Photochromism of Dithiazolylethenes Having Methoxy Groups at the Reaction Centers

Article abstract of DOI:10.1002/1099-0690(200211)2002:22<3796::AID-EJOC3796>3.0.CO;2-X

Photochromic dithiazolylethenes [1,2-bis(5-methoxy-2-phenylthiazol-4-yl)perfluorocyclopentene (1a) and (5-methoxy-2-phenylthiazol-4-yl)-2-(5-methyl-2-phenylthiazol-4-yl)perfluorocyclopentene (2a)] having methoxy substituents at the reaction centers were synthesized and their photochromic reactivity was compared with 1,2-bis(5-methyl-2-phenylthiazol-4-yl)perfluorocyclopentene (3a), which has methyl substituents at the reaction centers. All dithiazolylethene derivatives underwent reversible photocyclization reactions from the open-ring forms 1a, 2a, and 3a to the closed-ring forms 1b, 2b, and 3b, respectively. The photocyclization quantum yields of 1a and 2a were only slightly lower than that of 3a, while the photocycloreversion quantum yields of 1b and 2b dramatically decreased relative to that of 3b by factors of 100 and 10, respectively. Absorption maxima of dithiazolylethene derivatives 1b, 2b, and 3b showed a hypsochromic shift as much as 50-80 nm relative to that of dithienylethene derivatives. This is explained by the difference in the HOMO-LUMO band gap between the two systems.

Full text of DOI:10.1002/1099-0690(200211)2002:22<3796::AID-EJOC3796>3.0.CO;2-X

FULL PAPER
Photochromism of Dithiazolylethenes Having Methoxy Groups
at the Reaction Centers
Shizuka Takami,[b] Tsuyoshi Kawai,[a,b] and Masahiro Irie*[a,b]
Keywords: Diarylethenes / Cyclizations / Photochemistry / Photochromism
Photochromic dithiazolylethenes [1,2-bis(5-methoxy-2-phen-
ylthiazol-4-yl)perfluorocyclopentene (1a) and (5-methoxy-2-
phenylthiazol-4-yl)-2-(5-methyl-2-phenylthiazol-4-yl)per-
fluorocyclopentene (2a)] having methoxy substituents at the
reaction centers were synthesized and their photochromic re-
activity was compared with 1,2-bis(5-methyl-2-phenylthia-
zol-4-yl)perfluorocyclopentene (3a), which has methyl sub-
yields of 1a and 2a were only slightly lower than that of 3a,
while the photocycloreversion quantum yields of 1b and 2b
dramatically decreased relative to that of 3b by factors of 100
and 10, respectively. Absorption maxima of dithiazolylethene
derivatives 1b, 2b, and 3b showed a hypsochromic shift as
much as 50−80 nm relative to that of dithienylethene derivat-
ives. This is explained by the difference in the
stituents at the reaction centers. All dithiazolylethene deriv- HOMO−LUMO band gap between the two systems.
atives underwent reversible photocyclization reactions from
the open-ring forms 1a, 2a, and 3a to the closed-ring forms
1b, 2b, and 3b, respectively. The photocyclization quantum
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
in the production of, for example, memory cards, write-once
memory media and color dosimeters.[6]
Dithiazolylethene[7] has a structure isoelectronic with di-
thienylethene, and both exhibit thermally irreversible
photochromic reactions.[2][7a] Recently, we found that the
position of substitution of the thiazole rings in the per-
fluorocyclopentene moiety strongly affected the absorption
spectra.[7a] The absorption maximum of the closed-ring
form of 1,2-bis(4-methyl-2-phenylthiazol-5-yl)perfluorocy-
clopentene shifted to a shorter wavelength relative to that
of 1,2-bis(5-methyl-2-phenylthiazol-4-yl)perfluorocyclopen-
tene.[7a] Although the photochromic reactivity of dithiazo-
lylethene derivatives is of great interest, very little work on
their photochromic reactions has been reported. In this pa-
per, the photochromic properties of dithiazolylethene deriv-
atives having methoxy substituents at the reaction centers
has been examined, in order to probe the substituent effects
of methoxy groups on the photocyclization/cycloreversion
quantum yields. The photochromic reactivity of dimethoxy-
substituted 1 and monomethoxy-substituted 2 was also
compared with that of 1,2-bis(5-methyl-2-phenylthiazol-4-
yl)percyclopentene (3) which has methyl substituents at the
reaction centers (Scheme 1).
Photochromic compounds have attracted much attention
due to their potential applications in optical memory media
and photo-optical switching devices.[1] In particular, diary-
lethenes with heterocyclic aryl groups, such as thiophene or
benzothiophene groups, are the most promising candidates
for applications, because they undergo fatigue resistant and
thermally irreversible photochromic reactions.[2] Several at-
tempts to control the photocyclization and photocyclore-
version quantum yields by the introduction of various sub-
stituents to the diarylethenes have been reported.[3] When
electron-donating groups are introduced at the para-posi-
tions of the phenyl groups of 1,2-bis(2,4-dimethyl-5-phenyl-
thiophen-3-yl)perfluorocyclopentene, the photocyclorever-
sion quantum yields decrease.[4] Methoxy substitution at
the reaction centers of 1,2-bis(2-methyl-5-phenylthiophen-
3-yl)perfluorocyclopentene has been reported to decrease
the photocycloreversion quantum yield by a factor of 103.[5]
Such a low photobleaching quantum yield could be useful
[a]
Department of Chemistry and Biochemistry, Graduate School
of Engineering, Kyushu University, and CREST, Japan Science
and Technology Corporation, 6-10-1 Hakozaki, Higashi-ku,
Fukuoka 812Ϫ8581, Japan
Fax: (internat.) ϩ81Ϫ92/642-3568
E-mail: irie@cstf.kyushu-u.ac.jp
Results and Discussion
E-mail: tkawai@cstf.kyushu-u.ac.jp
[b]
1,2-Bis(5-methoxy-2-phenylthiazol-4-yl)perfluorocyclo-
pentene (1a) and 1-(5-methoxy-2-phenylthiazol-4-yl)-2-(5-
Fukuoka IST, Fukuoka Industry, Science
Foundation,
& Technology
6Ϫ10Ϫ1 Hakozaki, Higashi-ku, Fukuoka 812Ϫ8581, Japan
Fax: (internat.) ϩ81Ϫ92/642-3568
E-mail: takami@cstf.kyushu-u.ac.jp
methyl-2-phenylthiazol-4-yl)perfluorocyclopentene
(2a)
were synthesized by the reaction of 4-bromo-5-methoxy-2-
3796
 2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/02/1122Ϫ3796 $ 20.00ϩ.50/0 Eur. J. Org. Chem. 2002, 3796Ϫ3800

Photochromism of Dithiazolylethenes Having Methoxy Groups at the Reaction Centers
FULL PAPER
diation with visible light (λ Ͼ 480 nm), however, the photo-
bleaching rate of 1b was much slower than that of 3b. The
red color of 3b was bleached rapidly by irradiation with
visible light for 1 min,[7a] while it took more than 1 h for
the purple color of 1b to be bleached. The conversion from
the open- to the closed-ring form by irradiation with
313 nm light was almost 100% in the photostationary state.
In the 1H NMR spectrum of 1a in CDCl3, the resonance of
the methoxy proton was observed at δ ϭ 3.84 ppm. Upon
irradiation with 313 nm light, this signal decreased in in-
tensity, while a new singlet appeared at δ ϭ 3.57 ppm.This
new singlet was assigned to the methoxy protons attached
to the photogenerated sp3 carbon of compound 1b. Figure 2
Scheme 1
phenylthiazole (6) with monosubstituted perfluorocyclo-
pentenes 8 and 9, respectively, by bromineϪlithium ex-
change followed by nucleophilic displacement of fluoride,
as illustrated in Scheme 2. Dithiazolylethenes 1a and 2a
1
shows H NMR spectra of the methoxy protons of 1 in
CDCl3 before and after photo-irradiation with 313 nm
light. This indicates that the closed-ring form has a single
structure with two methoxy groups in the trans position, as
predicted theoretically.[8]
1
were characterized by H NMR spectroscopy, MS, and ele-
mental analysis. Dithiazolylethene 3a was also prepared,[7a]
in order to compare its reactivity with dimethoxy-substi-
tuted 1 and monomethoxy-substituted 2.
Figure 1. Absorption spectra of a toluene solution of dimethoxy-
substituted 1 (1.3·10Ϫ5 ): (dashed line) open-ring form 1a, (solid
line) closed-ring form 1b, and (dotted line) in the photostationary
state under irradiation with 313 nm
Scheme 2
Figure 1 shows the spectral changes of compound 1 dis-
solved in toluene (1.3·10Ϫ5 ). The toluene solution of 1a
has an absorption maximum at 322 nm. Upon irradiation
with 313 nm light the colorless solution of the open-ring
form turned purple, showing an absorption maximum at
555 nm. The purple color is due to the closed-ring form, 1b.
The colored product was isolated by HPLC (silica gel; ethyl
acetate/hexane, 1:3 as the eluent), and the structure of 1b
was confirmed by 1H NMR spectroscopy, MS, and ele-
Figure 2. 1H NMR spectra (200 MHz) of 1 in CDCl3: (a) before
irradiation; (b) after 10 min under irradiation with 313 nm; (c) at
the photostationary state under irradiation with 313 nm
Figure 3 shows the spectral changes of compound 2 dis-
mental analysis. All data were in good agreement with the solved in toluene (1.2·10Ϫ5 ). Similar color and spectral
closed-ring form 1b. The purple color was bleached by irra- changes to those of compound 1 were observed. The red-
Eur. J. Org. Chem. 2002, 3796Ϫ3800
3797

S. Takami, T. Kawai, M. Irie
FULL PAPER
purple color due to the ring-closed form 2b appeared upon
The photocyclization and photocycloreversion quantum
irradiation with 313 nm light and was bleached by irradi- yields of 1؊3 shown in Table 1 were measured in toluene
ation with visible light (λ Ͼ 480 nm) for 5 min. The photo- at 25 °C with fulyl fulgide[9] as a reference. The photocyc-
cycloreversion efficiency of 2b was intermediate between lization quantum yields were measured by irradiation with
those of 1b and 3b. On photobleaching the spectrum con- 313 nm light, while the photocycloreversion quantum yields
verted back into the original one yielding an isosbestic were measured by irradiation at the absorption maxima. A
point at 323 nm. The conversion from the open-ring to the cyclization quantum yield as high as 0.42 was observed for
closed forms by irradiation with 313 nm light was almost 3a, but this decreased to 0.29 when methoxy groups were
1
96%. In the H NMR spectrum of 2a in CDCl3, the reson- introduced at the reaction centers of the dithiazolylethenes.
ances due to the methoxy and methyl protons at the reac- Dimethoxy-substituted derivative 1a and monomethoxy-
tion centers were observed at δ ϭ 3.84 and 2.19 ppm, re- substituted derivative 2a gave similar cyclization quantum
spectively. Upon irradiation with 313 nm light new singlet yields. In contrast, the photocycloreversion quantum yield
signals corresponding to 2b appeared at δ ϭ 3.40 and 2.12 dramatically decreased when methoxy groups were intro-
ppm along with the decrease in intensity of the original sig- duced at the reaction centers. The cycloreversion quantum
nals.
yields of 1b and 2b were 3.3·10Ϫ4 and 4.0·10Ϫ3, which are
respectively 100 and 10 times smaller than that of 3b
(1.7·10Ϫ2). It should be noted that no degradation of the
test solution was observed by HPLC analysis during the
photocyclization and cycloreversion experiments of 1. This
means that no photochemical side-reaction having a
quantum yield higher than 10Ϫ6 takes place in the photo-
chemistry of 1. Additionally, we measured the thermal
stability of the ring-closed isomer 1b at 100 °C in toluene.
It was found that the closed-ring form 1b was thermally
stable at 100 °C for 48 h. The methoxy substituent effect on
the quantum yields for the photocycloreversion reactions is
similar to that observed for the dithienylethene derivatives.
The introduction of methoxy groups is considered to affect
the electronic structures[10] of the excited states of 1b and
2b.
Figure 3. Absorption spectra of a toluene solution of monome-
thoxy-substituted 2 (1.2·10Ϫ5 ): (dashed line) open-ring form 2a,
(solid line) closed-ring form 2b, and (dotted line) in the photo-
stationary state under irradiation with 313 nm
The absorption spectra of closed-ring forms 1b, 2b, and
3b of dithiazolylethene derivatives containing imine CϭN
Table 1 summarizes absorption maxima and absorption moieties (absorption maxima of 1b: 544 nm, 2b: 531 nm,
coefficients of the open- and closed-ring isomers 1؊3 in and 3b: 525 nm in hexane) showed a hypsochromic shift of
toluene. The absorption maxima of the open-ring (1aϪ3a) as much as about 50Ϫ80 nm relative to their dithienyle-
and closed-ring (1bϪ3b) forms were dependent on the num- thene analogues[5] (absorption maxima of dimethoxy-sub-
ber of methoxy substituents at the reaction centers. The ab- stituted: 625 nm, monomethoxy-substituted: 600 nm, and
sorption maximum of dimethoxy-substituted 1 (1a: λmax
ϭ
dimethyl-substituted: 575 nm in hexane). In order to invest-
322 nm, 1b: λmax ϭ 555 nm) showed a bathochromic shift igate this difference in the absorption maxima, molecular
of as much as about 20 nm relative to the maximum of 3 orbital calculations both for 3b and for the closed-ring form
(3a: λmax ϭ 305 nm, 3b: λmax ϭ 534 nm). Additionally, the of 1,2-bis(2-methyl-5-phenylthiophen-3-yl)percyclopentene
absorption coefficient of 1 is slightly lower than that of 3. (10) were undertaken using standard MOPAC software
The absorption maxima and coefficients of monomethoxy- with CNDO/S parameterization.[11] Although the con-
substituted 2 were intermediate between those of 1 and 3. formations of 3b and 10 were similar (as judged by the di-
Dithienylethene derivatives have also been reported to ex- hedral angle between phenyl and aryl groups), a consider-
hibit a bathochromic shift of the absorption maximum and able difference between the HOMO states was observed.
a decrease of the absorption coefficient when methoxy sub- The orbital profiles of HOMO and LUMO based on the
stituents were introduced to the reaction centers.[5]
CNDO/S parameterization are illustrated in Figure 4. In
Table 1. Absorption maxima and coefficients of the open- and closed-ring isomers of dithiazolylethene, and the quantum yields in toluene
λ max / nm
ΦaǞb
λ max / nm
ΦbǞa
Conversion
(313 nm)
(ε / Ϫ1·cmϪ1
)
(ε / Ϫ1·cmϪ1
)
1a
2a
3a
322 (33000)
311 (34500)
305 (37000)
0.29 (313 nm)
0.28 (313 nm)
0.42 (313 nm)
1b
2b
3b
555 (13100)
540 (15000)
534 (14500)
3.3·10Ϫ4 (555 nm)
4.0·10Ϫ3 (540 nm)
1.7·10Ϫ2 (534 nm)
1.00
0.96
0.95
3798
Eur. J. Org. Chem. 2002, 3796Ϫ3800

Photochromism of Dithiazolylethenes Having Methoxy Groups at the Reaction Centers
FULL PAPER
measured with a Hitachi U-3500 absorption spectrophotometer.
Photoirradiation was carried out using USHIO 500-W superhigh-
pressure mercury lamp or an USHIO 500-W xenon lamp. Mono-
chromatic light was obtained by passing the light through a com-
bination of Toshiba band-pass filter (UV-D33S) or sharp cut filter
(Y-46, Y-47, and Y-48) and monochromator (Ritsu MC-10N). Ele-
mental analyses were performed by the Microanalytical Laboratory
at the Department of Chemistry, Faculty of Science, Kyushu Uni-
versity. The cyclization quantum yields were determined by com-
paring the photocyclization rate of furyl flugide in toluene with a
the HOMO states, the orbital profiles of the 3, 4, 5, and 6
positions of 3b are significantly bigger than those of 10.
This means that electron density of 3b is more localized
than it is in 10, at the 3, 4, 5, and 6 positions. The visible
transitions of 3b and 10 were also calculated by using
CNDO/S. The HOMOϪLUMO energy gap of 3b is
5.86 eV, slightly higher than that (5.66 eV) of 10. The hyp-
sochromic shift of 3b relative to 10 is attributable to the
difference in the wavefunction of HOMO level, which is due
to localization of the electrons at the central cyclo- standard procedure.[9a] The cycloreversion quantum yields were
also measured using furyl flugide in toluene as a reference.[9b]
hexadiene structure.
Materials: Compounds 5 and 7 were prepared according to
methods reported previously.[7a] Spectroscopic grade solvents were
purified by distillation before use. All reactions were monitored by
thin-layer chromatography carried out on 0.2 mm Merck silica gel
plates (60F-254). Column chromatography was performed on silica
gel (Merck, 70Ϫ230 mesh).
5-Methoxy-2-phenylthiazole (4): N-benzoyl glycine methyl ester[12]
(1.00 g, 5.18 mmol) and phosphorus pentasulfide (1.40 g,
6.30 mmol) were rapidly added to 15 mL of dry chloroform, and
the mixture was stirred at 80 °C under an atmosphere of argon.
After 1 h, white precipitate had formed. Then the mixture was re-
fluxed for 24 h under an atmosphere of argon. The reaction mix-
ture was poured into aqueous NaOH and extracted with dichloro-
methane. The organic layer was dried with MgSO4 and concen-
Figure 4. CNDO/S calculation[11] of HOMO and LUMO for dithi-
enylethene 10 and dithiazolylethene 3b
trated under reduced pressure. The residue was purified by column
chromatography (ethyl acetate/hexane, 1:1) to afford 566 mg (57%)
of 4 as a red oil: H NMR (200 MHz, CDCl3): δ ϭ 3.96Ϫ3.95 (d,
1
J ϭ 2.2 Hz, 3 H), 7.12 (s, 1 H), 7.43Ϫ7.38 (m, 3 H), 7.82Ϫ7.78 (m,
2 H) ppm. MS m/z ϭ 191 [Mϩ]. C10H9NOS (191.3): calcd. C 62.80,
H 4.74, N 7.32; found C 62.64, H 4.78, N 7.34.
Conclusion
4-Bromo-5-methoxy-2-phenylthiazole (6): N-bromosuccinimide
(447 mg, 2.51 mmol) was added to a stirred solution of 4 (400 mg,
2.09 mmol) in dry chloroform (10 mL). The mixture was stirred at
room temperature for 4 h and extracted with ethyl acetate. The or-
ganic layer was dried with MgSO4 and concentrated under reduced
pressure. The residue was purified by column chromatography
(ethyl acetate/hexane, 1:3) to afford 550 mg (97%) of 6 as colorless
We have examined the photochromic reactivity of dithia-
zolylethene derivatives having methoxy substituents at the
reaction centers. The quantum yields of photocyclorever-
sion reaction were greatly diminished by the introduction
of methoxy groups at the reactiong centers. Dimethoxy-
substituted 1b and monomethoxy-substituted 2b showed,
respectively, 100-fold and 10-fold smaller cycloreversion
quantum yields than 3b. In contrast, the cyclization
quantum yields of 1a and 2a were scarcely affected by the
substitution. Furthermore, it was found that the closed
form 1b was thermally stable at 100 °C for 48 h. The ab-
sorption maxima of the closed-ring forms of dithiazolyl-
ethene derivatives showed a hypsochromic shift of as much
as 50Ϫ80 nm relative to the maximum of their dithienyl-
ethene analogues. The hypsochromic shift was explained by
the difference in the HOMOϪLUMO band gap between
the two systems.
1
prisms: m.p. 71Ϫ72 °C. H NMR (200 MHz, CDCl3): δ ϭ 4.03 (s,
3 H), 7.45Ϫ7.36 (m, 3 H), 7.85Ϫ7.76 (m, 2 H) ppm. MS m/z ϭ
271 [Mϩ]. C10H8BrNOS (269.0): calcd. C 44.46, H 2.98, N 5.18;
found C 44.56, H 2.99, N 5.19.
1-(5-Methoxy-2-phenylthiazol-4-yl)perfluorocyclopentene (8): To a
solution of 6 (500 mg, 1.85 mmol) in dry THF (5 mL) was slowly
added dropwise n-butyllithium (1.22 mL, 1.6
 in hexane,
1.94 mmol) at Ϫ78 °C under an atmosphere of argon. After the
mixture had been stirred for 15 min at Ϫ78 °C, perfluorocyclopen-
tene (0.20 mL, 0.93 mmol) in dry THF (2 mL) was added. The re-
action mixture was stirred at Ϫ78 °C for 2.5 h, and then distilled
water was added. The product was extracted with diethyl ether,
dried with MgSO4, and concentrated under reduced pressure. The
residue was purified by column chromatography (ethyl acetate/hex-
ane, 1:3) to afford 510 mg (72%) of 8 as colorless needles: m.p.
79Ϫ80 °C. 1H NMR (200 MHz, CDCl3): δ ϭ 4.13 (s, 3 H),
7.48Ϫ7.40 (m, 3 H), 7.88Ϫ7.82 (m, 2 H) ppm. MS m/z ϭ 383 [Mϩ].
C15H8F7NOS (383.0): calcd. C 47.00, H 2.10, N 3.65; found. C
47.25, H 2.08, N 3.66.
Experimental Section
General Remarks: 1H NMR spectra were recorded on a Varian Ge-
mini 200 spectrometer. HPLC was performed on a Hitachi L-7100
liquid chromatograph coupled with a Hitachi L-7400 spectrophoto-
meteric detector. A silica gel column [Si 60 250-20 (5µm)] was used.
Mass spectra were taken with a Shimadzu GCMS-QP5050A gas
chromatography-mass spectrometer. Absorption spectra were
1-(5-Methyl-2-phenylthiazol-4-yl)perfluorocyclopentene (9): Treat-
ment of 7 under the same conditions as for the synthesis of 8 gave
500 mg (69%) of 9 as colorless plates. M.p. 71Ϫ72 °C. 1H NMR
Eur. J. Org. Chem. 2002, 3796Ϫ3800
3799

S. Takami, T. Kawai, M. Irie
FULL PAPER
(200 MHz, CDCl3): δ ϭ 2.54 (d, J ϭ 3 Hz, 1 H), 7.48Ϫ7.42 (m, 3
H), 7.94Ϫ7.86 (m, 2 H) ppm. MS m/z ϭ 367 [Mϩ]. C15H8F7NS
Closed-Ring Form for 2a (2b): Compound 2b was isolated as a
purple solid by passing a photostationary solution containg 2a, 2b
(383.0): calcd. C 49.05, H 2.20, N 3.81; found. C 49.23, H 2.18, thorough HPLC (ethyl acetate/hexane, 1:4): 1H NMR (200 MHz,
N 4.11.
CDCl3): δ ϭ 2.12 (s, 3 H), 3.34 (s, 3 H), 7.26Ϫ7.62 (m, 6 H),
8.00Ϫ7.04 (m, 4 H) ppm. MS: m/z ϭ 538 [Mϩ]. C25H16F6N2OS2
(538.1): calcd. C 55.76, H 2.99, N 5.20; found. C 56.00, H 3.06,
N 5.04.
1,2-Bis(5-methoxy-2-phenylthiazol-4-yl)perfluorocyclopentene (1a):
To a solution of 6 (540 mg, 2.00 mmol) in dry THF (8 mL) was
added n-butyllithium (1.30 mL, 1.6  in hexane, 2.10 mmol) at Ϫ78
°C under an atmosphere of argon. After the mixture had been
stirred for 15 min at Ϫ78 °C, 8 (510 mg, 1.33 mmol) in dry THF
(2 mL) was added. The reaction mixture was further stirred at Ϫ78
°C for 2.5 h, and then distilled water was added. The product was
extracted with diethyl ether, dried with MgSO4, and concentrated
under reduced pressure. The residue was purified by column chro-
matography (ethyl acetate/hexane, 3:7) and HPLC (ethyl acetate/
hexane, 1:3) to afford 540 mg (68%) of 1a as a colorless solid. A
small portion of this product was recrystallized from hexane/ethyl
acetate to give colorless needles: m.p. 142Ϫ142.5 °C. 1H NMR
(200 MHz, CDCl3): δ ϭ 3.84 (s, 6 H), 7.44Ϫ7.35 (m, 6 H),
7.84Ϫ7.74 (m, 4 H) ppm. MS m/z ϭ 554 [Mϩ], 523 [Mϩ Ϫ OMe].
C25H16F6N2O2S2 (554.1): calcd. C 54.15, H 2.91, N 5.05; found. C
54.25, H 2.97, N 5.10.
Acknowledgments
This work was partly supported by Fukuoka Industry, Science &
Technology Foundation (Fukuoka-IST) and by CREST (Core Re-
search for Evolutional Science and Technology) of Japan Science
and Technology Corporation (JST).
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1-(5-Methoxy-2-phenylthiazol-4-yl)-2-(5-methyl-2-phenylthiazol-4-
yl)perfluorocyclopentene (2a): To
a solution of 6 (500 mg,
[7] [7a]
K. Uchida, T. Ishikawa, M. Takeshita, M. Irie, Tetrahedron
1.85 mmol) in dry THF (8 mL) was slowly added n-butyllithium
(1.22 mL, 1.6  in hexane, 1.94 mmol) at Ϫ78 °C under an atmo-
sphere of argon. After the reaction mixture had been stirred at Ϫ78
°C for 15 min, 9 (480 mg, 1.31 mmol) in dry THF (2 mL) was ad-
ded. The reaction mixture was further stirred at Ϫ78 °C for 2.5 h,
and then distilled water was added. The product was extracted with
diethyl ether, dried with MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography
(ethyl acetate/hexane, 1:9) and HPLC (ethyl acetate/hexane, 1:4) to
afford 260 mg (37%) of 2a as a colorless solid. A small portion of
this product was recrystallized from hexane/ethyl acetate to give
[7b]
1998, 54, 6627Ϫ6638.
S. Iwata, Y. Ishihara, C.-P. Qian, K.
Tanaka, J. Org. Chem. 1992, 57, 3726Ϫ3727.
[8]
S. Nakamura, M. Irie, J. Org. Chem. 1988, 53, 6136Ϫ6138.
[9] [9a]
Y. Yokoyama, Y. Kurita, J. Synth. Org. Chem. Jpn. 1991,
[9b]
49, 364Ϫ372.
H. G. Heller, J. R. Langan, J. Chem. Soc.,
Perkin Trans. 2 1981, 341Ϫ343.
[10]
[11]
D. Guillaumont, T. Kobayashi, K. Kanda, H. Miyasaka, K.
Uchida, S. Kobatake, K. Shibata, S. Nakamura, Irie, M. sub-
mitted for publication.
Calculation and visualization of molecular orbitals was per-
formed on a MOPAC 97 program in WinMOPAC ver. 2 of
Fujitsu Co. at Chiba, Japan.
1
colorless needles: m.p. 171Ϫ172 °C. H NMR (200 MHz, CDCl3):
[12] [12a] T. Miyazawa, T. Yamada, S. Kuwata, Bull. Chem. Soc. Jpn.
δ ϭ 2.19 (s, 3 H), 3.84 (s, 3 H), 7.48Ϫ7.30 (m, 6 H), 7.70Ϫ7.64 (m, 2
H), 7.97Ϫ7.91 (m, 2 H) ppm. MS m/z ϭ 538 [Mϩ]. C25H16F6N2OS2
(538.1): calcd. C 55.76, H 2.99, N 5.20; found. C 55.83, H 3.09,
N 5.23.
[12b]
1984, 57, 3605Ϫ3606.
K.-D. Ginzel, P. Brungs, E. Steck-
han, Tetrahedron 1989, 45, 1691Ϫ1701.
Received March 20, 2002
[O02154]
3800
Eur. J. Org. Chem. 2002, 3796Ϫ3800