Microwave-assisted Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions of aryl chlorides and bromides in water using stable benzothiazole-based palladium(II) precatalysts

Article abstract of DOI:10.1016/j.tet.2007.07.029

The catalytic activity of benzothiazole-based Pd(II)-complexes was evaluated in Suzuki-Miyaura and Heck-Mizoroki C-C cross-coupling reactions of aryl chlorides and bromides with olefins and arylboronic acids both under thermal as well as microwave irradiation conditions in water. The factors affecting the optimization of such reactions as well as the reusability of the Pd-precatalysts are studied.

Full text of DOI:10.1016/j.tet.2007.07.029

Tetrahedron 63 (2007) 9642–9651
Microwave-assisted Suzuki–Miyaura and Heck–Mizoroki
cross-coupling reactions of aryl chlorides and bromides in water
using stable benzothiazole-based palladium(II) precatalysts
*
Kamal M. Dawood
Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt
Received 5 May 2007; revised 24 June 2007; accepted 12 July 2007
Available online 19 July 2007
Abstract—The catalytic activity of benzothiazole-based Pd(II)-complexes was evaluated in Suzuki–Miyaura and Heck–Mizoroki C–C cross-
coupling reactions of aryl chlorides and bromides with olefins and arylboronic acids both under thermal as well as microwave irradiation
conditions in water. The factors affecting the optimization of such reactions as well as the reusability of the Pd-precatalysts are studied.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
catalysts and microwave assistance is of particular impor-
tance. In addition, organic reactions that can proceed well
in aqueous media offer advantages over those occurring in
Modern synthetic chemistry is sustained by the use of tran-
sition metal catalysts as powerful tools for carbon–carbon
bond-forming processes. The formation of carbon–carbon
bonds is a fundamental reaction in organic synthesis, the ef-
ficiency of which has interested organic chemists for a long
time ago. Biaryls are versatile intermediates in organic syn-
thesis and are recurring functional groups in many natural
products, bioactive compounds, and liquid crystal mate-
rials. As a result, considerable effort has been directed
toward the development of efficient and selective methods
for the synthesis of biaryls.
Suzuki–Miyaura cross-coupling reaction represents one of
the most widely used processes for the synthesis of bi-
Modern techniques are focused on the design
of new methodologies able to make the already known
chemical transformations simpler, faster, cheaper and in
general, more efficient processes. Solid-phase organotran-
sition metal complexes having high activity and selectivity,
particularly those based on palladium, offer several signifi-
cant practical advantages in synthetic and industrial chemis-
try; among those, the ease of separation of the catalyst from
the desired reaction products and the ease of recovery and
re-use of the catalyst are most important. In addition, mi-
crowave irradiation methodology assists in achieving rapid
incorporation of organic synthesis into broad industrial di-
1
5
organic solvents. Homogenous oxime-palladacycles 1, 2,
and the immobilized one 3 (Fig. 1) recently appeared in
the literature with high activity and often they are air sta-
1
1
6–19
ble.
In continuation of our recent publications concern-
2
ing the use of the immobilized Pd-catalyst 4 under
microwave irradiation conditions in Suzuki–Miyaura,
Heck–Mizoroki and Sonogashira cross-coupling reactions
3
,4
20
in aqueous media, we report herein the development of
new homogenous benzothiazole-oxime Pd(II) precatalyst 5
as well as its immobilized form 6 anchored to a glass/poly-
mer composite material shaped as Raschig rings, which is
a material with relevance in industrial applications, in order
to evaluate their suitability in Suzuki–Miyaura and Heck–
Mizoroki cross-coupling reactions of aryl bromides and
chlorides under thermal as well as microwave irradiation
conditions in water.
5
–7
The palladium-catalyzed
8
–11
aryls.
1
2
H
OH
N
N OH
OH
N
N
HO
Pd 2
Pd Cl
Cl
O
1
3
Cl
Pd 2
Cl
3
1
2
1
4
Cl
Cl
versities. The combination of immobilized homogenous
N
N
Pd Cl
N
Pd Cl
N
Pd Cl
Cl
N
N
O
S
S
OH
O
Keywords: Pd(II) precatalysts; Microwave irradiation; Suzuki–Miyaura;
Heck–Mizoroki cross-coupling reactions.
4
5
6
*
Fax: +20 2 5727556; e-mail: dr_dawood@yahoo.com
Figure 1.
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.029

K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
9643
Cl
N
NH OH
N
Pd Cl
2
Dioxane / MeOH
Na2PdCl4 / r.t.
N
N
S
S
N
OH
S
OH
O
7
8
5
NaH
DMF
Cl
9
Cl
Pd Cl
N
N
Na2PdCl4
MeOH, r.t.
N
N
O
S
O
S
10
6
Scheme 1. New benzothiazole-oxime-based palladium(II) precataylsts.
2
. Results and discussion
potassium carbonate (120 mmol), and water (100 mL) to give
4-acetyl-1,1 -biphenyl in 100% (GC-yield) with a turnover
0
number (TON) 133,000 and turnover frequency (TOF)
2
.1. Preparation of Pd-precatalysts 5 and 6
ꢁ
1
5
3,500 h , revealing the high activity of the catalytic system.
Benzothiazole-oxime-based Pd(II) precatalyst 5 was pre-
pared by dissolving the 2-acetylbenzothiazole-oxime (8) in
dioxane followed by the addition of an equimolar amount
of sodium tetrachloropalladate in methanol at room temper-
ature (Scheme 1). The immolilized Pd-precatalyst 6 was ob-
tained via coupling of 2-acetylbenzothiazole-oxime (8) with
Finally, we repeated the same experiment with the same mmol
scale as above using 0.0005 mol % of the catalyst 5 to give
62% GC-yield with TON 124,000 and turnover frequency
(TOF) 49,600 h . As can be readily seen from the data in Ta-
ble 1, the Pd-prectalayst 5 shows excellent catalytic activity,
giving rise to extremely high TONs.
ꢁ
1
ꢀ
the polymer matrix 9 by heating it at 80 C in DMF in the
presence of sodium hydride. Finally, the heterogenous pre-
catalyst 6 was obtained by treatment of 10 with a solution
of sodium tetrachloropalladate in methanol at room temper-
ature. The synthesis of benzothiazole-oxime-based Pd(II)
precatalysts 5 and 6 directly from 2-acetylbenzothiazole-
oxime (8) in methanol under mild conditions has made these
important precursors for C–C cross-coupling reactions. The
elucidation of structure 5 and N–Pd bonding instead of S–Pd
bonding in the complexe 5, and consequently the analogous
heterogeneous catalyst 6, was based on spectral data as well
Deactivated aryl bromides are important for measuring the
2
4
high catalytic activity of catalytic systems. Thus, we
studied the Suzuki–Miyaura cross-coupling reaction of 4-
bromoanisole under different concentrations of the precata-
lysts 5 and 6 and the results are shown in Table 2, runs 1–5.
The precatalyst 5 was found to be highly active and resulted
in full conversion into 16 even at 0.001 mol % and 20 mmol
scale of coupling partners with high turnover number (TON)
ꢁ
1
100,000 and turnover frequency (TOF) 25,000 h (run 5,
Table 2). When the above reaction was repeated under
2
1,22
ꢀ
97% isolated yield) after 10 min was obtained with TON
as in comparison with related reported literature data.
microwave irradiation at 160 C (250 W) full conversion
(
ꢁ1
2
.2. Precatalysts 5 and 6 in Suzuki–Miyaura
2000 and TOF 12,000 h . 4-Bromotoluene (15) was
similarly coupled with phenylboronic acid using 0.5 and
0.05 mol % of the precatalyst 5 resulting in the formation of
cross-coupling reactions of activated and
deactivated aryl bromides
The search for coupling catalyst systems exhibiting high
efficiency (i.e., high turnover frequency (TOF)) and greater
stability (i.e., high turnover number (TON)) has recently
Table 1. Effect of Pd concentration on the reactivity of the catalyst 5 in
Suzuki–Miyaura cross-coupling of 4-bromoacetophenone 11
2
3
been receiving much interest. Firstly, we studied the fac-
tors affecting the optimization of the catalytic activity of
the Pd-precatalyst 5. Thus, the effect of concentration of
palladium precatalyst 5 on the coupling reaction between
phenylboronic acid and p-bromoacetophenone under ther-
Br
B(OH)2
Pd-Cat. 5
+
Water/TBAB/K2CO3
O
11
12
O
13
ꢀ
a
ꢁ1
TOF [h ]
mal conditions in water at 100 C was evaluated as shown
in Table 1. At first, the reaction was conducted using
Entry mmol scale mol %
of 11
Time Yield,
of cat. 5 (h) %
TON
1
mol % of the precatalyst 5 with a molar ratio of p-bromo-
1
2
3
4
5
6
7
8
9
1
1
1
1
0.5
0.1
0.05
0.01
5ꢂ10
1ꢂ10
7ꢂ10
5ꢂ10
2
2
2
2
100 (98)
100
200
1000
2000
10,000
20,000
100,000 40,000
133,000 53,500
124,000 49,600
50
100
500
1000
5000
8000
acetophenone/phenylboronic acid/tetrabutylammonium bro-
mide/potassium carbonate: 1:1.2:0.6:2, to give 98% isolated
yield of 4-acetyl-1,1 -biphenyl. In the second experiment,
100 (99)
100 (96)
100 (98)
100
100
100
0
5
10
20
40
60
60
2
we used 0.5 mol % of the catalyst to give full conversion in
9
ꢁ3
2.5
2.5
2.5
2.5
ꢁ3
ꢁ4
ꢁ4
9% isolated yield. The reaction was repeated with different
catalytic mol % as shown in Table 1. Full conversion was ob-
tained even in the presence of 0.0007 mol % of the catalyst 5
using p-bromoacetophenone (60 mmol), phenylboronic acid
100
62
a
Conditions: Bromide/boronic acid/K /TBAB/water (mL): 1:1.2:2:
ꢀ
0.6:2, heating at 100 C. The values in parentheses are the isolated yields.
2
CO
3
(
72 mmol), tetrabutylammoium bromide (36 mmol),

9644
K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
Table 2. Suzuki–Miyaura cross-coupling of deactivated aryl bromides
Table 4. Suzuki–Miyaura reactions of aryl chlorides under thermal and
microwave heating
Br
B(OH)2
Pd-Cat. 5 or 6
+
Cl
B(OH)2
Water/TBAB/K2CO3
Pd-Cat. 5 or 6
Water/TBAB/NaOH
X
+
X
X
14,15
12
14,16: X = MeO
16,17
X
1
5,17: X = Me
18-21
12
13,22-24
ꢁ
1
a
a
Run Aryl
Pd-cat/mol Time Product:
%
TON
TOF [h
]
Run X
Pd-cat/ Product Thermal heating Microwave heating
mol %
a
Yield, %
bromide
(h)
b
b
Yield, %
Time Yield,
%
Time
(min)
1
2
3
4
5
6
7
8
14
14
14
14
14
15
15
15
5/0.5
6/0.5
5/0.05
4
4
4
4
4
6
6
6
16: 100 (99)
16: 100 (99)
16: 100
200
200
2000
20,000
50
50
500
5000
(h)
b
1
2
3
4
5
6
7
8
9
MeCO 5/1
MeCO 5/0.2 13
MeCO 5/0.02 13
MeCO 6/1
MeCO 6/0.2 13
NO
NO
NO
NO
13
7
7
7
100 (90) 10
100 (83)
100
85
100
73
10
10
5/0.005
5/0.001
5/0.5
16: 100
16: 100 (97) 100,000 25,000
13
7
7
4
4
4
4
4
4
100 (94) 10
100 (86)
98
100 (84)
100
100 (90)
100
100 (95)
100
17: 100 (91)
17: 100 (95)
17: 81
182
1900
162
32
330
27
c
92
10
7
7
7
7
7
7
7
30
30
5/0.05
6/0.5
2
2
2
2
2
5/1
22
100 (89)
100
85
100 (94)
100
100 (93)
100
15
5/0.2 22
5/0.02 22
a
b
c
Conditions: Bromide/boronic acid/K
0
2
CO
.6:2, thermal heating at 100 C. The values in parentheses are the isolated
yields.
3
/TBAB/water (mL): 1:1.2:2:
ꢀ
6/1
6/0.2 22
22
10 NO
11 CN
12 CN
13 Me
14 Me
ꢀ
Under microwave irradiation (160 C and 250 W) full conversion (97%
isolated yield) after 10 min was obtained with TON 2000 and TOF
5/1
6/1
5/1
6/1
23
23
24
24
4
20
20
100 (92)
7
3
ꢁ
1
12,000 h
.
ꢀ
Under microwave irradiation (160 C and 250 W) full conversion (94%
isolated yield) after 10 min was obtained with TON 1880 and TOF
13
a
ꢁ
1
1,300 h .
Conditions: 1 mmol of aryl chloride, 1.2 mmol of phenylboronic acid,
1
2
1
mmol of NaOH, 0.6 mmol TBAB, water (2 mL), thermal heating at
ꢀ
ꢀ
00 C, microwave heating at 160 C (250 W).
0
91% and 95% isolated yields, respectively) after 6 h of ther-
4
-methyl-1,1 -biphenyl (17) with full conversion in all cases
b
GC-yields; values in parentheses refer to isolated yields of pure products.
(
mal heating (runs 6 and 7, Table 2). When the above reaction
extra three successive runs were carried out with the same
portion of Pd-precatalysts 5 and 6. Full conversion was
achieved till the third run when the Pd-precatalyst 6 that an-
chored to solid support was used and 86% conversion was
obtained in the fourth run. The Pd-precatalyst 5 resulted in
80% conversion in the second run and lost its activity, after
that where only 68% was observed in the third run. These
findings demonstrate the high thermo stability of the solid-
phase precatalyst 6 over its soluble analog 5.
ꢀ
250 W) full conversion (94% isolated yield) after 10 min
was repeated under microwave irradiation at 160 C
(
ꢁ
1
was obtained with TON 1880 and TOF 11,300 h . The
use of 0.5 mol % of precatalyst 6 resulted in 81% conversion
into 17 after 6 h of thermal heating (run 8, Table 2).
The longevity effect of the Pd-precatalysts 5 and 6 was tested
in the model Suzuki–Miyaura cross-coupling reaction using
p-bromoacetophenone (5 mmol) and phenylboronic acid
(
conducted in the presence of Pd-precatalyst 5 or 6
6 mmol) as coupling partners (Table 3). The reaction was
2.3. Precatalysts 5 and 6 in Suzuki–Miyaura
cross-coupling reactions of activated and
deactivated aryl chlorides
ꢀ
(
0.5 mol %) in water at 100 C under air using potassium
carbonate (10 mmol) as base and TBAB (3 mmol) as phase
transfer agent. Under these conditions, the reaction was
completed within 2 h (run 1, Table 3). At this point, fresh
portions of the coupling partners and the base (the same
amounts as for the first run; 5 mmol scale) were added to
the flask thus repeating the reaction for 2 h. In this manner,
We next turned our attention on the cross-coupling reaction
of phenylboronic acid with variety of aryl chlorides, which
are of particular importance for highly active catalysts.
2
5
The results of their cross-couplings under thermal as well as
microwave heating conditions are summarized in Table 4. At
first, p-choloroacetophenone 18 (1 mmol) was coupled with
phenylboronic acid (1.2 mmol) in water (2 mL) in the pres-
ence of tetrabutylammonium bromide (0.6 mmol) using
NaOH (2 mmol) as base. Under this condition, full conver-
sions were obtained after 7 h of thermal heating or 10 min
of microwave irradiation when the palladium precatalyst
5 was used in either 1 or 0.2 mol %. As an evidence of its
high activity, 0.02 mol % of the precatalyst 5 was enough
for 73% conversion after 7 h of thermal heating and 85%
conversion after 10 min of microwave irradiation of the
above coupling reaction with turnover numbers (TON)
Table 3. The longevity effect of the Pd-precatalysts 5 and 6 in Suzuki–
Miyaura cross-coupling of p-bromoacetophenone
Pd-Cat. 5 or 6
Br
B(OH)2
(
0.5 mol%)
+
Water/TBAB/K2CO3
100 °C, 2 h
O
11
12
O
13
Run
Number of mmol of 11
GC yield, %
Pd-cat 5 Pd-cat 6
3650 and 4250, and turnover frequencies (TOF) 521 and
25,500 h , respectively. The use of Pd-precatalyst 6 for
similar coupling reaction in 1 and 0.2 mol % resulted in
100% and 92% conversions, respectively, after 7 h of
thermal heating. It is noteworthy also to mention here that
the activated p-nitrochlorobenzene 19 could be completely
1
2
3
4
5
10
15
20
100
80
68
n.t.
100
100
100
86
ꢁ1
Conditions: Bromide/boronic acid/K
; n.t.: not tested.
2
CO
3
/TBAB/water (mL): 1:1.2:2:0.6:
2

K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
9645
coupled with phenylboronic acid under microwave (7 min)
or thermal heating (7 h) with 100% conversion using Pd-pre-
catalyst 5 in 1 or 0.2 mol %. Interestingly, at 0.02 mol % of
Pd-precatalyst 5 the conversion was 100% under microwave
Table 5. Suzuki–Miyaura coupling of 3-bromo-4-chromone and 2-bromo-
1
,4-naphthoquinone
O
O
Br
Pd-Cat. 5, 0.5 mol%
Ar
ꢁ1
+
Ar B(OH)2
(
7 min) [TON¼5000 and TOF¼42,850 h ] and 85% under
Toluene/K2CO3
X
ꢁ
1
X
thermal heating (7 h) [TON¼4250 and TOF¼607 h ].
Similarly, Pd-precatalyst 6 when used in 1 or 0.2 mol % it re-
sulted, in both cases, in 100% conversionsafter 7 h of thermal
heating or 7 min of microwave irradiation. p-Chlorobenzoni-
trile 20 was also successfully coupled with phenylboronic
acid under similar conditions with full conversion using
either Pd-precatalyst 5 or 6 in 1 mol %. However, p-chloro-
toluene 21 did not give reasonable coupling product even
at 2 mol % of catalyst under thermal or microwave heating
for long time (runs 13 and 14, Table 4).
25: X = O
12, 27
28-31
2
6: X = CO
Run
Product
Thermal
heating
Microwave
heating
a
a
b
b
Time Yield,
(
Time Yield,
(min) %
h)
%
O
O
Ph
1
2
28
4
100 (89)
36
8
8
100 (93)
60
2.4. Precatalysts 5 and 6 in Suzuki–Miyaura
cross-coupling reactions of heterocyclic bromides
15
O
O
O
29
30
Isoflavones represent a very important class of natural prod-
ucts andexhibitremarkablydiverse biologicalproperties.
2
6,27
O
c
c
3
4
3
4
100 (79)
8
8
100
Therefore, we explored the synthesis of some isoflavones via
the Suzuki–Miyaura cross-coupling reaction between aryl-
boronic acids and 3-bromo-4-chromone. Thus, treatment of
phenylboronic acid 12 (1.2 equiv) and 3-bromo-4-chromone
O
O
Ph
d
100 (85)
100 (90)
100 (87)
2
5 (1 equiv) in the presence of precatalyst 5 (0.5 mol %) in
toluene (3 mL) and potassium carbonate (2 equiv) under
thermal heating for 4 h afforded 100% GC-conversion
O
O
O
O
(
5
89% isolated yield) of the known isoflavone 28 (run 1, Table
). Full conversion (93% isolated yield) was also achieved
5
31 15
30
8
within 8 min when the same coupling in toluenewas repeated
under microwave irradiation. In contrast to phenylboronic
acid, 3,4-methylenedioxyphenylboronic acid 27 did not
give a satisfied coupling results with 3-bromo-4-chromone
a
Conditions: 1 mmol of aryl bromide, 1.2 mmol of boronic acid, 2 mmol of
ꢀ ꢀ
2 3
K CO , toluene (3 mL), 110 C for conventional heating; 150 C for
microwave irradiation (200 W).
b
c
d
2
5 neither thermal (15 h) nor under microwave irradiation
GC-yields; values in parentheses refer to isolated yields of pure products.
Water/TBAB was used instead of toluene.
When water was used, full conversion (100%) was obtained after 2 h
heating.
(
(
8 min), especially when toluenewas used as reaction solvent
run 2, Table 5).
However, when water was used as the reaction solvent, full
conversion into 3-(3,4-methylenedioxy-phenyl)-4-chromone
of carbon–carbon bond. Generally, aryl bromides, iodides,
and activated alkenes are typically employed as the cross-
2
9 was achieved after 3 h of thermal heating or 8 min of mi-
crowave irradiation (run 3, Table 5). Coupling of 2-bromo-
,4-naphthoquinone 26 with phenylboronic acid 12 in
2
8
coupling partners. Aryl chlorides are cheaper and more
readily available than bromides and iodides, but less reac-
tive. The catalyst systems, which show high catalytic activity
in Heck–Mizoroki reactions of aryl chlorides are of great
1
refluxing toluene using 0.5 mol % of precatalyst 5 resulted
in full conversion into 2-phenyl-1,4-naphthoquinone 30
2
9
(
85% isolated yield) (run 4, Table 5). However, its coupling
importance. Our research work aims also at developing
efficient catalyst systems for the cross-coupling of aryl
chlorides with activated and deactivated alkenes. Thus, the
catalytic activities of the benzothiazole-oxime Pd(II)-preca-
talysts 5 and 6 were tested in Heck–Mizoroki cross-coupling
reaction of aryl chlorides with styrene and tert-butyl acrylate
under various reaction conditions and the results are summa-
rized in Table 6. In contrast to its suitability for Suzuki–
Miyaura cross-couplings for aryl bromides, as shown above,
water as a solvent was not suitable enough for Heck–Mizor-
oki cross-coupling of aryl chlorides (runs 1 and 12 Table 6).
Tetrabutylammonium bromide is essential for the Heck–
with 3,4-methylenedioxyphenylboronic acid 27 under simi-
lar reaction conditions gave much lower yield (30% GC-con-
version) after longer time (15 h) (run 5, Table 5). Moreover,
2
-bromo-1,4-naphthoquinone 26 was smoothly coupled with
phenylboronic acid 12 and with 3,4-methylenedioxyphenyl-
boronic acid 27 in toluene under microwave irradiation
(
8 min) with complete conversion into the corresponding
2
4
-aryl-1,4-naphthoquinones 30 and 31 in high yields (runs
and 5, Table 5).
2
.5. Precatalysts 5 and 6 in Heck–Mizoroki
3
0
cross-coupling reactions of activated and
deactivated aryl chlorides
Mizoroki cross-coupling of aryl chlorides as shown in
Table 6 and its absence even with highly activated chlorides
and olefins (run 10) resulted in sharp decrease of the cou-
pling products regardless of the heating technique. Both
Pd-precatalysts 5 and 6 showed high activity for the Heck–
Mizoroki coupling of activated aryl chlorides 18 and 19
Palladium-catalyzed Heck–Mizoroki cross-coupling reac-
tions of aryl halides with alkenes have become one of the
most powerful tools in organic synthesis for the construction

9646
K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
Table 6. Heck–Mizoroki cross-coupling reaction of aryl chlorides
R
Cl
+
Pd-Cat. 5 or 6, 2 mol%
R
NaOH
X
X
18-21
32-37
a
a
Run
X/R
Pd-cat
Product
Thermal heating
Microwave heating
b
Yield %
b
Yield %
Time (h)
Time (min)
c
1
2
3
4
5
6
7
8
9
MeCO/Ph
MeCO/Ph
MeCO/Ph
5d
32
32
32
33
33
34
35
35
36
36
36
36
37
30
10
10
8
61
87
89 (83)
100 (96)
100
30
30
30
10
10
30
20
20
10
15
10
30
30
21
52
100 (88)
100 (98)
100
5
d
6
5
6
5
5
6
5
d
NO
NO
2
/Ph
/Ph
d
2
8
d
Me/Ph
MeCO/COO Bu
30
12
12
4
15
4
0
5
t
d
100 (83)
100
100 (82)
13
100 (88)
0
3
100 (77)
100
100 (95)
30
100 (96)
0
5
t
MeCO/COO Bu
d
t
/COO Bu
d
NO
NO
NO
NO
2
2
2
2
t
/COO Bu
e
5d
10
11
12
13
t
/COO Bu
6
t
/COO Bu
c
6d
15
10
t
Me/COO Bu
5
a
ꢀ
ꢀ
ꢀ
Condition: chloride/olefin/NaOH/TBAB¼1:1.5:3:0.6, DMF or water (3 mL), 100 C for thermal heating in water and 130 C in DMF; 150 C (200 W) for
microwave irradiation in water or DMF.
GC-yields; isolated yields are in parentheses.
Solvent: water with TBAB.
b
c
d
e
Solvent: DMF with TBAB.
Solvent: DMF without TBAB.
with both tert-butyl acrylate and styrene either thermal or
under microwave heating. Using DMF/TBAB cross-cou-
pling of 4-chloroacetophenone 18 with tert-butyl acrylate
was slightly better than with styrene although in all cases
high yields were obtained (runs 2, 3 and 7, 8, Table 6). Under
similar reaction conditions, the cross-coupling of 4-chloro-
nitrobenzene 19 with both tert-butyl acrylate and styrene re-
sulted, in all cases, in full conversion to the corresponding
disubstituted olefins in high yields (runs 4, 5 and 9, 11, Table
Table 7. Synthesis of 3-(b-styryl)-4-chromone via Heck–Mizoroki cross-
coupling
O
O
Ph
Br
Pd-Cat. 5 or 6
Ph
Et3N
O
O
25
38
a
a
Run Pd-cat Solvent
Thermal heating
Microwave heating
b
Time (h) Yield, % Time (min) Yield, %
b
6
). Heck–Mizoroki cross-coupling is, however, not effective
for 4-chlorotoluene 21 (runs 6 and 13, Table 6). Interestingly,
the cross-coupling reaction of aryl chlorides was highly
regio- and stereoselective and provided only the thermo-
dynamically more stable E-isomer of stilbene derivatives
1
2
3
5
5
6
Toluene 15
12
79
37
15
15
15
23
100 (86)
40
c
DMF
DMF
12
12
a
Conditions: 1 mmol of 3-bromochromone 25, 2 mmol of styrene, 3 mmol
ꢀ
3
2–33 and b-substituted tert-butyl acrylates 35–36 where
of Et
3
N, 3 mL solvent, 0.5 mol % Pd-precatalyst 5 or 6 at 110 C for
1
ꢀ
ꢀ
GC, GC–MS, and H NMR spectra of the crude reaction
mixture did not reveal any evidence for the formation of
Z-isomers.
conventional heating in toluene and 130 C in DMF; 150 C (200 W)
for microwave irradiation in toluene or DMF.
Isolated yields are given in parentheses.
The product was associated with the formation of 2-(a-styryl)-4-chro-
mone in 9%.
b
c
2.6. Precatalysts 5 and 6 in synthesis of 3-styryl-4-chro-
mone via Heck–Mizoroki cross-coupling reactions
Synthesis of 3-styryl-4-chromone could be easily conducted
through Heck–Mizoroki cross-coupling of 3-bromo-4-chro-
mone 25 (1 equiv) with styrene (1.5 equiv) using the pre-
catalyst 5 or 6 (0.5 mol %) in either toluene or DMF in the
presence triethylamine under thermal and microwave heat-
ing as shown in Table 7. Full conversion (86% isolated yield)
was obtained when DMF was used as solvent especially
under microwave irradiation in the presence of precatalyst
In conclusion, the benzothiazole-oxime-based palladium(II)
precatalysts 5 and 6 were found to be efficient and highly
active precatalysts for Suzuki–Miyaura and Heck–Mizoroki
cross-coupling reactions of activated aryl bromides and
chlorides and heterocyclic bromides, with very high TON,
under thermal heating as well as microwave irradiation con-
ditions. Deactivated aryl bromides were more effective for
both C–C cross-coupling reactions than their chloride ana-
logs. The immobilized catalyst 6 was found to have high
longevity compared with its mobilized one 5. The high turn-
over number associated with the catalytic activity of the
aforementioned precatalysts is highly important for mass
production in industrial scales.
5
(run 2, Table 7), the precatalyst 6 was, however, not
convenient and resulted in about 40% conversion under
both thermal as well as microwave heating (run 3, Table
7
). Toluene was not appropriate for similar cross-coupling
reaction neither thermal nor under microwave heating (run
, Table 7).
1

K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
9647
3
. Experimental
.1. Materials and methods
NMR spectra were recorded with a Bruker DPX-400 spec-
3.4. Effect of concentration of the palladium precatalyst
on the Suzuki–Miyaura cross-coupling in water under
thermal heating
5
3
A mixture of p-bromoacetophenone (1 mmol), phenylbor-
onic acid (1.2 mmol), TBAB (0.6 mmol), palladium catalyst
5 (1 mol %), KOH (2 mmol), and water (3 mL) was shaken
1
13
trometer at 400 MHz ( H NMR) and at 100 MHz ( C
NMR) using CDCl3 as solvent and internal standard
1
13
ꢀ
(
d¼7.26 and 77.36 ppm, for H NMR and C NMR, respec-
at 100 C under air for 2 h (monitored by GC). The same ex-
tively). Mass spectra (EI) were obtained at 70 eV with a type
VG autospec apparatus (Micromass). GC analyses were con-
ducted using an HPGC series 6890 Series Hewlett Packard
equipped with an SE-54 capillar column (25 m, Macherey–
Nagel) and an FID detector 19231 D/E. Melting points were
determined in open glass capillaries with a Gallenkamp ap-
paratus and are uncorrected. Microwave experiments were
carried out using a CEM Discover LabmateÔ microwave
apparatus (300 W with ChemDriverÔ Software). Commer-
cially available reagents and dry solvents were used as re-
periment was repeated using 0.5 mol % of palladium preca-
talyst. The amount (mol %) of the palladium precatalyst 5
was changed with respect to p-bromoacetophenone (0.1,
0.05, 0.01, 0.005, and 0.001 mol % Pd-catalyst with scales
of 1, 5, 10, 20 and 40 mmol of p-bromoacetophenone with
reaction times 2, 2, 2, 2.5 and 2.5 h, respectively). Finally,
the same reaction was repeated using 60 mmol of p-bromoa-
cetophenone and only 0.0007 mol % palladium complex 5
ꢀ
and the reaction mixture was heated for 2.5 h at 100 C un-
der air. The molar ratio of the reaction components was in all
cases as follows; p-bromoacetophenone/phenylboronic acid/
tetrabutylammonium bromide (TBAB)/KOH/water: 1:1.2:
0.6:2:2 mL. The conversion (in %) versus concentration of
palladium catalyst 5 is outlined in Table 1.
3
1
ceived. 2-Acetylbenzothiazole 7 and its oxime derivative
3
2
8
were prepared as reported in the literature.
.2. Preparation of Pd-precatalyst 5
3
A solution of sodium tetrachloropalladate (294 mg, 1 mmol)
in MeOH (2 mL) was added dropwise to a stirred solution of
3.5. Effect of concentration of the palladium precatalysts
5 and 6 for the Suzuki–Miyaura coupling of deactivated
aryl bromides in water with thermal heating
1
-(benzothiazol-2-yl)ethanone oxime (8) (192 mg, 1 mmol)
in dioxane/methanol (4 mL, 1:1 v/v). After stirring for 2 h,
the yellow precipitate was filtered off, washed with methanol
then with water, and dried in vacuum over P O . The pre-
A mixture of p-bromoanisole (1 mmol), phenylboronic
acid (1.2 mmol), tetrabutylammonium bromide (TBAB)
(0.6 mmol), palladium precatalyst 5 (0.5 mol %), K CO
2
5
catalyst 5 (Scheme 1) was obtained as a yellow powder
2
3
1
ꢀ
(
339 mg, 90%) after recrystallization from DMSO. The H
NMR spectrum revealed the presence of two isomers in a
(2 mmol), and distilled water (2 mL) was shaken at 100 C
under air for 4 h. The same experiment was repeated and
the amount (mol %) of the palladium precatalyst 5 was
changed with respect to p-bromoanisole (0.05, 0.005 and
0.001 mol % Pd-catalyst with scales of 5, 10 and 20 mmol
of p-bromoanisole with reaction time, in all cases, 4 h).
The molar ratio of the reaction components was in all cases
as follows; p-bromoanisole/phenylboronic acid/tetrabutyl-
ammonium bromide (TBAB)/K CO /water: 1:1.2:0.6:
ꢀ
1
ratio of about 13:1. Mp>300 C; H NMR (DMSO-d ) d
6
2
2
1
.34 (s, 3H, CH ), 7.46–7.55 (m, 2H, ArH), 8.03–8.08 (m,
3
H, ArH), 12.26 (s, 1H, OH); C NMR d 11.9, 123.1,
23.9, 127.1, 127.2, 134.9, 152.3, 153.6, 167.0. Anal. Calcd
1
3
for C H Cl N OPdS: C, 29.25; H, 2.18; N, 7.58. Found: C,
2 2
9
8
2
9.14; H, 2.40; N, 7.59.
2
3
3
.3. Preparation of Pd-precatalyst 6
2:2 mL. The conversion (in %) versus concentration of pal-
ladium catalyst 5 is outlined in Table 2. The reaction product
was extracted with EtOAc (3ꢂ30 mL). The combined or-
To a mixture of glass/polymer composite shaped Raschig
rings 9 (10 g, 5 mmol) containing 10% chloromethylpolys-
tyrene–divinylbenzene polymer (0.53 mmol polymer/g
Raschig rings) and 1-(benzothiazol-2-yl)ethanone oxime 8
ganic extracts were dried over anhydrous MgSO , filtered,
4
and the solvent was evaporated under reduced pressure.
The product was purified by flash column chromatography
on silica gel using EtOAc/petroleum ether (1:20) as an eluant.
(
1.92 g, 10 mmol) in dimethylformamide (DMF) (50 mL),
sodium hydride (0.72 g, 60% in oil, 30 mmol) was added
portionwise over a period of 20 min. The mixture was shaken
at 80 C for 3 days then cooled to room temperature and
quenched with water (100 mL). The Raschig rings were
filtered and washed successively with DMF, water, ethanol,
dichloromethane, and again with ethanol (20 mL, each
time), and finally well-dried under vacuum These well-dried
Raschig rings 10 (10.934 g) were added to a solution of
sodium tetrachloropalladate (1.8 g, 6 mmol) in methanol
Similarly, a mixture of p-bromotoluene (1 mmol), phenyl-
boronic acid (1.2 mmol), tetrabutylammonium bromide
(TBAB) (0.6 mmol), palladium precatalyst 5 or 6 (0.5 or
0.05 mol %), K CO (2 mmol), and distilled water (2 mL)
was shaken at 100 C under air for 6 h. The conversion (in
%) versus palladium catalysts is outlined in Table 2. The
product was purified as above.
ꢀ
2
3
ꢀ
(
80 mL) and the mixture was left to be shaken at room tem-
3.6. Longevity of the palladium precatalysts
5 and 6 with thermal heating in water
perature for additional 3 days. The resulting Raschig rings
were dried in vacuo and the loading of catalyst 6 was esti-
mated to be ca. 0.07 mmol/g Raschig rings according to
weight increase (the weight increase of each single Raschig
ring was determined; each ring was loaded with about
A mixture of p-bromoacetophenone (5 mmol), phenylbor-
onic acid (6 mmol), TBAB (3 mmol), palladium catalyst 5
or 6 (0.5 mol %), K CO (10 mmol), and water (10 mL)
2
3
ꢀ
2
tions).
mol % palladium with reference to 1 mmol scaled reac-
was shaken at 100 C under air for 2 h, where all p-bromo-
acetophenone was completely consumed (GC-monitored).
2
0

9648
K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
At this point, fresh portions of the coupling partners and the
base (the same amounts as for the first run) were added to the
flask thus repeating the reaction. In this manner, four succes-
sive runs were carried out with the same portion of precata-
lyst 5 or 6 as shown in Table 3. Finally the product was
purified by flash column chromatography on silica gel using
EtOAc/petroleum ether (1:10) as an eluant.
3.10. Suzuki–Miyaura coupling in the synthesis of
3-aryl-4-chromone and 1,4-naphthoquinone
derivatives with thermal heating
To a mixture of 3-bromo-4-chromone 25 or 2-bromo-1,4-
naphthoquinone 26 (1 mmol) and the appropriate arylbor-
onic acid 12 or 17 (1.2 mmol) dissolved in toluene (3 mL)
in the presence of K CO (0.28 g, 2 mmol), palladium preca-
2
3
3
.7. Effect of mol % of precatalysts 5 and 6 for the
talyst 5 (0.5 mol %) was added. The reaction mixture was
then heated to reflux temperature with stirring for a period
of 4–15 h, and the reaction flask was then allowed to cool
to room temperature. The reaction mixture was extracted
three times with EtOAc (60 mL total) and then the organic
fractions were combined together, dried over Na SO , fil-
tered, and then the solvent was removed under vacuum.
The residue was then subjected to separation via flash col-
umn chromatography with petroleum ether/EtOAc (10:1)
as an eluant to give the pure products 28–31.
Suzuki–Miyaura coupling of deactivated aryl
bromides in water with thermal heating
A mixture of p-bromoanisole (1 mmol), phenylboronic acid
(
(
(
1.2 mmol), tetrabutylammonium bromide (TBAB)
0.6 mmol), palladium precatalyst 5 (0.5 mol %), K CO
2 mmol), and distilled water (2 mL) was shaken at 100 C
2
4
2
3
ꢀ
under air for 4 h. The same experiment was repeated and
the amount (mol %) of the palladium precatalyst 5 was
changed with respect to p-bromoanisole (0.05, 0.005 and
0
.001 mol % Pd-catalyst with scales of 5, 10 and 20 mmol
3.11. Suzuki–Miyaura coupling in the synthesis of
3-aryl-4-chromone and 1,4-naphthoquinone
derivatives with microwave heating
of p-bromoanisole with reaction time, in all cases, 4 h).
The molar ratio of the reaction components were in all cases
as follows; p-bromoanisole/phenylboronic acid/tetrabutyl-
ammonium bromide (TBAB)/K CO /water: 1:1.2:0.6:2:
To a mixture of 3-bromo-4-chromone 25 or 2-bromo-1,4-
naphthoquinone 26 (1 mmol) and the appropriate aryl-
boronic acid 12 or 17 (1.2 mmol), K CO (2 mmol) and
2
3
2
mL. The conversion (in %) versus concentration of palla-
dium catalyst 5 is outlined in Table 2. The reaction product
was extracted with EtOAc (3ꢂ30 mL). The combined or-
2
3
palladium precatalyst 5 (0.5 mol %) in toluene (3 mL)
were thoroughly mixed in a process vial. The vial was cap-
ped properly, and thereafter the mixture was heated under
ganic extracts were dried over anhydrous MgSO , filtered,
4
and the solvent was evaporated under reduced pressure.
The product was purified by flash column chromatography
on silicagel using EtOAc/petroleum ether(1:20)as an eluant.
ꢀ
microwave irradiation conditions at 150 C and 200 W for
8 min, and then the process vial was allowed to cool to
room temperature. The reaction mixture was extracted three
times with EtOAc (60 mL total) and then the organic frac-
tions were combined together, dried over Na SO , filtered,
3.8. General procedure for the Suzuki–Miyaura
coupling of aryl chlorides in water with thermal heating
2
4
and then the solvent was removed under vacuum. The pure
products were obtained as described above.
A mixture of the appropriate aryl chlorides 18–21 (1 mmol),
phenylboronic acid 12 (1.2 mmol), tetrabutylammonium
bromide (TBAB) (0.6 mmol), palladium precatalyst 5 or 6
3.12. General procedure for the Heck–Mizoroki
coupling of aryl chlorides with thermal heating
(
(
1, 0.2 or 0.02 mol %), NaOH (2 mmol), and distilled water
ꢀ
2 mL) was shaken at 100 C under air for 4–20 h (GC-mon-
itored) as outlined in Table 4. The product was extracted
with EtOAc (3ꢂ20 mL). The combined organic extracts
A mixture of the appropriate aryl chloride (1 mmol), the ap-
propriate olefin (1.5 mmol), TBAB (0.6 mmol), precatalyst
5 or 6 (2 mol %), and sodium hydroxide (3 mmol) in water
were dried over anhydrous MgSO , filtered, and the solvent
4
ꢀ
was evaporated under reduced pressure. The product was pu-
rified with flash column chromatography as described above.
or DMF (3 mL) was shaken at 100 C (for water as solvent)
ꢀ
or at 130 C (for DMF as solvent) under air for the given re-
action time listed in Table 6. After the reaction was almost
completed (monitored by GC), the reaction mixture was
cooled to room temperature The reaction mixture was ex-
tracted three times with EtOAc (60 mL total) and then the or-
ganic fractions were combined together, dried over Na SO ,
filtered, and then the solvent was removed under vacuum.
The residue was then subjected to purification via flash
column chromatography with petroleum ether/EtOAc
(10:1) as an eluant to give the pure products 32–36.
3.9. General procedure for the Suzuki–Miyaura cou-
pling of aryl chlorides in water with microwave heating
A mixture of the appropriate aryl chlorides 18–21 (1 mmol),
phenylboronic acid (1.2 mmol), tetrabutylammonium bro-
mide (TBAB) (0.6 mmol), palladium precatalyst 5 or 6
2
4
(
(
1, 0.2 or 0.02 mol %), NaOH (2 mmol), and distilled water
2 mL) was mixed in a process vial. The vial was capped
properly, and thereafter the mixture was heated under micro-
ꢀ
wave irradiation conditions at 160 C and 250 W for the ap-
3.13. General procedure for the Heck–Mizoroki
coupling of aryl chlorides under microwave irradiation
propriate reaction time 7–30 min as listed in Table 4. After
the reaction was almost complete (monitored by GC), the
reaction mixture was extracted with EtOAc (3ꢂ20 mL).
The combined organic extracts were dried over anhydrous
MgSO , filtered, and the solvent was evaporated under re-
4
duced pressure. The product was purified with flash column
chromatography as described above.
To a mixture of the appropriate aryl chloride (1 mmol) and
the appropriate olefin (1.5 mmol), TBAB (0.6 mmol), preca-
talyst 5 or 6 (2 mol %), and sodium hydroxide (3 mmol) in
water or DMF (3 mL) were mixed in a process vial. The
vial was capped properly, and thereafter the mixture was

K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
9649
ꢀ
00 W in either solvents for the appropriate reaction time as
listed in Table 6. The products were purified as described
above.
heated under microwave irradiation conditions at 150 C and
2
NMR d 118.4, 124.9, 125.6, 125.7, 126.8, 128.5, 128.8,
129.3, 132.2, 133.9, 153.4, 156.5, 176.5; MS (m/e) 222
(M ), 194, 165, 120, 111, 92, 82, 76.
+
3
Pale yellow powder, mp 156–158 C; H NMR (CDCl )
.14.7. 3-(3,4-Methylenedioxyphenyl)-4-chromone (29).
ꢀ
1
3
.14. General procedure for the Heck–Mizoroki
3
synthesis of 3-styryl-4-chromone under thermal
and microwave heating
d 5.99 (s, 2H, –OCH O–), 6.86 (d, 1H, J¼8.04 Hz), 6.98 (dd,
2
1H, J¼8.04, 1.76 Hz), 7.1 (d, 1H, J¼1.76 Hz), 7.39–7.48
(
m, 2H), 7.65–7.69 (m, 1H), 7.98 (s, 1H), 8.28 (m, 1H);
1
3
A mixture of 3-bromo-4-chromone 25 (1 mmol), styrene
(1.5 mmol), precatalyst 5 or 6 (0.5 mol %), and triethyl-
amine (3 mmol) in toluene or DMF (3 mL) was shaken at
C NMR d 101.5, 106.9, 108.7, 110, 118.3, 122.7, 124.7,
125.4, 125.5, 125.9, 126.7, 133.9, 148, 148.1, 153, 156.5,
176.6; MS (m/e) 266 (M ), 209, 180, 146, 118, 104, 88, 76.
Anal. Calcd for C H O : C, 72.18; H, 3.79. Found: C,
71.74; H, 3.93.
+
ꢀ
ꢀ
1
10 C (for toluene as solvent) or at 130 C (for DMF as
1
6 10 4
solvent) under air for 12 or 15 h as listed in Table 7. Similar
components were also mixed in the same ratio in a process
vial. The vial was capped properly, and thereafter the mix-
3.14.8. 2-Phenyl-1,4-naphthoquinone (30). Yellow crys-
tals, mp 106–108 C (Ref. 39, mp is not mentioned); H
ꢀ
NMR (CDCl ) d 7.08 (s, 1H), 7.46–7.57 (m, 3H), 7.58–
1
ture was heated under microwave irradiation conditions at
ꢀ
1
50 C and 200 W in either solvents for 15 min. The reaction
3
1
3
mixture, in both case, was cooled to room temperature then
extracted three times with EtOAc (60 mL total) and the or-
ganic fractions were combined together, dried over Na SO ,
filtered, and then the solvent was removed under vacuum.
The residue was then subjected to purification via flash
column chromatography with petroleum ether/EtOAc
7.59 (m, 2H), 7.75–7.80 (m, 2H), 8.11–8.15 (m, 2H);
C
NMR d 126.3, 127.4, 128.8, 129.8, 130.4, 132.4, 132.8,
133.7, 134.1, 134.2, 135.6, 148.5, 184.7, 185.5; MS (m/e)
234 (M ), 206, 178, 151, 129, 105, 89, 76.
2
4
+
3.14.9. 2-(3,4-Methylenedioxyphenyl)-1,4-naphthoqui-
ꢀ
1
(
10:1) as an eluant to give the pure product 38.
none (31). Orange-red crystals, mp 184–186 C; H NMR
(
CDCl ) d 6.04 (s, 2H, –OCH O–), 6.90 (d, 1H, J¼8 Hz),
3
2
0
19–120 C (Ref. 33, mp 118–120 C); H NMR (CDCl )
3
1
.14.1. 4-Acetyl-1,1 -biphenyl (13). Colorless crystals, mp
7.02 (s, 1H), 7.09–7.13 (m, 2H), 7.75–7.78 (m, 2H), 8.09–
8.16 (m, 2H); C NMR d 101.9, 108.9, 110.1, 124.4, 126.2,
127.4, 127.5, 132.4, 132.8, 134.1, 134.2, 134.5, 147.8, 148.2,
149.8, 184.9, 185.4; MS (m/e) 278 (M ), 248, 220, 192, 163,
124, 104, 76. Anal. Calcd for C H O : C, 73.38; H, 3.62.
1
Found: C, 73.03; H, 3.48.
ꢀ
d 2.64 (s, 3H, CH CO), 7.36–7.42 (m, 1H), 7.46–7.49 (m,
ꢀ
1
13
3
3
+
2
2
1
H), 7.62–7.65 (m, 2H), 7.69 (d, 2H, J¼8.52 Hz), 8.03 (d,
1
3
H, J¼8.52 Hz); C NMR d 27.0, 127.5, 127.6, 128.6,
7 10 4
29.2, 129.3, 136.2, 140.2, 146.1, 198.1; MS (m/e) 196
+
(
M ), 181, 152, 127, 102, 91, 76.
3.14.10. (E)-4-Acetylstilbene (32). Colorless crystals, mp
143–144 C (Ref. 40, mp 141–142 C); H NMR (CDCl )
0
mp 87–88 C (Ref. 34, mp 86–87 C); H NMR (CDCl )
ꢀ
ꢀ
1
3
.14.2. 4-Methoxy-1,1 -biphenyl (16). Pale yellow powder,
3
ꢀ
d 3.87 (s, 3H, –OCH ), 6.99–7.02 (m, 2H), 7.31–7.59 (m,
ꢀ
1
d 2.58 (s, 3H, CH CO), 7.10 (d, 1H, J¼16.4 Hz), 7.20 (d,
3
3
1H, J¼16.4 Hz), 7.27–7.31 (m, 1H), 7.36 (m, 2H), 7.51–
13
3
1
3
7
1
8
H); C NMR d 55.7, 114.5, 126.9, 127.1, 128.5, 129.1,
34.1, 141.2, 159.5; MS (m/e) 184 (M ), 169, 141, 115,
9, 76, 63.
7.53 (m, 2H), 7.56 (d, 1H, J¼8.4 Hz), 7.93 (d, 1H,
+
J¼8.4 Hz); C NMR d 26.9, 126.8, 127.1, 127.7, 128.6,
129.1, 129.2, 131.7, 136.2, 136.9, 142.3, 197.7; MS (m/e)
222 (M ), 207, 178, 152, 103, 89, 76, 63, 51.
+
0
4–45 C (Ref. 35, mp 43.5–44.5 C); H NMR (CDCl )
3
4
.14.3. 4-Methyl-1,1 -biphenyl (17). White crystals, mp
ꢀ
d 2.41 (s, 3H, –CH ), 7.25–7.60 (m, 9H); C NMR d 21.4,
ꢀ
1
3.14.11. (E)-4-Nitrostilbene (33). Yellow powder, mp 146–
ꢀ
3
1
3
ꢀ
1
148 C (Ref. 41, mp 140 C); H NMR (CDCl ) d 7.13 (d,
3
3
1
(
27.31, 127.32, 127.34, 129.1, 137.4, 138.7, 141.5; MS
m/e) 168 (M ), 152, 139, 115, 91, 82, 63.
1H, J¼16.4 Hz), 7.26 (d, 1H, J¼16.4 Hz), 7.32–7.36 (m,
+
1H), 7.39–7.42 (m, 2H), 7.54–7.56 (m, 2H), 7.61 (d, 2H,
J¼8.52 Hz), 8.21 (d, 2H, J¼8.52 Hz); C NMR d 124.4,
1
3
0
07–108 C (Ref. 36, mp 107.5–108.5 C); H NMR
3
1
.14.4. 4-Nitro-1,1 -biphenyl (22). Pale yellow powder, mp
ꢀ
126.5, 127.1, 127.3, 129.1, 129.2, 133.6, 136.4, 144.1, 147;
MS (m/e) 225 (M ), 195, 178, 165, 152, 102, 89, 76, 63, 51.
ꢀ
1
+
(
2
1
CDCl ) d 7.41–7.55 (m, 3H), 7.61–7.75 (m, 4H), 8.29 (d,
3
+
H, J¼8.78 Hz); MS (m/e) 199 (M ), 169, 141, 127, 115,
3.14.12. (E)-tert-Butyl 3-(4-acetylphenyl)prop-2-enoate
(35). Yellowish-white crystals, mp 99–100 C (Refs. 24,
ꢀ
2, mp is not mentioned); H NMR (CDCl ) d 1.54 (s, 9H,
01, 76, 63.
1
4
3
3
9
7
.14.5. 4-Phenylbenzonitrile (23). White solid, mp 91–
2 C (Ref. 37, mp is not mentioned); H NMR (CDCl ) d
C(CH ) ), 2.61 (s, 3H, CH CO), 6.46 (d, 1H, J¼
3
4
3
ꢀ
.41–7.51 (m, 3H), 7.58–7.61 (m, 2H), 7.67–7.74 (m, 4H);
1
16.04 Hz), 7.58 (d, 1H, J¼16.04 Hz), 7.60 (d, 2H, J¼
3
1
3
8.52 Hz), 7.95 (d, 2H, J¼8.52 Hz); C NMR d 26.9, 28.3,
1
3
C NMR d 111.2, 119.3, 127.5, 128, 128.9, 129.4, 132.9,
39.5, 145.9; MS (m/e) 179 (M ), 164, 151, 126, 100, 76, 63.
81.2, 123.1, 128.3, 129.1, 138.1, 139.4, 142.3, 166.1, 197.6;
MS (m/e) 246 (M ), 190, 175, 147, 131, 102, 91, 79, 57.
+
+
1
3.14.6. 3-Phenyl-4-chromone (isoflavone) (28). White
powder, mp 132–133 C (Ref. 38, mp 131.5–132 C); H
3.14.13. (E)-tert-Butyl 3-(4-nitrophenyl)prop-2-enoate
(36). White crystals, mp 144–146 C (Ref. 43, mp is not
ꢀ
NMR (CDCl ) d 7.39–7.49 (m, 5H), 7.56–7.58 (m, 2H),
ꢀ
1
ꢀ
mentioned); H NMR (CDCl ) d 1.54 (s, 9H, C(CH ) ),
1
3
3
3 4
1
3
7
.59–7.70 (m, 1H), 8.03 (s, 1H), 8.35–8.36 (m, 1H);
C
6.48 (d, 1H, J¼16.04 Hz), 7.60 (d, 1H, J¼16.04 Hz), 7.64

9650
K. M. Dawood / Tetrahedron 63 (2007) 9642–9651
1
3
(
2
d, 2H, J¼8.84 Hz), 8.23 (d, 2H, J¼8.84 Hz); C NMR d
11. (a) Bedford, R. B.; Cazin, C. S. J.; Hazelwood, S. L. Angew.
Chem., Int. Ed. 2002, 41, 4120–4122; (b) Littke, A. F.; Fu,
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13. (a) Blaser, H.-U. Chem. Commun. 2003, 293–296; (b) Blaser,
H.-U.; Siegrist, U.; Steiner, H. M. Fine Chemicals Through
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8.4, 81.7, 124.5, 124.9, 128.8, 140.9, 141.2, 148.7, 165.6;
MS (m/e) 249 (M ), 234, 194, 176, 146, 130, 102, 90, 76, 57.
+
3.14.14. (E)-3-(b-Styryl)-4-chromone (38). Yellowish-
ꢀ
white powder, mp 169–170 C (Ref. 44, mp 170–171 C);
ꢀ
1
H NMR (CDCl ) d 6.98 (d, 1H, J¼16.32 Hz), 7.25–7.29
3
(
m, 1H), 7.34–7.38 (m, 2H), 7.41–7.54 (m, 4H), 7.63 (d, 1H,
J¼16.32 Hz), 7.65–7.69 (m, 1H), 8.1 (s, 1H), 8.31–8.36 (m,
1
3
1
1
H); C NMR d 118.4, 119.4, 122.2, 124.4, 125.6, 126.6,
26.9, 128.2, 128.9, 132, 133.9, 137.7, 153.4, 156.2, 176.9;
MS (m/e) 248 (M ), 231, 189, 171, 155, 128, 115, 92, 77, 63.
+
1
4. (a) Desai, B.; Kappe, C. O. Kirschning, A., Ed.; Top. Curr.
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Acknowledgements
The author is very thankful to Prof. Dr. A. Kirschning, Insti-
tute of Organic Chemistry, University of Hanover, for provid-
ing polymer glass composite material, arylboronic acids, and
sod tetrachloropalladate. He is also deeply indebted to the
Alexander-von-Humboldt (AvH) Foundation for donating
him a CEM Discover LabmateÔ microwave apparatus.
15. (a) Li, C. J.; Chan, T. H. Organic Reactions in Aqueous Media;
Wiley: New York, NY, 1997; (b) Organic Synthesis in Water;
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