Synthesis, X-ray crystallographic analysis, and theoretical structure analysis of tetrathienylethenes designed for photo- and electrochromism

Article abstract of DOI:10.1016/j.tetlet.2007.09.100

As part of an effort to develop a new chromic system that responds to both photoexcitation and electron transfer, tetrakis(2-methylthien-3-yl)ethene (3a) and its tetrakismethylthio derivative (3b) were synthesized. The results of X-ray crystallographic and theoretical analyses of these substances suggest that (1) conformers of 3 with an antiparallel arrangement of two vicinal thienyl groups will undergo photocyclization, and (2) the most stable conformer of 3 having an anti-double parallel conformation will not. These predictions were preliminarily confirmed by the results of photochemical and cyclic voltammetry studies.

Full text of DOI:10.1016/j.tetlet.2007.09.100

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Tetrahedron Letters 48 (2007) 8338–8342
Synthesis, X-ray crystallographic analysis, and theoretical
structure analysis of tetrathienylethenes designed
for photo- and electrochromism
a,
a
b
a
*
Hiroshi Ikeda, Azusa Sakai, Hayato Namai, Akinori Kawabe and
a,
*
Kazuhiko Mizuno
a
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
b
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Received 13 August 2007; revised 7 September 2007; accepted 18 September 2007
Available online 21 September 2007
Dedicated to the memory of Professor Yoshihiro Matsumura (Nagasaki University)
Abstract—As part of an effort to develop a new chromic system that responds to both photoexcitation and electron transfer,
tetrakis(2-methylthien-3-yl)ethene (3a) and its tetrakismethylthio derivative (3b) were synthesized. The results of X-ray crystallo-
graphic and theoretical analyses of these substances suggest that (1) conformers of 3 with an antiparallel arrangement of two vicinal
thienyl groups will undergo photocyclization, and (2) the most stable conformer of 3 having an anti-double parallel conformation
will not. These predictions were preliminarily confirmed by the results of photochemical and cyclic voltammetry studies.
ꢀ
2007 Elsevier Ltd. All rights reserved.
1
. Introduction
F2
F2
(
(
a)
b)
F2
S
F2
S
F2
S
F2
S
UV
Vis
The reversible reaction interconverting cis-stilbene (cis-
,2-diphenylethene) and dihydrophenanthrene is a fun-
1
damental process in organic photochemistry. By replac-
ing the phenyl groups of stilbene by thienyl groups and
introducing a perfluoropropano-bridge, Irie et al. were
able to develop so-called diarylethene photochromic sys-
1
S
S
S
S
S
S
1
–2e–
tems (Scheme 1a, 1). Another consequence associated
S
S
S
S
S
S
+
S
S
S
+
with incorporating thienyl groups is an enhancement
of the oxidation ability of diarylethenes. In fact, Suzuki
and Miyashi reported that tetrakis[5-(methylthio)thien-
2e–
S
+
2
2
-yl]ethene (2) displays electrochromic behavior associ-
ated with a dynamic change in its molecular geometry
on two-electron transfer oxidation and reduction
Scheme 1. (a) Photochromism of 1 and (b) electrochromism of 2.
3
a) and its tetrakismethylthio derivative (3b), of which
(
Scheme 1b) and proposed a concept of ‘dynamic redox
2
expected photo- and electrochromism as shown in
Scheme 2. In this Letter, we report the preparation of
systems’.
3
and the results of X-ray crystallographic and theore-
Based on these earlier findings and as part of an effort to
develop a new chromic system that responds to both
photoexcitation and electron transfer, we have
designed tetrakis(2-methylthien-3-yl)ethene (Scheme 2,
tical analyses. This investigation has provided important
information about their photo- and electrochromic
properties, which are also reported preliminarily.
3
5
2. Synthesis
Keywords: Photochromism; Electrochromism; Electron transfer;
Reaction mechanism.
*
Corresponding authors. Fax: +81 72 254 9289 (H.I.); e-mail addresses:
ikeda@chem.osakafu-u.ac.jp; mizuno@chem.osakafu-u.ac.jp
Tetrathienylethenes 3a–b were synthesized starting with
commercially available 3-bromothiophene (5) by the
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.100

H. Ikeda et al. / Tetrahedron Letters 48 (2007) 8338–8342
8339
R
R
S
S
R
R
R
R
S
S
R
UV
Vis
4
3
3' 4'
2
2'
5
5'
S
S
1'
S
S
R
1
3
a: R = H
b: R = SMe
4a: R = H
4b: R = SMe
3
open form
closed form
–
2e– +2e–
–2e–
S
+2e–
S
2+
R
R
S
R
R
R
S
R
+
+
R
S
S
S
S
R
Scheme 2. Expected photo- and electrochromic behavior of 3 and 4.
(1) n-BuLi
O
S
(2)
(
1) LDA
2) MeI
Br
Br
(
Cl
NMe
2
O
THF
y. 82%
Ether
y. 48%
S
S
5
6
S
7
(
1) n-BuLi
TiCl / Zn dust /
4
N
(2) MeSSMe
Figure 1. ORTEP drawings of 3a (top, syn-double parallel) and 3b
3a
3b
(
bottom, anti-double parallel), derived from X-ray crystallographic
THF
y. 59%
THF
y. 76%
data displayed with 50% probability thermal ellipsoids. Hydrogen
atoms are not shown for clarity.
Scheme 3. Synthesis of 3.
searched for a possible Sꢀ ꢀ ꢀS contact that often induces
geometric changes in the crystalline state. Although no
significant Sꢀ ꢀ ꢀS contact was found, we conclude that
the crystal structures of 3a and 3b may be a result of
crystal packing forces because the calculation result
described below indicated that the energy gap between
the most stable anti-double parallel conformer and the
most unstable syn-double parallel conformer is only ca.
sequence shown in Scheme 3. 3-Bromo-2-methylthio-
phene (6) was produced from 5 by regioselective methyl-
6
ation and then converted to bis(2-methylthien-3-yl)-
ketone (7) by reaction with N,N-dimethylcarbamoyl
7
chloride. McMurry coupling reaction of 7 using TiCl
4
8
and Zn gave 3a, which was converted to 3b by sequen-
tial lithiation and treatment with dimethyl disulfide.
2
1.4 kcal/mol for 3a and ca. 1.9 kcal/mol for 3b.
3
. X-ray crystallographic analysis
4. Semiempirical theoretical analysis
It is important to gain information about the structures
of 3a–b because it is known that the antiparallel orienta-
tion of vicinal thienyl groups in 1 is essential for facile
photocyclization to take place, especially in the crystal-
The existence of two pairs of vicinal thienyl groups with
parallel orientations in the structures of 3a and 3b indi-
cates that these substances will only reluctantly undergo
photocyclization reactions to form 4 in the crystalline
state. However, if the antiparallel conformers can be
populated even to a small extent in solution, 3a and 3b
might be capable of undergoing photocyclization reac-
tions. Therefore, knowledge about the structures of
3a–b in solution and the gas phase is important to
understand the potential chromic properties of these
substances. For this purpose, the structures and con-
former energies of 3b were determined by using PM3
1
line state. The X-ray crystallographic structures of 3a
9
–11
and 3b are shown in Figure 1.
In the case of 3a,
two pairs of vicinal thienyl groups are oriented in a par-
allel arrangement, while the pairs of geminal thienyl
groups exist in a syn orientation (Fig. 1, top). Likewise,
in 3b two pairs of vicinal thienyl groups are arranged in
a parallel orientation (Fig. 1, bottom). In contrast, two
pairs of the geminal thienyl groups in 3b exist in an anti
arrangement. Therefore, in the crystalline state, 3a and
1
2
3
b have syn-double parallel and anti-double parallel con-
based calculations.
formations, respectively.
In Figure 2 is shown the five, theoretically derived,
To gain more insight into the differences of 3a (syn-dou-
ble parallel) and 3b (anti-double parallel) in the mole-
cular structures, we analyzed the crystal structures and
major conformations of 3b, which include in order of
rel
their decreasing stability (i) anti-double parallel (E
=
0 kcal/mol), (ii) antiparallel and parallel (ca. 0.9 kcal/mol),

8340
H. Ikeda et al. / Tetrahedron Letters 48 (2007) 8338–8342
(
v)
(v) 3b (syn-double parallel
)
ca. 1.9 (3%)
(
iv)
(
iv) 3b (anti-double antiparallel)
ca. 1.3 (7%)
ca. 1.2 (9%)
(
iii) 3b (syn-double antiparallel
)
(ii) 3b (antiparallel & parallel
)
ca. 0.9 (15%)
(
iii)
parallel for vicinal thienyl groups
R
(i) 3b (anti-double parallel
)
0
(66%)
(
ii)
S
R
S
anti for two methyl groups
S
S
R
R
parallel for vicinal thienyl groups
i) 3b (anti-double parallel), R = SMe
(
(
i)
1
5
Figure 2. Conformers of 3b, their relative energies (kcal/mol) calculated by using the PM3 method, and the existence ratios at 298 K. Left: front
view, right: side view.
(
iii) syn-double antiparallel (ca. 1.2 kcal/mol), (iv) anti-
the thienyl groups are arranged in a parallel orientation
of the vicinal thienyl groups in the single crystalline state
(Fig. 1).
double antiparallel (ca. 1.3 kcal/mol), and (v) syn-
double parallel (ca. 1.9 kcal/mol). The conformers
1
5
are predicted to exist in an approximate ratio of
6
6:15:9:7:3 at T = 298 K. The most stable anti-double
In contrast, photochromism of 3 was observed in solu-
parallel conformer of 3b is the one that exists in
the crystalline state of this substance. Although photo-
cyclization reaction of this conformer is predicted to
tion. Upon irradiation with UV light (350 nm) for
ꢁ5
1 min, a CH Cl solution of 3a (5 · 10 M) underwent
2
2
a change from colorless to pale yellow associated with
1
be difficult, the metastable antiparallel and parallel,
growth of absorption bands at k = 314 and ca.
ab
1
8
syn-double antiparallel, and anti-double antiparallel
conformers, calculated to comprise 31% of 3b, should
undergo this photocyclization. This prediction is sup-
463 nm (A = ca. 0.03). The 463-nm band disappeared
almost completely, when the resulting solution was irra-
1
7
18
diated with Vis light (450 nm) for 30 min. Similar but
even more facile photochromism was observed with 3b.
A colorless solution of 3b in CH Cl quickly turned to
˚
ported by the relatively short Cꢀ ꢀ ꢀC contacts (4.23 A
for the antiparallel and parallel conformer, 3.93 and
2
2
˚
4
4
.36 A for the syn-double antiparallel conformer, and
orange when irradiated with UV light (350 nm) for
0.5 min. The new absorption bands at kab = 327 and
489 nm (A = ca. 0.08) along with the orange color
slowly disappeared when the solution was exposed to
Vis light (490 nm) for 5 min (Fig. 3). The similar absorp-
tion band at 490 nm, which arose by irradiating 3b in
cyclohexane, also disappeared when the solution was
heated at 60 ꢁC. The photochromic processes were
repeated several times, suggesting that the colored pro-
ducts formed in the photoreactions are cyclic isomers
˚
.33 and 4.51 A for the anti-double antiparallel con-
0
former) seen between C2 and C2 of the vicinal thienyl
groups of 3b. This observation suggests that photoreac-
tion of 3b to 4b should be facile.16
5
. Preliminary studies of the photo- and electrochromic
properties
1
8
The crystal state photochemistry of 3a–b was investi-
gated first. Single crystals of 3a or 3b, prepared by
crystallization from EtOH and CH Cl –MeOH, respec-
4. The results demonstrate that 3a–b are photochromic
in the solution phase.
2
2
1
7
Cyclic voltammetry (CV)19 studies have been used to
establish the electrochromic properties of 3b. Initial
information came from inspection of the cyclic voltam-
mogram of 3b in CH CN containing 0.1 M Et NClO .
tively, were irradiated with 335 nm UV light. No obvi-
ous changes were observed in the color of the crystals or
the UV–vis absorption spectra of CH Cl solutions of
2
2
the crystals even after 1-h irradiation. The lack of
3
4
4
photoreactivity of 3a–b is likely due to the fact that
The cyclic voltammogram of 3b showed at first a wave

H. Ikeda et al. / Tetrahedron Letters 48 (2007) 8338–8342
8341
6. Conclusion
0.8
0.8
327
327
0
.6
.4
0.6
0.4
The results described above show that the new tetrathi-
enylethenes 3 are dual chromic compounds in photo-
and electrochromism: they undergo color changes in
response to both photoexcitation (3a–b) and SET oxida-
tion (3b). X-ray crystallographic analysis and semiem-
pirical calculations suggest that the antiparallel
conformations of 3 allow them to cyclize to form 4,
while the most stable anti-double parallel conformer will
be reluctant to cyclize. The predictions gain support
from the observation that irradiation of these substances
in the crystalline state does not result in formation of 4.
In contrast, upon irradiation or electrochemical oxida-
0
min
0
1 min
5 min
89
A
b
s
0.5 min
As
0
min
0
.2
.0
0.2
0.0
4
4
89
0
3
00 400 500 600
300 400 500 600
λ ab / nm
λ ab / nm
ꢁ5
Figure 3. UV–vis spectral changes of 3b (5.0 · 10 M) (a) on UV
350 nm) irradiation for 0.5 min and (b) on the succeeding Vis
490 nm) irradiation for 5 min in CH Cl
(
(
2
2
.
tion 3 are transformed to 4. Detailed studies of the
+
at Eap (anodic peak potential) = ca. +0.76 V vs Ag/Ag
20,21
photo- and electrochromic properties
are now in progress.
of 3 and 4
for single electron transfer (SET) oxidation (Fig. 4). This
wave was not completely reversible, the reduction wave
being observed at Ecp (cathodic peak potential) = ca.
+
0.14 V. A successive scanning of the solution gave a
Acknowledgements
new wave at Eap = ca. +0.21 V, which was shown to
correspond to the SET oxidation potential of 4b by
the observation that the CV of 4b, generated on UV
irradiation of 3b in CH CN containing 0.1 M Et N-
ClO , has an E = ca. +0.23 V and an Ecp = ca.
+
H.I. and K.M. gratefully acknowledge financial support
from a Grant-in-Aid for Scientific Research on Priority
Areas (Nos. 14050008 and 17029058 in the Area No.
17) and others (Nos. 19350025) from the Ministry of
Education, Culture, Sports, Science, and Technology
MEXT) of Japan. H.I. also thanks the Shorai Founda-
3
4
4
ap
4
0.17 V. Thus, the occurrence of an ECE mechanism
strongly suggests that 3b is irreversibly transformed to
Å+
Å+
(
4
b via 3b and 4b upon SET promoted oxidation.
tion, the Mazda Foundation, and the Iketani Science
and Technology Foundation for providing financial
support for the work. We also thank Drs. H. Maeda
and A. Nomoto (Osaka Prefecture University) for their
technical assistance with the X-ray crystallographic
analysis.
Considering that cycloreversion of 4b to 3b occurs ther-
mally, the observations conclude that 3b displays elec-
trochromic behavior (Scheme 4), which is quite
different form the first expectation shown in Scheme 2.
The cyclization of 3b is assumed to proceed also from
its antiparallel conformers.
Å+
Supplementary data
0
The PM3 calculation result for 3b [(i) anti-double paral-
lel], and 4b [(vi) anti-antiparallel and trans], and energy
diagram for the conformers of 3a/4a and 3b/4b. Supple-
mentary data associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.2007.09.100.
—
100
+
0.8
+0.4
E / V vs Ag/Ag+
0.0 +0.8
+0.4
E / V vs Ag/Ag+
0
Figure 4. Cyclic voltammograms (scan rate, 10 mV/s) of 3b on one-
left) and two-cycle scans (right) in CH CN containing 0.1 M
Et NClO
(
3
4
4
.
References and notes
1
. (a) Matsuda, K.; Irie, M. J. Photochem. Photobiol., C
2
2
1
004, 5, 169–182; (b) Matsuda, K.; Irie, M. Chem. Lett.
006, 35, 1204–1209; (c) Irie, M. Chem. Rev. 2000, 100,
685–1716.
R
S
S
S
S
R
R
UV (λ = 350 nm)
R
R
S
S
R
Photochromism
2. (a) Suzuki, T.; Ohta, E.; Kawai, H.; Fujiwara, K.;
Fukushima, T. Synlett. 2007, 851–869; (b) Suzuki, T.;
Shiohara, H.; Monobe, M.; Sakimura, T.; Tanaka, S.;
Yamashita, Y.; Miyashi, T. Angew. Chem. Int. Ed. Engl.
1992, 31, 455–458.
3. Recently, Belen’kii and his co-workers reported the
synthesis and photochromic properties of tetrakis(3,5-
dimethylthien-2-yl)- and tetrakis(2,5-dimethylthien-3-
yl)ethenes. See Ref. 4.
Vis (λ = 490 nm)
R
S
S
R
or heating
3
b, R = SMe
open form
4b, R = SMe
closed form
Electrochromism
SET Oxidation
λab = 327 nm (sh)
λab = 489 nm
Eap = ca. +0.76 V
Eap = ca. +0.21 V
SET Oxidation
4
. Belen’kii, L. I.; Gromova, G. P.; Kolotaev, A. V.;
Nabatov, B. V.; Krayushkin, M. M. Russ. Chem. Bull.
Int. Ed. 2005, 54, 1208–1213.
Scheme 4. A plausible photo- and electrochromism of 3b and 4b.

8342
H. Ikeda et al. / Tetrahedron Letters 48 (2007) 8338–8342
5
. (a) Gorodetsky, B.; Branda, N. R. Adv. Funct. Mater.
007, 17, 786–796; (b) Matsuda, K.; Yokojima, S.;
Moriyama, Y.; Nakamura, S.; Irie, M. Chem. Lett. 2006,
5, 900–901; (c) Moriyama, Y.; Matsuda, K.; Tanifuji, N.;
Irie, S.; Irie, M. Org. Lett. 2005, 7, 3315–3318; (d)
Gorodetsky, B.; Samachetty, H. D.; Donkers, R. L.;
Workentin, M. S.; Branda, N. R. Angew. Chem. Int. Ed.
12. PM3 calculations were performed using the program
1
3
2
GAUSSIAN 98. The Cartesian coordinates for the opti-
mized structures of 3b [(i) anti-double parallel] and 4b [(vi)
anti-antiparallel and trans] are given in the Supplementary
data. Molecular geometries in Figure 2 were drawn using
3
1
4
the WinMOPAC 3.9 software.
13. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G.
E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;
Montgomery, J. A.; Stratmann, R. E.; Burant, J. C.;
Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K.
N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P.
Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill,
P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.;
Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople,
J. A. Gaussian 98, Revision A.11.4; Gaussian, Inc.:
Pittsburgh PA, 1998.
2004, 43, 2812–2815; (e) Peters, A.; Branda, N. R. J. Am.
Chem. Soc. 2003, 125, 3404–3405; (f) Peters, A.; Branda,
N. R. Chem. Commun. 2003, 954–955.
6
. Ewen, J. A.; Elder, M. J.; Jones, R. L.; Rheingold, A. L.;
Liable–Sands, L. M.; Sommer, R. D. J. Am. Chem. Soc.
2001, 123, 4763–4773.
7
8
. Lucas, P.; Mehdi, N. E.; Ho, H. A.; B e´ langer, D.; Breau,
L. Synthesis 2000, 9, 1253–1258.
. Physical data of key and new compounds 6: Pale yellow oil;
1
H NMR (CDCl
H), 7.06 (d, J = 5.4 Hz, 1H); C NMR (CDCl ) d
3
) dppm 2.40 (s, 3H), 6.89 (d, J = 5.4 Hz,
13
1
1
7
2
9
1
3
ppm
4.44, 109.39, 122.79, 129.96, 134.21; IR (neat) 590, 766,
85, 853, 1003, 1084, 1155, 1340, 1439, 1528, 2856,
ꢁ1
+
920 cm ; EIMS m/z 177 (35, M ), 176 (66), 175 (33),
7 (100). Compound 7: Colorless solid (n-hexane), mp 99–
1
00 ꢁC; H NMR (CDCl
3
) dppm 2.66 (s, 6H), 7.01 (d,
1
3
J = 5.4 Hz, 2H), 7.12 (d, J = 5.4 Hz, 2H); C NMR
14. WinMOPAC 3.9, Fujitsu Ltd, Tokyo, Japan, 2004.
15. The energies obtained by using the PM3 method were
assumed to contain considerable errors as compared with
those arising from DFT calculations, which are now in
progress.
(
CDCl ) d
14.95 (2C), 121.08 (2C), 129.63 (2C), 137.80
3
ppm
(
1
2C), 147.66 (2C), 187.46; IR (KBr) 716, 739, 849, 1265,
366, 1435, 1520, 1638 cm ; EIMS m/z 222 (63, M ), 221
ꢁ
1
+
(
(
24), 209 (10), 208 (15), 207 (100), 189 (36), 174 (13), 161
13), 125 (46), 97 (19), 96 (12), 53 (22); Anal. Calcd for
16. Calculations indicate that photoproduct 4b can exist in
three conformationally isomeric forms, including (vi) anti-
antiparallel and trans{ca. 20.1 kcal/mol relative to 3b [(i)
anti-double parallel]}, (vii) parallel and trans (ca. 20.7 kcal/
mol), and (viii) syn-antiparallel and trans (ca. 21.2 kcal/
C
11
H
10
S
2
O: C, 59.43; H, 4.53; S, 28.84. Found: C, 59.73;
H, 4.62; S, 29.08. Compound 3a: Colorless solid (CH Cl
1.92 (s,
2
2
–
1
MeOH); mp 203–204 ꢁC; H NMR (CDCl ) d
3
ppm
1
2H), 6.49 (d, J = 5.4 Hz, 4H), 6.84 (d, J = 5.4 Hz, 4H);
1
3
15
C NMR (CDCl
3
) dppm 13.72 (4C), 120.49 (4C), 130.23
mol), in a ratio of 66:24:10 at 298 K. A similar energy
(
6
4C), 131.65 (2C), 136.18 (4C), 139.18 (4C); IR (KBr) 646,
diagram was obtained for 3a and 4a. For the detail, see the
Supplementary data.
ꢁ
60, 708, 725, 835, 1256, 1429 cm ; UV (CH Cl )
2 2
1
k = 314 nm (max, loge = 4.17); EIMS m/z 412 (100,
M ), 397 (15), 207 (12), 414 (20); Anal. Calcd for
17. A single crystal or solution of 3 was irradiated with a
150 W Xe lamp [k = 335 or 350 nm for UV, 450 or 490 nm
for Vis, band pass 20 nm] through a spectrometer
equipped to a JASCO FP-6300 spectrofluorometer.
18. A prolonged UV irradiation of 3 resulted in the formation
of an unidentified product (8). The photocycloreversion of
4 to 3 may be concurrent with the formation of 8.
Isolation of 4 and 8 and identification of 8 are now in
progress and will be published elsewhere.
+
C
22
H
20
S
4
: C, 64.04; H, 4.89; S, 31.08. Found: C, 3.84;
H, 4.98; S, 31.78. Compound 3b: Colorless solid
1
(
d
CH
ppm 1.90 (s, 12H), 2.34 (s, 12H), 6.50 (s, 4H);
NMR (CDCl ) d ppm 14.02 (4C), 22.47 (4C), 131.21 (2C),
31.82 (4C), 134.63 (4C), 138.83 (4C), 139.60 (4C);
IR (KBr) 507, 860, 966, 1151, 1188, 1204, 1312, 1418,
2
Cl
2
–n-hexane): mp 119–120 ꢁC; H NMR (CDCl )
3
13
C
3
1
ꢁ1
1
431 cm
;
UV (CH
2
Cl
2
)
k = 327 nm (sh, loge =
19. Eap and Ecp were measured on the ALS model 600C
electrochemical analyzer by CV (Pt electrode, scan rate
10 mV/s) in CH CN containing Et NClO (0.1 M) as a
4
.10); HRMS (ESI) Calcd for C H S +Na, 618.9849;
2
6
28 8
found, 618.9846. Anal. Calcd for C H S : C,
2
6
28
8
3
4
4
5
4
2.31; H, 4.73; S, 45.05. Found: C, 52.40; H, 4.94; S,
3.94.
supporting electrolyte.
20. An attempt of electron-transfer reactions using one-
electron oxidant was also investigated preliminarily. For
example, the oxidation of 3b with tris(p-bromophenyl)-
aminium hexachloroantimonate (2 equiv kmax = 728 nm)
9
. Crystallographic data of 3a and 3b have been deposited
with the Cambridge Crystallographic Data Center as
supplementary publication nos. CCDC 654282 and
6
54283, respectively. These data can be obtained free of
in CH Cl resulted in the coloration of the solution
2 2
2+
charge via http://www.ccdc.cam.ac.uk/data_request/cif,
by emailing data_request@ccdc.cam.ac.uk, or by contact-
ing The Cambridge Crystallographic Data Center, 12,
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
(kmax = 582 nm), suggesting a formation of 4b
The
detail will be given elsewhere.
21. As one of the reviewers pointed out, the stereochemistry of
the products of photochemical and electrochemical
reactions is a quite important issue. In our case, it is
strongly suggested that the product 4b of photochemical
reaction is identical with that of electrochemical reaction,
because their oxidation potentials are almost the same (See
the text). The detail will be given elsewhere.
3
36033.
1
1
0. Figure 1 was depicted with CrystalMaker for Mac OS X
1
1
Ver. 7.2.3 2006.
1. CrystalMaker Software Limited. Website: http://
www.crystalmaker.com.