Novel ladder π-conjugated materials - Sila-pentathienoacenes: Synthesis, structure, and electronic properties

Article abstract of DOI:10.1002/asia.201000287

A novel series of ladder π-conjugated materials-sila-pentathienoacenes (Si-PTA) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on m

Full text of DOI:10.1002/asia.201000287

FULL PAPERS
DOI: 10.1002/asia.201000287
Novel Ladder p-Conjugated Materials—Sila-Pentathienoacenes: Synthesis,
Structure, and Electronic Properties
Jun-Hua Wan, Wei-Fen Fang, Zhi-Fang Li, Xu-Qiong Xiao, Zheng Xu, Yuan Deng,
Li-Hong Zhang, Jian-Xiong Jiang, Hua-Yu Qiu, Lian-Bin Wu,* and Guo-Qiao Lai*[a]
Abstract: A novel series of ladder p-
conjugated materials—sila-pentathie-
noacenes (Si-PTA) are synthesized and
characterized. Crystal structures of the
compounds show that the length of
alkyl chains substituting on the thio-
phene ring has a significant influence
compound with shorter alkyl chains.
However, a large interfacial distance
(7.99 ꢀ) is obtained for another com-
pound because of the insertion of long
alkyl chains between two planes. The
investigation of the optical and electro-
chemical properties shows that the sily-
lene bridge incorporated into the pen-
tathienoacene framework exerts a clear
effect on the electronic properties by
the s*–p* conjugation. Although only
a slight enhancement is observed for
the HOMO levels, with respect to that
of pentathienoacene, the LUMO levels
are significantly lowered. The observed
electronic properties are consistent
with the theoretical calculations.
on molecular packing.
A
densely
Keywords: conjugation
·
ladder
packed structure with an interfacial dis-
tance of about 3.66 ꢀ between the ad-
jacent molecules is observed for the
compounds · polycycles · semicon-
ductors · silicon
Introduction
attained by introducing fused thiophene aromatics into the
p-conjugated polymers.
The design and synthesis of new molecular building blocks
in the field of organic electronics are attracting much atten-
tion because of their application in organic field-effect tran-
sistors (OFETs),[1] organic light-emitting diodes (OLEDs),[2]
and photovoltaic cells.[3] Ladder p-conjugated systems with
fused polycyclic skeletons are an important class of com-
pounds for organic-electronic materials because of their ef-
fective extension of the p-conjugation without any confor-
mational disorder.[4] Among various ladder p-conjugated
systems, fused thiophene aromatics have recently been de-
veloped as new organic semiconductors, which are one of
the most promising candidates for organic field-effect tran-
sistors (OFETs) because of their high hole mobility.[5–7] Fur-
thermore, several recent reports have shown that a high
hole mobility[8] and power conversion efficiency (PCE)[9] are
The incorporation of silylene into the p-conjugated frame-
work forming silole rings is a powerful strategy for the
design of new promising functional molecules applicable for
organic electronics.[10] The electronic properties of the whole
p-conjugated system will be remarkably modified by the
silole substructure, because the LUMO is significantly low-
ered arising from the effective s*–p* conjugation between
an exocyclic s* orbital on the silicon atom and the p* orbi-
tal of the butadiene moiety.[11] In this context, we have de-
signed and synthesized new p-conjugated systems obtained
by replacing the central sulfur atom of pentathienoacene
(PTA) with a silylene moiety (sila-pentathienoacene, Si-
PTA). By introducing long alkyl chains on two terminal
thiophene rings, the soluble sila-pentathienoacene was ob-
tained (Scheme 1). However, the crystal structure showed
that the unexpected molecular-packing structure was formed
because of the insertion of the long alkyl chains between
the adjacent molecular planes. For the sake of densely face-
to-face stacking of the new fused polycyclic skeleton in the
solid state, the other sila-pentathienoacene compound with
two methyl groups was also synthesized (see Scheme 1). The
length of alkyl chains has a clear influence on the molecu-
lar-packing structures. Systematic studies of their electronic
properties have shown that the HOMO and LUMO levels,
and the optical properties in solution are very different from
[a] Dr. J.-H. Wan, W.-F. Fang, Dr. Z.-F. Li, Dr. X.-Q. Xiao, Dr. Z. Xu,
Y. Deng, L.-H. Zhang, Prof. J.-X. Jiang, Prof. H.-Y. Qiu,
Dr. L.-B. Wu, Prof. G.-Q. Lai
Key Laboratory of Organosilicon Chemistry and Material Technology
of Ministry of Education
Hangzhou Normal University
222 Wenyi Road, Hangzhou, 310012(P.R. China)
Fax : (+86)571-2886-8081
E-mail: gqlai@hznu.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201000287.
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ꢀ
group (7b), the signal of Si CH3 was shifted to ꢀ4.97 ppm.
Similarly, the 29Si NMR signal at ꢀ8.13 for SiMe2 in 7a was
shifted reasonably to d=ꢀ13.9 ppm for SiMePh in 7b.
Crystal Structures of 7a and 8
Single crystals of 7a and 8 suitable for X-ray analysis were
obtained by slow evaporation from a hexane/CH2Cl2 mixed
solvent at room temperature. As shown in Figure 1, the mo-
lecular structure of 7a shows that the ring skeleton is almost
planar, and the alkyl chains adopt an extended trans zig-zag
conformation. In the crystal structure, the ring planes stack
face-to-face but the distance between two adjacent molecu-
lar planes (7.99 ꢀ) is very large because of the insertion of
long alkyl chains between the two planes. However, it is in-
teresting that the crystal structure of 8 is clearly different
from that of 7a (see Figure 2). The close p-stacking was
formed with an interfacial distance of 3.66 ꢀ between the
adjacent molecules. Because of the tetracoordinate silicon
bridge, all adjacent molecules stack with trans configurations
to form a densely packed structure. This might be beneficial
for achieving high carrier mobility. Remarkably, the length
of the alkyl chains has a pronounced influence on the mo-
Scheme 1. Synthetic routes for Si-PTA.
those of PTA and the related p-conjugated system, bis(ben-
zothieno)silole (BBTS) that have recently been synthesized
by Ohshita and Kunai.[12] Like chemically modified small di-
thienosiloles (DTS)[8a,b,9a,13] and tetrathienoacenes,[8c] Si-PTA
is a promising building block in p-conjugated polymers and
oligomers for FET and photovoltaic applications.
Results and Discussion
Synthesis
Scheme 1 depicts the synthetic route to sila-pentathienoa-
cenes 7a,b, and 8. A key intermediate 6 was synthesized
using the reported methodology.[14] Through the five-step re-
action, 6 was synthesized with an acceptable yield (total
yield: 17%) starting from 3,4-dibromothiophene. The target
compounds were obtained according to the classical method
from 6. Thus, 6 was treated with two equivalents of nBuLi
to produce the corresponding dianion, which was then
quenched with the corresponding dichlorosilane. All sila-
pentathienoacene derivatives were obtained in moderate
yields.
Figure 1. Crystal packing of 7a. a) Molecular arrangement in a single
crystal; b) side view; c) top view.
The structure and purity of 7a,b, and 8 were confirmed by
1H, 13C, and 29Si NMR, and MALDI–HRMS. A singlet at
about d=6.90 ppm, a triplet in the region of d=2.69–
2.74 ppm, and a singlet at higher fields than d=1.0 ppm
(0.53 ppm and 0.77 ppm for 7a and 7b, 0.52 ppm for 8) ob-
1
served in the H NMR spectra of 7a,b, and 8 are assigned to
be the terminal thiophene ring protons, methylene protons
ꢀ
attached to the thiophene rings, and Si CH3 protons, respec-
tively. All the signals showed relative integration values ex-
pected for their structures. A 13C NMR signal at below
ꢀ4.0 ppm (ꢀ4.12 ppm and ꢀ4.18 ppm for 7a and 8, respec-
ꢀ
tively) is assigned to the Si CH3 carbons in these Si-PTAs.
Figure 2. Crystal packing of 8. a) Molecular arrangement in a single crys-
tal; b) side view; c) top view.
When one of the methyl group was replaced with a phenyl
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L.-B. Wu, G.-Q. Lai et al.
FULL PAPERS
lecular-packing structures. To the best of our knowledge, the
significant effect of alkyl length on the molecular-packing
structure is seldom reported as yet.[15]
Optical Absorption and Fluorescence Behavior
UV/Vis absorption spectra of 7a,b, and 8 in toluene solu-
tions and those of thin films prepared by a drop-casting
method are shown in Figures 3 and 4, respectively. In solu-
tion, 7a shows two distinct absorption bands with maxima at
292 and 392 nm. A similar two-band feature was observed
for 7b in toluene, but the two bands are slightly red-shifted
ꢀ
with maxima at 294 and 397 nm, indicating that Si Ph ex-
Figure 4. Absorption and photoluminescence spectra of 8 in different en-
vironments. The concentration of all the solutions is kept to be 1ꢂ
10ꢀ4 molLꢀ1. The films were prepared by drop-casting from a solution of
toluene.
tends the molecular conjugation to a certain degree. The ab-
sorption spectra of the films of 7a and 7b are similar to the
corresponding spectra in toluene solution, but show a slight
red-shift and clear broadening compared to those in solu-
tion, suggesting a weak intermolecular interaction. There is
no dependence of the absorption maxima on the solvent po-
larity. The spectrum of 7a in THF is the same as that in tol-
uene (Figure 3a). It is expected that the absorption of 8 in
dilute toluene exhibited no difference compared to that of
7a as shown in Figure 4. However, a large blue shift (30 nm)
and broadening in the absorption spectra of the solid film of
8 was observed with the absorption band exhibiting a maxi-
mum at about 358 nm. The absorption band with maximum
at about 290 nm exhibited no clear shift besides broadening.
Based on the exciton-coupling theory, a pronounced blue
shift of the absorption with remarkable spectrum broaden-
ing strongly suggests the formation of H-aggregates with
face-to-face stacking of the fused polycyclic skeleton.[16] Ap-
parently, this point is consistent with its crystal structure.
Fluorescence spectra of 7a,b, and 8 in solution and film
states are also shown in Figures 3 and 4, respectively. In tol-
uene, all compounds exhibit only one maximum emission at
around 470 nm. The emission of 8 in film showed a slight
red shift (5 nm) in comparison with that in solution. In
Table 1, the absorption, emission, and estimated band gap
data are summarized.
The absorption spectra of Si-PTAs are evidently different
from those of pentathienoacene (PTA) and FT5 reported by
Liu and He, which show only one broad absorption band in
the region of 250–360 nm with distinct vibronic fine struc-
ture.[5a,14] The emission maxima of 7 and 8 are far longer
than that of PTA (407 nm). All these results demonstrate
that replacing the central sulfur in PTA with a silylene, re-
sults in unexpectedly large effects on the electronic structure
of the whole p-system arising from the effective s*–p* con-
jugation in the silole moiety. Fluorescence quantum yields
of 7a and 7b in solution (0.7 and 0.81) are remarkably high
in comparison to that of PTA (0.27), whereas the emission
of the solid films of the Si-PTA is very weak, similar to that
of the oligothiophene films.
The UV absorption and emission maxima of bis(benzo-
thieno)siloles (BBTS) are reported to be approximately 40
and 35 nm longer than those of DTS, respectively.[10e,12] In-
terestingly, the absorption and emission of 7a and 7b occur
at wavelengths 10 nm longer than those of BBTS. Namely,
terminal thieno groups are more effective to extend the p-
delocalization of DTS than terminal benzo groups.
Electrochemical Properties
Figure 3. Absorption and photoluminescence spectra of a) 7a and b) 7b
in different environments. The concentration of all the solutions is kept
to be 1ꢂ10ꢀ4 molLꢀ1. The films were prepared by drop-casting from a so-
lution of toluene.
The oxidation properties of 7a and 8 were determined by
cyclic voltammetry in CH2Cl2 solutions (1 mm) of tetrabutyl-
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Novel Ladder p-Conjugated Materials—Sila-Pentathienoacenes
Table 1. Photophysical data and the band gaps derived from different approaches.
Compound
Absorption l [nm]
Emission l [nm]
Oxidation Potential
Epa/Epc
Band Gap [eV]
[d]
[e]
Eg
[f]
Toluene[a]
THF[a]
Film[b]
Toluene[a]
F [%][c]
Eg
opt
7a
7b
8
292, 392
294, 397
291, 389
292, 392
N[g]
N
292, 392
296, 404
290, 358
467
473
466
70
81
N
0.62/0.39
N
0.61/0.35
2.76
2.74
2.77
2.83
N
2.83
[a] Measured in solution (1ꢂ10ꢀ4 m). [b] Measured in solid thin film on quartz plates prepared by spin-coating from solution. [c] 9,10-Diphenylanthracene
standard. [d] Epa and Epc stand for anodic peak potential and cathodic peak potential, respectively. [e] Optical band gap derived from the onset of UV/
Vis absorption spectra of solutions. [f] Cyclic voltammetric band gap derived from the difference between HOMO and LUMO energy levels, HOMO/
LUMO=Eonset +4.7 eV. [g] Not measured.
ammonium hexafluorophosphate (TBAPF6, 0.1m) using a Pt
wire as the counter electrode and a Ag/AgNO3 (0.1m) as
the reference electrode. The detailed data are listed in
Table 1, and the cyclic voltammograms are given in Figure 5.
which is shifted negatively by 0.06 eV. The cathodic peak
film
potential (E =0.21 eV) of film for 8 is remarkably lower
pc
sol
pc
than that (E =0.33 eV) of solution. In view of the exis-
tence of densely face-to-face stacking in single crystal of 8,
this point strongly suggests that the resulting oxidation state
in a film is more stable because of the delocalization of elec-
tron in the whole p–p system. As for 7a, the expected small
difference for the cathodic peak potential (Epc) between so-
lution and film is observed because of the weak molecular
interaction in the film.
Arising from the invisible signal of cyclic voltammograms
for the reduction potential in THF solution, the reduction
potential of 7a and 8 were estimated from the cyclic voltam-
mograms measured in films (see Supporting Information).
Both compounds displayed irreversible reduction processes
ðRÞ
ðRÞ
Figure 5. Cyclic voltammograms of 7a (a) and 8 (c), a) in CH2Cl2
with E
at ꢀ2.33 eV. According to the E , the LUMO
onset
onset
solution and b) in film. Scan rate: 100 mVsꢀ1
.
level can be obtained to be ꢀ2.38 eV. It is expected that the
LUMO level of sila-pentathienoacene is clearly lower than
that of pentathienoacene (ꢀ2.04 eV). Apparently, s*–p*
conjugation caused by a silylene bridge exerts a significant
impact on LUMO levels. The band gap is derived as the dif-
ference between the HOMO and the LUMO energy levels
as determined by cyclic voltammetry. The band gap (Eg =
On sweeping anodically, 7a undergoes two quasireversible
Ox
onset
oxidation peaks. The first oxidation potential with E
is
0.51 eV versus Ag/Ag+. The HOMO energy level of 7a is
estimated from the onset of oxidation wave to be ꢀ5.21 eV.
The HOMO level is lower than that of pentacene
(ꢀ4.60 eV),[17] being in accord with the more stable nature
of 7a against oxygen than pentacene. Compared with the
HOMO of pentathienoacene (ꢀ5.33 eV), the slight enhance-
ment of HOMO level for 7a may be ascribed to silylene
bridge. It is expected that the redox properties of 8 in solu-
tion would exhibit no clear difference compared with that of
7a.
2.83 eV) is very close to that (Eg =2.76 eV) determined by
the onset of the UV/Vis absorption spectra.
opt
Theoretical Calculations
To get further insight into the electronic structures of the
polycyclic p-electron systems, the density functional theoret-
ical calculations (B3LYP)[18] were performed for model-ring
systems, Si-PTA, PTA, DTS, and BBTS at the 6-31G* level
using the Gaussian 03 program.[19] The contours of the
HOMO and LUMO of 7a are plotted in Figure 6b. The cal-
culated HOMO levels shown in Figure 6a are in good
accord with those determined by electrochemical measure-
ments, whereas the agreement for the LUMO levels is mar-
ginal. The reason is ascribed in part to the less than satisfac-
tory reversibility of the reduction of Si-PTA and other sys-
tems. The theoretical calculations indicate that the HOMO
of Si-PTA is higher than that of PTA. The difference be-
tween Si-PTA and PTA could be caused by the inductive ef-
fects of the central group. An electropositive Me2Si group
raises the HOMO, while electronegative sulfur lowers the
HOMO. The LUMO level of Si-PTA is even lower than
that of PTA because of the effective s*–p* conjugation in
Generally, the orbital interaction between the silylene
bridge and p-conjugated framework mainly affects the
LUMO level through the s*–p* conjugation. Furthermore,
the oxidation potential of 7a is shifted by 0.22 V toward less
positive values with respect to that of bis(benzothieno)silole
with analogous structure.[12]
To investigate the influence of molecular-packing struc-
ture on the electrochemical properties, the oxidation proper-
ties of 7a and 8 in solid film (drop-casting on Pt disk elec-
trode from toluene solution) were also measured using
cyclic voltammetry in MeCN (see Figure 5b). The molecules
in dilute solution are mostly present as single molecules and
almost no aggregation occurs. As for films, both compounds
undergo two quasireversible oxidation peaks. The first oxi-
Ox
dation potential, E , is around 0.45 eV versus Ag/Ag+,
onset
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Experimental Section
General Methods
All starting materials were obtained from commercial suppliers and used
as received. Reagent-grade solvents were dried and purified according to
the following procedures: methylene chloride (MC) and N,N-dimethyl-
formamide (DMF) were distilled over calcium hydride. THF and diiso-
propylamine were dried over sodium metal and distilled. NMR spectra
were recorded on a Bruker DPX 400 (1H NMR 400 MHz and 13C NMR
100 MHz) spectrometer. The mass spectra were obtained using the Ion-
Spec 4.7 T HiResMALDI instrument. The luminescence spectra were
measured on an Edinburgh LFS920 fluorescence spectrophotometer (the
pathlength of the quartz cell is 1 cm). The emission bandwidth was 3 nm.
UV absorption spectra were obtained using a scinco S-3150 UV/Vis spec-
trophotometer.
Single crystals of 7a and 8 were obtained by slow evaporation of hexane/
CH2Cl2 solution at room temperature. Diffraction data were obtained
with CuKa (l=1.54184 nm) radiation for 7a and MoKa (l=0.71073 nm)
for 8 at 293 K using an Oxford Diffraction X-Calibur CCD system. 7a:
monoclinic, P21/c, crystal size: 0.36ꢂ0.20ꢂ0.06 mm3, cell dimensions: a=
25.0751(11) ꢀ; b=8.1932 (5) ꢀ; c=14.0853 (6) ꢀ; alpha=90.008; beta=
103.088 (4)o; gamma=90.008; Z=4, GOF=0.997, R1 =0.0414, wR2 =
0.1113. CCDC: 772506 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre at www.ccdc.cam.ac.uk/data_
request/cif. 8: monoclinic, P21/m, crystal size: 0.40ꢂ0.20ꢂ0.18 mm3, cell
dimensions: a=11.2504 (19) ꢀ; b=7.3279 (10) ꢀ; c=21.376 (3) ꢀ;
alpha=90.008; beta=91.536 (13)8; gamma=90.008, Z=4, GOF=1.050 ,
R1 =0.0974, wR2 =0.2704, CCDC: 772507 contains the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre at
www.ccdc.cam.ac.uk/data_request/cif.
Figure 6. DFT calculations of several p-conjugated ring systems (B3LYP/
6-31G): a) Kohn–Sham HOMO and LUMO energy levels and b) picto-
graphical presentation of the Kohn–Sham HOMO and LUMO of 7a.
Syntheses
1-(3,4-Dibromothiophen-2-yl)heptan-1-one (2): Heptanoyl chloride
(4.75 g, 32 mmol) was added dropwise to a mixture of 3, 4-dibromothio-
phene (1) (7.20 g, 30 mmol) and AlCl3 (9.25 g, 69 mmol) in CH2Cl2
(30 mL) with stirring at 08C under argon. The mixture was stirred for 4 h
and then poured into HCl (50 mL, 0.6m). The mixture was extracted with
CH2Cl2. The organic layer was washed with brine and water, then dried
over MgSO4, and concentrated. Chromatography on silica gel (petroleum
ether) afforded the pure product 2 (9.66 g, 91%). 1H NMR (400 Hz,
CDCl3): d=7.60 (s, H), 3.06–3.02 (t, 2H), 1.77–1.71 (m, 2H), 1.40–1.30
(m, 6H), 0.91–0.87 ppm (t, 3H); 13C NMR (100 Hz, CDCl3): d=191.98,
139.76, 129.19, 117.03, 116.99, 41.26, 31.63, 28.88, 24.02, 22.52, 14.06 ppm;
GC–MS: m/z (%): 354.8.
the silole moiety, though the inductive raising of the LUMO
should be operative in Si-PTA. As a result, the HOMO/
LUMO energy gap of Si-PTA is much smaller than that of
PTA and the smallest among the systems investigated here.
Conclusions
A novel series of ladder p-conjugated materials—sila-penta-
thienoacenes (Si-PTA) are synthesized and characterized.
The length of alkyl chains substituting on the thiophene ring
has a significant influence on molecular packing. For both
7a and 8, the fused polycyclic skeletons form face-to-face
packing structures in single crystals. However, a large inter-
facial distance (7.99 ꢀ) is obtained for 7a because of the in-
sertion of long alkyl chains between the two planes. A
densely packed structure with an interfacial distance of
about 3.66 ꢀ for the adjacent molecules is observed for 8
with shorter alkyl chains. We find that the silylene bridge in-
corporated into the pentathienoacene framework exerts a
clear effect on the electronic properties because of the s*–
p* conjugation. The HOMO/LUMO gap of the new extend-
ed p-systems is even smaller than that of the related extend-
ed silole systems like BBTS. The novel p-conjugated system
is a good candidate as a building block incorporated to p-
conjugated polymers for FET and photovoltaic applications.
Studies on the synthesis of the polymers with low band gap
based on sila-pentathienoacene are now in progress.
6-Bromo-3-hexylthieno
captoacetate (3.28 mL, 30 mmol) and then a catalytic amount of 18-
crown-6 (20 mg) were added dropwise to mixture of (10.62 g,
ACHTUNGTREN[NGNU 3,2-b]thiophene-2-carbonic ester (3): Ethyl mer-
a
2
30 mmol) and K2CO3 (19.67 g, 143 mmol) in DMF (25 mL) with stirring
under argon. The resulting mixture was heated at 60–708C overnight.
The mixture was then poured into water. After filtration, the solid was
washed with water. The collected solid (3) was further washed with meth-
anol and used directly for the next reaction (9.20 g, 82%). 1H NMR
(400 Hz, CDCl3): d=7.43 (s, H), 4.39–4.34ACTHNUTRGNE(NUG q, 2H), 3.15–3.11 (t, 2H),
1.72–1.68 (m, 2H), 1.41–1.29 (m, 6H), 0.89–0.86 ppm (t, 3H); 13C NMR
(100 Hz, CDCl3): d=162.70, 143.92, 141.85, 140.17, 128.64, 127.28, 103.19,
61.14, 31.59, 29.35, 29.28, 29.09, 22.59, 14.33, 14.08 ppm; GC–MS: m/z
(%): 375.9.
6-Bromo-3-hexylthieno
ACHTUNGTRENNUNG
26 mmol) was dissolved into
a
(5 mL), and LiOH (10 mL, 10% solution). The resulting mixture was re-
fluxed overnight and poured into concentrated hydrochloric acid. The
acidic mixture was then diluted with water (to 100 mL). The resulting
precipitate was filtered and washed with water, then washed with metha-
nol and dried under vacuum overnight (8.55 g, 95%). 1H NMR (400 Hz,
CDCl3): d=7.49 (s, H), 3.18–3.14 (t, 2H), 1.75–1.72 (t, 2H), 1.41–1.30 (m,
6H), 0.90–0.87 ppm (t, 3H); 13C NMR (100 Hz, CDCl3): d=168.57,
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Novel Ladder p-Conjugated Materials—Sila-Pentathienoacenes
145.92, 143.11, 140.35, 128.30, 127.68, 103.32, 31.56, 29.32, 29.29, 29.23,
22.57, 14.11 ppm; GC–MS: m/z (%): 303.9.
7b (0.22 g, 39%). 1H NMR (400 Hz, CDCl3): d=7.69–7.68
7.34(m, 2H), 6.93(s, 2H), 2.74–2.70 (t, 4H), 1.79–1.71 (m, 4H), 1.32–1.30
ACHTUNGTREN(NUNG d, 2H), 7.40–
N
ACHTUNGTRENNUNG
(m, 12H), 0.89–0.85 (t, 6H), 0.77 ppm (s,3H); 13C NMR (100 Hz, CDCl3):
d=151.26, 141.46, 141.17, 135.50, 134.36, 132.49, 131.60, 130.37, 128.40,
120.92, 31.65, 30.15, 29.10, 28.69, 22.64, 14.15, ꢀ4.97 ppm; 29Si NMR
(CDCl3): d=ꢀ13.9 ppm; HRMS (MALDI/DHB): m/z (%) calcd for
C31H36S4Si: 564.15; found: 564.1452ꢁ0.002.
8: A mixture of 6b (0.46 g, 1 mmol) and dry THF (8 mL) was stirred
under argon. nBuLi (1.5 mL, 1.60m) was added dropwise at ꢀ788C. The
mixture was then reacted at ꢀ788C for 15 min, and dichlorodimethylsi-
lane (0.13 g, 1 mmol) was added. The resulting mixture was stirred over-
night at room temperature and quenched with water. After evaporating
most of the THF, the mixture was dissolved into hexane, washed with
water, and dried over anhydrous MgSO4. After evaporation of hexane,
chromatography on silica gel (petroleum ether) afforded the pure prod-
uct 8 (0.11 g, 31%). 1H NMR (400 Hz, CDCl3): d=6.92 (s, 2H), 2.37 (s,
6H), 0.52 ppm (s, 6H); 13C NMR (100 Hz, CDCl3): d=150.7, 141.9, 141.2,
133.5. 130.1, 122.5, 121.3, 116.5, 15.1, ꢀ4.18 ppm; 29Si NMR (100 Hz,
CDCl3): d=ꢀ8.35 ppm; HRMS (MALDI/DHB): m/z (%) calcd for
C16H14S4Si: 361.97; found: 361.9726ꢁ0.002.
3-Bromo-6-hexylthienoACHTUNGTRENNUNG[3,2-b]thiophene (5): Copper powder (0.628 g), as
a catalyst, was added into a mixture of 4 (3.46 g, 10 mmol) and quinoline
(12 mL). The mixture was heated to 220–2308C until no gas bubbles
were observed. After slightly cooling the solution, the mixture was fil-
tered and hexane (20 mL) was added to the filtrate. The organic solution
was washed with a solution of HCl (10%) until it turned clear. The or-
ganic solution was washed with water until the washes were neutral.
After drying over anhydrous MgSO4, the solution was concentrated.
Chromatography on silica gel (petroleum ether) afforded the pure prod-
uct 5 (2.14 g, 71%). 1H NMR (400 Hz, DMSO): d=7.77 (s, 1H), 7.41
ACTHNUTRGNE(UNG s,
1H), 2.67–2.64 (t, 2H), 1.65–1.62 (t,2H), 1.25 (m, 6H), 0.84–0.81 ppm (t,
3H); 13C NMR (100 Hz, CDCl3): d=139.97, 139.10, 135.93, 123.36,
122.67, 103.02, 31.62, 29.72, 29.03, 28.64, 22.64, 14.15 ppm; GC–MS: m/z
(%): 303.8 (M-COOH)+; MS (ESI): m/z (%): 345.04.
3-Bromo-2-(3-bromo-6-hexylthieno
ACHTUNGTRENUN[NG 3,2-b]thiophen-2-yl)-6-hexylthieno-
ACHTUNGTRENNUNG[3,2-b]thiophene (6a): Fresh LDA was prepared by the reaction of diiso-
propylamine (0.44 g, 4 mmol) in dry THF (10 mL) with nBuLi (2.5 mL,
1.60m in hexane) at 08C under argon. To the LDA solution stirred at
08C for 15 min, 5 (1.21 g, 4 mmol) in THF (6 mL) was added dropwise.
After stirring at 08C for 1 h, CuCl2 (0.62 g, 4 mmol) powder was added to
the mixture. The final mixture was stirred overnight, and the reaction
was then quenched with water. After evaporating most of the THF, the
residue was extracted with hexane, washed with brine and water, and
dried over MgSO4. After evaporating hexane, the residue was recrystal-
lized from ethanol to give 6 as a crystalline solid (1.09 g, 45%). 6a:
Acknowledgements
This Project was supported by National Natural Science Foundation of
China (No. 20802014, 20974031), the National High Technology Research
and Development Program of China (No.2006AA050203), Zhejiang Pro-
vincial Natural Science Foundation of China (Y4080380), and the Qian-
jiang Talent Program of Zhejiang Province (2008R10018). We also thank
Prof. M. Kira (Tohoku University, Japan) for his helpful discussion.
1H NMR (400 Hz, CDCl3): d=7.10 (s, 2H), 2.74–2.70
ACTHNUTRGNE(NUG t, 4H), 1.79–1.73
(m, 4H), 1.41–1.33 (m, 12H), 0.91–0.88 ppm (t, 6H); 13C NMR (100 Hz,
CDCl3): d=140.53, 138.92, 135.92, 129.74, 122.86, 105.62, 105.62, 31.58,
29.77, 29.02, 28.64, 22.64, 14.12 ppm; MS (ESI): m/z (%): 604.89.
3-bromo-2-(3-bromo-6-methylthieno
ACHTUNGTRENNUNG
methylthieno[3,2-b] thiophene (6b): A
(0.44 g, 4 mmol) and dry THF (10 mL) was stirred under argon. nBuLi
(2.5 mL, 1.60m) was added dropwise at 08C. The freshly made LDA was
G
[1] a) T. M. Pappenfus, R. J. Chesterfield, C. D. Frisbie, K. R. Mann, J.
Casado, J. D. Raff, L. L. Miller, J. Am. Chem. Soc. 2002, 124, 4184–
4185; b) Naraso, J. Nishida, D. Kumaki, S. Tokito, Y. Yamashita, J.
Am. Chem. Soc. 2006, 128, 9598–9599; c) K. Ito, T. Suzuki„ Y. Saka-
moto, D. Kubota, Y. Inoue, F. Sato, S. Tokito, Angew. Chem. 2003,
115, 1191–1194; Angew. Chem. Int. Ed. 2003, 42, 1159–1162; d) Y.
Sun, Y. Q. Liu, D. Zhu, J. Mater. Chem. 2005, 15, 53–65; e) Y. Wu,
Y. Li, S. Gardner, B. S. Ong, J. Am. Chem. Soc. 2005, 127, 614–618;
f) A. L. Briseno, Q. Miao, M. M. Ling, C. Reese, H. Meng, Z. Bao,
F. Wudl, J. Am. Chem. Soc. 2006, 128, 15576–15577; g) M. Heeney,
C. Bailay, K. Genevicius, M. Shkunov, D. Sparrowe, S. Tierney, I.
McCulloch, J. Am. Chem. Soc. 2005, 127, 1078–1079; h) R. J. Li,
W. P. Hu, Y. Q. Liu, D. B. Zhu, Acc. Chem. Res. 2010, 43, 529–540.
[2] a) R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N.
Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos, J. L. Bredas,
M. Logdlund, W. R. Salaneck, Nature 1999, 397, 121–128; b) G. Bar-
barella, M. Melucci, G. Sotgiu, Adv. Mater. 2005, 17, 1581–1593;
c) W. Y. Lai, R. Zhu, Q. L. Fan, L. T. Hou, Y. Cao, W. Huang, Mac-
romolecules 2006, 39, 3707–3709; d) J. Liu, Q. G. Zhou, Y. X.
Cheng, Y. H. Geng, L. X. Wang, D. Ma, X. B. Jing, F. Wang, Adv.
Mater. 2005, 17, 2974–2978; e) T. Noda, Y. Shirota, J. Am. Chem.
Soc. 1998, 120, 9714–9715.
[3] a) J. W. Chen, Y. Cao, Acc. Chem. Res. 2009, 42, 1709–1718; b) Y.
He, H. Y. Chen, J. Hou, Y. Li, J. Am. Chem. Soc. 2010, 132, 1377–
1382; c) G. Li, V. Shrotriya, J. S. Huang, Y. Yao, T. Moriarty, K.
Emery, Y. Yang, Nat. Mater. 2005, 4, 864–868; d) S. C. Lo, P. L.
Burn, Chem. Rev. 2007, 107, 1097–1116; e) S. H. Chan, C. P. Chen,
T. C. Chao, C. Ting, C. S. Lin, B. T. Ko, Macromolecules 2008, 41,
5519–5526; f) Y. J. Cheng, S. H. Yang, C. S. Hsu, Chem. Rev. 2009,
109, 5868–5923; g) J. L. Wang, C. Zhong, Z. M. Tang, H. Wu, Y.
Ma, Y. Cao, J. Pei, Chem. Asian J. 2010, 5, 105–113.
stirred at 08C for 15 min, and then 3-bromo-6-methylthienoACTHNUTRGNEUG[N 3,2-b]thio-
phene (0.93 g, 4 mmol) in THF (6 mL) was added dropwise. The mixture
then was stirred at 08C for one hour, and CuCl2 (0.618 g, 4 mmol)
powder was added. The final mixture was stirred overnight, and the reac-
tion was then quenched with water. After evaporating most of the THF,
the residue was extracted with hexane, washed with water and brine, and
dried over MgSO4. After evaporating hexane, the residue was recrystal-
lized from ethanol to give 6b as
a crystalline solid (0.31 g,
33%).1H NMR (400 Hz, CDCl3): d=7.09 (s, 2H), 2.37
(EI): m/z (%): 465.63.
ACHTUNGTREN(NUNG s, 6H) ppm; MS
7a: nBuLi (1.5 mL, 1.60m in hexane) was added dropwise to a solution
of 6 (0.60 g, 1 mmol) in dry THF (8 mL) at ꢀ788C under argon. After
stirring the mixture at the same temperature for 15 min, dichlorodime-
thylsilane (0.129 g, 1 mmol) was added to the mixture. The resulting mix-
ture was stirred overnight at room temperature and quenched with
water. After evaporating most of solvent, the mixture was dissolved into
hexane and washed with water. The organic phase was dried with anhy-
drous MgSO4 and concentrated. Chromatography on silica gel (petrole-
um ether) afforded the pure 7a (0.21 g, 42%). 7a: 1H NMR (400 Hz,
CDCl3): d=6.92ACHTUNGTRENNUNG(s, 2H), 2.74–2.70 (t, 4H), 1.79–1.73 (m, 4H), 1.41–1.33
(m, 12H), 0.90–0.88 (t, 6H), 0.53 ppm (s, 6H); 13C NMR (100 Hz,
CDCl3): d=150.57, 140.96, 141.33, 135.46, 133.2, 120.68, 127.5, 31.66,
30.15, 29.11, 28.69, 22.65, 14.16, ꢀ4.12 ppm; 29Si NMR (CDCl3): d=
ꢀ8.33 ppm; HRMS (MALDI/DHB): m/z (%) calcd for C26H34S4Si:
502.13; found: 502.1301ꢁ0.002.
7b: nBuLi (1.5 mL, 1.60m in hexane) was added dropwise to a solution
of 6 (0.60 g, 1 mmol) in dry THF (8 mL) at ꢀ788C under argon. The mix-
ture was then reacted at ꢀ788C for 15 min, and dichloromethylphenylsi-
lane (0.191 g, 1 mmol) was added. The resulting mixture was stirred over-
night at room temperature and quenched with water. After evaporating
most of the THF, the mixture was dissolved into hexane and washed with
water. The organic phase was dried with anhydrous MgSO4 and concen-
trated. Chromatography on silica gel (petroleum ether) afforded the pure
[4] a) A. Fukazawa, S. Yamaguchi, Chem. Asian J. 2009, 4, 1386–1400;
b) U. Scherf, J. Chem. Mater. 1999, 9, 1853–1864; c) M. D. Watson,
A. Fechtenkçtter, K. Mꢃllen, Chem. Rev. 2001, 101, 1267–1300;
d) M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104,
4891–4946; e) R. G. Harvery, Polycyclic Aromatic Hydrocarbons;
Chem. Asian J. 2010, 5, 2290 – 2296
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
2295

L.-B. Wu, G.-Q. Lai et al.
FULL PAPERS
Wiley-VCH, New York, 1997; f) J. E. Anthony, Chem. Rev. 2006,
106, 5028–5048; g) H. Usta, C. Risko, Z. Wang, H. Huang, M. K.
Deliomeroglu, A. Zhukhovitskiy, A. Facchetti, T. J. Marks, J. Am.
Chem. Soc. 2009, 131, 5586–8608; h) F. Liu, L.-H. Xie, C. Tang, J.
Liang, Q.-Q. Chen, B. Peng, W. Wei, Y. Cao, W. Huang, Org. Lett.
2009, 11, 3850–3853; i) A. Fukazawa, H. Yamada, Y. Sasaki, S.
Akiyama, S. Yamaguchi, Chem. Asian J. 2010, 5, 466–469; j) J. Bou-
chard, S. Wakim, M. Leclerc, J. Org. Chem. 2004, 69, 5705–5711;
k) K. Kawaguchi, K. Nakano, K. Nozaki, J. Org. Chem. 2007, 72,
5119–5128; l) T. Qi, W. F. Qiu, Y. Q. Liu, H. J. Zhang, X. K. Gao, Y.
Liu, K. Lu, C. Y. Du, G. Yu, D. B. Zhu, J. Org. Chem. 2008, 73,
4638–4643; m) K.-T. Wong, T.-C. Chao, L.-C. Chi, Y.-Y. Chu, A. Ba-
laiah, S.-F. Chiu, Y.-H. Liu, Y. Wang, Org. Lett. 2006, 8, 5033–5036.
[5] a) K. Xiao, Y. Q. Liu, T. Qi, W. Zhang, F. Wang, J. H. Gao, W. F.
Qiu, Y. Q. Ma, G. L. Cui, S. Y. Chen, X. W. Zhan, G. Yu, J. G. Qin,
W. P. Hu, D. B. Zhu, J. Am. Chem. Soc. 2005, 127, 13281–13286;
b) K. Yamada, T. Okamoto, K. Kudoh, A. Wakamiya, S. Yamaguchi,
J. Takeya, Appl. Phys. Lett. 2007, 90, 072102; c) L. Tan, L. Zhang, X.
Jiang, X. D. Yang, L. J. Wang, Z. H. Li, L. Q. Wang, W. P. Hu, Z. G.
Shuai, L. Li, D. B. Zhu, Adv. Funct. Mater. 2009, 19, 272–276;
d) Q. F. Yan, Y. Zhou, B.-B. Ni, Y. G. Ma, J. Wang, J. Pei, Y. Cao, J.
Org. Chem. 2008, 73, 5328–5339; e) X. Zhang, A. P. Cote, A. J.
Matzger, J. Am. Chem. Soc. 2005, 127, 10502–10503; f) T. Izawa, E.
Miyazaki, K. Takimiya, Chem. Mater. 2009, 21, 903–912.
[6] a) K. Takimiya, H. Ebata, K. Sakamoto, T. Izawa, T. Otsubo, Y.
Kunugi, J. Am. Chem. Soc. 2006, 128, 12604–12605; b) X.-C. Li, H.
Sirringhaus, F. Garnier, A. B. Holmes, S. C. Moratti, N. Feeder, W.
Clegg, S. J. Teat, R. H. Friend, J. Am. Chem. Soc. 1998, 120, 2206–
2207; c) C. Hunziker, X. Zhan, P. A. Losio, H. Figi, O.-P. Kwon, S.
Barlow, P. Gꢃnter, S. R. Marder, J. Mater. Chem. 2007, 17, 4972–
4979; d) I. Afonina, P. J. Skabara, F. Vilela, A. L. Kanibolotsky, J. C.
Forgie, A. K. Bansal, G. A. Turnbull, I. D. W. Samuel, J. G. Labram,
T. D. Anthopoulos, S. J. Coles, M. B. Hursthouse, J. Mater. Chem.
2010, 20, 1112–1116.
[7] a) H. Ebata, T. Izawa, E. Miyazaki, K. Takimiya, M. Ikeda, H. Ku-
wabara, T. Yui, J. Am. Chem. Soc. 2007, 129, 15732–15733; b) M. L.
Tang, T. Okamoto, Z. Bao, J. Am. Chem. Soc. 2006, 128, 16002–
16003; c) S. Subramanian, S. K. Park, S. R. Parkin, V. Podzorov,
T. N. Jackson, J. E. Anthony, J. Am. Chem. Soc. 2008, 130, 2706–
2707; d) M. Miyasaka, A. Rajca, M. Pink, S. Rajca, J. Am. Chem.
Soc. 2005, 127, 13806–13807; e) P. Gao, D. Cho, X. Y. Yang, V. En-
kelmann, M. Baumgarten, K. Mꢃllen, Chem. Eur. J. 2010, 16, 5119–
5128.
[8] a) H. Usta, G. Lu, A. Facchetti, T. J. Marks, J. Am. Chem. Soc. 2006,
128, 9034–9035; b) G. Lu, H. Usta, C. Risko, L. Wang, A. Facchetti,
M. A. Ratner, T. J. Marks, J. Am. Chem. Soc. 2008, 130, 7670–7685;
c) H. H. Fong, V. A. Pozdin, A. Amassian, G. G. Malliaras, D.-M.
Smilgies, M. He, S. Gasper, F. Zhang, M. Sorensen, J. Am. Chem.
Soc. 2008, 130, 13202–13203.
Y. Harima, K. Yamashita, M. Ishikawa, Organometallics 1999, 18,
1453–1459; f) L. C. Li, J. F. Xiang, C. H. Xu, Org. Lett. 2007, 9,
4877–4879.
[11] a) S. Yamaguchi, K. Tamao, Bull. Chem. Soc. Jpn. 1996, 69, 2327–
2334; b) M. Hissler, P. W. Dyer, R. C. Rꢄau, Chem. Rev. 2003, 244,
1–44; c) K. Tamao, M. Uchida, T. Izumizawa, K. Furukawa, S. Ya-
maguchi, J. Am. Chem. Soc. 1996, 118, 11974–11975; d) Y. Dong,
J. W. Y. Lam, A. Qin, Z. Li, J. Liu, J. Sun, Y. Dong, B. Z. Tang,
Chem. Phys. Lett. 2007, 446, 124; e) J. Yu, W. Li, Y. Jiang, L. Li,
Jpn. J. Appl. Phys. 2007, 46, L31; f) N. J. Watkins, A. J. Makinen, Y.
Gao, M. Uchida, Z. H. Kafafi, J. Appl. Phys. 2006, 100, 103706;
g) S. H. Lee, B.-B. Jang, Z. H. Kafafi, J. Am. Chem. Soc. 2005, 127,
9071–9078; h) A. J. Boydston, Y. Yin, B. L. Pagenkopf, J. Am.
Chem. Soc. 2004, 126, 3724–3725.
[12] J. Ohshita, K.-H. Lee, K. Kimura, A. Kunai, Organometallics 2004,
23, 5622–5625.
[13] a) D.-H. Kim, J. Ohshita, K.-H. Lee, Y. Kunugi, A. Kunai, Organo-
metallics 2006, 25, 1511–1516; b) J. W. Chen, Y. Cao, Macromol.
Rapid Commun. 2007, 28, 1714–1742.
[14] M. Q. He, F. X. Zhang, J. Org. Chem. 2007, 72, 442–451.
[15] a) J. H. Chen, S. Subramanian, S. R. Parkin, M. Siegler, K. Gallup,
C. Haughn, D. C. Martin, J. E. Anthony, J. Mater. Chem. 2008, 18,
1961–1969; b) C. Kitamura, Y. Abe, T. Ohara, A. Yoneda, T.
Kawase, T. Kobayashi, H. Naito, T. Komatsu, Chem. Eur. J. 2010,
16, 890–898; c) M. D. Curtis, J. Cao, J. W. Kampf, J. Am. Chem. Soc.
2004, 126, 4318–4328; d) B. M. Sheikh-Ali, M. Rapta, G. B. James-
on, C. X. Cui, R. G. Weiss, J. Phys. Chem. 1994, 98, 10412–10418;
e) C. H. Zheng, S. Z. Pu, J. K. Xu, M. B. Luo, D. C. Huang, L. Shen,
Tetrahedron 2007, 63, 5437–5449.
[16] a) E. G. McRae, M. Kasha, J. Phys. Chem. 1958, 28, 721–722;
b) C. E. Evans, Q. Song, P. W. Bohn, J. Phys. Chem. 1993, 97,
12302–12308; c) A. P. H. J. Schenning, P. Jonkheijm, E. Peeters,
E. W. Meijer, J. Am. Chem. Soc. 2001, 123, 409–416; d) E. H. A.
Beckers, S. C. J. Meskers, A. P. H. J. Schenning, Z. J. Chen, F. Wꢃrth-
ner, P. Marsal, D. Beljonne, J. Cornil, R. A. J. Janssen, J. Am. Chem.
Soc. 2006, 128, 649; e) S. Ikeda and A. Okamoto, Chem. Asian J.
2008, 3, 958–968.
[17] H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao,
T. Siegrist, C. Kloc, C.-H. Chen, Adv. Mater. 2003, 15, 1090–1093.
[18] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) C. Lee, W.
Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[19] Gaussian 03, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian Inc., Wall-
ingford CT, 2004.
[9] a) J. H. Hou, H.-Y. Chen, S. Q. Zhang, G. Li, Y. Yang, J. Am. Chem.
Soc. 2008, 130, 16144–16145; b) Y. Y. Liang, D. Q. Feng, Y. Wu, S.-
T. Tsai, G. Li, C. Ray, L. P. Yu, J. Am. Chem. Soc. 2009, 131, 7792–
7799; c) S. Q. Xiao, A. C. Stuart , S. B. Liu, H. X. Zhou, W. You,
Adv. Funct. Mater. 2010, 20, 635–643.
[10] a) S. Yamaguchi, C. H. Xu, K. Tamao, J. Am. Chem. Soc. 2003, 125,
13662–13663; b) M. Shimizu, H. Tatsumi, K. Mochida, K. Oda, T.
Hiyama, Chem. Asian J. 2008, 3, 1238–1247; c) K. Mouri, A. Waka-
miya, H. Yamada, T. Kajiwara, S. Yamaguchi, Org. Lett. 2007, 9, 93–
96; d) Y. Suzuki, T. Okamoto, A. Wakamiya, S. Yamaguchi, Org.
Lett. 2008, 10, 3393–3396; e) J. Ohshita, M. Nodono, H. Kai, T. Wa-
tanabe, A. Kunai, K. Komaguchi, M. Shiotani, A. Adachi, K. Okita,
Received: April 21, 2010
Published online: July 28, 2010
2296
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Chem. Asian J. 2010, 5, 2290 – 2296