Synthesis of 1,2-Dicarbonyl-3-enes by Hydroacylation of 1-Alkynes with Glyoxal Derivatives Using Metal-Organic Framework Cu/MOF-74 as Heterogeneous Catalyst

Article abstract of DOI:10.1002/cplu.201600075

A crystalline copper-based metal-organic framework Cu/MOF-74 was synthesized, and used as an efficient heterogeneous catalyst for the synthesis of 1,2-dicarbonyl-3-enes by means of the hydroacylation of 1-alkynes with glyoxal derivatives in the presence o

Full text of DOI:10.1002/cplu.201600075

DOI: 10.1002/cplu.201600075
Full Papers
Synthesis of 1,2-Dicarbonyl-3-enes by Hydroacylation of
1
-Alkynes with Glyoxal Derivatives Using Metal–Organic
Framework Cu/MOF-74 as Heterogeneous Catalyst
[
a]
Nguyen B. Nguyen, Giao H. Dang, Dung T. Le, Thanh Truong,* and Nam T. S. Phan*
A crystalline copper-based metal–organic framework Cu/MOF-
4 was synthesized, and used as an efficient heterogeneous
Fe O(BDC) , In(OH)(BDC), and Zr O (OH) (BDC) . Cu/MOF-74
3 3 6 4 4 6
7
also exhibited better performance than other homogeneous
copper catalysts, including Cu(OAc) , Cu(NO ) , CuI, CuBr, CuCl,
catalyst for the synthesis of 1,2-dicarbonyl-3-enes by means of
the hydroacylation of 1-alkynes with glyoxal derivatives in the
presence of a base. Cu/MOF-74 was found to be more catalyti-
cally active for the synthesis of 1,2-dicarbonyl-3-enes than
other MOFs including Cu (BDC) (DABCO), Cu (BTC) , Cu(BDC),
2
3 2
CuCl , and CuBr . The Cu/MOF catalyst was able to be recov-
2
2
ered and reused several times without a significant degrada-
tion in catalytic activity. To the best of our knowledge, the for-
mation of 1,2-dicarbonyl-3-enes has not previously been car-
ried out under heterogeneous catalysis conditions.
2
2
3
2
Cu (NDC) (DABCO), Cu I (DABCO) , Ni-MOF-74, Zn-MOF-74,
2
2
4 4
2
Introduction
[
12,13]
1
,2-Dicarbonyl derivatives have attracted significant attention
mediate.
To achieve more environmentally benign ap-
as important intermediates in numerous organic transforma-
tions that lead to the formation of a variety of pharmaceutical
proaches towards 1,2-dicarbonyl-3-enes in terms of the ease of
handling, simple workup, recyclability, and reusability, hetero-
geneous catalysts should be investigated for the hydroacyla-
tion reaction.
[1–6]
candidates and agrochemicals.
Whereas simple alkyl- and
aryl-substituted 1,2-diketones can be readily prepared by the
[7–9]
oxidation of alkynes,
the synthesis of alkenyl-substituted
Metal–organic frameworks (MOFs), also known as porous co-
ordination polymers, are a new generation of crystalline mate-
rial consisting of coordination bonds between metal cations
1
,2-diketones still remains challenging. Feng and co-workers
previously reported a protocol to produce alkenyl-, alkynyl-,
and aryl-substituted 1,2-diketones by utilizing treatment of
benzotriazole derivatives with butyllithium and subsequent re-
[
14–19]
and multidentate organic linkers.
By combining a variety
of organic linkers with many metal cations of diverse oxidation
states and coordination geometries, a large number of MOFs
[10]
action with esters or acid chlorides. Lo and co-workers dem-
onstrated a ruthenium-catalyzed oxidation of alkynes to form
[
20]
can be produced, which offers several advantages such as
structural diversity, well-defined structures, high surface areas,
[11]
alkenyl-substituted 1,2-diketones.
However,
a
general
method for the synthesis of alkenyl-substituted 1,2-diketones
high porosity, and the ability to tune the surface hydrophobici-
[11]
[14–19,21–24]
still remains to be explored. Hashmi and co-workers recently
reported the first example of a AuCl-catalyzed synthesis of 1,2-
dicarbonyl-3-enes by means of the formal hydroacylation of
terminal alkynes with a-ketoaldehydes in the presence of pi-
ty/hydrophilicity.
Although the commercialization of
MOFs still remains a challenge, potential applications of these
sponge-like materials in many fields have been extensively ex-
[
14,15,25–30]
plored.
MOFs as heterogeneous catalysts have recently
[
12]
peridine. Independently, Li and co-workers also developed
a CuBr-promoted approach for the synthesis of 1,2-dicarbonyl-
gained significant interest from both industry and academ-
[
31–33]
ia.
Metal cations or functional groups on the organic link-
3
-enes based on the formal hydroacylation reaction of terminal
ers in the framework can be used to catalyze organic transfor-
alkynes with a-carbonyl aldehydes in the presence of morpho-
mations, thus maximizing the opportunity for high dispersion
[13]
[32,34–40]
line.
The transformation proceeded through three-compo-
and high loading of catalytically active sites.
During the
[
41–51]
nent coupling to afford a propargylamine intermediate, and
subsequently isomerized to a conjugated allenylamine inter-
last few years, both carbon–carbon
and carbon–heteroa-
[
52–60]
tom-forming organic reactions
using MOF-based catalysts
[
31–33,61,62]
have been reported in the literature.
Among many
popular MOFs, copper-based frameworks have been investigat-
ed as catalysts for a variety of organic transformations owing
[
a] N. B. Nguyen, Dr. G. H. Dang, Dr. D. T. Le, Dr. T. Truong,
Prof. Dr. N. T. S. Phan
Department of Chemical Engineering
HCMC University of Technology, VNU-HCM
[
51,55,63–69]
to their unsaturated open copper metal sites.
Herein,
we wish to report the synthesis of 1,2-dicarbonyl-3-enes by
means of the hydroacylation of 1-alkynes with glyoxal deriva-
tives in the presence of morpholine as a base using a copper-
based metal–organic framework Cu/MOF-74 as an efficient het-
erogeneous catalyst. To the best of our knowledge, the forma-
2
68 Ly Thuong Kiet, District 10, Ho Chi Minh City 84 (Vietnam)
E-mail: ptsnam@hcmut.edu.vn
tvthanh@hcmut.edu.vn
Supporting information for this article can be found under http://
dx.doi.org/10.1002/cplu.201600075.
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tion of 1,2-dicarbonyl-3-enes has not been previously carried
out under heterogeneous catalysis conditions.
Results and Discussion
The metal–organic framework Cu/MOF-74 was synthesized ac-
[70]
cording to a slightly modified literature procedure, and was
characterized by a variety of different techniques, including X-
ray diffraction (XRD), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), thermogravimetric
analysis (TGA), Fourier transform infrared (FTIR) spectroscopy,
atomic absorption spectrophotometry (AAS), and nitrogen
physisorption measurements (Figures S1–S7 in the Supporting
Information). Cu/MOF-74 was assessed for its catalytic activity
in the hydroacylation of phenylacetylene with ethyl glyoxalate
to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate as the principal
product (Scheme 1). Initial studies addressed the effect of tem-
Figure 1. Effect of temperature on the reaction yield.
with a-carbonyl aldehydes, and demonstrated that 1,4-dioxane
[
13]
should be the solvent of choice. It was therefore decided
that the effect of different solvents on the hydroacylation of
phenylacetylene with ethyl glyoxalate to form (E)-ethyl 2-oxo-
4
-phenylbut-3-enoate using Cu/MOF-74 catalyst should be in-
vestigated. The hydroacylation reaction was carried out at
008C under argon for four hours, using two equivalents of
1
ethyl glyoxalate and two equivalents of morpholine, at a phe-
Scheme 1. The hydroacylation of 1-alkynes with glyoxal derivatives using
the Cu/MOF-74 catalyst.
nylacetylene concentration of 0.5m, in the presence of
7
.5 mol% Cu/MOF-74 catalyst, in toluene, 1,4-dioxane, n-buta-
nol, N,N-dimethylformamide (DMF), N-methylpyrrolidone
(NMP), dimethylacetamide (DMA), diglyme, dimethylsulfoxide
(DMSO), p-xylene, and acetonitrile, respectively. n-Butanol was
not suitable for the reaction, and afforded only a 6% yield
after four hours. The reactions carried out in DMF and DMSO
also offered low yields. Although 1,4-dioxane was previously
reported to be the best solvent, it was found that only 34%
yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate was detected
after four hours for the transformation using Cu/MOF-74 cata-
lyst. The reaction afforded 43% yield after four hours in NMP
or p-xylene, and this value could be improved to 47% when
acetonitrile was used as solvent. Among these solvents, both
toluene and diglyme exhibited the best performance, with
58% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate being ach-
ieved after four hours (Figure 2).
perature on the yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate.
In the first example of the AuCl-catalyzed synthesis of 1,2-di-
carbonyl-3-enes by means of the formal hydroacylation of ter-
minal alkynes with a-ketoaldehydes in the presence of piperi-
dine, Hashmi and co-workers carried out the transformation at
[
12]
5
08C. Li and co-workers performed the CuBr-promoted hy-
droacylation reaction of terminal alkynes with a-carbonyl alde-
[13]
hydes in the presence of morpholine at 1008C. The hydroa-
cylation reaction was carried out in toluene under argon for
four hours, using two equivalents of ethyl glyoxalate and two
equivalents of morpholine, at a phenylacetylene concentration
of 0.5m, in the presence of 7.5 mol% Cu/MOF-74 catalyst, at
room temperature and 80, 90, 100, and 110 8C, respectively. It
was observed that the transformation could not occur at room
temperature, with no trace amount of product being detected
after four hours. Increasing the temperature to 808C resulted
in a 31% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate after
four hours. Only 40% yield was observed after four hours for
the reaction carried out at 908C, and this value could be im-
proved to 58% for the reaction carried out at 1008C. Interest-
ingly, increasing the temperature to higher than 1008C was
found to exhibit a negative impact on the reaction, with only
As mentioned earlier, the hydroacylation of phenylacetylene
with ethyl glyoxalate proceeds by means of three-component
coupling to afford a propargylamine intermediate, which sub-
sequently isomerized to a conjugated allenylamine intermedi-
ate, and the hydrolyzed form (E)-ethyl 2-oxo-4-phenylbut-3-
[
12,13]
enoate.
The presence of a base was therefore necessary
for the three-component coupling step in the catalytic cycle.
Hashmi and co-workers previously employed several amines
for the AuCl-catalyzed hydroacylation of terminal alkynes with
a-ketoaldehydes, and reported that piperidine was the best
3
9% yield being detected after four hours (Figure 1).
For organic transformations using solid catalysts, the solvent
[
12]
could exhibit a significant impact on the reaction rate, depend-
base. Li and co-workers performed the CuBr-promoted hy-
droacylation reaction of terminal alkynes with a-carbonyl alde-
hydes in the presence of different amines, and pointed out
[71,72]
ing on the nature of the catalyst.
Hashmi and co-workers
previously carried out the AuCl-catalyzed hydroacylation of ter-
minal alkynes with a-ketoaldehydes in different solvents, and
pointed out that none of the other solvents was superior to
[
13]
that morpholine was the base of choice. It was therefore de-
cided to investigate the effect of different bases on the forma-
tion of (E)-ethyl 2-oxo-4-phenylbut-3-enoate. The hydroacyla-
tion reaction was carried out in toluene at 1008C under argon
[
12]
toluene. Li and co-workers employed several solvents for the
CuBr-promoted hydroacylation reaction of terminal alkynes
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and 4 equivalents of morpholine as the base, respectively. It
was found that the amount of morpholine exhibited a signifi-
cant effect on the reaction yield. As mentioned earlier, the re-
action using two equivalents of morpholine afforded 58%
yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate after four hours.
Increasing the amount of morpholine resulted in a significant
drop in the reaction yield, with 42, 20, and 11 % yields being
detected after four hours for the reaction using 2.5, 3, and
4
equivalents of morpholine as the base, respectively. It was
found that decreasing the amount of morpholine led to an im-
provement in the reaction yield. Indeed, 66% yield of (E)-ethyl
2
-oxo-4-phenylbut-3-enoate was obtained after four hours for
the reaction using 1.5 equivalents of morpholine. Interestingly,
the reaction yield could be improved to 70% after four hours
in the presence of 0.5 equivalents of morpholine. However,
using less than 0.5 equivalent of morpholine resulted in a drop
in the yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate (Figure 4).
Figure 2. Effect of solvent on the reaction yield.
for four hours, using two equivalents of ethyl glyoxalate and
two equivalents of the base, at a phenylacetylene concentra-
tion of 0.5m, with 7.5 mol% Cu/MOF-74 catalyst, in the pres-
ence of morpholine, piperidine, pyridine, imidazole, cyclohexyl-
amine, tBuOK, K CO , and K PO as the base, respectively. The
2
3
3
4
reaction using piperidine as the base proceeded with difficulty
with only 5% yield being detected after four hours. It was
found that using pyridine resulted in 19% yield of (E)-ethyl 2-
oxo-4-phenylbut-3-enoate after four hours. Indeed, among
these bases, morpholine exhibited the best performance, af-
fording 58% yield after four hours. Other bases, including, imi-
dazole, cyclohexylamine, tBuOK, 1,4-diazabicyclo[2.2.2]octane
(
DABCO), K CO , and K PO , were found to be inactive for the
2 3 3 4
transformation (Figure 3).
Figure 4. Effect of the morpholine amount on the reaction yield.
It should be noted that almost no reaction occurred in the ab-
sence of morpholine, which indicates the necessity of using
this base for the transformation. Previously, Hashmi and co-
workers used up to two equivalents of piperidine for the AuCl-
[
12]
catalyzed synthesis of 1,2-dicarbonyl-3-enes. Li and co-work-
ers also performed the CuBr-promoted hydroacylation reaction
of terminal alkynes with a-carbonyl aldehydes in the presence
[
13]
of two equivalents of morpholine. The fact that the amount
of morpholine could be minimized for the reaction using the
Cu/MOF-74 catalyst should be of advantage. Moreover, the re-
actant molar ratio also exhibited a significant impact on the
yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate, and the best
yield was achieved when two equivalents of ethyl glyoxalate
were employed (Figure 5).
Figure 3. Effect of base on the reaction yield.
For liquid-phase organic transformations using solid cata-
lysts, the reaction rate might be significantly affected by the
reactant concentration due to the mass-transfer phenomenon.
It was therefore decided to explore the impact of the reactant
concentration on the yield of (E)-ethyl 2-oxo-4-phenylbut-3-
enoate. The hydroacylation reaction was carried out in toluene
at 1008C under argon for four hours, using two equivalents of
ethyl glyoxalate, with 0.5 equivalent of morpholine as the
base, in the presence of 7.5 mol% Cu/MOF-74 catalyst, at phe-
With these results in mind, we then investigated the effect
of the amount of morpholine on the yield of (E)-ethyl 2-oxo-4-
phenylbut-3-enoate. The hydroacylation reaction was carried
out in toluene at 1008C under an atmosphere of argon for
four hours, using two equivalents of ethyl glyoxalate, at a phe-
nylacetylene concentration of 0.5m, in the presence of
7
.5 mol% Cu/MOF-74 catalyst, with 0.25, 0.5, 1, 1.5, 2, 2.5, 3,
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more than 10 mol% catalyst was found to be unnecessary as
the reaction yield was not improved significantly. It should be
noted that no (E)-ethyl 2-oxo-4-phenylbut-3-enoate was de-
tected in the absence of the catalyst, which indicated the im-
portance of Cu/MOF-74 for the hydroacylation of phenylacety-
lene with ethyl glyoxalate (Figure 7).
Figure 5. Effect of the phenylacetylene/ethyl glyoxalate molar ratio on the
reaction yield.
nylacetylene concentrations of 0.25, 0.33, 0.4, 0.5, 0.67, 1, and
2
m, respectively. It was observed that the reactant concentra-
tion exhibited a significant impact on the formation of (E)-
ethyl 2-oxo-4-phenylbut-3-enoate, and the best yield was ob-
served at a phenylacetylene concentration of 0.5m (Figure 6).
Figure 7. Effect of the catalyst concentration on the reaction yield.
Because the hydroacylation of phenylacetylene with ethyl
glyoxalate to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate using
Cu/MOF-74 catalyst was performed in the liquid phase, the
possibility that some of the catalytically active sites on the
solid Cu/MOF could dissolve into the solution during the
course of the reaction should be addressed. In several cases,
owing to leaching, the transformation proceeded under both
[
72]
heterogeneous and homogeneous catalysis conditions.
To
clarify whether active copper species dissolved from the solid
Cu/MOF-74 catalyst contributed to the formation of (E)-ethyl 2-
oxo-4-phenylbut-3-enoate in the hydroacylation reaction, a con-
trol experiment was carried out. The hydroacylation reaction
was carried out in toluene at 1008C under an atmosphere of
argon for six hours, using two equivalents of ethyl glyoxalate,
at a phenylacetylene concentration of 0.5m, with 0.5 equiva-
lents of morpholine as the base, in the presence of 10 mol%
Cu/MOF-74 catalyst. After the first two hours of reaction time
with a 38% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate ob-
tained, the Cu/MOF-74 catalyst was separated from the reac-
tion mixture by simple centrifugation. The liquid phase was
then transferred to a new reactor vessel, and stirred for an ad-
ditional four hours at 1008C with aliquots being sampled at
different time intervals, and analyzed by GC. Experimental re-
sults indicated that almost no further yield of (E)-ethyl 2-oxo-4-
phenylbut-3-enoate was observed after the Cu/MOF catalyst
was removed from the reaction mixture (Figure 8). Additionally,
the content of copper species in the reaction filtrate was mea-
sured using AAS. It was found that approximately 4 ppm of
copper was detected in the reaction filtrate, which correspond-
ed to 0.13% of the total amount of copper in the Cu/MOF-74
catalyst used for the transformation. It was therefore proposed
that the hydroacylation of phenylacetylene with ethyl glyoxa-
late to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate using the
Cu/MOF-74 catalyst could only proceed in the presence of the
Figure 6. Effect of the phenylacetylene concentration on the reaction yield.
Another factor that exhibits a significant effect on the hydroa-
cylation of phenylacetylene with ethyl glyoxalate to form (E)-
ethyl 2-oxo-4-phenylbut-3-enoate using Cu/MOF-74 catalyst is
the catalyst concentration. Li and co-workers previously em-
ployed up to 50 mol% CuBr catalyst for the synthesis of 1,2-di-
carbonyl-3-enes based on the formal hydroacylation reaction
of terminal alkynes with a-carbonyl aldehydes in the presence
[
13]
of morpholine. The hydroacylation reaction was carried out
in toluene at 1008C under an atmosphere of argon for four
hours, using two equivalents of ethyl glyoxalate, at a phenyla-
cetylene concentration of 0.5m, with 0.5 equivalent of morpho-
line as the base, in the presence of 1, 3, 5, 7.5, 10, and
1
2.5 mol% Cu/MOF-74 catalyst, respectively. As mentioned ear-
lier, the reaction using 7.5 mol% catalyst afforded a 70% yield
after four hours. Decreasing the catalyst concentration led to
a drop in the reaction yield. Increasing the catalyst concentra-
tion to 10 mol% resulted in a 93% yield of (E)-ethyl 2-oxo-4-
phenylbut-3-enoate being achieved after four hours. Using
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Figure 8. A leaching test indicated no contribution from homogeneous cat-
alysis of active species leaching into the reaction solution.
Figure 9. Different homogeneous catalysts for the hydroacylation reaction.
solid Cu/MOF catalyst, and the contribution of leached active
copper species to the formation of (E)-ethyl 2-oxo-4-phenyl-
but-3-enoate, if any, was negligible.
were synthesized by means of a solvothermal method, and
[
69,70,73–77]
The catalytic activity of Cu/MOF-74 in the hydroacylation of
phenylacetylene with ethyl glyoxalate to form (E)-ethyl 2-oxo-
characterized according to literature procedures.
The
hydroacylation reaction was carried out in toluene at 1008C
under argon for four hours, using two equivalents of ethyl
glyoxalate, at a phenylacetylene concentration of 0.5m, with
0.5 equivalent of morpholine as the base, in the presence of
10 mol% catalyst. Ni-MOF-74, Zn-MOF-74, Fe O(BDC) (BDC=
4
-phenylbut-3-enoate was also compared to that of common
homogeneous copper catalysts, including Cu(OAc) , Cu(NO ) ,
2
3 2
CuI, CuBr, CuCl, CuCl , and CuBr . The hydroacylation reaction
2
2
was carried out in toluene at 1008C under argon for four
hours, using two equivalents of ethyl glyoxalate, at a phenyla-
cetylene concentration of 0.5m, with 0.5 equivalent of morpho-
line as the base, in the presence of 10 mol% copper catalyst.
Previously, Li and co-workers carried out the synthesis of 1,2-
dicarbonyl-3-enes based on the formal hydroacylation reaction
of terminal alkynes with a-carbonyl aldehydes in the presence
of morpholine, and pointed out that a high yield could be ach-
3
3
1,4-benzenedicarboxylic
acid),
In(OH)(BDC),
and
Zr O (OH) (BDC) were found to be inactive for the transforma-
6
4
4
6
tion, with only a trace amount of (E)-ethyl 2-oxo-4-phenylbut-
3-enoate being detected after four hours. Although several Cu/
MOFs could be used as catalyst for the hydroacylation reaction,
Cu I (DABCO) was completely inactive. The reaction using the
4
4
2
Cu(BDC) catalyst proceeded with 45% yield of (E)-ethyl 2-oxo-
[13]
ieved when 50 mol% CuBr was used as catalyst.
In this
4-phenylbut-3-enoate after four hours. Cu (NDC) (DABCO)
2
2
study, it was found that using 10 mol% CuBr catalyst resulted
in a 48% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate being
detected after four hours. The reaction using CuCl catalyst also
proceeded with 48% yield of (E)-ethyl 2-oxo-4-phenylbut-3-
enoate after four hours. CuBr and CuCl were found to be less
(NDC=naphthalenedicarboxylate) was observed to be more
active than Cu(BDC) for the hydroacylation reaction, and af-
forded 53% yield after four hours. Cu (BDC) (DABCO) and
2
2
Cu (BTC) (BTC=1,3,5-benzenetricarboxylate) also offered simi-
3
2
lar activity, with 59 and 57% yields being obtained after four
hours. Among these MOFs, it was found that Cu/MOF-74 ex-
hibited the best performance, producing (E)-ethyl 2-oxo-4-phe-
nylbut-3-enoate in a yield of 93% after four hours (Figure 10).
The fact that Cu/MOF-74 gave a significantly higher activity for
the transformation than several homogeneous copper catalysts
and MOF-based catalysts is therefore an advantage.
2
2
active in the hydroacylation reaction than CuBr and CuCl, with
3 and 45% yields of (E)-ethyl 2-oxo-4-phenylbut-3-enoate
4
being observed after four hours, respectively. Cu(OAc)2 and
Cu(NO ) exhibited similar activity in the hydroacylation reac-
3
2
tion, and afforded 44 and 45% yields of (E)-ethyl 2-oxo-4-phe-
nylbut-3-enoate after four hours. It should be noted that 2,5-
dihydroxyterephthalic acid, the linker of Cu/MOF-74, was inac-
tive for the transformation, with no trace amount of the de-
sired product being detected after four hours. Interestingly,
Cu/MOF-74 offered a better performance than the homogene-
ous copper catalyst, and produced (E)-ethyl 2-oxo-4-phenylbut-
To gain insights into the reaction pathway of the hydroacyla-
tion of phenylacetylene with ethyl glyoxalate to form (E)-ethyl
2-oxo-4-phenylbut-3-enoate using Cu/MOF-74 catalyst, some
mechanistic studies were carried out. In the first experiment,
the hydroacylation reaction was carried out in toluene at
1008C under air for four hours, using two equivalents of ethyl
glyoxalate, at a phenylacetylene concentration of 0.5m, with
0.5 equivalent of morpholine as the base, in the presence of
10 mol% Cu/MOF-74 catalyst. It was observed that the trans-
formation afforded a 44% yield of (E)-ethyl 2-oxo-4-phenylbut-
3-enoate after four hours under air. It should be noted that the
reaction carried out under argon could proceed to 93% yield
of (E)-ethyl 2-oxo-4-phenylbut-3-enoate after four hours. In the
3
-enoate in a yield of 93% after four hours (Figure 9).
To emphasize the advantages of using Cu/MOF-74 as cata-
lyst for the hydroacylation of phenylacetylene with ethyl glyox-
alate to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate, the catalyt-
ic activity of Cu/MOF-74 was compared with that of other
MOFs including Cu (BDC) (DABCO), Cu (BTC) , Cu(BDC),
2
2
3
2
Cu (NDC) (DABCO), Cu I (DABCO) , Ni-MOF-74, Zn-MOF-74,
2
2
4 4
2
Fe O(BDC) , In(OH)(BDC), and Zr O (OH) (BDC) . These MOFs
3
3
6
4
4
6
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glyoxalate to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate over
eight successive runs, by repeatedly separating the Cu/MOF
catalyst from the reaction mixture, washing it, and then reus-
ing it. The hydroacylation reaction was carried out in toluene
at 1008C under argon for four hours, using two equivalents of
ethyl glyoxalate, at a phenylacetylene concentration of 0.5m,
with 0.5 equivalents of morpholine as the base, in the pres-
ence of 10 mol% Cu/MOF-74 catalyst. After the first run, the
catalyst was separated from the reaction mixture by simple
centrifugation, washed with copious amounts of DMF and
methanol, and dried at 1508C under vacuum for two hours.
The recovered Cu/MOF-74 catalyst was then reused in further
reactions under identical conditions to those of the first run. It
was observed that the Cu/MOF-74 catalyst could be recovered
and reused many times in the hydroacylation of phenylacety-
lene with ethyl glyoxalate to form (E)-ethyl 2-oxo-4-phenylbut-
3-enoate without a significant degradation in catalytic activity.
Indeed, a 91% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate
was still achieved in the eighth run (Figure 11). Moreover, the
structure of the Cu/MOF-74 catalyst could be maintained
during the course of the reaction, as indicated by the XRD
(Figure 12) and FTIR (Figure 13) results of the recovered Cu/
MOF-74.
Figure 10. Different MOFs as catalyst for the hydroacylation reaction.
second experiment, the reaction was carried out under argon
for two hours, producing the desired product in a yield of
3
8%. After that, the argon was replaced by air, and the reac-
tion mixture was heated at 1008C under air for a further two
hours. Under these conditions, a 79% yield of (E)-ethyl 2-oxo-
4
-phenylbut-3-enoate was obtained. In a third experiment, the
reaction was carried out under an argon atmosphere in the
presence of water (5% by volume). It was found that the per-
formance of the Cu/MOF-74 catalyst was significantly affected
by the water, with only 18% yield of (E)-ethyl 2-oxo-4-phenyl-
but-3-enoate detected after four hours. These observations
proposed that the formation of (E)-ethyl 2-oxo-4-phenylbut-3-
enoate by means of the hydroacylation of phenylacetylene
with ethyl glyoxalate using Cu/MOF-74 catalyst was not fa-
vored by the presence of air or water residue in the solvent. In
the fourth experiment, the Cu/MOF-74 catalyst was soaked in
pyridine as catalyst poison prior to use in the hydroacylation
of phenylacetylene with ethyl glyoxalate. Under these condi-
tions, only a 29% yield of (E)-ethyl 2-oxo-4-phenylbut-3-enoate
was observed after four hours. This result suggested that the
strong adsorption of pyridine on the copper sites in Cu/MOF-
Figure 11. Catalyst recycling studies.
7
4 would deactivate the catalyst. However, further mechanistic
studies would be necessary to elucidate the reaction pathway
of the hydroacylation of phenylacetylene with ethyl glyoxalate
to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate using a Cu/MOF-
The study was then extended to the hydroacylation of ethyl
glyoxalate with different phenylacetylenes, including phenyla-
cetylene, 4-methoxyphenylacetylene, 4-methylphenylacetylene,
4-trifluoromethylphenylacetylene, and 4-bromophenylacety-
lene, respectively, in the presence of the Cu/MOF-74 catalyst
(see Table 1). The hydroacylation reaction was carried out in
toluene at 1008C under an atmosphere of argon for four
hours, using two equivalents of ethyl glyoxalate, at a phenyla-
cetylene concentration of 0.5m, with 0.5 equivalent of morpho-
line as the base, in the presence of 10 mol% Cu/MOF-74 cata-
lyst. As mentioned earlier, the hydroacylation of phenylacety-
lene with ethyl glyoxalate could proceed to 93% GC yield of
(E)-ethyl 2-oxo-4-phenylbut-3-enoate being obtained after four
hours. The product was also purified by column chromatogra-
phy (ethyl acetate/petroleum ether 1:3) to afford 90% isolated
yield (entry 1), and its structure was confirmed by GC-MS and
7
4 catalyst.
As mentioned earlier, Cu/MOF-74 offered advantages over
several homogeneous and heterogeneous catalysts in terms of
catalytic activity. To emphasize the significant point of this Cu/
MOF catalyst in the hydroacylation of phenylacetylene with
ethyl glyoxalate to form (E)-ethyl 2-oxo-4-phenylbut-3-enoate,
one issue that should be taken into account is the ease of sep-
aration as well as the deactivation and reusability of the Cu/
MOF-74 catalyst. In the best case, the Cu/MOF catalyst can be
facilely separated from the reaction mixture, and can be
reused many times before it eventually deactivates completely.
Cu/MOF-74 was therefore investigated for recoverability and
reusability in the hydroacylation of phenylacetylene with ethyl
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1
13
H and C NMR spectroscopy. It was found that the presence
of a substituent on the benzene ring in phenylacetylene result-
ed in a drop in the yield of the desired product. The hydroacy-
lation of 4-methoxyphenylacetylene with ethyl glyoxalate
using Cu/MOF-74 catalyst produced (E)-ethyl 4-(4-methoxy-
phenyl)-2-oxobut-3-enoate in a yield of 76% (entry 2). By re-
placing 4-methoxyphenylacetylene by 4-methylphenylacety-
lene, the hydroacylation reaction with ethyl glyoxalate could
offer 68% yield of (E)-ethyl 2-oxo-4-p-tolylbut-3-enoate
(
entry 3). Using the same protocol, (E)-ethyl 2-oxo-4-[4-(trifluor-
omethyl)phenyl]but-3-enoate was obtained in a yield of 51%
entry 4). 4-Bromophenylacetylene exhibited lower reactivity in
the hydroacylation reaction with ethyl glyoxalate, affording
9% yield of (E)-ethyl 4-(4-bromophenyl)-2-oxobut-3-enoate
entry 5). These observations were comparable to those previ-
(
4
(
ously reported by Li and co-workers in the CuBr-promoted syn-
thesis of 1,2-dicarbonyl-3-enes based on the formal hydroacyla-
tion reaction of terminal alkynes with a-carbonyl aldehydes in
Figure 12. X-ray powder diffractograms of (a) fresh and (b) reused Cu/MOF-
4 catalyst.
7
[
13]
the presence of morpholine.
Moreover, it was also found
that the reaction between phenylacetylene and 2-oxo-2-phe-
nylacetaldehyde using Cu/MOF-74 catalyst could produce (E)-
1
,4-diphenylbut-3-ene-1,2-dione in a yield of 62% (entry 6).
Conclusion
In summary, the metal–organic framework Cu/MOF-74 was
synthesized by a solvothermal method, and was characterized
by a variety of different techniques including XRD, SEM, TEM,
FT-IR, TGA, AAS, and nitrogen physisorption measurements.
The Cu/MOF could be used as an efficient heterogeneous cata-
lyst for the synthesis of 1,2-dicarbonyl-3-enes by means of the
hydroacylation of 1-alkynes with glyoxal derivatives in the
presence of a base. The nature of the base exhibited a pro-
found impact on the formation of the desired product, and
Figure 13. FTIR spectra of (a) fresh and (b) reused Cu/MOF-74 catalyst.
Table 1. The hydroacylation of phenylacetylenes with glyoxalates using the Cu/MOF-74 catalyst.
[a]
Entry
1
Glyoxalates
Phenylacetylenes
Products
Yields [%]
90
1a
1b
1c
2
3
4
5
6
1a
1a
1a
1a
2a
2b
3b
4b
5b
6b
2c
3c
4c
5c
6c
76
68
51
49
62
[
a] Yields of isolated products.
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morpholine offered the best performance as the base for the
transformation. Moreover, the amount of morpholine in the re-
action mixture also significantly affected the hydroacylation re-
action between 1-alkynes with glyoxal derivatives. Cu/MOF-74
exhibited higher catalytic activity for the synthesis of 1,2-dicar-
bonyl-3-enes than that of other MOFs including
Cu (BDC) (DABCO), Cu (BTC) , Cu(BDC), Cu (NDC) (DABCO),
Synthesis of the metal–organic framework Cu/MOF-74
In a typical preparation, a solid mixture of H dhtp (H dhtp=2,5-di-
2
2
hydroxyterephthalic acid; 0.440 g, 2.22 mmol), and Cu(NO ) ·3H O
3
2
2
(
1.180 g, 4.88 mmol) was dissolved in a mixture of DMF (47 mL)
and 2-propanol (3 mL). The suspension was stirred to achieve a ho-
mogeneous solution. The resulting solution was then distributed
to six 10 mL vials. The vials were then heated at 858C in an isother-
mal oven for 18 h. After cooling the vials to room temperature, the
solid product was removed by decanting with mother liquor and
washed in DMF (3”20 mL). Solvent exchange was carried out with
methanol (3”20 mL) at room temperature. The material was then
evacuated under vacuum at 1508C for 5 hours, yielding 0.4544 g of
Cu/MOF-74 in the form of reddish black crystals (63% based on
2
2
3
2
2
2
Cu I (DABCO) , Ni-MOF-74, Zn-MOF-74, Fe O(BDC) , In-
4
4
2
3
3
(
OH)(BDC), and Zr O (OH) (BDC) . Cu/MOF-74 also offered
6 4 4 6
better performance in this transformation than other homoge-
neous copper catalysts, including Cu(OAc) , Cu(NO ) , CuI,
2
3 2
CuBr, CuCl, CuCl , and CuBr . The hydroacylation reaction could
2
2
only proceed in the presence of the solid Cu/MOF catalyst, and
the contribution of leached active copper species to the for-
mation of the desired product, if any, was negligible. The Cu/
MOF catalyst was able to be separated from the reaction mix-
ture by centrifugation, and could be recovered and reused sev-
eral times without a significant degradation in catalytic activity.
H dhtp).
2
Catalytic studies
In a typical experiment, a mixture of phenylacetylene (0.102 g,
1.0 mmol), ethyl glyoxalate (50% in toluene) (0.408 g, 2.0 mmol),
morpholine (0.174 g, 2.0 mmol), and diphenyl ether (0.170 g,
1
.0 mmol) as an internal standard in toluene (2 mL) was added into
a 8 mL vial containing the pre-determined amount of Cu/MOF-74
catalyst under an argon atmosphere. The catalyst amount was cal-
culated with respect to the copper/phenylacetylene molar ratio.
The reaction mixture was stirred at 1008C for 240 min. The reaction
yield was monitored by withdrawing aliquots from the reaction
mixture at different time intervals, and quenching with water
Experimental Section
Materials and instrumentation
(
1 mL). The organic components were then extracted into ethyl
acetate (3 mL), dried over anhydrous Na SO , and analyzed by GC
All reagents and starting materials were obtained commercially
from Sigma–Aldrich and Merck, and were used as received without
any further purification unless otherwise noted. Nitrogen physi-
sorption measurements were conducted using a Micromeritics
2
4
with reference to diphenyl ether. The combined organic layers
were concentrated under reduced pressure. The resulting residue
was purified by column chromatography (ethyl acetate/petroleum
ether 1:3) to afford (E)-ethyl 2-oxo-4-phenylbut-3-enoate. The prod-
2
020 volumetric adsorption analyzer system. Samples were pre-
1
13
uct identity was further confirmed by GC-MS and H and C NMR
spectroscopy. To investigate the recyclability of Cu/MOF-74, the
catalyst was separated from the reaction mixture by simple centri-
fugation, washed with copious amounts of DMF and methanol,
dried at 1508C under vacuum for 2 hours, and reused if necessary.
For the leaching test, a catalytic reaction was stopped after
treated by heating under vacuum at 1508C for 3 h. A Netzsch Ther-
moanalyzer STA 409 was used for TGA with a heating rate of
À1
1
08Cmin under a nitrogen atmosphere. XRD patterns were re-
corded using a CuKa radiation source on a D8 Advance Bruker
powder diffractometer. Scanning electron microscopy studies were
conducted on a S4800 scanning electron microscope. TEM studies
were performed using a JEOL JEM 1400 transmission electron mi-
croscope at 80 kV. The Cu/MOF-74 sample was dispersed on holey
carbon grids for TEM observation. Elemental analysis with AAS was
performed on an AA-6800 Shimadzu. FTIR spectra were obtained
on a Nicolet 6700 instrument, with samples being dispersed on po-
tassium bromide pellets.
2
hours, analyzed by GC, and centrifuged to remove the solid cata-
lyst. The reaction solution was then stirred for a further 4 hours.
Reaction progress, if any, was monitored by GC as previously de-
scribed.
Acknowledgements
GC analyses were performed using a Shimadzu GC 2010-Plus
equipped with a flame ionization detector (FID) and an SPB-5
column (length=30 m, inner diameter=0.25 mm, and film thick-
ness=0.25 mm). The temperature program for GC analysis held
The Viet Nam National Foundation for Science and Technology
Development–NAFOSTED is acknowledged for financial support
through project code 104.05-2014.77.
samples at 1008C for 1 min; heated them from 100 to 2808C at
À1
4
08Cmin ; and held them at 2808C for 4.5 min. Inlet and detector
temperatures were set constant at 2808C. Diphenyl ether was used
as an internal standard to calculate the GC yield. GC-MS analyses
were performed using a Shimadzu GCMS-QP2010Ultra with a ZB-
Keywords: acylation · alkynes · copper · heterogeneous
catalysis · metal–organic frameworks
5
MS column (length=30 m, inner diameter=0.25 mm, and film
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Accepted Article published: February 23, 2016
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