Iridium-Catalyzed Benzylamine C-H Alkenylation Enabled by Pentafluorobenzoyl as the Directing Group

Article abstract of DOI:10.1021/acs.orglett.8b04005

The first iridium-catalyzed oxidative alkeynylation of benzylamines with acrylates enabled by a new directing group pentafluorobenzoyl has been developed. The reaction proceeded efficiently in the presence of silver acetate as oxidant and chlorobenzene as

Full text of DOI:10.1021/acs.orglett.8b04005

Letter
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Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Iridium-Catalyzed Benzylamine C−H Alkenylation Enabled by
Pentafluorobenzoyl as the Directing Group
Xiao Yang,† Rui Sun,† Chunchun Zhang,‡ Xueli Zheng,*,† Maolin Yuan,† Haiyan Fu,*,†
Ruixiang Li,† and Hua Chen†
†Key Laboratory of Green Chemistry & Technology, Ministry of Education College of Chemistry, Sichuan University Chengdu
610064, P.R. China
‡Analytical & Testing Center, Sichuan University, Chengdu, Sichuan 610064, P.R. China
S
* Supporting Information
ABSTRACT: The first iridium-catalyzed oxidative alkeynyla-
tion of benzylamines with acrylates enabled by a new directing
group pentafluorobenzoyl has been developed. The reaction
proceeded efficiently in the presence of silver acetate as
oxidant and chlorobenzene as solvent. A good range of
benzylamines could be selectively monoalkenylated without
interfering with further aza-Michael addition. The kinetic
isotope effect experiments showed that C−H activation is not
the rate-limiting step. In addition, a five-membered iridacycle species was isolated and established as the possible key
intermediate.
Scheme 1. Transitional-Metal-Catalyzed Direct C−H
enzylamines have been widely used in the synthetic
Bchemistry community as a class of inexpensive starting
matrials,1 and the installation of the pendant o-alkenyl group
on it would be serve as a versatile synthetical handle.2
However, only limited methodology has been available in the
literature for the synthesis of such ortho-alkenylated benzylic
amines.2a−c,3 In recent years, the transition-metal-catalyzed
oxidative alkenylation reaction (Fujiwara−Moritani reaction4)
would provide a step and an atom-economic way to introduce
alkenes group onto arenes via direct C−H activation. Since its
discovery, it has been utilized to accomplish the ortho-
alkenylation of a variety of arene compounds,5 and the
activated olefin−acrylates are widely used as the alkenylating
reagents.5a,c,d,g,6 Generally, a suitable directing group is
required to ensure the ortho site-selectivty. For example,
anilines could successfully undergo ortho-selective alkenylation
through assistance by different directing groups, such as Ac,7f
Boc,7h and ureas,7g under palladium,7b,c,i rhodium,7d−h or
iridium7a catalysis (Scheme 1a). Compared with anilines, the
oxidative alkenylation of benzylamines substrates is rarely
reported. An elegant palladium-catalyzed ortho alkenylation of
N,N-dimethylbenzylamines by carefully tuning the acidity of
the reaction condition was reported by Shi in 2007,8 but the
substrates are only limited to the tertiary benzylamine (Scheme
1b). The main challenges met with the oxidative alkenylation
between primary benzylamines and acrylates may be as
follows: (1) under the oxidative conditions, the benzyl amines
are easily to oxidize;9 (2) the olefin hydroarylation would be a
potentially competitive reaction;10 and (3) since the acrylate is
a good Michael addition acceptor, it is difficult to stay in the
stage of the alkenylation products, which tend to cyclize via an
intramolecular aza-Michael addition.11 We envisaged that the
Alkenylation of Anilines and Benzylamines
installation of a proper amide auxiliary would solve the above
problems. It not only can increase the stability of the
benzylamine but also serve as a directing group to control
the chemoselectivity.
As mentioned above, a directing group played a vital role in
the ortho-C−H functionalization; in some cases, it even could
completely switch the reaction selectivity.12 An elegant
example has been reported by the Chang group.13 By
employing a different directing group, they can selectively
control the C−H alkenylation or the hydroarylation between
the reaction of arene and olefins. Only one example of primary
benzylamine alkenylation with acrylates was reported by the
Received: December 15, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b04005
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Organic Letters
Letter
Kim group14 in 2014, where they utilized a triflamide auxiliary
to realize the Rh(III)Cp*-catalyzed benzylamine alkenylation,
but the product rapidly cyclized into the isoindolines (Scheme
1c). Inspired by the seminal discovery of an amide auxiliary
CONHArF (ArF = 2,3,5,6-tetrafluoro-4-(trifluoromethyl)-
aniline) group by Yu,15 which is a well-behaved auxiliary in
the ortho-functionalization of benzoic acids, we herein
demonstrate the successful development of the NHCOArF
(ArF = 2,3,4,5,6-pentafluorobenzoyl) amide auxiliary to enable
the benzylamine alkenylation without further cyclization. By
using 2,3,4,5,6-pentafluoro-N-(benzyl)benzamide as the sub-
strate and [IrCp*Cl2]2 as the catalyst, a highly selective
alkenylation of benzylamines can be achieved (Scheme 1d). To
the best of our knowledge, this represents the first example of
benzylamine oxidative alkenylation with acrylates without
interfering with the further aza-Michael addition.
further aza-Michael addition product from 3a was detected
under the reaction conditions.
To clarify the importance of the pentafluorobenzoic acid as
the directing group, a series of benzamides (4a−h) in which
the pentafluorobenzoyl group was replaced by a different
directing group, such as acetyl, trifluoroacetyl, benzoyl, 2,6-
dimethylbenzoyl, 2-pyridylformyl, 4-(trifluoromethyl)benzoyl,
3,4,5-trifluorobenzoyl, or 2,6-difluorobenzoyl, were subjected
to the optimized reaction conditions. Obviously, the
investigated directing group only led to either negligible or
much lower yield of products. The results congruously showed
that the strong electron-withdrawing pentafluorobenzoyl
directing group was vital and could significantly improve the
reactivity (Scheme 2). Interestingly, the F atom at the ortho
a,b
Scheme 2. Comparison of Different Directing Groups
We initiated our studies by coupling 2,3,4,5,6-pentafluoro-
N-(2-methoxybenzyl)benzamide (1a) and ethyl acrylate (2a)
in the presence of AgOAc as oxidant in toluene (0.1 M) at 100
°C under air for 24 h. Gratifying, 48% yield of the desired
alkenylation product 3a was obtained (Table 1, entry 1). A
a
Table 1. Optimization of the Reaction Conditions
b
entry
catalyst
oxidant
solvent
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
[IrCp*Cl2]2
Pd(OAc)2
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
Ag2CO3
AgNO3
Ag2O
Cu(OAc)2
AgOAc
AgOAc
AgOAc
AgOAc
toluene
dioxane
xylene
DCE
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
48
26
14
77
85
56
trace
42
trace
76
a
Reaction conditions: 4a−h (0.1 mmol), 2a (0.3 mmol), [IrCp*Cl2]2
(2.5 mmol %), AgOAc (2.0 equiv) at 100 °C for 24 h under air in a
b
sealed tube. Isolated yield.
position of the benzoyl group is beneficial for the reaction as
illustrated by comparison of the results of the last three
directing groups.
With the optimized reaction conditions in hand, we set out
to explore the scope of this reaction (Scheme 3). The
alkenylation of the ortho-substituted N-benzyl-2,3,4,5,6-penta-
fluorobenzamides 1a−e with ethyl acrylate (2a) consistently
afforded the corresponding monoalkenylated products (3a−d)
in moderate to high yield of 62−87%, with excellent
chemoselectivity, and no Michael addition byproducts were
detected. The reaction seems to be more efficient for the
electron-rich substrates bearing the electron-donating groups
such as methoxy and methyl, whereas the moderately electron-
withdrawing groups such as chloro and fluoro groups
decreased the yields slightly, and the strong electron-with-
drawing o-CF3 completely inhibited the reaction. It is worth
noting that in the case of the chloro-substituted substrates
neither dehalogenation nor the Mizoroki−Heck byproducts
were detected. The remaining chloride atom subsequently
could be transformed into other functionalities via the classical
cross-couplings. The reaction was compatible with the meta-
substituted N-benzyl-2,3,4,5,6-pentafluorobenzamides 1f−j,
though the yields of the products was relatively lower in
comparison to their ortho-substituted counterparts (3f, 3h, 3i,
21−60%). For m-Me-, CF3-, and Br-substituted benzylamines,
only monoalkenylation products were obtained, and the
alkenylation proceeded exclusively at the less hindered ortho
position (3f, 3g, 3j), while for m-F or -Cl-substituted
benzylamines, a significant amount of alkenylation occurred
c
d
e
92 (87)
20
48
[RhCp*Cl2]2
a
Reaction conditions: 1a (0.1 mmol), 2a (0.2 mmol), catalyst (2.5
mmol %), oxidant (2.0 equiv), solvent (1 mL), at 100 °C for 24 h
b
under air in a sealed tube. Yield was determined by 1H NMR
c
spectroscopy using CH2Br2 as an internal standard. 2a (0.15 mmol).
2a (0.3 mmol). Isolated yield.
d
e
solvent screen illustrated that PhCl provided conversion higher
than other commonly used nonpolar solvents (entries 1−5),
giving 3a in 85% yield (entry 5). Then a variety of oxidants
were briefly examined in PhCl, and AgOAc proved to be the
most efficient oxidant for this reaction (entries 5−9). The ratio
of 2a/1a also affected the reaction (entries 5, 10, and 11), and
increasing the amount of 2a to 3 equiv led to a further
improvement of the yield to 92%. Other frequently used
catalysts in the Fujiwara−Moritani reaction, such as Pd(OAc)2
and [RhCp*Cl2]2, are totally ineffective (entries 12 and 13).
Therefore, the optimal conditions for this reaction were
established as follows: 1a (0.1 mmol), 2a (0.3 mmol),
[IrCp*Cl2]2 (2.5 mol %), and AgOAc (2 equiv) in PhCl
(0.1 M) at 100 °C for 24 h. It is worth noting that neither the
competitive hydroarylation product between 1a and 2a nor the
B
DOI: 10.1021/acs.orglett.8b04005
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Organic Letters
Letter
a,b
Scheme 3. Scope of the Reaction
Scheme 4. A 1 mmol Scale Experiment and Transformations
To illustrate the particular suitability of the new directing
group PFB for benzylamines. The PFB-based directing group
was installed to benzyl alcohol, N-methylbenzylamine and
aniline, respectively, for comparison with benzylamine
substrate (Scheme 5). The fact that no C−H alkenylation
Scheme 5. Controlled Experiment
occurred in the former two substrates 8 and 9 implied the N−
H bond is indispensable for the reaction. It was that the amide
nitrogen rather than oxygen coordinated to the iridium center.
Although there exists an N−H bond in PFB-protected aniline
10, it still failed to give any alkenylation product. The reason
might be that the formation of a strained four-membered
iridacycles species is thermodynamically unfavorable. Gen-
erally, the carbonyl oxygen in the aniline-based amides is
considered to coordinate to metal and serve as the directing
group.7a,f−h Therefore, the failure to observe any alkenylation
product of aniline might also resulted from a shift of lone pair
density from the carbonyl oxygen to PFB group, thus
disfavoring its coordination to iridium center.
In order to gain a better understanding of the reaction
mechanism, several experiments have been conducted. First, an
H/D exchange experiment was conducted between 0.2 mmol
of 1l and 10 equiv of acetic acid-d4 under standard conditions
(Scheme 6a). Sixty percent of the ortho C−H bond in 1l was
deuterated, showing that a reversible C−H activation process
occurred. In contrast, no deuterium incorporation occurred at
the ortho C−H bond of 1l in the absence of AgOAc. Therefore,
we believe that AgOAc not only plays a role as an oxidant to
reoxidize Ir(I) to Ir(III) but also as an efficient promoter for
C−H the activation process. Meanwhile, a KIE value of 1.3
a
Reaction conditions: 1a−s (0.1 mmol), 2 (0.3 mmol), [IrCp*Cl2]2
(2.5 mmol %), AgOAc (2.0 equiv) at 100 °C for 24 h under air in a
b
sealed tube. Isolated yield.
at the sterically crowded ortho-positions (3h, 3i). Surprisingly,
the para-substituted N-benzyl-2,3,4,5,6-pentafluorobenzamides
1k−m with two equally active sites only afforded the mono-/
dialkenylated products in 25−59% total yields (3k−m), much
lower than the corresponding ortho-substituted isomers. These
comparative data clearly revealed that the presence of an ortho
substituent on the aryl ring significantly promoted the reaction.
Such an ortho effect was also observed in Kim’s system.14 In
addition, the disubstituted or α-substituted benzyl amines
could also undergo the reaction smoothly, giving the product
in moderate yields (3n, 3o). In the case of 1-naphthaleneme-
thylamine, the alkenylation occurred completely at the β-
position with 57% yield (3p). Finally, the coupling partner was
successfully extended to other esters such as methyl, n-butyl,
tert-butyl, and phenyl acrylates (3q−t). It is also worth noting
that in most cases studied, the reaction conditions led
exclusively to the monoalkenylation products without the
undesired further intramolecular cyclization byproducts, except
for the 4-MeO-benzylamine in which both the dialkenylation
and aza-Michael addition products was detected. However, the
electron-deficient N,N-dimethylacrylamide and acrylonitrile
did not react in the present system.
Scheme 6. Mechanism Study
The practicability of present protocol was illustrated by the
scale-up preparation of 3a and the related transformation
(Scheme 4). The alkenylation of 1a on a 1 mmol scale gave 3a
in 60% yield. The double bond in 3a was smoothly
hydrogenated under the catalysis of Pd/C, producing 6 in
87% isolated yield. In addition, 3a could also be readily
converted into the isoindoline in 82% yield by treating with
lithium hydroxide monohydrate.
C
DOI: 10.1021/acs.orglett.8b04005
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Organic Letters
Letter
observed in the alkenylation of 1l/1l-d2 may support that ortho
C−H bond cleavage is not involved in the rate-determining
step (Scheme 6b). Subsequently, the reaction of 1d with 0.5
equiv of [IrCp*Cl2]2 was performed in the presence of 2.0
equiv of AgOAc in chlorobenzene at 100 °C for 24 h, and the
five-membered iridacycle species B was successfully separated
in the yield of 11%, which was unambiguously characterized by
NMR and HRMS. The compound B was then used as the
catalyst in the reaction between o-chlorobenzylamide 1d and
ethyl acrylate under the standard conditions and the product
3d was obtained in 48% yield (Scheme 6c), thus demonstrat-
ing that iridacycle species B is possibly the key reaction
intermediate.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b04005.
■
S
Experimental details and full spectroscopic data for all
new compounds (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: scufhy@scu.edu.cn.
*E-mail: zhengxueli@scu.edu.cn.
ORCID
On the basis of the literature reports13,14 and our experiment
results, we propose a possible mechanism (Scheme 7). First,
Xueli Zheng: 0000-0001-8394-0310
Haiyan Fu: 0000-0002-7185-2062
Ruixiang Li: 0000-0003-0756-3722
Hua Chen: 0000-0003-4248-8019
Notes
Scheme 7. Proposed Reaction Mechanism
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(Nos. 21871187 and 21572137) and the Key Program of
Sichuan Science and Technology Project (No. 2018GZ0312)
for their financial support. We also thank Chunchun Zhang
from the Centre of Testing & Analysis, Sichuan University, for
NMR measurements.
REFERENCES
■
(1) (a) Madia, V. N.; Messore, A.; Pescatori, L.; Saccoliti, F.;
Tudino, V.; De Leo, A.; Bortolami, M.; Scipione, L.; Costi, R.; Rivara,
S.; Scalvini, L.; Mor, M.; Ferrara, F. F.; Pavoni, E.; Roscilli, G.;
Cassinelli, G.; Milazzo, F. M.; Battistuzzi, G.; Di Santo, R.; Giannini,
G. J. Med. Chem. 2018, 61, 6918. (b) Abonia, B.; Garay, A.; Castillo, J.
C.; Insuasty, B.; Quiroga, J.; Nogueras, M.; Cobo, J.; Butassi, E.;
Zacchino, S. Molecules 2018, 23, 520. (c) Hirashima, H.; Narushima,
T.; Kawada, M.; Nakashima, K.; Hanai, K.; Koseki, Y.; Miura, T.
Chem. Pharm. Bull. 2017, 65, 1185. (d) Casimiro, C.; Groppi, J.;
Baroncini, M.; La Rosa, M.; Credi, A.; Silvi, S. Photochem. Photobiol.
Sci. 2018, 17, 734.
AgOAc activated the catalyst by chloride abstraction to give
the active IrCp*(OAc)2 species. It then coordinated to amide
nitrogen of 1d and activated the C−H bond through a
concerted metalation−deprotonation (CMD) pathway with
the aid of the acetate anion as shown in A to afford the
intermediate B. Subsequently an ethyl acrylate coordinated to
B followed by double-bond insertion to form the intermediate
C, which then afforded the alkenylated product 3d via a
sequential β-hydride elimination and reductive elimination
steps, concomitantly generating the Ir(I) species. Finally, the
Ir(I) was further oxidized by AgOAc to regenerate Ir(III) to
close the catalytic cycle.
In summary, we have developed the first example of a
selective ortho C−H bond alkenylation of benzylamines by
using [IrCp*Cl2]2 as catalyst and PBF as a new directing
group. A series of benzylamines bearing different functional
groups proceeded well under the present catalytic system,
affording alkenylation product in good to excellent yields. In
contrast to the previous report on the transitional metal
catalyzed oxidative benzylamine alkenylation, the present
protocol is characterized by being able to stay in the stage
the alkenylation without cyclization by aza-Michael addition.
This would allow for further transformation by virtue of the
double-bond functionality.
(2) (a) Mulet, C.; Escolano, M.; Llopis, S.; Sanz, S.; Ramírez de
́
́
Arellano, C.; Sanchez-Rosello, M.; Fustero, S.; del Pozo, C. Adv.
Synth. Catal. 2018, 360, 2885. (b) Hu, Y.; Xie, Y.; Shen, Z.; Huang, H.
Angew. Chem., Int. Ed. 2017, 56, 2473. (c) Hu, Y.; Shen, Z.; Huang, H.
ACS Catal. 2016, 6, 6785. (d) Toshio, K.; Tsubasa, W.; Kazuhiko, O.;
Hiroki, I.; Eisuke, N.; Takeshi, H.; Shunichiro, H.; Hiroshi, S.; Yuji,
K.; Ryo, M. PCT Int. Appl. 2014084312, 2014.
(3) (a) Bennasar, M. L.; Roca, T.; Monerris, M.; García-Díaz, D. J.
Org. Chem. 2006, 71, 7028. (b) Suzuki, Y.; Iwase, S.; Hashimoto, K.;
Tanaka, S.; Kitamura, M. Chem. Lett. 2017, 46, 1308. (c) Pierson, J.
M.; Ingalls, E. L.; Vo, R. D.; Michael, F. E. Angew. Chem., Int. Ed.
2013, 52, 13311. (d) Nadres, E. T.; Santos, G. I.; Shabashov, D.;
Daugulis, O. J. Org. Chem. 2013, 78, 9689.
(4) (a) Moritani, I.; Fujiwara, Y. Tetrahedron Lett. 1967, 8, 1119.
(b) Fujiwara, Y.; Moritani, I.; Matsuda, M.; Teranishi, S. Tetrahedron
Lett. 1968, 9, 633. (c) Fujiwara, Y.; Moritani, I.; Danno, S.; Asano, R.;
Teranishi, S. J. Am. Chem. Soc. 1969, 91, 7166.
(5) (a) Engle, K. M.; Wang, D.-H.; Yu, J.-Q. J. Am. Chem. Soc. 2010,
132, 14137. (b) Mochida, S.; Hirano, K.; Satoh, T.; Miura, M. Org.
Lett. 2010, 12, 5776. (c) Park, S. H.; Kim, J. Y.; Chang, S. Org. Lett.
2011, 13, 2372. (d) Itoh, M.; Hashimoto, Y.; Hirano, K.; Satoh, T.;
Miura, M. J. Org. Chem. 2013, 78, 8098. (e) Wang, S.-M.; Moku, B.;
Leng, J.; Qin, H.-L. Eur. J. Org. Chem. 2018, 2018, 4407. (f) Deb, A.;
D
DOI: 10.1021/acs.orglett.8b04005
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Hazra, A.; Peng, Q.; Paton, R. S.; Maiti, D. J. Am. Chem. Soc. 2017,
139, 763. (g) Deb, A.; Bag, S.; Kancherla, R.; Maiti, D. J. Am. Chem.
Soc. 2014, 136, 13602. (h) Dong, Y.; Liu, G. Chem. Commun. 2013,
49, 8066. (i) Liu, B.; Jiang, H.-Z.; Shi, B.-F. J. Org. Chem. 2014, 79,
1521.
(6) (a) Li, B.; Ma, J.; Liang, Y.; Wang, N.; Xu, S.; Song, H.; Wang, B.
Eur. J. Org. Chem. 2013, 2013, 1950. (b) Li, J.; Kornhaass, C.;
Ackermann, L. Chem. Commun. 2012, 48, 11343. (c) Ma, W.;
Graczyk, K.; Ackermann, L. Org. Lett. 2012, 14, 6318. (d) Suzuki, Y.;
Sun, B.; Yoshino, T.; Kanai, M. Tetrahedron 2015, 71, 4552.
(e) Manikandan, R.; Madasamy, P.; Jeganmohan, M. ACS Catal.
2016, 6, 230. (f) Fabry, D. C.; Rueping, M. Acc. Chem. Res. 2016, 49,
1969. (g) Simon, M. O.; Li, C. J. Chem. Soc. Rev. 2012, 41, 1415.
(h) Li, B.; Ma, J.; Wang, N.; Feng, H.; Xu, S.; Wang, B. Org. Lett.
2012, 14, 736.
(7) (a) Elumalai, K.; Leong, W. K. Tetrahedron Lett. 2018, 59, 113.
(b) Moghaddam, F. M.; Pourkaveh, R.; Karimi, A. J. Org. Chem. 2017,
82, 10635. (c) Ferlin, F.; Santoro, S.; Ackermann, L.; Vaccaro, L.
Green Chem. 2017, 19, 2510. (d) Patureau, F. W.; Glorius, F. J. Am.
Chem. Soc. 2010, 132, 9982. (e) Takahama, Y.; Shibata, Y.; Tanaka, K.
Chem. - Eur. J. 2015, 21, 9053. (f) Zhang, H. J.; Lin, W.; Su, F.; Wen,
T. B. Org. Lett. 2016, 18, 6356. (g) Morita, T.; Satoh, T.; Miura, M.
Org. Lett. 2017, 19, 1800. (h) Lv, H.; Shi, J.; Huang, J.; Zhang, C.; Yi,
W. Org. Biomol. Chem. 2017, 15, 7088. (i) Boele, M. D. K.; van
Strijdonck, G. P. F.; de Vries, A. H. M.; Kamer, P. C. J.; de Vries, J. G.;
van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2002, 124, 1586.
(8) Cai, G.; Fu, Y.; Li, Y.; Wan, X.; Shi, Z. J. Am. Chem. Soc. 2007,
129, 7666.
(9) (a) Morimoto, K.; Hirano, K.; Satoh, T.; Miura, M. Chem. Lett.
2011, 40, 600. (b) Martinez, A. M.; Rodriguez, N.; Gomez-Arrayas,
R.; Carretero, J. C. Chem. - Eur. J. 2017, 23, 11669. (c) Kim, D.-S.;
Park, J.-W.; Jun, C.-H. Adv. Synth. Catal. 2013, 355, 2667.
(10) (a) Ebe, Y.; Onoda, M.; Nishimura, T.; Yorimitsu, H. Angew.
́
Chem., Int. Ed. 2017, 56, 5607. (b) Grelaud, S.; Cooper, P.; Feron, L.
J.; Bower, J. F. J. Am. Chem. Soc. 2018, 140, 9351. (c) Huang, G.; Liu,
P. ACS Catal. 2016, 6, 809.
(11) Song, G.; Chen, D.; Pan, C. L.; Crabtree, R. H.; Li, X. J. Org.
Chem. 2010, 75, 7487.
(12) (a) De Sarkar, S.; Liu, W.; Kozhushkov, S. I.; Ackermann, L.
Adv. Synth. Catal. 2014, 356, 1461. (b) Leow, D.; Li, G.; Mei, T.-S.;
Yu, J.-Q. Nature 2012, 486, 518. (c) Lee, S.; Lee, H.; Tan, K. L. J. Am.
Chem. Soc. 2013, 135, 18778. (d) Engle, K. M.; Mei, T.-S.; Wasa, M.;
Yu, J.-Q. Acc. Chem. Res. 2012, 45, 788. (e) Lyons, T. W.; Sanford, M.
S. Chem. Rev. 2010, 110, 1147.
(13) Kim, J.; Park, S.-W.; Baik, M.-H.; Chang, S. J. Am. Chem. Soc.
2015, 137, 13448.
(14) Mishra, N. K.; Park, J.; Sharma, S.; Han, S.; Kim, M.; Shin, Y.;
Jang, J.; Kwak, J. H.; Jung, Y. H.; Kim, I. S. Chem. Commun. 2014, 50,
2350.
(15) (a) Wasa, M.; Engle, K. M.; Yu, J.-Q. J. Am. Chem. Soc. 2010,
132, 3680. (b) Wu, Q.-F.; Shen, P.-X.; He, J.; Wang, X.-B.; Zhang, F.;
Shao, Q.; Zhu, R.-Y.; Mapelli, C.; Qiao, J. X.; Poss, M. A.; Yu, J.-Q.
Science 2017, 355, 499. (c) Pei, Q.-L.; Che, G.-D.; Zhu, R.-Y.; He, J.;
Yu, J.-Q. Org. Lett. 2017, 19, 5860. (d) Wu, Q.-F.; Wang, X.-B.; Shen,
P.-X.; Yu, J.-Q. ACS Catal. 2018, 8, 2577. (e) Zhang, X. G.; Dai, H.
X.; Wasa, M.; Yu, J.-Q. J. Am. Chem. Soc. 2012, 134, 11948.
E
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