PdII-Catalyzed Intermolecular Amination of Unactivated C(sp3)-H Bonds

Article abstract of DOI:10.1002/chem.201502375

Pd^II-catalyzed intermolecular amination of unactivated C(sp³)-H bonds has been successfully developed for the first time. This method provides a new way to achieve the challenging intermolecular amination of unactivated C(sp³

Full text of DOI:10.1002/chem.201502375

DOI: 10.1002/chem.201502375
Communication
&
Organic Synthesis |Very Important Paper|
PdII-Catalyzed Intermolecular Amination of Unactivated C(sp3)ÀH
Bonds
Quan Gou, Gang Liu, Zi-Ning Liu, and Jun Qin*[a]
Abstract: PdII-catalyzed intermolecular amination of unac-
tivated C(sp3)ÀH bonds has been successfully developed
for the first time. This method provides a new way to ach-
ieve the challenging intermolecular amination of unacti-
vated C(sp3)ÀH bonds, producing a variety of unnatural
b2-amino carboxylic acid analogues. This C(sp3)ÀH amina-
tion protocol is demonstrated with a broad substrate
scope, good functional-group tolerance, and chemoselec-
tivity. It is operated without use of phosphine ligand or
external oxidant.
The construction of CÀN bonds is a highly important field
since nitrogenated compounds are widely present in pharma-
ceuticals, agricultural chemicals, and natural products.[1] The
importance of this field has led to the rapid development of
CÀN bond-forming reactions. Particularly notable among these
reactions are Ullman–Goldberg-[2] and Buchwald–Hartwig-
type[3] amination/amidation reactions, which involve metal-cat-
Scheme 1. Intermolecular amination of unactivated C(sp3)ÀH bonds.
alyzed coupling of preactivated (hetero)aryl (pseudo)halides
with amines or amides. Despite these advances, recent years
have seen significant progress in direct CÀH activation/CÀN
a monodentate fluorinated aniline and was successful in the
preparation of only b2,2-amino carboxylic acid derivatives. De-
bond-forming reactions since this strategy eliminates the step
of substrate preactivation and, therefore, shortens the synthet-
ic route. Nevertheless, the CÀH activation/CÀN bond-forming
reactions are primarily focused on C(sp2)ÀH amination/amida-
tion catalyzed by diverse metals.[4–10] Development of intermo-
lecular amination/amidation of unactivated C(sp3)ÀH bonds is
challenging and still in its infancy. Recently, several examples
of intermolecular amidation of unactivated C(sp3)ÀH bonds
have appeared in the literature.[11] In comparison, intermolecu-
lar amination of unactivated C(sp3)ÀH bonds is rare,[12] al-
though the intramolecular version of this reaction has been re-
ported.[13] Until now, only two examples of Pd0-catalyzed inter-
molecular amination of unactivated C(sp3)ÀH bonds were indi-
vidually reported by Buchwald[12a] and Yu[12b] (Scheme 1a,b),
and these represent a major breakthrough in this challenge. In
Buchwald’s protocol, the nitrogen source was limited to aryl
amines. Yu’s method was operated under the assistance of
velopment of new methods for intermolecular amination of
unactivated C(sp3)ÀH bonds to expand the current limitations
is in high demand. Herein, we report the first example of PdII-
catalyzed intermolecular amination of unactivated C(sp3)ÀH
bonds (Scheme 1c). This method works under the assistance of
a bidentate directing group, 2-aminothioether,[14] and offers
a different method to achieve the intermolecular amination of
unactivated C(sp3)ÀH bonds. This reaction produces a variety
of unnatural and functional b2-amino carboxylic acid ana-
logues, a set of compounds that have wide biological and me-
dicinal applications.[15]
In a program directed to develop new CÀH activation reac-
tions,[16] we became interested in the investigation of direct
amination of b-C(sp3)ÀH bonds of a-monosubstituted propion-
ic acid derivatives. If successful, this transformation could pro-
duce a variety of unnatural b2-amino carboxylic acid analogues
in a straightforward manner. Amination of substrate 1a by
aminating reagent 2a, O-benzoyl hydroxylmorpholine,[17] was
chosen as the model reaction to begin the optimization
(Table 1). After screening a variety of PdII catalysts with Cs2CO3
as the base and benzene as the solvent (Table 1, entries 1–5),
we quickly identified PdCl2 as an optimal catalyst which afford-
ed the amination product 3aa in 85% yield (entry 5). Pd0 cata-
[a] Q. Gou, G. Liu, Z.-N. Liu, Prof. Dr. J. Qin
Key Laboratory of Medicinal Chemistry for Natural Resource
Ministry of Education, School of Chemical Science and Technology
Yunnan University, Kunming, Yunnan, 650091 (P.R. China)
E-mail: qinjun@ynu.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502375.
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Table 1. Optimization of reaction conditions.[a]
Table 2. Substrate scope of carboxylic acid derivatives.[a,b]
Entry
Pd catalyst
Base
Solvent
Yield [%][b]
1
2
3
4
Pd(OAc)2
[Pd(tfa)2]
[Pd(MeCN)4(BF4)2]
[PdCl2(cod)]
PdCl2
[Pd2(dba)3]
[Pd(PPh3)4]
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
CsOAc
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
benzene
toluene
dioxane
t-AmylOH
DMF
61
26
20
72
85
0
0
0
0
28
6
69
0
0
0
92
5
6[c]
7[c]
8[d]
9[e]
10
11
12
13
14
15
16[f]
PdCl2
PdCl2
PdCl2
PdCl2
benzene
[a] General procedure: 1a (0.20 mmol), 2a (0.40 mmol), Pd catalyst
(10 mol%), and base (0.40 mmol) in solvent (1.0 mL) under 110 8C for
1
24 h. [b] Determined by H NMR spectroscopic analysis of the crude prod-
uct using CH2Br2 as an internal standard. [c] Reaction under rigorous N2
protection. [d] Reaction with 20 mol% PPh3 under rigorous N2 protection
[e] Reaction with 20 mol% BINAP under rigorous N2 protection.
[f] 2.5 equiv of 2a was used. cod=1,5-cyclooctadiene; tfa=trifluoroacetic
acid.
lysts, such as [Pd2(dba)3] (dba=dibenzylideneacetone) or
[Pd(PPh3)4] were not effective (entries 6–7). Addition of phos-
phine ligands (PPh3 or BINAP) (BINAP=(2,2’-bis(diphenylphos-
phino)-1,1’-binaphthyl)) to PdCl2 completely inhibited the reac-
tion (entries 8–9). Further investigation of bases revealed that
Cs2CO3 was optimal. Other bases with different cation or
anions from Cs2CO3 were inferior (entries 10–11). Solvent ef-
fects on the reaction were significant. We found that nonpolar
solvents were tolerated in general. For example, besides ben-
zene, toluene also afforded 3aa in a useful 69% yield
(entry 12). On the contrary, polar solvents were not effective
(entries 13–15). Gratifyingly, when the amount of 2a was used
in 2.5 equivalents, the yield of 3aa was further increased to
92% (entry 16).
[a] Optimal reaction conditions:
(10 mol%), and Cs2CO3 (0.40 mmol) in benzene (1.0 mL) under 1108C for
24–34 h. [b] Isolated yield.
1 (0.20 mmol), 2a (0.50 mmol), PdCl2
With the optimal reaction conditions in hand, we explored
the scope of the carboxylic acid derivatives. Various a-mono-
substituted propionic acid derivatives were examined. It was
delightful to find that the reaction conditions tolerated wide
substrate scope as illustrated in Table 2. Substrates substituted
by simple aliphatic chains were well tolerated to deliver the
amination products in excellent yields (3aa–ca). Substrates
containing cyclic aliphatic chains including cyclopropyl, cyclo-
pentyl, and cyclohexanyl groups also underwent the amination
reactions smoothly (3da–fa). In addition, benzyl analogues re-
gardless of their electronic properties afforded the correspond-
ing products in good yields (3ga–ja). Aryl substitution can be
further extended to the d-position without any problem (3ka).
Further exploration revealed that complex substrates such as
olefine (3la), indole (3ma), and thiophene (3na) analogues
also survived under the reaction conditions. The success of
these substrates revealed the high chemselectivity of this
method in the activation of C(sp3)ÀH over C(sp2)ÀH bonds.
Moreover, it was remarkable that other functional groups such
as TBS ether (3oa), benzyl ether (3pa), and tert-butyloxycar-
bonyl (Boc)-protected amine (3qa) were also well tolerated
without incident. It is worth noting that these functional
groups could be utilized as handles for further transformations
to diversify the product portfolio. Interestingly, tertiary sub-
strate 1r derived from 2,2-dimethylbutanoic acid did not
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afford amination product 3ra under the reaction con-
ditions presumably due to the steric factor (Table 2).
We then examined the scope of aminating re-
agents in the coupling with 1a (Table 3). We were de-
lighted to find that the reaction conditions tolerated
various amine partners. In addition to unsubstituted
morpholine, sterically hindered 2,6-dimethylmorpho-
line also afforded the amination product 3ab in 88%
yield. Other medicinally useful amine partners includ-
ing piperazine and piperidine also delivered the cor-
responding products without a problem (3ac–ad).
The scope of the amine partners can be further ex-
Scheme 2. Preparation of b-amino acid.
amine partner in the amination of unactivated C(sp3)ÀH bonds.
Intriguingly, similar to the early Pd0-catalyzed protocol,[12b] we
found that pyrrolidine was not an effective amine partner
under our reaction conditions.
Table 3. Substrate scope of aminating reagents.[a,b]
The utility of the method was demonstrated in Scheme 2.
Amination of 1a by 2k can be conducted on a gram scale to
afford 3ak in 71% yield. Following the literature procedure,[18]
the directing group and piperidone unit of 3ak were removed
sequentially to deliver the free b2-amino carboxylic acid, which
was then converted to Phth-protected b2-amino carboxylic
acid 4 in 53% overall yield. The a-proton of 4 could be manip-
ulated to introduce an additional substitution group for the
preparation of diverse b2,2-amino carboxylic esters.[19]
The significance of this method is worth noting in the fol-
lowing points. Firstly, the reaction shows broad substrate
scope demonstrated by the b-amination of a variety of func-
tional secondary carboxylic amides in Table 2. Additionally, the
resulting secondary b2-amino carboxylic amide products can
be further derivatized to prepare tertiary b2,2-amino carboxylic
acid analogues by utilizing the a-proton as a handle, as illus-
trated in Scheme 2. Overall, not only was it applicable to di-
rectly prepare the secondary b2-amino carboxylic acid ana-
logues, but also the tertiary b2,2-amino carboxylic acid ana-
logues after additional transformation. The broad functional-
group tolerance and strategic flexibility of this method was
not seen in the early Pd0-catalyzed protocol reported by Yu,
which was restricted to the preparation of only tertiary b2,2
-
amino carboxylic acid analogues.[12b] Secondly, this method
avoids the use of phosphine as a ligand, which was necessary
in the early Pd0-catalyzed protocol.[12b] Essentially, this phos-
phine ligand-free method utilizes a bidentata 2-aminothioether
as the directing group to achieve broader C(sp3)ÀH bond ami-
nations than the early Pd0-catalyzed protocol using a monoden-
tata fluorinated aniline as the directing group.
[a] Optimal reaction conditions: 1a (0.20 mmol), 2 (0.50 mmol), PdCl2
(10 mol%), and Cs2CO3 (0.40 mmol) in benzene (1.0 mL) under 110 8C for
24–34 h. [b] Isolated yield. [c] Unreacted 1a was recovered in 55% yield.
tended to a variety of functional piperidines. Not only simple
alkyl substitutions (3ae–ah), remarkably various functional
groups including ester (3ai–aj), ketal (3ak), and TBS ether
(3al) on the piperidines were also reserved under the reaction
conditions. These functional piperidines could be further deriv-
atized to synthesize other biologically active compounds. In
particular, acyclic dialkylamine also underwent the amination
reaction, albeit in moderate yield (3am). It is worth noting that
for the first time acyclic dialkylamine was successful as an
We conducted kinetic isotope experiments to probe the re-
action mechanism (Scheme 3). The result (parallel intermolecu-
lar KIE=2.9) suggested that the cleavage of the b-C(sp3)ÀH
bond of the substrate occurred as the rate-limiting step. Ami-
nation of chiral substrate (S)-1a (95% ee) with 2a produced
(R)-3aa (95% ee) without erosion of chirality (see the Support-
ing Information). This result implied that the reaction pathway
did not involve the a-proton of the substrate. We have shown
that Pd0 or in situ-generated Pd0 catalysts[20] were not effective
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Experimental Section
General method
A
10 mL teflon-capped vial was charged with
1 (0.20 mmol), 2 (0.50 mmol), PdCl2 (10 mol%), Cs2CO3
(0.40 mmol), and benzene (1.0 mL) under an air atmos-
phere. The vial was then tightly capped. The mixture
was stirred at RT for 1 min for proper mixing of the reac-
tants, and was then heated at 110 8C with vigorous stir-
ring for 24–34 h. After this time, the vial was cooled to
RT, diluted with ethyl acetate and filtered through
a short pad of Celite. The filtrate was concentrated in
vacuo and the residue was purified by flash chromatog-
raphy on silica gel (ethyl acetate/petroleum ether) to
afford the desired product 3.
Scheme 3. Kinetic isotope experiments.
Acknowledgements
for this reaction (see Table 1, entries 6–7 and 8–9). Based on
these observations, we exclude the involvement of a Pd0/PdII
catalytic cycle for the reaction. Although additional solid evi-
dence remains to be obtained, we propose a PdII/PdIV catalytic
cycle for this reaction.[4b–d] As shown in Scheme 4, under the
assistance of 2-aminothioether and Cs2CO3, substrate 1a can
coordinate with PdCl2 to form intermediate A as the initial
step. Further activation of the b-C(sp3)ÀH bond generates PdII
intermediate B. Oxidative addition of O-benzoyl hydroxylmor-
pholine into B takes place to form PdIV intermediate C, which
eventually affords product 3aa after reductive elimination. The
catalytic cycle is restored after ligand exchange of PdII catalyst.
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (no. 21272201), Program
for Changjiang Scholars and Innovation Research Team in Uni-
versity (IRT13095), Program of High-End Science and Technolo-
gy Talents of Yunnan Province (2012A003), Program of Hun-
dred Oversea High-Level Talents of Yunnan Province
(W8110305), and Yunnan University (XT412003).
Keywords: amination · C(sp3)ÀH activation · cross-coupling ·
palladium · b-amino acids
[1] a) P. Müller, C. Fruit, Chem. Rev. 2003, 103, 2905; b) F. Collet, R. H. Dodd,
P. Dauban, Chem. Commun. 2009, 5061; c) F. Collet, C. Lescot, P.
Dauban, Chem. Soc. Rev. 2011, 40, 1926; d) S. H. Cho, J. Y. Kim, J. Kwak,
S. Chang, Chem. Soc. Rev. 2011, 40, 5068; e) J. Yamaguchi, A. D. Yamagu-
chi, K. Itami, Angew. Chem. Int. Ed. 2012, 51, 8960; Angew. Chem. 2012,
124, 9092; f) T. A. Ramirez, B. Zhao, Y. Shi, Chem. Soc. Rev. 2012, 41, 931;
g) J. L. Jeffreya, R. Sarpong, Chem. Sci. 2013, 4, 4092; h) V. S. Thirunavuk-
karasu, S. I. Kozhushkov, L. Ackermann, Chem. Commun. 2014, 50, 29;
i) D. Intrieri, P. Zardi, A. Caselli, E. Gallo, Chem. Commun. 2014, 50, 11440.
[2] a) F. Ullmann, Ber. Dtsch. Chem. Ges. 1903, 36, 2382; b) I. Goldberg, Ber.
Dtsch. Chem. Ges. 1906, 39, 1691; c) S. V. Ley, A. W. Thomas, Angew.
Chem. Int. Ed. 2003, 42, 5400; Angew. Chem. 2003, 115, 5558; d) G.
Evano, N. Blanchard, M. Toumi, Chem. Rev. 2008, 108, 3054.
[3] a) A. R. Muci, S. L. Buchwald, Top. Curr. Chem. 2002, 219, 131; b) T. Ikawa,
T. E. Barder, M. R. Biscoe, S. L. Buchwald, J. Am. Chem. Soc. 2007, 129,
13001; c) D. S. Surry, S. L. Buchwald, Angew. Chem. Int. Ed. 2008, 47,
6338; Angew. Chem. 2008, 120, 6438; d) J. F. Hartwig, Acc. Chem. Res.
2008, 41, 1534.
[4] For selected examples of palladium-catalyzed intermolecular C(sp2)ÀH
activation/CÀN forming reactions: a) B. Xiao, T.-J. Gong, J. Xu, Z.-J. Liu,
L. Liu, J. Am. Chem. Soc. 2011, 133, 1466; b) E. J. Yoo, S. Ma, T.-S. Mei,
K. S. L. Chan, J.-Q. Yu, J. Am. Chem. Soc. 2011, 133, 7652; c) Z. Dong, G.-
B. Dong, J. Am. Chem. Soc. 2013, 135, 18350; d) D. Zhu, G. Yang, J. He,
L. Chu, G. Chen, W. Gong, K. Chen, M. D. Eastgate, J.-Q. Yu, Angew.
Chem. Int. Ed. 2015, 54, 2497; Angew. Chem. 2015, 127, 2527; for select-
ed examples of palladium-catalyzed intramolecular C(sp2)ÀH activation/
CÀN forming reactions: e) W. C. P. Tsang, N. Zheng, S. L. Buchwald, J.
Am. Chem. Soc. 2005, 127, 14560; f) M. Wasa, J.-Q. Yu, J. Am. Chem. Soc.
2008, 130, 14058; g) J. A. Jordan-Hore, C. C. C. Johansson, M. Gulias,
E. M. Beck, M. J. Gaunt, J. Am. Chem. Soc. 2008, 130, 16184; h) Y.-C. Tan,
J. F. Hartwig, J. Am. Chem. Soc. 2010, 132, 3676; i) E. T. Nadres, O. Daugu-
lis, J. Am. Chem. Soc. 2012, 134, 7.
Scheme 4. Proposed reaction mechanism.
In summary, we have successfully developed the first exam-
ple of PdII-catalyzed intermolecular amination of unactivated
C(sp3)ÀH bonds. This C(sp3)ÀH amination protocol produces di-
verse unnatural and functional b2-amino carboxylic acid ana-
logues. This method is demonstrated with broad substrate
scope, good functional-group tolerance, and chemselectivity.
In addition, this reaction is scalable on a gram scale. It is oper-
ated without use of phosphine ligand or external oxidant. Fur-
ther investigation of the detailed reaction mechanism and an
expansion of the reaction scope is currently in progress.
[5] For selected examples of rhodium-catalyzed intermolecular C(sp2)ÀH ac-
tivation/CÀN forming reactions: a) J. Y. Kim, S. H. Park, J. Ryu, S. H. Cho,
Chem. Eur. J. 2015, 21, 15491 – 15495
www.chemeurj.org
15494
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
S. H. Kim, S. Chang, J. Am. Chem. Soc. 2012, 134, 9110; b) D.-G. Yu, M.
Suri, F. Glorius, J. Am. Chem. Soc. 2013, 135, 8802.
[12] a) J. Pan, M.-J. Su, S. L. Buchwald, Angew. Chem. Int. Ed. 2011, 50, 8647;
Angew. Chem. 2011, 123, 8806; b) J. He, T. Shigenari, J.-Q. Yu, Angew.
Chem. Int. Ed. 2015, 54, 6545; Angew. Chem. 2015, 127, 6645.
[13] a) J. J. Neumann, S. Rakshit, T. Drçge, F. Glorius, Angew. Chem. Int. Ed.
2009, 48, 6892; Angew. Chem. 2009, 121, 7024; b) G. He, Y.-S. Zhao, S.-Y.
Zhang, C.-X. Lu, G. Chen, J. Am. Chem. Soc. 2012, 134, 3; c) G. He, S.-Y.
Zhang, W. A. Nack, Q. Li, G. Chen, Angew. Chem. Int. Ed. 2013, 52, 11124;
Angew. Chem. 2013, 125, 11330; d) A. McNally, B. Haffemayer, B. S. L.
Collins, M. J. Gaunt, Nature 2014, 510, 129; e) Q. Nguyen, K. Sun, T. G.
Driver, J. Am. Chem. Soc. 2012, 134, 7262.
[6] For selected examples of ruthenium-catalyzed intermolecular C(sp2)ÀH
activation/CÀN forming reactions: a) J. Kim, J. Kim, S. Chang, Chem. Eur.
J. 2013, 19, 7328; b) M. Shang, S.-H. Zeng, S.-Z. Sun, H.-X. Dai, J.-Q. Yu,
Org. Lett. 2013, 15, 5286; c) V. S. Thirunavukkarasu, K. Raghuvanshi, L.
Ackermann, Org. Lett. 2013, 15, 3286; d) M. R. Yadav, M. Shankar, E.
Ramesh, K. Ghosh, A. K. Sahoo, Org. Lett. 2015, 17, 1886.
[7] For selected examples of iridium-catalyzed intermolecular C(sp2)ÀH acti-
vation/CÀN forming reactions: a) J. Ryu, J. Kwak, K. Shin, D. Lee, S.
Chang, J. Am. Chem. Soc. 2013, 135, 12861; b) L. J. Allen, P. J. Cabrera,
M. Lee, M. S. Sanford, J. Am. Chem. Soc. 2014, 136, 5607.
[14] a) D. Shabashov, O. Daugulis, Org. Lett. 2005, 7, 3657; b) D. Shabashov,
O. Daugulis, J. Am. Chem. Soc. 2010, 132, 3965.
[15] a) Enantioselective Synthesis of b-Amino Acids (Ed.: E. Juaristi), Wiley-VCH,
New York, 1997; b) D. Seebach, S. Abele, K. Gademann, B. Jaun, Angew.
Chem. Int. Ed. 1999, 38, 1595; Angew. Chem. 1999, 111, 1700; c) K. Gade-
mann, T. Kimmerlin, D. Hoyer, D. Seebach, J. Med. Chem. 2001, 44, 2460;
d) S. Abele, D. Seebach, Eur. J. Org. Chem. 2000, 1; e) R. P. Cheng, S. H.
Gellman, W. F. DeGrado, Chem. Rev. 2001, 101, 3219.
[16] a) Q. Gou, B. Deng, H.-B. Zhang, J. Qin, Org. Lett. 2013, 15, 4604; b) Q.
Gou, Z.-F. Zhang, Z.-C. Liu, J. Qin, J. Org. Chem. 2015, 80, 3176; c) Q.
Gou, B. Deng, J. Qin, Chem. Eur. J. 2015, 21, 12586.
[17] A. M. Berman, J. S. Johnson, J. Am. Chem. Soc. 2004, 126, 5680.
[18] P. Aschwanden, C. R. J. Stephenson, E. M. Carreira, Org. Lett. 2006, 8,
2437.
[19] a) D. Seebach, H. Estermann, Tetrahedron Lett. 1987, 28, 3103; b) H. Es-
termann, D. Seebach, Helv. Chim. Acta 1988, 71, 1824.
[8] For selected examples of iron-catalyzed intermolecular C(sp2)ÀH activa-
tion/CÀN forming reactions: a) T. Matsubara, S. Asako, L. Ilies, E. Naka-
mura, J. Am. Chem. Soc. 2014, 136, 646; b) K. Foo, E. Sella, I. ThomØ,
M. D. Eastgate, P. S. Baran, J. Am. Chem. Soc. 2014, 136, 5279.
[9] For selected examples of copper-catalyzed intermolecular C(sp2)ÀH acti-
vation/CÀN forming reactions: a) T. Kawano, K. Hirano, T. Satoh, M.
Miura, J. Am. Chem. Soc. 2010, 132, 6900; b) D. Lubriks, I. Sokolovs, E.
Suna, J. Am. Chem. Soc. 2012, 134, 15436; c) L. D. Tran, J. Roane, O. Dau-
gulis, Angew. Chem. Int. Ed. 2013, 52, 6043; Angew. Chem. 2013, 125,
6159; d) M. Shang, S.-Z. Sun, H.-X. Dai, J.-Q. Yu, J. Am. Chem. Soc. 2014,
136, 3354.
[10] For selected examples of cobalt-catalyzed intermolecular C(sp2)ÀH acti-
vation/CÀN forming reactions: J. Y. Kim, S. H. Cho, J. Joseph, S. Chang,
Angew. Chem. Int. Ed. 2010, 49, 9899; Angew. Chem. 2010, 122, 10095.
[11] a) H.-Y. Thu, W.-Y. Yu, C.-M. Che, J. Am. Chem. Soc. 2006, 128, 9048; b) .
Iglesias, R. lvarez, R. . de Lera, K. MuÇiz, Angew. Chem. Int. Ed. 2012,
51, 2225; Angew. Chem. 2012, 124, 2268; c) T. Kang, Y. Kim, D. Lee, Z.
Wang, S. Chang, J. Am. Chem. Soc. 2014, 136, 4141.
[20] T. Satoh, T. Itaya, K. Okuro, M. Miura, M. Nomura, J. Org. Chem. 1995, 60,
7267.
Received: June 19, 2015
Published online on September 11, 2015
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