Preparations of bis[2-(2-arylethynyl)-3-thienyl]arenes and bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]arenes

Article abstract of DOI:10.1016/j.tet.2008.10.088

4,4′-Bis[2-(2-phenylethynyl)-3-thienyl]biphenyl, 4,4′-bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]biphenyl and their congeners were prepared and their properties were studied. Extension of π-system through the central benzene ring was suggested by UV-vis

Full text of DOI:10.1016/j.tet.2008.10.088

Tetrahedron 65 (2009) 145–151
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Preparations of bis[2-(2-arylethynyl)-3-thienyl]arenes
and bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]arenesq
*
Kozo Toyota , Kazuyuki Okada, Hiroshi Katsuta, Noboru Morita
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
a r t i c l e i n f o
a b s t r a c t
4,40-Bis[2-(2-phenylethynyl)-3-thienyl]biphenyl, 4,40-bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]bi-
Article history:
Received 14 July 2008
Received in revised form 25 October 2008
Accepted 28 October 2008
Available online 6 November 2008
phenyl and their congeners were prepared and their properties were studied. Extension of
p-system
through the central benzene ring was suggested by UV–vis spectra. Connection of two 1,4-bis[2-{2-
(trimethylsilyl)ethynyl}-3-thienyl]benzene units was exemplified.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Oligoarene
Thiophene
Heterocycles
Molecular architecture
1. Introduction
introduction of substituents at the terminal sp carbon and/or
5-position of the thiophene rings, this advantage was exemplified
Artificial molecular architecture is of current interest.1 This
category includes compounds so-called bio-mimetic or bio-in-
spired molecules, which resembles (from particular point of view
concerning to the structure and functionality) to bio-polymers such
as peptides, proteins, and so on. In the course of our continuing
research on developing novel phosphorus ligands,2 as well as their
transition-metal complexes3 and homogeneous catalysts,4 the au-
thor (K.T.) was inspired by structures of metalloproteins and
designed 1,4-bis(2-ethynyl-3-thienyl)benzene spacer (hereafter
abbreviated to the ETB spacer). The ETB spacer is a promising and
easily tunable spacer,5 which has a 1,4-phenylene axis and a pair of
3-thienyl moieties6 at the both ends of the axis. The spacer also has
the ethynyl side chains on the thiophene rings. The ETB system and
related systems [such as 4,40-bis(2-ethynyl-3-thienyl)biphenyls7]
may be applicable to construction of accumulated (or assembled)
transition-metal complex systems such as artificial enzymes or
metalloprotein-inspired molecules8 (general structure is shown as
A in Chart 1).
by preparation of compounds 4 and 5.5 Compounds 4 and 5 have
1,4-bis(5-alkyl-3-thienyl)benzene backbone and multiple ethynyl
side chains, which are fundamental forms of the ETB-linked sys-
tems such as A in Chart 1.
In order to progress the investigation of the ETB spacer-linked
compounds, establishment of fundamental synthetic technique
and evaluation of electronic properties of the spacer moieties are
necessary. We report here preparation and properties of 1,4-bis[2-
(2-phenylethynyl)-3-thienyl]benzene and its congeners, which will
help evaluation of the ETB spacer.9
2. Results and discussion
2.1. Preparation of 1,4-bis[2-(2-phenylethynyl)-3-
thienyl]benzene and related compounds
In the previous paper, we prepared 1,4-bis[2-(hetero-
arylethynyl)-3-thienyl]benzenes by Sonogashira reaction of 1 with
heteroaryl iodide.5 This time, however, compounds 3a and 7a were
prepared from 1,4-bis(2-iodo-3-thienyl)benzene (6)5 (Scheme 1).
For the purpose of comparison of properties, 3-phenyl-2-ethy-
nylthiophene derivatives 8–10 as well as 2-(2-phenyl-
ethynyl)thiophene (11)10 were also prepared by a similar manner.
Compound 3a is soluble in chloroform, however, the phenylethynyl
derivative 7a is hardly soluble in chloroform (compound 7a turned
out to be soluble in DMSO). Thus, alkyl-substituted derivatives 7b,c
In the previous paper,5 we have reported a preparation of
compounds 1 and 2 (Chart 1) as well as conversion of 1 to pyridyl
ligands 3b,c. Characteristics of the ETB spacer are easy and selective
q
Chemistry of bis(2-ethynyl-3-thienyl)arene and related systems, Part 2. For Part
1, see Ref. 5.
* Corresponding author. Tel.: þ81 22 795 6559; fax: þ81 22 795 6562.
E-mail address: toyota@mail.tains.tohoku.ac.jp (K. Toyota).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.10.088

146
K. Toyota et al. / Tetrahedron 65 (2009) 145–151
FG
(CH2)10
S
FG-(CH2)m
CH2
S
S
R
R
R
R
n'
R
R
S
S
S
(CH2)10
FG
(CH2)m
(CH2)m -FG
''
'
1: R = H
2: R = SiMe3
n
3a: R = 2-pyridyl
3b: R = 3-pyridyl
3c: R = 4-pyridyl
4: R = SiMe3, FG = I
A
5: R = SiMe3, FG = NMe2
FG: functional group
Chart 1.
were prepared. Fortunately, compounds 7b,c turned out to be sol-
uble in many solvents such as chloroform, dichloromethane, ben-
zonitrile, or tetrahydrofuran (THF), although the solubility in
hexane or acetonitrile is not very good.11
2.2. Preparation of 4,40-bis[2-(2-arylethynyl)-3-
thienyl]biphenyl derivatives
4,40-Bis(2-ethynyl-3-thienyl)biphenyl derivatives were also
prepared by a method similar to those of 3a and 7a–c (Scheme 2):
Suzuki coupling of 4,40-diiodobiphenyl with 3-thiopheneboronic
acid gave 4,40-di(3-thienyl)biphenyl (12), which was halogenated
by N-iodosuccinimide (NIS) to form 13. It should be noted that 12
was insoluble in common solvent and the iodination of 12 was
carried out in suspension. Because 13 is more soluble than 12, the
iodination reaction tends to afford a mixture of 13 and over-io-
dinated products as well as the starting 12; separation of 13 from
by-products by silica-gel column chromatography turned out to be
difficult. When 0.5 molar ratio (i.e., 0.25 equiv for diiodination) of
NIS was used, 13 was successfully isolated in ca. 10% yield (41% yield
based on NIS). However, from practical reason, crude 13 (obtained
from reaction of 12 with 2 molar ratio of NIS) was used as a starting
material in the following experiments: Sonogashira reaction of
crude 13 with ethynyltrimethylsilane, 2-ethynylpyridine, or ethy-
nylbenzene afforded 14–16, respectively.
S
S
I
R
R
PdCl2(PPh3)2
CuI, i-Pr2NH,
THF
R
I
S
S
6
3a: R = 2-pyridyl
7a: R = phenyl
7b: R = 4-butylphenyl
7c: R = 4-hexylphenyl
S
R1
S
R
I
R
PdCl2(PPh3)2
CuI, i-Pr2NH,
THF
R1
8: R = SiMe3, R1 = phenyl
9: R = 2-pyridyl, R1 = phenyl
10: R = R1 = phenyl
2.3. UV–vis spectra of 1,4-bis[2-(arylethynyl)-3-
thienyl]benzenes
11: R = phenyl, R1 = H
Figure 1 shows UV–vis spectra of parent spacer 1, trimethylsilyl-
substituted derivatives 2, 8, and 14, as well as 4-butylphenyl con-
gener 7b in CH2Cl2. Bathochromic shifts were observed among the
ETB derivatives in the order of 7b>2>1, as expected. Compared to 8,
compound 2 shows significant red shift and increase of molar
absorption coefficient, which indicates existence of significant
Scheme 1.
S
S
S
I
R
B(OH)2
4,4'-diiodobiphenyl
NIS
R
S
Pd(PPh3)4, K2CO3
THF, H2O
AcOH, CHCl3
AIBN
PdCl2(PPh3)2
CuI, i-Pr2NH,
THF
R
I
S
S
S
12
13
14: R = SiMe3
15: R = 2-pyridyl
16: R = phenyl
Scheme 2.

K. Toyota et al. / Tetrahedron 65 (2009) 145–151
147
60000
50000
40000
30000
20000
10000
0
60000
1
3a
3b
3c
9
2
7b
50000
8
14
15
40000
30000
ε
ε
20000
10000
0
280
300
320
340
360
380
Wavelength / nm
400
420
440
280
300
320
340
Wavelen
360
380
gth / nm
400
420
440
Figure 1. UV–vis spectra of 1, 2, 7b, 8, and 14 in CH2Cl2.
Figure 3. UV–vis spectra of 3a–c, 9, and 15 in CH2Cl2.
p
-conjugation through the central phenylene moiety. Compound
relatively similar. Among the three isomers, 3a shows the largest
molar absorption coefficient at the two peaks of ca. 300 and
320 nm, with the order 3a>3c>3b. Compound 15 possessing a bi-
14 with biphenyl moiety shows largest red shift and value, among
the three trimethylsilyl-substituted derivatives. However, the dif-
3
ference in lmax value between 14 and 2 is relatively small, in-
phenyl spacer shows much larger
3 value in this region. As expec-
dicating that extension of the p-system in 14 is not so good because
coplanarity of the biphenyl moiety is not very good.
Figure 2 shows UV–vis spectra of phenylethynyl derivatives
7a,b, 10, 11, and 16 in DMSO. Bathochromic shifts were observed in
the order of 7b>7a>10>11. The shape of the spectrum of 7b in
DMSO is significantly different from that in CH2Cl2 (Fig. 1), probably
ted, 15 do not show significant red shift, compared to 3. In contrast,
the spectra of 3a–c show large bathochromic shifts compared to
those of compounds 10 and 1 (Fig. 1). Again, this fact indicates
existence of significant
ene moiety in 3, i.e., the
p
-conjugation through the central phenyl-
-system of 1,4-bis[2-(arylethynyl)-3-
p
thienyl]benzene spreads throughout the molecule.
because red shifts of
p/p transition occurred in more polar
*
DMSO solvent. Similar to the cases of trimethylsilyl-substituted
derivatives, compound 7a exhibits much larger molar absorption
coefficients, compared to 10 and 11 and the spectrum of 16 does not
show significant red shift, compared to those of 7a.
Similar results were obtained in the case of the pyridyl de-
rivatives. Figure 3 shows absorption spectra of 3a–c in CH2Cl2,
along with those of 9, and 15. The spectra of 3a–c and 7b (Fig. 1) are
2.4. Some reactions of the ETB derivatives
When a clear yellow solution of 3a and dichloro(1,5-cyclo-
octadiene)palladium(II) (1.1 equiv) in THF was kept at room tem-
perature, pale yellow precipitate gradually formed. The precipitate
was collected and washed with chloroform. Elemental analysis of
the insoluble solid suggested formation of a dichloropalladium
complex of 3a. It is likely that the product is an intermolecular
coordination polymer 3a–PdCl2, because there is not enough space
for intramolecular chelation in the case of 3a. Insolubility of the
product may support coordination polymer structure. Elemental
analysis data of the product approximately correspond to n¼2
(Scheme 3), however, incorporation of other species in the solid is
also feasible. It should be mentioned that a mixture of 7b with
dichloro(1,5-cyclooctadiene)palladium(II) did not show such
a change under similar conditions, this fact may suggest that re-
action at the triple bond of 3a (or 7b) did not occur under these
conditions.
60000
7a
7b
10
50000
11
16
40000
30000
We then investigated connection of the ETB units (Scheme 4).
Compound 2 was used as a representative of substituted ETB units,
taking the solubility into account: to a solution of 2 in THF was
added butyllithium and the resulting red solution was reacted with
1,5-diiodopentane to give 17 in 74% yield. The conversion methods
described here, combined with those reported previously, are
expected to become fundamental tools for construction of ETB-
linked system, which may lead to artificial enzymes or metal-
loprotein-inspired molecules. Although there are problems in
solubility and compatibility of metalation in some particular cases,
further investigation on synthetic routes and strategy will conquer
the problem.
ε
20000
10000
0
280
300
320
340
360
Wavelength / nm
380
400
420
440
Figure 2. UV–vis spectra of 7a,b, 10, 11, and 16 in dimethylsulfoxide.

148
K. Toyota et al. / Tetrahedron 65 (2009) 145–151
N
N
N PdCl2
PdCl2(cod)
THF
S
S
S
7b
S
S
S
N
N
PdCl2
N
n
Scheme 3.
and the solvent was removed under reduced pressure. The residue
was treated with a silica-gel column chromatography (hexane–
EtOAc 5:1 to 0:1) to give 392.2 mg (0.571 mmol, 59% yield) of crude
3a. The crude product was recrystallized from CHCl3–hexane to
give 232.8 mg (0.339 mmol, 35% yield) of 3a. Pale yellow scales, mp
206–208 ꢀC (decomp.); Rf¼0.56 (SiO2–EtOAc); 1H NMR (400 MHz,
SiMe3
S
SiMe3
S
2
S
S
CDCl3)
d
¼7.23 (2H, m, pyridyl), 7.30 (2H, J¼5.2 Hz, thienyl), 7.40
(2H, d, J¼5.2 Hz, thienyl), 7.44 (2H, d, J¼8.0 Hz, pyridyl), 7.61 (2H,
SiMe3
SiMe3
17
ddd, J¼15.6, 8.0, and 2.0 Hz, pyridyl), 7.95 (4H, s, phenyl), and 8.60
(2H, d, J¼4.4 Hz, pyridyl); 13C{1H} NMR (100 MHz, CDCl3)
¼83.6
d
Scheme 4.
(C^C), 94.3 (C^C), 117.2 (2-thienyl), 122.7, 127.1, 127.9, 128.0, 128.2,
134.6, 136.2, 143.2, 145.7, and 150.0; UV (CH2Cl2) 243 (log 3 4.45),
256 (4.46), 302 (4.56), 323 (4.58), and 342 nm (sh, 4.48); IR (KBr)
2201 (C^C), 1580, 1561, 1539, 1505, 1466, 1439, 1426, 1404, 1368,
1302, 1281, 1246, 1152, 1113, 1088, 1048, 988, 872, 843, 830, 776,
750, 737, 631, 594, 534, and 504 cmꢁ1. Found: m/z 467.0644. Calcd
for C28H16N2NaS2: MþþNa, 467.0647. Found: C, 74.34; H, 3.88, N,
6.23%. Calcd for C28H16N2S2$(H2O)1/2: C, 74.14; H, 3.78; N, 6.18%.
3. Conclusion
In conclusion, we have prepared various bis[2-(arylethynyl or
heteroarylethynyl)-3-thienyl]arene derivatives. Fundamental syn-
thetic methods for ETB derivatives were studied, including con-
nection of the ETB spacers, which may lead to construction of
peptide-inspired architecture. Extension of
p-system through the
4.3. 1,4-Bis[2-(2-phenylethynyl)-3-thienyl]benzene (7a)
central benzene ring was suggested by UV–vis spectra and con-
nection of the units was demonstrated in the case of the ETB de-
rivatives. Further investigations on structure–property (such as
redox properties and fluorescence) relationships are now in
progress.
A mixture of 6 (1.08 g, 2.19 mmol), ethynylbenzene (560 mg,
5.48 mmol), dichlorobis(triphenylphosphine)palladium(II) (220 mg,
0.313 mmol), copper(I) iodide (31.3 mg, 0.164 mmol), and diiso-
propylamine (2.4 mL) in THF (30 mL) was stirred at 50 ꢀC for 24 h.
After removal of an insoluble material by filtration, chloroform and
water were added to the filtrate. The organic phase was washed
with brine and dried over MgSO4. The solvent was removed under
reduced pressure and the residue was treated with a silica-gel
column chromatography (hexane–CHCl3 50: 1) to give 700 mg
(1.58 mmol, 72% yield) of crude 7a. The crude product was dis-
solved in toluene (15 mL) and silica-based palladium scavenger
thiol (40 mg) was added. The resulting mixture was stirred for
30 min, filtered, and the filtrate was concentrated under reduced
pressure to give 7a (200 mg, 0.452 mmol, 21% yield). Pale yellow
powder, mp 194–196 ꢀC; Rf¼0.40 (SiO2–CCl4); 1H NMR (400 MHz,
4. Experimental
4.1. General
Melting points were measured on a Yanagimoto MP-J3 micro
melting points apparatus and were uncorrected. NMR spectra were
recorded on a Bruker Avance-400 or a JEOL JNM-GSX400. UV–vis
spectra were measured on a Hitachi U-3210 spectrometer. IR
spectra were obtained on a Horiba FT-300 spectrometer. MS spectra
were taken on a Hitachi M-2500S spectrometer. FT-ICR-MS spectra
were measured on a Bruker APEX III spectrometer. Gel permeation
chromatography was carried out using Bio-BeadsÒ S-X3 (Bio-Rad
Laboratories, Inc., 200–400 mesh). In some cross-coupling experi-
ments, silica-based palladium scavenger thiol (Silicycle, Nacalai
Tesque Inc.) was used in the work-up process.
DMSO-d6)
d
¼7.34–7.41 (6H, m), 7.50–7.52 (6H, m), 7.74 (2H, m), and
4.48), 301 (4.52), 322
8.03 (4H, s, phenyl); UV (DMSO) 283 (sh, log
3
(sh, 4.49), and 349 nm (sh, 4.37); IR (KBr) 2191 (C^C), 1593, 1503,
1487, 1487, 1433, 1300, 1067, 911, 870, 849, 822, 756, 737, 689,
652, 579, 529, and 502 cmꢁ1. Found: m/z 465.0740. Calcd for
C30H18NaS2: MþþNa, 465.0742. Found: C, 79.59; H, 4.25%. Calcd
for C30H18S2$(H2O)1/2: C, 79.79; H, 4.24%. 13C NMR spectrum was
not measured because of the poor solubility.
4.2. 1,4-Bis[2-{2-(2-pyridylethynyl)}-3-thienyl]benzene (3a)
A
mixture of 6 (480 mg, 0.972 mmol), 2-ethynylpyridine
(264.8 mg, 2.57 mmol), dichlorobis(triphenylphosphine)palla-
dium(II) (96.9 mg, 0.138 mmol), copper(I) iodide (13.7 mg,
0.0719 mmol), and diisopropylamine (1 mL) in THF (15 mL) was
stirred at 50 ꢀC for 12 h. To the resulting mixture were added
chloroform and water. The organic phase was dried over MgSO4
4.4. 1,4-Bis[2-{2-(4-butylphenyl)ethynyl}-3-thienyl]-
benzene (7b)
A mixture of 6 (1.6641 g, 3.37 mmol), 1-butyl-4-ethynylbenzene
(1.1121 g, 7.03 mmol), dichlorobis(triphenylphosphine)palladium(II)

K. Toyota et al. / Tetrahedron 65 (2009) 145–151
149
(354 mg, 0.504 mmol), copper(I) iodide (45 mg, 0.24 mmol), and
diisopropylamine (5 mL) in THF (70 mL) was stirred at 50 ꢀC for
40 h. Chloroform (ca. 200 mL) was added to the reaction mixture
and an insoluble material was removed by filtration. The organic
phase was washed with brine and dried over MgSO4. The solvent
was removed under reduced pressure and the residue was treated
with a silica-gel column chromatography (hexane–CHCl3 1:0 to
2:1) to give 1.0677 g (1.92 mmol, 57% yield) of 7b. Pale yellow
powder, mp 109–111 ꢀC; Rf¼0.49 (SiO2–CCl4); 1H NMR (400 MHz,
(hexane) to give 149.6 mg (0.583 mmol, 54% yield) of 8. Colorless
oil; Rf¼0.58 (SiO2–CCl4); 1H NMR (400 MHz, CDCl3)
¼0.23 (9H, s,
d
SiMe3), 7.19 (1H, d, J¼5.2 Hz, thienyl), 7.24 (1H, d, J¼5.2 Hz, thienyl),
7.33 (1H, m, p-phenyl), 7.41 (2H, m, m-phenyl), and 7.81 (2H, m,
o-phenyl); 13C{1H} NMR (100 MHz, CDCl3)
(C^C), 101.3 (C^C), 117.9 (2-thienyl), 126.4, 127.6, 127.7, 127.9
(o-phenyl), 128.3 (m-phenyl), 135.1 (ipso-phenyl), and 145.4
d
¼ꢁ0.28 (SiMe3), 98.2
(3-thienyl); UV (CH2Cl2) 292 nm (log 3 4.22); IR (neat) 2143 (C^C),
1489, 1250, 1094, 876, 857, 843, 758, 722, 695, and 639 cmꢁ1; MS
(70 eV) m/z (rel intensity) 256 (Mþ, 79) and 241 (MþꢁMe, 100).
Found: m/z 256.0738. Calcd for C15H16SSi: Mþ, 256.0737.
CDCl3)
d
¼0.92 (6H, t, J¼7.4 Hz, Me), 1.34 (4H, td, J¼7.6, 7.4 Hz,
CH2Me), 1.58 (4H, quin, J¼7.7 Hz, CH2), 2.60 (4H, t, J¼7.7 Hz), 7.10
(4H, d, J¼8.2 Hz, 30- and 50-phenyl), 7.28 (2H, d, J¼5.4 Hz, 4-thienyl),
7.31 (2H, d, J¼5.4 Hz, 5-thienyl), 7.39 (4H, d, J¼8.2 Hz, 20- and 60-
phenyl), and 7.95 (4H, s, 2-, 3-, 5-, and 6-phenyl); 13C{1H} NMR
4.7. 3-Phenyl-2-[2-(2-pyridyl)ethynyl]thiophene (9)
(100 MHz, CDCl3)
d
¼13.9 (CH3), 22.3 (CH2), 33.4 (CH2), 35.6 (CH2),
A mixture of 2-iodo-3-phenylthiophene (170.5 mg, 0.596 mmol),
2-ethynylpyridine (0.080 mL, 0.792 mmol), dichlorobis(triphenyl-
phosphine)palladium(II) (21.7 mg, 0.0309 mmol), copper(I) iodide
(2.1 mg, 0.011 mmol), and diisopropylamine (1 mL) in THF (10 mL)
was stirred at 50 ꢀC for 24 h. Chloroform and water were added to
the reaction mixture, the organic phase was washed with brine,
dried over MgSO4, and the solvent was evaporated under reduced
pressure. The residue was treated with a silica-gel column chro-
matography (CHCl3–EtOAc 1:0 to 25:1), silica-based palladium
scavenger thiol (100 mg) and CCl4 (10 mL) was added to crude 9,
and the mixture was stirred for 5 min. After removal of the scav-
enger by filtration, the solvent was removed under reduced pres-
sure to give 58.4 mg (0.223 mmol, 37% yield) of 9. Pale yellow oil;
82.7 (C^C), 95.7 (C^C), 118.5 (2-thienyl), 120.1 (10-phenyl), 126.3
(4-thienyl), 127.8 (5-thienyl), 127.9 (phenyl), 128.5 (phenyl), 131.2
(20- and 30-phenyl), 134.6 (1- and 4-phenyl), 143.5 (3-thienyl or
40-phenyl), and 143.8 (3-thienyl or 40-phenyl); UV (CH2Cl2) 241
(log
3
4.56), 283 (4.59), 296 (4.59), 319 (4.59), and 339 nm (sh, 4.51);
4.54), 301 (4.60), 322 (sh, 4.57), and
UV (DMSO) 283 (sh, log
3
350 nm (sh, 4.41); IR (KBr) 2195 (C^C), 1605, 1526, 1505, 1493,
1410, 1375, 1298, 1201, 1115, 1090, 1019, 866, 841, 727, 720, 644, 563,
529, and 504 cmꢁ1. Found: m/z 577.1993. Calcd for C38H34NaS2:
MþþNa, 577.1994.
4.5. 1,4-Bis[2-{2-(4-hexylphenyl)ethynyl}-3-thienyl]-
benzene (7c)
Rf¼0.65 (SiO2–EtOAc); 1H NMR (600 MHz, CDCl3)
¼7.21 (1H, ddd,
d
J¼7.6, 4.9, and 1.1 Hz, 5-pyridyl), 7.23 (1H, d, J¼5.3 Hz, 4-thienyl),
7.35 (1H, d, J¼5.3 Hz, 5-thienyl), 7.36 (1H, m, p-phenyl), 7.40 (1H,
ddd, J¼7.8, 1.1, and 0.9 Hz, 3-pyridyl), 7.45 (2H, m, m-phenyl), 7.64
(1H, ddd, J¼7.8, 7.6, and 1.7 Hz, 4-pyridyl), 7.83 (2H, m, o-phenyl),
and 8.60 (1H, ddd, J¼4.9, 1.7, and 0.9 Hz, 6-pyridyl); 13C{1H} NMR
A mixture of 6 (268.9 mg, 0.544 mmol), 1-ethynyl-4-hexyl-
benzene (289.6 mg, 1.55 mmol), dichlorobis(triphenylphosphine)-
palladium(II) (56.0 mg, 0.080 mmol), copper(I) iodide (8.5 mg,
0.045 mmol), and diisopropylamine (0.6 mL) in THF (8 mL) was
stirred at 50 ꢀC for 24 h. Chloroform (ca. 20 mL) was added to the
reaction mixture and an insoluble material was removed by fil-
tration. The organic phase was washed with brine and dried over
MgSO4. The solvent was removed under reduced pressure and the
residue was treated with a silica-gel column chromatography
(hexane–CCl4 1:0 to 0:1) to give 191.7 mg (0.314 mmol, 58% yield)
of 7c. Pale yellow solid, mp 86–88 ꢀC; Rf¼0.53 (SiO2–CCl4); 1H NMR
(150 MHz, CDCl3)
d
¼83.3 (C^C), 94.1 (C^C),117.0 (2-thienyl),122.7
(5-pyridyl), 127.0 (3-pyridyl), 127.8 (p-phenyl), 128.0 (4-thienyl,
o-phenyl), 128.5 (m-phenyl), 135.1 (ipso-phenyl), 136.0 (4-pyridyl),
143.3 (2-pyridyl), 146.1 (3-thienyl), and 150.1 (6-pyridyl); UV
(CH2Cl2) 287 (log 3 4.12) and 326 nm (4.29); IR (neat) 2201 (C^C),
1582, 1561, 1489, 1464, 1449, 1431, 1412, 1298, 1283, 1248, 1150,
1140, 988, 876, 776, 725, 696, 660, and 579 cmꢁ1. Found: m/z
262.0683. Calcd for C17H12NS: MþþH, 262.0685.
(400 MHz, CDCl3)
d
¼0.88 (6H, t, J¼6.7 Hz, Me), 1.29 (12H, m, CH2),
1.59 (4H, m, CH2), 2.59 (4H, t, J¼7.7 Hz), 7.10 (4H, d, J¼8.2 Hz, 30- and
50-phenyl), 7.28 (2H, d, J¼5.3 Hz, 4-thienyl), 7.31 (2H, d, J¼5.3 Hz,
5-thienyl), 7.39 (4H, d, J¼8.2 Hz, 20- and 60-phenyl), and 7.95 (4H, s,
4.8. 3-Phenyl-2-(2-phenylethynyl)thiophene (10)
2-, 3-, 5-, and 6-phenyl); 13C{1H} NMR (100 MHz, CDCl3)
d¼14.1
A
mixture
of
2-iodo-3-phenylthiophene
(201.6 mg,
(CH3), 22.6 (CH2), 28.9 (CH2), 31.2 (CH2), 31.7 (CH2), 35.9 (CH2), 82.7
(C^C), 95.7 (C^C), 118.4 (2-thienyl), 120.1 (10-phenyl), 126.3
(4-thienyl), 127.8 (5-thienyl), 127.9 (phenyl), 128.5 (phenyl), 131.2
(20- and 30-phenyl), 134.5 (1- and 4-phenyl), 143.5 (3-thienyl or
40-phenyl), and 143.8 (3-thienyl or 40-phenyl); UV (CH2Cl2) 282
0.705 mmol), ethynylbenzene (0.1 mL, 0.91 mmol), dichlorobis-
(triphenylphosphine)palladium(II) (24.9 mg, 0.0355 mmol), cop-
per(I) iodide (1.4 mg, 0.0074 mmol), and diisopropylamine (1 mL)
in THF (10 mL) was stirred at 50 ꢀC for 36 h. Chloroform and water
were added to the reaction mixture, the organic phase was washed
with brine, dried over MgSO4, and the solvent was evaporated
under reduced pressure. The residue was treated with a silica-gel
column chromatography using CCl4 as an eluent. A silica-based
palladium scavenger thiol (100 mg) was added to the collected
fraction of 10 and the mixture was stirred for 10 min. After removal
of the scavenger by filtration, the solvent was removed under re-
duced pressure to give 124.3 mg (0.477 mmol, 68% yield) of 10. Pale
(log 3 4.43), 297 (4.44), 318 (4.44), and 342 nm (sh, 4.34); IR (KBr)
1526, 1505, 1458, 866, 841, 820, 722, 716, 644, 562, 538, 521, and
504 cmꢁ1. Found: m/z 633.2618. Calcd for C42H42NaS2: MþþNa,
633.2620.
4.6. 3-Phenyl-2-[2-(trimethylsilyl)ethynyl]thiophene (8)
A
mixture
of
2-iodo-3-phenylthiophene12
(307.1 mg,
yellow oil; Rf¼0.49 (SiO2–CCl4); 1H NMR (600 MHz, CDCl3)
¼7.21
d
1.073 mmol), ethynyltrimethylsilane (0.20 mL, 1.4 mmol), dichlor-
obis(triphenylphosphine)palladium(II) (33.4 mg, 0.048 mmol),
copper(I) iodide (2.8 mg, 0.015 mmol), and diisopropylamine
(1.5 mL) in THF (16 mL) was stirred at 50 ꢀC for 48 h. Chloroform
(ca. 100 mL) and water (ca. 100 mL) were added to the reaction
mixture, the organic phase was washed with brine, dried over
MgSO4, and the solvent was evaporated under reduced pressure.
The residue was treated with a silica-gel column chromatography
(1H, d, J¼5.3 Hz, 4-thienyl), 7.28 (1H, d, J¼5.3 Hz, 5-thienyl), 7.3–7.4
(4H, m, p-, p0- and m0-phenyl), 7.4–7.5 (4H, m- and o0-phenyl), and
7.83 (2H, m, o-phenyl); 13C{1H} NMR (150 MHz, CDCl3)
d
¼83.3
(C^C), 95.1 (C^C), 118.1 (2-thienyl), 123.1 (ipso0-phenyl), 126.5 (5-
thienyl), 127.6 (p-phenyl), 127.9 (o-phenyl), 128.0 (4-thienyl), 128.3
(p0-phenyl), 128.3 (m0-phenyl), 128.4 (m-phenyl), 131.3 (o0-phenyl),
135.3 (ipso-phenyl), and 144.7 (3-thienyl); UV (DMSO) 283 (sh, log
3
4.12) and 323 nm (4.28); UV (CH2Cl2) 247 (log 4.31), 280 (sh, 4.09),
3

150
K. Toyota et al. / Tetrahedron 65 (2009) 145–151
and 321 nm (4.29); IR (neat) 2199 (C^C), 1599, 1485, 1449, 1443,
2143 (C^C),1491, 1250, 1092, 847, 828, 758, 733, and 712 cmꢁ1
.
1296, 1084, 1071, 914, 876, 768, 754, 723, 689, 656, and 565 cmꢁ1
.
Found: m/z 533.1220. Calcd for C30H30NaS2Si2: MþþNa, 533.1220.
Found: m/z 283.0552. Calcd for C18H12NaS: MþþNa, 283.0552.
4.12. 4,40-Bis[2-{2-(2-pyridyl)ethynyl}-3-thienyl]biphenyl (15)
4.9. 4,40-Di(3-thienyl)biphenyl (12)
A mixture of 13 (crude, 221 mg, ca. 0.39 mmol), 2-ethynylpyr-
idine (151 mg, 1.46 mmol), dichlorobis(triphenylphosphine)-
palladium(II) (49 mg, 0.698 mmol), copper(I) iodide (7.6 mg,
0.040 mmol), and diisopropylamine (0.6 mL) in THF (8 mL) was
stirred at 50 ꢀC for 24 h. To the resulting mixture were added
chloroform and water. The organic phase washed with brine, dried
over MgSO4, and the solvent was removed under reduced pressure.
The residue was treated with a silica-gel column chromatography
(hexane–EtOAc 3:1), gel permeation chromatography (Bio-BeadsÒ
S-X3 using CH2Cl2 as eluent), and silica-based palladium scavenger
thiol. The product was recrystallized from CHCl3–EtOH to give
126 mg (0.242 mmol, 38% yield based on 12) of 15. Yellow scales,
mp 273–275 ꢀC; Rf¼0.59 (SiO2–EtOAc); 1H NMR (400 MHz, CD2Cl2)
A mixture of 4,40-diiodobiphenyl (1.23 g, 3.03 mmol), 3-thio-
pheneboronic acid (1.0 g, 7.81 mmol), tetrakis(triphenylphos-
phine)palladium (234 mg, 0.202 mmol), K2CO3 (4.10 g), toluene
(15 mL), THF (10 mL), and water (5 mL) was heated at 85 ꢀC for
24 h. Precipitates was collected by filtration and washed with
chloroform to give 12 (900 mg, 2.83 mmol) in 93% yield. This
compound was almost insoluble in common solvents and used in
the succeeding reaction without recrystallization. Compound 12.
Colorless powder, mp>300 ꢀC; IR (KBr) 1530, 1491, 1206, 866, 831,
777, and 635 cmꢁ1; MS (70 eV) m/z (rel intensity) 318 (Mþ; 100).
Found: C, 69.84; H, 4.30%. Calcd for C20H14S2$(H2O)3/2: C, 69.53; H,
4.96%.
d¼7.28–7.32 (2H, m, pyridyl), 7.35 (2H, d, J¼5.2 Hz, thienyl), 7.47
4.10. 4,40-Bis(2-iodo-3-thienyl)biphenyl (13)
(2H, d, J¼5.2 Hz, thienyl), 7.51 (2H, d, J¼8.0 Hz, pyridyl), 7.75 (2H, m,
pyridyl), 7.82 (4H, m, phenyl), 7.99 (4H, m, phenyl), and 8.61 (2H, m,
A suspension of 12 (100 mg, 0.314 mmol), N-iodosuccinimide
(38.5 mg, 0.171 mmol, 0.54 molar ratio), and acetic acid (2 mL) in
chloroform (5 mL) was stirred at 50 ꢀC for 6 h. The insoluble
starting material was removed by filtration and the filtrate was
treated with saturated aqueous NaHCO3 and then saturated aque-
ous Na2S2O3 solution. The organic phase was washed with brine,
dried over MgSO4, and the solvent was removed under reduced
pressure. The residue was treated with a silica-gel column chro-
matography (hexane–CHCl3 50:1) to give 20 mg (0.035 mmol, 41%
yield based on N-iodosuccinimide) of 13 and 77.4 mg (77% re-
covery) of 12. Compound 13. Colorless powder, mp 180–184.5 ꢀC
pyridyl); 13C{1H} NMR (100 MHz, CDCl3)
117.1 (2-thienyl), 122.8 (arom), 127.1 (arom), 127.2 (arom), 127.9
(arom), 128.0 (arom), 128.5 (arom), 134.3 (arom), 136.3 (arom),
140.0 (arom), 143.2 (arom), 145.7 (arom), and 150.0 (arom); UV
d
¼83.7 (C^C), 94.3 (C^C),
(CH2Cl2) 302 (log 3 4.70), 336 (sh, 4.65), and 349 nm (4.60); IR (KBr)
2201 (C^C), 1582, 1561, 1493, 1466, 1420, 1298, 1283, 1244, 1150,
1003, 988, 874, 826, 776, 754, 745, 631, 579, and 502 cmꢁ1. Found:
m/z 543.0957. Calcd for C34H20N2NaS2: MþþNa, 543.0960. Found: C,
77.07; H, 4.03; N, 5.31%. Calcd for C34H20N2S2$(H2O)1/2: C, 77.10; H,
4.00, N, 5.29%.
(decomp.); 1H NMR (400 MHz, CDCl3)
d
¼7.02 (2H, dd, J¼5.6 Hz, 4-
4.13. 4,40-Bis[2-(2-phenylethynyl)-3-thienyl]biphenyl (16)
thienyl), 7.52 (2H, d, J¼5.6 Hz, 5-thienyl), 7.62 (4H, d, J¼7.8 Hz,
phenyl), and 7.72 (4H, d, J¼7.8 Hz, phenyl); 13C{1H} NMR (150 MHz,
A mixture of 13 (crude, 352 mg, ca. 0.62 mmol), ethynylbenzene
(0.19 mL, 1.70 mmol), dichlorobis(triphenylphosphine)palladium(II)
(49 mg, 0.095 mmol), copper(I) iodide (9.4 mg, 0.049 mmol), and
diisopropylamine (0.8 mL) in THF (10 mL) was stirred at 50 ꢀC for
24 h. To the resulting mixture were added chloroform and water.
The organic phase was dried over MgSO4, treated with silica-based
palladium scavenger thiol, and the solvent was removed under
reduced pressure. The residue was treated with a silica-gel column
chromatography (hexane to hexane–CCl4 10:1) and the product
was recrystallized from hexane–CHCl3 to give 103 mg (0.199 mmol)
of 16 (20% yield based on 12). Compound 16. Yellow powder, mp
206–209 ꢀC (decomp.); Rf¼0.38 (SiO2–CCl4); 1H NMR (600 MHz,
CDCl3)
d
¼73.1 (2-thienyl), 127.0 (biphenyl), 129.0 (5-thienyl), 129.2
(biphenyl), 131.2 (4-thienyl), 135.7 (ipso-biphenyl), 139.8 (ipso-bi-
phenyl), and 146.2 (3-thienyl); UV (CH2Cl2) 258 (log 4.43) and
298 nm (4.56); IR (KBr) 1526, 1491, 1406, 1347, 1312, 1242, 1003,
3
953, 866, 831, 816, 779, 729, 714, 679, 652, 629, 519, and 469 cmꢁ1
;
MS (70 eV) m/z (rel intensity) 570 (Mþ, 100). Found: m/z 569.8471.
Calcd for C20H12I2S2: Mþ, 569.8464.
4.11. 4,40-Bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]-
biphenyl (14)
A mixture of 13 (crude, 364.6 mg, ca. 0.64 mmol), ethynyl-
CDCl3)
d
¼7.28 (2H, d, J¼5.4 Hz, 4-thienyl), 7.33 (2H, d, J¼5.4 Hz,
trimethylsilane (226
mL, 1.6 mmol), dichlorobis(triphenylphos-
4-thienyl), 7.31–7.39 (6H, m, m- and p-Ph), 7.50 (4H, m, o-Ph),
7.75 (4H, d, J¼8.4 Hz, phenyl), and 7.95 (4H, d, J¼8.4 Hz, phenyl);
phine)palladium(II) (61.8 mg, 0.088 mmol), copper(I) iodide
(8.9 mg, 0.047 mmol), and diisopropylamine (0.6 mL) in THF (9 mL)
was stirred at 50 ꢀC for 17 h. After removal of an insoluble material
by filtration, chloroform and water were added to the filtrate. The
organic phase was washed with brine and dried over MgSO4. The
solvent was removed under reduced pressure and the residue was
treated with a silica-gel column chromatography (CCl4), and gel
permeation column chromatography (Bio-BeadsÒ S-X3 using
CH2Cl2 as eluent) to give 46.0 mg (0.090 mmol, 14% yield) of 14.
Colorless scales, mp 214–216 ꢀC; Rf¼0.49 (SiO2–CCl4); 1H NMR
13C{1H} NMR (150 MHz, CDCl3)
d¼83.4 (C^C), 95.4 (C^C), 118.2
(2-thienyl), 123.1 (ipso-Ph), 126.6 (5-thienyl), 127.0 (biphenyl),
127.9 (4-thienyl), 128.4 (biphenylþm- and p-Ph), 131.3 (o-Ph), 134.5
(ipso-biphenyl), 139.8 (ipso-biphenyl), and 144.2 (3-thienyl); UV
(DMSO) 296 (log 3 4.67); UV (CH2Cl2) 293 (log 3 4.69) and 317 nm
(sh, 4.64); IR (KBr) 2204 (C^C), 1597, 1572, 1524, 1497, 1487, 1443,
1431, 1402, 1375, 1298, 1082, 1069, 1026, 1003, 909, 872, 824, 754,
735, 714, 687, 525, and 450 cmꢁ1. Found: m/z 541.1057. Calcd for
C36H22NaS2: MþþNa, 541.1055.
(600 MHz, CDCl3)
d
¼0.26 (18H, s, SiMe3), 7.24 (2H, d, J¼5.1 Hz, 5-
thienyl), 7.27 (2H, d, J¼5.1 Hz, 4-thienyl), 7.69 (4H, AA0BB0, 2-, 20-, 6-,
4.14. Reaction of 3a with dichloro(1,5-cyclo-
octadiene)palladium(II)
60-phenyl), and 7.92 (4H, AA0BB0, 3-, 30-, 5-, 50-phenyl); 13C{1H} NMR
(150 MHz, CDCl3)
d
¼ꢁ0.23 (SiMe3), 98.3 (TmsC^C), 101.8
(TmsC^C), 118.0 (2-thienyl), 126.5 (5-thienyl), 126.9 (2-, 20-, 6-, 60-
phenyl), 127.6 (4-thienyl), 128.3 (3-, 30-, 5-, 50-phenyl), 134.3 (4-, 40-
phenyl), 139.8 (1-, 10-phenyl), and 144.7 (3-thienyl); UV (CH2Cl2)
Compound 3a (27.5 mg, 0.0619 mmol) and dichloro(1,5-cyclo-
octadiene)palladium(II) (18.9 mg, 0.0662 mmol) was solved in
15 mL of THF. The resulting clear yellow solution was kept at room
temperature for 75 h and pale yellow precipitates formed
271 (log 3 4.51), 293 (4.52), 302 (4.52), and 329 nm (4.56); IR (KBr)

K. Toyota et al. / Tetrahedron 65 (2009) 145–151
151
gradually. The precipitates were collected by filtration and washed
References and notes
with chloroform to give 26.7 mg (ca. 70% yield) of product. This
product was hardly soluble in common solvent. Yellow solid; IR
(KBr): 2197 (C^C), 1593, 1563, 1478, 1426, 1246, 1159, 874, 853, 826,
774, and 737 cmꢁ1. Found: C, 57.23; H, 3.27; Cl, 8.90, N, 4.74, S,
10.94%. Calcd for C28H16N2S2$(Cl2Pd)0.75(H2O)0.25: C, 57.78; H, 2.86,
Cl, 9.14, N, 4.81, S, 11.02%.
1. Reed, A. C. Acc. Chem. Res. 2005, 38, 215–216 and papers in this issue of the
journal; For recent reports on oligophenylene rods, see for example: Sisson, A.
L.; Sakai, N.; Banerji, N.; Fu¨ rstenberg, A.; Vauthey, E.; Matile, S. Angew. Chem.,
Int. Ed 2008, 47, 3727–3729; Tsubaki, K.; Takaishi, K.; Sue, D.; Matsuda, K.;
Kanemitsu, Y.; Kawabata, T. J. Org. Chem. 2008, 73, 4279–4282; Ryu, J.-H.; Hong,
D.-J.; Lee, M. Chem. Commun. 2008, 1043–1054 and references cited therein.
2. For 1,2-dithienyl-3,4-diphosphinidenecyclobutene (DPCBT) ligands, see:
Toyota, K.; Abe, K.; Horikawa, K.; Yoshifuji, M. Bull. Chem. Soc. Jpn. 2004, 77,
1377–1383; Nakamura, A.; Kawasaki, S.; Toyota, K.; Yoshifuji, M. J. Organomet.
Chem. 2007, 692, 70–78.
3. Toyota, K.; Tashiro, K.; Yoshifuji, M. Chem. Lett. 1991, 2079–2082; Toyota, K.;
Horikawa, K.; Jensen, R. S.; Omori, K.; Kawasaki, S.; Ito, S.; Yoshifuji, M.; Morita,
N. Bull. Chem. Soc. Jpn. 2007, 80, 1580–1586 and references cited therein.
4. Toyota, K.; Masaki, K.; Abe, T.; Yoshifuji, M. Chem. Lett. 1995, 221–222; Toyota,
K.; Ujita, J.; Kawasaki, S.; Abe, K.; Yamada, N.; Yoshifuji, M. Tetrahedron Lett.
2004, 45, 7609–7612.
5. Toyota, K.; Goto, Y.; Okada, K.; Morita, N. Heterocycles 2007, 71, 2227–2236.
6. Compared to the well-investigated 2,5-thienylene spacers, much less attention
hasbeenpaid to2,3-thienylene
p-spacerand studies were limited. For2,3-diaryl-
or diethynylthiophene derivatives, see for example: Nakano, M.; Satoh, T.; Miura,
M. J. Org. Chem. 2006, 71, 8309–8311; Su, Y. Z.; Lin, J. T.; Tao, Y.-T.; Ko, C.-W.; Lin, S.-
C.; Sun, S.-S. Chem. Mater. 2002, 14, 1884–1890; Johnson, C. A., II; Baker, B. A.;
Berryman, O. B.; Zakharov, L. N.; O’Connor, M. J.; Haley, M. M.
J. Organomet. Chem. 2006, 691, 413–421; Marsella, M. J.; Wang, Z.-Q.; Reid, R. J.;
Yoon, K. Org. Lett. 2001, 3, 885–887; For 1,4-bis(2-substituted-3-thienyl)benzene
derivatives, see forexample: Ribereau, P.; Queguiner, G.; Pastour, P. Bull. Soc. Chim.
Fr. 1972, 1581–1587; Nitschke, J. R.; Don Tilley, T. J. Organomet. Chem. 2003, 666,
15–22; Matsukawa, S.; Fukushima, T.; Aida, T. Japan Kokai Tokkyo Koho JP
320299, 2005; Chem. Abstr. 2005, 143, 460137; Fukushima, T.; Matsukawa, S.;
Aida, T.; Tokuhiro, A.; Saito, K.; Iida, K.; Nakayama, K. Japan Kokai Tokkyo Koho JP
347661, 2005; Chem. Abstr. 2005, 144, 62625; Ikeda, M.; Tanifuji, N.; Yamaguchi,
H.; Irie, M.; Matsuda, K. Chem. Commun. 2007, 1355–1357.
4.15. Compound 17
To a solution of 2 (200 mg, 0.46 mmol) in THF (20 mL) was
added 0.30 mL (0.48 mmol) of butyllithium (1.61 M solution in
hexane) at ꢁ78 ꢀC. The resulting mixture was stirred at ꢁ78 ꢀC for
5 min and allowed to warm. This solution was transferred to
a
cooled solution (ꢁ78 ꢀC) of 1,5-diiodopentane [30
mL
(0.23 mmol)] in THF (5 mL). The reaction mixture was stirred at
ꢁ78 ꢀC for 5 min, allowed to warm to room temperature, and
stirred at 50 ꢀC for 4 h. To the resulting mixture were added chlo-
roform and water. The organic phase was washed with brine, dried
over MgSO4, and the solvent was removed under reduced pressure.
Silica-gel column chromatography (hexane–CHCl3 3:1) followed by
gel permeation column chromatography (Bio-BeadsÒ S-X3 using
CH2Cl2 as eluent) afforded 160 mg (0.17 mmol, 74% yield) of 17.
Colorless solid, mp 31–34 ꢀC; Rf¼0.15 (SiO2–hexane); 1H NMR
(400 MHz, CDCl3)
(6H, br, CH2), 2.55 (4H, br, thienyl-CH2), 7.19–7.31 (6H, m, thienyl),
7.79–7.81 (4H, m, Ph), and 7.86–7.88 (4H, m, phenyl); UV (CH2Cl2)
d
¼0.25 (18H, s, SiMe3), 0.34 (18H, s, SiMe3), 1.58
7. For 4,40-di(3-thienyl)biphenyl derivatives, only two reports have been pub-
lished: Rodlovskaya, E. N.; Frolova, N. G.; Savin, E. D.; Nedel’kin, V. I. Russian
Patent 2230743, 2004; Chem. Abstr. 2004, 141, 261186; Cho, H. -N.; Jung, S. H.;
Park, S. -J.; Lee, S. -E. U.S. Patent 067,955, 2005; Chem. Abstr. 2005, 142, 363393
(No reports on 4,40-bis(2-substituted 3-thienyl)biphenyl derivatives without
fused ring.).
8. This concept of the ETB spacer for protein-inspired molecules was presented at
33rd Symposium on Main Group Element Chemistry, Fukuoka, Dec, 2006;
Abstr. O-45 and the 87th National Meeting of the Chemical Society of Japan,
Osaka, Mar, 2007; Abstr. No. 3D3-43. For related concept of benzoylurea as
peptide mimetics, see: Rodriguez, J. M.; Hamilton, A. D. Angew. Chem., Int. Ed.
2007, 46, 8614–8617.
263 (log 3 4.79), 288 (4.75), and 322 nm (4.58); IR (KBr) 2141 (C^C),
1539, 1491, 1406, 1350, 1250, 1177, 1115, 1090, 999, 839, 758, 723,
698, 652, 630, and 534 cmꢁ1. Found: m/z 959.2554. Calcd for
C53H60NaS4Si4: MþþNa, 959.2547.
9. A part of this work has been presented at the 88th National Meeting of the
Chemical Society of Japan, Tokyo, Mar, 2008; Abstr. No. 1H4-29.
Acknowledgements
10. Bohlmann, F.; Herbst, P. Chem. Ber. 1962, 95, 2945–2955.
The authors thank Dr. Hideji Osuga, Wakayama University, for
his suggestion about the use of DMSO for solvation of 7a. This work
was supported in part by the Grants-in-Aid for Scientific Research
(No. 20550030) from the Ministry of Education, Culture, Sports,
Science and Technology.
11. Because compound 7b turned out to be soluble in benzonitrile, cyclic voltam-
metric measurement of 7b was carried out in benzonitrile [1 mM solution,
supporting electrolyte: Et4NClO4 (0.1 M), scan rate: 100 mV sꢁ1]. Compound 7b
showed an irreversible oxidation wave with Ep(ox)¼1.20 V (vs Ag/AgNO3).
12. Johnson, A. L. J. Org. Chem. 1976, 41, 1320–1324; See also: Gronowitz, S.; Gjo¨s, N.
J. Org. Chem. 1967, 32, 463–464.