Pd(II)/(S)-t-BuPyOx-catalyzed asymmetric addition of arylboronic acids to N-sulfonyl-arylaldimines

Article abstract of DOI:10.1016/j.tetlet.2021.153057

The asymmetric version of Pd(II)/bipyridine-catalyzed nucleophilic addition of arylboronic acids to N-sulfonyl arylaldimines was developed, and excellent asymmetric induction was achieved by the use of chiral pyridinooxazoline ligand (S)-t-BuPyOx. Moistur

Full text of DOI:10.1016/j.tetlet.2021.153057

Tetrahedron Letters 72 (2021) 153057
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Pd(II)/(S)-t-BuPyOx-catalyzed asymmetric addition of arylboronic acids
to N-sulfonyl-arylaldimines
⇑
⇑
Kaixuan Song, Min Wen, Kai Shen, Chaogang Fan, Zhenyu Yang, Shaohui Lin , Qinmin Pan
State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, Key
Laboratory of Organic Synthesis of Jiangsu Province, Green Polymer and Catalysis Technology Laboratory (GAPCT), College of Chemistry, Chemical Engineering and Materials
Science, Soochow University, 199 Ren’ai Road, Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The asymmetric version of Pd(II)/bipyridine-catalyzed nucleophilic addition of arylboronic acids to N-sul-
fonyl arylaldimines was developed, and excellent asymmetric induction was achieved by the use of chiral
pyridinooxazoline ligand (S)-t-BuPyOx. Moisture and oxygen-insensitive catalysis was realized under
mild conditions, and 9 out of 16 examples gave 92–99% ee.
Received 14 December 2020
Revised 21 March 2021
Accepted 30 March 2021
Available online 6 April 2021
Ó 2021 Elsevier Ltd. All rights reserved.
Keywords:
Palladium-Catalysis
Asymmetric addition
Pyridinooxazoline ligand
Arylboronic acid
N-Sulfonyl arylaldimine
Introduction
be highly reactive, in which nitromethane as the solvent played
an important role for its high polarity and low coordination ability
Transition
metals-catalyzed
nucleophilic
addition
of
[8c,8g].
Asymmetric addition to b,b-disubstituted enones was highly
organometallic reagents to electron deficient olefins [1] and
C = X (X = N, O, etc.) unsaturated bonds [2] has been received
increasing attentions in the last two decades, which provided pow-
erful tools for carbon–carbon bonds formation and chiral carbon
centers construction. Compared with Cu(I)-catalyzed conjugate
addition developed by Feringa [3] and the well-documented Rh
(I)-catalyzed nucleophic addition reactions pioneered by Hayashi
[4], in which many types of highly effective chiral ligands have
been achieved, [5] the reactions of their palladium version were
relatively unexplored.Scheme 1.
challenging for the enantioselective construction of quaternary
carbons, [9] and Stoltz accomplished its fabulous asymmetric
induction with Pd(II)/t-butyl pyridinooxazoline ((S)-t-BuPyOx).
[10] In the following researches by Stoltz and other groups, [10]
pyridinooxazolines have been confirmed as an excellent ligand
for its chirality-inducing property and easy availability.
For the addition to imines, Lu and Dai reported cationic Pd(II)/
bipyridine-catalyzed highly diastereoselective addition of aryl-
boronic acids to N-t-butanesulfinyl imino esters; [11] Pd(II)/pyridi-
nooxazoline-catalyzed addition of arylboronic acids to N-sulfonyl
arylaldimines [11] and one-pot enantioselective synthesis of aryl-
glycine derivatives [11] were also explored by Lu’s group, in which
modest to good enantioselectivity were achieved. In 2009, Shi
demonstrated C2-Symmetric Cationic N-Heterocyclic Carbene-Pd
(II) Complexes-catalyzed enantioselective arylation of imines.
[12] In 2012, Zeng reported highly enantioselective arylation of
Initially Uemura reported palladium-catalyzed conjugate addi-
tion of arylboron reagents to enones, [6] and it was greatly devel-
oped by Miyaura with cationic Pd(II)/bisphosphine complexes. [7]
In 2005, our group published the first Pd(II)/bipyridine catalyzed
conjugate addition of arylboronic acids to different
a,b-unsatu-
rated carbonyl compounds, [8] and a series of nucleophilic addition
reactions were realized in our group with the same methodology.
[8] To accomplish the difficult addition to aldehydes [8], imines
[8], and b,b-disubstituted enones [8], cationic Pd(II)-bidentate
nitrogen ligand complexes were developed and were proved to
a-imino esters with Pd(II)/bisoxazoline catalyst, [13] and Mano-
likakes improved this reaction with a three-component synthesis,
in which excellent enantioselectivity were remained. [14] Zhang
developed a series of Pd(II)/pyridinooxazoline-catalyzed addition
of arylboronic acids to ketimines, [15] with very good functional
groups tolerance and high asymmetric induction obtained.
⇑
Corresponding authors.
E-mail addresses: linshaohui@suda.edu.cn (S. Lin), qpan@suda.edu.cn (Q. Pan).
https://doi.org/10.1016/j.tetlet.2021.153057
0040-4039/Ó 2021 Elsevier Ltd. All rights reserved.

K. Song, M. Wen, K. Shen et al.
Tetrahedron Letters 72 (2021) 153057
methane as the solvent, [8] in which the reaction can be greatly
accelerated and gave magnificent yields. Herein, we reported its
asymmetric version with (S)-t-butyl pyridinooxazoline ((S)-t-
BuPyOx) as the ligand.
Results and discussion
According to the 3-step-synthesis of (S)-t-BuPyOx by Stoltz,
[10] gram-scaled enantiopure ligand was prepared. Initially, (S)-
t-BuPyOx was tested under our published in-situ generated catio-
nic Pd(II)-catalyzed addition of arylboronic acids to imines, and p-
methoxyphenylboronic acid and N-tosylbenzaldimine were fixed
as the substrate invariables, nitromethane as the solvent, to do
the conditions optimization. Compared with PdCl2/2,20-bipyridine
catalysis, the involvement of (S)-t-BuPyOx ligand slowed the reac-
tion and a 93% yield was still given after 2 days (Table 1, entry 1),
but with only 42% ee. To improve the enantioselectivity, the reac-
tion temperature was lowered to 40 °C, and it did improve the
enantiomer excess to 92% ee after 60 h (Table 1, entry 2). The pro-
longed time caused more hydrolysis of arylboronic acid, and the
yield was only 53%. This reaction can hardly proceed at room tem-
perature (Table 1, entry 3). In Zeng’s research, Pd(OAc)2 also gave
Scheme 1. Proposed mechanism of enantioselective addition of arylbronic acids to
aldimines.
satisfactory asymmetric induction in nucleophilic addition to
a-
imino esters, [13] so we tried Pd(OAc)2 in this reaction. It’s found
that no reaction was detected at room temperature (Table 1, entry
4), but after 3 days at 40 °C, 52% of the target product was isolated
with a 93% ee (Table 1, entry 5). When the temperature was
increased to 60 °C, 83% yield and 95% ee were achieved after
Based on our systematic investigation to Pd(II)/nitrogen ligands
catalysis and Lu/Dai’s initial research on addition to imines, [11]
we have published a cationic Pd(II)/bipyridine-catalyzed addition
of arylboronic acids to N-sulfonyl-arylaldimines with nitro-
Table 1
Conditions optimization of Pd(II)-catalyzed addition of p-methoxyphenylboronic acid to N-tosylbenzaldimine.a
Entry
Catalyst
Solvent
Temperature (oC)
Time (h)
Yield (%)b
% eec
1
2
3
4
5
6
7
8
(S)-t-BuPyOx/PdCl2/2AgNO3
(S)-t-BuPyOx/PdCl2/2AgNO3
(S)-t-BuPyOx/PdCl2/2AgNO3
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(S)-t-BuPyOx/Pd(OAc)2
(R)-t-BuPyOx/Pd(OAc)2
(S)-i-PrPyOx/Pd(OAc)2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
Toluene
1,4-Dioxane
THF
ClCH2CH2Cl
CHCl3
CH3OH
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
60
40
RT
RT
40
60
80
60
60
60
60
60
60
60
60
60
60
60
48
60
60
72
72
60
60
72
72
72
72
72
60
60
60
60
60
60
93
53
Trace
Trace
52
83
59
NR
NR
Trace
NR
Trace
30
51
85
84
85
39
42
92
–
–
93
95
87
–
–
–
9
10
11
12
13
14
15
16
17
18
–
–
49
94d
95e
93f
93g
67
a
Reaction condition: p-methoxyphenylboronic acid (1.00 mmol), N-tosylbenzaldimine (0.50 mmol), Pd(II) (0.025 mmol, 5.0 mol%), chiral ligand (0.030 mmol, 6.0 mol%) in
solvent (2.0 mL).
b
Isolated yields.
Determined by chiral HPLC.
Pd(II) (0.0125 mmol, 2.5 mol%), chiral ligand (0.015 mmol, 3.0 mol%).
Pd(II) (0.050 mmol, 10.0 mol%), chiral ligand (0.060 mmol, 12.0 mol%).
p-methoxyphenylboronic acid (5.00 mmol), N-tosylbenzaldimine (2.50 mmol).
enantioselectivtiy opposite to (S)-t-BuPyOx.
c
d
e
f
g
2

K. Song, M. Wen, K. Shen et al.
Tetrahedron Letters 72 (2021) 153057
Table 2
Pd(II)/(S)-t-BuPyOx-catalyzed addition of arylboronic acids to N-sulfonyl arylaldimines.a
Entry
1
ArB(OH)2
Ar = NSO2R
2a
Product
Time (h)
60
Yield (%)b
83
% eec
95
1a
1b
3aa
3ba
2
60
79
97
2a
3
4
48
48
82
81
–
1c
2a
2a
3ca
97
1d
3da
3ea
5
60
80
93
1e
2a
6
7
8
48
72
72
78
83
–
2a
2a
2a
1f
3fa
Trace
Trace
1g
3ga
–
1h
3ha
9
60
60
48
80
85
91
99
93
97
2a
2a
1i
3ia
10
11
1j
3ja
1b
3bb
2b
12
13
14
15
16
60
60
60
60
60
83
76
82
81
73
92
95
21
86
70
1b
1b
1b
1a
1b
3bc
2c
3bd
3be
3af
2d
2e
2f
2g
3bg
a
b
c
Reaction condition: p-arylboronic acid (1.00 mmol), N-sulfonylarylaldimine (0.50 mmol), Pd(II) (0.025 mmol, 5.0 mol%) in solvent (2.0 mL), 60 °C, 3 days.
Isolated yields.
Determined by chiral HPLC.
3

K. Song, M. Wen, K. Shen et al.
Tetrahedron Letters 72 (2021) 153057
60 h (Table 1, entry 6). Higher temperature caused the yield and
enantioselectivity dropped sharply (Table 1, entry 7).
chiral products were determined by the comparison of their optical
activities with results in literature. [12,14]
The solvent effect was also surveyed, and the results revealed
that the solvents with low or medium polarity, such as toluene,
1,4-dioxane and THF gave no expected product (Table 1, entries
8–10). The reactions in chlorinated solvents failed to produce any
target product (Table 1, entries 11–12), but when the solvent
was methanol, 30% of 3aa was obtained with a 49% ee (Table 1,
entry 13). Then the Pd(II) catalyst loading was varied and it’s found
2.5 mol% of catalyst gave a dropped yield and a maintained enan-
tioselectivity (Table 1, entry 14). 10 mol% of catalyst didn’t improve
the yield (Table 1, entry 15). The imine can be scaled up to
2.50 mmol with the same results (Table 1, entry 16). Up to now,
the best yield and enantioselectivity was given in nitromethane.
(R)-t-BuPyOx was also tested in nitromethane, in which a same
yield and an opposite enantioselectivtiy were given (Table 1, entry
17). As a comparison, (S)-i-PrPyOx with a isopropyl group was
subjected to the same conditions to afford a 39% yield with 67%
ee (Table 1, entry 14), which might indicate the steric hinderance
is crucial to the good asymmetric induction in this reaction. Actu-
ally the result of (S)-i-PrPyOx was very similar to the reported
example in Lu’s research.11c
With the optimal conditions in hand, we started to probe the
scope of different substrates. N-tosylbenzaldimine was fixed as
the invariable imine to test arylboronic acid, and it’s found the
arylboronic acids with electron donating groups (Table 2, entries
1–2) gave good yields and excellent ee. For phenylboronic acid
and N-tosylbenzaldimine (Table 2, entry 3), 82% of the addition
product was isolated. When halogenated arylboronic acids were
subjected to the reaction, p-fluoro and p-chloro phenylboronic
acids (Table 2, entries 4–5) all produced target chiral products with
97% and 93% ee, respectively. In the case of m-chlorophenylboronic
acid, the enantioslectivity dropped to 83% ee with a 83% yield, and
for o-chlorophenylboronic acid (Table 2, entry 7) only trace of the
product can be observed on NMR. It might be the interaction of
ortho chlorine atom with the Pd(II) complex retarded the reaction.
As for the arylboronic acid with an electron withdrawing ester
group on the phenyl ring (Table 2, entry 8), no expected product
can be isolated, which could be explained by the weak nucle-
ophilicity of the arylboronic acid. The steric effect was also studied,
and 1-naphthyl and 2-naphthyl boronic acids were tested. For 1-
naphthylboronic acid (Table 2, entry 9) > 99% ee was achieved,
and 2-naphthylboronic acid (Table 2, entry 10) with a 93% ee. It
means the steric hindrance on arylboronic acids does favor the
enantioselectivity.
Based on the high enantioselectivity achieved in this reaction,
and according to the mechanistic research of Pd-catalyzed conju-
gate addition, [10,15] a mechanism was proposed to explain the
stereoselectivity.
The coordination of (S)-t-BuPyOx and Pd(II) afforded complex A,
and the transmetallation between A and arylboronic acids pro-
duced B, with aryl group on the less hindered side; The coordina-
tion of imines to Palladium and the repulsion between t-butyl
group and aryl groups on imines made a stereoselective addition
of Ar1 to imines (Transition C), which gave intermediate D; The
protonolysis of D produced the enantioselective product and
regenerated catalyst A.
Conclusion
In this research, highly enantioselective Pd(II)/(S)-t-BuPyOx
catalyzed addition of arylboronic acids to N-sulfonyl-arylaldimines
was developed. The optimal conditions provided a moisture and
oxygen insensitive method to prepare optically pure amines, and
excellent ee was achieved with good yields in most examples.
The scope of different subsrtates was investigated, and it revealed
that the electron donating substituents on arylboronic acids and
electron withdrawing substituents on arylaldimines favored the
enantioselectivities.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgments
We gratefully acknowledge the National Natural Science Foun-
dation of China (Nos. 21104049, 21176163, 21576174), Specialized
Research Fund for the Doctoral Program (SRFDP) of Higher Educa-
tion (No. 20113201120006), the Priority Academic Program Devel-
opment (PAPD) of Jiangsu Higher Education Institutions, Soochow
University Funds (Nos. 14109001, Q410900510) and Suzhou Indus-
trial Park Fund for financial support.
Appendix A. Supplementary data
In the screening of N-sulfonylarylaldimines, p-tolylbornic acid
was chosen as the invariable arylboronic acid because p-
methoxyphenylboronic acid might lead to more protonolysis for
its strong electron donating property, which may cause more boro-
nic acid consumption. For the N-sulfonylarylaldimine with strong
electron withdrawing nitro group (Table 2, entry 11), the reaction
gave 91% yield and 97% ee, which were extraordinarily good in all
the experiments. For halogenated arylaldimines (Table 2, entries
12–13), good yields and excellent ee were obtained. When methoxy
group was bonded to arylaldimine, the enantioselectivity dropped
to 21% dramatically and this result was reproduced and confirmed;
When the less electron donating methyl group was substituted
(Table 2, entry 15), the addition of p-methoxyphenylboronic acid
afforded a higher 86% ee. Compared these two results with entry 1
(Table 2), it’s hypothesized that the strong electron donating prop-
erty of the substituents on arylaldimines, which increase the insta-
bility of imines, could disfavor the steroslective addition under Pd
(II)/(S)-t-BuPyOx catalysis. In the last example (Table 2, entry 16),
when N-tosyl was replaced by N-mesyl, 73% of the product was iso-
lated with a lower 70% ee. It could be the less hindered N-mesyl that
decreased the enantioselectivity. All the absolute configurations of
Supplementary data (typical experimental procedures, charac-
terization of all products, 1H and 13C NMR spectra, HPLC diagrams,
etc.) associated with this article can be found, in the online version,
at Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2021.153057.
References
[1] (a) Berthon, G.; Hayashi, T. Rhodium- and Palladium-Catalyzed Asymmetric
Conjugate Additions, in Catalytic Asymmetric Conjugate Reactions; Córdova,
A., Ed.; Wiley-VCH: Weinheim, 2010;
(b) Alexakis, A. The conjugate addition reaction, in Transition Metals for
Organic Synthesis: Building Blocks and Fine Chemicals, 2nd ed.; Beller, M.,
Bolm, C., Eds.; Wiley-VCH: Weinheim, 2004;
(c) Perlmutter, P. Conjugate Addition Reactions in Organic Synthesis;
Pergamon Press: Oxford, 1992;
(d) Mauduit, M.; Baslé, O.; Clavier, H.; Crévisy, C.; Denicourt-Nowicki, A. Metal-
Catalyzed Asymmetric Nucleophilic Addition to Electron-Deficient Alkenes, in
Comprehensive Organic Synthesis II, Knochel, P., Eds.; Elsevier, 2014;
(e) Wu, L.; Shen, J.; Yang, G.; Zhang, W. Tetrahedron Lett. 2018, 59, 4055.
[2] (a) Suga, S.; Kitamura, M. Asymmetric 1,2-Addition of Organometallics to
Carbonyl and Imine Groups, in Comprehensive Chirality, Carreira, E. M.;
Yamamoto, H., Eds.; Elsevier, 2012;
(b) Liu, Y.-L.; Lin, X.-T. Adv. Synth. Catal. 2019, 361, 876.
4

K. Song, M. Wen, K. Shen et al.
Tetrahedron Letters 72 (2021) 153057
[8] (a) Lu, X.; Lin, S. J. Org. Chem. 2005, 70, 9651.;
[3] (a) Harutyunyan, S. R.; den Hartog, T.; Geurts, K.; Minnaard, A. J.; Feringa, B. L.
Chem. Rev. 2008, 108, 2824.;
(b) Lin, S.; Lu, X. Tetrahedron Lett. 2006, 47, 7167.;
(c) Lin, S.; Lu, X. J. Org. Chem. 2007, 72, 9757.;
(d) Lin, S.; Lu, X. Org. Lett. 2010, 12, 2536.;
(b) Lopez, F.; Minnaard, A. J.; Feringa, B. L. Acc. Chem. Res. 2007, 40, 179.;
(c) Feringa, B. L. Acc. Chem. Res. 2000, 33, 346.
[4] (a) Hayashi, T. Pure Appl. Chem. 2004, 76, 465. and the references therein.;
(b) Hayashi, T.; Senda, T.; Ogasawara, M. J. Am. Chem. Soc. 2000, 122, 10716.;
(c) Hayashi, T.; Senda, T.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc. 1999,
121, 11591.;
(d) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N. J. Am. Chem.
Soc. 1998, 120, 5579.;
(e) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16, 4229.
[5] For Rh(I)-catalyzed asymmetric addition to imines, please see: Chiral
phosphine ligands: (a) Weix, D. J.; Shi, Y.; Ellman, J. A. J. Am. Chem. Soc.
2005, 127, 1092.;
(e) Ji, J.; Yang, Z.; Liu, R.; Ni, Y.; Lin, S.; Pan, Q. Tetrahedron Lett. 2016, 57, 2723.;
(f) Liu, R.; Yang, Z.; Ni, Y.; Song, K.; Shen, K.; Lin, S.; Pan, Q. J. Org. Chem. 2017,
82, 8023.;
(g) Yang, Z.; Ni, Y.; Liu, R.; Song, K.; Lin, S.; Pan, Q. Tetrahedron Lett. 2017, 58,
2034.;
(h) Ni, Y.; Song, K.; Shen, K.; Yang, Z.; Liu, R.; Lin, S.; Pan, Q. Tetrahedron Lett.
2018, 59, 1192.
[9] (a) Liu, Y.; Han, S.-J.; Liu, W.-R.; Stoltz, B. M. Acc. Chem. Res. 2015, 48, 740.;
(b) Gottumukkala, A. L.; Matcha, K.; Lutz, M.; de Vries , J. G.; Minnaard, A. J.
Chem. —Eur. J. 2012, 18, 6907.
(b) Nakagawa, H.; Rech, J. C.; Sindelar, R. W.; Ellman, J. A. Org. Lett. 2007, 9,
5155. Chiral phosphite ligands.;
[10] (a) Kikushima, K.; Holder, J. C.; Gatti, M.; Stoltz, B. M. J. Am. Chem. Soc. 2011,
133, 6902.;
(c) Duan, H.-F.; Jia, Y.-X.; Wang, L.-X.; Zhou, Q.-L. Org. Lett. 2006, 8, 2567. Chiral
phosphoramidite ligands;
(d) Jagt, R. B. C.; Toullec, P. Y.; Geerdink, D.; de Vries, J. G.; Feringa, B. L.;
Minnard, A. J. Angew. Chem. Int. Ed. 2006, 118, 2855.;
(e) Marelli, C.; Monti, C.; Gennari, C.; Piarulli, U. Synlett 2007, 14, 2213. Chiral
P,O ligands;
(b) Holder, J. C.; Zou, L.; Marziale, A. N.; Liu, P.; Lan, Y.; Gatti, M.; Kikushima, K.;
Houk, K. N.; Stoltz, B. M. J. Am. Chem. Soc. 2013, 135, 14996.;
(c) Boeser, C. L.; Holder, J. C. ; Taylor, B. L. H.; Houk, K. N.; Stoltz, B. M.; Zare, R.
N. Chem. Sci. 2015, 6, 1917.;
(d) Shockley, S. E.; Holder, J. C.; Stoltz, B. M. Org. Process. Res. Dev. 2015, 19,
974.
(f) Kuriyama, M.; Soeta, T.; Hau, X.; Chen, Q.; Tomioka, K. J. Am. Chem. Soc.
2004, 126, 8128. Chiral olefin ligands.;
(g) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.; Shintani, R.; Hayashi,
T. J. Am. Chem. Soc. 2004, 126, 13584.;
(h) Berthon-Gelloz, G.; Hayashi, T. J. Org. Chem. 2006, 71, 8957.;
(i) Wang, Z.-Q.; Feng, C.-G.; Xu, M.-H.; Lin, G.-Q. J. Am. Chem. Soc. 2007, 129,
5336.
[11] (a) Dai, H.; Lu, X. Org. Lett. 2007, 9, 3077;
(b) Dai, H.; Yang, M.; Lu, X. Adv. Synth. Catal. 2008, 350, 249.;
(c) Dai, H.; Lu, X. Tetrahedron Lett. 2009, 50, 3478.
[12] G.-N. Ma, T. Zhang, M. Shi, Org. Lett. 11 (2009) 875.
[13] J. Chen, X. Lu, W. Lou, Y. Ye, H. Jiang, W. Zeng, J. Org. Chem. 77 (2012) 8541.
[14] (a) Beisel, T.; Manolikakes, G. Org. Lett. 2015, 17, 3162.;
(b) Beisel, T.; Diehl, A. M.; Manolikakes, G. Org. Lett. 2016, 18, 4116.
[15] (a) Quan, M.; Wu, L.; Yang, G.; Zhang, W. Chem. Commun. 2018, 54, 10394.;
(b) He, Q.; Wu, L.; Kou, X.; Butt, N.; Yang, G.; Zhang, W. Org. Lett. 2016, 18,
288.;
[6] C.S. Cho, S. Motofusa, K. Ohe, S. Uemura, J. Org. Chem. 60 (1995) 883.
[7] (a) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Angew. Chem. Int. Ed. 2003, 42,
2768.;
(b) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Tetrahedron Lett. 2007, 48, 4007.;
(c) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Chem. Lett. 2005, 34, 720.;
(d) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Organometallics 2004, 23, 4317.
(c) Quan, M.; Yang, G.; Xie, F.; Gridnev, I. D.; Zhang, W. Org. Chem. Front. 2015,
2, 398.;
(d) Yang, G.; Zhang, W. Angew. Chem. Int. Ed. 2013, 52, 7540.
5