Nickel Catalysis Enables Oxidative C(sp2)–H/C(sp2)–H Cross-Coupling Reactions between Two Heteroarenes

Article abstract of DOI:10.1002/anie.201606529

Nickel can be used to promote oxidative C(sp²)?H/C(sp²)?H cross-coupling between two heteroarenes. The reaction scope can be extended to aromatic carboxamides as the coupling partner. The reaction exhibits high functional-group compatibility and broad substrate scope. The silver oxidant can be recycled to reduce costs and waste, which is very useful for practical applications.

Full text of DOI:10.1002/anie.201606529

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201606529
German Edition: DOI: 10.1002/ange.201606529
Homogeneous Catalysis
Nickel Catalysis Enables Oxidative C(sp2)–H/C(sp2)–H Cross-Coupling
Reactions between Two Heteroarenes
Yangyang Cheng, Yimin Wu, Guangyin Tan, and Jingsong You*
2
À
Abstract: Nickel can be used to promote oxidative C(sp ) H/
2
À
C(sp ) H cross-coupling between two heteroarenes. The
reaction scope can be extended to aromatic carboxamides as
the coupling partner. The reaction exhibits high functional-
group compatibility and broad substrate scope. The silver
oxidant can be recycled to reduce costs and waste, which is very
useful for practical applications.
B
iheteroaryl structural motifs are frequently found in
various bioactive molecules, natural products, agrochemicals,
pharmaceuticals, and organic functional materials.[1] The
development of straightforward access to biheteroarenes
has thus been a topic of immense importance in organic
synthesis. Over the past few decades, transition-metal-cata-
lyzed cross-coupling reactions with organometallic reagents,
organic halides, or pseudohalides have been used to assemble
these biheteroaryl units. However, these methods unavoid-
ably require tedious preactivation of substrates and suffer
from low efficiency with coupling partners with reactive
functional groups. From a step- and atom-economy stand-
À
Scheme 1. Nickel-catalyzed C H (hetero)arylation of heteroarenes.
ily available aryl esters and phenol derivatives.[9] Recently,
À
nickel salts have emerged as effective catalysts for direct C
À
À
À
point, oxidative C H/C H cross-coupling between two
heteroarenes would be an ideal approach to forge biheter-
oaryl structural motifs.[2] Tremendous efforts have been
H/C H cross-coupling reactions. Chatani and Shi have
disclosed that a nickel/N,N-bidentate directing group can be
used to promote oxidative C(sp ) H/C(sp ) H and C(sp ) H/
2
3
2
À
À
À
[7g,10]
À
À
À
focused on the direct C H/C H cross-coupling of two
(hetero)arenes in recent years. In general, these methods
employ a noble-metal catalyst, such as Pd,[3] Rh,[4] Ru,[4b] and
Au[5] complexes. However, the rarity and costliness of these
complexes often restricts the practicality to some extent. The
development of inexpensive and naturally abundant metals
(Fe, Co, Ni, Cu, etc.) instead of noble metals as the catalysts is
an appealing yet challenging task. To date, only copper-
C(sp) H cross-coupling reactions.
However, except for
examples of deprotonative dimerization of heteroarenes,[11]
2
2
À
À
nickel-catalyzed oxidative C(sp ) H/C(sp ) H cross-coupling
of two heteroarenes has not yet been achieved. Herein, we
wish to demonstrate the potential of nickel catalysis in
oxidative C H/C H cross-coupling reactions between two
heteroarenes (Scheme 1b).
À
À
Given that 8-aminoquinoline is a highly efficient N,N-
À
À
À
catalyzed or -mediated oxidative C H/C H cross-coupling
reactions between two heteroarenes have been reported.[6]
As an abundant and low-cost transition metal, nickel has
bidentate directing group in transition metal-catalyzed C H
bond activation,[12] we initially focused on the nickel-cata-
À
À
lyzed oxidative C H/C H cross-coupling of N-(quinolin-8-
yl)thiophene-2-carboxamide 1a with benzothiazole 2a
[Eq. (1); Table S1 in the Supporting Information]. To our
À
shown its great potential in direct C H bond functionaliza-
tions.[7] Recent reports have disclosed that nickel catalysis
À
assisted by bases or ligands can promote the direct C H
(hetero)arylation of heteroarenes with (hetero)aryl halides,
pseudohalides, or organometallic reagents to assemble bi-
(hetero)arenes (Scheme 1a).[8] Unlike other metal catalysts,
nickel catalysts have also been utilized to catalyze the direct
(hetero)arylation of heteroarenes with inexpensive and read-
[*] Y. Cheng, Y. Wu, G. Tan, Prof. Dr. J. You
Key Laboratory of Green Chemistry and Technology
of Ministry of Education, College of Chemistry, Sichuan University
29 Wangjiang Road, Chengdu 610064 (PR China)
E-mail: jsyou@scu.edu.cn
delight, the desired product 3a was obtained in 28% yield
when employing 15 mol% of NiCl2·6H2O as the catalyst,
2.0 equiv of AgOAc as the oxidant, and 1.0 equiv of PivOH as
the additive in 1,2-dichloroethane at 1208C for 12 h (Table S1,
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201606529.
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Table 1: The scope with respect to the heteroarenes.[a,b]
entry 1). Analysis of the single crystal X-ray diffraction
pattern of 3a demonstrated that the reaction selectively
occurred at the thiophene C3 position (Figure S1 in the
Supporting Information).[13] After screening several solvents
(N,N-dimethylformamide (DMF), 1,4-dioxane, toluene, and
o-xylene), toluene proved to be the best choice, and the yield
was improved to 44% (Table S1, entries 2–5). Further opti-
mization of the silver oxidants showed that Ag2CO3 was the
most efficient oxidant (Table S1, entries 8–10). Other oxi-
dants such as manganese salt (Mn(OAc)2·4H2O), chlorate
(NaClO3), persulfate (K2S2O8), and organic oxidants (BQ and
DDQ) were ineffective (Table S1, entries 11–15). It is worth
noting that PivOH as an additive was necessary. Only 34%
yield was achieved in the absence of PivOH (Table S1,
entry 16). Further addition of PPh3 increased the yield to 76%
(Table S1, entry 17). Subsequently, both the amount of nickel
catalyst and the nickel source were investigated. Using
10 mol% of NiCl2·6H2O resulted in a decreased yield of
63% (Table S1, entry 18). The more inexpensive Ni-
(OAc)2·4H2O[14] proved to be the most efficient catalyst and
delivered the desired product in 78% yield (Table S1,
entries 19–24). Finally, the best result was observed under
a catalytic system comprising Ni(OAc)2·4H2O (15 mol%),
Ag2CO3 (2.0 equiv), PivOH (1.0 equiv), and PPh3 (30 mol%)
in toluene at 1208C for 12 h. Under the optimized conditions,
several structurally similar thiophene-2-carboxamides were
examined and no desired product was observed (Scheme S1).
These control experiments suggest that the 8-aminoquinoline
moiety plays an indispensable role. It is notable that only
trace amounts of the homocoupled product of 1a was
produced and no homocoupling reaction of 2a was detected
under the catalytic system.
By using the optimized conditions, we set out to explore
the scope with respect to the heteroarenes, as summarized in
Table 1. To our delight, a variety of heteroarenes could
directly couple with 1a in moderate to good yields. Thiazoles
and benzothiazoles with both electron-donating and electron-
withdrawing groups could be engaged in this transformation
(Table 1, 3a–m). A series of sensitive functional groups,
including aldehyde, cyano, ester, nitro, acyl, chloro, bromo,
and even hydroxy groups, were well tolerated under the
current conditions, which may allow high diversity in the
synthesis of functionalized biheteroarenes. Other heteroar-
enes such as benzoxazole, purine, and caffeine could also be
converted into the desired products (Table 1, 3n–q).
[1,2,4]Triazolo[1,5-a]pyrimidine reacted with 1a at the C7
position to deliver 3r in 74% yield. To our delight, besides
1,3-azoles, the 1,2-azole-like indazole also smoothly under-
went the heteroarylation in 63% yield (Table 1, 3s). It is
worthy of note that these reactions proceeded at the relatively
[a] Reaction conditions: N-(Quinolin-8-yl)thiophene-2-carboxamide 1a
(0.2 mmol), heteroarene (1.5 equiv), Ni(OAc)2·4H2O (15 mol%),
Ag2CO3 (2.0 equiv), and PivOH (1.0 equiv) in toluene (0.5 mL) at 1208C
for 12 h under N2 atmosphere. [b] Yield of isolated product. [c] 4.0 mmol
scale. [d] 24 h. [e] PivOH (2.0 equiv) and o-xylene instead of toluene.
[f] PivOH (2.0 equiv) and o-xylene instead of toluene at 1408C for 24 h.
out on a gram scale (4.0 mmol), and an acceptable yield of
68% was obtained (Table 1, 3a), thus demonstrating the
applicability of this method for mass production.
Next, we turned our efforts to the scope with respect to
the heteroaromatic carboxamide derivatives (Table 2). An
array of electron-rich heteroaromatic carboxamides, such as
thienyl, benzothienyl, indolyl, and pyrrolyl carboxamides,
underwent the coupling reaction in satisfactory yields
(Table 2, 4a–g). Chloro and bromo groups on the thienyl
moiety were tolerated, which could provide an opportunity
for further functionalization through cross-coupling (Table 2,
4b–c). It is worth noting that our method was also suitable for
benzamide derivatives (Table 2, 4h–k). For unsubstituted
benzamide, which bears two potentially reactive sites, the
disubstituted product was detected (Table 2, 4h). Reactions
of meta-substituted benzamide derivatives only occurred at
the less sterically hindered position (Table 2, 4i,j). 1-Naph-
thamide could also be transformed into the corresponding
bi(hetero)arene (Table 2, 4k).
À
À
acidic C H bond of the azoles. The pKa range of reactive C H
bonds is approximately 25–35 (benzothiazole: ca. 27, thiazo-
le: ca. 29, benzoxazole: ca. 25, purine: ca. 29; indazo-
le: ca. 35).[15] However, the pKa value is not the sole governing
factor determining reactivity and thus cannot be used to
forecast the reactivity of other (hetero)arenes. For example,
À
pentafluorobenzene bearing an acidic C H bond (pKa: 29)
did not undergo coupling under the optimized conditions. It is
Subsequently, we attempted to remove the directing
group. Gratifyingly, the 8-aminoquinoline moiety could be
worthy of note that the reaction of 1a with 2a could be carried
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Table 2: The scope with respect to the (hetero)aromatic carbox-
amides.[a,b]
To gain some insights into the reaction mechanism,
hydrogen/deuterium (H/D) exchange control experiments
were first conducted [Eq. (S2)–(S4)]. When N-(quinolin-8-
yl)benzamide 1i was treated with D2O under the optimized
conditions, 14% of 1i was deuterated in 2 h [Eq. (S2)]. On the
other hand, 85% H/D scrambling was obtained with benzox-
azole 2n [Eq. (S3)]. Treatment of 1i and 2n with D2O gave
a similar H/D exchange ratio for 2n, whereas deuterated [Dn]-
1i was not obtained [Eq. (S4)]. These results suggest that the
metalation order 2n then 1i could be reasonable. Subse-
quently, kinetic isotope effect (KIE) experiments for both
coupling partners were carried out [Eq. (S5),(S6)]. The KIE
value of two parallel competition reactions of 1i and [D5]-1i
with 2n was found to be 1.92, while a value of 1.03 was
observed for the reactions of 2n and [D1]-2n with 1i, which
[a] Reaction conditions: heteroaromatic carboxamide (0.2 mmol), het-
eroarene (1.5 equiv), Ni(OAc)2·4H2O (15 mol%), Ag2CO3 (2.0 equiv),
and PivOH (1.0 equiv) in toluene (0.5 mL) at 1208C for 12 h under N2
atmosphere. [b] Yield of isolated product. [c] 1408C for 24 h. [d] AgOAc
(2.5 equiv) instead of Ag2CO3, and PivOH (2.0 equiv) in o-xylene
(0.5 mL). [e] AgOAc (2.5 equiv) instead of Ag2CO3, and PivOH
(2.0 equiv) in o-xylene (0.5 mL) at 1408C.
À
implies that C H bond cleavage of 1i could be involved in the
rate-determining step.[16] Furthermore, radical trapping
experiments were conducted. The reaction of 1a with 2a
gave only a slightly decreased yield in the presence of
1.0 equiv of 2,2,6,6-tetramethylpiperidine oxide (TEMPO;
for details, see Section XI in the Supporting Information). A
mixture of Ni(OAc)2·4H2O and 2a in toluene did not show
a significant electron paramagnetic resonance (EPR) signal
with the addition of free-radical spin-trapping agent DMPO
(5,5-dimethyl-1-pyrroline N-oxide). These observations indi-
cate a low possibility that a free-radical pathway is involved in
the reaction.
smoothly removed through base-assisted hydrolysis of heter-
oaromatic carboxamide. For example, the coupled product 3a
was hydrolyzed to produce the corresponding biheteroaro-
matic acid 3aa in a 61% yield in the presence of KOH
[Eq. (2)].
Based on the above results and some relevant publica-
tions,[6e,17] a plausible mechanism is proposed as shown in
Scheme 2. Initially, benzothiazole 2a reacts with the NiIII
species to give the intermediate IM1. Next, coordination of
N-(quinolin-8-yl)thiophene-2-carboxamide (1a) to the NiIII
center generates the nickel complex IM2. The resulting IM2
undergoes an intramolecular cyclonickelation to give the
diaryl nickel complex IM3, which was detected by MALDI-
TOF-MS (See Section XIII in the Supporting Information).
Reductive elimination of IM3 affords the NiI intermediate
IM4, which is then protonated to deliver the desired product
3a. Finally, reoxidation of the NiI species with Ag2CO3
regenerates the NiIII species to complete the catalytic cycle.
In conclusion, we have disclosed for the first time a nickel-
In order to reduce the cost and waste of the reaction, we
attempted to recycle the silver salt on a gram scale. To our
delight, Ag2CO3 could be simply regenerated after successive
dissolution of the silver residue with nitric acid, washing with
acetone, and precipitation with sodium carbonate [Eq. (3)].
The regenerated Ag2CO3 could smoothly promote the
coupling reaction to afford 3a in approximately 80% yield
without loss of activity even after third-round recovery
[Eq. (4); for details, see Section IX in the Supporting
Information].
À
À
catalyzed oxidative C H/C H cross-coupling reaction
between two heteroarenes with the aid of the 8-aminoquino-
line group. The method can also be applied with aromatic
carboxamides as the coupling partner. This reaction features
broad substrate scope, good functional-group tolerance,
gram-scale production capability, and recycling of the silver
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Angew. Chem. 2011, 123, 5477; d) C.-Y. He, Z. Wang, C.-Z. Wu,
F.-L. Qing, X. Zhang, Chem. Sci. 2013, 4, 3508; e) Y. Cheng, G.
Li, Y. Liu, Y. Shi, G. Gao, D. Wu, J. Lan, J. You, J. Am. Chem.
Soc. 2016, 138, 4730.
À
À
[4] Selected examples of Rh-catalyzed oxidative C H/C H cross-
coupling of two (hetero)arenes: a) N. Kuhl, M. N. Hopkinson, F.
Glorius, Angew. Chem. Int. Ed. 2012, 51, 8230; Angew. Chem.
2012, 124, 8354; b) 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; c) X. Qin, H. Liu, D. Qin, Q. Wu, J. You, D. Zhao,
Q. Guo, X. Huang, J. Lan, Chem. Sci. 2013, 4, 1964; d) Y. Huang,
D. Wu, J. Huang, Q. Guo, J. Li, J. You, Angew. Chem. Int. Ed.
2014, 53, 12158; Angew. Chem. 2014, 126, 12354; e) X. Qin, X. Li,
Q. Huang, H. Liu, D. Wu, Q. Guo, J. Lan, R. Wang, J. You,
Angew. Chem. Int. Ed. 2015, 54, 7167; Angew. Chem. 2015, 127,
7273; f) B. Li, J. Lan, D. Wu, J. You, Angew. Chem. Int. Ed. 2015,
54, 14008; Angew. Chem. 2015, 127, 14214.
[5] X. C. Cambeiro, N. Ahlsten, I. Larrosa, J. Am. Chem. Soc. 2015,
137, 15636.
À
[6] Recent examples of Cu-catalyzed or mediated oxidative C H/
À
C H cross-coupling of two (hetero)arenes: a) M. Kitahara, N.
Umeda, K. Hirano, T. Satoh, M. Miura, J. Am. Chem. Soc. 2011,
133, 2160; b) Z. Mao, Z. Wang, Z. Xu, F. Huang, Z. Yu, R. Wang,
Org. Lett. 2012, 14, 3854; c) X. Qin, B. Feng, J. Dong, X. Li, Y.
Xue, J. Lan, J. You, J. Org. Chem. 2012, 77, 7677; d) M. Nishino,
K. Hirano, T. Satoh, M. Miura, Angew. Chem. Int. Ed. 2012, 51,
6993; Angew. Chem. 2012, 124, 7099; e) M. Nishino, K. Hirano,
T. Satoh, M. Miura, Angew. Chem. Int. Ed. 2013, 52, 4457;
Angew. Chem. 2013, 125, 4553; f) S. Zhao, J. Yuan, Y.-C. Li, B.-F.
Shi, Chem. Commun. 2015, 51, 12823.
Scheme 2. Proposed reaction mechanism.
À
oxidant. Preliminary mechanistic studies suggest that C H
bond cleavage of (hetero)aromatic carboxamide is involved in
the rate-determining step. Further mechanistic studies and
applications of this method are ongoing in our laboratory.
À
[7] Recent reviews on iron, cobalt, and manganese-catalyzed C H
activations: a) E. Nakamura, N. Yoshikai, J. Org. Chem. 2010, 75,
6061; b) M. Moselage, J. Li, L. Ackermann, ACS Catal. 2016, 6,
498; c) W. Liu, L. Ackermann, ACS Catal. 2016, 6, 3743; Recent
Acknowledgements
À
reviews on nickel-catalyzed C H activations: d) Y. Nakao,
This work was supported by grants from the National NSF of
China (Nos 21432005, 21272160 and 21321061).
Chem. Rec. 2011, 11, 242; e) J. Yamaguchi, K. Muto, K. Itami,
Eur. J. Org. Chem. 2013, 19; f) L. C. M. Castro, N. Chatani,
Chem. Lett. 2015, 44, 410; Selected recent examples on nickel-
À
catalyzed C H activations: g) Y. Aihara, M. Tobisu, Y. Fuku-
Keywords: heteroarenes · homogeneous catalysis · nickel ·
oxidative cross-coupling · synthetic methods
moto, N. Chatani, J. Am. Chem. Soc. 2014, 136, 15509; h) A.
Yokota, N. Chatani, Chem. Lett. 2015, 44, 902; i) Z. Ruan, S.
Lackner, L. Ackermann, Angew. Chem. Int. Ed. 2016, 55, 3153;
Angew. Chem. 2016, 128, 3205; j) Z. Ruan, S. Lackner, L.
Ackermann, ACS Catal. 2016, 6, 4690.
[8] a) M. Tobisu, I. Hyodo, N. Chatani, J. Am. Chem. Soc. 2009, 131,
12070; b) J. Canivet, J. Yamaguchi, I. Ban, K. Itami, Org. Lett.
2009, 11, 1733; c) H. Hachiya, K. Hirano, T. Satoh, M. Miura,
Angew. Chem. Int. Ed. 2010, 49, 2202; Angew. Chem. 2010, 122,
2248; d) H. Hachiya, K. Hirano, T. Satoh, M. Miura, Chem-
CatChem 2010, 2, 1403; e) T. Yamamoto, K. Muto, M.
Komiyama, J. Canivet, J. Yamaguchi, K. Itami, Chem. Eur. J.
2011, 17, 10113; f) G.-R. Qu, P.-Y. Xin, H.-Y. Niu, D.-C. Wang,
R.-F. Ding, H.-M. Guo, Chem. Commun. 2011, 47, 11140.
[9] a) K. Muto, J. Yamaguchi, K. Itami, J. Am. Chem. Soc. 2012, 134,
169; b) K. Amaike, K. Muto, J. Yamaguchi, K. Itami, J. Am.
Chem. Soc. 2012, 134, 13573; c) K. Muto, T. Hatakeyama, J.
Yamaguchi, K. Itami, Chem. Sci. 2015, 6, 6792.
[10] Y.-H. Liu, Y.-J. Liu, S.-Y. Yan, B.-F. Shi, Chem. Commun. 2015,
51, 11650.
[11] The nickel-promoted deprotonative dimerization of heteroar-
enes: T. Truong, J. Alvarado, L. D. Tran, O. Daugulis, Org. Lett.
2010, 12, 1200.
[12] a) M. Corbet, F. D. Campo, Angew. Chem. Int. Ed. 2013, 52,
9896; Angew. Chem. 2013, 125, 10080; b) G. Rouquet, N.
Chatani, Angew. Chem. Int. Ed. 2013, 52, 11726; Angew.
Chem. 2013, 125, 11942.
[1] a) A. R. Murphy, J. M. J. Frꢀchet, Chem. Rev. 2007, 107, 1066;
b) R. A. Hughes, C. J. Moody, Angew. Chem. Int. Ed. 2007, 46,
7930; Angew. Chem. 2007, 119, 8076; c) R. E. Dolle, B. L.
Bourdonnec, K. Worm, G. A. Morales, C. J. Thomas, W. Zhang,
J. Comb. Chem. 2010, 12, 765; d) I. S. Young, P. D. Thornton, A.
Thompson, Nat. Prod. Rep. 2010, 27, 1801; e) C. Wang, H. Dong,
W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012, 112, 2208.
[2] Recent reviews: a) X. Bugaut, F. Glorius, Angew. Chem. Int. Ed.
2011, 50, 7479; Angew. Chem. 2011, 123, 7618; b) C. S. Yeung,
V. M. Dong, Chem. Rev. 2011, 111, 1215; c) C. Liu, H. Zhang, W.
Shi, A. Lei, Chem. Rev. 2011, 111, 1780; d) S. H. Cho, J. Y. Kim, J.
Kwak, S. Chang, Chem. Soc. Rev. 2011, 40, 5068; e) D. Zhao, J.
You, C. Hu, Chem. Eur. J. 2011, 17, 5466; f) Y. Wu, J. Wang, F.
Mao, F. Y. Kwong, Chem. Asian J. 2014, 9, 26; g) C. Liu, J. Yuan,
M. Gao, S. Tang, W. Li, R. Shi, A. Lei, Chem. Rev. 2015, 115,
12138.
À
À
[3] Selected examples of Pd-catalyzed oxidative C H/C H cross-
coupling of two (hetero)arenes: a) P. Xi, F. Yang, S. Qin, D.
Zhao, J. Lan, G. Gao, C. Hu, J. You, J. Am. Chem. Soc. 2010, 132,
1822; b) W. Han, P. Mayer, A. R. Ofial, Angew. Chem. Int. Ed.
2011, 50, 2178; Angew. Chem. 2011, 123, 2226; c) Z. Wang, K. Li,
D. Zhao, J. Lan, J. You, Angew. Chem. Int. Ed. 2011, 50, 5365;
4
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[13] CCDC 1447854 (3a) contains the supplementary crystallo-
[17] a) T. Yao, K. Hirano, T. Satoh, M. Miura, Angew. Chem. Int. Ed.
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
[14] Prices of frequently used nickel complexes from Aldrich:
Ni(OAc)2·4H2O: $170/1 kg, NiCl2·6H2O: $206/1 kg, Ni(OTf)2:
$38.1/1 g, Ni(cod)2: $33.8/1 g, Ni(acac)2: $33.2/5 g.
[15] K. Shen, Y. Fu, J.-N. Li, L. Liu, Q.-X. Guo, Tetrahedron 2007, 63,
1568.
2012, 51, 775; Angew. Chem. 2012, 124, 799; b) K. Yang, C.
Zhang, P. Wang, Y. Zhang, H. Ge, Chem. Eur. J. 2014, 20, 7241;
c) Q. Yan, Z. Chen, W. Yu, H. Yin, Z. Liu, Y. Zhang, Org. Lett.
2015, 17, 2482.
[16] E. M. Simmons, J. F. Hartwig, Angew. Chem. Int. Ed. 2012, 51,
3066; Angew. Chem. 2012, 124, 3120.
Received: July 6, 2016
Published online: && &&, &&&&
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Communications
Homogeneous Catalysis
Y. Cheng, Y. Wu, G. Tan,
J. You*
&&&& — &&&&
Nickel Catalysis Enables Oxidative
C(sp2)–H/C(sp2)–H Cross-Coupling
Reactions between Two Heteroarenes
An odd couple: The title reaction with the
aid of the 8-aminoquinoline group gives
biheteroaryl structural motifs. The reac-
tion exhibits high functional-group com-
patibility and broad substrate scope, and
the silver oxidant can be recycled to
reduce costs and waste.
6
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These are not the final page numbers!