Synthesis of novel thermally reversible photochromic spiro[adamantane-2,7′(6′H)-benzothiophene]

Article abstract of DOI:10.1246/bcsj.76.355

A new thermally reversible photochromic compound, 4′,5′-hexafluoropropano-6′-phenylspiro[adamantane-2, 7′(6′H)-benzothiophene], derived from UV-irradiation of 2-(1-adamantylidene-1-phenylmethyl)-3,3,4,4,5,5-hexafluoro-1- (3-thienyl)cyclopentene via the ph

Full text of DOI:10.1246/bcsj.76.355

c. Jpn.
© 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 355–361 (2003)
355
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Synthesis of Novel Thermally Reversible Photochromic
Spiro[adamantane-2,7ꢀ(6ꢀH)-benzothiophene]
Novel Thermally Reversible Photochrome
Y. Yokoyama et al.
Yasushi Yokoyama,* Hitoshi Nagashima, Sujen Man Shrestha, Yayoi Yokoyama,† and
03
5
Kensaku Takada
1
Department of Advanced Materials Chemistry, Graduate School of Engineering, Yokohama National University,
79-5, Tokiwadai, Hodogaya-ku, Yokohama, 240-8501
SJA8
09-2673
204
†Department of Home Economics, Faculty of Home Economics, Tokyo Kasei Gakuin University,
2600, Aihara-cho, Machida, Tokyo 194-0292
02
02
(Received July 24, 2002)
A new thermally reversible photochromic compound, 4ꢀ,5ꢀ-hexafluoropropano-6ꢀ-phenylspiro[adamantane-
2,7ꢀ(6ꢀH)-benzothiophene], derived from UV-irradiation of 2-(1-adamantylidene-1-phenylmethyl)-3,3,4,4,5,5-hexafluo-
ro-1-(3-thienyl)cyclopentene via the photochemical 6π-electrocyclization followed by the thermal 1,5-hydrogen migra-
tion, was synthesized and its photochemical and thermal properties were examined. The structurally more simplified
3,3,4,4,5,5-hexafluoro-2-(2-methyl-1-phenyl-1-propenyl)-1-(3-thienyl)cyclopentene did not yield the thermally revers-
ible photochromic compound upon UV irradiation.
In order to realize a molecular or supramolecular system
whose physical as well as chemical properties can be switched
from outside of the system, photochromic molecules are suit-
able because all of their properties, including the structure and
absorption spectral properties, can be changed by light irradia-
tion. Although there have been found and developed so many
photochromic compounds, the submission of a new class of
compounds to increase the assortment in the showcase of pho-
tochromic compounds is still important because of adequate
selection for a particular use in the future, such as optical re-
cording, opto-electronic switching and the auto-regulation of
light.
Photochromic compounds are categorized into two classes.
One is that conversion between the stable states occurs only by
photoirradiation (P-type); the other is that conversion occurs
Scheme 1. Heliochromism of a benzothienylfulgide.
by photoirradiation as well as a thermal treatment (T-type). A
unique category is so-called “heliochromism,” which belongs
to T-type photochromism. For fulgide1 derivatives, Whittall
stated that “the heliochromic compounds have high efficiency
for coloring with near UV irradiation while the colored forms
have a low efficiency for photochemical reverse action but
have thermal reverse at ambient temperatures so that these
compounds color in sunlight”.2 The structural features of these
heliochromic fulgides (heliofulgides)3 like 1 are: (1) they have
a hydrogen atom at the terminal olefin of the hexatriene moiety
on the aromatic ring, and (2) they have an adamantylidene
group as the other terminal of the hexatriene moiety, although
the reason is not clear. The mechanism for the heliochromism
of 1 is shown in Scheme 1.
pound produced from the arylbutadiene; a following article
will deal with new P-type photochromic arylbutadienes.
Results and Discussion
Design of the Molecules. The necessary units for ther-
mally reversible photochromic molecules like 1 are: (i) an aryl
group as one of two terminal double bonds which does not
have a substituent on the bond-forming carbon atom upon pho-
toirradiation, (ii) an adamantylidene group as the other termi-
nal double bond, and (iii) the central double bond of the
hexatriene moiety. To append photochemical fatigue resistivi-
ty as well as to remove the energy-wasting E–Z isomerization
of the olefin, we employed perfluorocyclopentene, which is
frequently used for diarylethenes,5 as the central ethene moi-
ety. The aryl group is attached to the perfluorocyclopentene
ring with its C-3, and a hydrogen atom is necessary on C-2. In
As a part of our research to seek new photochromic sys-
tems,4 we envisioned that arylbutadienes may produce a new
photochromic class of compounds based on 6π-electrocycliza-
tion. This article deals with a new T-type photochromic com-

356 Bull. Chem. Soc. Jpn., 76, No. 2 (2003)
Novel Thermally Reversible Photochrome
order to secure the possibility to tune the absorption maximum
of the colored form as the later modification, a phenyl group
participating in the conjugation may be useful. Consequently,
we chose 2 as the target molecule. The anticipated reaction
course of 2 is shown in Scheme 2.
To clarify the generality of the photochromic reaction, we
also designed a simpler molecule 3, which has an isopropy-
lidene group instead of the adamantylidene group.
Synthesis of 2O. The synthesis of 2 was carried out as
shown in Scheme 3. The right part 7 was prepared in four
steps in 43% yield, starting from 2-adamantanone and benzyl-
magnesium chloride. After the right part was attached to per-
fluorocyclopentene in 92% yield to form 8, 3-lithiothiophene,
generated from 3-bromothiophene, was introduced to 8 to ac-
complish the synthesis of 2O in 20% yield.
Photochemical 6π-electrocyclization, followed by a thermal
sigmatropic 1,5-hydrogen shift, subsequently occurred at r.t. to
give 2R in 57% yield. Because the intermediate 2C was not
detected by UV-vis spectroscopy, the hydrogen rearrangement
to give 2R from 2C occurred rapidly. The structure of 2R was
1
determined by H NMR, IR, MS, and finally X-ray crystallo-
graphic analysis. The chemical shift of the migrated hydrogen
of 2R appeared at δ 4.57 in CDCl3, which is in good agreement
with the chemical shift of that of the heliofulgide 9R6 (Chart 1;
δ 4.20). The structure of 2R was unequivocally determined by
X-ray crystallographic analysis. An ORTEP drawing is shown
in Fig. 1, and the crystallographic data are listed in Table 1. It
is thus clarified that the photochemical electrocyclization of
2O to give 2C followed by hydrogen migration on 2C oc-
curred to afford 2R.
Structure Determination of 2. In order to obtain the T-
type photochromic compound, a toluene solution of 2O was
irradiated with 313-nm light at room temperature for 5 h.
Photocoloration of 2R and Thermal Decoloration of 2Q.
When 2R in toluene was irradiated with 313-nm light, all of
the absorption above 300 nm increased with the emergence of
a new absorption band in the visible region (λmax 500 nm). The
changes in the absorption spectra by 313-nm light irradiation
in toluene at room temperature and by a thermal treatment to
cause a back reaction are shown in Fig. 2. Although an obser-
vation of 1H NMR spectra of the colored species was not suc-
cessful because of its low concentration as well as the internal
filter effect of 2R, the colored species was assigned to the
ortho-quinodimethane-type compound 2Q as an analogy with
1Q. The absorption of 2Q became smaller when the solution
was kept in the dark at room temperature, and disappeared
completely within 150 min. Because the coloration-decolora-
tion cycles were repeatable many times, it was proved that 2R
and 2Q compose the thermally reversible photochromic sys-
tem.
The decoloration rate constants at different temperatures in
toluene are given in Table 2. The activation energy of decolor-
ation in toluene was calculated to be 84.0 kJ mol−1.
Simplified Compound 3. The adamantylidene unit is
considered to be necessary for heliofulgides to show thermally
reversible photochromism.2 Because 2 showed thermally re-
versible photochromism, we intended to replace the adaman-
tylidene group with a simple isopropylidene group in order to
know whether the adamantylidene group is also necessary for
the present photochromic system. If the replacement would be
Scheme 2. Photochemical and thermal reactions of 2.
Scheme 3. Synthetic route of 2.

Y. Yokoyama et al.
Bull. Chem. Soc. Jpn., 76, No. 2 (2003) 357
Table 1. Crystallographic Data of 2R
Empirical Formula
Formula Weight
Crystal Color, Habit
Crystal size/mm
Crystal System
Lattice Type
C26H22F6S
480.51
Colorless, prismatic
0.5 × 0.5 × 0.5
Monoclinic
Primitive
11.339(2)
9.760(2)
a/Å
b/Å
Chart 1. Heliochromic benzothienylfulgide.
c/Å
19.868(2)
97.20(1)
2181.4(6)
P21/c (No. 14)
4
1.463
0.203; 0.469
0.141
β/degree
Volume/Å3
Space Group
Z
Density (calculated)/g cm−3
Residuals: R; Rw (all data)
Residuals: R1 (for I > 2.0σ(I))
Goodness-of-fit Indicator
2.21
sorption band in the visible region did not fade when the solu-
tion was kept in the dark at room temperature for a few hours.
Instead, the color disappeared upon visible-light irradiation,
and the increase in the amount of 3O was then detected by
HPLC.
1
The photoreaction was followed by H NMR in toluene-d8.
After the irradiation of 313-nm light for about 100 min, two
doublet peaks (δ 6.15 and δ 6.35, both d, J = ca. 6 Hz) with
the same intensity and one doublet (δ 6.24, d, J = 1.7 Hz) ap-
peared, while most of the signals of the starting material re-
mained. Upon 437-nm light irradiation to the resulting solu-
tion for 70 min, the former set of doublet peaks disappeared,
while the latter doublet remained unchanged. When 313-nm
light was irradiated to the resulting solution for 380 min, the
former set of doublet peaks appeared again, and the latter dou-
blet became larger. The former doublets are attributed to the
cis-oriented olefinic protons on the dihydrothiophene ring, that
Fig. 1. ORTEP drawing of 2R.
effective, the molecular design for this system would be more
flexible.
The synthesis of 3O was carried out as shown in Scheme 4
in 13% yield from 2-methyl-1-phenyl-1-propene.
The irradiation of 313-nm light to the toluene solution of 3O
yielded a small amount of the colored species possessing the
absorption maximum at 417 nm, together with side products,
detected by absorption spectra, HPLC, and 1H NMR. The ab-
Fig. 2. Change in absorption spectra of 2 in toluene. (a) During 313-nm light irradiation to 2R. Irradiation time/min; 0, 1, 3, 5, 7,
8. (b) When the solution of 2R irradiated with 313-nm light for 8 min was kept at 26.2 °C in the dark. Time/min; 0, 20, 60, 150.

358 Bull. Chem. Soc. Jpn., 76, No. 2 (2003)
Novel Thermally Reversible Photochrome
Table 2. Decoloration Rate Constants k at Different Temper-
atures, Activation Energy Ea, and Preexponential Factor A,
of the Reaction from 2Q to 2R in Toluene
Similar structural characteristics for the adamantylidene and
isopropylidene groups were previously reported for thermally
irreversible furylfulgides.7 Because the cyclohexadiene ring
attaching the adamantylidene group as the spiro-connection is
considerably distorted, the steric hindrance over the cyclo-
hexadiene ring became rather small.
Thus, while the thermal hydrogen migration in 2C occurred
smoothly to yield 2R, it hardly occurred in 3C, and the pho-
toirradiation (and less possibly by the application of heat) on
3C may have caused the side reaction(s). A possible reaction
scheme is shown in Scheme 6.
T/K
k/min−1
Ea/kJ mol−1
ln A/min−1
290.05
299.35
309.75
7.99 × 10−3
2.84 × 10−2
7.37 × 10−2
84.0
30.1
can be found in 3C for example, and the latter one is the proton
of an unidentified non-photochromic compound that is pro-
duced irreversibly by 313-nm light irradiation on this system.
From the behavior of 3 on HPLC and 1H NMR during pho-
toirradiation, we concluded that the colored species produced
with a small amount should be 3C, generated by the photo-
chemical 6π-electrocyclization of 3O. Although prolonged ir-
radiation of 313-nm light caused a decomposition of the com-
pound, no sign of the production of hydrogen-rearranged com-
pound 3R was observed. Thus, the isopropylidene group is not
adequate for this system, and the adamantylidene group is nec-
essary as a terminal substituent to obtain a thermally reversible
photochromic compound at this stage. It is clear that the mi-
gration of hydrogen is easier for 2C than 3C.
Conclusion
A new thermally reversible photochromic 6,7-dihydroben-
zothiophene 2R was synthesized. It was prepared from a buta-
diene 2O, equipped with a thienyl group, a perfluorocyclopen-
tene ring, a phenyl group, and an adamantylidene group, by
way of photochemical 6π-electrocyclization followed by a
thermal 1,5-sigmatropic rearrangement. The replacement of
the adamantylidene group with the isopropylidene group af-
forded 3O, which did not yield the hydrogen-migrated ther-
mally reversible photochromic 3R by UV irradiation by way of
3C. The difference in the photochemical and thermal behav-
iors of 2 and 3 was explained in terms of the steric effect.
In order to explain this result, AM1 semiempirical MO cal-
culations were carried out for 2C and 3C. The difference in
the atom distances and the bond angle (Scheme 5) may reflect
the easiness and difficulty for the migration of the hydrogen on
Cα (Hm). The data are given in Table 3. Both bond lengths of
Cα–Cβ and Cβ–Cγ in 2C are longer than those in 3C. As a re-
sult, the angle Cα–Cβ–Cγ in 2C is smaller than that in 3C.
Therefore, the open space above the cyclohexadiene ring
where the hydrogen atom travels along should be larger for 2C
than 3C. In addition, because the atom distance Hm–Cγ in 2C
is considerably smaller than that in 3C, and also the bond
length of Cα–Hm in 2C is slightly longer than 3C, the relevant
hydrogen Hm on 2C can migrate more easily than that on 3C.
Furthermore, although the hydrogen atoms on the methyl
group of the isopropylidene moiety on 3C may disturb the
transfer of the hydrogen on Cα by free rotation of the Cβ–CδH3
bond, whose bond length is shorter than the corresponding
bond (Cβ–CδH) in 2C, the corresponding hydrogen atom on
the adamantylidene group in 2C does not interfere very much,
because of the rigidity of the adamantylidene framework.
Experimental
General. 1H NMR spectra were recorded with a JEOL JNM-
EX-270 (270 MHz) spectrometer in CDCl3. The signals are ex-
pressed as parts per million down field from tetramethylsilane,
used as an internal standard (δ value). Splitting patterns are indi-
cated as s, singlet; d, doublet; t, triplet; m, multiplet. IR spectra
were measured using a Perkin-Elmer 1650 FT-IR spectrometer.
Low- and high-resolution mass spectra were taken with a JEOL
JMS AX-500 mass spectrometer. UV-vis spectra were recorded
on a JASCO Ubest-50 UV-vis spectrophotometer or a JASCO V-
550 UV-vis spectrophotometer. The emission line of 313 nm of a
500 W high-pressure mercury lamp (Ushio Electric) was separat-
ed by filters (5-cm water filter, a UV-D35 glass filter, 5 cm aque-
ous NiSO4•6H2O solution, 1 cm aqueous K2CrO4–NaOH solution,
and 1 cm aqueous potassium hydrogen phthalate solution). The
emission line of 437 nm of a 500 W high-pressure mercury lamp
(Ushio Electric) was separated by filters (5-cm water filter, a Pyr-
ex glass filter, Toshiba glass filters V-40 (two pieces) and Y-43).
The silica-gel column chromatographic separation was carried out
Scheme 4. Synthetic route of 3.

Y. Yokoyama et al.
Bull. Chem. Soc. Jpn., 76, No. 2 (2003) 359
added a 1 mol dm−3 THF solution of benzylmagnesium chloride
(36 mL, 36 mmol), and the mixture was refluxed for 5 h. The re-
action mixture was poured onto an aqueous saturated ammonium
chloride solution at 0 °C. The resulting mixture was extracted
with ethyl acetate three times, and the combined organic layer was
washed with aqueous 10% sodium hydrogencarbonate and satu-
rated brine; the resulting solution was dried with anhydrous sodi-
um sulfate. After the drying agent was filtrated off, the solvent
was removed in vacuo, and the residue was purified by silica-gel
column chromatography to give 4 (6.72 g, 92%). Mp 59–61 °C. IR
(Nujol) ν/cm−1 3502, 3027, 2919, 702. 1H NMR (270 MHz,
CDCl3) δ 1.38 (1H, s), 1.49–2.18 (14H, m), 2.99 (2H, s), 7.22–
7.34 (5H, m).
Scheme 5. Bond lengths and angle which showed difference
between 2C and 3C.
Synthesis of 2-Benzylideneadamantane (5). A mixture of
2-benzyl-2-adamantanol 4 (253 mg, 1.04 mmol) and a catalytic
amount of 4-toluenesulfonic acid in 20 mL benzene was refluxed
for 45 min. To this mixture at r.t. was added aqueous 10% sodium
carbonate, and was extracted with ethyl acetate three times. The
combined organic layer was washed with aqueous saturated brine,
and dried with anhydrous sodium sulfate. The drying agent was
removed, and the solvent evaporated. The residue was purified by
silica-gel column chromatography to give 5 (187 mg, 80%). Mp
30–32 °C. IR (KBr) ν/cm−1 3019, 2906, 1446, 696. 1H NMR
(270 MHz, CDCl3) δ 1.84–1.98 (12H, m), 2.48 (1H, s), 3.15 (1H,
s), 6.18 (1H, s), 7.14–7.30 (5H, m).
Table 3. Selected Bond lengths and Angles of 2C and 3C
Obtained by AM1 Calculations
2C
3C
Cα–Cβ bond length/nm
Cβ–Cγ bond length/nm
Cβ–Cδ bond length/nm
Cα–Hm bond length/nm
Hm–Cγ atm distance/nm
0.1544
0.1542
0.1543
0.1131
0.2548
0.1528
0.1523
0.1525
0.1128
0.2809
Cα–Cβ–Cγ angle/°
102.6
109.0
α
Synthesis of 2-Bromo-2-( -bromobenzyl)adamantane (6).
To a stirred solution of 5 (517 mg, 2.31 mmol) in 20 mL carbon
tetrachloride was added bromine (0.1 mL, 2.3 mmol) at 0 °C, and
stirring was continued for 4 h at 0 °C. To the reaction mixture was
successively added 20% aqueous sodium thiosulfate and aqueous
saturated sodium hydrogencarbonate. The mixture was extracted
with ethyl acetate three times, and the combined organic layer was
washed with saturated brine. After the organic layer was dried
with anhydrous sodium sulfate, the drying agent was removed and
the solvent evaporated in vacuo. The residue was purified by sili-
ca-gel column chromatography to give 6 (2.21 g, 98%). Mp 102–
with a Merck Kieselgel 60 (230–400 mesh) with a mixture of eth-
yl acetate and hexane as an eluent. Analytical thin-layer chroma-
tography was performed on Merck pre-coated silica gel 60 F-254,
0.25-mm thick TLC plates. All of the synthetic reactions were
carried out under a dry nitrogen atmosphere. Tetrahydrofuran
(THF) was freshly distilled from benzophenone ketyl, and diethyl
ether and dichloromethane were distilled from CaH2 immediately
before use.
Synthesis of 2-Benzyl-2-adamantanol (4). To a solution of
2-adamantanone (4.50 g, 30.0 mmol) in 20 mL THF at 0 °C was
Scheme 6. Expected and real photochemical and thermal reactions of 3.

360 Bull. Chem. Soc. Jpn., 76, No. 2 (2003)
Novel Thermally Reversible Photochrome
1
104 °C. IR (KBr) ν/cm−1 3028, 2903, 1447, 713, 656. H NMR
(270 MHz, CDCl3) δ 1.65–2.71 (14H, m), 5.91 (1H, s), 7.28–7.78
(5H, m).
31), 479 ((M − 1)+, 100), 388 (22), 347 (8), 333 (20). Found: m/z
480.1385. Calcd for C26H22F6S: M, 480.1346.
X-ray Crystallographic Analysis of 2R.
A colorless pris-
α
Synthesis of 2-( -Bromobenzylidene)adamantane (7).
A
matic crystal of C26H22F6S having approximate dimensions of
0.50 × 0.50 × 0.50 mm, obtained by recrystallization from hex-
ane, was mounted on a glass fiber. All measurements were made
on a Rigaku AFC-7R diffractometer with graphite monochromat-
ed Mo-Kα radiation (λ = 0.71069 Å) and a rotating anode gener-
ator. The data were collected at a temperature of 23 1 °C using
the ω–2θ scan technique to a maximum 2θ value of 60.0°. The
structure was solved by direct methods7 and expanded using Fou-
rier techniques.8 Non-hydrogen atoms were refined anisotropical-
ly. Hydrogen atoms were included, but not refined. Several cy-
cles of a full-matrix least-squares refinement with anisotropic tem-
perature factors for non-hydrogen atoms led to final R and RW
values of 0.203 and 0.469, respectively (6341 all reflections).
That the R values and the equivalent thermal factor of some of the
fluorine atoms are relatively large may be ascribable to the crystal
nature to some extent. The large thermal ellipsoids of some of the
fluorine atoms (F(3) and F(4)) may be due to the flip-flop motion
of the top CF2 group of the perfluorocyclopentene ring. However,
the structure of the molecule can be discussed unequivocally.
All calculations were performed using the TEXSAN9 crystallo-
graphic software package of Molecular Structure Corporation.
Crystallographic data are summarized in Table 1.
solution of 6 (4.94 g, 12.2 mmol) in pyridine (15 mL) was stirred
at 60 °C for 12 h. After the solvent was removed in vacuo, ethyl
acetate was added to the residue, and the organic layer was
washed with dil. hydrochloric acid, aqueous 10% sodium hydro-
gencarbonate, and saturated brine successively, and dried with an-
hydrous sodium sulfate. The drying agent was removed, and the
solvent removed in vacuo. The residue was purified by silica-gel
column chromatography to give 7 (2.35 g, 60%). Mp 74–76 °C. IR
(KBr) ν/cm−1 3022, 2923, 1446, 735, 693. H NMR (270 MHz,
CDCl3) δ 1.73–1.96 (12H, m), 2.70 (1H, s), 3.30 (1H, s), 7.25–
7.35 (5H, m).
1
Synthesis of 1-(1-Adamantylidene-1-phenylmethyl)-2,3,3,4,-
4,5,5-heptafluorocyclopentene (8). To a solution of 7 (465 mg,
1.54 mmol) in 30 mL of THF at −78 °C was added a hexane solu-
tion of butyllithium (1.50 mol dm−3, 1.2 mL, 1.84 mmol); the so-
lution was stirred for 30 min. To it was added at that temperature
octafluorocyclopentene (0.6 mL, 4.60 mmol), and the resulting
mixture was stirred for 15 h. To it was added water, and the mix-
ture was extracted with ethyl acetate three times. The organic lay-
er was washed with saturated brine, and dried with anhydrous so-
dium sulfate. After the drying agent was removed, the solvent was
removed in vacuo. The residue was purified by silica-gel column
chromatography to give 8 (513 mg, 92%). Mp 85–87 °C. IR (KBr)
ν/cm−1 3022, 2923, 1446, 1381, 698. 1H NMR (270 MHz, CDCl3)
δ 1.57–2.00 (12H, m), 2.50 (1H, s), 2.73 (1H, s), 7.13–7.35 (5H,
m). MS (EI, 70 eV) m/z 416 (M+, 100), 392 (16), 380 (28), 343
(21), 331 (33). Found: m/z 416.1352. Calcd for C22H19F7: M,
416.1375.
Synthesis of 1-(1-Adamantylidene-1-phenylmethyl)-3,3,4,4,-
5,5-hexafluoro-2-(3-thienyl)cyclopentene (2O). To a solution
of 3-bromothiophene (230 mg, 1.40 mmol) in 30 mL THF at
−78 °C was added a hexane solution of butyllithium (1.59 mol
dm−3, 0.86 mL, 1.37 mmol). This mixture was added dropwise to
a THF (10 mL) solution of 8 (568 mg, 1.37 mmol) at − 78 °C, and
the resulting mixture was kept stirring for 18 h. After the reaction
was quenched with water, the mixture was extracted with ethyl ac-
etate three times. The organic layer was washed with saturated
brine, and dried with anhydrous sodium sulfate. After the drying
agent was removed, the solvent was removed in vacuo. The resi-
due was purified by silica-gel column chromatography to give 2O
(134 mg, 20%). Mp 103–105 °C. IR (KBr) ν/cm−1 3027, 2917,
1340, 1274, 699. 1H NMR (270 MHz, CDCl3) δ 1.25–2.20 (12H,
m), 2.51 (1H, s), 3.06 (1H, s), 7.24–7.40 (6H, m), 7.69 (1H, d, J =
5.28 Hz), 8.00 (1H, s). MS (EI, 70 eV) m/z 480 (M+, 31), 479 ((M
− 1)+, 100). Found: m/z 480.1292. Calcd for C26H22F6S: M,
480.1346.
Crystallographic data have been deposited at the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK and copies can be ob-
tained on request, free of charge, by quoting the publication cita-
tion and the deposition number CCDC 195759.
Synthesis of 1,2-Dibromo-2-methyl-1-phenylpropane (10).
To a stirred solution of 2-methyl-1-phenyl-1-propene (5.03 g,
38.0 mmol) in 80 mL carbon tetrachloride was added bromine
(2.33 mL, 7.26 g, 45.4 mmol) at 0 °C, and stirring was continued
for 4 h at 0 °C. To the reaction mixture was added 10% aqueous
sodium thiosulfate and aqueous saturated sodium hydrogencar-
bonate successively. The mixture was extracted with dichlo-
romethane three times, and the combined organic layer was
washed with saturated brine. After the organic layer was dried
with anhydrous sodium sulfate, the drying agent was removed and
the solvent evaporated in vacuo. The residue was purified by sili-
ca-gel column chromatography to give 10 (10.9 g, 99%) as a yel-
low liquid. IR (neat) ν/cm−1 3087, 3062, 3030, 2974, 2930, 2864,
1495, 1451, 1386, 1369, 1200, 1098, 743, 699, 614, 567. 1H NMR
(270 MHz, CDCl3) δ 1.91 (3H, s), 2.01 (3H, s), 5.26 (1H, s), 7.25–
7.4 (3H, m), 7.45–7.55 (2H, m). MS (EI, 70 eV) m/z (rel intensity)
293 ((M + 4 − H)+, 48), 291 ((M + 2 − H)+, 100), 289 ((M −
H)+, 52).
Synthesis of 1-Bromo-2-methyl-1-phenyl-1-propene (11).
To a solution of 10 (10.01 g, 34.27 mmol) in methanol (50 mL)
was added a suspension of sodium hydride (60% in mineral oil,
1.54 g, 38.5 mmol, 1.12 equiv) in 60 mL methanol via cannular at
r.t., and the resulting mixture was stirred overnight. After adding
water, the mixture was extracted with ethyl acetate three times.
The organic layer was washed with saturated brine, and dried with
anhydrous sodium sulfate. The drying agent was removed, and
the solvent removed in vacuo. The residue was purified by silica-
gel column chromatography to give 11 (6.52 g, 90%) as a color-
less liquid. IR (neat) ν/cm−1 3055, 2992, 2913, 1487, 1441, 1066,
877, 850, 754, 696, 647. 1H NMR (270 MHz, CDCl3) δ 1.72, 2.04
(each 3H, s), 7.2–7.4 (5H, m). MS (EI, 70 eV) m/z 212 ((M + 2)+,
37), 210 (M+, 30), 131 ((M − Br)+, 100).
Synthesis of 4ꢀ,5ꢀ-Hexafluoropropano-6ꢀ-phenylspiro[ada-
mantane-2,7ꢀ(6ꢀH)-benzo[b]thiophene] (2R). A toluene solu-
tion of 2O (ca. 8 mg in 80 mL) was irradiated with 313-nm light
for 5 h. The resulting mixture was kept in the dark for 12 h, and
the solvent removed in vacuo. This procedure was repeated eight
times, and the combined residue was purified by silica-gel column
chromatography to give 2R (36 mg, 57%). Mp 184–185 °C. IR
(KBr) ν/cm−1 3027, 2912, 1453, 1259, 700. 1H NMR (270 MHz,
CDCl3) δ 1.25–2.84 (14H, m), 4.57 (1H, d, J = 8.91 Hz), 6.71
(1H, d, J = 7.59 Hz), 6.79 (1H, d, J = 7.59 Hz), 7.10–7.27 (3H,
m), 7.39–7.42 (1H, br), 7.69 (1H, s). MS (EI, 70 eV) m/z 480 (M+,

Y. Yokoyama et al.
Bull. Chem. Soc. Jpn., 76, No. 2 (2003) 361
Synthesis of 2,3,3,4,4,5,5-Heptafluoro-1-(2-methyl-1-phenyl-
1-propenyl)cyclopentene (12). To a solution of 11 (1.99 g,
9.47 mmol) in 80 mL THF at −78 °C was added a hexane solution
of butyllithium (1.56 mol dm−3, 7.28 mL, 11.36 mmol); the solu-
tion was stirred for 30 min. To it was added octafluorocyclopen-
tene (3.8 mL, 6.0 g, 28.41 mmol) at that temperature, and the re-
sulting mixture was stirred overnight. To it was added water, and
the mixture was extracted with ethyl acetate three times. The or-
ganic layer was washed with saturated brine, and dried with anhy-
drous sodium sulfate. After the drying agent was removed, the
solvent was removed in vacuo. The residue was purified by silica-
gel column chromatography to give 12 (2.27 g, 74%) as a color-
less liquid. IR (KBr) ν/cm−1 3059, 3024, 2991, 2925, 1697, 1380,
1320, 1280, 1200, 1156, 1132, 989, 975, 744, 699, 565. 1H NMR
(270 MHz, CDCl3) δ 1.78, 1.85 (each 3H, s), 7.13 (2H, d, J =
6.27 Hz), 7.3–7.5 (3H, m). MS (EI, 70 eV) m/z 324 (M+, 100),
309 ((M − 15)+, 85). Found: m/z 324.0758. Calcd for C15H11F7:
M, 324.0749.
mol dm−3 for 3O) was irradiated with 313-nm light, and the UV-
vis spectra were recorded at designated time intervals.
Thermal Decoloration of 2R. A toluene solution of a mix-
ture of 2R and 2O obtained by the 313-nm-light irradiation was
kept at the designated temperature in the cell holder of a UV-vis
spectrometer equipped with a temperature controller, and the de-
crease in the absorption in the visible region was monitored.
Since only 2O has absorption in the visible region, the decolora-
tion rate constant was calculated from the decrease in the absorp-
tion in the visible region.
The authors thank Dr. Yoshitaka Yamaguchi, our Depart-
ment, Yokohama National University, for X-ray crystallo-
graphic analysis of 2R, and Shorai Foundation for Science and
Technology for financial support.
References
Synthesis of 3,3,4,4,5,5-Hexafluoro-1-(2-methyl-1-phenyl-1-
propenyl)-2-(3-thienyl)cyclopentene (3O). To a solution of 3-
bromothiophene (460 mg, 2.85 mmol) in 1 mL THF at −78 °C
was added a hexane solution of butyllithium (1.55 mol dm−3, 1.8
mL, 2.79 mmol) and the mixture was stirred for 3 h. This mixture
was added dropwise to a THF (1 mL) solution of 12 (300 mg,
0.93 mmol) at −78 °C, and the resulting mixture was kept stirring
for 20 h. After the reaction was quenched with water, the mixture
was extracted with ethyl acetate three times. The organic layer
was washed with saturated brine, and dried with anhydrous sodi-
um sulfate. After the drying agent was removed, the solvent was
removed in vacuo. The residue was purified by silica-gel column
chromatography to give 3O (72 mg, 20%) as a colorless liquid. IR
(neat) ν/cm−1 2992, 2914, 2859, 1492 , 1442, 1374, 1341, 1275,
1
2
Y. Yokoyama, Chem. Rev., 100, 1717 (2000).
J. Whittall, “4n + 2 Systems: Fulgides,” in “Photo-
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3
Y. Yokoyama, H. Nakata, K. Sugama, and Y. Yokoyama,
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4
5
6
7
See the following article.
M. Irie, Chem. Rev., 100, 1685 (2000).
K. Sugama and Y. Yokoyama, unpublished result.
Y. Yokoyama, T. Inoue, M. Yokoyama, T. Goto, T. Iwai, N.
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8
A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, and R.
Spagna, J. Appl. Crystallogr. 32, 115 (1999).
1
1257, 1214, 1192, 1128, 1080, 1036, 1020, 975, 700. H NMR
(270 MHz, CDCl3) δ 1.70 (3H, s), 1.89 (3H, s), 7.1–7.2 (2H, m),
7.2–7.35 (3H, m), 7.40 (1H, dd, J = 2.97, 4.95 Hz), 7.54 (1H, d, J
= 4.6 Hz), 7.94 (1H, br. s). MS (EI, 70 eV) m/z 388 (M+, 49), 387
((M − H)+, 98), 373 ((M − CH3)+, 71), 372 ((M − H − CH3)+,
100). Found: m/z 388.0707. Calcd for C19H14F6S: M, 388.0720.
9
P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman,
R. de Gelder, R. Israel, and J. M. M. Smits, “The DIRDIF-94 pro-
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10 “Crystal Structure Analysis Package,” Molecular Structure
Corporation (1985 & 1999).
Photoreaction of 2 and 3 by 313-nm Light Irradiation.
A
toluene solution (1.02 × 10−4 mol dm−3 for 2O and 1.38 × 10−4