Zirconium-mediated coupling reaction for synthesis of substituted thiophene-fused acenes

Article abstract of DOI:10.1021/ol900903w

Image Presented A novel zirconium-mediated synthesis of substituted thiophene-fused acenes is described. A variety of substituents, such as alkyl, aryl, silyl, iodo, and alkynyl groups, could be introduced to the acene skeleton by this method. Moreover, t

Full text of DOI:10.1021/ol900903w

ORGANIC
LETTERS
2009
Vol. 11, No. 16
3702-3705
Zirconium-Mediated Coupling Reaction
for Synthesis of Substituted
Thiophene-Fused Acenes
Yang Ni,† Kiyohiko Nakajima,‡ Ken-ichiro Kanno,† and Tamotsu Takahashi*,†
Catalysis Research Center and Graduate School of Life Science, Hokkaido UniVersity,
and SORST, Japan Science and Technology Agency (JST), Kita-ku, Sapporo 001-0021,
Japan, and Department of Chemistry, Aichi UniVersity of Education,
Igaya, Kariya 448-8542, Aichi, Japan
tamotsu@cat.hokudai.ac.jp
Received May 17, 2009
ABSTRACT
A novel zirconium-mediated synthesis of substituted thiophene-fused acenes is described. A variety of substituents, such as alkyl, aryl, silyl,
iodo, and alkynyl groups, could be introduced to the acene skeleton by this method. Moreover, the double coupling with tetraiodothiophene
gave the corresponding dianthrathiophene.
Recently, thiophene-fused higher acenes (TFHA) have been
highlighted as promising candidates for organic semiconduc-
tors due to their higher durability and solubility compared
to the hydrocarbon analogues without significant loss of the
device performance.1 To synthesize such a compound, the
coupling reaction of metalacyclopentadienes with o-dihal-
othiophenes is a direct and efficient method. However, there
was no report for preparation of TFHA using the coupling
reaction.
“double homologation method”,2e and the other is a zirconium-
mediated coupling method.3 Among them, the coupling
reaction can provide a direct and simple route to highly
substituted benzothiophenes3a and quinolines3b using the
corresponding zirconacyclopentadienes and 1,2-dihaloge-
nated thiophenes or pyridines, respectively. Thus, the
construction of TFHA is expected by our metal-mediated
(2) (a) Takahashi, T.; Kitamura, M.; Shen, B.; Nakajima, K. J. Am. Chem.
Soc. 2000, 122, 12876. (b) Takahashi, T.; Li, S.; Huang, W.; Kong, F.;
Nakajima, K.; Shen, B.; Ohe, T.; Kanno, K. J. Org. Chem. 2006, 71, 7967.
(c) Takahashi, T.; Li, Y.; Hu, J.; Kong, F.; Nakajima, K.; Zhou, L.; Kanno,
K. Tetrahedron Lett. 2007, 48, 6726. (d) Li, S.; Zhou, L.; Song, Z.; Bao,
F.; Kanno, K.; Takahashi, T. Heterocycles 2007, 692, 55. (e) Li, S.; Li, Z.;
Nakajima, K.; Kanno, K.; Takahashi, T. Chem. Asian J. 2009, 4, 2722.
See also: (f) Stone, M. T.; Anderson, H. L. J. Org. Chem. 2007, 72, 9776.
(3) (a) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora, M. J. Am. Chem.
Soc. 1996, 118, 5154. (b) Takahashi, T.; Li, Y.; Stepnicka, P.; Kitamura,
M.; Liu, Y.; Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 2002, 124, 576.
(c) Takahashi, T.; Kashima, K.; Li, S.; Nakajima, K.; Kanno, K. J. Am.
Chem. Soc. 2007, 129, 15752. (d) Seri, T.; Qu, H.; Zhou, L.; Kanno, K.;
Takahashi, T. Chem. Asian J. 2008, 3, 388. (e) Zhou, L.; Nakajima, K.;
Kanno, K.; Takahashi, T. Tetrahedron Lett. 2009, 50, 2722.
Our group has reported two methods for the synthesis of
substituted acenes based on zirconium-mediated reactions.2,3
One is the “homologation method”2a,b and its modified
† Hokkaido University and SORST.
‡ Aichi University of Education.
(1) (a) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. J. Am. Chem.
Soc. 1998, 120, 664. (b) Dimitrakopoulos, C. D.; Malenfant, P. R. L. AdV.
Mater. 2002, 14, 99. (c) Tang, M. L.; Okamoto, T.; Bao, Z. J. Am. Chem.
Soc. 2006, 128, 16002. (d) Yuan, Q.; Mannsfeld, S. C. B.; Tang, M. L.;
Toney, M. F.; Lu¨ning, J.; Bao, Z. J. Am. Chem. Soc. 2008, 130, 3502.
10.1021/ol900903w CCC: $40.75
Published on Web 07/28/2009
 2009 American Chemical Society

coupling methodology, although several other methods have
been developed.4-6
In this paper, we would report a novel synthesis of
variously substituted thiophene-fused higher acenes by
zirconium-mediated coupling reactions.
1. Diynes 5 were treated with Cp2ZrBu2 to form the
corresponding tricyclic zirconacyclopentadienes 6, which
were coupled with 2,3-diiodothiophene in the presence of
CuCl and DMPU to afford dihydroanthrathiophenes 7.
Aromatization of 7 with DDQ proceeded efficiently to afford
the corresponding anthrathiophenes 8.
For effective coupling with zirconacyclopentadienes, employ-
ment of 2,3-diiodothiophene was found to be essential. Table
1 showed the results of coupling of 2,3-dihalothiophene 1 and
tetraethylzirconacyclopentadiene 2 under various conditions. As
we reported previously, a reaction of 2 with 2-iodo-3-bro-
mothiophene gave benzothiophene 3 but in a low yield (entry
1).3a We found that the major product of the reaction was a
partially coupled product, iodobutadienylthiophene 4. Although
this would be converted to the desired 3, modifications of the
reaction conditions did not improve the yield of 3 (entries 2-4).
When the ratio of 2 was increased, the total yield of the coupling
products 3 and 4 decreased (entry 2). On the other hand,
increasing the amount of 1 reduced the ratio of the desired
product 3 (entry 3). Changing the solvent and reaction temper-
ature did not improve the results (entry 4). In striking contrast
to the above results with 2-iodo-3-bromothiophene, the reaction
with 2,3-diiodothiophene dramatically improved the yield of 3
(entry 5). In this case, the formation of noncyclized 4 was not
observed. Although the reaction of 2 with 1,2-diiodo- or
1-bromo-2-iodobenzene gave the corresponding 1,2,3,4-tetra-
ethylnaphthalene in comparable yields, the reactivity of 2,3-
diiodothiophene is significantly different from that of 2-iodo-
3-bromothiophene, especially at the final cyclization coupling
step.
Scheme 1
As summarized in Table 2, the coupling and the subsequent
aromatization proceeded efficiently in all cases. When alkyl-
substituted zirconacyclopentadienes were employed for the
coupling reaction, the corresponding anthrathiophenes were
obtained in good yields (entries 1-3). For diphenyl-substituted
zirconacycle, the coupling reaction and aromatization also
worked well to give diphenylated derivatives in good yields
(entries 4 and 5). It is worth mentioning that silyl-substituted
zirconacycle 6f did react with 2,3-diiodothiophene, since no
coupling products were obtained from the reaction of disilyl-
substituted zirconacyclopentadienes with diiodobenzene under
the same conditions. As mentioned above, a series of substituted
anthrathiophenes were synthesized by this zirconium-mediated
coupling reaction efficiently.
Table 1. Coupling of Dihalothiophene 1 and Zirconacycle 2
Table 2. Synthesis of Anthrathiophenes
yield of 3a/%
yield of 4a/%
entry
R1
R2
yield of 7a/%
yield of 8a/%
entry
1:2
X
solvent
1
2
3
4
5
6
Pr
Bu
Bu
Ph
Ph
SiMe3
Pr
Bu
H
Pr
H
7a, 64 (57)
7b, 70 (55)
7c, 70 (43)
7d, 71 (65)
7e, 62 (51)
7f, 54 (41)
8a, 89 (81)
8b, 92 (80)
8c, 91 (84)
8d, 95 (84)
8e, 78 (71)
8f, 89 (65)
1
2
3
4
5
1.2:1
1:4
2:1
1.2:1
1.2:1
Br
Br
Br
Br
I
THF
THF
THF
toluene
THF
22 (18)
15
48 (31)
7
61
59
0
13
81 (76)
a Yields were determined by GC analyses and based on the amount of
the zirconacyclopentadiene. Isolated yields are shown in parentheses.
Pr
a Yields were determined by NMR analyses and based on the amount
of the zirconacyclopentadiene. Isolated yields are shown in parentheses.
Thus, an optimized coupling reaction was applied for the
synthesis of a series of anthrathiophenes as shown in Scheme
Furthermore, the coupling reaction was applicable for
tetraiodothiophene and the corresponding doubly coupled
products were obtained (Scheme 2). The reaction of tetra-
(4) (a) Payne, M. M.; Odom, S. A.; Parkin, S. R.; Anthony, J. E. Org.
Lett. 2004, 6, 3325. (b) Lloyd, M. T.; Mayer, A. C.; Subramanian, S.;
Mourey, D. A.; Herman, D. J.; Bapat, A. V.; Anthony, J. E.; Malliaras,
G. G. J. Am. Chem. Soc. 2007, 129, 9144. (c) Tang, M. L.; Reichardt, A. D.;
(6) (a) Takimiya, K.; Kunugi, Y.; Konda, Y.; Niihara, N.; Otsubo, T.
J. Am. Chem. Soc. 2004, 126, 5084. (b) Takimiya, K.; Konda, Y.; Ebata,
H.; Niihara, N.; Otsubo, T. J. Org. Chem. 2005, 70, 10569. (c) Yamamoto,
T.; Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224. (d) Takimiya, K.;
Kunugi, Y.; Otsubo, T. Chem. Lett. 2007, 36, 578.
Miyaki, N.; Stoltenberg, R. M.; Bao, Z. J. Am. Chem. Soc. 2008, 130, 6064
.
(5) (a) Okamoto, T.; Kudoh, K.; Wakamiya, A.; Yamaguchi, S. Org.
Lett. 2005, 7, 5301. (b) Okamoto, T.; Kudoh, K.; Wakamiya, A.; Yamaguchi,
S. Chem.sEur. J. 2007, 13, 548
.
Org. Lett., Vol. 11, No. 16, 2009
3703

Scheme 2
Scheme 3
ethylzirconacyclopentadiene 2 (4 equiv) with tetraiodot-
hiophene gave the corresponding dibenzothiophene. The
excess use of the zirconacycle compared to tetraiodot-
hiophene was needed to obtain the coupling product in
acceptable yield. Furthermore, the double coupling could be
performed with tricyclic zirconacyclopentadiene 6c, and the
subsequent aromatization afforded the corresponding dian-
thrathiophene 12 in high yield. This is the first example of
the formation of dianthrathiophene to the best of our
knowledge. Its structure was determined by X-ray analysis
as shown in Figure 1.
with ICl at -78 °C. After DDQ aromatization, thus obtained
diiodoanthrathiophene 14 was subjected to cross-coupling
reactions. Thus, Negishi coupling with phenylzinc chloride and
Sonogashira coupling with trimethylsilylacetylene gave the
corresponding coupling products 8d and 15, respectively, in
excellent yields. Methylation of 14 with AlMe3 was also
possible and yielded dimethylanthrathiophene 16 in high yield.
These results clearly exhibited the wide applicability of the
present zirconium-mediated method for introduction of various
substituents on the acene skeletons. The structure of 15 was
determined by X-ray analysis as shown in Figure 2.
All of the thiophene-fused acene derivatives were highly
soluble in common organic solvents, such as chloroform,
ethyl acetate, hexane, and so on.
Table 3. Photophysical Properties of Anthrathiophenesa
λmax(abs) (nm)/
λmax(ems)
(nm)
compd
R1
R2
ε (M-1cm-1
)
Figure 1. Perspective view of dianthrathiophene 12.
8a
8b
8c
8d
8e
8f
14
16
15
12
Pr
Pr
Bu
H
Pr
H
Pr
Pr
Pr
Pr
459 (8100)
460 (8900)
450 (9400)
463 (7600)
451 (8700)
467 (9200)
473 (5500)
457 (6200)
467
468
464
480
470
482
489
466
525
530
Bu
Bu
Ph
Ph
SiMe3
I
When TMS-substituted dihydroanthrathiophene 7f was used,
further derivatization was possible by utilization of well-
established palladium-catalyzed cross-coupling reactions.7 As
shown in Scheme 3, trimethylsilyl groups of dihydroanth-
rathiophene 7f were cleanly substituted with iodine by a reaction
Me
SiMe3CC-
506 (10200)
506 (1100)
(7) Handbood of Organopalladium Chemistry for Organic Synthesis;
Negishi, E., Meijere, A. D., Eds.; John Wiley & Sons. Inc.: New York,
2002; Vol. 1.
a Measured in CHCl3 at room temperature.
3704
Org. Lett., Vol. 11, No. 16, 2009

absorption maxima of diphenylanthrathiophenes 8d and 8e
were located at almost the same wavelength as those of their
alkylated counterparts 8a and 8c, respectively. This suggests
that the two phenyl groups in 8d and 8e do not take part in
extension of π-conjugation, probably due to their preferred
conformation perpendicular toward the anthrathiophene
plane. In addition, substitution of heteroatoms, such as silyl
(8f) and iodine (14), changes the absorption maxima slightly.
In contrast, dialkynyl-substituted 15 showed the maximum
at a much longer wavelength region than those of the other
anthrathiophenes. In fact, the wavelength of the absorption
maxmum of 15 is the same as that for dianthrathiophene
12. This illustrates that alkynyl groups can effectively extend
the π-conjugation system of the anthrathiophene moiety in
contrast to the phenyl group. The substituent-dependent
fluctuation of the emission maxima was almost similar to
those of the absorption maxima.
In conclusion, we have developed a novel and convenient
method for the synthesis of substituted anthrathiophene and
dianthrathiophene derivatives mediated by zirconium. This
method enables us to control various types of substitution
patterns on the anthrathiophene skeletons, and alkyl, aryl,
and silyl groups were introduced directly. Moreover, iodi-
nation of disilylated derivative 7f can provide further
derivatization via 14 by palladium-catalyzed cross-coupling
reactions.
Figure 2. Perspective view of anthrathiophene 15.
Photophysical properties of these thiophene-fused acenes
were examined in chloroform as shown in Table 3, and the
substituent effects were evaluated. Compared with the
wavelength of the absorption maximum of dibutylanth-
rathiophene (8c), those of hexaalkyl-substituted ones were
red-shifted approximately 10 nm. However, introduction of
a phenyl group did not affect the outcome significantly. The
Supporting Information Available: Experimental pro-
cedures and spectral data for all new compounds. Crystal-
lographic data for 12 and 15 (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
OL900903W
Org. Lett., Vol. 11, No. 16, 2009
3705