Photochromism of diarylethene derivatives having n-alkylbenzothiophene and n-alkylbenzofuran units

Article abstract of DOI:10.1246/bcsj.79.1100

Photochromic diarylethenes having benzofuran and benzothiophene rings have been synthesized and their photochromic performance in a single-crystalline phase has been examined. Although 1,2-bis(2-methyl-1-benzothiophen-3-yl) perfluorocyclopentene (1a) is photochemically inactive in the single-crystalline phase, diarylethene derivatives having a benzofuran ring (2a and 3a) undergo photochromism in the single-crystalline phase. 1-(1-Benzofuran-3-yl)-2-(1- benzothiophen-3-yl)hexafluorocyclopentene having ethyl, propyl, and butyl chains at the 2-position (4a-6a) were also synthesized. The derivative having propyl chains (5a) underwent photochromism in a single-crystalline phase. Upon UV irradiation, the crystal showed a brilliant red color in the single-crystalline phase.

Full text of DOI:10.1246/bcsj.79.1100

1100 Bull. Chem. Soc. Jpn. Vol. 79, No. 7, 1100–1105 (2006)
ꢀ 2006 The Chemical Society of Japan
Photochromism of Diarylethene Derivatives Having
n-Alkylbenzothiophene and n-Alkylbenzofuran Units
ꢀ
ꢀ
Tadatsugu Yamaguchi and Masahiro Irie
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581
Received January 6, 2006; E-mail: tyamagu@cstf.kyushu-u.ac.jp
Photochromic diarylethenes having benzofuran and benzothiophene rings have been synthesized and their photo-
chromic performance in a single-crystalline phase has been examined. Although 1,2-bis(2-methyl-1-benzothiophen-3-
yl)perfluorocyclopentene (1a) is photochemically inactive in the single-crystalline phase, diarylethene derivatives having
a benzofuran ring (2a and 3a) undergo photochromism in the single-crystalline phase. 1-(1-Benzofuran-3-yl)-2-(1-ben-
zothiophen-3-yl)hexafluorocyclopentene having ethyl, propyl, and butyl chains at the 2-position (4a–6a) were also syn-
thesized. The derivative having propyl chains (5a) underwent photochromism in a single-crystalline phase. Upon UV
irradiation, the crystal showed a brilliant red color in the single-crystalline phase.
Photochromism has attracted considerable attention because
of its potential application to molecular devices, such as optical
F2
F2
F2
F2
memories and switches.1,2 Among various thermally irreversi-
ble photochromic compounds diarylethene derivatives are the
most promising candidates for the application because of their
fatigue resistant and thermally irreversible properties.3–9 Di-
arylethene derivatives so far synthesized have heteroaryl moi-
eties such as thiophene,10 benzothiophene,11 benzofuran,12
thiazole,13 chrysothiophene,14 and indole rings.15
F2
F2
h
ν
R
R
hν'
O
S
R
O
S
ð2Þ
R
3a: R=CH3
3b: R=CH3
4a: R=C2H5
4b: R=C2H5
5a: R=n-C3H7
6a: R=n-C4H9
5b: R=n-C3H7
6b: R=n-C4H9
We have reported on 1,2-bis(2-n-alkyl-1-benzothiophen-3-
yl)ethene derivatives,16 which undergo photochromism in the
single-crystalline phase. Their photochromic performance is
strongly dependent on the distance between the reactive car-
bons. When the distance is within 0.42 nm, they undergo pho-
tochromism in the crystalline phase,17 but compounds that
have a distance larger than 0.42 nm did not show any photo-
chromism in the single-crystalline phase. 1,2-Bis(2-methyl-1-
benzothiophen-3-yl)perfluorocyclopentene (1a), which has
the distance of 0.435 nm, was photochemically inactive.12
However, 1,2-bis(2-methyl-1-benzofuran-3-yl)perfluorocyclo-
pentene (2a) showed photochromism in the single-crystalline
phase. The reaction distance is as short as 0.356 nm. Diaryl-
ethene derivatives having benzothiophene and benzofuran
rings may undergo a photochromic reaction in the single-crys-
talline phase. In this work, various diarylethene derivatives
having benzofuran and benzothiophene rings with n-alkyl sub-
stituent at the 2-position of the rings were synthesized and the
photochromic performance was examined in solution as well
as in the single-crystalline phase.
Results and Discussion
1-(2-Methyl-1-benzofuran-3-yl)-2-(2-methyl-1-benzothio-
phen-3-yl)hexafluorocyclopentene (3a) was synthesized as
shown in Scheme 1. The coupling reaction between 1-(2-
methyl-1-benzothiophen-3-yl)heptafluorocyclopentene and 3-
bromo-2-methyl-1-benzofuran (7) gave 3a in 42% yield.
The diarylethenes 4a, 5a, and 6a having ethyl, propyl, and
butyl units were synthesized following the procedures used
for the synthesis of 3a.
Photochromic Reactions in Hexane. Figure 1a shows the
absorption spectral change of 3 in hexane. In the photostation-
ary state, upon irradiation with 313 nm light, the open-ring iso-
mers 3a, which has the maximum at 299 nm (": 0:69 ꢁ 104
F2
F2
O
F2
S
i), ii)
Br
F2
CH3
F2
F2
F2
F2
F2
O
h
ν
CH3
H3C
ð1Þ
Me
Me
Me
Me
3a
hν'
X
X
X
X
Scheme 1. Synthesis of the diarylethene 3a. i) n-Butyllithi-
um (1.1 equiv), THF at ꢂ78 ꢃC. ii) 1-(2-Methyl-1-benzo-
thiophen-3-yl)heptafluorocyclopentene (42%).
1a: X=S
2a: X=O
1b: X=S
2b: X=O
Published on the web July 4, 2006; doi:10.1246/bcsj.79.1100

T. Yamaguchi et al.
ꢂ1 cmꢂ1), was transformed into 3b, which has the maximum
at 493 nm (": 1:53 ꢁ 104 Mꢂ1 cmꢂ1). Upon irradiation with
visible light (ꢀ > 480 nm) the closed-ring isomer returned to
the original 3a.
Bull. Chem. Soc. Jpn. Vol. 79, No. 7 (2006) 1101
M
tochromism of 5 in hexane. In the photostationary state under
irradiation with 313 nm light, 47% of the open-ring isomers,
converted to the closed-ring isomers 5b, having the maximum
at 507 nm. The colorless solution changed to red. By changing
alkyl units from methyl to propyl, the absorption maximum of
the closed-ring isomer shifted to longer wavelengths by as
much as 14 nm. Upon irradiation with visible light (ꢀ > 440
nm), the closed-ring isomer returned to the original 5a.
The cyclization and cycloreversion quantum yields were
measured for compounds 3–6. Table 1 summarizes the quan-
tum yields along with the absorption characteristics. The prop-
erties of bisbenzothiophene and bisbenzofuran derivatives 1
and 2 are also included in the Table. The cyclization quantum
yield of 2 is slightly larger than those of 1 and 3. The cy-
clization quantum yield increases with increasing the chain
length. As observed for the benzothiophene and benzofuran
derivatives, the increase in the relative population of the
anti-parallel conformers enhances the quantum yield of the
cyclization reaction.12,16 Compounds 4, 5, and 6 gave similar
cycloreversion quantum yield. The value is slightly larger than
the value of 3. The molar absorption coefficient for 3b is the
largest among 3b–6b.
Just as 3, 4–6 underwent photochromism upon irradiation
with UV and visible light in hexane. Figure 1b shows the pho-
0.6
(a)
0.4
0.2
0.0
300
400
500
600
700
Wavelength / nm
0.8
0.6
0.4
0.2
0.0
X-ray Crystallographic Analysis for 3a and 5a. A single
crystal was obtained by recrystallization from hexane and X-
ray crystallographic analysis of the crystal was carried out.
Suitable crystals for X-ray crystallographic analysis were ob-
tained for 3a and 5a.
Figure 2 shows an ORTEP drawing of 3a. The drawing
indicates that 3a is packed in an anti-parallel conformation
in the single-crystalline phase. The distance between the reac-
(b)
300
400
500
600
700
Wavelength / nm
Fig. 1. (a) Absorption spectra of 3a (solid line), 3b (dashed
line), and in the photostationary state (dotted line) un-
der irradiation with 313 nm light in hexane (2:6 ꢁ 10ꢂ5
mol Lꢂ1). (b) Absorption spectra of 5a (solid line), 5b
(dashed line), and in the photostationary state (dotted line)
under irradiation with 313 nm light in hexane (4:6 ꢁ 10ꢂ5
mol Lꢂ1).
Fig. 2. An ORTEP drawing of 3a. The ellipsoid represents
50% displacement of atoms.
Table 1. Absorption Characteristics and Photoreactivity of the Diarylethene Derivatives 1–6 in Hexane
"/104 dm3 molꢂ1 cmꢂ1
Quantum yield
Conversion
(313 nm)
Compound
a
b
Cyclization
Cycloreversion
1
1.41
(254 nm)
1.00
(274 nm)
0.69
(299 nm)
0.64
(299 nm)
0.60
0.91
(517 nm)
1.44
(469 nm)
1.53
(493 nm)
1.15
(507 nm)
1.00
0.35
(313 nm)
0.38
(313 nm)
0.32
(313 nm)
0.40
(313 nm)
0.44
0.35
(517 nm)
0.35
(469 nm)
0.25
(493 nm)
0.30
(507 nm)
0.31
47%
48%
47%
55%
47%
58%
2
3
4
5
6
(299 nm)
0.58
(299 nm)
(507 nm)
1.09
(508 nm)
(313 nm)
0.50
(313 nm)
(507 nm)
0.30
(508 nm)

1102 Bull. Chem. Soc. Jpn. Vol. 79, No. 7 (2006)
Photochromism of Diarylethene
tive carbons is 0.402 nm, which is between that of 1a and 2a.
The distance is short enough for the reaction to take place in
the crystalline phase.
Figure 5a shows the polarized absorption spectra upon irra-
diation with 365 nm light. The clear dichroism was observed
by rotating the single crystal. Figure 5b shows a polar plot
of the absorption at 510 nm. The clear dichroism confirms that
the photochromism of 3 occurs in the single-crystalline phase.
In the case of 5a, the crystal was colorless before irradia-
tion (Fig. 6a). Upon irradiation with 365 nm light, the crystal
turned brilliant red (Fig. 6b). When the crystal was rotated
by as much as 90ꢃ, the color of the crystal changed to pale yel-
low. The colors disappeared by irradiation with visible light
(ꢀ > 440 nm).
Figure 7a shows the polarized absorption spectra of the col-
ored crystal. The observed crystal face is (001). The absorption
maximum of the closed-ring is 540 nm at 0ꢃ. By rotating the
crystal sample under polarized light, the absorption intensity
was changed as shown in Fig. 7b. The coloration/decoloration
cycles of the crystals of 3 and 5 could be repeated more than
10000 times without destruction of the crystal shape. The bril-
liant red color of 5 after UV irradiation may be used for a kind
of display.
Figure 3 shows an ORTEP drawing of 5a. The aryl moieties
are in an anti-parallel conformation, and the distance between
the reactive carbons is 0.398 nm. The distance is also short
enough for the reaction to take place in the crystalline phase.
Photochromism in the Single-Crystalline Phase. Both 3a
and 5a undergo photochromism even in the single-crystalline
phase. Figures 4a–4d show photographs of a single crystal of 3
observed using a polarizing microscope (Nikon, OPTIPOL-
2POL). The surface corresponds to (021) face. Upon irradia-
tion with 365 nm light, compound 3 showed an orange color
(Figs. 4c and 4d). Upon irradiation with visible light (>440
nm), the orange color disappeared immediately. The color
change was observed deep in the crystal bulk when the crystal
was irradiated with 390 nm light. The light could penetrate the
crystal as deep as several hundred mm.
In the case of 4a and 6a, crystals large enough to study the
single-crystalline photochromism were not obtained. Although
the crystals showed color changes upon UV irradiation, de-
tailed analysis could not be carried out.
In conclusion, new types of photochromic compounds having
benzofuran and benzothiophene units were synthesized and
their photochromic reactivity has been examined in hexane as
well as in the single-crystalline phase. Single crystals of 3 and
5 showed photochromism upon irradiation with UV and visible
light. A single crystal of 5 showed a color change from color-
less to a brilliant red color. The benzofuran derivatives showed
fatigue resistant photochromism in the single-crystalline phase.
Experimental
Fig. 3. An ORTEP drawing of 5a. The ellipsoid represents
50% displacement of atoms.
General.
The solvents used were spectrograde and were
Fig. 4. Photographs of a single crystal of 3 ((a) ꢁ ¼ 0ꢃ and (b) 90ꢃ) and after irradiation with 365 nm light ((c) ꢁ ¼ 0ꢃ and (d) 90ꢃ).

T. Yamaguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 7 (2006) 1103
90°
1.2
1.0
1.0
0.8
0.6
0.4
0.2
0.0
120°
60°
(a)
(b)
30°
0.8
0.6
θ
= 0°
0°
0.4
0.2
330°
210°
θ
= 90°
300°
240°
0.0
400
270°
500
600
700
Wavelength / nm
Fig. 5. (a) Absorption spectra of a single crystal of 3 after irradiation with 365 nm light. (b) Polar absorption plot of a single crystal
of 3 after irradiation with 365 nm light at 510 nm.
Fig. 6. Photographs of 5 (a) before and (b) after irradiation with 365 nm light.
1.0
0.8
90°
120°
60°
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
30°
θ
= 0°
0.6
0.4
0.2
0.0
0°
θ
= 90°
330°
210°
300°
240°
270°
400
500
600
700
Wavelength / nm
Fig. 7. (a) Absorption spectra of a single crystal of 5 after irradiation with 365 nm light. (b) Polar absorption plot of a single crystal
of 5 after irradiation with 365 nm light at 540 nm.
purified by distillation before use. Absorption spectra were mea-
sured with a spectrophotometer (Hitachi, U-3310). The quantum
yields were determined by comparing the reaction rates of the
diarylethene derivatives in hexane against that of furylfulgide in
toluene. The samples were not degassed. Absorption spectra in
the single-crystalline phases were measured using an OPTI-POL
2POL polarizing microscope connected to a Hamamatsu PMA-11
detector. Photoirradiation for single-crystal measurements was
carried out using a 100 W mercury lamp (Nikon, C-SHG1 and
LH-M100CB-1) as the light source. For solution measurements,
a mercury lamp (Ushio, 500 W) was used as the light source. Light
of appropriate wavelength was isolated by passing light through a
monochromator (RITSU MC-10N) or through Y-44 and UV-
1
D33S filters. H NMR was recorded on a Gemini 200 spectrome-
ter (200 MHz) with CDCl3 as the solvent and tetramethylsilane as
an internal standard at room temperature. At low temperature
(ꢂ90 ꢃC), 1H NMR was recorded on a 400 MHz spectrometer
(JEOL, JNM-ECP400) at the Center of Advanced Instrumental
Analysis (Kyushu University) in CD3OD as the solvent and tetra-
methylsilane as an internal standard. Good quality crystals (3a:
0:2 ꢁ 0:1 ꢁ 0:1 mm3 and 5a: 0:15 ꢁ 0:1 ꢁ 0:1 mm3) were select-
ed for the X-ray diffraction study. The data collection was per-
formed on a Bruker SMART 1000 CCD-based diffractometer
(55 kV, 35 mA) with Mo Kꢂ irradiation. Fatigue resistance mea-

1104 Bull. Chem. Soc. Jpn. Vol. 79, No. 7 (2006)
Photochromism of Diarylethene
unique reflections. CCDC deposition number: 289583.
surements of the single crystals were carried out using the appara-
tus described in Ref. 18.
1-(2-Ethyl-1-benzofuran-3-yl)-2-(2-ethyl-1-benzothiophen-
3-yl)perfluorocyclopentene (4a): The coupling of 3-bromo-2-
ethyl-1-benzofuran (0.668 g, 2.97 mmol), 7 (1.05 g, 2.97 mmol),
and a 1.6 M butyllithium hexane solution (2.04 mL, 3.27 mmol)
was performed as described for compound 3a. The crude product
was purified by column chromatography on silica gel (hexane) to
give 0.401 g of 4a in 28% yield. 4a: colorless crystals; mp 85.9–
87.2 ꢃC; 1H NMR (200 MHz, CDCl3, rt) ꢃ 0.68 (t, J ¼ 7:6 Hz,
3H), 1.02 (t, J ¼ 7:6 Hz, 3H), 2.17–2.84 (m, 4H), 7.19–7.39 (m,
Synthesis.
1-(2-Ethyl-1-benzothiophen-3-yl)heptafluoro-
cyclopentene (7): To a stirred THF solution (20 mL) contain-
ing 3-bromo-2-ethyl-1-benzothiophene (0.548 g, 2.27 mmol) was
slowly added 1.56 mL of a 1.6 M butyllithium hexane solution
(2.50 mmol) at ꢂ78 ꢃC, and the solution was stirred for 15 min at
ꢂ78 ꢃC. Then, the solution was slowly added dropwise to a mix-
ture of octafluorocyclopentene (0.530 mL, 4 mmol) and THF (20
mL) at ꢂ78 ꢃC, and left to stand with stirring at ꢂ78 to 30 ꢃC
for 12 h. The reaction mixture was poured into a concentrated
sodium chloride solution and extracted with diethyl ether. The
organic phase was dried over anhydrous magnesium sulfate and
evaporated in vacuo. The crude product was purified by column
chromatography on silica gel (hexane) to give 0.487 g of 7 in
1
5H), 7.54–7.63 (m, 2H), 7.69–7.73 (m, 1H). H NMR (400 MHz,
CD3OD, ꢂ90 ꢃC) ꢃ 0.05 (brs, 2.1H), 0.68 (brs, 2.1H), 0.82 (brs,
0.9H), 1.37 (brs, 0.9H), 2.15 (brs, 0.7H), 2.31–2.46 (m, 1.9H),
2.64–2.79 (m, 0.9H), 2.96–3.02 (m, 0.5H), 7.08–7.13 (m, 0.7H),
7.25–7.54 (m, 4.3H), 7.65–7.95 (m, 3H). MS (EI) m=z 480
(Mþ); Anal. Calcd for C25H18F6OS: C, 62.50; H, 3.78%. Found:
C, 62.50; H, 3.79%.
1
61% yield. 7: colorless liquid; H NMR (200 MHz, CDCl3, rt) ꢃ
1.36 (t, J ¼ 3:6 Hz, 3H), 2.85 (q, J ¼ 3:6 Hz, 2H), 7.34–7.51 (m,
3H), 7.81–7.83 (m, 1H). HRMS(FAB) m=z 354.0314 ([Mþ]),
calcd for C15H9F7S 354.0316.
1-(2-Propyl-1-benzofuran-3-yl)-2-(2-propyl-1-benzothiophen-
3-yl)perfluorocyclopentene (5a): The coupling of 3-bromo-2-
propyl-1-benzofuran (0.591 g, 2.47 mmol), 8 (0.910 g, 2.47 mmol),
and a 1.6 M butyllithium hexane solution (1.70 mL, 2.71 mmol)
was performed as described for compound 3a. The crude product
was purified by column chromatography on silica gel (hexane) to
give 0.493 g of 5a in 39% yield. 5a: colorless crystals; mp 133.6–
134.4 ꢃC; 1H NMR (200 MHz, CDCl3, rt) ꢃ 0.49 (t, J ¼ 7:2 Hz,
3H), 0.69 (t, J ¼ 7:2 Hz, 3H), 0.77–1.51 (m, 4H), 2.11–2.82 (m,
4H), 7.22–7.40 (m, 5H), 7.57–7.67 (m, 2H), 7.72–7.76 (m, 1H).
1H NMR (400 MHz, CD3OD, ꢂ90 ꢃC) ꢃ ꢂ0:28 (brs, 0.9H),
ꢂ0:08 (brs, 2.7H), 0.29 (brs, 2.7H), 0.55 (brs, 0.9H), 0.90 (brs,
0.3H), 1.08 (brs, 0.3H), 1.25–1.34 (m, 1.8H), 1.70–1.80 (brs,
0.4H), 2.05 (brs, 0.9H), 2.21–2.43 (m, 1.9H), 2.49–2.58 (m,
1.0H), 2.85 (brs, 0.2H), 7.14–7.27 (m, 0.2H), 7.36–7.52 (m,
5.0H), 7.76–7.81 (m, 1.9H), 7.94–7.96 (m, 0.9H). MS (EI) m=z
508 (Mþ); Anal. Calcd for C27H22F6OS: C, 63.77; H, 4.36%.
Found: C, 63.80; H, 4.36%. Crystal data for 5a: C27H22F6OS,
1-(2-Propyl-1-benzothiophen-3-yl)heptafluorocyclopentene
(8): The reaction of 3-bromo-2-propyl-1-benzothiophene (1.00 g,
3.9 mmol), a 1.6 M butyllithium hexane solution (2.69 mL, 4.3
mmol), and octafluorocyclopentene (1.06 mL, 8.0 mmol) was per-
formed as described for compound 7. The crude product was puri-
fied by column chromatography on silica gel (hexane) to give 0.918
g of 8 in 64% yield. 8: colorless liquid; 1H NMR (200 MHz, CDCl3,
rt) ꢃ 1.00 (t, J ¼ 3:6 Hz, 3H), 1.74–1.80 (m, 2H), 2.79 (t, J ¼ 3:6
Hz, 2H), 7.35–7.46 (m, 3H), 7.79–7.82 (m, 1H). HRMS(FAB) m=z
368.0474 ([Mþ]), calcd for C16H11F7S 368.0478.
1-(2-Butyl-1-benzothiophen-3-yl)heptafluorocyclopentene (9):
The reaction of 3-bromo-2-butyl-1-benzothiophene (1.23 g, 4.57
mmol), a 1.6 M butyllithium hexane solution (3.14 mL, 5.0 mmol),
and octafluorocyclopentene (1.19 mL, 9.0 mmol) was performed
as described for compound 7. The crude product was purified
by column chromatography on silica gel (hexane) to give 1.05 g
of 9 in 60% yield. 9: colorless liquid; 1H NMR (200 MHz, CDCl3,
rt) ꢃ 0.94 (t, J ¼ 3:8 Hz, 3H), 1.38–1.48 (m, 2H), 1.68–1.77 (m,
2H), 2.81 (t, J ¼ 3:8 Hz, 2H), 7.35–7.48 (m, 3H), 7.80–7.82 (m,
1H). HRMS(FAB) m=z 382.0617 ([Mþ]), calcd for C17H13F7S
382.0626.
˚
MW ¼ 508:51, monoclinic, space group Cc, a ¼ 19:1296ð9Þ A,
ꢃ
ꢃ
˚
˚
b ¼ 12:8476ð6Þ A, c ¼ 11:5394ð6Þ A, ꢂ ¼ 90 , ꢄ ¼ 123:047ð3Þ ,
ꢅ ¼ 90 , V ¼ 2377:2ð2Þ A , Z ¼ 4, Dcalcd ¼ 1:421 g cmꢂ3, R1 ¼
0:0538 for 3158 observed reflections with I > 2ꢆðIÞ from 4193
unique reflections. CCDC deposition number: 294195.
ꢃ
3
˚
1-(2-Methyl-1-benzofuran-3-yl)-2-(2-methyl-1-benzothio-
phen-3-yl)perfluorocyclopentene (3a): To a stirred THF solu-
tion (30 mL) containing 3-bromo-2-methyl-1-benzofuran (0.632 g,
2.99 mmol) was slowly added 2.06 mL of a 1.6 M butyllithium
hexane solution (3.29 mmol) at ꢂ78 ꢃC, and the solution was stir-
red for 15 min at ꢂ78 ꢃC. Then, the 1-(2-methyl-1-benzothiophen-
3-yl)heptafluorocyclopentene (1.02 g, 2.99 mmol) was added
slowly to the reaction mixture at ꢂ78 ꢃC, and left to stand with
stirring at ꢂ78 to 30 ꢃC for 12 h. The reaction mixture was poured
into a concentrated sodium chloride solution and extracted with
diethyl ether. The organic phase was dried over anhydrous magne-
sium sulfate and evaporated in vacuo. The crude product was
purified by column chromatography on silica gel (hexane) to give
0.569 g of 3a in 42% yield. 3a: colorless crystals; mp 102.5–
1-(2-Butyl-1-benzofuran-3-yl)-2-(2-butyl-1-benzothiophen-
3-yl)perfluorocyclopentene (6a): The coupling of 3-bromo-2-
butyl-1-benzofuran (0.663 g, 2.62 mmol), 9 (1.00 g, 2.62 mmol),
and a 1.6 M butyllithium hexane solution (1.80 mL, 2.87 mmol)
was performed as described for compound 3a. The crude product
was purified by column chromatography on silica gel (hexane) to
give 0.351 g of 6a in 25% yield. 6a: colorless crystals; mp 82.1–
83.6 ꢃC; 1H NMR (200 MHz, CDCl3, rt) ꢃ 0.62–0.72 (m, 6H),
0.85–1.48 (m, 8H), 2.08–2.83 (m, 4H), 7.21–7.41 (m, 5H), 7.58–
7.75 (m, 3H). 1H NMR (400 MHz, CD3OD, ꢂ90 ꢃC) ꢃ ꢂ0:46 (brs,
2H), 0.21 (brs, 1H), 0.32–0.39 (m, 6.8H), 0.62 (brs, 1H), 0.90–
0.96 (m, 1.2H), 1.20 (brs, 2H), 2.00–2.05 (m, 1H), 2.24–2.37
(m, 2H), 2.56–2.86 (m, 1H), 7.10–7.26 (m, 0.1H), 7.37–7.58 (m,
4.9H), 7.77–7.79 (m, 2H), 7.94–7.97 (m, 1H). MS (EI) m=z 536
(Mþ); Anal. Calcd for C29H26F6OS: C, 64.91; H, 4.88%. Found:
C, 64.94; H, 4.88%.
1
103.2 ꢃC; H NMR (200 MHz, CDCl3, rt) ꢃ 2.01 (s, 3H), 2.29 (s,
3H), 7.17–7.36 (m, 5H), 7.52–7.72 (m, 3H). MS (EI) m=z 452
(Mþ); Anal. Calcd for C23H14F6OS: C, 61.06; H, 3.12%. Found:
C, 60.94; H, 3.21%. Crystal data for 3a: C23H14F6OS, MW ¼
Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre. Copies of the data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html (or from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge, CB2 1EZ, UK; Fax: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk).
˚
452:41, monoclinic, space group P21=n, a ¼ 11:539ð4Þ A, b ¼
ꢃ
ꢃ
˚
˚
14:539ð5Þ A, c ¼ 13:147ð4Þ A, ꢂ ¼ 90 , ꢄ ¼ 114:700ð4Þ , ꢅ ¼
90 , V ¼ 2003:9ð11Þ A , Z ¼ 4, Dcalcd ¼ 1:500 g cmꢂ3, R1 ¼
ꢃ
3
˚
0:0477 for 2199 observed reflections with I > 2ꢆðIÞ from 2891

T. Yamaguchi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 7 (2006) 1105
9
W. R. Browne, J. J. D. de Jong, T. Kudernac, M. Walko,
This work was supported by a Grant-in-Aid for Scientific
Research (S) (No. 15105006) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
L. N. Lukas, K. Uchida, J. H. van Esch, B. L. Feringa, Chem.
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