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CuI-catalyzed homocoupling of terminal alkynes to 1 3-diynes.

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Full Paper
Received: 9 February 2010
Revised: 26 April 2010
Accepted: 26 April 2010
Published online in Wiley Online Library: 27 May 2010
(wileyonlinelibrary.com) DOI 10.1002/aoc.1681
CuI-catalyzed homocoupling of terminal
alkynes to 1,3-diynes
Kun Yina , Chun-Ju Lia , Jian Lia and Xue-Shun Jiaa,b∗
A simple and efficient protocol for CuI-catalyzed oxidative homocoupling reaction of terminal alkynes to symmetrical 1,4disubstituted 1,3-diynes was reported. The reaction can be carried out in the open air, using NaOAc as a base in the absence of
any other additives. A variety of terminal alkynes were converted to the corresponding 1.3-diynes in good to excellent yields
c 2010 John Wiley & Sons, Ltd.
without any side product formation. Copyright Supporting information may be found in the online version of this article.
Keywords: homocoupling; terminal alkynes; 1,3-diynes; copper(I) iodide; NaOAc
Introduction
16
1,3-Diynes occur widely in numerous natural products, pharmaceuticals and bioactive compounds with antiinflammatory,
antifungal, anti-HIV, antibacterial or anticancer activities.[1] For
example, diplyne derivatives (Scheme 1), isolated from the Philippines sponge Diplastrella, exhibit effective anti-HIV activities.[1a]
In addition, conjugated diynes play an important role in the
construction of macrocyclic annulenes,[2,3] organic conductors,[4,5]
supramolecular switches[6] and carbon-rich materials.[2,5] Therefore, much attention[7] has been devoted to the development
of new and efficient methods for the synthesis of diynes since
1869.[8] Catalytic systems mediated by a combination of palladium (Pd) and copper salts are one of the most attractive
routes for the homocoupling of terminal alkynes due to their
efficiency and mildness.[9] However, palladium reagents are expensive, and they often require air-sensitive and expensive phosphine
ligands as well as amine reagents.[9a – i] Very recently, the CuClcatalyzed homocoupling reaction of terminal alkynes has been
reported.[10] However, this protocol requires TMEDA or DBEDA as
a ligand (other ligands are unsuccessful, such as salen, DCU and
1,5-cis-diazadecalin) and the sterically hindered amine (DBU or
DABCO) as a base (other bases are unsuccessful, such as K2 CO3 ,
Cs2 CO3 , TEA, DIPA and 1,5-naphthy-ridine) as well as a long reaction time. This method is also unsuccessful in the coupling
of some alkynes, especially the alkyl-substituted alkynes to give
diynes in low yields. In some cases, side products were also
generated.
From the economic and environmental point of view, it is
significant to search new approaches for Pd-, ligand- and aminefree homocoupling of terminal alkynes. Mizuno and co-workers
have demonstrated Pd- and amine-free oxidative terminal alkyne
homocoupling catalyzed by a monomeric dicopper-substituted
silicotungstate, [tetra-n-butylammonium]4 [γ -H2 SiW10 -O36 Cu2 (µ1,1-N3 )2 ],[11] but the catalyst was not commercially available, and
was synthesized using explosive sodium azide as reagents.[11,12]
Recently, we described the CuI-mediated homocoupling reaction of terminal alkynes.[13] However, a stoichiometric amount
of CuI and an expensive and harmful oxidant iodine were required. Herein, we wish to report our recent finding that a
Appl. Organometal. Chem. 2011, 25, 16–20
Scheme 1. Diplyne derivatives with anti-HIV activities.
catalytic amount of CuI (5.0 mol%), in the presence of 1.0
equiv. of NaOAc (instead of amine reagents as base) and
environmentally benign air (as the oxidant), is an efficient catalytic system for the homocoupling of various terminal alkynes
(Scheme 2). The present procedure is interesting due to the
simple experimental procedures, use of air as environmentally friendly oxidant, and avoidance of harmful and expensive
reagents.
Results and Discussion
Our initial experiments were carried out using 1-ethyl-4ethynylbenzene (1b) as a model substrate, CuI as catalyst, air
as oxidant, and inorganic base as base (Table 1). Some preliminary studies revealed that the best result was obtained when
the homocoupling was run with 5.0 mol% CuI, 1.0 equiv. sodium
acetate and N,N-dimethyl formamide (DMF) as solvent at 90 ◦ C
(Table 1, entry 6). The results employing various inorganic bases
are also listed in Table 1. Apparently, NaOAc is the most optimal
base among the inorganic bases used in this paper. Using the
∗
Correspondence to: Xue-Shun Jia, Shanghai University, Department of Chemistry, 99 Shangda Road, Shanghai, 200444, China.
E-mail: xsjia@mail.shu.edu.cn
a Department of Chemistry, Shanghai University, Shanghai, 200444, China
b Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling
Road, Shanghai 200032, China
c 2010 John Wiley & Sons, Ltd.
Copyright Cul-catalyzed homocoupling of terminal alkynes to 1,3-diynes
Scheme 2. Alkynes 1a-m used for the homocoupling.
Table 1. Inorganic base screening for the homocoupling of 1ba
Table 2. Solvent and temperature screening for the homocoupling
of 1ba
5 mol% CuI,
air, bases
Et
5 mol% CuI,
Et
air, NaOAc
DMF, 90°C
1b
1b
Et
Et
Et
Et
2b
2b
Entry
Base (equiv.)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
Na2 CO3 (1.0)
K2 CO3 (1.0)
Cs2 CO3 (1.0)
NaHCO3 (1.0)
NaOH (1.0)
NaOAc (1.0)
NaOAc (0.75)
NaOAc (0.3)
NaOAc (2.0)
24
24
24
24
24
5
6
12
5
21
52
55
30
40
91
86
78
92
a Reaction conditions: 1b (1.0 mmol), CuI (5.0 mol%), air, base, DMF
(1.5 ml), 90 ◦ C. b Isolated yield.
Appl. Organometal. Chem. 2011, 25, 16–20
1
2
3
4
5
6
7
8
9
10
Solvent
Nitromethane
Dioxane
Cyclohexanone
n-Heptane
Toluene
N-Methylpyrrolidone
Dimethyl sulfoxide
DMF
DMF
DMF
Temperature (◦ C) Time (h) Yield (%)b
90
90
90
90
90
90
90
90
65
25
10
10
10
10
10
5
5
5
16
48
7
12
11
10
– c
72
85
91
83
28
a
Reaction conditions: 1b (1.0 mmol), CuI (5.0 mol %), air, NaOAc
(1.0 mmol), solvent (1.5 ml), 90 ◦ C. b Isolated yield. c No reaction
occurred.
high polarity solvents, DMF and dimethyl sulfoxide (Table 2, entries
7 and 8), exhibited significant superiorities over low-polarity solvents. For example, the employment of n-heptane led to very low
yield (Table 2, 10%, entry 4), whereas no reaction occurred when
toluene was used as solvent (Table 2, entry 5). On the other hand,
the product conversion was susceptible to temperature changes
(Table 2, entries 8–10). The decrease of reaction temperature to
25 ◦ C led to long reaction time and low yields (Table 2, entry 10).
Encouraged by these experimental results, we then focused our
attention on substrate generality using the optimized reaction
conditions. Various terminal alkynes including aliphatic and
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
17
CuI–NaOAc system, the effect of base concentrations was also
studied. As can be seen from Table 1, the reaction can be carried out in 78% yield in the presence of 0.3 equiv. base (Table 1,
entry 8). The increase of NaOAc amount from 0.3 to 1.0 equiv.
results in a significant improvement of reaction yield from 78 to
91% (Table 1, entries 6–8), while the increase in NaOAc amount
from 1.0 to 2.0 equiv. does not obviously enhance transformation yields (Table 1, entry 9). All of the following experiments
were thus performed using a 1.0 equiv. amount of NaOAc as
bases.
To study the influence of solvents and temperature (Table 2), the
experiments were first carried out in different solvents with higher
boiling point (>90 ◦ C). From Table 2, the results clearly show that
Entry
K. Yin et al.
Conclusions
Table 3. CuI-catalyzed homocoupling of terminal alkynesa
5 mol% CuI, NaOAc
2R
DMF, 90°C, air
1a~m
Entry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
R
R
2a~m
1
CuI (mol%)
1a
1a
1b
1c
1d
1e
1e
1f
1f
1g
1h
1i
1j
1k
1k
1l
1m
5
10
5
5
5
5
20
5
15
5
5
5
5
5
10
5
5
Time(h)
30
8
5
5
5
30
8
24
14
3.5
4
3
5
12
5
3.5
10
Yield (%)b
97(2a)
95(2a)
91(2b)
92(2c)
92(2d)
80(2e)
85(2e)
70(2f)
92(2f)
80(2g)
73(2h)
90(2i)
75(2j)
18(2k)
78(2k)
85(2l)
72(2m)
a
Reaction conditions: 1 (1.0 mmol), CuI (5–20 mol%), air, NaOAc
(1.0 mmol), DMF (1.5 ml), 90 ◦ C. b Isolated yield.
18
aromatic acetylenes were examined under the optimal conditions
and the results are summarized in Table 3. As can be seen in
Table 3, aromatic acetylenes with the electron-donating groups on
aromatic rings such as ethyl, n-propyl, and n-penyl groups facilitate
the reaction, allowing shorter reaction time (Table 3, entries 3–5),
while the reaction proceeded more slowly for other substituents,
–H, electron-donating group –OCH3 and electron-withdrawing
group, –F (Table 3, entries 1, 6 and 8). In such cases, increasing
the amount of catalyst (CuI) could make significant improvements
(Table 3, entries 2, 7 and 9). For example, the reaction time of
homocoupling of phenylacetylene (1a) was shortened from 30 to
8 h by increasing the amount of CuI to 10 mol% (Table 3, entries
1 and 2). On the other hand, the method is also applicable to
the aliphatic alkyne, which could be converted to corresponding
1,3-diynes within 5 h (Table 3, entries 10–13 and 16). The reaction
was sluggish in the case of propargyl alcohol (1k) and cyclohex1-enylacetylene (1m). In particular, propargyl alcohol (1k) gave
a very low yield after a longer reaction time (Table 3, entry
14). Similarly to the above aromatic alkynes, the increase in the
amount of CuI (5 → 10%) facilitates the transformation, allowing
shorter reaction time (12 → 5 h) and better yield (18 → 78%).
It is obvious that alkenyl, hydroxyl, cyclopropyl, fluoride and
ether groups are not affected under the reaction conditions. The
transformations proceeded smoothly without any side product
formation.
The advantages of our method include the use of commercially
available and cheap CuI (5 mol%) and an inorganic base (NaOAc)
instead of amines, environmentally benign air as an oxidant
instead of the stoichimetric oxidants such as I2 , PhI(OAc)2 , PhI O,
BrCH2 CO2 Et and Me3 NO, simple experimental procedure, good
to excellent yields, avoiding expensive palladium catalysts and
ligands.
wileyonlinelibrary.com/journal/aoc
In conclusion, we have successfully developed a facile and efficient
protocol for CuI-catalyzed oxidative homocoupling reaction of
terminal alkynes to 1,3-diynes. [All of the products (2a–2m) are
known and were characterized by comparison of their spectral
data with those of authentic samples.] The reaction proved
to be tolerant to a variety of functional groups. The great
attractiveness of the current protocol lies in simple experimental
procedure, avoidance of expensive palladium catalysts and
ligands, the use of air as oxidant instead of iodine, PhI(OAc)2 ,
PhI O, BrCH2 CO2 Et and Me3 NO, the use of an inorganic
solid base (NaOAc) instead of amines, and good to excellent
yields without any side product formation. We believe that our
present procedure will be an excellent alternative to existing
methods.
Experimental Section
All commercially available reagents were used without further
purification unless otherwise stated. Melting points were recorded
using melting point apparatus and were uncorrected. All 1 H NMR
spectra were recorded on Brucker AC-500 (500 MHz) spectrometer.
13 C NMR spectra were recorded on Brucker AC-125 spectrometer.
Chemical shifts (δ) are reported in ppm relative to TMS using
CDCl3 . EI-MS were determined with a HP5989B mass spectrometer.
IR spectra were taken as KBr disks with a Bruck vector 22
spectrometer. Chemical yields refer to pure isolated product.
General Procedure for the Homocoupling of Terminal Alkynes
To a stirred solution of alkyne (1 mmol) in DMF (1.5 ml), CuI
(5–20 mol%, see Table 3) and NaOAc (1 mmol) were added
successively in the open air. The resulting mixture was then
allowed to react at 90 ◦ C in air. Progress of this reaction was
monitored by TLC. After completion of the reaction, 6 ml of ethyl
acetate was added. The mixture was filtered through a pad of
diatomite under reduced pressure, and the filtration residue was
washed with ethyl acetate. The filtrate was washed with water,
and dried over anhydrous Na2 SO4 . The solvent was removed
under reduced pressure. The residue was then purified by column
chromatography on silica gel using petroleum ether as eluent to
afford the corresponding 1,3-diynes.
1,4-Diphenyl buta-1,3-diyne (2a)
White solid. M.p. 85–86 ◦ C (lit.[9i] 86–88 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 7.54–7.53 (m, 4H), 7.39–7.33 (m, 6H); 13 C NMR (CDCl3 ,
125 MHz) δ 132.6, 129.3, 128.6, 121.9, 81.7, 74.1; MS: m/z (%) 202
(M+ , 100).
1,4-Bis(4-ethylphenyl) buta-1,3-diyne (2b)
White solid. M.p. 95–96 ◦ C (lit.[14] 98–99 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 7.46 (d, J = 8.5 Hz, 4H), 7.18 (d, J = 8.0 Hz, 4H), 2.67 (q,
J = 7.5 Hz, 4H), 1.25 (t, J = 7.5 Hz, 6H); 13 C NMR (CDCl3 , 125 MHz)
δ 145.9, 132.6, 128.2, 119.1, 81.7, 73.6, 29.1, 15.4; MS: m/z (%) 258
(M+ , 100).
c 2010 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2011, 25, 16–20
Cul-catalyzed homocoupling of terminal alkynes to 1,3-diynes
1,4-Bis(4-n-propylphenyl) buta-1,3-diyne (2c)
Eicosa-9,11-diyne (2l)[9i]
White solid. M.p. 108–109 ◦ C (lit.[15] 107.6 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 7.44 (d, J = 8.0 Hz, 4H), 7.14 (d, J = 8.0 Hz, 4H), 2.59
(t, J = 7.5 Hz, 4H), 1.62 (m, 4H), 0.94 (t, J = 7.5 Hz, 6H); 13 C NMR
(CDCl3 , 125 MHz) δ 144.4, 132.5, 128.8, 119.2, 81.7, 73.6, 38.2, 24.4,
13.9; MS: m/z (%) 286 (M+ , 57).
Colorless oil; 1 H NMR (CDCl3 , 500 MHz) δ 2.23 (t, J = 7.5 Hz, 4H),
1.53–1.26 (m, 24H), 0.87 (t, J = 7.5 Hz, 6H); 13 C NMR (CDCl3 ,
125 MHz) δ 77.6, 65.4, 31.9, 29.3, 29.2, 28.9, 28.5, 22.8, 19.3, 14.2.
1,4-Bis(4-n-pentylphenyl) buta-1,3-diyne (2d)
White solid. M.p. 64–66 ◦ C (lit.[9i] 63–65 ◦ C). 1 H NMR (CDCl3 ,
500 MHz) δ 6.25 (t, J = 4.0 Hz, 2H), 2.03–2.01 (m, 8H), 1.65–1.54
(m, 8H); 13 C NMR (CDCl3 , 125 MHz) δ 138.2, 120.0, 82.8, 71.6, 28.8,
25.9, 22.2, 21.4.
White solid. M.p. 83–84 ◦ C (lit.[9j] 85–86 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 7.43 (d, J = 8.5 Hz, 4H), 7.14 (d, J = 8.0 Hz, 4H),
2.60 (t, J = 7.5 Hz, 4H), 1.63–1.56 (m, 4H), 1.36–1.25 (m, 8H), 0.89
(t, J = 7.0 Hz, 6H); 13 C NMR (CDCl3 , 125 MHz) δ 144.6, 132.5, 128.7,
119.1, 81.7, 73.6, 36.1, 31.6, 31.0, 22.7, 14.2; MS: m/z (%) 342 (M+ ,
100).
1,4-Bis(4-methoxylphenyl) buta-1,3-diyne (2e)
White solid. M.p. 138–139 ◦ C (lit.[9i] 138–140 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 7.46 (d, J = 8.5 Hz, 4H), 6.85 (d, J = 8.5 Hz, 4H), 3.82
(s, 6H); 13 C NMR (CDCl3 , 125 MHz) δ 160.3, 134.1, 114.2, 113.9, 81.4,
73.1, 55.4; MS: m/z (%) 262 (M+ , 100).
1,4-Bis(cyclohex-1-enyl)buta-1,3-diyne (2m)
Acknowledgments
We thank the National Natural Science Foundation of China
(nos 20872087 and 20902057), the Key Laboratory of Synthetic
Chemistry of Natural Substances, Chinese Academy of Sciences,
Leading Academic Discipline Project of Shanghai Municipal
Education Commission (no. J50101) and the Innovation Fund
of Shanghai University for financial support.
Supporting information
1,4-Bis(4-fluorophenyl) buta-1,3-diyne (2f)
◦
(lit.[16]
◦
1H
190–191 C);
NMR (CDCl3 ,
White solid. M.p. 193 C
500 MHz) δ 7.53–7.49 (m, 4H), 7.04 (t, J = 8.5 Hz, 4H); 13 C
NMR (CDCl3 , 125 MHz) δ 164.2, 162.2, 134.7, 134.6, 118.0, 117.9,
116.1, 116.0, 80.6, 73.7; 19 F NMR (CDCl3 , 470.5 MHz) δ −108.430,
−108.449, −108.459, −108.466, −108.471, −108.478, −108.488;
MS: m/z (%) 238 (M+ , 100).
Ttetradeca-6,8-diyne (2g)[9i]
Colorless oil; 1 H NMR (CDCl3 , 500 MHz) δ 2.23 (t, J = 7.0 Hz, 4H),
1.54–1.48 (m, 4H), 1.36–1.29 (m, 8H), 0.87 (t, J = 7.0 Hz, 6H); 13 C
NMR (CDCl3 , 125 MHz) δ 77.6, 65.3, 31.1, 28.1, 22.3, 19.3, 14.0; MS:
m/z (%) 190 (M+ , 26).
2,2,7,7-Tetramethyl octa-3,5-diyne (2h)
White solid. M.p. 128–129 ◦ C (lit.[9i] 128–130 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 1.23 (s, 18H); 13 C NMR (CDCl3 , 125 MHz) δ 86.5, 63.8,
30.8, 28.1.
1,4-Dicyclopropyl buta-1,3-diyne (2i)[17]
Colorless liquid; 1 H NMR (CDCl3 , 500 MHz) δ 1.29–1.25 (m, 2H),
0.80–0.71 (m, 8H); 13 C NMR (CDCl3 , 125 MHz) δ 80.2, 60.9, 8.8, 0.14.
1,8-Bis(benzyloxy) octa-3,5-diyne (2j)
White solid. M.p. 38–39 ◦ C (lit.[18] 39 ◦ C); 1 H NMR (CDCl3 , 500 MHz)
δ 7.36–7.27 (m, 10H), 4.49 (s, 4H), 3.53 (t, J = 6.5 Hz, 4H), 2.59 (t,
J = 6.5 Hz, 4H); 13 C NMR (CDCl3 , 125 MHz) δ 138.0, 128.6, 127.9,
74.5, 73.2, 67.9, 66.4, 20.8; MS: m/z (%) 317 (M+ − 1, 1).
Hexa-2,4-diyne-1,6-diol (2k)
Appl. Organometal. Chem. 2011, 25, 16–20
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Copyright wileyonlinelibrary.com/journal/aoc
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White solid. M.p. 113–114 ◦ C (lit.[9e] 112 ◦ C); 1 H NMR (CDCl3 ,
500 MHz) δ 5.41 (t, J = 6.0 Hz, 2H), 4.17 (d, J = 6.0 Hz, 4H); 13 C
NMR (CDCl3 , 125 MHz) δ 79.6, 67.9, 49.4; MS: m/z (%) 110 (M+ , 70).
Supporting information may be found in the online version of this
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