Copper-impregnated magnetite as a heterogeneous catalyst for the homocoupling of terminal alkynes

Article abstract of DOI:10.1055/s-0032-1316872

Copper-impregnated magnetite is a versatile heterogeneous catalytic system for the synthesis of 1,3-diynes by the homocoupling of terminal alkynes. This catalyst does not require the use of pressurized oxygen as the oxidant and it does not need a solvent or harsh conditions to give the expected products. Moreover, the catalyst can be removed from the reaction medium simply by using a magnet. The reaction occurs at the lowest copper loading reported for any heterogeneous catalyst.

Full text of DOI:10.1055/s-0032-1316872

PAPER
▌1373
pCapoerpper-Impregnated Magnetite as a Heterogeneous Catalyst for the
Homocoupling of Terminal Alkynes
Copper/Magnetite-Catalyzed Homocoupling of Terminal Alkynes
Juana M. Pérez, Rafael Cano, Miguel Yus, Diego J. Ramón*
Departamento Química Orgánica and Instituto de Síntesis Orgánica, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Fax +34(96)5903549; E-mail: djramon@ua.es
Received: 29.01.2013; Accepted after revision: 03.03.2013
1
5
16
molecular sieves, or mesoporous silica. However, the
use of such catalysts entails some drawbacks that require
Abstract: Copper-impregnated magnetite is a versatile heteroge-
neous catalytic system for the synthesis of 1,3-diynes by the homo-
coupling of terminal alkynes. This catalyst does not require the use
9
–16
elimination, such as the need for a high metal loading,
of pressurized oxygen as the oxidant and it does not need a solvent the need to use high temperatures,1
2,13a,14,15
the need for
9
b,10b,c,12,13a,14–16
or harsh conditions to give the expected products. Moreover, the non-environmentally benign solvents,
the
1
0a,b,13a,14,15
catalyst can be removed from the reaction medium simply by using
a magnet. The reaction occurs at the lowest copper loading reported
for any heterogeneous catalyst.
need to use pressurized oxygen,
cases, the lack of recyclability of the catalyst.
and, in some
9a,b,10b,11,12,13a
An interesting cooperative effect was observed when the
reaction was carried out in the presence of homogeneous
mixtures containing a copper and an iron salt. In this
case, the loading of the copper salt could be reduced to 0.1
mol% in the presence of 10 mol% of iron(III) acetylaceto-
nate. We recently developed a new, simple, and robust
method for immobilizing various metal oxides on mag-
netite. With the cooperative effect of copper and iron in
mind, we decided to test a copper-impregnated magnetite
catalyst in the Glaser–Hay reaction. Here, we report the
first catalyst for this reaction that is derived from copper,
a cheap and safe first-row transition metal, impregnated
on magnetite and we report its use in the coupling of sev-
eral terminal alkynes.
Key words: alkynes, copper, heterogeneous catalysis, iron, sup-
ported catalysis, coupling, furans
1
7
1
The homocoupling of terminal alkynes to give 1,3-diynes
has attracted a great deal of attention in organic chemistry
because of the role of diynes as building blocks for many
1
8
1
9
2
natural products or for pharmaceuticals with antiinflam-
matory, antibacterial, antitumor, or antifungal activities.
Furthermore, 1,3-diynes have attracted the attention of
chemists as interesting materials that are useful as precur-
2
0
3
4
sors of polymers, macrocycles, or supramolecular struc-
tures.5
The symmetric coupling of simple terminal acetylenes,6
known as the Glaser–Hay reaction, was discovered over a
century ago, and the methodology for this reaction was
We selected the homocoupling of ethynylbenzene (1a) in
the presence of piperidine as a base as a model reaction for
optimizing the conditions (Table 1). Initially, we exam-
ined the reaction in various solvents (Table 1, entries 1–
), and we found that the best results were, in fact, ob-
tained in the absence of any solvent. Increasing the tem-
perature for the reaction did not improve the results (entry
7
improved shortly afterwards. Among the various metallic
salts that were used, copper emerged as the best metal for
catalyzing the transformation. In fact, the number of cop-
per complexes that have been identified as being capable
of successfully inducing this transformation continues to
9
1
0), whereas the reaction at room temperature only gave
8
increase. However, homogeneous catalysts have some
traces of product 2a (entry 11). The reaction failed in the
absence of the base (entry 12). We also examined the ef-
fects of changing the base by using various amines (en-
tries 13–15), and we obtained similar yields in only four
hours with various primary amines; however, the corre-
sponding amides were also obtained as byproducts. When
we used other organic or inorganic bases (entries 16–20),
we obtained lower yields. The product 2a was obtained in
quantitative yield only when we used potassium tert-bu-
toxide as the base, (entry 21). When the reaction was car-
ried out in the presence of 50 mol% of the base, the yield
decreased (entry 22); we therefore concluded that a stoi-
chiometric amount of the base is needed for the homocou-
pling (entries 21–22). Increasing the amount of base
further did not reduce the reaction time (entry 23). When
the reaction was performed under an argon atmosphere,
the yield decreased to 38% (entry 24). This confirmed that
the oxygen present in the air plays an important role in the
process and that it acts as the ultimate source of oxygen.
important drawbacks, such the need for high metal load-
ings and the inability to recycle the catalyst. A homoge-
neous copper acetate–poly(ethylene glycol) catalyst
system has been recycled up to five times, although this
was accompanied by a decrease in activity after each re-
activation step of treatment with acetic acid.
8b
Heterogeneous catalysts have been designed for perform-
ing this transformation and to facilitate the removal, re-
covery, and recycling of the catalysts. Although, there are
several examples of insoluble copper derivatives that are
9
able to induce the Glaser–Hay reaction, the most widely
used strategy has involved the use of copper salts support-
1
0
ed on various inert oxides, such as hydrotalcite, alumi-
1
1
12
13
14
na, zeolites, titania, silicotungstate complexes,
SYNTHESIS 2013, 45, 1373–1379
Advanced online publication: 14.03.2013
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0
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8
8
1
1
4
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DOI: 10.1055/s-0032-1316872; Art ID: SS-2012-Z0085-OP
Georg Thieme Verlag Stuttgart · New York
©

1374
J. M. Pérez et al.
PAPER
We then examined the effects of the amount of catalyst Table 1 Optimization of the Reaction Conditions (continued)
used (entries 25–27). Decreasing the amount of catalyst to
CuO–Fe3O4 (1.3 mol%)
0.26 mol% produced a 99% yield of 2a, although a longer
Ph
Ph
Ph
base
reaction time (48 hours) was needed (entry 25). Reactions
with a higher or lower loading of the metal did not im-
prove the results (entries 26 and 27). Finally, when we re-
peated the reaction under the optimized conditions but in
the absence of the catalyst, we recovered the starting ma-
terial after one week (entry 28). Note that performing the
reaction under an atmosphere of pure oxygen did not
change the results (entries 21 and 29).
solvent (2 mL)
1
a
2a
Entrya Base (mol%)
b
Solvent
Temp Time Yield of
(°C)
(h)
2a (%)
2
2
2
7g
t-BuOK (100)
t-BuOK (100)
t-BuOK (100)
–
–
–
60
60
60
24
99
0
8h
168
24
9i
99
Table 1 Optimization of the Reaction Conditions
a
b
c
d
e
f
Reaction carried out using 1a (2 mmol) under air.
Isolated yields after column chromatography.
N-Butyl-2-phenylacetamide was isolated in 13% yield.
Reaction carried out under argon.
Reaction carried out with 0.26 mol% of catalyst.
Reaction carried out with 0.13 mol% of catalyst.
Reaction carried out with 2.6 mol% of catalyst.
Reaction carried out in the absence of the catalyst.
Reaction carried out under O2.
CuO–Fe3O4 (1.3 mol%)
Ph
Ph
Ph
base
solvent (2 mL)
1a
2a
Entrya Base (mol%)
Solvent
Temp Time Yield of
b
g
h
i
(°C)
(h)
2a (%)
1
2
3
4
5
6
7
8
9
0
1
2
3c
4
5
6
7
8
9
0
1
2
3
4d
5e
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
piperidine (100)
–
THF
60
60
60
24
24
24
24
24
24
24
24
24
24
24
24
4
84
85
57
87
54
6
toluene
MeCN
Having determined the optimal conditions, we examined
the reactions with a variety of catalysts, prepared by a
simple impregnation protocol (Table 2). First, we evaluat-
ed the activity of the support by using magnetite as the
sole catalyst. Nanoparticles or microparticles of magnetite
were used, and the results showed that bare magnetite had
1,4-dioxane 60
DMF
60
60
60
60
60
90
25
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
H O
2
DMSO
14
0
Table 2 Optimization of the Catalyst
EtOH
catalyst
Ph
Ph
Ph
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
90
73
2
t-BuOK (100 mol%)
0 °C
6
1
a
2a
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
Entrya
Catalyst (mol%)
Time
d)
Yield (%)
b
(
of 2a
0
1
2
3
4
5
6
7
8
9
CuO/Fe O (0.26)
2
7
7
2
2
2
2
2
2
2
2
2
2
99
68
78
0
3
4
BuNH (100)
87
5
2
Fe O (0.13)
3
4
Et N (100)
24
24
24
24
24
24
24
24
24
24
24
48
48
3
c
Fe O (0.13)
3
4
DABCO (100)
KOAc (100)
79
0
Ru O /Fe O (0.28)
2
3
3
4
CoO/Fe O (0.35)
0
3
4
t-BuONa (100)
MeONa (100)
16
2
IrO /Fe O (0.03)
0
2
3
4
NiO/Fe O (0.2)
41
1
3
4
CsOH·H O (100)
60
88
99
75
99
38
99
26
2
PdO/Fe O (0.24)
3
4
KOH (100)
PtO–PtO /Fe O (0.12)
1
2
3
4
t-BuOK (100)
t-BuOK (50)
t-BuOK (200)
t-BuOK (100)
t-BuOK (100)
t-BuOK (100)
1
1
1
1
0
1
2
3
Pd(II,0)–Cu(II)/Fe O (0.3:0.16)
89
99
89
88
3
4
Cu(II,0)–Ni(II)/Fe O (0.22:0.18)
3
4
CuO (0.26)
CuO (0.26) + Fe O (0.13)
3
4
a
b
c
Reactions were carried out by using 1a (2 mmol) under air.
Isolated yields after column chromatography.
Reaction performed with nanoparticulate magnetite (< 50 nm).
2 f
6
Synthesis 2013, 45, 1373–1379
© Georg Thieme Verlag Stuttgart · New York

PAPER
Copper/Magnetite-Catalyzed Homocoupling of Terminal Alkynes
1375
a lower activity than the copper-impregnated form, need- gave the expected products 2 (Table 3). The reactions
ing longer reaction times and giving lower yields (Table seems to be more affected by the presence of chelating
1
8b
18b
18e
2
, entries 1, 2, and 3). Ruthenium, cobalt, iridium,
groups than by the electronic nature of the substrates, and
1
8c
18d
palladium, and platinum did not show any activity in reactants with the strongest chelating ability gave the low-
this transformation. The nickel catalyst showed a mod- est yields (entries 1–5). The presence of steric hindrance
erate activity, giving the expected product in 41% yield in the aryl moiety decreased the yield (entry 6). Finally,
18b
(entry 7). Reactions using bimetallic catalysts gave the ex- the reaction could also be performed by using less-reac-
pected product in high yields (entries 10–11), with the tive aliphatic alkynes, and the expected products 2 were
copper–nickel1 catalyst attaining a quantitative yield. obtained in all the cases, albeit in slightly lower yields
Reactions using copper oxide alone or together with mag- (entries 10–14).
8c
netite gave slightly lower yields than that obtained with
the impregnated catalyst (compare entries 1, 12, and 13),
Table 3 Preparation of Various 1,3-Diynes
but we do not have any clear explanation for this cooper-
ative effect.
CuO–Fe O4 (0.26 mol%)
3
R
R
R
t-BuOK (100 mol%)
Having established the optimal reaction conditions, we
examined the problem of recycling (Figure 1). When the
catalyst was recovered from the reaction mixture by using
a magnet, washed with methanol, and reused under the
same conditions, we obtained the expected product 2a in
60 °C
1
2
Entrya
R
Product
Time (d) Yield (%)
b
1
2
3
4
5
6
7
8
9
Ph
2a
2b
2c
2d
2e
2f
2
99 (99c)
20
99% yield. However, in the fourth cycle of use and recov-
4-Me NC H
4
6
2
6
ery, the yield was only 75%, indicating that there is a
small decrease in the activity of the catalyst. In the fifth
cycle, the yield fell sharply to 20%.
4-MeOC H
7
57
6
4
4-MeC H
2 (1)c
91 (99)c
99
6
4
4-ClC H
4
6
4
4
2-ClC H
2
32
6
4-F CC H
4
2g
2h
2i
2
99
3
6
4-BrC H
7
26 (17)c
99
6
4
3-MeC H
3
6
4
1
1
1
0
1
2
c-Hex
2j
3
70 (88)c
92
(CH ) Me
2k
2l
3
2
5
(CH ) Me
7 (3)c
50 (74)c
31
2
7
Figure 1 Yields obtained with recycled CuO/Fe O catalyst
3
4
13
(CH ) Me
2m
2n
7
2
2
9
1
4
(CH ) Cl
99
2
3
The nanosize distribution of the catalyst, as measured
from transmission electron microscopy, remained about
the same before and after the reaction. Before the reaction,
a
b
c
Reactions were carried out by using 1a (2 mmol) under air.
Isolated yields after column chromatography.
With Cu(II,0)–Ni(II)/Fe O (0.22/0.18 mol%) catalyst.
3
4
7
3% of the copper oxide particles on the surface of the cat-
alyst measured between 2 and 6 nm, whereas the corre-
sponding figure after the reaction was 68%. X-ray
photoelectron spectroscopy studies on the used catalyst
showed that the copper was partially reduced from an ini-
tial 4:1 mixture of Cu(II) and Cu(0) to a 1:1 mixture of
these oxidation states. The inductively coupled plasma–
mass spectroscopy analysis of the reaction solution
showed the presence of copper (6.2% of the initial
amount) and iron (0.22% of the initial amount). A similar
result was obtained when the catalyst was removed before
the mixture was cooled. These results appear to show that
not all copper on the surface of magnetite has the same ac-
tivity, and that the most-active species appear to leach
fastest.
Encouraged by the success that we achieved in homocou-
pling of terminal alkynes, we examined the hydration re-
action of 1,3-diynes to afford the corresponding 2,5-
disubstituted furans, a reaction that is catalyzed by various
21
copper salts. We performed the reaction with compound
a in dimethyl sulfoxide in the presence of potassium hy-
2
droxide and copper oxide/magnetite at 80 °C. To our de-
light, we obtained the desired furan 3a in quantitative
yield. However, it should be pointed out that the hydration
reaction performed in the absence of the catalyst also, sur-
prisingly, gave furan 3a in the same yield. We then at-
tempted a direct, two-step, one-pot transformation of
various alkynes into the corresponding 2,5-disubstituted
furans 3 (Table 4). Having obtained the diyne in the first
reaction step, we removed the catalyst with a magnet and,
without purification of the reagents, we added dimethyl
We also applied our optimized conditions to other sub-
strates. Reaction using various substituted arylalkynes 1
©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 1373–1379

1376
J. M. Pérez et al.
PAPER
sulfoxide and aqueous potassium hydroxide. Excellent re- trometer. TLC was performed on Schleicher & Schuell F1400/LS
2
54 plates coated with a 0.2-mm layer of silica gel. Detection was
sults were obtained for various types of 4-substituted aryl
diynes (entries 2–5). Unfortunately, when we used a cy-
cloaliphatic diyne, the reaction failed (entry 5) and the
substrate was recovered.
performed by irradiation with UV254 after staining with phosphomo-
lybdic acid [phosphomolybdic acid (25 g), Ce(SO ) 4 H O (10 g),
concd H SO (60 mL), and H O (940 mL)]. Chromatographic anal-
yses were performed by using an instrument equipped with a flame-
4
2·
2
2
4
2
ionization detector and a 30-m capillary column (0.32 mm diameter,
Table 4 One-Pot Preparation of 2,5-Furans
0.25 μm film thickness, HP–5 stationary phase) and with N (2
2
mL/min) as the carrier gas; the chromatograph was operated at a
pressure of 10 psi with an injector temperature of 270 °C and a de-
i) CuO–Fe3O4 (2.6 mol%)
t-BuOK (100 mol%), 60 °C
O
tector temperature of 300 °C. Retention times (t ) for all samples are
R
R
R
R
reported for the same gradient: 60 °C for 3 min, increasing by 15
ii) KOH (1000 mol%)
H2O (400 mol%)
DMSO (5 mL), 80 °C
°
C/min to 270 °C, then 270 °C for 15 min. Column chromatography
1
3
was performed by using 35–70 mesh silica gel 60. All reagents were
commercially available (Acros, Aldrich, Fluorochem) and were
used as received. Inductively coupled plasma–mass spectral analy-
ses were carried out on a Thermo Elemental VGPO-ExCell spec-
trometer. X-ray fluorescence analyses were carried out on a Philips
Magix Pro (PW2400) X-ray spectrometer equipped with a Rh X-ray
tube and a Be window. The reactions were performed in a twelve-
vessel carousel reaction station (Radleys). The NiO–Cu/Fe O and
Entrya
b
R
Product
Time (d) Yield (%)
1
2
3
4
Ph
3a
3b
3c
3d
3e
3
8
3
3
5
99
59
90
99
0
4-MeOC H
6
4
3
4
4-MeC H
CuO/Fe O catalyst were prepared according to the procedures de-
6
4
3 4
1
8c,20c
scribed in the literature.
4-F CC H
3
6
4
Catalyst Preparation; General Procedure
5
c-Hex
2
Commercially available Fe O (< 5 μm, BET area: 9.86 m /g; 4 g,
3
4
1
7 mmol) was added to a stirred soln of the appropriate metal chlo-
a
Reaction carried out by using 1 (2 mmol) and H O (4 mmol) under
1
2
2
ride MCl (1 mmol) [or a mixture of M Cl (1 mmol) and M Cl (1
mmol) for bimetallic species] in deionized H O (120 mL). In the
cases of the Pd and Cu–Pd catalysts, a large excess of KCl (1 g, 13
n
n
n’
air.
b
2
Isolated yield after column chromatography.
mmol) was also added to the initial soln to increase the solubility of
the PdCl . After 10 min at r.t., the mixture was slowly basified with
2
Finally, we examined the decarboxylative coupling
1
1
M aq NaOH to a pH of about 13. The mixture was then stirred for
d at r.t. under air. The catalyst was collected by filtration, washed
reaction22 of 3-phenylprop-2-ynoic acid (4). The copper
catalyst gave only a 21% yield of the expected diyne 2a. with deionized H O (3 × 10 mL), and dried for 24 h at 100 °C in a
2
However, this product was obtained quantitatively when standard glassware oven.
we used NiO–Cu/Fe O as the catalyst (Scheme 1).
3
4
1
,3-Diynes 2a–n; General Procedure
t-BuOK (224 mg, 2 mmol) and CuO/Fe O (10 mg, 0.26 mol%) or
3
4
catalyst
NiO–Cu/Fe O (10 mg, 0.18/0.22 mol%) were added to a stirred
3 4
Ph
CO2H
Ph
Ph
soln of the appropriate alkyne 1 (2 mmol) under air, and the mixture
was vigorously stirred at 60 °C until the reaction was complete. The
catalyst was collected by using a magnet and washed successively
Et3N (0.07 mL)
DMF (1.5 mL)
30 °C, 2 d
4
2a
1
CuO–Fe3O4
21%
100%
with EtOAc (2 × 5 mL) and H O (2 × 5 mL). The collected organic
2
(
2.1 mol%)
NiO/Cu-Fe3O4
1.5/1.83 mol%)
phases were dried (MgSO ) and concentrated under reduced pres-
4
sure. The crude product was purified by column chromatography.
(
1
,1′-Buta-1,3-diyne-1,4-diyldibenzene (2a)13b
Scheme 1 Decarboxylative coupling reaction of 3-phenylprop-2-
White solid; yield: 200 mg (99%); t = 15.8 min; mp 83–85 °C
R
ynoic acid
(hexane); R = 0.67 (hexane–EtOAc, 4:1).
f
–
1
IR (ATR): 3050, 1593, 1485 cm .
1
In conclusion, we have demonstrated that copper-impreg-
H NMR (300 MHz, CDCl ): δ = 7.25–7.30 (m, 6 H, ArH), 7.45–
3
nated magnetite is a good catalyst for homocoupling of 7.50 (m, 4 H, ArH).
terminal alkynes under solvent-free conditions and in the
absence of oxygen pressure. Furthermore, this reaction re- 128.4 (4 C), 129.2 (2 C), 132.5 (4 C).
quires the lowest reported loading of copper for any het-
13
C NMR (75 MHz, CDCl ): δ = 73.9 (2 C), 81.5 (2 C), 121.8 (2 C),
3
MS (EI, 70 eV): m/z (%) = 101 (8), 200 (22), 201 (11), 202 (100)
+
+
erogeneous catalysis. Moreover, the catalyst can be easily [M ], 203 (17) [M + H] .
removed from the reaction medium merely by using a
4
,4′-Buta-1,3-diyne-1,4-diylbis(N,N-dimethylaniline) (2b)9a
magnet, and it can be reused up to three times without any
reduction in yield.
Pale-brown solid; yield: 58 mg (20%); t = 13.4 min; mp 215–217
R
°C (hexane); R = 0.43 (hexane–EtOAc, 4:1).
f
–
1
IR (ATR): 1598, 1358, 1225 cm .
Melting points were determined by using a Reichert Thermovar ap-
paratus. NMR spectra were recorded on a Bruker AC–300 spec-
1
H NMR (300 MHz, CDCl ): δ = 3.00 (s, 12 H, CH × 4), 6.65–6.70
d, J = 8.8 Hz, 4 H, ArH), 7.35–7.40 (d, J = 8.8 Hz, 4 H, ArH).
3
3
(
1
13
trometer (300 MHz for H and 75 MHz for C) with CDCl as the
3
13
C NMR (75 MHz, CDCl ): δ = 40.2 (4 C), 74.7 (2 C), 84.8 (2 C),
solvent and TMS as internal standard. FTIR spectra were recorded
on a JASCO 4100LE (Pike Miracle ATR) spectrophotometer. Mass
spectra (EI) were obtained at 70 eV on a Himazdu QP–5000 spec-
3
1
08.8 (2 C), 111.7 (4 C), 133.2 (4 C), 150.4 (2 C).
Synthesis 2013, 45, 1373–1379
© Georg Thieme Verlag Stuttgart · New York

PAPER
Copper/Magnetite-Catalyzed Homocoupling of Terminal Alkynes
1377
MS (EI, 70 eV): m/z (%) = 51 (15), 77 (40), 78 (11), 155 (19), 183
12), 201 (70), 202 (100), 203 (22), 207 (60), 208 (14), 229 (19),
1,1′-Buta-1,3-diyne-1,4-diylbis(4-bromobenzene) (2h)25
Pale-yellow solid; yield: 94 mg (26%); t = 20.7 min; mp 140–141
°C (hexane); R = 0.73 (hexane–EtOAc, 4:1).
(
R
+
269 (10), 288 (10) [M ].
f
–
1
IR (ATR): 1480, 1066 cm .
1
1
,1′-Buta-1,3-diyne-1,4-diylbis(4-methoxybenzene) (2c)23
Pale-yellow solid; yield: 150 mg (57%); t = 20.7 min; mp 131–133
H NMR (300 MHz, CDCl ): δ = 7.35–7.40 (d, J = 8.5 Hz, 4 H,
R
3
°
C (hexane); R = 0.37 (hexane–EtOAc, 4:1).
ArH), 7.45–7.50 (d, J = 8.5 Hz, 4 H, ArH).
f
–
1
13
IR (ATR): 3004, 2939, 2837, 1598, 1502 cm .
C NMR (75 MHz, CDCl ): δ = 77.2 (2 C), 81.0 (2 C), 120.6 (2 C),
3
1
131.7 (2 C), 131.8 (4 C), 133.8 (4 C).
H NMR (300 MHz, CDCl ): δ = 3.82 (s, 6 H, CH × 2), 6.80–6.85
3
3
(
d, J = 8.8 Hz, 4 H, ArH), 7.45–7.50 (d, J = 8.8 Hz, 4 H, ArH).
MS (EI, 70 eV): m/z (%) = 174 (10), 199 (11), 200 (34), 207 (19),
+
+
13
281 (12), 358 (52), 360 (100) [M ], 361 (18) [M + H] , 362 (45) [M
C NMR (75 MHz, CDCl ): δ = 55.3 (2 C), 72.9 (2 C), 81.2 (2 C),
3
+
+
2] .
1
13.9 (2 C), 114.1 (4 C), 134.0 (4 C), 160.2 (2 C).
MS (EI, 70 eV): m/z (%) = 131 (13), 176 (15), 219 (14), 247 (58),
1,1′-Buta-1,3-diyne-1,4-diylbis(3-methylbenzene) (2i)15
+
+
248 (11), 262 (100) [M ], 263 (19) [M + H] .
Pale-yellow solid; yield: 228 mg (99%); t = 17.3 min; mp 65–67
C (hexane); R = 0.67 (hexane–EtOAc, 4:1).
R
°
f
1
,1′-Buta-1,3-diyne-1,4-diylbis(4-methylbenzene)(2d)15
–
1
IR (film): 3035, 1479 cm .
Pale-yellow solid; yield: 209 mg (91%); t = 17.5 min; mp 118–120
R
1
°
C (hexane); R = 0.8 (hexane–EtOAc, 4:1).
H NMR (300 MHz, CDCl ): δ = 2.33 (s, 6 H, CH × 2), 7.15–7.25
f
3
3
–
1
(m, 4 H, ArH), 7.30–7.35 (m, 4 H, ArH).
IR (ATR): 3032, 1501 cm .
1
13C NMR (75 MHz, CDCl
21.6 (2 C), 128.3 (2 C), 129.6 (2 C), 130.1 (2 C), 132.9 (2 C), 138.1
2 C).
): δ = 21.1 (2 C), 73.6 (2 C), 81.6 (2 C),
3
H NMR (300 MHz, CDCl ): δ = 2.34 (s, 6 H, CH × 2), 7.10–7.15
d, J = 8.0 Hz, 4 H, ArH), 7.35–7.40 (d, J = 8.0 Hz, 4 H, ArH).
3
3
1
(
(
13
C NMR (75 MHz, CDCl ): δ = 21.6 (2 C), 73.4 (2 C), 81.5 (2 C),
3
+
MS (EI, 70 eV): m/z (%) = 228 (10), 229 (10), 230 (100) [M ], 231
1
18.8 (2 C), 129.2 (4 C), 132.4 (4 C), 139.5 (2 C).
+
(
19) [M + H] .
MS (EI, 70 eV): m/z (%) = 215 (17), 226 (13), 228 (12), 229 (22),
30 (100) [M ], 231 (19) [M + H] .
+
+
1,1′-Buta-1,3-diyne-1,4-diyldicyclohexane (2j)13b
Pale-yellow solid; yield: 150 mg (70%); t = 15.1 min; mp 77–82
2
R
1
,1′-Buta-1,3-diyne-1,4-diylbis(4-chlorobenzene) (2e)15
Pale-yellow solid; yield: 268 mg (99%); t = 18.0 min; mp 165–167
C (hexane); R = 0.77 (hexane–EtOAc, 4:1).
°C (hexane); R = 0.97 (hexane–EtOAc, 4:1).
f
R
IR (film): 2925, 2852, 1447 cm–1.
°
f
1H NMR (300 MHz, CDCl
): δ = 1.15–1.25 (m, 6 H, CH
× 3),
2
–
1
3
IR (ATR): 1483, 1395, 1092 cm .
1
.35–1.45 (m, 6 H, CH × 3), 1.60–1.75 (m, 8 H, CH × 4), 2.35–
2
2
1
H NMR (300 MHz, CDCl ): δ = 7.30–7.35 (d, J = 8.7 Hz, 4 H,
ArH), 7.45–7.50 (d, J = 8.7 Hz, 4 H, ArH).
3
2.40 (m, 2 H, CH × 2).
13
C NMR (75 MHz, CDCl ): δ = 24.8 (4 C), 25.7 (2 C), 29.5 (2 C),
3
13
C NMR (75 MHz, CDCl ): δ = 76.6 (2 C), 80.8 (2 C), 119.3 (2 C),
3
32.3 (4 C), 65.1 (2 C), 81.9 (2 C).
1
28.9 (4 C), 133.7 (4 C), 134.0 (2 C).
MS (EI, 70 eV): m/z (%) = 51 (13), 53 (13), 55 (23), 63 (18), 65
+
MS (EI, 70 eV): m/z (%) = 200 (28), 270 (100) [M ], 271 (18) [M +
H] , 272 (65) [M + 2] , 273 (11), [M + 3] , 274 (11), [M + 4] .
(
(
(
(
(
(
17), 67 (39), 75 (10), 76 (14), 77 (33), 78 (17), 79 (43), 80 (26), 89
15), 91 (100), 92 (23), 93 (15), 95 (17), 102 (11), 103 (16), 104
32), 105 (33), 115 (55), 116 (16), 117 (82), 118 (28), 119 (17), 127
14), 128 (47), 129 (63), 130 (20), 131 (62), 132 (15), 133 (11), 141
14), 143 (39), 144 (14), 145 (27), 157 (21), 158 (11), 171 (35), 185
+
+
+
+
1
,1′-Buta-1,3-diyne-1,4-diylbis(2-chlorobenzene) (2f)9c
White solid; yield: 87 mg (32%); t = 18.4 min; mp 135–138 °C
hexane); R = 0.5 (hexane–EtOAc, 4:1).
R
(
f
+
+
16), 207 (18), 214 (84) [M ], 215 (15) [M + H] .
–
1
IR (ATR): 3068, 1463, 1433, 1053 cm .
Hexadeca-7,9-diyne (2k)23
1
4
H NMR (300 MHz, CDCl ): δ = 7.20–7.25 (td, J = 7.5 Hz, J = 1.2
3
Colorless oil; yield: 201 mg (92%); t = 14.1 min; R = 0.87 (hex-
4
R
f
Hz, 2 H, ArH), 7.30–7.35 (td, J = 7.5 Hz, J = 1.7 Hz, 2 H, ArH),
.40–7.45 (dd, J = 8.0 Hz, J = 1.2 Hz, 2 H, ArH), 7.55–7.60 (dd,
J = 7.6 Hz, J = 1.7 Hz, 2 H, ArH).
ane–EtOAc, 4:1).
4
7
–
1
4
IR (ATR): 1465, 1459, 1378, 724 cm .
1
13
H NMR (300 MHz, CDCl ): δ = 0.85–0.95 (m, 6 H, CH × 2),
3 3
C NMR (75 MHz, CDCl ): δ = 78.3 (2 C), 79.4 (2 C), 121.8 (2 C),
3
1
.25–1.45 (m, 12 H, CH × 6), 1.45–1.55 (m, 4 H, CH × 2), 2.20–
1
26.5 (2 C), 129.4 (2 C), 130.3 (2 C), 134.4 (2 C), 136.9 (2 C).
2
2
2
.25 (t, J = 6.8 Hz, 4 H, CH × 2).
+
2
MS (EI, 70 eV): m/z (%) = 200 (34), 270 (100) [M ], 271 (18) [M +
H] , 272 (64) [M + 2] , 273 (12), [M + 3] , 274 (12), [M + 4] .
13
+
+
+
+
C NMR (75 MHz, CDCl ): δ = 14.0 (2 C), 19.2 (2 C), 22.5 (2 C),
3
28.3 (2 C), 28.5 (2 C), 31.3 (2 C), 65.2 (2 C), 77.5 (2 C).
1
,1′-Buta-1,3-diyne-1,4-diylbis[4-(trifluoromethyl)benzene]
MS (EI, 70 eV): m/z (%) = 51 (13), 55 (37), 63 (11), 65 (17), 67
2
4
(2g)
(
(
(
[
46), 69 (14), 76 (10), 77 (37), 78 (31), 79 (56), 80 (12), 81 (41), 91
100), 92 (20), 93 (43), 95 (26), 105 (63), 106 (12), 107 (26), 117
15), 119 (43), 121 (12), 133 (25), 147 (16), 161 (10), 218 (0.3)
Pale-yellow solid; yield: 335 mg (99%); t = 15.0 min; mp 165–168
R
°C (hexane); R = 0.7 (hexane–EtOAc, 4:1).
f
–
1
IR (ATR): 1610, 1407 cm .
+
M ].
1
H NMR (300 MHz, CDCl ): δ = 7.60–7.65 (m, 8 H, ArH).
3
Icosa-9,11-diyne (2l)23
13
C NMR (75 MHz, CDCl ): δ = 75.6 (2 C), 80.9 (2 C), 123.7 (q,
Colorless oil; yield: 137 mg (50%); t = 16.6 min; R = 0.8 (hexane–
3
R
f
1J = 272.4 Hz, 2 C), 125.3 (2 C), 125.4 (q, J = 3.8 Hz, 4 C),
3
C–F
C–F
EtOAc, 4:1).
IR (ATR): 2924, 2854, 1464, 722 cm–1.
2
131.1 (q, J = 33 Hz, 2 C), 132.8 (4 C).
C–F
+
MS (EI, 70 eV): m/z (%) = 319 (17), 338 (100) [M ], 339 (22) [M +
H] .
1
H NMR (300 MHz, CDCl ): δ = 0.85–0.90 (t, J = 6.5 Hz, 6 H,
+
3
CH × 2), 1.25–1.40 (m, 20 H, CH × 10), 1.45–1.55 (m, 4 H,
3
2
CH × 2), 2.20–2.25 (t, J = 6.9 Hz, 4 H, CH × 2).
2
2
©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 1373–1379

1378
J. M. Pérez et al.
PAPER
13
13
C NMR (75 MHz, CDCl ): δ = 14.1 (2 C), 19.2 (2 C), 22.6 (2 C),
C NMR (75 MHz, CDCl ): δ = 107.2 (2 C), 123.7 (4 C), 127.3 (2
3
3
28.4 (2 C), 28.8 (2 C), 29.0 (2 C), 29.1 (2 C), 31.8 (2 C), 65.2 (2 C),
C), 128.7 (4 C), 130.7 (2 C), 153.3 (2 C).
7
7.5 (2 C).
MS (EI, 70 eV): m/z (%) = 51 (10), 77 (29), 105 (16), 115 (32), 191
(20), 220 (100) [M ], 221 (18) [M + H] .
+
+
MS (EI, 70 eV): m/z (%) = 55 (38), 57 (14), 65 (13), 67 (50), 69
19), 77 (32), 78 (25), 79 (61), 80 (15), 81 (57), 82 (12), 91 (100),
2 (22), 93 (52), 94 (17), 95 (38), 103 (12), 105 (60), 106 (14), 107
(
2
,5-Bis(4-methoxyphenyl)furan (3b)27
9
White solid; yield: 83 mg (59%); t = 17.5 min; mp 189–192 °C
(
(
(
41), 108 (10), 109 (15), 115 (13), 117 (21), 119 (55), 120 (15), 121
41), 131 (10), 133 (45), 134 (12), 135 (20), 147 (32), 148 (10), 149
12), 161 (25), 175 (14), 274 (0) [M ].
R
(
hexane); R = 0.20 (hexane–EtOAc, 4:1).
f
+
IR (ATR): 2839, 1600, 1509, 1018 cm–1.
1
Tetracosa-11,13-diyne (2m)26
H NMR (300 MHz, CDCl ): δ = 3.85 (s, 6 H, CH × 2), 6.58 (s, 2
3 3
H, CH × 2), 6.90–6.95 (d, J = 9.0 Hz, 4 H, ArH), 7.65–7.70 (d,
J = 9.0 Hz, 4 H, ArH).
Pale-yellow oil; yield: 102 mg (31%); t = 19.5 min; R = 0.8 (hex-
R
f
ane–EtOAc, 4:1).
13
–
1
C NMR (75 MHz, CDCl ): δ = 55.3 (2 C), 105.5 (2 C), 114.1 (4
3
IR (ATR): 2953, 2923, 2853, 1464, 721 cm .
C), 124.0 (2 C), 125.0 (4 C), 152.8 (2 C), 158.8 (2 C).
1
H NMR (300 MHz, CDCl ): δ = 0.85–0.90 (m, 6 H, CH × 2),
3
3
MS (EI, 70 eV): m/z (%) = 140 (14), 265 (87), 266 (16), 280 (100)
[
1
.25–1.30 (m, 28 H, CH × 14), 1.45–1.55 (m, 4 H, CH × 2), 2.20–
2
2
+
+
M ], 281 (20) [M + H] .
2.25 (t, J = 7.1 Hz, 4 H, CH × 2).
2
1
3
C NMR (75 MHz, CDCl ): δ = 14.1 (2 C), 19.2 (2 C), 22.7 (2 C),
2,5-Bis(4-tolyl)furan (3c)27
3
2
3
8.3 (2 C), 28.8 (2 C), 29.1 (2 C), 29.3 (2 C), 29.5 (2 C), 29.6 (2 C),
1.9 (2 C), 65.2 (2 C), 77.5 (2 C).
White solid; yield: 112 mg (90%); t = 17.9 min; mp 114–117 °C
R
(hexane); R = 0.73 (hexane–EtOAc, 4:1).
f
–
1
MS (EI, 70 eV): m/z (%) = 55 (50), 57 (27), 65 (11), 67 (65), 69
IR (ATR): 3020, 2914, 2856, 1605, 1503, 1021 cm .
(33), 77 (27), 78 (24), 79 (66), 80 (21), 81 (71), 82 (20), 83 (20), 91
1
H NMR (300 MHz, CDCl ): δ = 2.40 (s, 6 H, CH × 2), 6.70 (s, 2
3
3
(
100), 92 (25), 93 (55), 94 (24), 95 (57), 96 (12), 103 (11), 105 (59),
H, CH × 2), 7.20–7.25 (d, J = 8.1 Hz, 4 H, ArH), 7.60–7.65 (d,
J = 8.1 Hz, 4 H, ArH).
1
1
1
1
06 (17), 107 (48), 108 (15), 109 (25), 115 (12), 117 (25), 119 (60),
20 (19), 121 (67), 122 (16), 123 (11), 131 (14), 133 (54), 134 (21),
35 (30), 147 (38), 148 (17), 149 (15), 161 (35), 162 (11), 163 (11),
13C NMR (75 MHz, CDCl
): δ = 21.2 (2 C), 106.3 (2 C), 123.4 (4
C), 128.0 (2 C), 129.2 (4 C), 136.9 (2 C), 153.0 (2 C).
3
+
75 (21), 189 (15), 330 (0) [M ].
+
MS (EI, 70 eV): m/z (%) = 129 (9), 248 (10) [M ], 249 (20) [M +
H] .
1
,10-Dichlorodeca-4,6-diyne (2n)23
+
Pale-yellow oil; yield: 200 mg (99%); t = 13.5 min; R = 0.67 (hex-
R
f
ane–EtOAc, 4:1).
,5-Bis[4-(trifluoromethyl)phenyl]furan (3d)21
2
–
1
IR (ATR): 2960, 2927, 1288 cm .
Pale-yellow solid; yield: 176 mg (99%); t = 15.5 min; mp 139–141
R
°
C (hexane); R = 0.57 (hexane–EtOAc, 4:1).
1
f
H NMR (300 MHz, CDCl ): δ = 1.95–2.00 (p, J = 6.5 Hz, 4 H,
3
–1
ClCH CH ), 2.45–2.50 (t, J = 6.8 Hz, 4 H, ClCH CH CH ), 3.60–
IR (film): 1617 cm .
2
2
2
2
2
3
.65 (t, J = 6.3 Hz, 4 H, ClCH2).
1
H NMR (300 MHz, CDCl ): δ = 6.90 (s, 2 H, CH × 2), 7.65–7.70
3
13
C NMR (75 MHz, CDCl ): δ = 16.6 (2 C), 31.0 (2 C), 43.4 (2 C),
(d, J = 8.1 Hz, 4 H, ArH), 7.85–7.90 (d, J = 8.1 Hz, 4 H, ArH).
3
6
6.0 (2 C), 75.8 (2 C).
13
C NMR (75 MHz, CDCl ): δ = 109.4 (2 C), 123.9 (4 C), 124.1 (q,
3
2
MS (EI, 70 eV): m/z (%) = 51 (29), 53 (11), 62 (10), 63 (36), 64
JC–F = 271.8 Hz, 2 C), 125.8 (q, JC–F = 3.7 Hz, 4 C), 129.4 (q, JC–F
=
(12), 65 (22), 74 (16), 76 (25), 77 (86), 78 (25), 79 (12), 89 (29), 91
33.2 Hz, 2 C), 133.4 (2 C), 152.8 (2 C).
(
100), 102 (14), 103 (93), 104 (33), 105 (33), 111 (11), 112 (26),
14 (61), 116 (38), 117 (45), 125 (47), 127 (20), 128 (10), 129 (20),
MS (EI, 70 eV): m/z (%) = 145 (17), 173 (11), 183 (21), 337 (10),
1
1
2
+
+
3
56 (100) [M ], 357 (20) [M + H] .
30 (10), 131 (39), 139 (42), 141 (15), 167 (20), 174 (20), 176 (16),
+
+
+
02 (88) [M ], 204 (61) [M + 2] , 206 (10) [M + 4] .
1,1′-Buta-1,3-diyne-1,4-diyldibenzene (2a) by Decarboxylative
Coupling of 3-Phenylprop-2-ynoic Acid (4)
2
,5-Furans 3a–d; General Procedure
Et N (0.07 mL, 138 mol%), DMF (1.5 mL), and CuO–Fe O (50
3
3
4
CuO/Fe O (10 mg, 0.26 mol%) and t-BuOK (112 mg, 1 mmol)
3
4
mg, 2.1 mol%) or NiO–Cu/Fe O (50 mg, 1.5 + 1.83 mol%) were
3 4
were added to a stirred soln of the appropriate alkyne 1 (2 mmol),
and the resulting mixture was stirred at 60 °C until the reaction was
complete (2–7 days; see Table 3). The catalyst was then removed by
using a magnet and washed with DMSO (5 mL). The DMSO wash-
ings were combined with the original reaction soln, and KOH (280
added to a stirred soln of alkynoic acid 4 (0.6 mmol) under air, and
the resulting mixture was stirred at 130 °C for 2 days. The catalyst
was removed by using a magnet and washed with EtOAc (2 × 5 mL)
and H O (2 × 5 mL). The collected organic phases were dried
2
(
MgSO ) and concentrated under reduced pressure. The residue was
4
mg, 5 mmol, 250 mol%) and H O (4 mmol, 400 mol%) were added
2
purified by column chromatography; yield: 21% (CuO–Fe O ) or
3 4
under air. The resulting soln was stirred at 80 °C for 1 day, then the
quant (NiO–Cu/Fe O ).
3
4
reaction was quenched by addition of H O (5 mL). The resulting
2
mixture was extracted with EtOAc (2 × 5 mL) and the combined or-
ganic phases were dried (MgSO ), and concentrated under reduced Acknowledgment
4
pressure. The residue was purified by column chromatography.
This work was supported by the Spanish Ministerio de Economía y
Competitividad (M.E.C) (Consolider Ingenio 2010 CSD2007-
00006, CTQ2011-24151) and by the Generalitat Valenciana (G.V)
(Prometeo 2009/03, FEDER). J.M.P. and R.C. thank the M.E.C.
(FPI program) and the G.V., (PROMETEO program), respectively,
for their fellowships. We gratefully acknowledge the polishing of
our English by Mrs. Oriana C. Townley.
2
,5-Diphenylfuran (3a)21
Pale-yellow solid; yield: 109 mg (99%); t = 15.8 min; mp 47–52
R
°
C (hexane); R = 0.73 (hexane–EtOAc, 4:1).
f
–
1
IR (ATR): 3022, 1259, 1023, 927 cm .
1
H NMR (300 MHz, CDCl ): δ = 6.75 (s, 2 H, CH × 2), 7.25–7.30
3
(m, 2 H, ArH), 7.40–7.45 (m, 4 H, ArH), 7.70–7.75 (m, 4 H, ArH).
Synthesis 2013, 45, 1373–1379
© Georg Thieme Verlag Stuttgart · New York

PAPER
Copper/Magnetite-Catalyzed Homocoupling of Terminal Alkynes
1379
Supporting Information for this article is available online at
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nfo itrmart
Chem. Commun. 1995, 2057. (b) Auer, S. M.; Wandeler, R.;
Göbel, U.; Baiker, A. J. Catal. 1997, 169, 1. (c) Zhu, B. C.;
Jiang, X. Z. Appl. Organomet. Chem. 2007, 21, 345.
(11) Sharifi, A.; Mirzaei, M.; Naimi-Jamal, M. R. Monatsh.
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Synthesis 2013, 45, 1373–1379