Redox-Neutral Access to Isoquinolinones via Rhodium(III)-Catalyzed Annulations of O-Pivaloyl Oximes with Ketenes

Article abstract of DOI:10.1021/acs.orglett.8b00906

A mild and redox-neutral [4 + 2] annulation of O-pivaloyl oximes with ketenes has been realized for synthesis of quaternary-carbon-stereocenter-containing (QCSC) isoquinolinones, where the N-OPiv not only acts as an oxidizing group but also offers coordination saturation to inhibit protonolysis. The reaction mechanism has been studied by DFT calculations.

Full text of DOI:10.1021/acs.orglett.8b00906

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Redox-Neutral Access to Isoquinolinones via Rhodium(III)-Catalyzed
Annulations of O‑Pivaloyl Oximes with Ketenes
Xifa Yang,†,§ Song Liu,‡ Songjie Yu,† Lingheng Kong,† Yu Lan,*,‡ and Xingwei Li*,†
†Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
‡School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, China
§University of Chinese Academy of Sciences, Beijing 100049, China
S
* Supporting Information
ABSTRACT: A mild and redox-neutral [4 + 2] annulation of
O-pivaloyl oximes with ketenes has been realized for synthesis
of quaternary-carbon-stereocenter-containing (QCSC) isoqui-
nolinones, where the N-OPiv not only acts as an oxidizing
group but also offers coordination saturation to inhibit
protonolysis. The reaction mechanism has been studied by DFT calculations.
n the past several decades, metal-catalyzed direct C−H
(electrophilic) directing group (B1)5 or by the nucleophilic
attack of a directing group at a proximal (electrophilic) π-allyl
group (B2),6 where the allyl moiety was generated via insertion
of an alkyne or allene in C−H activation ststems. In the third
strategy (path c),7 the organorhodium intermediate undergoes
migratory insertion into an unsaturated partner to deliver a
sterically congested Rh−C(tertiary) species (C). Subsequently,
the tertiary carbon and an anionic group reductively eliminate
from C to deliver the final product. Despite these achievements,
the coupling partners are mostly limited to reactive diazo
compounds and alkynes.
I
activation of arenes has witnessed tremendeous progress.1 In
particular, C−H activation and annulation catalyzed by
Cp*Rh(III) complexes has emerged as a powerful strategy to
construct complex cyclic scaffolds in a streamlined and step-
economical fashion.2 Among those cyclic scaffolds, the
synthesis of cyclic products bearing a quaternary carbon
stereocenter, which provides important bioactive molecules
for biological studies,3 has been realized. To date, the synthetic
strategies can be classified into three categories on the basis of
the intrinsic differences in reaction pathways. In the first
category (Scheme 1, path A), following the Rh(III)-catalyzed
Ketenes (R1R2CCO) are reactive reagents in synthetic
and polymer chemistry.8 In particular, ketenes have been widely
used in the synthesis of complex carbonyl compounds in metal-
catalyzed addition and cross-coupling reactions. Despite their
high activity, the corresponding catalytic transformations in C−
H activation chemistry largely lag behind. The insertion of
arene C−H bonds into polar unsaturated bonds via C−H
activation has been well-studied,9 and we have also successfully
achieved acylation of arenes via insertion of a C−H bond into
the CC bond of ketenes under redox-neutral conditions.10
Recently, the Zeng group reported cyclization of N-nitrosoani-
lines with α-diazo-β-ketoesters through a cobalt(III)-catalyzed
C−H activation/Wolff rearrangement, in which a ketene was
established as a key intermediate via a Co-mediated rearrange-
ment of carbenes.11 Very recently, we also realized oxidative [4
+ 2] annulation of ketenes with 2-phenylindoles, a specific class
of arene, by taking advantage of the high reactivity of the C(3)
of the indole.10b However, oxidative conditions are required.
Encouraged by these reports, we aimed to further explore
redox-neutral synthesis of quaternary-carbon-stereocenter-con-
taining (QCSC) heterocycles via reductive elimination that
involves a sterically hindered enolate tertiary carbon (path C).
To achieve this annulation, several challenges nevertheless
Scheme 1. Construction of Stereogenic Quaternary Centers
via C−H Activation and Annulation
ortho C−H activation that gives an organorhodium inter-
mediate, the Rh−C bond underwent functionalization by a
coupling partner to give a multifunctional organic intermediate
A. Subsequently, intramolecular cyclization/functionalization
took place to give a quaternary-carbon stereocenter without the
participation of any rhodium species.4 In the second category
(path b), the quaternary-carbon stereocenter was accessed
either through nucleophilic attack of a Rh−C species at the
Received: March 20, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00906
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
exist: (1) the annulation requires sufficient suppression of
protonolysis12 of the Rh(III)-C(tertiary) species and (2)
reductive elimination involving a sterically congested tertiary
carbon generated from the insertion of ketene into a Rh−
C(aryl) bond generally requires a higher activation barrier.
Given the electrophilic nature of ketenes, as well as their
tendency toward dimerization or decomposition, introduction
of additives or high temperature may accelerate background
reactions. We now report the Rh(III)-catalyzed efficient
synthesis of QCSC isoquinolinones using ketene as a C2
synthon under redox-neutral conditions.
To ensure the high activity and selectivity of arenes and to
realize annulative coupling under the relatively simple, redox-
neutral conditions, our strategy is to take advantage of the
coordinating and oxidizing nature of an N-pivaloxy directing
group.7,13 The chelation of the pivaloyl oxygen saturates the
coordination sphere, so as to inhibit undesired protonation, as
well as to accelerate reductive elimination.7,13 Thus, we initiated
our studies by reacting O-pivaloyl acetophenone oxime 1a with
ethyl phenyl ketene 2a under redox-neutral conditions with
[Cp*RhCl2]2/AgSbF6 as a catalyst (Table 1). No reaction took
place until a base with a small ionic radius was employed
(entries 1−6). Among those bases, NaOAc gives a good yield
of the desired annulation product (3aa), together with the
simple acylation side product 4aa (entries 4−6). In
comparison, lowering or increasing the reaction temperature
all resulted in inferior results (entries 7, 8). Introduction of
PivOH and AgOAc also decreased the reaction efficiency
(entries 9, 10). DCM seems to the optimal solvent among the
various solvents examined (entries 12−16), and control
experiments verified that both [RhCp*Cl2]2 and AgSbF6 were
necessary (entry 17). Furthermore, replacement of the catalyst
by [RhCp*(MeCN)3]2(SbF6)2 improved the yield to 86% in
the presence of 4 Å molecular sieves (MS, entries 18−19).
Examination of the oxime moiety revealed that simple oxime or
other oxime esters only coupled with poor efficiency under the
optimized conditions (entries 20−22), and these results were
consistent with our hypothesis.
With the optimized conditions in hand, the scope of
annulation between O-pivaloyl oximes and ketenes was then
explored (Scheme 2). Introduction of diverse electron-
Scheme 2. Scope of Coupling of O-Pivaloyl Oximes with
a
Ketenes
a
Table 1. Optimization Studies
b
yield (%)
entry
additive
solvent
DCE
temp (°C)
3aa
4aa
1
2
3
4
5
6
7
8
CsOAc
KOAc
60
60
60
60
60
60
80
40
60
60
60
60
60
60
60
60
60
60
60
60
60
60
ND
ND
trace
70
DCE
NaOPiv
NaOAc
Na2CO3
LiOAc
DCE
DCE
<5
0
DCE
62
DCE
75
12
trace
13
trace
<5
10
<5
0
NaOAc
NaOAc
NaOAc
NaOAc
LiOAc
DCE
60
DCE
60
c
9
DCE
66
d
10
DCE
59
11
12
13
14
15
16
DCM
DCM
CH3CN
PhCH3
THF
72
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
82
<5
23
20
0
10
1,4-dioxane
DCM
DCM
DCM
DCM
DCM
DCM
72
<5
a
Conditions: arene (0.2 mmol), ketene (0.4 mmol), [RhCp*-
e
17
NR
82
(MeCN)3]2(SbF6)2 (8 mol %), NaOAc (0.4 mmol), 4 Å MS (50
mg), and DCM (2.0 mL) at 60 °C for 15 h. The reaction was
f
b
18
19 ,
<5
<5
ND
<5
<5
fg
86
conducted at a 4 mmol scale with [RhCp*Cl2]2/AgSbF6 (4 mol %/16
mol %).
h
20
ND
28
i
21
j
22
48
donating, -withdrawing, and halogen groups into the para
position of the acetophenone O-pivaloyl oxime was fully
tolerated (3aa−3la, 35−98%) although the reaction efficiency
was obviously lower with installation of electron-withdrawing
and halogen groups. In addition, a gram-scale synthesis of
product 3ca has been realized in 69% yield. Oxime esters
bearing an o-OMe group also coupled with moderate efficiency
(3ma), indicating tolerance of steric hindrance. While the
electron-drawing group at the meta position of the oxime esters
a
Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), [RhCp*Cl2]2 (4
mol %), AgSbF6 (16 mol %), base (0.4 mmol), solvent (2.0 mL) under
b
c
N2 for 15 h. Isolated yield after column chromatography. PivOH
d
e
(0.2 equiv). AgOAc (0.2 equiv). No rhodium or AgSbF6 was used.
f
[RhCp*(MeCN)3]2(SbF6)2 (8 mol %) was used instead of
g
[RhCp*Cl2]2/AgSbF6. 4 Å MS (50 mg) was introduced.
h
i
Acetophenone oxime was used instead of 1a. O-Acetyloxime was
j
used. O-Benzoyl oxime was used.
B
DOI: 10.1021/acs.orglett.8b00906
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
almost lead to no activity (3na), meta electron-donating group
substituted arenes exhibited high reactivity and regioselectivity
at the less hindered site (3oa−3qa, 3sa), except for isomeric
products 3ra and 3ra′, likely due to the secondary coordination
effect of the oxygen group. Of note, O-pivaloyl oximes in cyclic
frameworks were also applicable, and the desired products 3ta
and 3ua were isolated both in 78% yields. The C−H activation
was not limited to a benzene ring (3va, 3wa); both ortho
positions of a thiophene ring underwent C−H activation with
moderate regioselectivity (3wa and 3wa′). We next evaluated
the generality of ketenes in the coupling with several O-pivaloyl
oximes. Introductions of a chloro, fluoro, or methyl group into
the benzene ring of ethylaryketenes were well tolerated (3cb−
3ce, 3ad), and the reaction efficiency was only slightly affected
by steric hindrance of the ketene. In addition to using an ethyl
substituent, arylketenes substituted by methyl and n-propyl also
coupled with comparably high efficiency (3af, 3cg).
affording piperidone 4 in 76% yield and in a 1.4:1
diastereomeric ratio (Scheme 3e).14
On the basis of these observations, previous reports,7,13,15
and our DFT studies (see the Supporting Information for
details), a plausible mechanism of the coupling of oxime ester
1a and 2a is proposed in Scheme 4. The catalytic cycle starts
Scheme 4. Proposed Pathways of Coupling of Oxime Esters
with Ketenes (See the Supporting Information for Detailed
DFT Studies)
To gain insight into the mechanism of the coupling reaction,
experimental studies have been performed. H/D exchange
between oxime ester 1a and CD3OD under the standard
conditions (Scheme 3a) revealed significant H/D exchange at
Scheme 3. Mechanistic Studies and a Derivatization
Reaction
from a cationic rhodium complex I, which could be generated
by the ligand exchange with oxime ester 1. With assistance of
coordination of the oxime moiety, ortho C−H cleavage takes
place via concerted metalation−deprotonation (CMD) to give
a rhodacyclic intermediate II with an activation free energy of
19.8 kcal/mol. Coordination of a ketene is followed by
migratory insertion of the Rh−C(alkyl) bond into the CC
bond of ketene, affording a fused rhodacycle IV with an
activation free energy of 11.6 kcal/mol. The coordination
saturation in rhodacycle IV serves to inhibit protonolysis of the
Rh−C(alkyl) bond. Meanwhile, N−O bond cleavage and
corresponding N−C bond formation might occur in either a
concerted (pathway a) or stepwise (pathway b) fashion to
furnish the coupled product 3, together with regeneration of
the active Rh(III) intermediate I by the ligand exchange of
oxime ester 1a. In the stepwise pathway b, a high oxidation
state Rh(V) intermediate is generated prior to reductive
elimination. Our DFT studies by an intrinsic reaction
coordinate (IRC) indicated that the concerted pathway can
readily occur, and is consequently a favored pathway, in which
the reaction proceeds via all-Rh(III) intermediates. In
particular, the concerted C−N formation/N−O cleavage
takes place with an activation barrier of only 11.8 kcal/mol.
In summary, we have realized Rh(III)-catalyzed annulative
couplings between arenes and ketenes. The coupling of O-
pivaloyl oxime occurred under redox-neutral conditions to give
isoquinolones, and the OPiv group played a key role in
suppressing protonolysis of the Rh−C(alkyl) bond. DFT
studies suggest that the C−N coupling/N−O cleavage occurs
via a concerted all-Rh(III) process. This concise protocol to
the ortho positions, indicating reversibility of the C−H cleavage.
The kinetic isotopic effect was then measured in two side-by-
side reactions using 1a and 1a-d5 at a low conversion under the
standard conditions, from which kH/kD = 3.2 was obtained by
1H NMR analysis (Scheme 3b). This result indicates that a C−
H activation process is probably involved in the turnover-
limiting step. In addition, intermolecular competition has been
performed for two arenes that differ in electronic effect, and the
electron-rich arene exhibited significantly higher reactivity
(Scheme 3c), which is consistent with higher nucleophilicity
of the Rh−C bond. Then, we performed a control experiment
by subjecting the simple acylation product 4aa to the standard
conditions (Scheme 3d), and no reaction was detected,
suggesting that full C−H acylation could not lead to the final
annulation. Encouraged by the wide abundance of piperidone
in biologically active compounds, we turned our attention to
the reduction of the CN bond. Treatment of 3aa with
NaBH4/PhCOOH led to chemoselctive reduction of the imine,
C
DOI: 10.1021/acs.orglett.8b00906
Org. Lett. XXXX, XXX, XXX−XXX

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Letter
N.; Glorius, F. J. Am. Chem. Soc. 2011, 133, 2154. (c) Dong, L.; Qu, C.
H.; Huang, J. R.; Zhang, W.; Zhang, Q. R.; Deng, J. G. Chem. - Eur. J.
2013, 19, 16537. (d) Zhou, M. B.; Pi, R.; Hu, M.; Yang, Y.; Song, R. J.;
Xia, Y.; Li, J. H. Angew. Chem., Int. Ed. 2014, 53, 11338. (e) Li, X.;
Yang, X.; Qi, Z. ACS Catal. 2016, 6, 6372. (f) Mei, S. T.; Liang, H. W.;
Teng, B.; Wang, N. J.; Shuai, L.; Yuan, Y.; Wei, Y. Org. Lett. 2016, 18,
1088. (g) Pham, M. V.; Cramer, N. Chem. - Eur. J. 2016, 22, 2270.
(6) (a) Burns, D. J.; Lam, H. W. Angew. Chem., Int. Ed. 2014, 53,
9931. (b) Gandeepan, P.; Rajamalli, P.; Cheng, C. H. Chem. - Eur. J.
access QCSC scaffolds may find applications in the synthesis of
complex biologically active products.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00906.
2015, 21, 9198. (c) Casanova, N.; Seoane, A.; Mascarenas, J. L.;
̃
Detailed experimental procedures, characterization of
new compounds, DFT calculation data, and copies of
NMR spectra (PDF)
Gulías, M. Angew. Chem., Int. Ed. 2015, 54, 2374. (d) Kuppusamy, R.;
Gandeepan, P.; Cheng, C. H. Org. Lett. 2015, 17, 3846. (e) Wu, X.;
Wang, B.; Zhou, Y.; Liu, H. Org. Lett. 2017, 19, 1294.
(7) (a) Hyster, T. K.; Ruhl, K. E.; Rovis, T. J. Am. Chem. Soc. 2013,
135, 5364. (b) Zhang, H.; Wang, K.; Wang, B.; Yi, H.; Hu, F.; Li, C.;
Wang, J. Angew. Chem., Int. Ed. 2014, 53, 13234. (c) Seoane, A.;
AUTHOR INFORMATION
Corresponding Authors
■
Casanova, N.; Quinones, N.; Mascarenas, J. L.; Gulías, M. J. Am. Chem.
̃
̃
Soc. 2014, 136, 7607. (d) Zhang, Y.; Wang, D.; Cui, S. Org. Lett. 2015,
17, 2494. (e) Zhou, B.; Chen, Z.; Yang, Y.; Ai, W.; Tang, H.; Wu, Y.;
Zhu, W.; Li, Y. Angew. Chem., Int. Ed. 2015, 54, 12121. (f) Yu, S.; Liu,
S.; Lan, Y.; Wan, B.; Li, X. J. Am. Chem. Soc. 2015, 137, 1623.
(g) Zheng, J.; Wang, S.-B.; Zheng, C.; You, S.-L. J. Am. Chem. Soc.
2015, 137, 4880. (h) Zheng, J.; Wang, S. B.; Zheng, C.; You, S. L.
Angew. Chem., Int. Ed. 2017, 56, 4540. (i) Li, Y.; Tang, Y.; He, X.; Shi,
D.; Wu, J.; Xu, S. Chem. - Eur. J. 2017, 23, 7453.
(8) (a) Tidwell, T. T. Eur. J. Org. Chem. 2006, 2006, 563.
(b) Hodous, B. L.; Fu, G. C. J. Am. Chem. Soc. 2002, 124, 1578.
(c) Schaefer, C.; Fu, G. C. Angew. Chem., Int. Ed. 2005, 44, 4606.
(d) Dai, X.; Nakai, T.; Romero, J. A.; Fu, G. C. Angew. Chem., Int. Ed.
2007, 46, 4367. (e) Ibrahim, A. A.; Wei, P. H.; Harzmann, G. D.;
Kerrigan, N. J. J. Org. Chem. 2010, 75, 7901. (f) Kumar, P.; Troast, D.
M.; Cella, R.; Louie, J. J. Am. Chem. Soc. 2011, 133, 7719. (g) Ogata,
K.; Ohashi, I.; Fukuzawa, S. I. Org. Lett. 2012, 14, 4214. (h) Allen, A.
D.; Tidwell, T. T. Chem. Rev. 2013, 113, 7287.
(9) Reviews: (a) Zhang, X.-S.; Chen, K.; Shi, Z.-J. Chem. Sci. 2014, 5,
2146. (b) Song, G.; Li, X. Acc. Chem. Res. 2015, 48, 1007. (c) Yang, L.;
Huang, H. Chem. Rev. 2015, 115, 3468. (d) Hummel, J. R.; Boerth, J.
A.; Ellman, J. A. Chem. Rev. 2017, 117, 9163.
(10) (a) Yu, S.; Li, Y.; Kong, L.; Zhou, X.; Tang, G.; Lan, Y.; Li, X.
ACS Catal. 2016, 6, 7744. (b) Yang, X.; Li, Y.; Kong, L.; Li, X. Org.
Lett. 2018, 20, 1957. For a marginally related report, see: (c) Minami,
Y.; Kanda, M.; Sakai, M.; Hiyama, T. Tetrahedron 2015, 71, 4522.
(11) Hu, X.; Chen, X.; Shao, Y.; Xie, H.; Deng, Y.; Ke, Z.; Jiang, H.;
Zeng, W. ACS Catal. 2018, 8, 1308.
(12) (a) Ikemoto, H.; Yoshino, T.; Sakata, K.; Matsunaga, S.; Kanai,
M. J. Am. Chem. Soc. 2014, 136, 5424. (b) Ikemoto, H.; Tanaka, R.;
Sakata, K.; Kanai, M.; Yoshino, T.; Matsunaga, S. Angew. Chem., Int.
Ed. 2017, 56, 7156. (c) Wang, C.; Wang, A.; Rueping, M. Angew.
Chem., Int. Ed. 2017, 56, 9935. (d) Chen, S. Y.; Han, X. L.; Wu, J. Q.;
Li, Q.; Chen, Y.; Wang, H. Angew. Chem., Int. Ed. 2017, 56, 9939.
(13) (a) Rakshit, S.; Grohmann, C.; Besset, T.; Glorius, F. J. Am.
Chem. Soc. 2011, 133, 2350. (b) Xu, L.; Zhu, Q.; Huang, G.; Cheng,
B.; Xia, Y. J. Org. Chem. 2012, 77, 3017. (c) Zhao, D.; Li ed, F.;
Glorius, F. Chem. Sci. 2014, 5, 2869. (d) Romanov-Michailidis, F.;
Sedillo, K. F.; Neely, J. M.; Rovis, T. J. Am. Chem. Soc. 2015, 137, 8892.
(e) Wu, J. Q.; Zhang, S. S.; Gao, H.; Qi, Z.; Zhou, C. J.; Ji, W. W.; Liu,
Y.; Chen, Y.; Li, Q.; Li, X.; Wang, H. J. Am. Chem. Soc. 2017, 139,
3537.
*E-mail: lanyu@cqu.edu.cn.
*E-mail: xwli@dicp.ac.cn.
ORCID
Songjie Yu: 0000-0001-9156-8774
Yu Lan: 0000-0002-2328-0020
Xingwei Li: 0000-0002-1153-1558
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the NSFC (Nos. 21472186 and
21525208) and the Fund for New Technology of Methanol
Conversion of Dalian Institute of Chemical Physics (Chinese
Academy of Sciences) are gratefully acknowledged.
REFERENCES
■
(1) Selected reviews: (a) Daugulis, O.; Do, H.-Q.; Shabashov, D. Acc.
Chem. Res. 2009, 42, 1074. (b) Colby, D. A.; Bergman, R. G.; Ellman,
J. A. Chem. Rev. 2010, 110, 624. (c) Lyons, T. W.; Sanford, M. S.
Chem. Rev. 2010, 110, 1147. (d) McMurray, L.; O’Hara, F.; Gaunt, M.
J. Chem. Soc. Rev. 2011, 40, 1885. (e) Yeung, C. S.; Dong, V. M. Chem.
Rev. 2011, 111, 1215. (f) Ackermann, L. Chem. Rev. 2011, 111, 1315.
(g) Li, B.- J.; Shi, Z.-J. Chem. Soc. Rev. 2012, 41, 5588. (h) Hartwig, J.
F. Acc. Chem. Res. 2012, 45, 864. (i) Fukui, M.; Hoshino, Y.; Satoh, T.;
Miura, M.; Tanaka, K. Adv. Synth. Catal. 2014, 356, 1638. (j) Zheng,
Q. Z.; Jiao, N. Tetrahedron Lett. 2014, 55, 1121. (k) Gensch, T.;
Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J. Chem. Soc. Rev.
2016, 45, 2900. (l) Wang, F.; Yu, S.; Li, X. Chem. Soc. Rev. 2016, 45,
6462. (m) He, J.; Wasa, M.; Chan, K. S.; Shao, Q.; Yu, J. Q. Chem. Rev.
2017, 117, 8754. (n) Ping, L.; Chung, D. S.; Bouffard, J.; Lee, S.-g.
Chem. Soc. Rev. 2017, 46, 4299. (o) Wei, Y.; Hu, P.; Zhang, M.; Su, W.
Chem. Rev. 2017, 117, 8864. (p) Kim, D.-S.; Park, W.-J.; Jun, C.-H.
Chem. Rev. 2017, 117, 8977. (q) Park, Y.; Kim, Y.; Chang, S. Chem.
Rev. 2017, 117, 9247. (r) Chen, Z.; Wang, B.; Zhang, J.; Yu, W.; Liu,
Z.; Zhang, Y. Org. Chem. Front. 2015, 2, 1107.
(2) (a) Satoh, T.; Miura, M. Chem. - Eur. J. 2010, 16, 11212.
(b) Gulias, M.; Mascarenas, J. L. Angew. Chem., Int. Ed. 2016, 55,
11000. (c) Yang, Y.; Li, K.; Cheng, Y.; Wan, D.; Li, M.; You, J. Chem.
Commun. 2016, 52, 2872.
(3) (a) Trost, B. M.; Jiang, C. Synthesis 2006, 3, 369. (b) Nan, J.;
Zuo, Z.; Luo, L.; Bai, L.; Zheng, H.; Yuan, Y.; Wang, Y. J. Am. Chem.
Soc. 2013, 135, 7. (c) Zeng, X. P.; Cao, Z. Y.; Wang, Y. H.; Zhou, F.;
Zhou, J. Chem. Rev. 2016, 116, 7330.
(14) Cho, B. T.; Kang, S. K. Tetrahedron 2005, 61, 5725.
(15) (a) Huang, H.; Ji, X.; Wu, W.; Jiang, H. Chem. Soc. Rev. 2015,
44, 1155. (b) Mo, J.; Wang, L.; Liu, Y.; Cui, X. Synthesis 2015, 47, 439.
(c) Liu, X. G.; Gao, H.; Zhang, S. S.; Li, Q.; Wang, H. ACS Catal.
2017, 7, 5078.
(4) (a) Chen, Y.; Wang, D.; Duan, P.; Ben, R.; Dai, L.; Shao, X.;
Huang, Y. Nat. Commun. 2014, 5, 4610. (b) Zhou, Z.; Liu, G.; Chen,
Y.; Lu, X. Org. Lett. 2015, 17, 5874. (c) Li, D. Y.; Jiang, L. L.; Chen, S.;
Huang, Z. L.; Dang, L.; Wu, X. Y.; Liu, P. N. Org. Lett. 2016, 18, 5134.
(5) (a) Muralirajan, K.; Parthasarathy, K.; Cheng, C.-H. Angew.
Chem., Int. Ed. 2011, 50, 4169. (b) Patureau, F. W.; Besset, T.; Kuhl,
D
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