Polystyrene-supported zinc bromide-ethylenediamine complex as a reusable and highly efficient heterogeneous catalyst for the synthesis of α,β-acetylenic ketones

Article abstract of DOI:10.1055/s-0030-1258365

A polystyrene-supported zinc bromide-ethylenediamine complex was shown to be useful as a recyclable heterogeneous catalyst for the rapid and efficient synthesis of ,-acetylenic ketones in good-to-excellent yields by cross-coupling of acid chlorides with t

Full text of DOI:10.1055/s-0030-1258365

PAPER
325
Polystyrene-Supported Zinc Bromide–Ethylenediamine Complex as a
Reusable and Highly Efficient Heterogeneous Catalyst for the Synthesis of
a,b-Acetylenic Ketones
Ali Keivanloo,* Mohammad Bakherad, Bahram Bahramian, Mahrokh Rahmani, Sayed Ali Naghi Taheri
School of Chemistry, Shahrood University of Technology, Shahrood, Iran
Fax +98(273)3395441; E-mail: akeivanloo@yahoo.com; E-mail: keivanloo@shahroodut.ac.ir
Received 4 October 2010
chlorides with terminal alkynes under aerobic condi-
tions.14 Here, we describe a copper- and palladium-free
method for the preparation of a,b-acetylenic ketones by
means of zinc-catalyzed reactions of terminal alkynes
Abstract: A polystyrene-supported zinc bromide–ethylenediamine
complex was shown to be useful as a recyclable heterogeneous cat-
alyst for the rapid and efficient synthesis of a,b-acetylenic ketones
in good-to-excellent yields by cross-coupling of acid chlorides with
terminal alkynes. The catalyst is easily prepared, stable, reusable, with various acyl chlorides in the presence of a polysty-
and efficient under the reaction conditions.
rene-supported zinc bromide–ethylenediamine complex
as a heterogeneous catalyst under aerobic conditions
(Scheme 1).
Key words: heterogeneous catalysis, cross-coupling, acid chlo-
rides, alkynes, ketones
[PS-en-ZnBr2] (6 mol%)
O
O
toluene, pyridine
R2
CH
a,b-Acetylenic ketones are important intermediates in or-
ganic synthesis,1 and because of their bifunctional electro-
philicity they have found a broad range of applications as
three-carbon building blocks for the synthesis of hetero-
cycles. Efficient, mild, and catalytic methods for their
preparation are therefore highly desirable. A common
route for preparing these compounds involves the catalyt-
ic acylation of a terminal alkyne2 with an acid chloride or
the reaction of an alkynyl organometallic reagent, such as
a silver,3 copper,4 sodium,5 lithium,6 cadmium,7 zinc,8 sil-
icon,9 or tin10 reagent, with an acid chloride. Another
method for the preparation of a,b-acetylenic ketones uti-
lizes the coupling reaction of a terminal alkyne or a meta-
lated derivatives thereof with an organic halide in the
presence of carbon monoxide and a transition-metal cata-
lyst, a reaction that is known as the carbonylative
Sonogashira coupling rection.11 Carbonylations of aryl
halides usually require carbon monoxide or a suitable
source thereof, such as molybdenum hexacarbonyl. Most
of the reported methods, however, have some drawbacks,
such as low yields, the use of toxic or expensive reagents,
or long reaction times.
+
R1
R1
Cl
1
2
R2
3
PS-en-ZnBr2 = polystyrene-supported ethylenediamine–ZnBr2 complex
Scheme 1
We used chloromethylated polystyrene crosslinked with
2% of divinylbenzene as the support because it sufficient-
ly flexible and because metallic atoms can be grafted to it
through ligands attached to the polymer beads. Treatment
of the polystyrene resin with ethylenediamine in refluxing
acetonitrile, followed by treatment of the resulting ami-
nated polystyrene with a solution of zinc(II) bromide in
ethanol resulted in covalent attachment of zinc to give the
required polymer-supported zinc complex (Scheme 2).
Cl
MeCN, NaI
+
N
H
NH2
reflux, 48 h
ZnBr2
EtOH
reflux, 6 h
H2N
NH2
The use of heterogeneous catalysts in coupling reactions
leads to a reduction in waste. Furthermore, the catalysts
can be conveniently handled and separated from the reac-
tion mixture, making the experimental procedure simple
and eco-friendly. Highly active polymer-supported transi-
tion metal complexes have attracted considerable atten-
tion because they can be easily recovered and reused.12As
part of our continuing interest in palladium-catalyzed
cross-coupling reactions,13 we recently developed a mild
protocol for the copper-free coupling reaction of acid
HN
NH2
Zn
Br
Br
A
Scheme 2
The successful functionalization of the polymer was con-
firmed by means of elemental analysis. The nitrogen con-
tent of resin was 2.42% (0.82 mmol/g, indicating that only
58% of all the chlorine atoms were replaced by amine
groups). The metal loading of polymer-supported zinc
complex, as determined by inductively coupled plasma
atomic-emission spectrometry, was 1.76% (0.29 mmol/g).
SYNTHESIS 2011, No. 2, pp 0325–0329
x
x
.
x
x
.2
0
1
0
Advanced online publication: 15.12.2010
DOI: 10.1055/s-0030-1258365; Art ID: P15010SS
© Georg Thieme Verlag Stuttgart · New York

326
A. Keivanloo et al.
PAPER
In the IR spectrum of polymer-bound ethylenediamine, a shown in Table 2, increasing the amount of palladium cat-
sharp C–Cl peak (corresponding to –CH2Cl groups) at 670 alyst shortened the reaction time, but did not increase the
cm–1 and the strong peak at 1260 cm–1 (corresponded to yield of product (entry 6). A low zinc concentration led to
the H–C–Cl wagging modes in the starting polymer) were a long reaction time (entry 7). The optimum conditions for
practically eliminated or were seen as a weak bands after the coupling reaction were 0.6 mol% of catalyst in toluene
the introduction of ethylenediamine and zinc onto the as solvent with pyridine as the base at room temperature
polymer. This confirmed that a metal complex was (entry 3).
formed on the surface of the polymer.
Table 2 Copper-Free and Palladium-Free Coupling Reaction of
Benzoyl Chloride with Phenylacetylene in the Presence of Various
Amount of the Catalyst for Different Reaction Times
The catalytic activity of complex A (6 mol%) was studied
at room temperature under aerobic conditions for the cou-
pling of phenylacetylene with benzoyl chloride, and the
conditions for the reaction were optimized (Table 1).
Entry
ZnBr2 complex (mmol) Time (min)
Yield (%)b
The reaction was significantly affected by the nature of
the solvent and the base that were used. Of the solvents
tested, toluene was to be the most suitable, and of the
bases used, pyridine was the optimal choice (entry 20). As
1
2
3
4
5
6
7
0.06
0.06
0.06
0.06
0.03
0.12
0.03
10
20
45
78
96
96
70
96
85
40
Table 1 Polystyrene-Supported Zinc Bromide Ethylenediamine
Complex-Catalyzed Coupling of Benzoyl Chloride (1a) with Phenyl-
acetylene in the Presence of Various Bases and Solvents
60
40
Entrya
1
Solvent
MeCN
MeCN
MeCN
MeCN
THF
Base
DIPEA
Et3N
py
Yield (%)b
80
30
100
a Reaction conditions: BzCl (1.2 mmol), PhC≡CH (1.0 mmol), py (1.2
2
62
mmol), catalyst, r.t.
b By GC.
3
83
4
NMP
DIPEA
Et3N
py
85
5
45
To examine the scope of the coupling reaction, we cou-
pled a variety of terminal alkynes 2 with various acid
chlorides 3 containing electron-withdrawing or electron-
donating groups. As shown in Table 3, the coupling reac-
tions proceeded under very mild conditions to give the
corresponding products in excellent yields.
6
THF
20
7
THF
34
8
DMF
DIPEA
Et3N
py
75
9
DMF
58
The stability of the polystyrene-supported zinc bromide
ethylenediamine complex was studied by recycling the
catalyst for a subsequent reaction of benzoyl chloride with
phenylacetylene. The catalyst was separated from the re-
action mixture by filtration after each experiment, then
washed with chloroform and acetonitrile, and dried care-
fully before use in subsequent runs. Compound 1a was
obtained in 91% yield when catalyst that was recycled for
the fifth time was used (Table 4, entry 3).
10
11
12
13
14
15
16
17
18
19
20
21
DMF
83
DMF
NMP
DIPEA
Et3N
py
90
1,4-dioxane
1,4-dioxane
1,4-dioxane
30
48
40
c
–
DIPEA
Et3N
py
46
In conclusion, we prepared polystyrene-supported zinc
bromide–ethylenediamine complex for use as a reusable
heterogeneous catalyst for a copper- and palladium-free
synthesis of a,b-acetylenic ketones at room temperature
through coupling of various acid chlorides with terminal
alkynes under aerobic conditions. The simple procedure,
short reaction times, high selectivity, and excellent isolat-
ed yields make this method well-suited to the generation
of combinatorial libraries of a,b-acetylenic ketones.
c
–
53
py
89
c
–
NMP
Et3N
py
42
toluene
toluene
toluene
88
96
DIPEA
91
a Reaction conditions: BzCl (1.2 mmol), PhC≡CH (1.0 mmol), base
Melting points were determined using a Barned Electrothermal and
are uncorrected. IR spectra in KBr were recorded on a Shimadzu
Model 460 spectrophotometer. 1H NMR and 13C NMR spectra were
recorded on a Bruker BRX 500 Avance (500 MHz) spectrometer in
(1.2 mmol), solvent (1 mL), catalyst (0.06 mmol), r.t., aerobic condi-
tions.
b By GC.
c Neat.
Synthesis 2011, No. 2, 325–329 © Thieme Stuttgart · New York

PAPER
Heterogeneous Catalyst for the Synthesis of a,b-Acetylenic Ketones
327
Table 3 Copper-Free and Palladium-Free Coupling Reactions of
Table 4 Copper-Free and Palladium-Free Coupling Reactions of
Benzoyl Chloride with Phenylacetylene Catalyzed Using Recycled
Various Acyl Chlorides with Terminal Alkynesa
Catalyst
O
O
[PS-en-ZnBr2] (6 mol%)
toluene, pyridine
+
R2
CH
Entrya
No. of cycles
Yield (%)b
R1
Cl
R1
1
2
3
R2
1
2
3
1
3
5
96
94
91
Entrya
1
R1
Ph
R2
Product Yield (%)b
3a
Ph
96
82
94
98
80
78
75
80
79
95
98
92
94
85
98
99
94
91
78
86
96
94
88
93
a Reaction conditions: BzCl (1.2 mmol), PhC≡CH (1.0 mmol), py (1.2
mmol), catalyst (0.06 mmol), r.t., aerobic conditions.
b GC yield
2
4-MeC6H4
2,4-Cl2C6H3
4-ClC6H4
2-ClC6H4
4-MeOC6H4
4-BrC6H4
2-MeC6H4
2-IC6H4
Ph
3b
3c
3d
3e
3f
3
Ph
4
Ph
5
Ph
1:1 MeOH–H2O (5 × 40 mL), and Et2O (3 × 40 mL), then dried in
an oven.
6
Ph
Polymer-Bound Ethylenediamine Zinc Complex
7
Ph
3g
3h
3i
The functionalized polymer was steeped in EtOH (100 mL) for 30
min. A soln of ZnBr2 (0.50 g) in EtOH (10 mL) was then added, and
the mixture was heated to 50 °C for 6 h. The metal complex-impreg-
nated polymer was filtered off, washed thoroughly with EtOH (2 ×
30 mL), and finally dried in vacuum at 70 °C for 24 h.
8
Ph
9
Ph
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3-O2NC6H4
4-O2NC6H4
2-MeC6H4
4-MeOC6H4
2-ClC6H4
Cy
Ph
3j
a,b-Acetylenic Ketones 3: General Procedure
Ph
3k
3l
A test tube was charged with the acyl chloride (1.2 mmol), the ter-
minal alkyne (1.0 mmol), the Zn complex catalyst (0.2 g, 0.06
mmol), and pyridine (1.2 mmol). The mixture was then stirred at r.t.
for 30 min under aerobic conditions. Upon completion of the reac-
tion, the mixture was extracted with EtOAc (3 × 5 mL). The com-
bined organic layers were washed with H2O (2 × 5 mL) to remove
the pyridinium hydrochloride that formed. The organic layer was
separated, dried (MgSO4), filtered, and concentrated in vacuum to
give a crude product that was further purified by column chroma-
tography [hexane–EtOAc (20:1)].
Bu
Bu
3m
3n
3o
3p
3q
3r
3s
Bu
Bu
2-thienyl
Cy
Bu
Compounds 3b,15a 3e,15b 3g,15c 3h,15a 3j,15d 3k,2g 3l,15a 3n,14a 3o,15a
3p,15e 3r,15f 3s,15g and 3u15a are known. Analytical data for
3a,c,d,f,i,m,q,t,v–x are given below.
(CH2)4Me
(CH2)4Me
(CH2)5Me
(CH2)5Me
(CH2)5Me
(CH2)5Me
Pr
2-thienyl
4-ClC6H4
4-O2NC6H4
Cy
1,3-Diphenylprop-2-yn-1-one (3a)
Yellow oil.
IR (neat): 2201, 1643 cm–1.
1H NMR (500 MHz, CDCl3): d = 7.44–7.66 (m, 6 H), 7.72 (d, J =
7.8 Hz, 2 H), 8.26 (d, J = 8.2 Hz, 2 H).
3t
3u
3v
3w
3x
2-thienyl
3-O2NC6H4
4-O2NC6H4
13C NMR (125 MHz, CDCl3): d = 86.8, 93.0, 119.6, 128.0, 128.2,
129.2, 130.3, 132.6, 133.5, 136.4, 177.2.
Pr
1-(2,4-Dichlorophenyl)-3-phenylprop-2-yn-1-one (3c)
a Reaction conditions: acid chloride (1.2 mmol), alkyne (1.0 mmol),
py (1.2 mmol), catalyst (0.06 mmol), r.t., aerobic conditions.
b By GC.
IR (CH2Cl2): 2200, 1660 cm–1.
1H NMR (500 MHz, CDCl3): d = 7.15–7.58 (m, 7 H), 8.20 (d, J =
8.5 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 88.2, 92.5, 120.2, 128.9, 130.8,
CDCl3 by using TMS as the internal reference. All chemicals were
of commercial grade and were used as received without further pu-
rification.
131.2, 133.1, 135.4, 137.8, 138.2, 139.4, 143.2, 177.5.
1-(4-Chlorophenyl)-3-phenylprop-2-yn-1-one (3d)
Solid; mp 104–105 °C.
IR (KBr): 2200, 1658 cm–1.
1H NMR (500 MHz, CDCl3): d = 7.41–7.50 (m, 5 H), 7.63–7.71 (m,
2 H), 8.18 (d, J = 8.5 Hz, 2 H).
13C NMR (125 MHz, CDCl3): d = 86.50, 93.60, 119.82, 128.67,
128.93, 130.82, 130.95, 133.10, 135.23, 140.63, 176.58.
Polymer-Bound Ethylenediamine
A 250-mL round-bottomed flask equipped with a magnetic stirrer
bar was charged with MeCN (120 mL). Chloromethylated polysty-
rene (2 g, 2.5 mmol/Cl), H2N(CH2)2NH2 (25 mmol), and NaI (0.13
mmol) were added to the flask, and the mixture was refluxed for 48
h. The mixture was filtered and the residue was washed sequentially
with MeCN (5 × 40 mL), 1:1 MeOH–1 M aq K2CO3 (5 × 40 mL),
Synthesis 2011, No. 2, 325–329 © Thieme Stuttgart · New York

328
A. Keivanloo et al.
PAPER
1-(4-Methoxyphenyl)-3-phenylprop-2-yn-1-one (3f)
Solid; mp 98–99 °C.
1H NMR (500 MHz, CDCl3): d = 1.20 (t, J = 7.2 Hz, 3 H), 1.78 (m,
2 H), 2.51 (t, J = 7.2 Hz, 2 H), 8.35 (s, 4 H).
IR (KBr): 2205, 1637 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.87 (s, 3 H), 6.98 (d, J = 8.8 Hz,
2 H), 7.40–7.52 (m, 3 H), 7.64–7.68 (m, 2 H), 8.21 (d, J = 8.8 Hz, 2
13C NMR (125 MHz, CDCl3): d = 18.2, 25.5, 32.3, 83.2, 96.1,
130.6, 132.8, 140.5, 150.3, 175.2.
H).
Acknowledgment
13C NMR (125 MHz, CDCl3): d = 55.55, 86.86, 92.25, 113.85,
120.23, 128.62, 130.20, 130.57, 131.93, 132.91, 164.44, 176.64.
The authors would like to thank the Research Council of Shahrood
University of Technology for supporting this work.
1-(2-Iodophenyl)-3-phenylprop-2-yn-1-one (3i)
IR (CH2Cl2): 2198, 1650 cm–1.
1H NMR (500 MHz, CDCl3): d = 7.10–7.52 (m, 7 H), 7.70–8.10 (m,
2 H).
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1-(3-Nitrophenyl)hex-2-yn-1-one (3w)
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2 H), 2.48 (t, J = 7.1 Hz, 2 H), 7.24–7.56 (m, 1 H), 7.83–7.90 (m, 2
H), 8.62 (s, 1 H).
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Heterogeneous Catalyst for the Synthesis of a,b-Acetylenic Ketones
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Synthesis 2011, No. 2, 325–329 © Thieme Stuttgart · New York