Oxidative Coupling of Dimethylformamide with β-Dicarbonyl Compounds Using γ-Fe2O3?CuO Nanoparticles

Article abstract of DOI:10.1134/S1070428020090249

Abstract: Maghemite–copper oxide nanocomposite catalyzed oxidative coupling of formamides with β-dicarbonyl compounds in the presence of tert-butyl hydroperoxide as an oxidant to produce the corresponding enol carbamates in excellent yields (up to 92%) under the optimized conditions. The simple preparation and the ability to be recycled and magnetically separated are salient features of this catalytic system.

Full text of DOI:10.1134/S1070428020090249

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 9, pp. 1654–1659. © Pleiades Publishing, Ltd., 2020.
Oxidative Coupling of Dimethylformamide with β-Dicarbonyl
Compounds Using γ-Fe O @CuO Nanoparticles
2
3
a,
a
a
H. Hassani *, F. Shaghayeghi Toosi , and N. Feizi
a
Department of Chemistry, Payame Noor University, Tehran, 19395-4697 Iran
e-mail: hassaniir@yahoo.com
*
Received March 20, 2020; revised April 1, 2020; accepted April 10, 2020
Abstract—Maghemite–copper oxide nanocomposite catalyzed oxidative coupling of formamides with β-di-
carbonyl compounds in the presence of tert-butyl hydroperoxide as an oxidant to produce the corresponding
enol carbamates in excellent yields (up to 92%) under the optimized conditions. The simple preparation and the
ability to be recycled and magnetically separated are salient features of this catalytic system.
Keywords: nanocatalyst, oxidation, maghemite–copper oxide
DOI: 10.1134/S1070428020090249
INTRODUCTION
for the formation of amides from alcohols and amines
using [20]. In continuation of our interest in using
magnetic nanoparticles as a catalyst support [21],
herein we report the preparation of enol carbamates by
oxidative coupling of formamides with β-dicarbonyl
compounds in the presence of γ-Fe O @CuO and
tert-butyl hydroperoxide (TBHP) [22]. Various enol
carbamates were obtained in good to excellent yields in
a one-pot manner under our conditions (Scheme 1).
Magnetic nanoparticles are easy dispersed in a solution,
which facilitates catalyst recovery. Simple separation
by using an external magnet and the recyclability up to
five times are two virtues of this system [23, 24].
Coupling reactions underlie an important synthetic
strategy widely used in both academia and industry for
the formation of carbon–carbon and carbon–hetero-
atom bonds [1–5]. Several reports have appeared in the
literature on direct C–H functionalization for the
formation of C–C and C–X bonds (X = O, S, N, P, etc.)
catalyzed by transition metals, which has become
a very useful tool in organic chemistry [6].
2
3
In vivo data support the pharmacological efficacy of
enol carbamates as promising anxiolytics [7]. Carba-
mates are mixed ester–amides of carbonic acid. Their
chemical behaviour is similar to that of carbonates.
Dixneuf et al. have shown that enol carbamates can be
prepared by addition of carbamic acids to terminal
alkynes catalyzed by Ru (CO) [8] or Ru(Cl) [9].
RESULTS AND DISCUSSION
3
12
3
The maghemite–copper(II) oxide nanocomposite
was prepared as shown in Scheme 2. The obtained
heterogeneous catalyst was characterized using scan-
ning electron microscopy (SEM), X-ray diffraction
However, the yields and selectivities were low for ali-
phatic acetylenes. Among the supports used, magnetic
nanocomposites have attracted more attention because
they can be easily recovered from the reaction mixture
simply by using an external magnet [10–19].
(
XRD), vibrating sample magnetometry (VSM), and
transmission electron microscopy (TEM). The crystal-
line structure of γ-Fe2O3@CuO NPs and phase purity
were determined using powder XRD as shown in
Fig. 1. The XRD pattern of magnetic NPs is indexed to
We have previously reported the preparation of
γ-Fe O @CuO nanocomposite and its application as
a highly efficient and magnetically separable catalyst
2
3
Scheme 1.
O
O
O
DMF, catalyst, oxidant, 2 h
Me N
O
O
2
R1
R2
R1
R2
1
654

OXIDATIVE COUPLING OF DIMETHYLFORMAMIDE
1655
Scheme 2.
Aq. NH3
reflux, 1 h
Si(OEt)4
EtOH, 24 h
FeCl ·6H O + FeCl ·4H O
Fe O
4
3 4
Fe O
3
2
2
2
3
CuCl ·2H O
110°C, 24 h
2
2
1
40°C, 24 h
γ-Fe
3
O
4
γ-Fe O @CuO
3 4
the spinel phases (Fe O : 2θ = 35, 42, 51, 63, 68, and
γ-Fe O @CuO promoted coupling of ethyl acetoacetate
2 3
2
3
7
5°) and CuO (2θ = 42, 45, and 75°). For investigating
with DMF to afford the corresponding enol carbamate
(Table 1, entry no. 9). The amount of the catalyst was
initially optimized: it was found that 20 mg of
γ-Fe O @CuO was sufficient to promote the reaction
(entry no. 6). The effect of temperature was also evalu-
ated. Elevated temperature was generally effective for
the oxidative coupling of ethyl acetoacetate with DMF.
As can be seen from Table 1, heating at 80°C proved to
be the most suitable (entry no. 9), and further increas-
ing the temperature to 100°C did not enhance the yield
the surface, morphology, and size of γ-Fe O @CuO
2
3
NPs, we used SEM and TEM. The resulting image
Fig. 2) shows uniform and minuscule nanoparticles.
The approximate size of the particles was estimated at
0–50 nm. The magnetic properties of γ-Fe O @CuO
(
2
3
3
2
3
were studied by vibrating sample magnetometry
VSM). Figure 3 shows the magnetization curve as
a function of applied field in the range from –10000 to
(
1
0000 Oe. The saturation magnetization is 48.8 emu/g.
(
entry no. 10). No desired carbamate was formed in the
Initially, the oxidative coupling of ethyl acetoacetate
absence of a catalyst or oxidant (entry nos. 11 and 12).
with N,N-dimethylformamide was carried out using
γ-Fe O @CuO as catalyst in the presence of various
Under the optimized conditions, the scope of this
2
3
oxidants. When TBHP was used as an external oxidant,
reaction was explored with various β-dicarbonyl com-
γ-Fe O3
2
CuO
2
0
30
40
50
2
60
θ, deg
Fig. 1. X-Ray diffraction patterns of γ-Fe O and γ-Fe O @CuO.
70
80
90
2
3
2
3
(a)
(b)
Fig. 2. SEM (a) and TEM (b) images of γ-Fe O @CuO.
2
3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 9 2020

1656
HASSANI et al.
6
4
2
0
0
0
91
8
8
87
8
5
8
0
80
6
4
0
0
–
10000
5000
0
5000
10000
–
–
–
20
40
60
20
0
1
2
3
4
5
Applied field, Oe
Fig. 3. Magnetization curve of γ-Fe O @CuO.
Cycle number
Fig. 4. Recyclability of γ-Fe O @CuO.
2
3
2
3
pounds, and the results are summarized in Table 2. All
products were characterized by measuring their melting
catalyst was separated from the reaction mixture using
an external magnet, washed, dried under reduced
pressure at room temperature for 12 h, and used for
the next reaction. The catalyst could be reused at least
five times without any significant loss of catalytic
activity (Fig. 4).
1
points (in some cases) and recording IR and H and
13
C NMR spectra.
Scheme 3 shows a plausible mechanism for the
coupling of N,N-dimethylformamide with β-dicarbonyl
compounds in the presence of γ-Fe O @CuO. The
2
3
copper complex generated from copper salt and β-di-
carbonyl compounds coordinates to DMF and under-
goes internal nucleophilic addition to form copper
hemiacetal species 1. Intermediate 3 is protonated to
give compound 5, and the latter reacts with the radical
generated by copper-catalyzed decomposition of
TBHP, followed by single-electron transfer (SET) in
hemiacetal radical 6, yielding gives the final enol
carbamate.
EXPERIMENTAL
All solvents and chemical were analytical-grade
commercial products and were used without further
purification. The FT-IR spectra were obtained over the
–
1
range 400–4000 cm with a Nicolet IR100 FT-IR
spectrometer from samples pressed with spectroscopic
grade KBr. The X-ray powder diffraction pattern was
recorded at room temperature using a Philips X-Pert
1710 diffractometer (Co Kα radiation, λ = 1.78897 Å;
voltage 40 kV, current 40 mA, scan range 10 ≤ 2θ ≤
The reusability of the catalyst was also evaluated.
After completion of the reaction, the magnetic nano-
Table 1. Optimization of reaction conditionsa
b
Entry no.
Oxidant
H O
Catalyst amount, mg
Temperature, °C
Yield, %
1
2
3
4
5
6
7
8
9
5
5
Room temperature
<10
<10
<5
30
51
62
73
84
90
90
–
2
2
m-CPBA
UHPc
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
–
Room temperature
5
Room temperature
5
Room temperature
10
20
20
20
20
20
–
Room temperature
Room temperature
40
60
80
1
0
100
80
11
1
2
20
80
–
a
b
c
All reactions were run with ethyl acetoacetate (1 mmol), DMF (2 mL), and oxidant (1.5 equiv); reaction time 2 h.
Isolated yield.
UHP is urea hydrogen peroxide.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 9 2020

OXIDATIVE COUPLING OF DIMETHYLFORMAMIDE
Table 2. Synthesis of enol carbamate derivativesa
1657
b
Entry no.
Substrate
Product
Yield, %
O
O
O
1
Me
Me
Me
2
2
2
N
O
O
O
O
O
O
O
O
O
O
O
90
92
87
85
84
88
82
80
88
82
90
86
Me
OEt
Me
O
OEt
OMe
O
O
O
O
2
3
4
5
6
7
8
9
N
Me
Me
OMe
Me
O
O
O
CH2
N
CH2
Me
O
O
O
O
O
Me
Me
N
2
Me
Ph
OEt
OEt
OEt
O
O
O
Me
N
2
OEt
Ph
O
Me
N
O
O
2
Me
O
Ph
Me
Me N
Ph
O
O
2
O
O
O
Me
2
N
O
O
O
O
Me Me
Me Me
O
O
Me
Me
N
O
O
O
2
2
Me
Me
OBu-t
Me
O
OBu-t
O
O
1
0
N
O
Me
Me
O
Me
O
O
O
11
Et
2
N
O
O
Me
Me
OEt
O
Me
OEt
O
1
2
Et
N
2
O
O
OEt
Me
OEt
a
Reaction conditions: 1,3-dicarbonyl compound (1 mmol), N,N-dialkylformamide (2 mL), TBHP (1.5 equiv), catalyst (20 mg), 80°C, 2 h.
Isolated yields.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 9 2020

1658
HASSANI et al.
Scheme 3
O
O
R1
R2
Cu(II)
TBHP
Cu(II)
O
O
R1
R2
Cu(I)
·
+ –OH
t-Bu
O
Cu(II)
4
O
O
R1
O
Me
N
O–
N
R2
O
Me
TBHP
R1
O
1
·
+
+
t-Bu OO + H
Me
R2
Me
3
2
H+
O
OH
N
O
OH
N
O
O
N
R1
R1
R1
O
O
O
·
Me
Me
t-Bu O·
Me
R2
R2
R2
Me
Me
t-Bu OH
Me
5
6
t-Bu OOH
9
0°, scan speed 0.02 deg/s). The morphology of the
stirred for 1 h at room temperature and was then
refluxed for 1 h. To modify the magnetic surface,
40 mL ethanol was added to the suspension, the mix-
ture was stirred at 40°C for 1 h, 10 mL of tetraethyl
orthosilicate was added, and the suspension was stirred
catalyst was studied with scanning electron microscopy
using Philips XL 30 and S-4160 scanning electron
microscopes on gold-coated samples. The magnetic
properties of γ-Fe O @CuO nanoparticles were
measured with a vibrating magnetometer/Alternating
Gradient Force Magnetometer (MDK, Iran).
2
3
for 24 h. The precipitate of Fe O nanoparticles was
3
4
separated from the aqueous solution by magnetic
decantation, washed with diethyl ether and pure water
several times, and dried at 140°C for 24 h to obtain
γ-Fe O . The product was dispersed in water, 2 mmol
Preparation of γ-Fe O @CuO nanoparticles.
2
3
A mixture of 3.7 mmol of FeCl ·6H O and 1.85 mmol
of FeCl ·4H O was dissolved in 30 mL of deionized
3
2
2
3
2
2
of CuCl ·2H O was added, and the mixture was stirred
2 2
water under vigorous stirring (700 rpm). Aqueous
ammonia (25%, w/w, 10 mL) was added dropwise to
the mixture under stirring to maintain the pH value
at 11. The resulting black dispersion was continuously
at room temperature for 24 h. The nanocatalyst was
separated from the aqueous solution by magnetic
decantation, washed with water, and dried at 110°C
for 24 h.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 9 2020

OXIDATIVE COUPLING OF DIMETHYLFORMAMIDE
1659
ACKNOWLEDGMENTS
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CONFLICT OF INTEREST
The authors declare no conflict of interest.
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