Palladium-catalyzed construction of heteroatom-containing π-conjugated systems by intramolecular oxidative C-H/C-H coupling reaction

Article abstract of DOI:10.1002/chem.201501116

Synthesis of heteroatom-containing ladder-type π-conjugated molecules was successfully achieved via a palladium-catalyzed intramolecular oxidative C-H/C-H cross-coupling reaction. This reaction provides a variety of π-conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur atoms, and a carbonyl group. The π-conjugated molecules were synthesized efficiently, even in gram scale, and larger π-conjugated molecules were also obtained by a double C-H/C-H cross-coupling reaction and successive oxidative cycloaromatization.

Full text of DOI:10.1002/chem.201501116

DOI: 10.1002/chem.201501116
Communication
&
CÀH Activation
Palladium-Catalyzed Construction of Heteroatom-Containing
p-Conjugated Systems by Intramolecular Oxidative
CÀH/CÀH Coupling Reaction
Kenta Saito,[a] Prasanna Kumara Chikkade,[a] Motomu Kanai,*[a, b] and Yoichiro Kuninobu*[a, b]
An important factor in the progress of organic electronics is
Abstract: Synthesis of heteroatom-containing ladder-type
p-conjugated molecules was successfully achieved via
a palladium-catalyzed intramolecular oxidative CÀH/CÀH
cross-coupling reaction. This reaction provides a variety of
p-conjugated molecules bearing heteroatoms, such as ni-
trogen, oxygen, phosphorus, and sulfur atoms, and a car-
bonyl group. The p-conjugated molecules were synthe-
sized efficiently, even in gram scale, and larger p-conjugat-
ed molecules were also obtained by a double CÀH/CÀH
cross-coupling reaction and successive oxidative cycloaro-
matization.
the development of new synthetic methods. For the synthesis
of ladder-type p-conjugated molecules bearing heteroatoms,
construction of heterocyclic rings, which are crucial backbones
of the p-conjugated molecules, is an important step. Therefore,
several synthetic methods have been developed for construct-
ing heterocycles, and the most popular method involves cou-
pling reactions between dilithiated biaryls and heteroatom
compounds bearing two or more halogen atoms (Figure 2a).[2]
As the reaction requires the use of pre-activated substrates (di-
lithiated biaryls) and moisture-sensitive heteroatom (Y) diha-
lides, the formation of side products, such as metal halides,
and low functional group tolerance cannot be avoided. Anoth-
er method utilizes intramolecular reductive double cyclization
with an alkyne moiety (Figure 2b).[3] In this reaction, a strong
reductant (lithium naphthalenide) is necessary to promote the
reaction. There are many recent reports of direct CÀH transfor-
mations, and several research groups have reported the syn-
thesis of organic functional molecules using CÀH bond trans-
formations.[4] Two other methods synthesize ladder-type p-con-
jugated molecules containing heteroatoms by either intramo-
lecular cross-coupling reactions between CÀH and CÀOTf
bonds (Figure 2c)[5] or intramolecular[6] and intermolecular[7]
coupling reactions between CÀH and heteroatomÀH bonds
(Figure 2d).
Ladder-type p-conjugated molecules containing heteroatoms
have recently received much attention because of their useful-
ness as organic functional materials, such as organic light-emit-
ting diodes, organic thin film transistors, and photovoltaic de-
vices (Figure 1).[1]
The CÀH/CÀH coupling reactions are also attractive because
such transformations are more direct and efficient than transi-
tion metal-catalyzed cross-coupling reactions between organo
halides (or triflates) and organometallic reagents.[8] Several ex-
amples of such transformations have been reported.[9–22] Syn-
thesis of heteroatom-containing ladder-type p-conjugated
molecules by transition metal-catalyzed oxidative CÀH/CÀH
coupling reactions, however, is still rare.[23,24] We report herein
general palladium-catalyzed intramolecular oxidative CÀH/CÀH
coupling reactions between heteroaromatic and aromatic
rings, and its application to the synthesis of several classes of
heteroatom-containing ladder-type p-conjugated molecules
(Figure 2e).
Figure 1. Several examples of heteroatom-containing ladder-type p-conju-
gated molecules.
[a] K. Saito, Dr. P. K. Chikkade, Prof. Dr. M. Kanai, Prof. Dr. Y. Kuninobu
Graduate School of Pharmaceutical Sciences
The University of Tokyo
We first optimized the reaction conditions using 1-([1,1’-bi-
phenyl]-2-yl)-1H-imidazole (1a) as a model substrate (for de-
tails of the optimization, see Tables S1 and S2). The intramolec-
ular CÀH/CÀH coupling reaction did not proceed well under
the reported reaction conditions (Table S1, entries 1–3).[11c,13c,16c]
Therefore, we investigated the reaction conditions to efficiently
promote the desired coupling reaction. As a result, the desired
coupling product 2a was obtained in 62% yield (Table 1).
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
E-mail: kanai@mol.f.u-tokyo.ac.jp
kuninobu@mol.f.u-tokyo.ac.jp
[b] Prof. Dr. M. Kanai, Prof. Dr. Y. Kuninobu
ERATO (Japan) Science and Technology Agency (JST)
Kanai Life Science Catalysis Project
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501116.
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a ladder-type product 2b in 88% yield.[22] When using biphen-
yl-substituted heteroaromatic compounds as substrates, such
as imidazole, indole, benzothiophene, and benzofuran, the cor-
responding p-conjugated molecules 2c–2e were obtained in
moderate to good yields.[25]
The reaction conditions in Table 1 were applied to the syn-
thesis of heteroatom- or carbonyl-bridged ladder-type mole-
cules (Table 2). Reaction of 3-(naphthalen-1-yloxy)benzo[b]thio-
phene (3a) under the optimized reaction conditions gave the
desired product 4a in only 22% yield. Re-optimization of the
reaction conditions by increasing the amount of AgOPiv with-
out the addition of [Cu(OPiv)2] and CsF improved the yield of
4a to 80%. Benzothiophene, benzofuran, and indole skeletons
could also be incorporated into the synthesis of ladder-type
products, 4a–4d, 4k, 4e, and 4 f–4j, respectively.[26] The bridg-
ing heteroatoms, oxygen, nitrogen, phosphorus, and sulfur
atoms introduced into the products (oxygen: 4a, 4b, and 4k;
nitrogen: 4c, 4e, 4 f, and 4g; phosphorus: 4i; and sulfur: 4j)
broaden the scope of the developed method. Carbonyl
bridged ladder-type molecules 4d and 4h were also synthe-
sized in moderate to high yield. Notably, CÀH/CÀH coupling
occurred at both the 2- and 3-positions of the heteroaromatic
moieties. For synthesis of 4k, the oxidative CÀH/CÀH coupling
reaction proceeded without loss of the bromine atom. Further
transformations could be achieved using the bromine atom.
Figure 2. Several synthetic methods of heteroatom-containing ladder-type
p-conjugated molecules.
Table 1. Synthesis of ladder-type p-conjugated molecules 2 from ortho-
phenylene-bridged biaryl compounds 1.
Table 2. Synthesis of ladder-type p-conjugated molecules 4 from heter-
oatom- or carbonyl-bridged biaryl compounds 3.
[a] [Pd(OPiv)2] (5.0 mol%), AgOPiv (15 mol%), [Cu(OPiv)2] (2.0 equiv), CsF
(2.0 equiv), DMF, 48 h. [b] [Pd(OPiv)2] (10 mol%), [Cu(OPiv)2] (2.0 equiv),
DMF, 36 h. [c] [Pd(OPiv)2] (10 mol%), AgOPiv (3.0 equiv), PivOH, 36 h.
[d] [Pd(OPiv)2] (10 mol%), AgOPiv (3.0 equiv), DMF, 48 h. [e] [Pd(OPiv)2]
(20 mol%), AgOPiv (3.0 equiv), DMF, 24 h. [f] [Pd(OPiv)2] (10 mol%),
AgOPiv (3.0 equiv), DMF, 36 h.
[a] [Pd(OPiv)2] (10 mol%), AgOPiv (3.0 equiv), DMF, 48 h. [b] [Pd(OPiv)2]
(10 mol%), [Cu(OPiv)2] (2.0 equiv), DMF, 36 h. [c] [Pd(OPiv)2] (10 mol%),
[Cu(OPiv)2] (2.0 equiv), PivOH, 36 h. [d] [Pd(OPiv)2] (10 mol%), AgOPiv
(3.0 equiv), PivOH, 36 h. [e] [Pd(OPiv)2] (20 mol%), AgOPiv (3.0 equiv),
DMF, 36 h.
We then investigated intramolecular C(aromatic)ÀH/
C(heteroaromatic)ÀH coupling reactions of several ortho-phen-
ylene-bridged substrates (Table 1). Reaction of 1-biphenylbenz-
imidazole (1b) under the optimized reaction conditions gave
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In Tables 1 and 2, the use of a suitable oxidant (AgOPiv or
[Cu(OPiv)2]) tended to depend on the nature of the substrates
and this tendency was enhanced by electronic factors (see
Table S3 for the details): 1) In the case of substrates with an
electron-withdrawing cross-linking, such as a carbonyl group
or phosphine oxide moiety, a stronger oxidant, AgOPiv,[27] was
necessary. In contrast, a weaker oxidant [Cu(OPiv)2][27] gave
higher yields when using substrates with an electron-donating
cross-linking, such as a nitrogen atom; and 2) AgOPiv was
a suitable oxidant for substrates with a benzothiophene or
benzofuran moiety. In contrast, [Cu(OPiv)2] served as a better
oxidant when using substrates bearing an indole or imidazole.
The proposed reaction mechanism for the formation of het-
eroatom-containing ladder-type p-conjugated molecules is as
follows (Scheme 1):[28,29] 1) CÀH bond activation of a heteroaro-
matic ring to give a heteroaryl–palladium species by a concert-
ed metalation–deprotonation mechanism via the elimination
of pivalic acid; 2) CÀH bond activation of an aromatic ring to
give a palladacyclic intermediate by a concerted metalation–
deprotonation mechanism via the elimination of pivalic acid;
and 3) AgOPiv- or [Cu(OPiv)2]-mediated oxidative reductive
elimination to give p-conjugated molecule 4 and regenerate
the palladium catalyst [Pd(OPiv)2].
cross-coupling reaction, and the desired ladder-type p-conju-
gated molecule 6 was obtained in 62% yield.
A larger p-conjugated system 9 could be constructed by
double cyclization of 7 and successive oxidative cycloaromati-
zation of the formed 8 [Eq. (3)]. Irradiation of product 9 with
365 nm UV/Vis light produced blue and light blue fluorescence
in chloroform (or tetrahydrofuran) solution and in the solid
state, respectively. The fluorescent quantum yield was 0.82 (for
details, see Supporting Information).
Scheme 1. Proposed mechanism for the formation of CÀH/CÀH coupling
products 4.
The reaction could be performed in gram-scale, and the
yield was not decreased much compared with the yield in
Table 2 (3a: 55.3 mg scale). Treatment of 2.10 g of 3a with
a catalytic amount of [Pd(OPiv)2] and oxidant AgOPiv produced
1.46 g of 4a in 70% yield [Eq. (1)].
In summary, we successfully achieved palladium-catalyzed
construction of heteroatom-containing p-conjugated systems
by intramolecular oxidative CÀH/CÀH coupling reactions be-
tween phenyl (or naphthyl) and heteroaryl groups (benzothio-
phene, benzofuran, and indole skeletons). Using ortho-phenyl-
ene-, heteroatom-, and carbonyl-bridged biaryl compounds as
substrates, we synthesized a variety of ladder-type p-conjugat-
ed molecules containing heteroatoms, such as nitrogen,
oxygen, phosphorus, and sulfur atoms. The coupling reactions
proceeded at both the 2- and 3-positions of the heteroaryls.
This synthetic method is highly efficient and affords the de-
sired products in a smaller number of reaction steps compared
with the previously reported methods. The reaction also pro-
ceeded in good yield even in gram scale. A double intramolec-
ular oxidative CÀH/CÀH cross-coupling reaction and successive
A ladder-type p-conjugated molecule was synthesized by
double cyclization [Eq. (2)]. Treatment of a biphenyl derivative
bearing two benzothiophene moieties linked with oxygen
atoms 5 and a mixture of a palladium catalyst [Pd(OPiv)2] and
oxidant AgOPiv led to an intramolecular double CÀH/CÀH
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gulis, J. Am. Chem. Soc. 2011, 133, 13577; e) N. Kuhl, M. N. Hopkinson, F.
Glorius, Angew. Chem. Int. Ed. 2012, 51, 8230; Angew. Chem. 2012, 124,
8354.
oxidative cycloaromatization gave p-conjugated molecules
with a large p-conjugated system. We expect that this reaction
will be a useful and practical method for the synthesis of het-
eroatom-containing ladder-type p-conjugated molecules.
[12] Y. Izawa, S. S. Stahl, Adv. Synth. Catal. 2010, 352, 3223.
[13] a) D. R. Stuart, K. Fagnou, Science 2007, 316, 1172; b) D. R. Stuart, E. Vil-
lemure, K. Fagnou, J. Am. Chem. Soc. 2007, 129, 12072; c) T. A. Dwight,
N. R. Rue, D. Charyk, R. Josselyn, B. DeBoef, Org. Lett. 2007, 9, 3137; d) S.
Potavathri, A. S. Dumas, T. A. Dwight, G. R. Naumiec, J. M. Hammann, B.
DeBoef, Tetrahedron Lett. 2008, 49, 4050; e) C. C. Malakar, D. Schmidt, J.
Conrad, U. Beifuss, Org. Lett. 2011, 13, 1378. See also, Ref. [11d].
[14] H. Li, J. Liu, C.-L. Sun, B.-J. Li, Z.-J. Shi, Org. Lett. 2011, 13, 276.
[15] a) M. Kitahara, N. Umeda, K. Hirano, T. Satoh, M. Miura, J. Am. Chem. Soc.
2011, 133, 2160; b) M. Nishino, K. Hirano, T. Satoh, M. Miura, Angew.
Chem. Int. Ed. 2012, 51, 6993; Angew. Chem. 2012, 124, 7099; c) M. Nish-
ino, K. Hirano, T. Satoh, M. Miura, Angew. Chem. Int. Ed. 2013, 52, 4457;
Angew. Chem. 2013, 125, 4553.
[16] a) K. L. Hull, M. S. Sanford, J. Am. Chem. Soc. 2007, 129, 11904; b) J.
Wencel-Delord, C. Nimphius, H. Wang, F. Glorius, Angew. Chem. Int. Ed.
2012, 51, 13001; Angew. Chem. 2012, 124, 13175; c) J. Dong, Z. Long, F.
Song, N. Wu, Q. Guo, J. Lan, J. You, Angew. Chem. Int. Ed. 2013, 52, 580;
Angew. Chem. 2013, 125, 608; d) X. Qin, H. Liu, D. Qin, Q. Wu, J. You, D.
Zhao, Q. Guo, X. Huang, J. Lan, Chem. Sci. 2013, 4, 1964; e) B. Liu, Y.
Huang, J. Lan, F. Song, J. You, Chem. Sci. 2013, 4, 2163.
Experimental Section
Gram-scale procedure for palladium-catalyzed synthesis of het-
eroatom-containing p-conjugated molecule via intramolecular
CÀH/CÀH coupling: A mixture of 3-(1-naphthalenyloxy)benzo[b]-
thiophene (3a, 2.10 g, 7.60 mmol), [Pd(OPiv)2] (235 mg,
0.760 mmol), and AgOPiv (4.76 g, 22.8 mmol) in DMF (76 mL) was
heated at 1508C for 48 h under Ar atmosphere. To the resulting
mixture was added sat. aq. NaHCO3. The mixture was extracted
with toluene (3ꢁ200 mL) for three times. The combined organic
layer was dried over anhydrous Na2SO4. The organic layer was fil-
trated and concentrated under vacuum. The residue was purified
by column chromatography on silica gel (eluent: hexane) to give
benzo[4,5]thieno[3,2-b]naphtho[2,1-d]furan (4a, 1.46 g, 70% yield).
[17] a) B. Akermark, L. Eberson, E. Jonsson, E. Petterson, J. Org. Chem. 1975,
40, 1365; b) T. Watanabe, S. Ueda, S. Inuki, S. Oishi, N. Fujii, H. Ohno,
Chem. Commun. 2007, 4516; c) B. Liꢂgault, D. Lee, M. P. Huestis, D. R.
Stuart, K. Fagnou, J. Org. Chem. 2008, 73, 5022; d) T. Watanabe, S. Oishi,
N. Fujii, H. Ohno, J. Org. Chem. 2009, 74, 4720; e) H. J. Knçlker, Chem.
Lett. 2009, 38, 8.
Acknowledgements
This work was supported in part by ERATO from JST and the
Ministry of Education, Culture, Sports, Science, and Technology
of Japan.
[18] A. Shiotani, H. Itatani, Angew. Chem. Int. Ed. Engl. 1974, 13, 471; Angew.
Chem. 1974, 86, 478.
[19] N. Ishida, Y. Nakanishi, T. Morita, M. Murakami, Chem. Lett. 2011, 40,
1047.
Keywords: CÀH activation · CÀH/CÀH coupling · heteroatom ·
palladium · pi-conjugated system
[20] K. Morimoto, M. Itoh, K. Hirano, T. Satoh, Y. Shibata, K. Tanaka, M. Miura,
Angew. Chem. Int. Ed. 2012, 51, 5359; Angew. Chem. 2012, 124, 5455.
[21] a) H. Li, R.-Y. Zhu, W.-J. Shi, K.-H. He, Z.-J. Shi, Org. Lett. 2012, 14, 4850;
b) P. Gandeepan, C.-H. Hung, C.-H. Cheng, Chem. Commun. 2012, 48,
9379.
[22] a) L. Ackermann, R. Jeyachandran, H. K. Potukuchi, P. Novꢃk, L. Buttner,
Org. Lett. 2010, 12, 2056; b) D. G. Pintori, M. F. Greaney, J. Am. Chem.
Soc. 2011, 133, 1209; c) M. Sun, H. Wu, J. Zhen, W. Bao, Adv. Synth.
Catal. 2012, 354, 835; d) G. Meng, H.-Y. Niu, G.-R. Qu, J. D. Fossey, J.-P. Li,
H.-M. Guo, Chem. Commun. 2012, 48, 9601; e) V. P. Reddy, T. Iwasaki, N.
Kambe, Org. Biomol. Chem. 2013, 11, 2249. See also, ref. [13c].
[23] S. K. Guchhait, M. Kashyap, S. Kandekar, Tetrahedron Lett. 2012, 53,
3919.
[24] During our investigation, synthesis of carbonyl-bridged or sulfur-con-
taining ladder-type molecules by palladium-catalyzed intramolecular
oxidative CÀH/CÀH coupling reaction was reported; a) Y. Ma, J. You, F.
Song, Chem. Eur. J. 2013, 19, 1189; b) P. Oechsle, J. Paradies, Org. Lett.
2014, 16, 4086.
[25] These products 2a–2e showed blue or purple fluorescence in both
chloroform solution and solid state by irradiation of 365 nm UV/Vis
light.
[1] For a review of ladder-type molecules, see: a) U. Scherf, J. Mater. Chem.
1999, 9, 1853; b) A. Fukazawa, S. Yamaguchi, Chem. Asian J. 2009, 4,
1386; c) K. Takimiya, S. Shinamura, I. Osaka, E. Miyazaki, Adv. Mater.
2011, 23, 4347; d) J.-S. Wu, S.-W. Cheng, Y.-J. Cheng, C.-S. Hsu, Chem.
Soc. Rev. 2015, 44, 1113.
[2] a) J. Dubac, A. Laporterie, G. Manuel, Chem. Rev. 1990, 90, 215; b) R. F.
Chen, Q. L. Fan, C. Zheng, W. Huang, Org. Lett. 2006, 8, 203.
[3] S. Yamaguchi, C. Xu, K. Tamao, J. Am. Chem. Soc. 2003, 125, 13662.
[4] For a recent review, see: J. Wencel-Delord, F. Glorius, Nat. Chem. 2013,
5, 369.
[5] a) M. Shimizu, K. Mochida, T. Hiyama, Angew. Chem. Int. Ed. 2008, 47,
9760; Angew. Chem. 2008, 120, 9906; b) K. Mochida, M. Shimizu, T.
Hiyama, J. Am. Chem. Soc. 2009, 131, 8350; c) R. Shintani, H. Otomo, K.
Oka, T. Hayashi, J. Am. Chem. Soc. 2012, 134, 7305.
[6] a) T. Ureshino, T. Yoshida, Y. Kuninobu, K. Takai, J. Am. Chem. Soc. 2010,
132, 14324; b) Y. Kuninobu, T. Yoshida, K. Takai, J. Org. Chem. 2011, 76,
7370; c) Y. Kuninobu, K. Origuchi, K. Takai, Heterocycles 2012, 85, 3029;
d) Y. Kuninobu, K. Yamauchi, N. Tamura, T. Seiki, K. Takai, Angew. Chem.
Int. Ed. 2013, 52, 1520; Angew. Chem. 2013, 125, 1560.
[26] These products 4a–4c, 4e, 4g, and 4i–4k showed blue or light blue
fluorescence in both chloroform solution and solid state by irradiation
of 365 nm UV/Vis light except a chloroform solution of 4d and 4h.
[27] A. J. Bard, R. Parsons, J. Jordan, Standard Potentials in Aqueous Solution,
CRC Press, Florida, 1985.
[28] The similar possible mechanism was proposed using [Pd(OAc)2] as a cat-
alyst. See: ref. [11b–d], [22b], and [22d].
[29] For KIE experiments, see Supporting Information.
[7] Q. Xiao, X. Meng, M. Kanai, Y. Kuninobu, Angew. Chem. Int. Ed. 2014, 53,
3168; Angew. Chem. 2014, 126, 3232.
[8] For reviews of oxidative CÀH/CÀH cross-coupling reactions, see a) W.
Han, A. R. Ofial, Synlett 2011, 1951 (catalytic reactions); b) K. Hirano, M.
Miura, Chem. Commun. 2012, 48, 10704 (stoichiometric reactions).
[9] For recent reviews, see: a) S.-L. You, J.-B. Xia, Top. Curr. Chem. 2009, 292,
165; b) C. S. Yeung, V. M. Dong, Chem. Rev. 2011, 111, 1215.
[10] K. Masui, H. Ikegami, A. Mori, J. Am. Chem. Soc. 2004, 126, 5074.
[11] a) Y. Li, J. Jin, W.-X. Qian, W.-L. Bao, Org. Biomol. Chem. 2010, 8, 326; b) P.
Xi, F. Yang, S. Qin, D. Zhao, J. Lan, G. Gao, C. Hu, J. You, J. Am. Chem.
Soc. 2010, 132, 1822; c) W. Han, P. Mayer, A. R. Ofial, Angew. Chem. Int.
Ed. 2011, 50, 2178; Angew. Chem. 2011, 123, 2226; d) H.-Q. Do, O. Dau-
Received: March 23, 2015
Published online on && &&, 0000
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COMMUNICATION
Up the ladder: Synthesis of heteroa-
tom-containing ladder-type p-conjugat-
ed molecules was successfully achieved
via palladium-catalyzed intramolecular
oxidative CÀH/CÀH cross-coupling reac-
tion (see scheme). This reaction pro-
vides a variety of p-conjugated mole-
cules bearing heteroatoms, such as ni-
trogen, oxygen, phosphorus, and sulfur
atoms, and a carbonyl group.
&
CÀH Activation
K. Saito, P. K. Chikkade, M. Kanai,*
Y. Kuninobu*
&& – &&
Palladium-Catalyzed Construction of
Heteroatom-Containing p-Conjugated
Systems by Intramolecular Oxidative
CÀH/CÀH Coupling Reaction
Chem. Eur. J. 2015, 21, 1 – 5
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These are not the final page numbers! ÞÞ