Trifluoromethyl-substituted donor-acceptor norbornadiene, useful solar energy material

Article abstract of DOI:10.1246/bcsj.74.1673

Trifluoromethyl (CF₃)-substituted donor-acceptor norbornadiene (NBD) derivatives were synthesized. The photo-isomerization of CF₃-NBD derivatives proceeded smoothly. The thermal stability of quadricyclane (QC) derivatives obtained from CF₃-NBD derivatives was examined, and it was found that the CF₃ group increased the thermal stability of the QC derivatives. Furthermore, CF₃-NBD derivatives exhibited efficient fatigue resistance.

Full text of DOI:10.1246/bcsj.74.1673

c. Jpn.
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1673–1678 (2001) 1673
e Chemical
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Trifluoromethyl-Substituted Donor–Acceptor Norbornadiene, Useful
Solar Energy Material
Trifluoromethyl-Substituted Norbornadiene
T. Nagai et al.
Takabumi Nagai,* Kazuhisa Fujii, Ikuko Takahashi, and Miwa Shimada
01
73
78
SJA8
09-2673
045
Daikin Environmental Laboratory, Ltd., 3 banchi, Miyukigaoka, Tsukuba, Ibaraki 305-0841
(Received Feburuary 9, 2001)
Trifluoromethyl (CF3)-substituted donor–acceptor norbornadiene (NBD) derivatives were synthesized. The photo-
isomerization of CF3-NBD derivatives proceeded smoothly. The thermal stability of quadricyclane (QC) derivatives ob-
tained from CF3-NBD derivatives was examined, and it was found that the CF3 group increased the thermal stability of
the QC derivatives. Furthermore, CF3-NBD derivatives exhibited efficient fatigue resistance.
01
01
Photochemical valence isomerization between norborna-
diene (NBD) and quadricyclane (QC) is of interest as a solar
energy conversion and storage system,1 because photoenergy
can be stored as strain energy (about 20 kcal/mol) in a QC
molecule (Scheme 1). Recently, this photochemical reaction
has also been investigated as an optical waveguide utilizing
photoinduced refractive index changes2a–d or as a photochro-
mic system potentially applicable to data storage.2e
Scheme 1.
Results and Discussion
However, the photochemical reaction of NBD does not ordi-
narily occur upon irradiation with sunlight, because NBD does
not efficiently absorb visible light. To solve this problem,
there are two different methods used. One is the use of photo-
sensitizers such as benzophenone derivatives in the NBD reac-
tion system.3 However, the wavelength which can be utilized
is limited to the shorter region in visible light,3a,b and decom-
position of the photosensitizer frequently results from by pro-
longed irradiation.3f The other is the introduction of suitable
chromophores into the NBD molecule to extend the absorption
to longer wavelength. To this end, many NBD derivatives have
been synthesized.4 Maruyama et al. and Mukai et al. reported
the synthesis of the NBDs which have several chromophores
on one of the two double bonds of the NBD molecule, but the
quantum yield of the photoisomerization was relatively low.4a–d
On the other hand, Yoshida et al. and Yonemitsu et al. have
found that donor–acceptor (D–A) NBDs have C-T absorption
in a visible region and photoisomerize to give QCs in high
quantum yield.4f–j However, these NBDs do not absorb visible
light efficiently (low ε ~ 1000) and the QCs that are obtained
from NBDs whose absorption edge reaches above 500 nm are
not stable enough, namely, they revert to the starting NBDs
rapidly at room temperature.4g
Synthesis of D–A NBDs Containing CF3 Group.
CF3-
NBDs (1) were synthesized according to the reaction sequenc-
es shown in Schemes 2 and 3.6 As shown in Scheme 2, cyclo-
pentadiene derivatives (3b–f) were synthesized from 4.7 2-Hy-
droxy ketone (5-1) was obtained from the reaction of 4 with 4-
(dimethylamino)phenyl lithium reagent (8) in 68.6% yield,
then a second 4-dimethylaminophenyl group was introduced in
23% yield to give diol 6. It seems that the relatively lower
yield of 6 than that of 5-1 may be due to the steric effect of the
substituent. Then, 6 was dehydrated by p-TsOH in toluene to
give 3b in 86% yield. 3c–e were obtained in a similar way
from 7-1, which was obtained from dehydration of 5-1 in
89.7% yield, with a suitable phenyllithium reagent in 22.3,
59.4, and 74.0% yield, respectively. Similarly, addition of 2-
lithiobenzofuran (9) to 4 gave 5-2 in 85.8% yield, followed by
dehydration to give 7-2 in 77.4% yield, and finally, reaction
with 9 to give 3f in 79.9% yield. 3a was prepared according to
the literature.8 As shown in Scheme 3 and Table 1, 1 was syn-
thesized in good yields by the Diels–Alder reaction of hexaflu-
oro-2-butyne (2) with 3. This NBD synthesis strategy involves
the facile introduction of a variety of substituents into the 2,3
positions, the C-T donor site, of the NBD framework.
It is known that a perfluoroalkyl group often serves to pro-
duce a stable valence isomer of aromatic compounds.5 As in
the case of NBDs, introduction of a CF3 group would be ex-
pected to give the corresponding QCs with increased stability.
Therefore, we synthesized new NBDs (1) containing a CF3
group on the C-T acceptor site and examined the photoisomer-
ization of these NBDs. We also examined the thermal stability
of QCs obtained from CF3-NBDs. Furthermore, we examined
the durability of CF3-NBDs.
Photochemical Property and Photoisomerization of CF3-
NBDs. Absorption spectra of the NBDs in the UV-visible re-
gion are shown in Fig. 1. Thus, CF3-NBDs have a quite large
absorption coefficient (ε value) in the visible region as com-
pared with those of NBDs having other groups such as
COOMe (10) or CN (11).9 The absorption maxima of NBDs
tend to red shift (1a < c < d < b < e < f) with the electron-
donating ability of the donor group. Especially, 1f having 2-
benzofuryl as a donor group, has logε 4.30 at 414 nm and the

1674 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Trifluoromethyl-Substituted Norbornadiene
Table 1.
λ
max/nma)
Yield/%
λ
AE/nma)
1
R1
R2
(log ε)
from 3
a
b
c
d
e
f
p-MeOC6H4
p-Me2NC6H4
p-Me2NC6H4
p-Me2NC6H4
p-Me2NC6H4
2-Benzofuryl
p-MeOC6H4
p-Me2NC6H4
p-MeOC6H4
2-Thiophenyl
2-Benzofuryl
2-Benzofuryl
346 (3.71)
390 (3.93)
374 (3.93)
385 (3.89)
407 (4.11)
414 (4.30)
440
510
500
520
580
480
91
100
80.1
88.2
97.3
87
a) 1 × 10−4 mol dm−3 solution in acetonitrile.
Scheme 2.
Scheme 3.
absorption cut-off of 1e reaches 580 nm (Table 1 and Fig. 1).
The photoisomerization of the CF3-NBDs in CH3CN solu-
tion (1×10−4 mol/L) was carried out by the irradiation of a
500-W xenon lamp. Changes in the UV spectra of 1a are
shown in Fig. 2. The maximum absorption of the NBDs de-
creased and the NBDs isomerized to the corresponding QCs
after 10 min by irradiation. In addition, two isosbestic points
at 219 and 240 nm were observed. This result means that the
photoisomerization of the CF3-NBD to the corresponding QCs
occurred selectively without any side reactions. As shown in
Fig. 3, the photoisomerization rate of CF3-NBDs was higher
Fig. 1. Absorption spectra of NBD derivatives(1 × 10−4 mol
dm−3 solution in acetonitrile).

T. Nagai et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1675
Table 2. Thermal Stability of QC Derivatives at Room Tem-
perature (20 °C) in the Dark
No. of NBDs
T1/2 of QCs
k/min−1
Temp/°C
109
119
1a
1b
1c
1d
1e
1f
6.5 h
1.45 × 10−2
14.7 × 10−2
5.38 × 10−2
6.44 × 10−2
20.3 × 10−2
0.325 × 10−4
3.78 × 10−4
1.27 × 10−4
35
25
130
70
130
20
11 min
stable
1.1 year
stable
500 h
31 h
20
20
72 h
Table 3. Stored Thermal Energy in the CF3-QC Derivatives
No. of NBDs
1a
1c
1e
1f
Stored thermal
80
78
76
63
energy/kJ mol−1
obeyed the first-order kinetics. The rate constants are shown in
Table 2.
Fig. 2. Change in UV spectra of 1a upon irradiation with a
xenon lamp(1 × 10−4 mol dm−3 solution in acetonitrile).
It was reported that the QC groups contained in polymer
chains were more stable than monomer QC, and that the rigid-
ity of the polymer chains was intimately reflected in the stabil-
ity of the QC.10 Furthermore, it was reported that the CF3
group was rigid and spherical, and showed as large a steric ef-
fect as an s-butyl group.11 On the other hand, it was reported
that QCs containing a CF3 group and a ketone group on the C-
T acceptor site were rather unstable.5c Therefore, it seems that
both CF3 groups introduced into the acceptor olefin parts are
necessary and the large steric effect of these CF3 groups con-
tributes to the stability of QC as the rigidity of the polymer
chain.
Measurement of Stored Thermal Energy in the CF3-
QCs. The stored thermal energy in the CF3-QCs obtained
from 1a, c, e, and f was measured on DSC. The irradiated 1a,
c, e, and f released 80, 78, 76, and 63 kJ/mol of thermal energy,
respectively (Table 3). The value of stored thermal energy in
these QCs was lower than that reported (about 84 kJ/mol) for
other QCs. It is possible that the stored thermal energy in the
QCs obtained from the NBDs, which absorb longer wave-
length light, was lower than that from other NBDs.
Fig. 3. Rates of photoisomerization of NBDs in solution:
(ꢀ)1a; (ꢁ)1f; (ꢂ)109.
Examination of Durability of the CF3-NBDs.
We also
than that of the other D–A NBD (10)9 bearing ester groups on
the C-T acceptor site. It seems that the higher photoisomeriza-
tion rate of CF3-NBDs is attributable to its large absorption in
the visible region.
The quantum yields of 1a and 1f of photoisomerization
from NBDs to QCs in CH3CN solution (1 × 10−4 mol/L) were
evaluated with a chemical actinometer. The quantum yield at
354 nm of 1a and at 400 nm of 1f were 0.7 and 0.6, respective-
ly. These results suggest that CF3-NBDs have high photo-
chemical reactivity.
Thermal Stability of the QCs. Next, we examined the
thermal stability of QCs at room temperature (20 °C) in a
PMMA solid film (Table 2). As shown in Table 2, the CF3
group increased the thermal stability of QCs. In particular, 1b,
d, e, and f not only have larger absorption in the visible region
but also produce far more stable QCs than 109 and 11.9 The
thermal reversion rate of the QCs to the corresponding NBDs
examined the ability of the CF3-NBDs to turn over the cycles
of photochemical valence isomerization (NBDs → QCs) and
thermal reversion isomerization (QCs → NBDs). Few studies
concerning the reversibility of NBD compounds have been re-
ported so far.4g, 12 Fatigue resistance of NBDs 1a, b, c, and f in
PMMA solid film is shown in Fig. 4. While 1b and c having a
p-(dimethylamino)phenyl group showed low fatigue resis-
tance, 1a and f having p-methoxyphenyl groups and 2-benzo-
furyl groups, respectively, showed excellent fatigue resistance.
After 103 times of the cycle, the loss in extinction was 30% and
3% for 1a and f, respectively. These results possibly indicate
that the dimethylaminophenyl group seems to be more labile
for photo or thermal degradation than the methoxylphenyl and
benzofuryl groups.
Conclusion
From all these results, the following conclusions can be ob-

1676 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Trifluoromethyl-Substituted Norbornadiene
H), 1.32 (s, 3 H), 2.91 (s, 12H), 3.77 (s, 2 H), 6.34 (d, J = 9.0 Hz,
4 H), 7.13 (d, J = 9.0 Hz, 4 H); 19F NMR (CDCl3) δ −60.21 (bs);
IR (KBr) 1610, 1524, 1345, 1299, 1175, 1133 cm−1. Found: C,
65.53; H, 5.67%. Calcd for C27H28F6N2: C,65.58; H, 5.71%.
Synthesis of 1c. The Diels–Alder reaction of 2 with 3c was
carried out in the same way as above to give 1c in 80.1% yield as
yellow needles, mp 110–111 °C. 1H NMR (CDCl3) δ 1.17 (s, 3
H), 1.27 (s, 3 H), 2.87 (s, 6 H), 3.59 (d, J = 3.5 Hz, 1 H), 3.63 (d,
J = 3.5 Hz, 1 H), 3.71 (s, 3 H), 6.54 (d, J = 8.9 Hz, 2 H), 6.73 (d,
J = 8.9 Hz, 2 H), 7.08 (d, J = 8.9 Hz, 2 H), 7.22 (d, J = 8.9 Hz, 2
H); 19F NMR (CDCl3) δ −61.26 (q, J = 9.0 Hz, 3F), −61.50 (q, J
= 9.0 Hz, 3F); IR (KBr) 1609, 1522, 1508, 1298, 1175, 1139 cm−1
.
Found: C, 64.82; H, 5.20; N, 2.91%. Calcd for C26H25F6NO: C,
64.86; H, 5.28; N, 2.91%.
Synthesis of 1d. The Diels–Alder reaction of 2 with 3d was
carried out in the same way as above to give 1d in 88.2% yield as
yellow needles, mp 56–57 °C. 1H NMR (CDCl3) δ 1.25 (s, 3 H),
1.33 (s, 3 H), 2.98 (s, 6 H), 3.66 (d, J = 3.6 Hz, 1 H), 3.71 (d, J =
3.6 Hz, 1 H), 6.72 (d, J = 8.9 Hz, 2 H), 6.95 (dd, J = 5.1, 3.7 Hz,
1 H), 7.04 (dd, J = 3.7, 1.2 Hz, 1 H), 7.15 (dd, J = 5.1, 1.2 Hz, 1
H), 7.27 (d, J = 8.7 Hz, 2 H); 19F NMR (CDCl3) δ −61.25 (q, J =
6.6 Hz, 3F), −61.34 (q, J = 6.6 Hz, 3F); IR (KBr) 1610, 1525,
Fig. 4. Durability of CF3-NBD derivatives: (ꢀ)1a; (ꢂ)1b;
(ꢃ)1c; (ꢁ)1f.
tained. 1) CF3-substituted donor–acceptor NBD derivatives
were synthesized. 2) This NBD synthesis strategy involves the
facile introduction of a variety of substituents into the 2,3 posi-
tions, the C-T donor site, of the NBD framework. 3) The pho-
toisomerization of CF3-NBD derivatives proceeded smoothly.
4) The CF3 group increased the thermal stability of QC deriva-
tives. 5) CF3-NBD derivatives exhibited efficient fatigue resis-
tance.
1346, 1298, 1175, 1132 cm−1
. Found: C, 60.38; H, 4.60; N,
3.06%. Calcd for C23H21F6NS: C, 60.38; H, 4.63; N, 3.06%.
Synthesis of 1e. The Diels–Alder reaction of 2 with 3e was
carried out in the same way as above to give 1e in 97.3% yield as
orange viscous oil. 1H NMR (CDCl3) δ 1.28 (s, 3 H), 1.31 (s, 3
H), 3.03 (s, 6 H), 3.78 (d, J = 3.6 Hz, 1 H), 3.95 (d, J = 3.6 Hz, 1
H), 6.70–6.80 (m, 3 H), 7.10–7.43 (m, 3 H), 7.45–7.60 (m, 3 H);
19F NMR (CDCl3) δ −61.00 (q, J = 9.4 Hz, 3F), −61.48 (q, J =
Experimental
9.4 Hz, 3F); IR (KBr) 1676, 1609, 1345, 1297, 1176, 1136 cm−1
;
Apparatus. Melting points were determined with a Yanaco
MP-500D hot stage microscope and not corrected. Infrared spec-
tra were obtained on a Perkin Elmer 1600 FT-IR either neat or in
KBr pellets. Absorption was expressed as reciprocal centimeters
(cm−1). 1H NMR were recorded at 200 MHz on a Varian Gemini-
200 instrument and indicated in parts per million (ppm) downfield
from tetramethylsilane as the internal standard (δ). 19F NMR
spectra were measured at 188 MHz on a Varian Gemini-200 in-
strument and indicated in parts per million (ppm) upfield from
CCl3F as the internal standard. Low- and high-resolution mass
spectral analyses were performed under 70 eV electron-impact
(EI) conditions on a Kratos CONCEPT-1H double-focusing mag-
netic sector spectrometer. Elemental analyses were made at Toray
Research Center, Inc., Tokyo.
MS m/z 491 (M+; 100), 476 (M+−Me; 36), 461 (8), 448 (11), 422
(6), 385 (11), 261 (37). HRMS Found: m/z 491.16766. Calcd for
C27H23F6NO: M, 491.16838.
Synthesis of 1f. The Diels–Alder reaction of 2 with 3f was
carried out in the same way as above to give 1f in 87% yield as
yellow needles, mp 105–106 °C. 1H NMR (CDCl3) δ 1.29 (s, 3
H), 1.34 (s, 3 H), 4.16 (s, 2H), 7.22–7.40 (m, 6 H), 7.55 (d, J =
8.2 Hz, 2 H), 7.61–7.68 (m, 2 H); 19F NMR (CDCl3) δ −61.57 (s);
IR (KBr) 1681, 1451, 1352, 1297, 1172, 1133, 749 cm−1. Found:
C, 66.55; H, 3.75%. Calcd for C27H18F6O2: C, 66.40; H, 3.71%.
Synthesis of 2-Hydroxy-4,4-dimethyl-2-[4-(dimethylami-
no)phenyl]-cylopentan-1-one (5-1). A solution of 4 (5.0 g, 40
mmol) in ether (150 mL) was added dropwise at 0 °C to an ether
solution (350 mL) of lithium reagent (8) obtained from 4-bromo-
N,N-dimethylaniline (22.8 g, 114 mmol) with n-BuLi (1.59 M, 75
mL, 120 mmol). The mixture was stirred for 18 h at room temper-
ature, then poured into ice-water, and extracted with ether. The
ether layer was washed with brine, and dried over anhydrous
MgSO4. After evaporation of the solvent, the product was separat-
ed by column chromatography (SiO2, hexane–EtOAc, 5:1) to give
5-1 (6.79 g, 68.6%) as colorless viscous oil. 1H NMR (CDCl3) δ
1.10 (s, 3 H), 1.20 (s, 3 H), 2.23 (d, J = 13.8 Hz, 1H), 2.35 (d, J =
15.8 Hz, 1H), 2.38 (d, J = 13.8 Hz, 1H), 2.45 (d, J = 15.8 Hz,
1H), 2.70 (s, 1 H), 2.93 (s, 6 H), 6.70 (d, J = 9.1 Hz, 2 H), 7.22 (d,
J = 9.1 Hz, 2 H); IR (KBr) 3448, 2950, 1741, 1618, 1528, 1365
cm−1 ; MS m/z 247 (M+; 17), 229 (M+−H2O; 81), 214 (M+−
H2O−Me; 83), 186 (71), 163 (100), 148 (36). HRMS Found: m/z
247.15777. Calcd for C15H21NO2: M, 247.15723.
Synthesis of CF3-NBD Derivatives. Synthesis of 1a.
3a
(306 mg, 1 mmol), which was prepared according to the litera-
ture,8 was placed in a stainless steel tube with toluene (5 mL). To
this tube, 2 (0.2 mL) was introduced by a vacuum line. The mix-
ture was stirred at 100 °C for 6 h in the tube. After the tube was
cooled in an ice bath, it was opened and the mixture was extracted
with ether. After evaporation of the solvent, the product was sepa-
rated by column chromatography (SiO2, hexane–EtOAc, 30:1) to
give 1a (427 mg, 91%), as slightly yellow needles, mp 80–81 °C.
1H NMR (CDCl3) δ 1.26 (s, 3 H), 1.36 (s, 3 H), 3.69 (s, 2 H), 3.80
(s, 6 H), 6.81 (d, J = 9.0 Hz, 4 H), 7.18 (d, J = 9.0 Hz, 4 H); 19
NMR (CDCl3) δ −61.46 (bs); IR (KBr) 1607, 1514, 1302, 1253,
1180, 1138, 1036 cm−1. Found: C, 64.17; H, 4.73%. Calcd for
C25H22F6O2: C,64.10; H, 4.73%.
F
Synthesis of 1b. The Diels–Alder reaction of 2 with 3b was
carried out in the same way as above to give 1b in 100% yield as
yellow needles, mp 126–127 °C. 1H NMR (CDCl3) δ 1.22 (s, 3
Synthesis of 4,4-Dimethyl-1,2-bis[4-(dimethylamino)phen-
yl]cyclopentane-1,2-diol (6). A solution of 5-1 (822 mg, 3.3
mmol) in THF (10 mL) was added dropwise at 0 °C to a solution

T. Nagai et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1677
of 8 (10 mmol) in THF (30 mL). The mixture was stirred for 15 h.
After normal workup, the product was separated by column chro-
matography (SiO2, hexane–EtOAc, 4:1) to give 5-1 (309 mg,
38%) and 6 (283 mg, 23%) as colorless needles, mp 175–176 °C.
1H NMR (CDCl3) δ 1.35 (s, 6 H), 1.74 (s, 2 H), 1.89 (d, J = 13.9
Hz, 2H), 2.76 (d, J = 13.9 Hz, 2H), 2.93 (s, 12H), 6.63 (d, J = 9.0
Hz, 4 H), 7.08 (d, J = 9.0 Hz, 4 H); IR (KBr) 3535, 3285, 2947,
2864, 1610, 1516, 1475, 1440, 1336, 1199, 1142, 1055, 967, 936,
5.1, 3.6 Hz, 1 H), 7.12 (dd, J = 5.1, 1.1 Hz, 1 H), 7.15 (d, J = 8.6
Hz, 2 H); IR (KBr) 2928, 2810, 1620, 1525, 1445, 1364, 1228,
1197, 814 cm−1; MS m/z 295 (M+; 100), 280 (M+−Me; 60), 266
(8), 250 (4), 235 (10), 221 (12). HRMS Found: m/z 295.13981.
Calcd for C19H21NS: M, 295.13947.
Synthesis of 3e. A solution of 7-1 (229 mg, 1.0 mmol) in
THF (3 mL) was added dropwise at −78 °C to a solution of 2-
lithiobenzofuran (9, 2 mmol) in ether (2 mL) and stirred for 15
min at this temperature. The mixture was poured into ice-water
and extracted with EtOAc. The organic layer was washed with
brine, dried over anhydrous MgSO4, and concentrated in vacuo. A
mixture of the crude product and p-TsOH (190 mg, 1 mmol) in
toluene (10 mL) was refluxed for 15 min. After normal workup,
the product was separated by column chromatography (SiO2, hex-
ane–EtOAc, 20:1) to give 3e (243.3 mg, 74.0%) as slightly yellow
viscous oil (sensitive to air). 1H NMR (CDCl3) δ 1.33 (s, 6 H),
2.99 (s, 6 H), 6.16 (d, J = 2.6 Hz, 1 H), 6.19 (s, 1H), 6.74 (d, J =
8.9 Hz, 2 H), 6.85 (d, J = 2.6 Hz, 1 H), 6.89 (dd, J = 5.1, 3.6 Hz,
1 H), 7.04–7.32 (m, 2 H), 7.26 (d, J = 8.9 Hz, 2 H), 7.37–7.48 (m,
2 H); IR (KBr) 2960, 2859, 1612, 1512, 1450, 1352, 1256, 1163,
814 cm−1; MS m/z 329 (M+; 100), 314 (M+−Me; 45), 300 (6),
284 (3), 255 (9). HRMS Found: m/z 329.17769. Calcd for
C23H23NO: M, 329.17796.
819 cm−1
.
Found: C, 74.87; H, 8.79; N, 7.61%. Calcd for
C23H32N2O2: C, 74.96; H, 8.77; N, 7.60%.
Synthesis of 3b. A solution of 6 (282 mg, 0.76 mmol) and p-
TsOH•H2O (260 mg, 1.37 mmol) in toluene (10 mL) was refluxed
for 30 min. The mixture was poured into 10% NaOH solution and
extracted with ether. The ether layer was washed with brine, and
dried over anhydrous MgSO4. After evaporation of the solvent,
the product was separated by column chromatography (SiO2, hex-
ane–EtOAc, 10:1) to give 3b (156 mg, 86%) as slightly yellow
needles (sensitive to air). 1H NMR (CDCl3) δ 1.28 (s, 6 H), 2.93
(s, 12H), 6.19 (s, 2 H), 6.65 (d, J = 8.9 Hz, 4 H), 7.08 (d, J = 8.9
Hz, 4 H); IR (KBr) 2950, 2858, 1617, 1516, 1352, 1225, 1195,
814 cm−1; MS m/z 332 (M+; 20), 317 (M+−Me; 9), 295 (4), 281
(14), 264 (4). HRMS Found: m/z 332.22434. Calcd for
C23H28F6N2:M, 332.22525.
Synthesis of 4,4-Dimethyl-2-[4-(dimethylamino)phenyl]-2-
cyclopenten-1-one (7-1). A solution of 5-1 (1.31 g, 5.3 mmol)
and p-TsOH•H2O (1.11 g, 5.8 mmol) in toluene (50 mL) was re-
fluxed for 20 min. After normal workup, the product was separat-
ed by column chromatography (SiO2, hexane–EtOAc, 10:1) to
give 7-1 (1.089 g, 89.7%) as colorless needles, mp 87–88 °C. 1H
NMR (CDCl3) δ 1.27 (s, 6 H), 2.44 (s, 2 H), 2.97 (s, 6 H), 6.72 (d,
J = 9.1 Hz, 2 H), 7.41 (s, 1H), 7.65 (d, J = 9.1 Hz, 2 H); IR (KBr)
2962, 1695, 1614, 1522, 1360, 819 cm−1. Found: C, 78.76; H,
8.14; N, 5.99%. Calcd for C15H19NO: C, 78.56; H, 8.35; N,
6.11%.
Synthesis of 3c. A solution of 7-1 (229 mg, 1.0 mmol) in
THF (3 mL) was added dropwise at 0 °C to a solution of Grignard
reagent, which was formed by treatment of Mg (36.3 mg, 1.5
mmol) with 4-bromoanisole (280.6 mg, 1.5 mmol) in THF (2 mL),
and stirred for 19 h at room temperature. After normal workup,
the product was separated by column chromatography (SiO2, hex-
ane–EtOAc, 10:1) to give 7-1 (25.7 mg 11.2%) and 3c (72.5 mg,
22.3%) as slightly yellow viscous oil (sensitive to air). 1H NMR
(CDCl3) δ 1.29 (s, 6 H), 2.93 (s, 6 H), 3.79 (s, 3 H), 6.20 (d, J =
2.6 Hz, 1 H), 6.22 (d, J = 2.6 Hz, 1 H), 6.62 (d, J = 8.8 Hz, 2 H),
6.78 (d, J = 8.9 Hz, 2 H), 7.04 (d, J = 8.9 Hz, 2 H), 7.12 (d, J =
8.8 Hz, 2 H); IR (KBr) 2957, 1609, 1508, 1351, 1245, 1176, 1039,
821 cm−1; MS m/z 319 (M+; 100), 304 (M+−Me; 57), 290 (7),
274 (3), 245 (5), 214 (20). HRMS Found: m/z 319.19425. Calcd
for C22H25NO:M, 319.19361.
Synthesis of 3d. A solution of 7-1 (229 mg, 1.0 mmol) in
THF (3 mL) was added dropwise at −78 °C to a solution of 2-
lithiothiophene (3 mmol) in THF (3 mL) and stirred for 1 h at
room temperature. The mixture was poured into ice-water and ex-
tracted with EtOAc. The organic layer was washed with brine,
dried over anhydrous MgSO4, and concentrated in vacuo. A mix-
ture of the crude product and p-TsOH (190 mg, 1 mmol) in tolu-
ene (10 mL) was refluxed for 15 min. After normal workup, the
product was separated by column chromatography (SiO2, hexane–
EtOAc, 20:1) to give 3d (175.1 mg, 59.4%) as slightly yellow
needles (sensitive to air). 1H NMR (CDCl3) δ 1.29 (s, 6 H), 2.97
(s, 6 H), 6.17 (d, J = 2.5 Hz, 1 H), 6.40 (d, J = 2.5 Hz, 1 H), 6.63
(dd, J = 1.1, 3.6 Hz, 1 H), 6.70 (d, J = 8.6 Hz, 2 H), 6.89 (dd, J =
Synthesis of 3f. Synthesis of (2-Benzofuryl)-2-hydroxy-4,4-
dimethylcylopentan-1-one (5-2). A solution of 4 (9.0 g, 71
mmol) in THF (80 mL) was added dropwise at 0 °C to a solution
of 9 (237 mmol) in ether (240 mL). The mixture was stirred for 1
h at room temperature. After normal workup, the product was
separated by column chromatography (SiO2, hexane–EtOAc,
10:1–5:1) to give 5-2 (16.94 g, 85.8%) as colorless viscous oil.
1H NMR (CDCl3) δ 1.18 (s, 3 H), 1.21 (s, 3 H), 2.21 (dd, J = 14.3,
1.7 Hz, 1H), 2.37 (dd, J = 17.4, 1.7 Hz, 1H), 2.60 (d, J = 17.4 Hz,
1H), 2.63 (d, J = 14.3 Hz, 1H), 3.32 (s, 1 H), 6.69 (d, J = 0.9 Hz,
1 H), 7.15–7.35 (m, 2 H), 7.42–7.55 (m, 2 H); IR (neat) 3348,
2959, 1752, 1457, 1251 cm−1 ; MS m/z 244 (M+; 11), 226 (M+−
H2O; 45), 211 (M+−H2O−Me; 42), 183 (39), 160 (83). HRMS
Found: m/z 244.11034. Calcd for C15H16O3: M, 244.10994.
Synthesis of 2-(2-Benzofuryl)-4,4-dimethyl-2-cyclopenten-
1-one (7-2). A solution of 5-2 (6.49 g, 26.6 mmol) and p-
TsOH•H2O (465 mg, 2.7 mmol) in toluene (260 mL) was refluxed
for 40 min. After normal workup, the product was separated by
column chromatography (SiO2, hexane–EtOAc, 20:1) to give 7-2
(4.66 g, 77.4%) as colorless needles, mp 65–66 °C. 1H NMR
(CDCl3) δ 1.33 (s, 6 H), 2.48 (s, 2 H), 2.97 (s, 6 H), 7.22 (dd, J =
7.2, 1.3 Hz, 1 H), 7.30 (dd, J = 7.7, 1.6 Hz, 1 H), 7.42–7.49 (m, 2
H), 7.57–7.63 (m, 1 H), 7.80 (s, 1H); IR (neat) 2956, 1713, 1449,
1364, 1250, 1112 cm−1. Found: C, 79.57; H, 6.26%. Calcd for
C23H32N2O2: C, 79.62; H, 6.24; N.
Synthesis of 3f. A solution of 7-2 (485 mg, 2.1 mmol) in
THF (3 mL) was added dropwise at −78 °C to a solution of 9 (4.2
mmol) in ether (5 mL) and stirred for 1 h at room temperature.
The mixture was poured into ice-water and extracted with EtOAc.
The organic layer was washed with brine, dried over anhydrous
MgSO4, and concentrated in vacuo. A mixture of the crude prod-
uct and p-TsOH (5 mg, 0.026 mmol) in toluene (10 mL) was re-
fluxed for 30 min. After normal workup, the product was separat-
ed by column chromatography (SiO2, hexane–EtOAc, 50:1) to
give 3f (547 mg, 79.9%) as slightly yellow viscous oil (sensitive to
air). 1H NMR (CDCl3) δ 1.38 (s, 6 H), 6.70 (d, J = 0.9 Hz, 2 H),
6.82 (s, 2 H), 7.17–7.34 (m, 4 H), 7.45–7.64 (m, 4 H); IR (neat)
2962, 1451, 1256, 749 cm−1; MS m/z 326 (M+; 100), 311 (M+−
Me; 35), 297 (5), 281 (5), 252 (5), 239 (9). HRMS Found: m/z

1678 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Trifluoromethyl-Substituted Norbornadiene
326.12959. Calcd for C23H18O2: M, 326.13068.
(1968). b) T. Nishikubo, T. Kawashima, T. Inoue, and A.
Kameyama, Macromolecules, 25, 2312 (1992). c) R. B. King and
E. M. Sweet, J. Org, Chem., 44, 385 (1979). d) D. P.
Schwendiman, C. Kutal, Inorg. Chem., 16, 719 (1977). e) D. P.
Schwendiman, J. Am. Chem. Soc., 99, 5677 (1977). f) K.
Maruyama, K. Terada, and Y. Yamamoto, J. Org. Chem., 46, 5294
(1981). g) P. A. Grutsch and C. Kutal, J. Am. Chem. Soc., 108,
3108 (1986). h) C. Kutal, Adv. Chem, Ser., 168, 1 (1978). i) R. R.
Hautala and J. L. Little, Adv. Chem, Ser., 184, 1 (1980). j) G. W.
Sluggett, N. J. Turro, and H. D. Roth, J. Phys. Chem. A, 101, 8834
(1997).
Typical Procedure for the Photoisomerization of CF3-NBDs
in Solution. A solution of CF3-NBDs in MeCN (1.0 × 10−4 mol
dm−3) was charged into a quartz cell, and then the solution was ir-
radiated by a 500-W xenon lamp (Ushio Electric Co., UXL-500D-
O) with a UV transmitting filter (Hoya: UV-34) and a thermal-ray
cut filter (ULTRAFINE TECHNOLOGY) in air. The conversion
and the photoisomerization rates from NBDs to QCs were calcu-
lated by the disappearance of the maximum absorption of the
NBDs, as measured by a UV spectrophotometer.
Typical Procedure for the Preparation of the PMMA Solid
Film Doped with CF3-NBDs. A PMMA (Wako Pure Chemical
LTD., 250 mg) solution incorporating with 1c (12.2 mg, 0.025
mmol) in CHCl3 (2.5 mL) was degassed three times by consecu-
tive freeze-pump-thaw cycles and cast on a quartz plate under ar-
gon atmosphere and dried in vacuo at 80 °C for 1 day.
Determination of the Quantum Yield for the Photoisomer-
ization of CF3-NBDs in Solution. The monochromatic light
(1a: 354 nm; 1f: 400 nm) was isolated by passing the light through
a monochromator (JASCO, M10-T) from a 150-W xenon lamp.
The quantum yield was measured in MeCN solution of CF3-NBDs
according to the method of Hatchard and Parker,13 which used a
potassium tris(oxalato)ferrate(ꢀ) aqueous solution as photon
counter.
Measurement of Stored Energy in CF3-QCs. A solution of
NBDs in MeCN was irradiated for enough time to change from
NBDs to QCs by a 500-W xenon lamp. After evaporation of the
solvent, QCs (5 mg) was packed in an aluminum sample tube for
DSC analysis. The sample was heated at 2 °C/min under nitrogen.
Examination of the Durability of CF3-NBDs. The experi-
ment was performed under argon atmosphere. Initially, the
PMMA solid film doped with NBDs was irradiated by a 500-W
xenon lamp until the absorbance of the maximum absorption of
NBDs disappeared. Then, the irradiated film was heated on a hot
plate until the absorbance of NBDs was reversed (1a: irradiated
for 10 min, then heated at 130 °C for 40 min; 1b: irradiated for 2
min, then heated at 100 °C for 10 min; 1c: irradiated for 1 min,
then heated at 120 °C for 20 min; 1f: irradiated for 1 min, then
heated at 80 °C for 15 min). The durability was evaluated from
the differences in the absorbance values between NBDs and QCs
at maximum absorption of NBDs on the 1st and n th cycles of re-
actions.
4
a) K. Maruyama, K. Terada, and Y. Yamamoto, J. Org.
Chem., 46, 5294 (1981). b) K. Maruyama, H. Tamiaki, and S.
Kawabata, J. Org. Chem., 50, 4742 (1985). c) T. Toda, E.
Hasegawa, T. Mukai, H. Tsuruta, T. Hagiwara, and T. Yoshida,
Chem. Lett., 1982, 1551. d) Y. Yamashita, T. Hanaoka, Y. Takeda,
and T. Mukai, Chem. Lett., 1986, 1279. e) H. Tomioka, Y.
Hamano, and Y. Izawa, Bull. Chem. Soc. Jpn., 60, 821 (1987). f)
Z. Yoshida, J. Photochem., 29, 27 (1985). g) S. Miki, Y. Asako,
and Z. Yoshida, Chem. Lett., 1987, 195. h) T. Kobayashi, Z.
Yoshida, Y. Asako, S. Miki, and S. Kato, J. Am. Chem. Soc., 109,
5103 (1987). i) K. Hirao, A. Yamashita, A. Ando, T. Hamada, and
O. Yonemitsu, J. Chem. Soc., Perkin Trans. 1, 1988, 2913. j) K.
Hirao, A. Ando, T. Hamada, and O. Yonemitsu, J. Chem. Soc.,
Chem.Commun., 1984, 300. k) A. Tsubata, T. Uchiyama, A.
Kameyama, and T. Nishikubo, macromolecules, 30, 5649 (1997).
5
a) D. M. Lemal and L. H. Dunlap, Jr., J. Am. Chem. Soc.,
94, 6562 (1972). b) Y. Kobayashi, I. Kumadaki, and Y. Hanzawa,
J. Synth. Org. Chem, Japan, 37, 183 (1979). c) K. Hirao, A.
Yamashita, and O. Yonemitsu, J. Fluorine Chem., 36, 293 (1987).
6
The preparation of the CF3-NBDs was reported as a com-
munication. T. Nagai, I. Takahashi, and M. Shimada, Chem. Lett.,
1999, 897.
7
Y. Naoshima, M. Yamaguchi, M. Kawai, I. Ichimoto, and
H. Ueda, Agr. Biol. Chem., 38, 2273 (1974).
K. Hirao, A. Yamashita, A. Ando, H. Yamamoto, H. Iijima,
T. Hamada, and O. Yonemitsu, J. Chem. Res., 1987, (M), 1401.
Compounds 10 and 11 were synthesized according to Ref.
4g (Chart 1).
8
9
We would like to thank Professors Itumaro Kumadaki of
Setsunan University, Sadao Miki of Kyoto Institute of Tech-
nology, and Tadatomi Nishikubo of Kanagawa University for
helpful discussions.
Chart 1.
10 a) T. Nishikubo, C. Hijikata, and T. Iizawa, J. Polym. Sci.,
Polym. Chem. Ed., 29, 671 (1991). b) T. T. Iizawa, C. Hijikata,
and T. Nishikubo, Macromolecules, 25, 21 (1992). c) A. Ikeda, A.
Kameyama, T. Nishikubo, and T. Nagai, Macromolecules, 34,
2728 (2001).
11 a) T. Nagai, G. Nishioka, M. Koyama, A. Ando, T. Miki,
and I. Kumadaki, Chem. Pharm. Bull., 40, 593 (1992). b) T.
Nagai, G. Nishioka, M. Koyama, A. Ando, T. Miki, and I.
Kumadaki, J. Fluorine Chem., 57, 229 (1992).
12 a) T. Iizawa, H. Ono, and F. Matsuda, Reactive Polymer,
30, 17 (1996). b) A. Tsubata, T. Uchiyama, A. Kameyama, and T.
Nishikubo, Macromolecules, 30, 5649 (1997). b) T. Iizawa, T.
Kurisu, K. Nakajima, and T. Nishikubo, Polym. J., 30, 446 (1998).
13 C. Hatchard, C. A. Parker, Proc. R. Soc. London, Ser. A ,
235, 518 (1956).
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