496, 1272 cm21; MS (m/z)
432 (Mþ); calcd for C20H14S2F6: C, 55.55; H, 3.26%.
Found: C, 56.40; H, 3.33%.
Acknowledgements
Method B. To a stirred anhydrous THF (10 mL) containing
0.14 g of 3-iodo-2,5-dimethylthiophene (0.58 mmol) was
This work was supported by the Fundamental Research of

F. Sun et al. / Tetrahedron 59 (2003) 7615–7621
7621
7. (a) Irie, M.; Sakemura, K.; Okinaka, M.; Uchida, K. J. Org.
Chem. 1995, 60, 8305–8309. (b) Jong, J. J. D.; Lucas, L. N.;
Hania, R.; Pugzlys, A.; Kellogg, R. M.; Feringa, B. L.;
Duppen, K.; Esch, J. H. Eur. J. Org. Chem. 2003, 1887–1893.
8. Irie, M.; Uchida, K. Bull. Chem. Soc. Jpn 1998, 71, 985–996.
9. Smith, M. B. Organic Synthesis; McGraw-Hill: New York,
1994.
Tsinghua University and the Projects of Development of the
State Key Fundamental Research (G199903305).
References
1. Ooki, H. Opt. Quantum Electron. 1993, 25, S587–S595.
2. (a) Gan, F. SPIE 1999, 3749, 415–417. (b) Gan, F.; Hou, L.;
Wang, G.; Liu, H.; Li, J. Mater. Sci. Engng B 2000, 76, 63–68.
3. (a) Irie, M. Photo-Reactive Materials for Ultrahigh Density
Optical Memory; Elsevier: Amsterdam, 1994; pp 1–7.
(b) Kawai, S. H.; Gilat, S. L.; Lehn, J.-M. Chem. Eur. J.
1995, 1, 285–293. (c) Fernandez-Asebes, A.; Lehn, J. M. Adv.
Mater. 1999, 11, 910–913. (d) Murguly, E.; Norsten, T. B.;
Branda, N. R. Angew. Chem. 2001, 113, 1802–1805. (e) Irie,
M. Chem. Rev. 2000, 100, 1685–1716.
10. Bchardt, O. Photochemistry of Heterocyclic Compounds;
Wiley: New York, 1976.
11. Higashiguchi, K.; Matsuda, K.; Yamada, T.; Kawai, T.; Irie,
M. Chem. Lett. 2000, 1358–1359.
12. Hanazawa, M.; Sumiya, R.; Nakayama, Y.; Irie, M. J. Chem.
Soc. Chem. Commun. 1992, 206–207.
¨
13. Sun, F.; Zhang, F.; Pu, S.; Wang, R. Zeitschrift fur
Kristallographie—New Cryst. Struct. 2002, 217, 417–418.
14. (a) Kobatake, S.; Yamada, M.; Yamada, T.; Irie, M. J. Am.
Chem. Soc. 1999, 121, 8450–8456. (b) Pu, S.; Zhang, F.; Sun,
F.; Wang, R.; Zhou, X.; Cheng, X. Tetrahedon Lett. 2003, 44,
1011–1014.
4. Uchida, K.; Ishikawa, T.; Takehita, M.; Irie, M. Tetrahedron
1998, 54, 6627–6638.
5. Uchida, K.; Matsuoka, T.; Kobatake, S.; Yamaguchi, T.; Irie,
M. Tetrahedron 2001, 57, 4559–4565.
6. Uchida, K.; Irie, M. Chem. Lett. 1995, 969–970.
15. Ramamurthy, V.; Venkatesan, K. Chem. Rev. 1987, 87,
433–481.