Aryldiazonium silica sulfates as efficient reagents for Heck-type arylation reactions under mild conditions

Article abstract of DOI:10.1016/j.tetlet.2011.06.095

An efficient and straightforward procedure for Heck-type arylation reactions was studied using aryldiazonium silica sulfates and olefins in the presence of a catalytic amount of Pd(OAc)₂. These reactions were carried out in water at room temperature without using a base or additional ligands. The use of a non-toxic solvent, a simple and clean work-up, short reaction times, and good yields are advantages of this method.

Full text of DOI:10.1016/j.tetlet.2011.06.095

Tetrahedron Letters 52 (2011) 4554–4557
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Tetrahedron Letters
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Aryldiazonium silica sulfates as efficient reagents for Heck-type arylation
reactions under mild conditions
Amin Zarei a, , Leila Khazdooz b, Azadeh Pirisedigh c, Abdol R. Hajipour d, Hojjat Seyedjamali c,
⇑
Hamidreza Aghaei e
a Department of Science, Fasa Branch, Islamic Azad University, Post Box No 364, Fasa 7461713591, Fars, Iran
b Department of Science, Khorasgan Branch, Islamic Azad University, Isfahan 81595-158, Iran
c Department of Chemistry, Kazerun Branch, Islamic Azad University, Kazerun, Iran
d Pharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
e Department of Chemistry, Shahreza Branch, Islamic Azad University, Shahreza 311-86145, Isfahan, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and straightforward procedure for Heck-type arylation reactions was studied using aryldi-
azonium silica sulfates and olefins in the presence of a catalytic amount of Pd(OAc)2. These reactions
were carried out in water at room temperature without using a base or additional ligands. The use of
a non-toxic solvent, a simple and clean work-up, short reaction times, and good yields are advantages
of this method.
Received 9 April 2011
Revised 14 June 2011
Accepted 24 June 2011
Available online 1 July 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Aryldiazonium silica sulfates
Heck-type reaction
Pd(OAc)2
Mild conditions
Palladium-catalyzed Heck coupling reactions using aryl halides
or aryl triflates and olefins are important and valuable reactions for
carbon–carbon bond formation in modern organic synthesis.1,2
Although some of these methods have convenient protocols and af-
ford good to high yields of products, the majority suffer from at
least one of the following disadvantages: high temperature with
an additional base, the use of an appropriate ligand to accelerate
the reaction, long reaction times, and the use of organic solvents.
Moreover, the use of high-cost aryl iodides or aryl triflates is a
drawback of these reactions. Aryldiazonium salts have several
advantages over aryl halides including the availability of aryl
amines as the arenediazonium salt precursors, and superior reac-
tivity as a better leaving group than halides or aryl triflates. In com-
parison with conventional Heck couplings, these reactions with
aryldiazonium salts are carried out under mild conditions, with
shorter times and higher yields of products.3–17 It is notable that
some of these reactions are carried out without using a base or
additional ligands. In continuation of our studies on the stabiliza-
tion of diazonium salts on silica sulfuric acid and their application
in organic synthesis,18 we report herein an efficient and convenient
procedure for Heck-type coupling reactions employing aryldiazo-
nium silica sulfates with methyl acrylate, styrene, and acrylic acid
in the presence of a catalytic amount of Pd(OAc)2 (Scheme 1). Un-
like traditional methods, these reactions were carried out in water
at room temperature without using a base or additional ligands.
Aryldiazonium salts have been prepared and studied as useful
intermediates in classical and modern organic synthesis due to
their ready availability and high reactivity.10,19 These salts, how-
ever, have a serious drawback in their intrinsic instability. They
are usually synthesized at around 10 °C and, to avoid their decom-
position, they are handled below 0 °C. Moreover, because of this
instability, subsequent reactions with diazonium salts must be car-
ried out under the same conditions. Thus, diazonium salts with
higher stability and versatility that can be easily made and stored
under solid state conditions with explosion-proof properties are
desired and necessary.11,17,20 For example, many diazonium tetra-
fluoroborates are relatively stable and can be stored over extended
periods of time without decomposition.17 Recently, we reported
an efficient, fast, and convenient method for the preparation of
aryldiazonium salts supported on the surface of silica sulfuric acid
(aryldiazonium silica sulfates).18 We found that these new
aryldiazonium salts, ArN2þꢀOSO3—SiO2, could be kept at room
Pd(OAc)2, 4 mol%
Ar
ArN2OSO3-SiO2
+
X
H2O, r.t.
X
X = CO2CH3, Ph, COOH
⇑
Corresponding author. Tel.: +98 917 1302528; fax: +98 311 2289113.
E-mail address: aj_zarei@yahoo.com (A. Zarei).
Scheme 1.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.06.095

A. Zarei et al. / Tetrahedron Letters 52 (2011) 4554–4557
4555
Table 1
Pd(OAc)2-catalyzed vinylation of aryldiazonium silica sulfates with olefins at room temperature
a
Entry
Olefin
Diazonium salt
Product
Time (min)
25
Yield (%)
O
O
1
Methyl acrylate
PhN2þꢀOSO3—SiO2
86
85
81
80
OMe
O
4-MeC6H4N2þꢀOSO3—SiO2
2-MeC6H4N2þꢀOSO3—SiO2
4-MeOC6H4N2þꢀOSO3—SiO2
30
35
35
OMe
2
3
4
Methyl acrylate
Methyl acrylate
Methyl acrylate
Me
Me
OMe
O
OMe
MeO
Br
O
O
O
OMe
OMe
OMe
5
6
Methyl acrylate
Methyl acrylate
4-BrC6H4N2þꢀOSO3—SiO2
4-ClC6H4N2þꢀOSO3—SiO2
30
30
87
85
Cl
Cl
7
8
Methyl acrylate
Methyl acrylate
3-ClC6H4N2þꢀOSO3—SiO2
30
35
83
82
Cl
O
2-ClC6H4N2þꢀOSO3—SiO2
OMe
O
OMe
9
Methyl acrylate
Methyl acrylate
4-NCC6H4N2þꢀOSO3—SiO2
30
30
84
83
NC
O
OMe
11
4-MeCOC6H4N2þꢀOSO3—SiO2
Me
O
O
OMe
12
13
Methyl acrylate
Methyl acrylate
4-PhC6H4N2þꢀOSO3—SiO2
4-O2NC6H4N2þꢀOSO3—SiO2
35
30
81
87
Ph
O
OMe
OMe
O2N
O2N
O
14
15
16
Methyl acrylate
Methyl acrylate
Methyl acrylate
3-O2NC6H4N2þꢀOSO3—SiO2
2-O2NC6H4N2þꢀOSO3—SiO2
2-HOCOC6H4N2þꢀOSO3—SiO2
30
30
35
84
83
81
NO2
O
O
OMe
COOH
OMe
Ph
Ph
17
18
Styrene
Styrene
PhN2þꢀOSO3—SiO2
45
80
85
88
Ph
4-MeC6H4N2þꢀOSO3—SiO2
Me
Me
19
Styrene
2-MeC6H4N2þꢀOSO3—SiO2
90
80
87
Ph
20
21
Styrene
Styrene
4-BrC6H4N2þꢀOSO3—SiO2
3-ClC6H4N2þꢀOSO3—SiO2
100
90
Br
Cl
Ph
82
(continued on next page)

4556
A. Zarei et al. / Tetrahedron Letters 52 (2011) 4554–4557
Table 1 (continued)
Entry
Olefin
Diazonium salt
Product
Time (min)
100
Yield (%)
81
Ph
4-PhCOC6H4N2þꢀOSO3—SiO2
4-MeCOC6H4N2þꢀOSO3—SiO2
Ph
O
22
23
Styrene
Ph
Me
O
Styrene
75
83
Ph
24
25
Styrene
Styrene
4-O2NC6H4N2þꢀOSO3—SiO2
2-O2NC6H4N2þꢀOSO3—SiO2
70
60
85
82
O2N
NO2
Ph
Ph
COOH
26
27
28
Styrene
2-HOCOC6H4N2þꢀOSO3—SiO2
PhN2þꢀOSO3—SiO2
70
45
50
84
84
82
COOH
COOH
Acrylic acid
Acrylic acid
Me
2-MeC6H4N2þꢀOSO3—SiO2
COOH
29
30
Acrylic acid
Acrylic acid
4-MeC6H4N2þꢀOSO3—SiO2
3-ClC6H4N2þꢀOSO3—SiO2
50
50
85
82
Me
Cl
COOH
COOH
31
Acrylic acid
4-O2NC6H4N2þꢀOSO3—SiO2
45
83
O2N
a
The yield refers to isolated pure products which were characterized from their spectral data and by comparison with authentic samples.
Table 2
Comparison of aryldiazonium silica sulfates with other aryldiazonium salts in Heck-type coupling reactions under different conditions
O
O
S
S
-
+
Ar N2N
O
Ar N2OTs
Ar N2OSO3 SiO2
Ar N2BF4
O
3
2
4
1
Diazonium salt
Ar
Olefin
Catalyst/Base/Solvent/ Temp.
Time
Yield (%)
Ref.
1
4
2
2
4
2
2
2
4
2
4
3
4
3
4
2
4
2
4
2
4
2
4
1
4
1
4
4-MeC6H4
4-MeC6H4
4-MeC6H4
Ph
Ph
Ph
2–MeC6H4
2-MeC6H4
2-MeC6H4
4-BrC6H4
4-BrC6H4
4-O2NC6H4
4-O2NC6H4
2-HCO2C6H4
2-HCO2C6H4
Ph
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Acrylic acid
Acrylic acid
Acrylic acid
Acrylic acid
Pd(OAc)2 (1 mol %)/–/EtOH/70 °C
Pd(OAc)2 (4 mol %)/–/EtOH/rt
14 h
80 min
5 h
4.25 h
45 min
6.5 h
4 h
5 h
60
88
83
97
85
88
38
75
80
91
87
75
85
65
84
76
86
82
87
80
84
64
87
93
85
55
83
9
—
16
7
—
16
7
5
—
5
—
11
—
11
—
8
—
8
—
8
Pd(OAc)2 (10 mol %)/–/bmimPF6/70–80 °C
Pd(OAc)2 (5 mol %)+ligand/–/EtOH/rt
Pd(OAc)2 (4 mol %)/–/EtOH/rt
Pd(OAc)2 (10 mol %)/–/bmimPF6/70–80 °C
Pd(OAc)2 (5 mol %)+ligand/–/EtOH/rt
Pd(OAc)2 (2 mol %)+ligand/–/THF/rt
Pd(OAc)2 (4 mol %)/–/EtOH/rt
Pd(OAc)2 (2 mol %)+ligand/–/THF/rt
Pd(OAc)2 (4 mol %)/–/EtOH/rt
Pd(OAc)2 (1.2 mol %)/–/EtOH/70 °C
Pd(OAc)2 (4 mol %)/–/EtOH/rt
Pd(OAc)2 (1.2 mol %)/–/ EtOH/70 °C
Pd(OAc)2 (4 mol %)/–/EtOH/rt
Pd(OAc)2 (2 mol %)/–/bmimPF6/rt
Pd(OAc)2 (4 mol %)/–/H2O/rt
Pd(OAc)2 (2 mol %)/–/bmimPF6/rt
Pd(OAc)2 (4 mol %)/–/H2O/rt
Pd(OAc)2 (2 mol %)/–/bmimPF6/rt
Pd(OAc)2 (4 mol %)/–/H2O/rt
90 min
4 h
100 min
20 min
70 min
20 min
70 min
3 h
25 min
3 h
30 min
2 h
30 min
27 min
30 min
12 h
50 min
3.5 h
Ph
4-BrC6H4
4-BrC6H4
4-NCC6H4
4-NCC6H4
4-O2NC6H4
4-O2NC6H4
4-MeC6H4
4-MeC6H4
4-O2NC6H4
4-O2NC6H4
—
13
—
9
—
9
Pd(OAc)2 (10 mol %)/–/AcOH, DMF/0–5 °C
Pd(OAc)2 (4 mol %)/–/H2O/rt
Pd(OAc)2 (1 mol %)/CaCO3/THF /60 °C
Pd(OAc)2 (4 mol %)/–/H2O/rt
Pd(OAc)2 (1 mol %)/CaCO3/THF /40 °C
Pd(OAc)2 (4 mol %)/–/H2O/rt
45 min
—

A. Zarei et al. / Tetrahedron Letters 52 (2011) 4554–4557
4557
Tetrahedron 2011, 67, 250; (d) Mao, H.; Wan, J. P.; Pan, Y.; Sun, C. Tetrahedron
Lett. 2010, 51, 1844; (e) Choudary, B. M.; Madhi, S.; Chowdari, N. S.; Kantam, M.
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Neuville, L.; Zhu, J. Tetrahedron 2010, 66, 8911; (g) Pan, D.; Jiao, N. Synlett 2010,
1577; (h) Bararjanian, M.; Balalaie, S.; Rominger, F.; Movassagh, B.; Bijanzadeh,
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temperature under anhydrous conditions. Moreover, these new
aryldiazonium salts are explosion-proof and can be used under dif-
ferent conditions18 because of their stability. In the present work,
different aryldiazonium silica sulfates, as electrophiles, were ex-
posed to Heck-type coupling reactions using methyl acrylate, sty-
rene, and acrylic acid as the olefins, under mild conditions. The
vinylation of these diazonium salts was catalyzed using Pd(OAc)2
at room temperature without using a base or additional ligands
(Table 1). Methyl acrylate, and acrylic acid reacted with the aryldi-
azonium silica sulfates in water and the products were obtained in
good yields and short reaction times. We studied the reaction of
styrene with phenyldiazonium silica sulfate under these condi-
tions. As styrene is not miscible with water, the product was ob-
tained in 40% yield after a prolonged reaction time (5 h). By
changing the solvent to ethanol, the corresponding stilbenes were
obtained in good yields and short reaction times (Table 1, entries
17–26). Aryldiazonium silica sulfates with electron-withdrawing
groups or electron-donating groups also reacted effectively. The
steric effects of ortho substituents and the electronic effects of
functional groups on the aryl rings of the aryldiazonium silica sul-
fates had relatively little influence on the yields and reaction times.
The products were trans-isomers. The corresponding phenol deriv-
atives were formed in trace amounts as by-products. We also stud-
ied the effect of temperature on these reactions and it was found
that on increasing the temperature phenol formation increased.
The optimum temperature for these reactions was room tempera-
ture. It was notable that a bromide or chloride on the aromatic ring
of the aryldiazonium silica sulfates remained intact during the
course of the reaction. Another advantage of this method was the
easy work-up since the crude products were extracted with ethyl
acetate and, if necessary, were purified by short column
chromatography.21,22
To show the merit of the present work in comparison with that
reported recently, we compared our results with the results ob-
tained from Heck-type reactions using arenediazonium tetra-
fluoroborates,5,7,8,13,16 arenediazonium o-benzenedisulfonimides,9
and arenediazonium tosylates.11 The results show that the reaction
yields were comparable with those reported, and in many cases,
the results using the aryldiazonium silica sulfates were superior
(Table 2). By supporting the aryldiazonium salt on silica sulfuric
acid, the surface area of the reaction increases lowering the reac-
tion time.18,23
To summarize, we have reported an efficient, rapid, and exper-
imentally simple method for Heck-type reactions of aryldiazonium
silica sulfates with methyl acrylate, styrene, and acrylic acid to
form the corresponding cinnamates, stilbenes and cinnamic acids
with trans-configuration.
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2009, 941; (c) Zarei, A.; Hajipour, A. R.; Khazdooz, L.; Aghaei, H. Tetrahedron
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21. General procedure for Heck-type reactions of arydiazonium silica sulfate with
methyl acrylate or acrylic acid: To a solution of Pd(OAc)2 (0.009 g, 4 mol %) in
H2O (10 mL), methyl acrylate or acrylic acid (2 mmol) was added and the
mixture was stirred for few minutes. Next, freshly prepared aryldiazonium
silica sulfate (1 mmol)17 was added gradually and the mixture was stirred
vigorously at room temperature for the time specified in Table 1. The reaction
progress was monitored by TLC (hexane/EtOAc, 75:25). After completion of the
reaction (absence of azo coupling with 2-naphthol), the mixture was diluted
with EtOAc (15 mL) and filtered after vigorous stirring. The residue was
extracted with EtOAc (3 ꢁ 10 mL) and the combined organic layer washed with
H2O and dried over anhydrous Na2SO4. The solvent was evaporated under
reduced pressure to afford the corresponding product and if necessary, the
crude product was purified by short column chromatography.
22. General procedure for Heck-type reactions of arydiazonium silica sulfate with
styrene: To a solution of Pd(OAc)2 (0.009 g, 4 mol %) in 95% aqueous EtOH
(10 mL), styrene (2 mmol) was added and the mixture was stirred for a few
minutes. Next, freshly prepared aryldiazonium silica sulfate (1 mmol)17 was
added gradually and the mixture was stirred vigorously at room temperature
for the time specified in (Table 1, entries 17–26). The reaction progress was
monitored by TLC (hexane/EtOAc, 75:25). After completion of the reaction
(absence of azo coupling with 2-naphthol), the mixture was diluted with EtOAc
(15 mL) and filtered. The residue was extracted with EtOAc (3 ꢁ 10 mL) and the
combined organic layer washed with H2O and then dried over anhydrous
Na2SO4. The solvent was evaporated under reduced pressure to afford the
corresponding product and if necessary, the crude product was purified by
short column chromatography.
Acknowledgments
We gratefully acknowledge the funding support received for
this project from the Islamic Azad University, Fasa Branch.
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