Copper-mediated tandem ring-opening/cyclization reactions of cyclopropanols with aryldiazonium salts: Synthesis of: N -arylpyrazoles

Article abstract of DOI:10.1039/c9cc09657d

A general method for the synthesis of structurally diverse N-arylpyrazoles from readily available cyclopropanols and aryldiazonium salts is disclosed. The reaction was conducted at room temperature within minutes with a broad substrate scope and excellent regioselectivity.

Full text of DOI:10.1039/c9cc09657d

View Article Online
View Journal
ChemComm
Chemical Communications
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Liu, E. Xu, J.
Jiang, Z. Huang, L. Zheng and Z. Liu, Chem. Commun., 2020, DOI: 10.1039/C9CC09657D.
Volume 54
This is an Accepted Manuscript, which has been through the
Number
January 2018
Pages 1-112
1
4
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Chemical Communications
rsc.li/chemcomm
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
S. J. Connon, M. O. Senge et al.
Conformational control of nonplanar free base porphyrins:
towards bifunctional catalysts of tunable basicity
rsc.li/chemcomm

Please do not adjust margins
ChemComm
Page 1 of 4
View Article Online
DOI: 10.1039/C9CC09657D
COMMUNICATION
Copper‐mediated tandem ring‐opening/cyclization reaction of
cyclopropanols with aryldiazonium salts: synthesis of N‐
arylpyrazoles
Received 00th January 20xx,
Accepted 00th January 20xx
Jidan Liu,*a Erjie Xu,a Jinyuan Jiang,a Zeng Huang,a Liyao Zhenga and Zhao‐Qing Liua
DOI: 10.1039/x0xx00000x
a) Chiba's work: vinyl azides as radical receptors
A general method for the synthesis of structurally diverse N‐
arylpyrazoles from readily available cyclopropanols and
aryldiazonium salts is disclosed. The reaction was conducted at
room temperature within minutes with broad substrate scope and
excellent regioselectivity.
R2
N
N3
OH
R4
R3
(1) Mn(acac)3 (1.7 equiv)
(2) HOAc, MeOH
R3
+
R1
R1
R4
R2
b) This work: aryldiazonium salts as radical receptors
R2
OH
Pyrazole, a five‐membered heterocycle with two adjacent
nitrogen atoms used extensively in agrochemical and
pharmaceutical applications, displays a broad spectrum of
biological activities such as anti‐inflammatory, antimicrobial,
antiobesity, antidepressant, antidiabetic, analgesic, and
antiviral activities,1 as exemplified by the presence of this core
structure in several commercial drugs, including Rimonabant,
Lonazolac, Celecoxib, as well as the insecticide Fipronil (Figure
N
2 BF4
N
R1
Cu(OAc)2
R1
N
+
R3
MeCN, rt, 5 min
R2
R3
Scheme 1 Ring‐opening coupling of cyclopropanols to construct N‐heterocycles.
Due to the important applications of
N‐arylpyrazole
scaffolds, the construction of these useful compounds has
attracted considerable attention during the past decades.6
Conventional approaches for the preparation of
N‐
1).2 In addition to their medicinal values,
also been applied as ligands in transition‐metal‐catalyzed
N‐arylpyrazoles have
arylpyrazoles mainly focus on the condensation of
arylhydrazines with 1,3‐dicarbonyl or α,β‐unsaturated carbonyl
compounds.7 Alternatively, the 1,3‐dipolar cycloaddition of
diazo compounds or their surrogates with olefins or alkynes8
followed by transition‐metal‐catalyzed
another popular approach.9 Although these strategies can
provide efficient routes to prepare ‐arylpyrazoles, some
drawbacks such as harsh reaction conditions, narrow substrate
scope, and poor regioselectivity, limit their synthetic
application to some extent. In order to overcome these
problems, several alternative strategies involving transition
metal catalyzed or mediated intermolecular coupling reactions
have been developed.10 Albeit great achievements have been
achieved, further exploration of convenient, efficient, and mild
cross‐coupling reactions,3
N‐heterocyclic carbenes precursors
(NHCs)4 and directing groups for C‐H bond functionalizations.5
Cl
N‐arylation represents
Cl
N
N
N
N
N
Cl
H
O
N
N
Me
Cl
HO
O
Rimonabant
(antiobesity)
Lonazolac
(NSAID)
F3C
H2NO2S
Cl
Cl
H2N
N
N
N
protocols to afford structurally diverse N‐arylpyrazoles from
N
Me
CN
readily available starting materials is still highly desirable.
Cyclopropanols are important and useful synthetic
intermediates in organic synthesis and can be readily prepared
via Kulinkovich cyclopropanation of the corresponding esters
in one step or Simmons‐Smith cyclopropanation of silyl‐enol
ethers.11 The tandem radical ring‐opening coupling of
cyclopropanols that proceed via single‐electron oxidation can
be easily realized owing to the intrinsic ring strain associated
with the three‐membered ring, and many efforts have been
devoted to synthesize β‐functionalized carbonyl compounds
CF3
S
O
CF3
Fipronil
(insecticide)
Celecoxib
(anti-inflammatory)
Figure 1 Representative commercialized bioactive N‐arylpyrazoles.
a. School of Chemistry and Chemical Engineering/Institute of Clean Energy and
Materials/Guangzhou Key Laboratory for Clean Energy and Materials, Guangzhou
University, Guangzhou, 510006, P. R. China. E‐mail: jdliu@gzhu.edu.cn
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
COMMUNICATION
Journal Name
with different single‐electron oxidants.12 In these Table 1 Substrate scope with aryldiazonium tetrafluoroboratesa,b
View Article Online
DOI: 10.1039/C9CC09657D
transformations, the β‐keto alkyl radical intermediates
generated from the oxidative ring‐opening of cyclopropanols
were involved. However, despite progresses in this area, the
tandem radical ring‐opening/coupling strategy for the
construction of nitrogen‐containing heterocycles via the
cyclization with the C=O bond of β‐functionalized carbonyl
compounds is quite rare. In 2009, Chiba and co‐workers
reported an efficient Mn(III)‐mediated ring‐opening coupling
reaction of cyclopropanols with vinyl azides for the synthesis
of substituted pyridines (Scheme 1a).13 Mechanistic studies
revealed that this transformation was initiated with the
generation of β‐keto alkyl radical intermediates via Mn(acac)3‐
mediated oxidative radical ring‐opening of cyclopropanols,
followed by radical addition to vinyl azides and annulations. In
light of our continuous interest on the chemistry of
cyclopropanols and the synthesis of heterocycles,14 we
envisioned that the β‐keto alkyl radicals derived from
cyclopropanols may be trapped by aryldiazonium salts
followed by the cyclization with intramolecular carbonyl
groups to afford important nitrogen‐containing heterocycles.
Herein, we described a copper‐mediated tandem ring‐
opening/cyclization reaction of cyclopropanols with
aryldiazonium salts for the construction of diversely
N
N
OH
N2BF4
Cu(OAc)2
MeCN, rt, 5 min
R
+
R
N
1a
2
N
N
N
N
N
N
Cl
24
71%,
R
Cl
N
R
R = Cl, 80%, 16
17
18
Br, 77%,
Me, 58%,
NO2, 74%, 19
CN, 66%
3
R = Cl, 82%,
Br, 79%, 4
5
F, 57%,
I, 70%, 6
, 20
25
78%,
7
H, 64%,
Me, 59%, 8
Cl
N
Cl
N
N
9
tBu, 53%,
CN, 74%, 10
R
11
NO2, 76%,
CF3, 78%, 12
CO2Et, 69%, 13
N
21
R = Cl, 72%,
Br, 69%, 22
23
14
COMe, 72%,
SO2Me, 61%, 15
MeO2C
26
74%,
NO2, 68%,
Me
aReaction conditions: 1a (0.3 mmol),
2 (0.2 mmol), and Cu(OAc)2 (0.2 mmol)
were stirred in 1.0 mL MeCN at room temperature for 5 min under N2. bIsolated
yield.
good yields (Table 1,
3
‐
15). It should be mentioned that the
remained intact, offering new
substituted
N‐arylpyrazoles (Scheme 1b). This procedure can
halogens in ‐arylpyrazoles 3‐6
N
be conducted at room temperature with high efficiency,
excellent regioselectivity and broad substrate scope.
possibilities for cross‐coupling‐type manipulations. Similar
yields could be achieved with ortho‐ and meta‐substituted
aryldiazonium salts, indicating that this transformation is not
We began our investigations with the use of 1‐
phenylcyclopropanol 1a and aryldiazonium tetrafluoroborate
2a as model substrates to optimize the reaction conditions and
these results are summarized in Table S1 (see the Supporting
Information). Encouragingly, treating 1‐phenylcyclopropanol
1a with aryldiazonium tetrafluoroborate 2a in the presence of
20 mol% Cu(OAc)2 in MeCN at room temperature under N2
sensitive to steric effect (Table 1, 16
aryldiazonium salts were also compatible to generate the
desired ‐arylpyrazole derivatives in yields ranging from 71%
to 78% (Table 1, 24 26). Unfortunately, diazonium salts
‐23). Disubstituted
N
‐
possessing other aromatic motifs such as 3‐thienyl and 3‐
pyridinyl were not suitable substrates for the reaction.
gave the expected
N‐arylpyrazole 3 in 18% yield (Table S1,
Next, the substrate scope with respect to cyclopropanol was
also tested, and the results were summarized in Table 2.
Phenylcyclopropanols with different substituents on the
entry 1). The yield of the desired product was dramatically
improved (82%) when increasing the loading of Cu(OAc)2 to 1.0
equiv (Table S1, entry 4). Extensive solvent screening revealed
that MeCN was important since reactions conducted in other
solvents, such as DMSO, DMF, toluene, DCE, and 1,4‐dioxane,
generated the desired product in less than 5% yield (Table S1,
entries 6‐10). Among various copper salts tested, Cu(OAc)2
gave the highest yield, whereas the others were far less
effective (Table S1, entries 11‐17), indicating the counter ions
of copper salts have a remarkable impact on the reaction yield.
Subsequently, various other metal salts were also examined,
and it was observed that only the acetate‐type metal salts such
as Fe(OAc)2, Mn(OAc)2, and Mn(OAc)3 could efficiently
promote the reaction to deliver the desired product in
moderate yields (Table S1, entries 18‐26).
phenyl rings, such as
p
‐Me,
‐Me, and ‐Br reacted smoothly with 2a to give
‐arylpyrazoles in moderate to good yields. A
p‐OMe, p‐F, p‐Cl, p‐Br, p‐CO2Me,
m
‐Me,
m‐Cl,
o
o
the desired
N
slightly decreased yield was observed for cyclopropanol with a
strong electron‐withdrawing CF3 group (Table 2, 32). Alkyl
substituted cyclopropanols were also viable for this reaction,
generating the corresponding products 38‐42 in 71% to 85%
yields. Functional groups such as alkyl bromide, alkene, aryl
ether and alkylsulfonamide were all well tolerated (Table 2,
43‐46). In addition, thiophene‐ and benzothiophene‐
containing cyclopropanols were also compatible to deliver the
expected N‐arylpyrazoles in 66% and 63% yields, respectively.
It is worth mentioning that when 1,2‐disubstituted
cyclopropanols were employed, the desired 1,3,5‐
With the optimized reaction conditions in hand, we set out
to investigate the scope and generality of the reaction
between various aryldiazonium tetrafluorobrorates and 1‐
phenylcyclopropanol 1a. As shown in Table 1, aryldiazonium
salts bearing either electron‐withdrawing groups or electron‐
donating groups at the para‐position of the benzene rings
trisubstituted pyrazoles 49‐52 could be obtained in better
yields than those of 1‐substituted cyclopropanols, which could
be attributed to the formation of thermodynamically more
stable secondary alkyl radical via the oxidative radical ring‐
opening
of
1,2‐disubstituted
cyclopropanols.
The
produced the corresponding N‐arylpyrazoles in moderate to
regioselectivity of the coupling was further confirmed by
2 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 4
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
Table 2 Substrate scope with cyclopropanolsa,b
View Article Online
DOI: 10.1039/C9CC09657D
Scheme 2 Control experiments.
β‐keto alkyl radical in this reaction, 1,4‐benzoquinone (3 equiv)
was subjected to the reaction and the expected coupling
product 54 was observed (Scheme 2, eq 2). This result
supports the generation of the β‐keto alkyl radical during the
reaction.
Based on the above control experiments and literature
precedents,13,15 a plausible mechanism for copper‐mediated
tandem ring‐opening/cyclization of cyclopropanols with
aryldiazonium salts is proposed in Scheme 3. Initially, the
coordination of the hydroxyl group of cyclopropanol 1a to
Cu(OAc)2 leads to the formation of a Lewis base‐acid complex
A, which undergoes an inner‐sphere electron‐transfer to
produce cyclopropoxy radical
B with the elimination of CuOAc
and AcOH.15a Subsequently, the oxygen‐centered radical
undergoes ring‐opening to generate a β‐keto alkyl radical
B
C.
The in situ generated β‐keto alkyl radical
C can be readily
trapped by aryldiazonium salt 2a to afford a radical cation
D 15b,c
Next, the radical cation D is reduced to intermediate E
.
via single‐electron transfer,12j,15d,16 which is followed by a
formal 1,3‐hydrogen atom transfer (1,3‐HAT) process to give a
phenylhydrazone
of the amino group on the ketone in intermediate
by elimination of water from intermediate yields the desired
‐arylpyrazole
In conclusion, we have developed a general method for the
synthesis of various ‐arylpyrazoles from readily available
F. Finally, intarmoleculer nucleophilic attack
F
followed
G
N
3.
N
cyclopropanols and aryldiazonium salts through a copper‐
mediated tandem ring‐opening/cyclization reaction. This
procedure can be conducted at room temperature with high
efficiency, excellent regioselectivity and broad substrate scope
with respect to cyclopropanol and the aryldiazonium salt
substrate. Due to the importance of this structural motif as
aReaction conditions:
1 (0.3 mmol), 2a (0.2 mmol), and Cu(OAc)2 (0.2 mmol)
were stirred in 1.0 mL MeCN at room temperature for 5 min under N2. bIsolated
OAc
OH
H
Cu
O
yield.
O
Cu(OAc)2
O
OAc
Ph
Ph
Ph
single‐crystal X‐ray analysis of 49. Finally, cyclopropanol
derived from an anti‐inflammatory drug ibuprofen participated
smoothly in this transformation to provide the desired product
53 in synthetically useful yield.
Ph
CuOAc
AcOH
1a
B
C
A
Cl
N
OH
Ph
N
N
N
N
-H2O
To gain more insights into the reaction mechanism, several
control experiments were conducted. First, the reaction of 1a
with 2a in the presence of 3.0 equiv of 2,2,6,6‐tetramethyl‐1‐
piperidinyloxy (TEMPO) or 2,6‐di‐tert‐butyl‐4‐methylphenol
(BHT), afforded only a trace amount of the desired product 3,
thus indicating that a radical pathway might be involved in this
transformation (Scheme 2, eq 1). To trap the possible formed
N
BF4
3
Cl
2a
Cl
G
Cl
1,3-HAT
Cl
Cl
Cu2+ Cu
Ph
O
Ph
O
Ph
O
N
N
HN
N
N
SET
N
F
E
D
Scheme3 Plausible mechanism.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Journal Name
) G.
Valdés, Angew. Chem., Int. Ed., 2013, 52, 7219‐7223; (
Zhang, H. Ni, W. Chen, J. Shao, H. Liu,DBO. IC: h10e.n10a3Vn9i/edCw9YAC.rtCYicu0le9,O6On5rl7ingDe.
Lett., 2013, 15, 5967‐5969; ( ) F.‐G. Zhang, Y. Wei, Y.‐P. Yi, J.
Nie and J.‐A. Ma, Org. Lett., 2014, 16, 3122‐3125; ( ) Z. Chen,
Y. Zheng and J.‐A. Ma, Angew. Chem., Int. Ed., 2017, 56
4569‐4574; ( ) Y. Shao, H. Zheng, J. Qian and X. Wan, Org.
Lett., 2018, 20, 2412‐2415; ( ) W. Wu, M. Li, J. Zheng, W. Hu,
C. Li and H. Jiang, Chem. Commun., 2018, 54, 6855‐6858; ( ) X.
Peng, X. Zhang, S. Li, Y. Lu, L. Lan and C. Yang, Org. Chem.
Front., 2019, , 1775‐1779.
) J. C. Antilla, J. M. Baskin, T. E. Barder and S. L. Buchwald, J.
e
well as the easy availability of starting materials and the
simplicity of the reaction conditions, we expect the protocol
will find broad applications in synthetic and medicinal
chemistry.
f
g
,
h
i
j
Acknowledgment
We thank the National Natural Science Foundation of China
(Grant Nos. 21875048 and 21576056), Guangdong Natural
Science Foundation (Grant No. 2017A030310620), and the
Science and Technology Research Project of Guangzhou (Grant
No. 201707010483) for financial support.
6
9
(a
Org. Chem., 2004, 69, 5578‐5587; (
A. Ouali, F. Ouazzani and M. Taillefer, Angew. Chem., Int. Ed.
2009, 48, 333‐336; (
Org. Chem., 2019, 84, 6508‐6515.
b
) H. Kaddouri, V. Vicente,
,
c
) S. Onodera, T. Kochi and F. Kakiuchi, J.
10 (
a
) X. Li, L. He, H. Chen, W. Wu and H. Jiang, J. Org. Chem.,
2013, 78, 3636‐3646; (b) X. Tang, L. Huang, J. Yang, Y. Xu, W.
Conflicts of interest
There are no conflicts to declare.
Wu and H. Jiang, Chem. Commun., 2014, 50, 14793‐14796; (
D. Li, X. Mao, H. Chen, G. Chen and P. Liu, Org. Lett., 2014, 16
3476‐3479; (
Org. Lett., 2014, 16, 3110‐3113; (
and F. Glorius, Angew. Chem., Int. Ed., 2010, 49, 7790‐7794.
11 For selected reviews, see: ( ) O. G. Kulinkovich, Chem. Rev.
2003, 103, 2597‐2632; ( ) A. Nikolaev and A. Orellana,
Synthesis, 2016, 48, 1741‐1768; ( ) X. Cai, W. Liang and M.
c
)
,
d
) H. Guo, D. Zhang, C. Zhu, J. Li, G. Xu and J. Sun,
) J. J. Neumann, M. Suri
e
a
,
Notes and references
b
1
(
a
) G. Szabó, J. Fischer, Á. Kis‐Varga and K. Gyires, J. Med.
c
Chem., 2008, 51, 142‐147; ( ) J. B. Thomas, A. M. Giddings, R.
b
Dai, Tetrahedron, 2019, 75, 193‐208; (
Chem. Commun., 2019, 55, 9747‐9756.
d) X. Wu and C. Zhu,
W. Wiethe, S. Olepu, K. R. Warner, P. Sarret, L. Gendron, J.‐M.
Longpre, Y. Zhang, S. P. Runyon and B. P. Gilmour, J. Med.
Chem., 2014, 57, 5318‐5332; (c) J. V. Faria, P. F. Vegi, A. G. C.
12 For selected examples, see: (
Funahashi, K. Isobe and K. Narasaka, Bull. Chem. Soc. Jpn.
1993, 66, 819‐827; ( ) S. Chiba, Z. Cao, S. A. A. E. Bialy and K.
Narasaka, Chem. Lett., 2006, 35, 18‐19; ( ) A. Ilangovan, S.
Saravanakumar and S. Malayappasamy, Org. Lett., 2013, 15
4968‐4971; ( ) D. G. Kananovich, Y. A. Konik, D. M. Zubrytski,
I. Järving and M. Lopp, Chem. Commun., 2015, 51, 8349‐8352;
) H. Zhao, X. Fan, J. Yu and C. Zhu, J. Am. Chem. Soc., 2015,
137, 3490‐3493; ( ) S. Wang, L.‐N. Guo, H. Wang and X.‐H.
Duan, Org. Lett., 2015, 17, 4798‐4801; ( ) X. Fan, H. Zhao, J.
Yu, X. Bao and C. Zhu, Org. Chem. Front., 2016, , 227‐232; (
K. Jia, F. Zhang, H. Huang and Y. Chen, J. Am. Chem. Soc.
2016, 138, 1514‐1517; ( ) Z. Ye, X. Cai, J. Li and M. Dai, ACS
Catal., 2018, , 5907‐5914; ( ) Q. Tan, Z. Yang, D. Jiang, Y.
a) N. Iwasawa, S. Hayakawa, M.
,
Miguita, M. S. dos Santos, N. Boechat and A. M. R.
Bernardino, Bioorg. Med. Chem., 2017, 25, 5891‐5903.
Ş. G. Küçükgüzel and S. Şenkardeş, Eur. J. Med. Chem., 2015,
97, 786‐815.
b
c
2
3
,
d
(a) R. A. Singer, S. Caron, R. E. McDermott, P. Arpin and N. M.
Do, Synthesis, 2003, 1727‐1731; (b) R. A. Singer, M. Doré, J. E.
(
e
Sieser and M. A. Berliner, Tetrahedron Lett., 2006, 47, 3727‐
f
3731.
g
4
5
A. Schmidt and A. Dreger, Curr. Org. Chem., 2011, 15, 2897‐
3
h)
,
2970.
(a) T. Asaumi, N. Chatani, T. Matsuo, F. Kakiuchi and S. Murai,
i
J. Org. Chem., 2003, 68, 7538‐7540; (
T. Satoh and M. Miura, J. Org. Chem., 2009, 74, 7094‐7099; (
V. S. Thirunavukkarasu, K. Raghuvanshi and L. Ackermann,
Org. Lett., 2013, 15, 3286‐3289; ( ) S.‐S. Zhang, C.‐Y. Jiang, J.‐
Q. Wu, X.‐G. Liu, Q. Li, Z.‐S. Huang, D. Li and H. Wang, Chem.
Commun., 2015, 51, 10240‐10243; ( ) T.‐J. Gong, M.‐Y. Xu,
b) N. Umeda, K. Hirano,
8
j
c
)
Cheng, J. Yang, S. Xi and M. Zhang, Angew. Chem., Int. Ed.
,
2019, 58, 6420‐6424.
d
13 (
12570‐12572; (
Chiba, J. Am. Chem. Soc., 2011, 133, 6411‐6421.
14 ( ) J. Sheng, J. Liu, L. Chen, L. Zhang, L. Zheng and X. Wei, Org.
Chem. Front., 2019, , 1471‐1475; ( ) J. Liu, J. Zou, J. Yao and
G. Chen, Adv. Synth. Catal., 2018, 360, 659‐663; ( ) J. Sheng,
J. Liu, H. Zhao, L. Zheng and X. Wei, Org. Biomol. Chem., 2018,
16, 5570‐5574; ( ) J. Liu, Z. Xue, Z. Zeng, Y. Chen and G. Chen,
Adv. Synth. Catal., 2016, 358, 3694‐3699.
15 ( ) E. Hasegawa, M. Tateyama, R. Nagumo, E. Tayama and H.
Iwamoto, Beilstein J. Org. Chem., 2013, , 1397‐1406; ( ) M.
R. Heinrich, O. Blank and S. Wölfel, Org. Lett., 2006, , 3323‐
3325; ( ) F. Liu, J.‐Y. Wang, P. Zhou, G. Li, W.‐J. Hao, S.‐J. Tu
and B. Jiang, Angew. Chem., Int. Ed., 2017, 56, 15570‐15574;
a) Y.‐F. Wang and S. Chiba, J. Am. Chem. Soc., 2009, 131
,
b
) Y.‐F. Wang, K. K. Toh, E. P. J. Ng and S.
e
S.‐H. Yu, C.‐G. Yu, W. Su, X. Lu, B. Xiao and Y. Fu, Org. Lett.,
2018, 20, 570‐573.
S. Fustero, M. Sánchez‐Roselló, P. Barrio and A. Simón‐
Fuentes, Chem. Rev., 2011, 111, 6984‐7034.
For selected examples, see: (
A. D. Gibb and D. J. Kennedy, Synthesis, 2004, 43‐52; (
Peruncheralathan, T. A. Khan, H. Ila and H. Junjappa, J. Org.
Chem., 2005, 70, 10030‐10035; ( ) S. T. Heller and S. R.
Natarajan, Org. Lett., 2006, , 2675‐2678; ( B. S.
Gerstenberger, M. R. Rauckhorst and J. T. Starr, Org. Lett.,
2009, 11, 2097‐2100; ( ) A. DeAngelis, D.‐H. Wang and S. L.
Buchwald, Angew. Chem., Int. Ed., 2013, 52, 3434‐3437; (
Tu, Z. Zhang, T. Wang, J. Ke and J. Zhao, Org. Lett., 2017, 19
a
6
b
6
7
c
a
) B. C. Bishop, K. M. J. Brands,
d
b
) S.
a
c
9
b
8
d)
8
c
e
f
) Y.
(d) S. E. Schaafsma, R. Jorritsma, H. Steinberg and T. J. de
,
Boer, Tetrahedron Lett., 1973, 14, 827‐830.
3466‐3469; (
g
) R. S. Thombal and Y. R. Lee, Org. Lett., 2018,
16 The need for a stoichiometric amount of Cu(OAc)2 in our
reaction suggests that the Cu(II) which was re‐generated
20, 4681‐4685.
8
For selected recent reviews, see: (
Namboothiri, Chem. Rec., 2017, 17, 939‐955; (b) Y. Xia and J.
a
) T. V. Baiju and I. N. N.
from Cu(I) and intermediate
D may not react again from A to
B
.
Wang, Chem. Soc. Rev., 2017, 46, 2306‐2362; For selected
examples, see: ( ) X. Qi and J. M. Ready, Angew. Chem., Int.
Ed., 2007, 46, 3242‐3244; ( ) M. C. Pérez‐Aguilar and C.
c
d
4 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins