Synthesis of arylethylene or diarylethylene compounds by Pd-catalyzed heck coupling reaction

Article abstract of DOI:10.1080/00397911.2012.741743

We have developed an effective palladium-catalyzed arylation or diarylation couplings of olefins with various aryl halides in the presence of readily available ligands. This method is simple, economical, and practical for the synthesis of arylethylene and diarylethylene. Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for full experimental and spectral details.

Full text of DOI:10.1080/00397911.2012.741743

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Synthesis of Arylethylene or
Diarylethylene Compounds by Pd-
Catalyzed Heck Coupling Reaction
Hong Yan a , Peng Sun a , Xiaoming Qu a , Linhua Lu a , Yan Zhu a ,
Hailong Yang a & Jincheng Mao a
a Key Laboratory of Organic Synthesis of Jiangsu Province, College
of Chemistry, Chemical Engineering and Materials Science, Soochow
University , Suzhou , China
Published online: 08 Jul 2013.
To cite this article: Hong Yan , Peng Sun , Xiaoming Qu , Linhua Lu , Yan Zhu , Hailong Yang &
Jincheng Mao (2013) Synthesis of Arylethylene or Diarylethylene Compounds by Pd-Catalyzed Heck
Coupling Reaction, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 43:20, 2773-2783, DOI: 10.1080/00397911.2012.741743
To link to this article: http://dx.doi.org/10.1080/00397911.2012.741743
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Synthetic Communications1, 43: 2773–2783, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.741743
SYNTHESIS OF ARYLETHYLENE OR DIARYLETHYLENE
COMPOUNDS BY Pd-CATALYZED HECK COUPLING
REACTION
Hong Yan, Peng Sun, Xiaoming Qu, Linhua Lu, Yan Zhu,
Hailong Yang, and Jincheng Mao
Key Laboratory of Organic Synthesis of Jiangsu Province, College of
Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou, China
GRAPHICAL ABSTRACT
Abstract We have developed an effective palladium-catalyzed arylation or diarylation
couplings of olefins with various aryl halides in the presence of readily available ligands.
This method is simple, economical, and practical for the synthesis of arylethylene and
diarylethylene.
Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for full experimental and spectral details.
Keywords Arylation; aryl halides; coupling reactions; Heck reaction; olefins
INTRODUCTION
The palladium-catalyzed arylation of alkenes using Heck-type transformations
has proven to be one of the most important methods for carbon–carbon bond for-
mation in organic chemistry. The reaction has been applied in the areas of natural
products and high-performance materials.[1–3] As we know, the 2010 Nobel Prize
in chemistry was awarded to Ei-ichi Negishi, Akira Suzuki, and Richard Heck for
developing new methods of linking carbon atoms together, which have allowed
scientists to make medicines and better electronics.[4] Among these basic types of
palladium-catalyzed transformations, the Heck reaction and related chemistry
occupy a special place for resourceful versatility.[5–7] In past decades, many efficient
catalytic systems have been developed for the Heck coupling reaction.[8] As usual,
Received August 27, 2012.
Address correspondence to Jincheng Mao, Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University,
Suzhou 215123, China. E-mail: jcmao@suda.edu.cn
2773

2774
H. YAN ET AL.
excessive amounts of olefins were employed for the coupling of aryl halides to
acquire good yields of the desired products. However, in view of the reaction cost,
there are few reports of Pd-catalyzed Heck reactions using equal amounts of aryl
halide and olefin until now. Compared with the traditional mono-Heck coupling
reaction, diarylation of olefins via the Heck reaction has scarcely been investi-
gated.[9–16] In addition, certain trisubstituted olefins have emerged that possess inter-
esting biological, chemical, and physical properties.[17–20] Gurtler and Buchwald
¨
synthesized trisubstituted olefins by coupling disubstituted alkenes with aryl
halides.[21] Therefore, it can be seen that the Heck coupling is one of the most impor-
tant and effective approaches for preparing substituted alkenes. In the long run, our
group is interested in cross-couplings using readily available catalysts.[22–28] Herein,
we show a general and efficient method for the synthesis of disubstituted alkenes
using readily available catalyst and preparing arylethylene using only the same
amounts of aryl halide and olefin by Heck coupling reaction.
RESULTS AND DISCUSSION
To find the most active catalyst system, we carried out the model reaction of
iodobenzene (1.0 mmol) with butyl acrylate (0.3 mmol) using Pd(OAc)2 (4 mol%)=
PPh3(A) (8 mol%) as catalyst and K2CO3 (1.0 mmol) as base. The diarylation
coupling product was obtained in 62% yield at 120 ꢀC after 24 h. In the initial
experiments, we investigated the influence of different ligands on the reaction
yield, including 1,2-bis(diphenylphosphino)ethane (B), N,N-dimethylglycine (C),
2,20-bipyridine (D), 1,10-phenanthroline (E), 1,4-diazabicyclo[2.2.2]octane (F),
N,N,N0,N0-tetramethylethylenediamine (G), and urotropine (H). For the purpose
of finding the most efficient catalyst system, several ligands have been investigated
in the reaction under the same conditions (Fig. 1). It can be seen that A afforded
the disubstituted alkenes predominantly, which is considered a general and useful
catalyst system in many coupling reactions. Subsequently, various bases were
screened for synthesis of diarylethylene by Pd-catalyzed Heck reaction. We found
t
that all the bases (except BuOK) gave good conversion, but the disubstituted
olefin product yields were different (Table 1, entries 1–9). We found that Cs2CO3
was the most efficient base. The use of other solvents such as dimethylsulfoxide
(DMSO), polyethylene glycol (PEG) 400, N-methylpyrrolidone (NMP), or DMAc
resulted in quite different yields (entries 10–13). Among them, dimethylformamide
(DMF) proved to be the best solvent, giving the desired product in 76% yield
(entry 2). It is noteworthy that the ratio of di- and mono-substituted products
was slightly greater when NMP was employed as solvent, whereas the conversion
was only 65% (entry 12). In the absence of A, the corresponding diarylation pro-
duct was not found, giving only 52% yield of arylethylene (entry 14). Then differ-
ent catalysts were employed in the coupling reaction (entries 15–19). Pd(OAc)2=A
as catalyst was the most efficient. To our disappointment, we did not get a better
yield of diarylethylene product when the reaction temperature was raised to 130 ꢀC
(entry 20). Increasing the amount of iodobenzene did not give a better result
(entries 21 and 22).

SYNTHESIS OF ARYLETHYLENE OR DIARYLETHYLENE
2775
Figure 1. Screening various ligands for the double-Heck coupling reaction.
With these optimized reaction conditions in hand, we then explored the gener-
ality of this reaction. The results are summarized in Table 2. In the presence of
Pd(OAc)2 (4 mol%), A (8 mol%), and Cs2CO3 (2 equiv), most of the processes gener-
ated the corresponding diarylethylene in moderate to good yields (Table 2, entries
1–10). Couplings of 4-iodoanisole with different acrylates gave good yields (entries
2–5 and 8). However, when using 3-iodoanisole or 2-iodoanisole as the substrates,
reduced yields of desired product were obtained (entries 6 and 7). It is worthwhile
to mention that diarylation with the 2-iodoanisole exclusively provided the mono-
arylated product in an excellent yield of 99% (entry 7). We next aimed to investigate
the cross couplings between aryl iodides with electron-withdrawing or
electron-donating groups and butyl acrylate, respectively. The desired products were
achieved in moderate to good yields (entries 8–11).

2776
H. YAN ET AL.
Table 1. Screening catalytic conditions for synthesis of diarylethylene by Pd-catalyzed Heck reactiona
Entry
Pd cat.=ligand
Base
Conv. (%)b
Di–monob
Yield (%)c
1
2
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2
K2CO3
Cs2CO3
KOH
99
99
61:39
76:24
43:57
46:54
43:57
—
62
76
43
46
42
—
15
20
—
15
—
52
63
—
69
71
—
35
—
62
68
69
3
99
99
4
NEt3
5
K3PO4
tBuOK
LiOAc
NaOAc
Na2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
98
6
Trace
97
99
7
15:85
20:80
0 :100
43:57
—
8
9
99
35
10d
11e
12f
13g
14
15
16
17
18
19
20h
21i
22j
Trace
65
92
80:20
68:32
0:100
69:31
71:29
0:100
38:62
0:100
62:38
68:32
69:31
52
99
PdCl2=A
Pd(dba)2=A
PdCl2(PPh3)2
PdCl2(Pcy3)2
PdCl2(dppf)2
Pd(OAc)2=A
Pd(OAc)2=A
Pd(OAc)2=A
99
99
92
99
99
99
99
aCatalytic conditions: iodobenzene (1.0 mmol), butyl acrylate (0.3 mmol), base (0.6 mmol), solvent
(2 ml), 120 ꢀC, 24 h, Ar.
bDetermined by GC-MS.
cIsolated yield of diarylethylene.
dDMSO.
ePEG-400.
fNMP.
gDMAc.
hAt 130 ꢀC.
iIodobenzene (1.5 mmol).
jIodobenzene (1.8 mmol).
Subsequently, the study of Pd-catalysis focused on the monoarylation of ole-
fins. As usual, we screened the optimal catalytic condition in the presence of some
efficient ligands based on these results. Thus, ligands A, E, and F were employed
in the coupling reaction, and the results are listed in Table 3. It can be seen that
the N,N-ligand F afforded the best results (Table 3, entries 1–3). The control experi-
ment showed that in the absence of ligand moderate yield of the desired product was
obtained (entry 4). PdCl2(PPh3)2 afforded the corresponding product in 64% yield
(entry 5).

SYNTHESIS OF ARYLETHYLENE OR DIARYLETHYLENE
2777
Table 2. Pd-catalyzed diarylation of olefins via the Heck reaction in the presence of A as the liganda
Entry
1
ArI
Olefin
Yield (%)b
76
2
3
77
66
4
5
73
61
6
7
38
Trace
8c
82
34
9c,d
10c,d
70
76
11cd
aReaction conditions: Aryl iodide (1.0 mmol), olefin (0.3 mmol), Pd(OAc)2 (4 mol%), A (8 mol%),
Cs2CO3 (0.6 mmol), DMF (2 ml), 120 ꢀC, 24 h, Ar.
bIsolated yield of diarylethylene.
cGC yield using n-decane as internal standard, because arylethylene product and diarylethylene product
cannot be separated by flash chromatography.
d48 h.

2778
H. YAN ET AL.
Table 3. Screening conditions for synthesis of arylethylene using various ligandsa
Entry
Pd cat.
Ligand
Yield (%)b
1
2
3
4
5
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2(PPh3)2
A
E
78
51
83
55
64
F
—
—
aReaction conditions: Iodobenzene (0.3 mmol), butyl acrylate (0.3 mmol), Pd(OAc)2 (4 mol%), ligand
(8 mol%), Cs2CO3 (0.6 mmol), DMF (2 ml), Ar.
bIsolated yield of monoarylethylene.
The optimized procedure was subsequently used to investigate the scope of the
coupling between various commercially available aryl halides and olefins (Table 4).
In sharp contrast to the diarylation, electronic effect from the aryl halides showed
little influence on the monoarylation of olefins catalyzed by the Pd(OAc)2=F system.
Moderate to good yields of desired products were obtained (Table 4, entries 1–3).
However, steric hindrance from aryl halides affected the arylation evidently (entry
4). Diarylation with the 3-iodoanisole provided the monoarylated product in a good
yield of 75% (entry 5). It can be seen that for the couplings of iodobenzene, different
types of olefins, such as acrylates, styrenes, and acrylamide, afforded the desired pro-
ducts in satisfactory yields (68–84%) (entries 6–13). Notably, the coupling between
1-fluoro-4-iodobenzene and n-butyl acrylate afforded the desired product in good
yield (90%, entry 14). In addition, 1-iodonaphthalene coupled with n-butyl acrylate
to give the product with 66% yield (entry 15).
Using the optimal catalytic condition, the coupling reaction between
1-bromo-4-iodobenzene and n-butyl acrylate afforded the desired iodo-substituted
product in 44% yield and bromo-substituted product in 23% yield, respectively, as
shown in Scheme 1.
Encouraged by these results, we then extended them to the one-pot coupling of
butyl acrylate with different aryl halides using Pd(OAc)2=F=Cs2CO3=DMF system as
shown in Scheme 2. Then we added 0.3 mmol of 4-iodoanisole for another 24 h. We
can see that only 48% of isolated yield was observed and the Z=E product ratio was
1=1.8.
On the other hand, we carried out a one-pot double-Heck coupling reaction
using Pd(OAc)2=F=Cs2CO3=DMF. As presented in Scheme 3, the coupling of iodo-
benzene and butyl acrylate was performed for 24 h, another 0.3 mmol of iodobenzene
was added, and the reaction was stirred for 24 h. We can see that only 54% of dia-
rylated product was obtained, which was less than in optimized condition (Table 2,
entry 1).

SYNTHESIS OF ARYLETHYLENE OR DIARYLETHYLENE
2779
Table 4. Pd-catalyzed synthesis of arylethylene via Heck reactions in the presence of F as the liganda
Entry
ArI
Olefin
Yield (%)b
1
2
74
66
3
4
70
60
5
75
6
7
8
9
73
80
70
69
10
72
68
11
12
76
(Continued )

2780
H. YAN ET AL.
Table 4. Continued
Entry
13
ArI
Olefin
Yield (%)b
84
14
15
90
66
aReaction conditions: Aryl iodide (0.3 mmol), olefin (0.3 mmol), Pd(OAc)2 (4 mol%), F (8 mol%),
Cs2CO3 (0.6 mmol), DMF (2 ml), Ar.
bIsolated yield of monoarylethylene.
Scheme 1. Mono-Heck coupling between 1-bromo-4-iodobenzene and n-butyl acrylate.
Scheme 2. One-pot double-Heck coupling using different aryl iodides.
Scheme 3. One-pot double-Heck coupling using the same aryl iodide.

SYNTHESIS OF ARYLETHYLENE OR DIARYLETHYLENE
2781
CONCLUSIONS
In summary, we have developed an efficient protocol for the synthesis of
mono-substituted or disubstituted alkenes via the coupling of various aryl halides
and olefins. The desired products were obtained in moderate to good yields in the
presence of readily available and low-cost ligand and the amounts of the substrates
were economical in view of possible application on a large scale or in industry. Actu-
ally these substituted alkenes could be further applied to pharmaceutical chemistry
and functional organic materials.[29] Studies into the further application of the
reaction will be the focus of future work.
EXPERIMENTAL
All reactions were carried out under an air atmosphere condition. Various aryl
halides and various olefins were purchased from Aldrich, Acros, or Alfa. Flash col-
umn chromatography was performed using silica gel (100–200 mesh). Analytical
thin-layer chromatography (TLC) was performed using glass plates precoated with
200- to 300-mesh silica gel impregnated with a fluorescent indicator (254 nm).
NMR spectra were recorded in CDCl3 on a Varian Inova-300 NMR spectrometer
(300 MHz) with tetramethylsilane (TMS) as an internal reference. Products were
characterized by comparison of 1H NMR, 13C NMR, and turnover frequency–mass
spectrometry (TOF-MS) data in the literature.
General Procedure for Synthesis of Diarylethylene by Pd-Catalyzed
Heck Reaction
A mixture of aryl halide (1.0 mmol), olefin (0.3 mmol), Pd(OAc)2(4 mol%),
A (8 mol%), Cs2CO3 (2 equiv), and DMF (2 mL) in a Schlenk tube was stirred under
an air atmosphere at 120 ꢀC for the desired time until complete consumption of start-
ing material as monitored by TLC. After the mixture was poured into ether, washed
with water, extracted with ethyl acetate, dried by anhydrous Na2SO4, filtered, and
evaporated under vacuum, the residue was purified by flash column chromatography
(petroleum ether or petroleum ether=ethyl acetate) to afford the corresponding
coupling products.
General Procedure for Synthesis of Arylethylene by Pd-Catalyzed
Heck Reaction
A mixture of aryl halide (0.3 mmol), olefin (0.3 mmol), Pd(OAc)2(4 mol%),
F (8 mol%), Cs2CO3 (2 equiv), and DMF (2 mL) in a Schlenk tube was stirred under
an air atmosphere at 120 ꢀC for the desired time until complete consumption of start-
ing material as monitored by TLC. After the mixture was poured into ether, washed
with water, extracted with ethyl acetate, dried by anhydrous Na2SO4, filtered, and
evaporated under vacuum, the residue was purified by flash column chromatography
(petroleum ether or petroleum ether=ethyl acetate) to afford the corresponding
coupling products.

2782
H. YAN ET AL.
Please see the Supporting Information, available online, for complete
experimental details.
ACKNOWLEDGMENTS
We are grateful to the grants from International S&T Cooperation Program of
Jiangsu Province (BZ2010048), the Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry, the Priority Academic
Program Development of Jiangsu Higher Education Institutions, and the Key
Laboratory of Organic Synthesis of Jiangsu Province.
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