Copper(I) hydroxyapatite catalyzed sonogashira reaction of alkynes with styrenyl bromides. Reaction of cis -styrenyl bromides forming unsymmetric diynes

Article abstract of DOI:10.1021/jo3015819

An efficient Sonogashira coupling of terminal alkynes and styrenyl bromides has been achieved under the catalysis of hydroxyapatite-supported copper(I). The trans-styrenyl bromides produce the usual trans-enyne products, whereas the cis-styrenyl bromides lead to unsymmetric 1,3-diynes by the cross coupling of terminal alkyne and the alkyne generated from the cis-styrenyl bromide. A series of trans-enynes and unsymmetric 1,3-diynes have been synthesized by this protocol.

Full text of DOI:10.1021/jo3015819

Note
pubs.acs.org/joc
Copper(I) Hydroxyapatite Catalyzed Sonogashira Reaction of
Alkynes with Styrenyl Bromides. Reaction of cis-Styrenyl Bromides
Forming Unsymmetric Diynes
Debasree Saha,† Tanmay Chatterjee,† Manabendra Mukherjee,‡ and Brindaban C. Ranu*,†
†Department of organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
‡Surface Physics Division, Saha Institute of Nuclear Physics, Kolkata 700067, India
S
* Supporting Information
ABSTRACT: An efficient Sonogashira coupling of terminal
alkynes and styrenyl bromides has been achieved under the
catalysis of hydroxyapatite-supported copper(I). The trans-
styrenyl bromides produce the usual trans-enyne products,
whereas the cis-styrenyl bromides lead to unsymmetric 1,3-
diynes by the cross coupling of terminal alkyne and the alkyne
generated from the cis-styrenyl bromide. A series of trans-
enynes and unsymmetric 1,3-diynes have been synthesized by
this protocol.
he conjugated enyne is of great importance because of its
presence in many bioactive naturally occurring and
catalyzed by hydroxyapatite-supported Cu(I) [Cu (I)-Hap]
(Scheme 1). We observed a usual coupling with trans-styrenyl
bromide to produce trans-1,3-enyne product, whereas the
corresponding cis-counterpart provides unsymmetric 1,3-diyne
by the cross coupling of terminal alkyne and the alkyne
generated from cis-styrenyl bromide.
T
synthetic molecules.1 Moreover, the enynes are valuable
synthons, frequently used for the synthesis of polysubstituted
benzenes2 and 1,3-dienes.3 Thus, several methods have been
developed for the synthesis of this scaffold. A widely employed
approach is the noble metal-catalyzed dimerization of terminal
alkynes.4 However, the lack of control of regio- and
stereoselectivity of the dimerization process is one of its
serious limitations. To overcome this problem the metal-
catalyzed coupling of an alkyne and a structurally defined
organometallic alkene was developed.5 The difficulty in the
preparation of organometallic alkene restricts their uses. A
recently developed straightforward approach involving Sonoga-
shira coupling of vinyl halides and terminal alkynes catalyzed by
Cu and Pd deserves special mention.6
The diynes are important structural motifs in many natural
products and are useful building blocks.9 Several compounds
such as norcapillene,10 thiarubrine,11 and falcarindiol12
containing this subunit showed interesting biological activities.
Thus, construction of conjugated diynes, particularly unsym-
metric ones, is of considerable interest. Although there are
many methods for the synthesis of symmetric diynes,13 those of
unsymmetric diynes are limited. The Cadiot−Chodkiewicz
coupling between a haloalkyne and a terminal alkyne under Cu
catalysis is the most widely used protocol for the construction
of the unsymmetric 1,3-diyne moiety.14A few other methods
involving coupling of two different alkynes with high loading of
one alkyne,15a coupling of terminal alkyne and ICHCHCl,15b
coupling of terminal bromoalkyne and alkynyl stannane,15c and
decarboxylative cross-coupling of propiolic acids and terminal
alkynes15d were also reported. However, there is scope for
further improvement with regard to yield, operational
simplicity, generality, and cost-efficiency using a novel protocol.
To standardize the reaction conditions, a series of experi-
ments were performed for a representative reaction of trans-4-
methylstyrenyl bromide and phenylacetylene in the presence of
Cu (I)-HAP under different conditions with variation of base,
solvent, temperature, and time. It was found that best results
were obtained using NaOH in DMF at 120 °C over 9 h (Table
The heterogeneous supported metal catalysts have received
considerable current interest because of their operational
advantages compared to their homogeneous counterparts.7
Recently, we demonstrated the application of hydroxyapatite-
supported Pd(II) catalyst for coupling of diiodoalkenes and
conjugated alkenes8a and hydroxyapatite-supported Cu(I)-
catalyzed cyanation of styrenyl bromides.8b This encouraged
us to explore the application of hydroxyapatite-supported Cu(I)
catalyst for Sonogashira reaction of terminal alkynes and
styrenyl halides with particular interest on coupling of both
stereoisomers of styrenyl halides, as in previous reports,6 only
trans-vinyl halides have been subjected to the reaction, and we
did not find any general Sonogashira reaction with cis-vinyl
halides except one example where cis-styrenyl bromide on
reaction with phenyl acetylene catalyzed by CuI in presence of
K3PO4 produced the corresponding cis-1,3-enyne in 27%
yield.6c We report here our results of Sonogashira coupling of
terminal alkynes with trans- as well as cis-styrenyl bromides
Received: July 28, 2012
Published: October 2, 2012
© 2012 American Chemical Society
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The Journal of Organic Chemistry
Note
Scheme 1. Sonogashira Coupling of cis- and trans-Styrenyl Bromides with Terminal Alkynes
1, entry 3). A milder base, K2CO3, was also effective (Table 1,
entry 1); however, use of NaOH improved the yield.
providing unsymmetric 1,3-diyne (A) as sole product when the
reaction was carried out in DMF at 120 °C for 12 h under
argon (Table 2, entry 3). Interestingly, when the reaction was
carried out in air under identical conditions, a mixture of
products containing A, B, and C in a 51:12:37 ratio was
obtained (Table 2, entry 6). Thus, the reaction conditions as
outlined in entry 3, Table 2, were accepted for the reaction of
cis-styrenyl bromides.
Table 1. Standardization of Reaction Conditions for
Coupling of trans-Styrenyl Bromide with Acetylene
In a typical experimental procedure, a mixture of (E)-β-
bromostyrene or (Z)-β-bromostyrene, phenylacetylene, NaOH,
and Cu (I)-HAP in DMF was heated at 120 °C under argon for
a certain period of time as required to complete the reaction
(TLC). Standard workup followed by purification by column
chromatography provided the product.
Several diversely substituted (E)-β-bromostyrenes were
subjected to reaction with phenylacetylenes and alkyl-
substituted alkyne (1-octyne) by this procedure to produce
the corresponding 1,3-enynes. The results are summarized in
Table 3. The stereochemistry of the double bond was found to
be trans in all products. The alkyl- and aryl-substituted alkynes
react uniformly.
entry
base
solvent
temp (°C)
time (h)
yield (%)
1
2
3
4
5
K2CO3
NaOH
NaOH
NaOH
NaOH
DMF
DMF
DMF
DMF
THF
120
120
120
120
75
7
7
68
75
82
82
65
9
12
12
Next, to standardize the reaction conditions for cis-stryrenyl
bromide, we carried out several experiments for a representative
reaction of cis-4-methylstyrenyl bromide and phenylacetylene in
the presence of Cu(I)-HAP with variation of base, solvent,
temperature, and time. The use of K2CO3 as base in DMF at
120 °C for 9 h produced a mixture of unsymmetric 1,3-diyne
(A) and cis-1,3-enyne (B) in a ratio of 55:45 with a chemical
yield of 60% (Table 2, entry 1). The change of base from
K2CO3 to NaOH significantly influenced the product formation
Table 3. Reaction of trans-Styrenyl Bromides with
Acetylenes
Table 2. Standardization of Reaction Conditions for
Coupling of cis-Styrenyl Bromide and Acetylene
a
a
b
entry
R
R′
yield (%)
ref
1
2
3
4
5
6
7
8
H
C6H5
C6H5
C6H5
C6H5
C6H5
84
86
84
82
80
76
84
80
6a
6a
6c
6a
4-Cl
4-F
4-Me
4-Et
4-F
4-OMeC6H4
CH3(CH2)5−
CH3(CH2)5−
H
17
4-Me
a
Yields refer to those of purified products characterized by IR and 1H
b
and 13C NMR spectroscopic data. The known compounds are
identified by comparison of their spectroscopic data with those
reported.
temp
(°C)
time
(h)
product ratio
(A:B:C)
yield
(%)
entry
base
solvent
In a similar procedure, when (Z)-β-bromostyrenes were
reacted with phenylacetylenes, the corresponding unsymmetric
1,3-diynes were obtained. The results are reported in Table 4.
Interestingly, we did not isolate the corresponding (Z)-1,3-
enyne in any reaction as observed by Mao et al.6c The alkyl-
substituted alkyne did not undergo this cross-dimerization;
instead, only self-dimerization of the alkyne, generated from
(Z)-bromostyrenes, was isolated (Table 4, entry 7). However,
an alkyl-substituted cis-vinyl bromide, (Z)-1-bromoundec-1-ene
underwent reaction with phenylacetylene successfully (Table 4,
entry 8).
1
2
3
4
5
K2CO3
NaOH
NaOH
NaOH
NaOH
NaOH
DMF
DMF
DMF
DMF
THF
DMF
120
120
120
120
75
9
9
55:45:0
100:0:0
100:0:0
100:0:0
100:0:0
51:12:37
60
72
81
81
62
75
12
15
12
12
b
6
120
a
The cis-styrenyl bromide was prepared by bromination of the
corresponding cinnamic acid followed by base-catalyzed (Et3N)
decarboxylative debromination under microwave irradiation following
b
standard procedures. The reaction was carried out in air.
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Note
the regenerated catalyst shows the oxidation state of copper as
Cu(I) supporting this proposition. This type of mechanism in
dimerization of acetylenes is not unprecedented.16
Table 4. Reaction of cis-Styrenyl Bromides with Acetylenes
The reactions are in general very clean and high yielding. The
products were obtained pure by simple column chromatog-
raphy. No ligand or additive was required. The catalyst was
recycled for three runs with a gradual decrease in yield of the
product (Tables 5 and 6). This might be due to the formation
a
b
entry
R
R1
C6H5−
C6H5−
C6H5−
C6H5−
C6H5−
4-OMeC6H4−
CH3(CH2)5−
C6H5−
yield (%)
ref
1
2
3
4
5
6
C6H5−
78
80
75
81
72
65
15c
18
4-ClC6H4−
4-FC6H4−
4-MeC6H4−
4-EtC6H4−
4-FC6H4−
C6H5-
15c
19
Table 5. Recyclability Study of Coupling of trans-Styrenyl
Bromide with Acetylene
15d
c
7
8
CH3(CH2)8−
65
a
1
Yields refer to those of purified products characterized by IR and H
b
and 13C NMR spectroscopic data. The known compounds are
no. of cycles
yield (%)
identified by comparison of their spectroscopic data with those
reported. No cross dimer was isolated. Only diphenyldiacetylene,
formed by the dimerization of the acetylene generated in situ from
styrenyl bromide, was obtained.
c
1
2
3
4
82
78
70
52
Interestingly, we did not observe any self-dimerization of
either phenylacetylene or the acetylene generated from (Z)-β-
bromostyrene in the crude reaction products of aryl-substituted
alkynes and cis-styrenyl bromides. As mentioned previously,
when this reaction was carried out in air the mixtures of cross-
dimerized and self-dimerized products were obtained. The
reason is not very clear to us. This indicates that under argon
the cross-dimerization leading to unsymmetric 1,3-diynes is
favored over other self-dimerization reactions. In a blank
experiment using only (Z)-β-bromostyrene we isolated a
mixture of symmetric 1,3-diynes formed by the self-
dimerization of acetylene formed and the cis- and trans- 1,3-
enynes by reaction of cis-styrenyl bromide and alkyne formed in
situ. This suggests that the reaction of (Z)-β-bromostyrenes
proceed through the intermediacy of alkyne, formed in situ by
dehydrohalogenation under basic reaction conditions. Thus, we
speculate that Cu(I)-HAP simultaneously interacts with the
acetylene generated from (Z)-β-bromostyrene in situ and
phenylacetylene to form a dinuclear Cu(II) acetylide complex
X which then produces the unsymmetric 1,3-diyne by single-
electron transfer with regeneration of Cu(I)-HAP catalyst, as
outlined in Scheme 2. The XPS (X-ray photoelectron
spectroscopy) analysis (see the Supporting Information) of
Table 6. Recyclability Study of Coupling of cis-Styrenyl
Bromide with Acetylene
no. of cycles
yield (%)
1
2
3
81
50
27
of a coating on the catalyst surface, which possibly reduces its
catalytic activity. We also observed considerable leaching of the
catalyst (Cu content in the fresh catalyst: 0.3237 mmol/g; Cu
content in the recovered catalyst after fourth cycle: 0.2127
mmol/g). This also contributes to the gradual loss of activity.
Certainly, our method provides a novel protocol for the
synthesis of unsymmetric 1,3-diynes from easily accessible (Z)-
β-bromostyrenes. Compared to other methods,14,15 this
reaction offers better substrate scope, simplicity in operation
without using any ligand and additive, uniformly high yields,15d
Scheme 2. Plausible Mechanism for Reaction of cis-Styrenyl Bromide with Acetylene
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The Journal of Organic Chemistry
Note
128.5 (2C), 131.6 (2C), 133.9, 141.4 (2C), 145.1. Anal. Calcd for
C18H16: C, 93.06; H, 6.94. Found: C, 93.13; H, 6.87.
and cost efficiency involving an inexpensive and recyclable (up
to three runs) heterogeneous catalyst.
1-Fluoro-4-[(E)-4-(4-methoxyphenyl)but-1-en-3-ynyl]-
benzene (Table 3, entry 6): white solid; mp 114−115 °C; IR (KBr)
3003, 2975, 2936, 2841, 2138, 1599, 1504, 1436, 1256, 1108, 985
cm−1; 1H NMR (500 MHz, CDCl3) δ 3.86 (s, 3H), 6.32 (d, J = 16 Hz,
1H), 6.90 (d, J = 8.5 Hz, 2H), 7.00 (d, J = 16 Hz, 1H), 7.06 (t, J = 8.5
HZ, 3H), 7.39−7.42 (m, 3H), 7.45 (d, J = 7.5 Hz, 2H); 13C NMR
(125 MHz, CDCl3) δ 55.4, 87.5, 91.9, 108.3, 114.2 (2C), 115.7 (2C),
127.9 (2C), 133.1 (2C), 134.2, 139.2, 159.7, 161.9, 163.9. Anal. Calcd
for C17H13FO: C, 80.93; H, 5.19. Found: C, 80.84; H, 5.23.
In conclusion, we have studied the Sonogashira reaction of
alkynes with trans- and cis- styrenyl bromides catalyzed by a
heterogeneous hydroxyapatite-supported Cu(I) catalyst. Sig-
nificantly, although (E)-β-bromostyrenes provided the usual
trans-1,3-enynes, the (Z)-β-bromostyrenes produced the
unsymmetric 1,3-diynes by the coupling of alkyne present
with the alkyne generated in situ by dehydrohalogenation of cis-
styrenyl bromide in basic reaction conditions. To the best of
our knowledge, we are not aware of any report addressing
Sonogashira reaction of alkyne with cis-styrenyl halides leading
to unsymmetric 1,3-diynes. The other attractive features of this
protocol are no use of toxic ligand and additive, easy recovery
of the catalyst, generality, and good yields of products.
Certainly, this methodology will find useful applications for
an easy access to a library of conjugated (E)-1,3-enynes and
unsymmetric 1,3-diynes.
1-[(E)-Dec-1-en-3-ynyl]-4-methylbenzene (Table 3, entry 8):
1
colorless liquid; IR (neat) 2928, 2857, 1448, 951, 746, 684 cm−1; H
NMR (500 MHz, CDCl3) δ 0.92 (t, J = 6.5 Hz, 3H), 1.27 −1.36 (m,
4H), 1.41−1.47 (m, 2H), 1.55−1.60 (m, 2H), 2.35−2.39 (m, 5H),
6.12 (d, J = 16.5 Hz, 1H), 6.86 (d, J = 16.5 Hz, 1H), 7.13 (d, J = 8 Hz,
2H), 7.27 (d, J = 8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 14.2,
19.8, 21.4, 22.7, 28.8, 28.9, 31.5, 80.0, 92.8, 107.9, 126.1 (2C), 129.5
(2C), 134.0, 138.3, 140.0. Anal. Calcd for C17H22: C, 90.20; H, 9.80.
Found: C, 90.25; H, 9.75.
1-[4-(4-Ethylphenyl)buta-1,3-diynyl]benzene (Table 4, entry
5): white solid; mp 80−81 °C; IR (KBr) 3049, 2970, 2145, 1655,
EXPERIMENTAL SECTION
1
■
1483, 1431, 1256, 1067, 915 cm−1; H NMR (500 MHz, CDCl3) δ
General Experimental Procedure for Sonogashira Coupling
of Alkynes and β-Bromostyrenes. Representative Procedure
for the Reaction of Phenylacetylene and (E)-β-Bromostyrene
(Table 3, Entry 1). A mixture of (E)-β-bromostyrene (183 mg, 1
mmol), phenylacetylene (123 mg, 1.2 mmol), NaOH (120 mg, 3
mmol), and Cu(I)-HAP catalyst (100 mg, 3.2 mol %) in DMF (4 mL)
was heated with stirring at 120 °C under argon for 9 h (TLC). The
reaction mixture was filtered to separate the solid catalyst, which was
used for successive cycles. The filtrate was extracted with Et2O (4 × 15
mL). The extract was washed with water and brine and then dried
(Na2SO4). Evaporation of the solvent left the crude product which was
purified by column chromatography over silica gel (60−120 mesh)
(hexane/ether 95: 5) to afford pure (E)-1,4-diphenylbut-1-en-3-yne
(172 mg, 84%) as a white solid: mp 102−103 °C; IR (KBr) 3002,
1.15 (t, J = 7.5 Hz, 3H), 2.57 (q, J = 7.5 Hz, 2H), 7.08 (d, J = 8 Hz,
2H), 7.23−7.28 (m, 3H), 7.35−7.37 (m, 2H), 7.43−7.45 (m, 2H); 13C
NMR (125 MHz, CDCl3) δ 15.3, 29.0, 73.4, 74.1, 81.4, 81.8, 119.1,
122.0, 128.1 (2C), 128.5 (2C), 129.3, 132.6 (4C), 146.4. Anal. Calcd
for C18H14: C, 93.87; H, 6.13. Found: C, 93.76; H, 6.24.
1-(Trideca-1,3-diynyl)benzene (Table 4, entry 8): colorless
viscous liquid; IR (neat) 3311, 2926, 2854, 2245, 1491, 1458, 1215,
1
754 cm−1; H NMR (300 MHz, CDCl3) δ 0.88 (t, J = 5.4 Hz, 3H),
1.25−1.43 (m, 12H), 1.52−1.62 (m, 2H), 2.35 (t, J = 7 Hz, 2H),
7.26−7.33 (m, 3H), 7.45−7.48 (m, 2H); 13C NMR (75 MHz, CDCl3)
δ 14.0, 19.6, 22.6, 28.7, 28.8, 29.1, 29.2, 29.4, 31.8, 65.1, 74.4, 74.7,
84.9, 122.3, 128.3 (2C), 128.7, 132.5 (2C). Anal. Calcd for C19H24: C,
90.42; H, 9.58. Found: C, 90.60; H, 9.40.
2972, 2841, 2192, 1592, 1214, 1020, 981 cm−1; H NMR (300 MHz,
1
ASSOCIATED CONTENT
■
CDCl3) δ 6.32 (d, J = 15 Hz, 1H), 6.98 (d, J = 15 Hz, 1H), 7.17−7.29
(m, 6H), 7.34−7.42 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 89.0,
91.9, 108.3, 123.5, 126.4 (2C), 128.3, 128.5 (2C), 128.7, 128.9 (2C),
131.6 (2C), 136.5, 141.4. The spectroscopic data (1H and 13C NMR)
are in good agreement with those reported for the authentic sample.6a
This procedure was followed for all the reactions listed in Table 3.
Representative Procedure for the Reaction of Phenyl-
acetylene and (Z)-β-Bromostyrene (Table 4, entry 1). The
same procedure as in the previous experiment was followed allowing
the reaction to go for 12 h (TLC). Extraction and workup provided
1,4-diphenylbuta-1,3-diyne (158 mg, 78%) as a white solid: mp 89−90
°C; IR (KBr) 3049, 2148, 1655, 1638, 1483, 1067, 1024, 915, 755,
S
* Supporting Information
Copies of XPS spectra of the fresh and regenerated Cu(I)-
1
HAP; H NMR and 13C NMR spectra of all products listed in
Tables 3 and 4. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: ocbcr@iacs.res.in.
■
Notes
1
685, 524 cm−1, H NMR (500 MHz, CDCl3) δ 7.32−7.39 (m, 6H),
The authors declare no competing financial interest.
7.53−7.55 (m, 4H); 13C NMR (125 MHz, CDCl3) δ 74.1 (2C), 81.7
(2C), 121.9 (2C), 128.5 (4C), 129.3 (2C), 132.6 (4C). The
spectroscopic data (1H and 13C NMR) are in good agreement with
those reported for an authentic sample.15c
ACKNOWLEDGMENTS
■
We are pleased to acknowledge the financial support from
CSIR, New Delhi (grant no. 01(2365/10/EMR-II)) for this
investigation. D.S. and T. C. also thank CSIR for their
fellowships. We acknowledge support of Nanoscience Project
Unit at IACS, funded by DST, New Delhi.
This procedure was followed for all of the reactions listed in Table
4.
Although these procedures were described with a 1 mmol scale, 10
mmol scale reactions also provided uniform results.
All of these products listed in Tables 3 and 4 were properly
characterized. The known compounds were identified by comparison
of their spectroscopic data with those reported. The new compounds
were characterized by their IR, 1H NMR, and 13C NMR spectroscopic
data and elemental analysis data which are provided below.
1-[(E)-4-(4-Ethylphenyl)but-3-en-1-ynyl]benzene (Table 3,
entry 5): white solid; mp 81−82 °C; IR (KBr) 3030, 2980, 2890,
2190, 1601, 1505, 1212, 1022, 985 cm−1; 1H NMR (500 MHz,
CDCl3) δ 1.29 (t, J = 7.5 Hz, 3H), 2.70 (q, J = 7.5 Hz, 2H), 6.40 (d, J
= 16.5 Hz, 1H), 7.10 (d, J = 16.5 Hz, 1H), 7.22 (d, J = 8 Hz, 2H),
7.34−7.40 (m, 5H), 7.53 (d, J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3) δ 15.5, 65.4, 89.3, 91.5, 107.2, 123.7, 126.4 (2C), 128.3, 128.4,
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