Synthesis of symmetrical 1,3-diynes via tandem reaction of (Z)-arylvinyl bromides in the presence of DBU and CuI

Article abstract of DOI:10.1016/j.cclet.2013.03.016

Microwave-assisted tandem reaction of (Z)-arylvinyl bromides involving an elimination and homocoupling in the presence of DBU and CuI in DMF affords a variety of symmetrical 1,3-diynes in good to excellent yields. This tandem process, eliminating the need

Full text of DOI:10.1016/j.cclet.2013.03.016

Chinese Chemical Letters 24 (2013) 407–410
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Chinese Chemical Letters
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Original article
Synthesis of symmetrical 1,3-diynes via tandem reaction of (Z)-arylvinyl bromides
in the presence of DBU and CuI
a
b
c,
Wen-Sheng Zhang a, , Wen-Jing Xu , Fei Zhang , Gui-Rong Qu
*
*
a School of Science, Jiaozuo Teachers’ College, Jiaozuo 450001, China
b Jiaozuo Vocational Education Center, Jiaozuo 450001, China
c College of Chemical and Environmental Engineering, Henan Normal University, Xinxiang 453007, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Microwave-assisted tandem reaction of (Z)-arylvinyl bromides involving an elimination and
homocoupling in the presence of DBU and CuI in DMF affords a variety of symmetrical 1,3-diynes in
good to excellent yields. This tandem process, eliminating the need of volatile and savory terminal
alkynes, provides an alternative to the conventional homocoupling methods for the synthesis of
symmetrical 1,3-diynes.
Received 17 December 2012
Received in revised form 29 January 2013
Accepted 27 February 2013
Available online 12 April 2013
ß 2013 Wen-Sheng Zhang, Gui-Rong Qu. Published by Elsevier B.V. on behalf of Chinese Chemical
Society. All rights reserved.
Keywords:
Catalysis
Copper
Conjugation
Coupling
Tandem reaction
1. Introduction
synthesis of poly(N-vinylazoles) serving as semiconductors and
photosensitive materials [12]. Additionally, the versatility of (Z)-
Conjugated diynes are recurring building blocks for the
synthesis of natural products, pharmaceuticals and bioactive
compounds with anti-inflammatory, antifungal, anti-HIV, antibac-
terial, anticancer activities, etc. [1]. In addition, conjugated diynes
have found wide applications in the construction of industrial
intermediates and materials, particularly macrocyclic annulenes,
organic conductors, supramolecular switches and carbon-rich
materials [2–4]. Therefore, much attention [5] has been devoted to
the development of new and efficient methods for the synthesis of
diynes. A classical and effective route for preparing symmetrical
1,3-diynes was the homocoupling of volatile and savory terminal
alkynes [6].
arylvinyl bromides has been exploited, notably, as alkyne
equivalents [13].
In this article, we report a CuI-catalyzed tandem reaction of (Z)-
arylvinyl bromides, which affords symmetrical diynes convenient-
ly and efficiently. Our proposed synthetic route, which includes a
cascade elimination and Glaser reaction, is shown in Scheme 1. We
hypothesized that, in this reaction process, an elimination of (Z)-
arylvinyl bromides 1 would occur in the presence of DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene) to produce the aryne A. Subse-
quently, a Glaser oxidative homocoupling of A through intermedi-
ate B catalyzed by CuI and DBU affords the desired product 2.
(Z)-Arylvinyl bromides, readily available from inexpensive
cinnamic acid derivatives [7], are also versatile precursors in
many useful organic transformations including the well-known
Stille [8], Suzuki [9], and Sonogashira [10] couplings, as well as the
Buchwald [11] methodology for stereospecific synthesis of
substituted alkenes. Using the CuI-ethylenediamine catalytic
system in toluene or 1,4-dioxane, they can be coupled with azoles
to afford stereocontrolled N-vinylazoles, a key unit for the
2. Experimental
Melting points were recorded using a WRS-1B digital melting
point apparatus and are uncorrected. 1H NMR spectra were
recorded using a Bruker DPX-400 spectrometer in CDCl3 with
SiMe4 as an internal standard. MS data were measured with a
Varian-310 mass spectrometer.
A Xinyi MAS-II microwave
synthesizer was used for all the microwave reactions. Commer-
cially obtained reagents were used without further purification.
All reactions were monitored by TLC with HuanghaiGF254 silica
gel coated plates. Column chromatography was carried out
using 300–400 mesh silica gel at medium pressure. The synthesis
* Corresponding authors.
E-mail addresses: tongjizws@163.com (W.-S. Zhang), quguir@sina.com
(G.-R. Qu).
1001-8417/$ – see front matter ß 2013 Wen-Sheng Zhang, Gui-Rong Qu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.03.016

[
W.-S. Zhang et al. / Chinese Chemical Letters 24 (2013) 407–410
92–93 8C); Rf = 0.8 (EtOAc/petroleum ether = 1/20). 1H NMR
(400 MHz, CDCl3): 3.81 (s, 6H, CH3), 6.93–7.24 (m, 8H, ArH).
1,4-Bis(2-chlorophenyl)buta-1,3-diyne (2g) [14]: Yield: 230 mg
(85%); yellow solid; mp 139–140.5 8C (lit. [5u] 138–140 8C);
Rf = 0.75 (EtOAc/petroleum ether = 1/20). 1H NMR (400 MHz,
DBU
CuI
DBU
d
R
R
Br
A
1
Elimination
Cu
CDCl3):
d 7.23–7.33 (m, 4H, ArH), 7.42 (d, 2H, J = 9.2 Hz, ArH),
7.58 (d, 2H, J = 6.0 Hz, ArH).
1,4-Bis(2-bromophenyl)buta-1,3-diyne (2h) [14]: Yield: 300 mg
(83%); yellow solid; mp 132.5–133.8 8C; Rf = 0.8 (EtOAc/petroleum
R
R
ether = 1/20). 1H NMR (400 MHz, CDCl3):
7.57–7.62 (m, 4H, ArH).
d 7.21–7.31 (m, 4H, ArH),
R
1,4-Bis(2-methoxypheny1)buta-1,3-diyne (2i) [14]: Yield:
223 mg (85%); white solid; mp 137.8–149.5 8C (lit. [5s] 138–
140 8C); Rf = 0.8 (EtOAc/petroleum ether = 1/20). 1H NMR
2
B
Dimerization
(400 MHz, CDCl3):
d 3.88 (s, 6H, CH3), 6.86–6.91 (m, 4H, ArH),
Scheme 1. Route for the synthesis of symmetrical diynes from (Z)-arylvinyl
7.29–7.42 (m, 4H, ArH).
bromides.
3. Results and discussion
of (Z)-arylvinyl bromides was achieved according to the reported
methods [7a].
To screen suitable reaction conditions, (Z)-1-(2-bromovinyl)-
benzene 1a has been used as a model substrate. The initial attempt
was carried out with 1a (1 mmol) and DBU (2.2 mmol) using DMF
(2 mL) as a solvent. The reaction mixture was stirred at 80 8C for
12 h and cooled to room temperature. CuI (2.5 mol%) was then
added and the system was stirred for 8 h at room temperature. The
expected product 2a was afforded in 45% yield (Table 1, entry 1).
The structure of compound 2a was confirmed by 1H NMR and was
consistent with those in the literature [15]. Almost no improve-
ment was observed when the reaction was prolonged to 24 h
(Table 1, entry 2). Lower yield was obtained when the reaction was
conducted at 120 8C (Table 1, entry 3). Fortunately, the reaction
worked efficiently under microwave conditions (Table 1, entries 4–
6). For instance, 85% yield of product 2a was observed when the
starting material 1a and DBU in DMF was irradiated under
microwave (120 W) for 1 min (Table 1, entry 4). The yield of 2a
reached 90% by increasing the irradiation time to 2 min (Table 1,
entry 5). Further increase of the irradiation time to 5 min, however,
decreased the yield to 80% (Table 1, entry 6). Other bases such as
Et3N, Cs2CO3 and EtONa were tested but failed to afford the desired
product 2a (Table 2, entries 7–9). When the amount of base was
reduced to 1.5 mmol, the yield dropped significantly to 50% (entry
10). Inferior results were observed when other solvents were
examined. When the solvent was changed to MeCN, DMSO, and
THF, the yields decreased to 70%, 77% and 68%, respectively
(Table 1, entries 11–13).
2.1. General procedure for 1,3-diynes (2)
(Z)-Arylvinyl bromides 1 (1 mmol) and DBU (2.2 mmol) were
dissolved in DMF (2 mL) and the reaction system was irradiated
using a microwave synthesizer (120 W) for 2 min. The reaction
mixture was then removed from the microwave synthesizer and
cooled to room temperature. To the reaction mixtures was added
CuI (0.2 mmol). The mixture was stirred at room temperature for
8 h. After the completion of the reaction screened by TLC, the
mixture was diluted with Et2O (20 mL) and filtered. The filtrate
was washed with brine (2ꢀ 10 mL) and H2O (10 mL). The Et2O
layer was dried over Na2SO4, concentrated under reduced pressure.
Purification of the residue by column chromatography on silica gel
(EtOAc/petroleum ether = 1/20) afforded products 2. The structure
of 1,3-diynes 2b–2i were fully consistent with their 1H NMR data
[14].
2.2. Selected data of compound 2
1,4-Diphenylbuta-1,3-diyne (2a) [14,1a]: Yield: 182 mg (90%);
white solid; mp 86–86.5 8C (lit. [5s] 86–87 8C); Rf = 0.9 (EtOAc/
petroleum ether = 1/20). 1H NMR (400 MHz, CDCl3):
d 7.32–7.37
(m, 6H, ArH), 7.52–7.54 (m, 4H, ArH). MS (ESI): m/z 202 [M+].
1,4-Bis(4-methylpheny1)buta-1,3-diyne (2b) [14,1a]: Yield:
212 mg (92%); white solid; mp 182.1–182.5 8C (lit. [5t] 182–
183 8C, lit. [5u] 137–138 8C); Rf = 0.85 (EtOAc/petroleum ether = 1/
Table 1
20). 1H NMR (400 MHz, CDCl3):
d 2.36 (s, 6H, CH3), 7.14 (d, 4H,
Optimization of the reaction conditions based on 1a.
J = 8.0 Hz, ArH), 7.42 (d, 4H, J = 8.0 Hz, ArH). MS (ESI): m/z 230 [M+].
1,4-Bis(4-methoxypheny1)buta-1,3-diyne (2c) [14,1a]: Yield:
228 mg (87%); white solid; mp 139–140.5 8C (lit. [5t] 140–
141 8C); Rf = 0.8 (EtOAc/petroleum ether = 1/20). 1H NMR
Entry
Solvent
Basea
‘‘4’’ or ‘‘MW’’
Timec
Yield (%)d
of 1a
1
2
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
MeCN
DMSO
THF
DBU
DBU
DBU
DBU
DBU
DBU
Et3N
Cs2CO3
EtONa
DBUb
DBU
DBU
DBU
ꢁ/808C
ꢁ/808C
ꢁ/120 8C
MW
12 h
24 h
45
47
(400 MHz, CDCl3):
d 3.82 (s, 6H, CH3), 6.85 (d, 4H, J = 8.8 Hz,
3
12 h
39
4
1 min
2 min
5 min
2 min
2 min
2 min
2 min
2 min
2 min
2 min
85
ArH), 7.46 (d, 4H, J = 8.8 Hz, ArH).
5
MW
90
1,4-Bis(4-fluorophenyl)buta-1,3-diyne (2d) [1a]: Yield: 138 mg
(56%); white solid; mp 187.3–188 8C (lit. [5t] 194–195 8C, lit. [5u]
187–189 8C); Rf = 0.8 (EtOAc/petroleum ether = 1/20). 1H NMR
6
MW
80
7
MW
Trace
Trace
Trace
50
8
MW
(400 MHz, CDCl3):
ArH).
d
7.04 (t, 4H, J = 8.5 Hz, ArH),7.49–7.53 (m, 4H,
9
MW
10
11
12
13
MW
MW
70
1,4-Bis(3-methylphenyl)buta-1,3-diyne (2e) [1a]: Yield: 205 mg
(89%); white solid; mp 68–68.5 8C (lit. [5t] 68–70 8C, lit. [5v] 74–
75 8C); Rf = 0.85 (EtOAc/petroleum ether = 1/20). 1H NMR
MW
77
MW
68
a
2.2 mmol amount of bases were used except for entry 10.
1.5 mmol amount of bases was used.
(400 MHz, CDCl3):
d 2.34 (s, 6H, CH3), 7.17–7.35 (m, 8H, ArH).
b
c
1,4-Bis(3-methoxypheny1)buta-1,3-diyne (2f) [14]: Yield:
233 mg (89%); yellow solid; mp 91.8–92.9 8C (lit. [5t,5u]
Heated or MV time for the elimination process in Scheme 1.
Isolated yield.
d

W.-S. Zhang et al. / Chinese Chemical Letters 24 (2013) 407–410
409
Table 2
Synthesis of 1,3-diynes 2 from (Z)-arylvinyl bromides 1 in the presence of DBU and CuIa.
Entry
1
Substrate 1
Product 2
Yield of 2 (%)b
1a
1b
2a
2b
90
Br
[DT$INLE]
[TD$INLINE]
2
92
Br
[DT$INLE]
H3C
CH3
[TD$INLINE]
H3C
3
4
5
1c
1d
1e
2c
2d
2e
87
56
89
Br
[DT$INLE]
H3CO
OCH3
[TD$INLINE]
H3CO
Br
[DT$INLE]
F
F
[TD$INLINE]
F
H3C
CH3
H3C
Br
[DT$INLE]
[TD$INLINE]
6
7
1f
2f
89
85
H3CO
OCH3
H3CO
Br
[DT$INLE]
[TD$INLINE]
1g
2g
Cl
Br
Cl
Br
Br
Br
[DT$INLE]
[TD$INLINE]
Cl
8
1h
1i
2h
2i
83
85
[DT$INLE]
[TD$INLINE]
Br
Br
9
OCH3
H3CO
[DT$INLE]
[TD$INLINE]
OCH3
a
Reaction conditions: (1) Reactions were conducted with (Z)-arylvinyl bromides 1 (1 mmol) and DBU (2.2 mmol) in DMF (2 mL) under MW (120 W) for 2 min; (2) CuI
(20 mol%) was added to the cooled reaction system of (1), the mixture was stirred at rt for 8 h.
b
Isolated yield based on substrate 1.
On the basis of these results, the optimal conditions involved
the following parameters: DMF as solvent, 2.2 equiv. of DBU as
base, microwave irradiation (120 W) for 2 min. and 20 mol% of CuI
as catalyst.
arylvinyl bromide bearing a strong electron-withdrawing group.
For instance, (Z)-1-(2-bromovinyl)-4-fluorobenzene 1d gave a
relatively low yield of the product 2d (56%, Table 2, entry 4). When
(Z)-1-(2-bromovinyl)-4-nitrobenzene was employed under the
optimized conditions, the reaction failed to furnish the expected
product. In addition, the effect of steric hindrance was also
screened. (Z)-arylvinyl bromide bearing Cl, Br and OMe functional
groups on the ortho-position of the aromatic ring readily reacted
under the established conditions, affording products 2g, 2h and 2i
in a yield of 85%, 83% and 85%, respectively (Table 2, entries 7–9).
Under the above optimized conditions, we have examined the
substrate scope of this reaction. Our experiments indicate that a
range of (Z)-arylvinyl bromides underwent the elimination-
homocoupling process to produce the corresponding 1,3-diynes
in good to excellent yields (Scheme 2 and Table 2). An electron-
donating group and a weak electron-withdrawing group in the (Z)-
arylvinyl bromide derivatives did not alter the efficiency of the
reaction. For example, a variety of substituents like Me, OMe, Cl
and Br on the aromatic ring are compatible with this reaction
condition. The results are listed in Table 2 (Table 2, entries 2–3 and
5–9). The reaction was sluggish, however, in the case of (Z)-
4. Conclusion
In conclusion, we have developed a new method for the
synthesis of symmetrical diynes from (Z)-arylvinyl bromides by
CuI-catalyzed tandem reaction, avoiding the direct use of volatile
terminal alkynes.
[(Scheme_2)TD$FIG]
1) DBU, DMF
M-W, 2 min
R
R
R
Br
2) CuI, DMF
r.t., 8h
Acknowledgments
1
2
This work was supported by the National Natural Science
Foundation of China (No. 21172059), Program for Science &
Scheme 2. Synthesis of symmetrical 1,3-diynes.

410
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