Synthesis of symmetrical 1,3-diynes in water-soluble ionic liquid [DMIM]Me2PO4

Article abstract of DOI:10.1007/s11164-013-1042-2

Treatment of a variety of arynes in water-soluble ionic liquid [DMIM]Me₂PO₄ in the presence of catalytic amount of CuI and inexpensive NH₃·H₂O under aerobic conditions afforded the corresponding symmetrical 1,3-diynes in high yields. The ionic liquid could be reused for at least five times without apparent decrease of the yield.

Full text of DOI:10.1007/s11164-013-1042-2

Res Chem Intermed
DOI 10.1007/s11164-013-1042-2
Synthesis of symmetrical 1,3-diynes in water-soluble
ionic liquid [DMIM]Me2PO4
•
Wensheng Zhang Wenjing Xu Fei Zhang
•
•
•
Hui Jin Yuzhe Wang Jitao Li
•
Received: 23 December 2012 / Accepted: 10 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Treatment of a variety of arynes in water-soluble ionic liquid [DMIM]-
Me2PO4 in the presence of catalytic amount of CuI and inexpensive NH3ÁH2O under
aerobic conditions afforded the corresponding symmetrical 1,3-diynes in high
yields. The ionic liquid could be reused for at least five times without apparent
decrease of the yield.
Keywords Diyne Á Glaser reaction Á CuI Á Synthesis Á Ionic liquid
Introduction
Conjugated diynes are recurring building blocks for the synthesis of natural
products, pharmaceuticals, and bioactive compounds with antiinflammatory,
antifungal, anti-HIV, antibacterial, or anticancer activities [1–9]. In addition,
conjugated diynes have found wide applications in the construction of industrial
intermediates and materials, particularly macrocyclic annulenes, organic conduc-
tors, supramolecular switches, and carbon-rich materials [10–14]. Therefore, much
attention [15–36] 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 has been the homocoupling of volatile and savory terminal alkynes [37].
W. Zhang (&) Á W. Xu Á Y. Wang Á J. Li
School of Biological and Chemical Engineering, Jiaozuo Teachers’ College, Shanyang Road 998,
Jiaozuo 450001, China
e-mail: tongjizws@163.com
F. Zhang
Jiaozuo Vocational Education Center, Huayuan Road 57, Jiaozuo 454001, China
H. Jin
School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China
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W. Zhang et al.
Ionic liquids have become solvents of choice in many applications [38–39]. More
often than not, symmetrical 1,3-diynes were obtained in organic solvents such as
DMF, DMSO, and MeCN. Yadav’s group reported that terminal alkynes undergo
oxidative-coupling smoothly in the presence of the CuCl–TMEDA catalytic system
in water-insoluble ionic liquid [BMIM]PF6 under aerobic conditions [39]. In this
article, with the desire to avoid the use of toxic organic solvent, we developed a
facile method for the synthesis of symmetrical diynes 2 from commercially
available arynes in water-soluble ionic liquid [DMIM]Me2PO4 (1,3-dimethylimi-
dazolium dimethylphosphate) (Scheme 1) in the presence of CuI and inexpensive
NH3ÁH2O.
Results and discussion
Our initial attempt began with an effort to optimize reaction conditions for the
oxidation coupling of terminal acetylenes. Phenylacetylene 1a and NH3ÁH2O were
chosen as the model substrate and base, respectively, for the optimization process
(Table 1, entries 1–8). The experiment was carried out with 1a (1 mmol), CuI
(20 mmol %), and NH3ÁH2O (2 equiv.) in water-insoluble ionic liquids (10 mL).
The reaction mixture was stirred at room temperature for 10 h. A series of water-
insoluble ionic liquids including 1-butyl-3-methylimidazolium hexafluorophosphate
([BMIM]PF6), 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM]BF4),
1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]imide ([EMIM]Tf2N),
and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTf) were
screened. The expected product 2a was afforded in only 22–37 % yields (Table 1,
entries 1–4). Fortunately, when water-soluble [DMIM]Me2PO4 was used, an
excellent yield of the desired 2a was obtained (Table 1, entry 5). The screening of
various bases (Table 1, entries 6–9) revealed that NH3ÁH2O was the best choice and
organic bases such as Et3N, DBU, DABCO, and Et2NH were less effective for the
water-soluble ionic liquid system.
Other terminal acetylenes besides phenylacetylene were employed successfully
using the optimized conditions (Table 2, entries 9–12). This ionic liquid system
proved to be applicable for arynes bearing both electron-donating groups such as
Me and MeO and electron-withdrawing groups like Cl, Br, and F, affording
products 2b–2i in 80–94 % yields (Table 2, entries 2–9). The steric hindrances of
the substituents like Cl, Br, and OMe on the ortho- position of the aromatic ring did
not alter the efficiency of the reaction (Table 2, entries 7–9).
CuI (20 mmol%)
NH3 H2O (2 equiv.)
R
R
R
[DMIM]Me2PO4, air
rt, 10 h
1
2
Scheme 1 Synthesis of symmetrical diynes from arynes in water-soluble ionic liquid
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Synthesis of symmetrical 1,3-diynes in [DMIM]Me2PO4
Table 1 Optimization of the reaction conditions based on 1a
Entry
Solvent
Base
1a yield (%)a
1
2
3
4
5
6
7
8
9
a
[BMIM]PF6
NH3ÁH2O
NH3ÁH2O
NH3ÁH2O
NH3ÁH2O
NH3ÁH2O
Et3N
37
33
22
30
94
55
48
49
55
[HMIM]BF4
[EMIM]Tf2N
[BMIM]OTf
[DMIM]Me2PO4
[DMIM]Me2PO4
[DMIM]Me2PO4
[DMIM]Me2PO4
[DMIM]Me2PO4
DBU
DABCO
Et2NH
Isolated yield
Experimental
Melting points were recorded using a WRS-1B digital melting point apparatus and
1
are uncorrected. H NMR spectra were recorded using Bruker DPX-400 spectrom-
eter in CDCl3 with SiMe4 as an internal standard. MS data were measured using a
Varian-310 mass spectrometer. Commercially 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- to
400-mesh silica gel at medium pressure.
1,3-Diynes (2); general procedure
Arynes 1 (1 mmol), NH3ÁH2O (2 equiv.) and CuI (0.2 mmol) were dissolved in
[DMIM]Me2PO4 (10 mL), and the reaction system was stirred at room temperature
for 10 h. After the completion of the reaction screened by TLC, the mixture was
filtered and extracted with Et2O (10 9 3 mL). The ionic liquid layer was collected
and dried under reduced pressure at 80 °C for 6 h before reuse. The combined ether
layer was washed with water, dried over anhydrous Na2SO4, and concentrated under
reduced pressure. Purification by column chromatography afforded products 2. The
1
structure of products 2 were fully consistent with their H NMR data [15–36]. The
IL could be reused for at least five times without effect of the yield.
1,4-Diphenylbuta-1,3-diyne (2a)
Yield: 182 mg (90 %); white solid; mp 86–86.5 °C (lit.33 86–87 °C); Rf = 0.9
1
(EtOAc-petroleum ether, 1:20). H 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-methylphenyl)buta-1,3-diyne (2b)
Yield: 212 mg (92 %); white solid; mp 182.1–182.5 °C (lit.34 182–183 °C, lit.35
137–138 °C); Rf = 0.85 (EtOAc-petroleum ether, 1:20). 1H NMR (400 MHz,
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W. Zhang et al.
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Synthesis of symmetrical 1,3-diynes in [DMIM]Me2PO4
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W. Zhang et al.
CDCl3): d = 2.36 (s, 6H, CH3), 7.14 (d, J = 8.0 Hz, 4H, ArH), 7.42 (d, J = 8.0 Hz,
4H, ArH). MS (ESI): m/z = 230 [M?].
1,4-Bis(4-methoxypheny1)buta-1,3-diyne (2c)
Yield: 228 mg (87 %); white solid; mp 139–140.5 °C (lit.34 140–141 °C); Rf = 0.8
1
(EtOAc-petroleum ether, 1:20). H NMR (400 MHz, CDCl3): d = 3.82 (s, 6H,
CH3), 6.85 (d, J = 8.8 Hz, 4H, ArH), 7.46 (d, J = 8.8 Hz, 4H, ArH).
1,4-Bis(4-fluorophenyl)buta-1,3-diyne (2d)
Yield: 138 mg (56 %); white solid; mp 187.3–188 °C (lit.34 194–195 °C, lit.35
187–189 °C); Rf = 0.8 (EtOAc-petroleum ether, 1:20). 1H NMR (400 MHz,
CDCl3): d = 7.04 (t, J = 8.5 Hz, 4H, ArH), 7.49–7.53 (m, 4H, ArH).
1,4-Bis(3-methylphenyl)buta-1,3-diyne (2e)
Yield: 205 mg (89 %); white solid; mp 68–68.5 °C (lit.34 68–70 °C, lit.36
74–75 °C); Rf = 0.85 (EtOAc-petroleum ether, 1:20). 1H NMR (400 MHz, CDCl3):
d = 2.34 (s, 6H, CH3), 7.17–7.35 (m, 8H, ArH).
1,4-Bis(3-methoxypheny1)buta-1,3-diyne (2f)
Yield: 233 mg (89 %); yellow solid; mp 91.8–92.9 °C (lit.34, 35 92–93 °C); Rf =
1
0.8 (EtOAc-petroleum ether, 1:20). H NMR (400 MHz, CDCl3): d = 3.81 (s, 6H,
CH3), 6.93–7.24 (m, 8H, ArH).
1,4-Bis(2-chlorophenyl)buta-1,3-diyne (2g)
Yield: 230 mg (85 %); yellow solid; mp 139–140.5 °C (lit.35 138–140 °C);
Rf = 0.75 (EtOAc-petroleum ether, 1:20). 1H NMR (400 MHz, CDCl3):
d = 7.23–7.33 (m, 4H, ArH), 7.42 (d, J = 9.2 Hz, 2H, ArH), 7.58 (d, J = 6.0 Hz,
2H, ArH).
1,4-Bis(2-bromophenyl)buta-1,3-diyne (2h)
Yield: 300 mg (83 %); yellow solid; mp 132.5–133.8 °C; Rf = 0.8 (EtOAc-
petroleum ether, 1:20). 1H NMR (400 MHz, CDCl3): d = 7.21–7.31 (m, 4H, ArH),
7.57–7.62 (m, 4H, ArH).
1,4-Bis(2-methoxypheny1)buta-1,3-diyne (2i)
Yield: 223 mg (85 %); white solid; mp 137.8–149.5 °C (lit.33 138–140 °C);
Rf = 0.8 (EtOAc-petroleum ether, 1:20). 1H NMR (400 MHz, CDCl3): d = 3.88 (s,
6H, CH3), 6.86–6.91 (m, 4H, ArH), 7.29–7.42 (m, 4H, ArH).
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Synthesis of symmetrical 1,3-diynes in [DMIM]Me2PO4
Conclusion
In conclusion, we have developed a new method for the synthesis of symmetrical
1,3-diynes from arynes catalyzed by CuI-NH3ÁH2O system in water-soluble ionic
liquid [DMIM]Me2PO4. The ionic liquid could be reused at least five times.
Acknowledgments This study was supported by the Program for Science & Technology Innovation
Talents in Universities of Henan Province (No. 2011HASTIT032), the Foundation of He’nan Educational
Committee (No. 2011C150001), the Foundation of Jiaozuo Scientific and Technological Bureau
(No. 201113), and the Foundation of Henan Scientific and technological Committee (No. 112300410236).
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