DOI: 10.1002/chem.201501015
Communication
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Synthesis Design
From-Core and From-End Direct CÀH Arylations: A Step-Saving
New Synthetic Route to Thieno[3,4-c]pyrrole-4,6-dione (TPD)-
Incorporated D–p–A–p–D Functional Oligoaryls
[
a]
Po-Han Lin, Kuan-Ting Liu, and Ching-Yuan Liu*
Abstract: In contrast to the traditional multistep synthesis,
herein an efficient and fewer-steps new synthetic strategy
is demonstrated for the facile preparation of organic-elec-
tronically important D–p–A–p–D-type oligoaryls through
sequential direct CÀH arylations. This methodology has
shown that the synthesis of thieno[3,4-c]pyrrole-4,6-dione
(TPD)- or furano[3,4-c]pyrrole-4,6-dione (FPD)-centred
Figure 1. Thieno[3,4-c]pyrrole-4,6-dione (TPD)-based D–p–A–p–D-type oli-
target molecules could be accessed step-economically
either from the core structure (acceptor) or from the end
structure (donor), which supplied a more flexible and suc-
cinct new synthetic alternative to the preparation of the
p-functional small-molecule semiconducting materials. In
addition, optical and electrochemical properties of the
synthesized oligoaryls were examined.
goaryls for organic optoelectronic materials. Previous work: six-step synthe-
sis including Suzuki and Stille coupling reaction. This work: two-step syn-
thesis by sequential direct CÀH arylations.
[
4d]
To the best of our knowledge, target-oriented direct (heter-
o)arylation combining the concept of from-core or from-end
synthetic strategy to access linear D–p–A–p–D-type p-func-
tional molecules has not been reported to date (Schemes 1
and 2).
Linear D–p–A–p–D (D: donor; A: acceptor)-type symmetrical
molecules constitute an important class of p-conjugated oli-
goaryls in modern organic electronics because their applica-
tions in organic photovoltaic cells (OPVCs) and organic field-
effect transistors (OFETs) have attracted considerable atten-
N-Alkyl TPD structures (1a, 1b) have exceptional planarity
and solubility and they have been widely used as electron-ac-
[5]
cepting units in numerous p-functional materials. Recently,
we reported an efficient CÀH arylation methodology using
TPD as core substrate and functionalized aryl bromides as cou-
pling partners, which led to the formation of various D–A–D-
[
1]
tion. For example, Nguyen reported high-performance bulk
heterojunction solar cells using diketopyrrolopyrrole (DPP)-
[6]
and A’–A–A’-type small molecules. However, direct CÀH cou-
pling reaction of TPD with important heteroaryls (e.g., thio-
phenes) enabling the formation of synthetically versatile p–A–
p-type building blocks (2a, 2b in Scheme 1) while leaving two
further arylable CÀH bonds at both ends still remains challeng-
ing because we envisaged that the self-oligomerization of 2-
bromothiophene by CÀH arylation would also take place and
become a competitive side-reaction. Nevertheless, as the first
part of this work (Scheme 1), we designed a sequential from-
core synthesis, in which we found, under the condition of
shortened reaction time (from 24 to 6 h), first CÀH heteroaryla-
tion of TPD (1a, 1b) with 2-bromothiophene successfully pro-
ceeded with unexpected regioselectivity between two different
CÀH bonds and the useful terthiophene derivatives (2a, 2b)
were obtained in moderate yields (66 and 51%, respectively).
Subsequent CÀH arylation of 2a or 2b with 4-bromotriphenyl-
amine (3) was performed under similar reaction conditions de-
scribed in previous step, giving the target D–p–A–p–D-type
oligoaryls (7a, 7b) as from-core products, in 85 and 46%
yields, respectively. More importantly, in order to further simpli-
fy the from-core strategy, the convenient two steps in one-pot
[
2]
based D–p–A–p–D small molecules. Frꢀchet reported similar
small-molecule solar cells that exhibit interesting properties of
[
3]
pyrene-directed self-assembly. Recently, the Zhan group dis-
[
4a,b]
[4c]
closed a series of benzothiadiazole-,
thiazolothiazole-,
[
4d]
and thieno[3,4-c]pyrrole-4,6-dione
(TPD)-centred oligomers
with D–p–A–p–D structures for organic solar cell or field-effect
transistor applications. The synthetic methods for the above-
mentioned target compounds, however, must rely on tradition-
al cross-coupling reactions that cannot avoid the process of
pre-functionalizations/metalations, thereby leading to the fre-
quent use and treatment with toxic reagents such as organotin
species. Hence, we introduce herein a greener and fewer-steps
synthetic approach for the facile preparation of TPD-incorpo-
rated symmetrical oligoaryls by sequential direct CÀH aryla-
tions (Figure 1).
[a] P.-H. Lin, K.-T. Liu, Prof. Dr. C.-Y. Liu
Department of Chemical and Materials Engineering
National Central University, Jhongli District, Taoyuan, Taiwan 320 (R.O.C)
E-mail: cyliu0312@ncu.edu.tw
[7]
reactions (2a, 2b not isolated) were tested, and we found,
Chem. Eur. J. 2015, 21, 1 – 5
1
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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