LCopper-catalyzed diarylation of activated alkenes with diaryliodonium salts

Article abstract of DOI:10.1055/s-0033-1339004

Cu(OTf)₂-catalyzed diarylation of activated alkenes by using diaryliodonium(III) salts has been developed. With this method, arylated oxindoles can be easily accessed in good yields. Insights into the mechanism of copper-catalyzed arylations are discussed, and the findings are expected to help increase the level of understanding of catalytic arylations with diaryliodonium salts. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0033-1339004

LETTER
▌1419
lCettoerpper-Catalyzed Diarylation of Activated Alkenes with Diaryliodonium
Salts
Diarylation of Activated Alkenes
Yang Yang,a Jianwei Han,*b Xunshen Wu,a Song Mao,a Jianjun Yu,a Limin Wang*a
a
Key Laboratory of Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road,
Shanghai 200237, P. R. of China
Fax +86(21)64253881; E-mail: wanglimin@ecust.edu.cn
b
Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, The Chinese Academy of Sciences,
345 Ling Ling Road, Shanghai, 200032, P. R. of China
Fax +86(21)54925583; E-mail: jianweihan@sioc.ac.cn
Received: 24.02.2014; Accepted after revision: 07.04.2014
alkenes described by Zhu and co-workers in 2010.9 How-
ever, reports on the direct arylation of alkenes for the syn-
thesis of arylated oxindoles are scarce.10 As outlined in
Scheme 1, the use of metal catalysts in combination with
Abstract: Cu(OTf)2-catalyzed diarylation of activated alkenes by
using diaryliodonium(III) salts has been developed. With this meth-
od, arylated oxindoles can be easily accessed in good yields. In-
sights into the mechanism of copper-catalyzed arylations are
discussed, and the findings are expected to help increase the level of diaryliodonium salts can catalytically generate electro-
understanding of catalytic arylations with diaryliodonium salts.
philic arylating species [Scheme 1, Eq. (1)], and the re-
sulting aromatic electrophiles can be used to arylate a
range of nucleophiles in an efficient way; for example, in
the arylation of polyfluoroarenes reported by us recent-
ly.11 We therefore envisioned that initial arylation of al-
kenes with arylating species would result in an activated
electrophilic intermediate that could conduct a second ar-
ylation through a C–H functionalization cascade process
[Scheme 1, Eq. (2)].
Key words: alkene activation, arylation, diaryliodonium salts, ox-
indoles, copper triflate
Direct arylation, which allows efficient incorporation of
arenes into functional molecules, has been one of the most
important synthetic methodologies to have been devel-
oped in modern organic chemistry. In particular, arylation
of alkenes such as the well-known Mizoroki–Heck reac-
tions,1 Meerwein coupling reactions,2 and conjugate addi-
tions of activated alkenes with aryl boronic acid or
organometallic reagents,3 have been widely investigated.
Among the available approaches, the use of diaryliodoni-
um salts (Ar2I+X–) as electrophilic arylating agents has re-
cently been developed for use in aryl-transfer reactions
with olefins. In this context, several groups have made
major contributions in the field of alkene arylation for
Heck-type coupling reactions by using hypervalent io-
dine(III) reagents in a straightforward way.4 Very recent-
ly, Gaunt et al. also developed an electrophilic
carbofunctionalization of allylic amides with diaryliodo-
nium salts for the preparation of oxazines under copper
catalysis.5
(1)
(III)
L
Cu(II)
X
I
Ph
Ph Cu
/
Ph
L
phenyl Intermediate
(2)
Ph
Ph
Me
H
Me
H
N
/
/
Ph
N
O
Me
O
Me
N
O
Me
nd arylation
Me
1st arylation
2
Scheme 1 Copper-catalyzed diarylation with diaryliodonium salts
Oxidative difunctionalization of activated alkenes for rap-
id access to oxindoles has also received much attention
because of the potential application of the products of
such reactions in pharmaceutical research.6 A wide range
of function groups including trifluoromethyl (CF3), azide
(N3), halogen (Br and I), diphenylphosphine oxide
[Ph2P(O)], carbonyl [RC(O)], nitro (NO2), substituted
alkane, trifluoromethylthio (CF3S), sulfonyl (Ts) and
oxaspirocycles have been introduced into oxindole frame-
works through the application of a difunctionalization
strategy7,8 since the elegant report of arylacetoxylation of
Herein, we present our primary results on the copper-cat-
alyzed diarylation of activated alkenes by using diaryli-
odonium(III) salts to mediate the simultaneous formation
of two carbon–carbon bonds.
Our investigation began with an examination of the reac-
tion of N-arylacrylamide 1a with diphenyliodonium tetra-
fluoroborate in the presence of various copper catalysts in
dichloroethane (DCE) at 130 °C. It was found that both
copper(I) and copper(II) salts could catalyze this reaction,
and that the use of 10 mol% Cu(OTf)2 gave the desired
product 3a in 82% yield; the use of CuCl, CuI, Cu(OAc)2
or copper thiopenecarboxylate (CuTC) resulted in de-
creased yields (Table 1, entries 1–5). An evaluation of the
effect of counter-anions of the diphenyliodonium salts
SYNLETT 2014, 25, 1419–1424
Advanced online publication: 19.05.2014
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1339004; Art ID: st-2014-w0159-l
© Georg Thieme Verlag Stuttgart · New York

1420
Y. Yang et al.
LETTER
Table 1 Optimization of Reaction Conditionsa
substrates with N-protecting groups n-butyl, benzyl and a
long chain (C12H25) afforded 3k–m in good yields of 65–
74%. Substituted olefin 1n, bearing a phenyl group, was
also converted into the desired product in 48% yield. Tri-
cyclic arylated oxindole 3o was prepared in 73% yield
from the corresponding acrylamide under the developed
conditions. The use of meta-substituted acrylamide 1p
provided a mixture of products in 66% yield with a regi-
oselectivity of 1:1.8.
Me
Me
Ph
Cu(OTf)2 (10 mol%)
solvent, 130 °C,16 h
X
+
I
O
Ph
Ph
N
O
N
Me
Me
3a
1a
2
Entry
X
Catalyst
Solvent
Yield (%)b
1
2
BF4
BF4
BF4
BF4
BF4
OTs
OTf
BF4
BF4
BF4
BF4
BF4
PhI
CuI
DCE
71
Subsequently, we examined the structural diversity of the
various diaryliodonium salts 2 as arylating partners (Table
2). Notably, regardless of the electronic nature of the sub-
stituents, a wide variety of functionalities were tolerated
in the diarylation of N-arylacrylamide. Some diaryliodo-
nium triflates were also applied in this protocol because of
their availability in the laboratory and, as expected, the
desired products were obtained in good yields (entries 3–
5). Steric factors severely affected the reactivity, and al-
most no reaction took place with bis(2,4,6-trimethylphe-
nyl)iodonium triflate (2f) as arylating reagent.
Unsymmetrical aryl-mesityl iodonium reagents were also
employed in the diarylation of 1a, and we were delighted
to find that salts with either electron-rich or -deficient
groups worked well; moreover, a broad range of ortho-,
meta-, and para-substituted aryl rings could be readily
transferred to give the desired products (entries 7–15). It
is worth mentioning that the unsymmetrical salt [(4-
MeOC6H4)(Ph)I]BF4 selectively transferred the Ar group
to give the desired products 3a/4e in a yield of 75% with
a ratio of 2.5:1 (entry 16). When [(2-thienyl)(Ph)I]OTf
was employed under the standard conditions, 3a was
formed exclusively; disappointingly, the heteroatomic
ring was not transferred to give the desired product (entry
17).
CuCl
DCE
70
3
Cu(OAc)2
Cu(OTf)2
CuTCc
DCE
48
4
DCE
82
5
DCE
50
6
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
DCE
trace
72
7
DCE
8
MeCN
DMF
EtOH
toluene
dioxane
DCE
trace
trace
trace
52
9
10
11
12
13d
62
0
a Reaction conditions: 1a (0.5 mmol), 2 (1 mmol), cat. (0.05 mmol),
solvent (2 mL), 130 °C, 16 h.
b Isolated yield.
c Copper thiopenecarboxylate.
d Iodobenzene in place of diphenyliodonium salt.
showed that [Ph2I]OTf give 3a in 72% yield, but We then analyzed in more detail the impurities formed in
[Ph2I]OTs gave no product. In the case of [Ph2I]OTs, a this reaction and found that, in several cases, trace
large amount of phenyl para-toluenesulfonate (PhOTs) amounts of the undesired diarylated product were ob-
was isolated as a byproduct, which was presumably pro- served by LC–MS spectrometry experiments. During the
duced from decomposition of iodonium salts. The influ- synthesis of 3j, although none of the desired product was
ence of solvent on the reaction was also examined. The formed, arylated and diarylated products were obtained in
results showed that DCE was the best choice and that only 21 and 39% yield, respectively [Scheme 3, Eq. (1)]. The
a trace amount of the desired product was observed in po- by-products were finally identified as 5 and a double ary-
lar solvents such as MeCN, DMF, or ethanol (Table 1, en- lated product 6, which is consistent with the meta-selec-
tries 8–10). Notably, when iodobenzene was used in place tivity observed in the copper-catalyzed C–H bond
of diphenyliodonium salts, no product at all was obtained. arylation by Gaunt et al.12a Moreover, when olefin 7 was
subjected to the reaction conditions [Scheme 3, Eq. (2)],
With the optimized reaction conditions in hand, we inves-
tigated the scope of the reaction with a range of substrates
1 with diphenyliodonium tetrafluoroborate 2a. As shown
in Scheme 2, substrates with various substituents on the
para-arylation of the aromatic ring of 7 was found, but no
cyclized product was observed.12b It was clear that the re-
action site on the aromatic ring or on the olefin (Scheme
3, A, B, or C) was determined by the directing groups
ortho-, meta-, and para-positions of arylacrylamides re-
(amide or ester) on the substrates; as a result, the product
acted well, and the desired products 3b–i were obtained in
yields of 51–83%. However, no desired product was
outcomes differ significantly using this procedure.
found in the case of N-free arylacrylamides. Nevertheless,
Synlett 2014, 25, 1419–1424
© Georg Thieme Verlag Stuttgart · New York

LETTER
Diarylation of Activated Alkenes
1421
R3
R3
Ph
Cu(OTf)2 (10 mol%)
DCE, 130 °C,16 h
BF4
Ph
R1
R1
+
O
I
N
Ph
N
O
R2
R2
1
2a
3
Me
Me
Me
Me
Ph
O
Ph
O
Ph
Br
Ph
O
F
Me
MeO
O
N
N
N
N
Me
3e: 72%
Me
Me
Me
3b: 79%
3c: 83%
3d: 68%
Me
Me
Me
CF3
Ph
O
Ph
Ph
O
Cl
Ph
O
O
N
N
N
N
F3C
Me
Me
Me
3f: 70%
Cl
Me
3i: 51%
3g: 60%
3h: 68%
Me
Me
Ph
Me
Me
Ph
Ph
O
Ph
O
O
O
N
N
N
N
Bn
H
n-Bu
C12H25
3m: 74%
3j: 0%
3k: 72%
3l: 65%
Cl
Me
Me
Me
Ph
Ph
O
Ph
Ph
Ph
O
O
O
N
N
N
Cl
N
Me
Me
Me
3n: 48%
3o: 73%
3p
3p'
3p/3p' (1:1.8), 66%
Scheme 2 Scope of the reaction with N-arylacrylamides. Reagents and conditions: 1 (0.5 mmol), 2a (1 mmol), Cu(OTf)2 (0.05 mmol), and
DCE (2 mL), 130 °C, 16 h; Isolated yields are given.
Table 2 Scope of Reaction with Diaryliodonium Saltsa
Me
Ar2
Me
X
Cu(OTf)2 (10 mol%)
DCE, 130 °C,16 h
I
+
O
Ar1
Ar2
N
O
N
Me
1a
Me
4
2
Entry
2
X
Ar1
Ar2
Product
Yield (%)b
1
2
3
4
5
6
7
8
2a′
2b
2c
BF4
BF4
OTf
OTf
OTf
OTf
BF4
BF4
2-MeC6H4
2-MeC6H4
4-ClC6H4
4-FC6H4
4-tBuC6H4
4-MeOC6H4
mesityl
4a
4b
4c
4d
4e
4f
56
70
55
57
60
–
4-ClC6H4
4-FC6H4
4-tBuC6H4
4-MeOC6H4
mesityl
2d
2e
2f
2a′′
2p
mesityl
Ph
3a
4a
75
49
mesityl
2-MeC6H4
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1419–1424

1422
Y. Yang et al.
LETTER
Table 2 Scope of Reaction with Diaryliodonium Saltsa (continued)
Me
Ar2
Me
X
Cu(OTf)2 (10 mol%)
I
+
O
Ar1
Ar2
DCE, 130 °C,16 h
N
O
N
Me
Me
4
1a
2
Entry
2
X
Ar1
Ar2
Product
Yield (%)b
9
10
11
12
13
14
15
16
17
2g
2h
2i
BF4
BF4
OTf
OTf
OTf
OTf
OTf
BF4
OTf
mesityl
4-MeC6H4
4-EtO2C-C6H4
3-MeC6H4
2-BrC6H4
4-BrC6H4
3-FC6H4
2-ClC6H4
Ph
4g
59
mesityl
4h
4i
67
mesityl
61
2j
mesityl
4j
40
2k
2l
mesityl
4k
4l
58
mesityl
56
2m
2n
2o
mesityl
4m
3a/4e
3a
48
4-MeOC6H4
2-Thienyl
54/21
53
Ph
a Reaction conditions: 1a (0.5 mmol), 2 (1 mmol), Cu(OTf)2 (0.05 mmol), DCE (2 mL), 130 °C, 16 h.
b Isolated yield.
We next sought to investigate the mechanism of this reac- Gaunt and Macmillan have pioneered the development of
tion. On the basis of previous reports,7 the possible pres- enantioselective arylations by employing Cu-PhBox cata-
ence of radical intermediates4d in the oxidative lyst 9.13 Thus, an asymmetric version of the diarylation of
difunctionalization of N-arylacrylamides was examined. 1a was also attempted by using the same chiral catalyst 9;
A control experiment to establish the involvement of rad- however, only 3% ee of 3a was obtained in 50% yield at
ical species in the reaction was carried out with the inclu- a temperature of 60 °C [Scheme 4, Eq. (2)]. Although it is
sion of the radical inhibitor 2,2,6,6-tetramethylpiperidine- premature to draw precise conclusions on the existence of
1-oxyl (TEMPO; 3 equiv) in the reaction of 1a and 2a un- radicals or carbocations in the reaction at this stage, the
der the same reaction conditions; in this case only 7% above results together with control experiments imply a
yield of the desired product 3a was obtained [Scheme 4, possible radical mechanism in the diarylation of activated
Eq. (1)].
alkenes 1.
/
Ph
/
Ph
Me
Me
N
H
O
N
Me
Me
O
O
O
/
Ph
/
Ph
B
C
A
Ph
Me
Cu(OTf)2 (10 mol%)
Ph2IBF4 (2 equiv)
Me
Me
+
(1)
DCE, 130 °C, 16 h
Ph
N
H
O
N
H
O
Ph
N
O
H
1j
5; 21% yield
6; 39% yield
Cu(OTf)2 (10 mol%)
Ph2IBF4 (2 equiv)
Me
Ph
Me
Me
(2)
+
Ph2
DCE, 130 °C, 16 h
O
O
O
O
O
O
7
8; 54% yield
small amounts
Scheme 3 The site reactivity of the copper-catalyzed arylation
Synlett 2014, 25, 1419–1424
© Georg Thieme Verlag Stuttgart · New York

LETTER
Diarylation of Activated Alkenes
1423
Me
Cu(OTf)2 (10 mol%)
Ph2IBF4 (2 equiv)
TEMPO (3 equiv)
(1)
Me
N
Ph
O
Me
N
DCE, 130 °C, 16 h
O
Me
1a
3a; 7% yield
Me
N
Me
N
Me
(2)
cat. 9 (10 mol%)
Ph2IBF4 (2 equiv)
Me
N
Ph
O
O
O
Me
DCE, 60 °C, 16 h
N
Cu
O
Ph
Ph
Me
3a, 50% yield, 3% ee
OTf
1a
9
Scheme 4 Control experiment and an asymmetric version of the diarylation of 1a
Chem. Commun. 2014, 50, 936. (e) Lu, Q.; Liu, C.; Peng, P.;
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In summary, the copper-catalyzed diarylation of activated
alkenes by using diaryliodonium(III) salts has been devel-
oped.14 Arylated oxindoles were synthesized in yields of
40–83%. A broad applicability of this method for the con-
struction of relevant chemical entities is anticipated, and
further studies on the reaction mechanism and asymmetric
catalysis in this reaction are ongoing in our laboratory.
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Acknowledgment
This work was supported by the National Nature Science Foundati-
on of China (NSFC, 21272069, 21202186) and the Fundamental
Research Funds for the Central Universities, Key Laboratory of Or-
ganofluorine Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000083.SunpfgIpi
m
o
nr
i
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© Georg Thieme Verlag Stuttgart · New York
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LETTER
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(13) (a) Bigot, A.; Williamson, A. E.; Gaunt, M. J. J. Am. Chem.
Soc. 2011, 133, 13778. (b) Harvey, J. S.; Simonovich, S. P.;
Jamison, C. R. D.; MacMillan, W. C. J. Am. Chem. Soc.
2011, 133, 13782.
(14) Cascade Reaction of N-Arylacrylamide with
Diaryliodonium Salts; General Procedure: Cu(OTf)2
(0.05 mmol, 0.1 equiv), N-arylacrylamide (0.5 mmol, 1.0
equiv) and diphenyliodonium salt (1.0 mmol, 2.0 equiv)
were added to a dried Schlenk tube. The tube was degassed
with nitrogen three times, then DCE (2.0 mL) was added by
using a syringe. The mixture was heated and stirred at
130 °C for 16 h, then cooled to r.t. and the solvent was
evaporated in vacuum. The crude products were directly
purified by flash column chromatography on silica gel
(petroleum ether–EtOAc, 10:1) to afford the desired
oxindole.
Synlett 2014, 25, 1419–1424
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