Copper ferrite superparamagnetic nanoparticles as a heterogeneous catalyst for directed phenol/formamide coupling

Article abstract of DOI:10.1016/j.tetlet.2017.07.049

The copper ferrite-catalyzed, directed coupling of ortho-arylated phenols and dialkylformamides in the presence of a peroxide oxidant is described. Acyclic and cyclic amides were compatible with the reaction conditions. The copper ferrite catalyst is hete

Full text of DOI:10.1016/j.tetlet.2017.07.049

Accepted Manuscript
Copper Ferrite Superparamagnetic Nanoparticles as a Heterogeneous Catalyst
for Directed Phenol/Formamide Coupling
Chung K. Nguyen, Ngon N. Nguyen, Kien N. Tran, Viet D. Nguyen, Tung T.
Nguyen, Dung T. Le, Nam T.S. Phan
PII:
S0040-4039(17)30904-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.07.049
TETL 49131
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
14 June 2017
6 July 2017
13 July 2017
Please cite this article as: Nguyen, C.K., Nguyen, N.N., Tran, K.N., Nguyen, V.D., Nguyen, T.T., Le, D.T., Phan,
N.T.S., Copper Ferrite Superparamagnetic Nanoparticles as a Heterogeneous Catalyst for Directed Phenol/
Formamide Coupling, Tetrahedron Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.07.049
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Tetrahedron Letters
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Copper Ferrite Superparamagnetic Nanoparticles as a Heterogeneous Catalyst for
Directed Phenol/Formamide Coupling
a
a
a
a
a
Chung K. Nguyen , Ngon N. Nguyen , Kien N. Tran , Viet D. Nguyen , Tung T. Nguyen , Dung T. Le ,
a,*
a,*
aand Nam T. S. Phan
Faculty of Chemical Engineering, HCMC University of Technology, VNU-HCM, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam
ARTICLE INFO
ABSTRACT
Article history:
Received
The copper ferrite-catalyzed, directed coupling of ortho-arylated phenols and dialkylformamides
in the presence of a peroxide oxidant is described. Acyclic and cyclic amides were compatible with
the reaction conditions. The copper ferrite catalyst is heterogeneous since substantial leaching was
not detected and re-use of the catalyst for 9 consecutive reactions proceeded without a significant
decrease in yield. To the best of our knowledge, this transformation has not been previously
performed under heterogeneous catalysis conditions.
Received in revised form
Accepted
Available online
Keywords:
2
009 Elsevier Ltd. All rights reserved.
copper ferrite
C-H activation
heterogeneous catalyst
formamide
phenol
The formation of carbon-carbon and carbon-heteroatom bonds
via direct C-H functionalization has emerged as an efficient
methodology for the synthesis of biologically active molecules
inferior oxidant compared with tBuOOH in water (Entry 2). The
inorganic oxidant K afforded 3 in low yield (Entry 3).
2 2 8
S O
Conducting the reaction at 60 °C substantially decreased the
reaction yield (Entry 4), whilst decreasing the amount of oxidant
still gave product 3 in good yield (Entry 5). Other heterogeneous
iron-based catalysts were inferior (Entries 6-8). Finally, the
reaction in air without an external oxidant was inefficient (Entry
9), and copper ferrite was found to be necessary (Entry 10).
1
and functionalized materials. Transition metals are commonly
2
required to accelerate the C-H activation step, however, the
recovery and reuse of “soluble” metal catalysts can be
challenging. It is therefore more beneficial that recyclable
materials replace conventional homogeneous analogues as
3
catalysts for organic transformations. The use of heterogeneous
4
a
a-c
4d-k
Table 1. Optimization conditions and control experiments
O
catalysts, such as a metal organic framework-,
4m-n
carbon-,
for C-H activation
4
l
alumina-, or polymer-supported catalysts,
NMe
2
HO
O
has been reported. However, complex catalytic systems are
scarcely available and expensive second- or third-row metals are
required. Few literature examples describe simple and first-row
catalyst (5 mol%)
oxidant (4 equiv.)
N
S
O
H
N
S
+
NMe2
100 oC, 1 h
5
1
2
3
transition metal-based catalysts for C-H functionalization.
Notably, reusable, heterogeneous copper catalysis is used in these
Entry
Catalyst
Oxidant
Yield 3 (%)
5d-g
rare cases.
As part of our continued interest in copper-
1
2
3
Nano CuFe O
tBuOOH/decane (6 M)
tBuOOH/water (70%)
59
2
2
2
2
2
4
6
promoted C-H activation/functionalization, herein, we report a
method for the copper ferrite nanoparticle-catalyzed, directed O-
H/C-H coupling of (2-hydroxyphenyl)benzoazoles and N,N-
dialkyl formamides.
Nano CuFe
Nano CuFe
Nano CuFe
Nano CuFe
O
4
72
O
4
K
2
S
2
O
8
< 5
b
4
O
4
tBuOOH/water (70%)
tBuOOH/water (70%)
tBuOOH/water (70%)
tBuOOH/water (70%)
tBuOOH/water (70%)
-
< 5
c
In this protocol, the benzothiazole motif acts as a directing
substituent, thus facilitating the coupling transformation to give a
hybrid benzothiazole-carbamate moiety. Based on previous C-H
5
O
4
76
c
6
Nano NiFe
2
O
4
< 5
c
6
,7
7
Nano Fe O
3
N.R.
N.R.
< 5
4
functionalization reactions reported by our group, copper ferrite
nanoparticles were used as the catalyst and tert-butyl
hydroperoxide (tBuOOH) was chosen as the oxidant.
c
8
Nano Fe O
2
3
d
9
Nano CuFe
-
2 4
O
Optimization with respect to the catalyst and oxidant is
illustrated in Table 1. tBuOOH in decane (Entry 1) was an
1
0
tBuOOH/water (70%)
N.R.
———
Corresponding author. Tel.: (+84 8) 38647256 ext. 5681; fax: (+84 8) 38637504; ltdung@hcmut.edu.vn (D.T.Le), ptsnam@hcmut.edu.vn
N.T.S. Phan)
*
(

2
a
Reagents and conditions: (2-hydroxyphenyl)benzothiazole 1 (0.5 mmol),
N,N’-dimethylformamide 2 (1.5 mL), catalyst (0.025 mmol, 5 mol%), oxidant
2 mmol), 100 °C, 1 h. Yields determined by GC analysis, with diphenyl
The reaction scope with respect to the ortho-arylated phenols
and dialkylformamides is presented in Table 2.
Diethylformamide and dimethylformamide were both coupled
with (2-hydroxyphenyl)benzothiazole in good yields (Entries 1-
2). Steric hindrance (Entry 3) or a longer alkyl chain (Entry 4) on
the formamide nitrogen did not significantly affect the reaction
yield. Formamides bearing a cyclic amide moiety afforded the
corresponding products in reasonable yields (Entries 5-6).
Additionally, benzoxazole (Entry 7) and benzimidazole (Entry 8)
were competent substrates for the reaction. In contrast to copper-
or iron-catalyzed, non-directed dehydrogenative coupling, the
reaction of benzimidazole did not favor C-N bond formation
(
b
c
ether as the internal standard. Temperature: 60 °C. tBuOOH/water (0.5
d
mmol). air as the sole oxidant. Further optimization is contained in the ESI
(
Table S1-2).
Table 2. Coupling of phenols containing the benzoazole motif
a
and formamides
O
NR
2
HO
CuFe
2
O
4
(5 mol%)
O
N
X
O
H
tBuOOH (1 equiv.)
N
X
NR
2
1
20 oC, 2 h
8
X = S, O, NH
(Entry 8).
The research was subsequently extended to the coupling of
other phenols with dialkylformamides in the presence of the
copper ferrite catalyst. It was found that phenols containing
carbonyl substituents at the ortho position were also reactive
towards this transformation, affording the corresponding
carbamates in reasonable yields (Entries 1-4, Table S3).
However, carbonyl substituents at the meta- or para- position did
not promote the coupling reaction (Entries 5-6, Table S3).
Interestingly, 2-(4,5-dihydro-1H-imidazol-2-yl)phenol (Entries 7-
Entry
1
Phenol
Formamide
Product
Yield
%)
(
HC(O)NMe
2
72
75
70
64
2
1
1
3
5
7
2
3
4
HC(O)NEt
2
8
, Table S3) was inactive, with no trace of the carbamates
4
detected. Similarly, phenol, 2-phenyl phenol, and 2-methyl
phenol were also inert in this reaction (Entries 9-11, Table S3).
1
00
HC(O)N(iPr)
2
5
mol% catalyst
6
8
6
4
0
0
0
Leaching test
1
HC(O)N(nBu)
2
8
1
1
9
20
0
5
6
71
66
1
0
2
0
10 20 30 40 50 60 70 80 90
Time (min)
11
Figure 1. Leaching test of copper ferrite nanoparticles.
1
00
80
1
1
1
3
5
6
4
2
0
0
0
0
7
HO
HC(O)NMe
2
72
N
O
2
1
4
1
8
HC(O)NMe
2
74
2
16
1
2
3
4
5
6
7
8
9
Run
17
Figure 2. Reusability of the copper ferrite catalyst.
a
Reagents and conditions: (2-hydroxyphenyl)benzoazole (0.5 mmol),
(0.025 mmol, mol%),
tBuOOH/water (0.5 mmol), 100 °C, 2 h. Isolated yields. See ESI for details.
dialkylformamide (19 mmol), CuFe
2
O
4
5

3
Leached homogeneous species have been reported to effect C-
9
H functionalization reactions; therefore control experiments
Cu(II)
were necessary to confirm the heterogeneity of the copper ferrite
nanoparticles. Obviously, if additional product 3 was generated
after the catalyst was separated from the reaction mixture, the
contribution of homogeneous catalysis to the reaction of 1 with 2
would be significant. It was observed that upon catalyst removal
after 30 min the reaction did not substantially yield additional
product 3, indicating that leaching of the active species was
negligible (Fig. 1).
S
N
tBuOOH
OH
(
II)
Cu
O
Cu(I)
N
Additionally, recovery and reuse of the copper ferrite catalyst
was demonstrated for the reaction of 1 with 2. After the first run,
the catalyst was gathered by magnetic decantation, washed
carefully with DMF and MeOH, dried under vacuum, and reused
in subsequent reactions. It was observed that the regenerated
catalyst afforded the desired product without a significant
decrease in yield; a 72% yield of compound 3 was achieved in
S
O
H
NMe
2
O
III)
S
N
NMe
2
(
tBuOOH
Cu
O
O
O
O
NMe2
N
NMe2
th
S
the 9 run (Fig. 2). Moreover, the structure of the nanoparticle
Figure 5. Plausible mechanism.
2 4
CuFe O was maintained during the reaction, as disclosed by
XRD analysis (Fig. 3).
To explore the pathway for the reaction of 1 with 2, (2,2,6,6-
7
6
5
4
3
2
1
000
000
000
000
000
000
000
0
tetramethylpiperidin-1-yl)oxy (TEMPO) and ascorbic acid were
added to the reaction mixture after 10 min. It was found that the
reaction was affected by the radical scavengers, with 26% and
3
8% yields of 3 obtained under these conditions (Fig. 4). These
observations demonstrated that the interaction of TEMPO or
ascorbic acid with the radical species generated in the catalytic
cycle could stop the transformation. Furthermore, the reaction of
phenol, 2-phenyl phenol, and 2-methyl phenol, respectively, with
(b)
2
did not occur (Entries 9-11, Table S3), confirming that the
nitrogen functionality in 1 is actually promoting the coupling
reaction. As mentioned earlier, 2-(4,5-dihydro-1H-imidazol-2-
yl)phenol (Entries 7-8, Table S3) was unable to react with
dialkylformamides, indicating the necessity of the benzene ring of
the (2-hydroxyphenyl)benzoazoles to the reaction.
(
a)
2
0
30
40
50
60
70
2-Theta-Scale
2 4
The reaction of 1 with 2 utilizing the nanoparticle CuFe O
2 3
catalyst proceeded in 76% yield, while both nanoparticle Fe O
Figure 3. XRD analysis of the new (a) and recovered (b) catalyst.
and nanoparticle Fe
sites on the CuFe
responsible for the catalytic activity. A possible mechanism is
proposed in Figure 5. Chelation of (2-
3
O
4
were inactive, suggesting that the copper
2
O superparamagnetic nanoparticles were
4
100
5
mol% catalyst
TEMPO test
hydroxyphenyl)benzothiazole to the copper sites forms a
cyclometalated species. Single-electron oxidative addition of
8
6
4
2
0
0
0
0
0
Ascorbic acid test
10
copper(II) by the formamide radical generates a copper(III)
species, which then undergoes reductive elimination to afford the
product and the copper(I) species. Catalyst regeneration proceeds
via oxidation of copper(I) by either peroxide or the oxygen in air.
In conclusion, we have developed a method for the copper
ferrite-catalyzed,
directed coupling of phenols and
dialkylformamides. Benzothiazole, benzoxazole, benzimidazole
and formamides bearing acyclic and cyclic substituents on
nitrogen are compatible with the reaction conditions. Copper
ferrite could be recovered by magnetic decantation, and reused
without significant leaching. To the best of our knowledge, this
transformation has not been previously performed under
heterogeneous catalysis conditions.
0
10 20 30 40 50 60 70 80 90
Time (min)
Figure 4. Affect of radical scavengers.
Acknowledgments
We would like to thank the Viet Nam National Foundation for
Science and Technology Development (NAFOSTED) for
financial support under Project code 104.01-2015.35 (Contract
number 14/2016/104/HĐTN)

4
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5
Copper Ferrite Superparamagnetic
Nanoparticles as a Heterogeneous Catalyst for
Directed Phenol/Formamide Coupling
Chung K. Nguyen, Ngon N. Nguyen, Kien N.
Tran, Viet D. Nguyen, Tung T. Nguyen, Dung T.
*
Le , Nam T. S. Phan
*
Faculty of Chemical Engineering, HCMC
University of Technology, VNU-HCM,
68 Ly Thuong Kiet, District 10, Ho Chi Minh
City, Viet Nam
2
*
Email: ltdung@hcmut.edu.vn,
ptsnam@hcmut.edu.vn
Ph: (+84 8) 38647256 ext. 5681
+84 8) 38637504
Fx:
(
Highlights
•
2 4
CuFe O nano particles were used as a catalyst
for directed phenol/formamide coupling.
High yields were obtained.
•
•
The magnetic catalyst could be recovered and
reused.

6
Graphical Abstract
Copper Ferrite Superparamagnetic
Nanoparticles as a Heterogeneous Catalyst
for Directed Phenol/Formamide Coupling
Chung K. Nguyen, Ngon N. Nguyen, Kien N. Tran, Viet D. Nguyen, Tung T. Nguyen, Dung T. Le, and Nam
T. S. Phan
O
N
O
HO
2
CuFe O
4
(5 mol%)
O
O
H
N
S
tBuOOH (1 equiv.)
N
S
N
O
1
20 oC, 2 h