Dithienylethenes with a novel photochromic performance

Article abstract of DOI:10.1021/jo020114o

Dithienylethenes with low decoloration quantum yields and thermal reversibility at high temperature above 100°C were prepared. Introduction of bulky alkoxy substituents at 2- and 2′-positions of the thiophene rings strongly suppressed the cycloreversion quantum yields. The quantum yields were lower than 10^-3, and the photogenerated color remained stable enough under room light. On the other hand, the bulky alkoxy substituent decreased the thermal stability of the colored closed-ring isomers at high temperature. The color of the dithienylethene with cyclohexyloxy substituents faded out in less than 1 min at 160°C.

Full text of DOI:10.1021/jo020114o

4574
J . Org. Chem. 2002, 67, 4574-4578
Dith ien yleth en es w ith a Novel P h otoch r om ic P er for m a n ce
Kentaro Morimitsu, Katsunori Shibata, Seiya Kobatake, and Masahiro Irie*
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, and
CREST, J apan Science and Technology Corporation, Hakozaki 6-10-1, Higashi-ku,
Fukuoka 812-8581, J apan
irie@cstf.kyushu-u.ac.jp
Received February 19, 2002
Dithienylethenes with low decoloration quantum yields and thermal reversibility at high temper-
ature above 100 °C were prepared. Introduction of bulky alkoxy substituents at 2- and 2′-positions
of the thiophene rings strongly suppressed the cycloreversion quantum yields. The quantum yields
were lower than 10-3, and the photogenerated color remained stable enough under room light. On
the other hand, the bulky alkoxy substituent decreased the thermal stability of the colored closed-
ring isomers at high temperature. The color of the dithienylethene with cyclohexyloxy substituents
faded out in less than 1 min at 160 °C.
Sch em e 1
In tr od u ction
Photochromic compounds undergo reversible photo-
isomerization between two isomers with different absorp-
tion spectra upon irradiation with appropriate wave-
length of light.1,2 Photogenerated colored isomers, in
general, return to the initial colorless isomers either
photochemically or thermally at room temperature.3-6 In
most cases thermally reversible photochromic compounds
are also photochemically reactive.5,6 Therefore, photo-
generated colored isomers are unstable under room light
at room temperature, and the compounds cannot be
applied to image recording. For the recording application,
the photochromic compounds should have very low pho-
todecoloration quantum yields and thermal stability at
room temperature. In addition, it is desired for the
reusability that the colored isomers can return to the
colorless isomers either thermally or photochemically at
high temperature, for example above 100 °C. So far, such
photochromic compounds have not yet been developed.
We have synthesized a new class of photochromic
compounds, named dithienylethenes, which undergo
thermally irreversible and fatigue-resistant photochromic
reactions.7-10 The photogenerated colored isomer of a
derivative, 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluo-
rocyclopentene (5b), is stable for more than 1900 years
at 30 °C.11 The colored isomer, however, returns to the
colorless isomer by visible irradiation (the photodecol-
oration quantum yield ) 0.013). Recently we have
preliminary reported that the photodecoloration quantum
yield is strongly suppressed by the introduction of meth-
oxy groups at the reactive 2- and 2′-positions of the
thiophene rings.12 In the present study we have designed
and synthesized dithienylethene molecules, which have
both very low decoloration quantum yields and thermal
reversibility at high temperature, though the colored
isomers are stable enough at room temperature.
Resu lts a n d Discu ssion
(1) Photochromism; Brown, G. H.; Ed.; Wiley-Interscience: New
York, 1971.
(2) Photochromism: Molecules and Systems; Du¨rr, H.; Bouas-Lau-
rent, H., Eds.; Elsevier: Amsterdam, 1990.
(3) Darcy, P. J .; Heller, H. G.; Strydom, P. J .; Whittall, J . J . Chem.
Soc., Perkin Trans. 1 1981, 202-205.
(4) Yokoyama, Y. Chem. Rev. 2000, 100, 1717-1739.
(5) Fischer, E.; Hirshberg, Y. J . Chem. Soc. 1952, 4522-4524.
(6) Nakamura, M.; Taniguchi, T. J . Synth. Org. Chem. J pn. 1991,
49, 392-402.
(7) Irie, M.; Mohri, M. J . Org. Chem. 1988, 53, 803-808.
(8) Hanazawa, M.; Sumiya, R.; Horikawa, Y.; Irie, M. J . Chem. Soc.,
Chem. Commun. 1992, 206-207.
(9) Irie, M.; Uchida, K. Bull. Chem. Soc. J pn. 1998, 71, 985-996.
(10) Irie, M. Chem. Rev. 2000, 100, 1685-1716.
(11) Irie, M.; Lifka, T.; Kobatake, S.; Kato, N. J . Am. Chem. Soc.
2000, 122, 4871-4876.
Syn th esis. Dithienylethene derivatives with various
types of alkoxy substituents at the reactive 2- and 2′-
positions of the thiophene rings were prepared. Bulky
alkoxy groups, such as ethoxy, isopropoxy, and cyclo-
hexyloxy groups, were specially selected, because bulky
substituents are known to enhance the thermal decol-
oration reactions at high temperature.13,14
(12) Shibata, K.; Kobatake, S.; Irie, M. Chem. Lett. 2001, 618-619.
(13) Kobatake, S.; Shibata, K.; Uchida, K.; Irie, M. J . Am. Chem.
Soc. 2000, 122, 12135-12141.
(14) Kobatake, S.; Uchida, K.; Tsuchida, E.; Irie, M. Chem. Lett.
2000, 1340-1341.
10.1021/jo020114o CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/01/2002

Novel Photochromic Dithienylethenes
J . Org. Chem., Vol. 67, No. 13, 2002 4575
Ta ble 1. Absor p tion Ma xim a a n d Coefficien ts of 1b-4b
in Hexa n e
compd
λ
max/nm
ꢀ/104 M-1 cm-1
volumea/Å3
1b
2b
3b
4b
625
625
635
635
1.5
1.3
1.3
1.3
62.8
89.4
116.0
185.6
a
Estimated for the alkoxy groups according to atomic increment
method.15
Ta ble 2. Cycliza tion a n d Cyclor ever sion Qu a n tu m
Yield s of 1-5 in Hexa n e
compd
cyclizationa
cycloreversiona
1
2
3
0.44
0.48
0.46
0.43
0.59
∼1.7 × 10-5
2.5 × 10-4
6.6 × 10-4
6.4 × 10-4
1.3 × 10-2
F igu r e 1. Absorption spectral change of 1 in hexane (2.1 ×
10-5 M) by photoirradiation: 1a (- - -), 1 in the photostationary
state under irradiation with 313-nm light (s), and 1b (s). The
absorption spectrum in the photostationary state under ir-
radiation with 313-nm light was overlapped with the spectrum
of 1b.12
4
511
a
Standard deviation of the experimental error: (5%.
2a , 3a , and 4a also exhibited similar photochromism.
Table 1 summarizes the main absorption bands of the
closed-ring form isomers 1b-4b. The visible absorption
maxima of the closed-ring form isomers shifted to longer
wavelengths by the introduction of bulky alkoxy groups.
The absorption maxima of 1b having methoxy substitu-
ents was observed at 625 nm, while it shifted to 635 nm
when cyclohexyloxy substituents were introduced. The
maximum wavelength of 4b was 10 nm longer than that
of 1b. The absorption maximum shift agrees to the order
of the bulkiness; MeO, EtO < i-PrO, cyclohexyloxy.15 It
is known that introduction of long π-conjugated aryl
groups to dithienylethene derivatives results in the shift
of the absorption maximum of the closed-ring form isomer
to longer wavelengths.16-18 The bulky alkoxy subutituent
at 2- and 2′-positions of the thiophene rings gave a similar
effect to shift the absorption maximum of the closed-ring
isomer to longer wavelengths.
Sch em e 2
Absorption coefficients (ꢀ, M-1 cm-1) of the closed-ring
form isomers were also affected by the alkoxy substitu-
ents. The values of ꢀ for 1b, 2b, 3b, and 4b were 1.5 ×
The synthetic procedure is shown in Scheme 2. The
dithienylethene derivatives were synthesized from 2-al-
koxy-3,5-dibromothiophenes by two-step procedures. 1a -
4a were purified by column chromatography and recrys-
tallization (hexane or acetone). The structures of all
104, 1.3 × 104, 1.3 × 104, and 1.3 × 104 M-1 cm-1
,
respectively. The alkoxy subustituents decreased ꢀ-values
as follows: MeO > EtO, i-PrO, cyclohexyloxy. This effect
is opposite to ꢀ-values observed in dithienylethene de-
rivatives with long π-conjugated aryl groups. In the
derivatives ꢀ-values increased with the shift of the
absorption maximum to longer wavelengths.16,17
1
compounds were confirmed by H NMR, mass spectros-
copy, and elemental analysis.
Absor p tion Sp ectr a . Figure 1 shows the absorption
spectral change of 1 by irradiation with 313-nm light.12
1a has the absorption maximum at 267 and 309 nm in
hexane. Upon irradiation with 313-nm light, the colorless
hexane solution of 1a turned blue, in which a visible
absorption band was observed at 625 nm. The blue color
is due to the closed-ring form isomer 1b.10 The colored
isomer was stable in the dark at room temperature and
could be isolated by high performance liquid chromatog-
raphy (HPLC, silica gel column, hexane/ethyl acetate )
80:20). The closed-ring form isomer very slowly reformed
the open-ring form isomer upon prolonged irradiation
with visible light. The absorption spectrum returned to
the original one after 4 h irradiation with an intense 500
W mercury lamp (λ > 500 nm). This indicates that the
introduction of the methoxy groups strongly suppressed
the cycloreversion reaction. The conversion from 1a to
1b in the photostationary state under irradiation with
313-nm light was 100%.
Qu a n tu m Yield s. The cyclization and cycloreversion
quantum yields of 1-4 were measured in hexane at room
temperature. As shown in Table 2, the cyclization quan-
tum yields of 1a , 2a , 3a , and 4a were 0.44, 0.48, 0.46,
and 0.43, respectively. The values were similar each other
and slightly smaller than that of 5a (Φafb ) 0.59).11 This
means that these alkoxy substituents scarcely affect the
cyclization reactions even when bulky cyclohexyloxy
substituents were introduced.
On the other hand, the cycloreversion quantum yields
of 1b-4b were strongly suppressed by the alkoxy sub-
stituents. As shown in Table 2, the cycloreversion quan-
(15) Edward, J . T. J . Chem. Educ. 1970, 47, 261-270.
(16) Bens, A. T.; Frewert, D.; Kodatis, K.; Kryschi, C.; Martin, H.-
D.; Trommsdorff, H. P. Eur. J . Org. Chem. 1998, 2333-2338.
(17) Irie, M.; Eriguchi, T.; Takada, T.; Uchida, K. Tetrahedron 1997,
53, 12263-12270.
(18) Saika, T.; Irie, M.; Shimidzu, T. J . Chem. Soc., Chem. Commun.
1994, 2123-2124.

4576 J . Org. Chem., Vol. 67, No. 13, 2002
Morimitsu et al.
F igu r e 2. Thermal fading curves of 1b (a), 2b (b), 3b (c), and 4b (d) in decalin.
tum yields of 1b, 2b, 3b, and 4b were estimated to be
∼1.7 × 10-5, 2.5 × 10-4, 6.6 × 10-4, and 6.4 × 10-4
,
respectively. The cycloreversion quantum yields of the
alkoxy-substituted dithienylethenes were lower than that
of 5b by a factor of 102-103. The decrease in the
cycloreversion quantum yield is attributed based on
molecular orbital theoretical calculations to the presence
of activation barriers in the cycloreversion process in the
singlet excited state.19 When the bulkiness of the alkoxy
groups increased, the cycloreversion quantum yields also
increased. The quantum yield ∼1.7 × 10-5 of 1b increased
to 6.4 × 10-4 when bulky cyclohexyloxy substituents were
introduced. The increase is ascribable to the molecular
strain of the closed-ring isomers by the bulky substitu-
ents.
F igu r e 3. Temperature dependence of the thermal fading
rates of 1b (b), 2b (O), 3b (9), and 4b (0).
Th er m a l Cyclor ever sion in Solu tion . 5 underwent
thermally irreversible photochromism. 5b was stable in
the dark and had the half-life time of 1900 years at 30
°C.11 Even at 100 °C 5b was stable for more than 18 days.
On the other hand, it was reported that dithienylethene
derivatives having bulky substituents such as isopropyl
groups at the reactive 2- and 2′-positions of the thiophene
rings are thermally unstable above 80 °C and return to
the open-ring isomers in 20 min at 100 °C.14
The thermal stability of the closed-ring form isomers
1b-4b were examined at 70∼150 °C in decalin. Figure
2 shows the decay curves of the absorbance of the closed-
ring isomers at several temperatures. The absorbance of
the closed-ring isomers decreases slowly above 70 °C. The
decay curves followed the first-order kinetics. The ab-
sorption spectra of the thermal-bleached solutions after
10 times photocoloration/thermal-decoloration cycles re-
mained almost same in shape and intensity with the
initial spectra of the open-ring isomers. This indicates
that the thermal fading of the color is due to the thermal
Ta ble 3. Ar r h en iu s P a r a m eter s of Th er m a l
Cyclor ever sion s a n d Ha lf-Life Tim es fr om th e Closed -
to th e Op en -Rin g Isom er s
compd
Ea/kJ mol-1
A/s-1
t
1/2(160 °C)
t1/2(30 °C)
1b
2b
3b
137
129
123
120
139
2.1 × 1013
5.5 × 1012
5.5 × 1012
4.4 × 1012
1.3 × 1013
18 min
7.4 min
1.6 min
45 s
420 y
65 y
7.0 y
2.2 y
1900 y
4b
5b11
51 min
cycloreversion to the open-ring isomer. The rates of
thermal cycloreversion were dependent on the substitu-
ents and increased in the following order: MeO <
EtO < i-PrO < cyclohexyloxy.
Figure 3 shows the temperature dependences of the
rates (k). The activation energy (Ea) and frequency factor
(A) of the cycloreversion were estimated from the linear
relation. The values are summarized in Table 3. When
bulky alkoxy substituents were introduced, the values
decreased as follows; MeO > EtO > i-PrO > cyclohexyl-
oxy. The decrease in Ea values enhanced the thermal
cycloreversion reaction at higher temperature. Bulky
substituents at the central bond induce the strain in the
(19) Guillaumont, D.; Kobayashi, T.; Kanda, K.; Miyasaka, H.;
Uchida, K.; Kobatake, S.; Shibata, K.; Nakamura, S.; Irie, M. J . Phys.
Chem., A, in press.

Novel Photochromic Dithienylethenes
J . Org. Chem., Vol. 67, No. 13, 2002 4577
F igu r e 5. Photocoloration and thermal and photochemical
fading of 4 (left side on the paper) and 5 (right side) in the
polymer film. Samples a and d are the colorless open-ring
isomers. Samples b and e are the colored isomers upon UV
irradiation. When the colored sample b was kept at 160 °C in
the dark for 5 min, sample b changed to sample c. The blue
color of 4b disappeared, while the blue color of 5b remained
the original color. When the colored sample e was irradiated
with visible light (>520 nm) for 10 min, sample e changed to
f. The blue color of 5b disappeared, while the color of 4b
remained.
F igu r e 4. Thermal fading of 4b in a polymer film. The film
was prepared by casting the toluene solution containing 4b
and poly[oxycarbonyloxy-1,4-phenylene(methyl)phenylmeth-
ylene-1,4-phenylene] (1/10 wt/wt) on the slide glass. The
thickness of the film was ca. 3 µm.
molecular structure of the closed-ring isomers, resulting
in the decrease in Ea values.
Table 3 also shows the estimated half-life times of the
thermal cycloreversion reactions for the closed-ring iso-
mers 1b-4b at 160 and 30 °C obtained by the extrapola-
tion of the temperature dependence. The half-life times
of 1b, 2b, 3b, and 4b, at 160 °C were 18 min, 7.4 min,
1.6 min, and 45 s, respectively. 4b has both reasonable
thermal cycloreversion rate at high temperature and
thermal stability at room temperature. In addition, 4b
has a very low photodecoloration quantum yield.
Th er m a l Cyclor ever sion in P olym er F ilm s. 4b
satisfies both requirements of photostability and ther-
mally reversibility at higher temperature. We measured
thermal cycloreversion of 4b in a polymer film. The
polymer film was prepared by casting the toluene solution
containing 4a and poly[oxycarbonyloxy-1,4-phenylene-
(methyl)phenylmethylene-1,4-phenylene] (1/10 wt/wt) on
the slide glass. The polymer film underwent photocol-
oration upon irradiation with UV light (366 nm). The
thermal stability was measured between 120 °C and 160
°C. Figure 4 shows the first-order plots of the decoloration
rate at several temperatures. The decoloration curves
deviated from the first-order kinetics. This kind of
phenomenon is often observed in polymer systems and
ascribed to distribution of first-order constant rates due
to existence of various microenvironments.20 Apparently,
the values are similar to those in solution. The absor-
bance of 4b decreased to 50% of the initial value in less
than 1 min at 160 °C.
Figure 5 shows the color changes of 4b and 5b by heat
and light. The samples were prepared by casting the
toluene solutions containing the dithienylethenes and the
polymer as used in the previous experiment. The sample
in the left side is 4 and right side is 5 on the paper. The
colorless open-ring isomers (Figure 5a and 5d) turned
blue upon UV irradiation (Figure 5b and 5e). Then, the
samples were kept at 160 °C in the dark. After storage
for 5 min, the blue color of 4b disappeared, while the blue
color of 5b remained the original color (Figure 5c). When
the colored sample (Figure 5e) was irradiated with visible
light (>520 nm) for 10 min, the blue color of 5b disap-
peared, while the color of 4b remained (Figure 5f). 4b is
photochemically stable but thermally reversible.
Con clu sion
This paper has demonstrated design and synthesis of
dithienylethenes, which have both very low decoloration
quantum yields and thermal reversibility at high tem-
perature. Introduction of the alkoxy groups at the react-
ing positions of the dithienylethenes extraordinarily
decreased the photocycloreversion quantum yields. The
bulky alkoxy substituents shifted the absorption maxi-
mum to longer wavelength and increased the thermal
cycloreversion rate at high temperature. Photochromic
compounds with such a new photochromic reactivity are
applicable for image recording.
Exp er im en ta l Section
Gen er a l. Solvents used were spectroscopic grade and
1
purified by distillation. H NMR spectra were recorded on at
200 MHz. A high-temperature chamber was used to maintain
constant temperature of the solution. Absorption spectra of
the polymer film were measured using a microscope connected
with
a PMA-11 photodetector. A hot stage was used to
maintain constant temperature of the polymer film. Photo-
irradiation was carried out using a 500 W super-high-pressure
mercury lump or a 500 W xenon lamp as the light sources.
Monochromic light was obtained by passing the light through
a monochromator. The quantum yields were determined by
comparing the reaction yields of the dithienylethenes in
hexane against furyl fulgide in hexane or toluene.21,22 The
samples were not degassed. The films were prepared by casting
the toluene solution containing 4a and poly[oxycarbonyloxy-
1,4-phenylene(methyl)phenylmethylene-1,4-phenylene] (1/10
wt/wt) on the glass substrate.
1,2-Bis(2-m eth oxy-5-p h en yl-3-th ien yl)p er flu or ocyclo-
p en ten e (1a ). 1a was prepared according to the method
described in the literature.12
3,5-Dibr om o-2-eth oxyth iop h en e (6). To a stirred solution
of 2-ethoxythiophene23 (3.1 g; 24 mmol) in dichloromethane
(48 mL) at 0 °C was slowly added N-bromosuccinimide (NBS)
(8.5 g, 48 mmol). The reaction mixture was stirred overnight
at room temperature. The mixture was cooled on the ice bath
(21) Hellar, H. G.; Langan, J . R. J . Chem. Soc., Perkin Trans. 2 1981,
341-343.
(22) Yokoyama, Y.; Kurita, Y. J . Synth. Org. Chem. J pn. 1991, 49,
364-372.
(20) Levitus, M.; Aramend´ıa, P. F. J . Phys. Chem. B 1999, 103,
1864-1870.
(23) Sice´, J .; J . Am. Chem. Soc. 1953, 75, 3697-3700.

4578 J . Org. Chem., Vol. 67, No. 13, 2002
Morimitsu et al.
and then filtered. The filtrate was neutralized and extracted
with chloroform. The chloroform extract was dried over MgSO4,
filtered, and concentrated. The residue was purified by silica
gel column chromatography using hexane as the eluent. 6 was
obtained as colorless oil of 6.5 g in 94% yield: 1H NMR (200
MHz, CDCl3) δ 1.43 (t, J ) 7 Hz, 3H), 4.13 (q, J ) 7 Hz, 2H),
6.75 (s, 1H); MS m/z (M+) 284, 286, 288. Anal. Calcd for C6H6-
Br2OS: C, 25.20; H, 2.11. Found: C, 25.50; H, 2.14.
a procedure similar to that used for 2a . The crude product was
purified by silica gel column chromatography using hexane/
chloroform (7:3) as the eluent to give 0.70 g of 3a in 35% yield
as pale yellow crystals: mp 191.3-192.3 °C; 1H NMR (200
MHz, CDCl3) δ 1.15 (d, J ) 6 Hz, 12H), 4.26 (sep, J ) 6 Hz,
2H), 7.16 (s, 2H), 7.2-7.5 (m, 10H); MS m/z (M+) 608. Anal.
Calcd for C31H26F6O2S2: C, 61.17; H, 4.31. Found: C, 61.20;
H, 4.33.
3-Br om o-2-eth oxy-5-p h en ylth iop h en e (7). To 150 mL of
dry THF containing 6 (6.5 g; 23 mmol) was added 15% n-BuLi
hexane solution (15 mL; 25 mmol) at -78 °C under argon
atmosphere, and the solution was stirred for 1 h at the low
temperature. Tri-n-butyl borate (9.1 mL; 34 mmol) was slowly
added to the reaction mixture at -78 °C, and the mixture was
stirred for 1.5 h at that temperature. After warming the
solution up to room temperature, 20 wt % Na2CO3(aq) (53 mL),
iodobenzene (4.6 g; 23 mmol), and tetrakis(triphenylphos-
phine)palladium(0) (1.1 g; 0.95 mmol) were added to the
reaction mixture. The mixture was refluxed overnight at 70
°C. The product was extracted with ether. The organic layer
was dried over MgSO4, filtered, and concentrated. The residue
was purified by silica gel column chromatography using
hexane as the eluent to give 4.9 g of 7 in 76% yield as colorless
oil: 1H NMR (200 MHz, CDCl3) δ 1.48 (t, J ) 7 Hz, 3H), 4.21
(q, J ) 7 Hz, 2H), 6.98 (s, 1H), 7.2-7.5 (m, 5H); MS m/z (M+)
282, 284. Anal. Calcd for C12H11BrOS: C, 50.90; H, 3.92.
Found: C, 51.17; H, 3.89.
2-Cycloh exyloxyth iop h en e (10). Sodium (1.6 g; 71 mmol)
was added into a flask containing dry cyclohexanol (100 mL)
under argon atmosphere and was completely dissolved by
stirring at 120 °C. 2-Iodothiophene (5.3 mL; 48 mmol), CuO
(1.9 g; 24 mmol), and KI (4.0 g; 24 mmol) were added to the
solution and stirred for 2 h at 130 °C. The product was
extracted with ether. The organic layer was dried over MgSO4,
filtered, and concentrated. The residue was purified by silica
gel column chromatography using hexane as the eluent to give
0.64 g of 10 in 7.4% yield as pale yellow oil: 1H NMR (200
MHz, CDCl3) δ 1.3-2.0 (m, 11H), 4.06 (tt, J ) 9, 4 Hz, 1H),
6.24 (d, J ) 4 Hz, 1H), 6.56 (d, J ) 6 Hz, 1H), 6.70 (dd, J ) 4
and 6 Hz, 1H); MS m/z (M+) 182. Anal. Calcd for C10H14OS:
C, 65.89; H, 7.74. Found: C, 65.73; H, 7.64.
3,5-Dibr om o-2-cycloh exyloxyth iop h en e (11). 11 was
prepared from 10 (0.60 g; 3.3 mmol) by a procedure similar to
that used for 6. The crude product was purified by silica gel
column chromatography using hexane as the eluent to give
0.94 g of 11 in 84% yield as pale yellow oil: 1H NMR (200
MHz, CDCl3) δ 1.3-2.0 (m, 11H), 4.05 (tt, J ) 9, 4 Hz, 1H),
6.73 (s, 1H); MS m/z (M+ - cyclohexene) 256, 258, 260. Anal.
Calcd for C10H12Br2OS: C, 35.32; H, 3.56. Found: C, 35.39;
H, 3.58.
1,2-Bis(2-et h oxy-5-p h en yl-3-t h ien yl)p er flu or ocyclo-
p en ten e (2a ). To 50 mL of dry THF solution containing 7 (4.9
g; 17 mmol) was added 15% n-BuLi hexane solution (12 mL;
19 mmol) at -78 °C under argon atmosphere, and the solution
was stirred for 1.5 h at that low temperature. Octafluorocy-
clopentene (1.2 mL; 8.6 mmol, Nippon Zeon) was slowly added
to the reaction mixture at -78 °C, and the mixture was stirred
for 3 h at that temperature. The reaction was stopped by the
addition of water. The product was extracted with ether. The
organic layer was dried over MgSO4, filtered, and concentrated.
The residue was purified by silica gel column chromatography
using hexane/chloroform (7:3) as the eluent and by recrystal-
lization from acetone to give 1.8 g of 2a in 36% yield as pale
yellow crystals: mp 199.6-200.6 °C; 1H NMR (200 MHz,
CDCl3) δ 1.08 (t, J ) 7 Hz, 6H), 3.92 (q, J ) 7 Hz, 4H), 7.22 (s,
2H), 7.2-7.5 (m, 10H); MS m/z (M+) 580. Anal. Calcd for
3-Br om o-2-cycloh exyloxy-5-p h en ylth iop h en e (12). 12
was prepared from 11 (1.6 g; 4.7 mmol) by a procedure similar
to that used for 7. The crude product was purified by silica
gel column chromatography using hexane as the eluent to give
0.96 g of 12 in 61% yield as pale yellow crystals: mp 58.3-
1
59.3 °C; H NMR (200 MHz, CDCl3) δ 1.3-2.0 (m, 11H), 4.15
(tt, J ) 9, 4 Hz, 1H), 6.96 (s, 1H), 7.2-7.5 (m, 5H); MS m/z
(M+) 336, 338. Anal. Calcd for C16H17BrOS: C, 56.98; H, 5.08.
Found: C, 56.94; H, 5.08.
1,2-Bis(2-cycloh exyloxy-5-p h en yl-3-th ien yl)p er flu or o-
cyclop en ten e (4a ). 4a was prepared from 12 (0.90 g; 2.7 mol)
by a procedure similar to that used for 2a . The crude product
was purified by silica gel column chromatography using
hexane/chloroform (7:3) as the eluent to give 0.41 g of 4a in
44% yield as pale yellow crystals: mp 134.3-135.3 °C; 1H
NMR (200 MHz, CDCl3) δ 1.2-1.8 (m, 22H), 4.03 (br, 2H), 7.14
(s, 2H), 7.2-7.5 (m, 10H); MS m/z (M+) 688. Anal. Calcd for
C
29H22F6O2S2: C, 59.99; H, 3.82. Found: C, 60.03; H, 3.80.
3,5-Dibr om o-2-isop r op oxyth iop h en e (8). 8 was prepared
from 2-isopropoxythiophene24 (3.5 g; 24 mmol) by a procedure
similar to that used for 6. The crude product was purified by
silica gel column chromatography using hexane as the eluent
to give 4.5 g of 8 in 62% yield as pale yellow oil: 1H NMR (200
MHz, CDCl3) δ 1.39 (d, J ) 6 Hz, 6H), 4.32 (sep, J ) 6 Hz,
1H), 6.74 (s, 1H); MS m/z (M+ - CH2dCHCH3) 256, 258, 260.
Anal. Calcd for C7H8Br2OS: C, 28.02; H, 2.69. Found: C, 27.95;
H, 2.63.
C
37H34F6O2S2: C, 64.52; H, 4.98. Found: C, 64.30; H, 5.00.
1,2-Bis(2-m et h yl-5-p h en yl-3-t h ien yl)p er flu or ocyclo-
p en ten e (5a ). 5a was prepared according to the method
described in the literature.11
3-Br om o-2-isop r op oxy-5-p h en ylth iop h en e (9). 9 was
prepared from 8 (4.3 g; 14 mmol) by a procedure similar to
that used for 7. The crude product was purified by silica gel
column chromatography using hexane as the eluent to give
3.0 g of 9 in 70% yield as pale yellow oil: 1H NMR (200 MHz,
CDCl3) δ 1.43 (d, J ) 6 Hz, 6H), 4.42 (sep, J ) 6 Hz, 1H), 6.97
(s, 1H), 7.2-7.5 (m, 5H); MS m/z (M+) 296, 298. Anal. Calcd
for C13H13BrOS: C, 52.53; H, 4.41. Found: C, 52.62; H, 4.52.
1,2-Bis(2-isop r op oxy-5-p h en yl-3-th ien yl)p er flu or ocy-
clop en ten e (3a ). 3a was prepared from 9 (2.0 g; 6.7 mol) by
Ack n ow led gm en t. This work was supported by
CREST (Core Research for Evolutional Science and
Technology) of J apan Science and Technology Corpora-
tion (J ST). We also thank NIPPON ZEON CO., Ltd. for
their supply of octafluorocyclopentene.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
2a , 3a , and 4a . This material is available free of charge via
the Internet at http://pubs.acs.org.
(24) Pedersen, E. B.; Lawesson, S.-O. Tetrahedron 1972, 28, 2479-
2488.
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