Bonded- A nd discreted-Lindqvist hexatungstate-based copper hybrids as heterogeneous catalysts for the one-pot synthesis of 2-phenylquinoxalines: Via 2-haloanilines with vinyl azides or 3-phenyl-2 H-azirines

Article abstract of DOI:10.1039/d0dt02625e

One bonded- A nd one discreted-Lindqvist hexatungstate-based copper hybrids (Cu-POMs) ([Cu2(O)OH (phen)2]2[W6O19]?6H2O (1) and [Cu2(phen)4Cl] [HW6O19]?2H2O (2) (phen = 1,10-phenanthroline)) were controllably synthesized and routinely characterized. Cu-POM

Full text of DOI:10.1039/d0dt02625e

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DOI: 10.1039/D0DT02625E
ARTICLE
Bonded- and Discreted- Linqvist Hexatungstate-Based Copper
hybrids as Heterogeneous Catalysts for One-pot Synthesis of 2-
Phenylquinoxalines via 2-Haloanilines with Vinyl Azides or 3-
Phenyl-2H-azirines
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Guodong Shen,*a Zeyou Wanga, Xianqiang Huang,*a Shuwen Gong,a Jiangong Zhang,a Zhenfei Tang,a
Manman Sun,b Xin Lvc
One bonded- and one discreted- Linqvist hexatungstate-based copper hybrids (Cu-POMs)
([Cu2(O)OH(phen)2]2[W6O19].6H2O (1) and [Cu2(phen)4Cl] [HW6O19]·2H2O (2) (phen= 1,10-phenanthroline) )
were controllably synthesized and routinely characterized. Cu-POMs 1-2 consisted of identical [W6O19] unit
and similar copper-phen complexes, the two units are bonded via four Cu-O chemical bonds in compound 1,
however, compound 2 is discreted and stabilized by intermolecular electrostatic interactions. Importantly,
these Cu-POMs catalysts were first applied in the novel reaction for preparation of 2-phenylquinoxalines via
the one-pot coupling and oxidation reactions of 2-haloanilines with vinyl azides or 3-phenyl-2H-azirines under
mild conditions, and Cu-POMs 1 showed higher catalytic performance in good yields (79-84%). The reactions
exhibit some functional group tolerance and allow for the preparation of a number of 2-phenylquinoxalines.
reactions.7 However, these protocols usually require a lot of
copper salts (10-20 mol%) and corresponding ligands. In the
past decade, lots of the structure of Cu-POMs have been
synthesized and showed great advantages in the field of
molecular electronics, adsorption and function materials, etc.8
However, the combination of Cu-POMs has seldom been used
in the organic synthesis for construction of new C-C and C-N
bonds, especially the assembly of heterocyclic compounds via
one-pot cascade coupling strategies.
Functionalized quinoxalines are an important class of
bioactive molecules and core unit in pharmaceuticals, dyes,
antibiotics and other applications.9 A large number of synthetic
methods have been developed to construct quinoxalines for
these important applications.10 Among these methods, there
are few synthetic methods for the synthesis of 2-
phenylquinoxalines including the oxidation-condensation or
condensation reaction, cross-coupling reaction and oxidation
reaction. Most catalytic methods for the synthesis of 2-
phenylquinoxalines rely on the oxidation-condensation or
condensation reaction of condensing partners and 1, 2-
Introduction
Polyoxometalates (POMs) are a unique class of discrete, anionic
metal oxides, which are generally constructed by early
transition elements (W, V, Mo, Nb and Ta, etc) in high oxidation
states.1 POMs are also good prospects in the areas of catalysis,
molecular electronics, biomedicine and dye-sensitized solar
cells, etc.2 Especially, POMs involved organic reactions have
aroused widespread interest and become a powerful tool in
chemical synthesis.3 For instance, Dwight, et al. presented the
aerobic oxidative coupling of arenes in the presence of Pd(OAc)2
and H4PMo11VO40;4 Sanford’s group reported the sp3 C-H
olefination catalyzed by Pd(OAc)2 and H4PMo11VO40.5 In the
previous work, the oxidation of alcohols and benzyl
hydrocarbon can be achieved by transition metal-organic POMs
catalysts.6 Among the transition metal catalysts, cheap copper-
catalyzed reactions have attracted much attention owing to
inexpensive and wide varieties, especially the majority of the
already developed combination of Cu salts and phen catalyzed
strategies have been made in catalytic C-N bond forming
This work
a. School of Chemistry and Chemical Engineering, Shandong Provincial Key
Laboratory of Chemical Energy Storage and Novel Cell Technology, Liaocheng
University, 1 Hunan Avenue, Liaocheng 252000, Shandong, P. R. China
b. Advanced Research Institute and Department of Chemistry, Taizhou University,
1139 Shifu Avenue, Taizhou 318000, Zhejiang, P. R. China.
N
N3
R1
N
R2
R2
R2
R2
NH2
I
b
Cu-POMs 1
c'
or
N
R1
Cs2CO3, toluene
c. Key Laboratory of the Ministry of Education for Advanced Catalysis Materials,
College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua
321004, P. R. China.
100 o
C
N
N
a
d
R1
c
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
Scheme 1 Synthesis of 2-phenylquinoxalines.
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ARTICLE
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diamines.11 There are only several reports about synthesis of 2- complexes.16 Remarkably, in the case, each [W6O19]2- anion acts
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phenylquinoxalines by the cross-coupling reaction including the as an polyanion inorganic ligand covDaOleI:n1t0ly.103b9o/nDd0DeTd02w62i5thE
coupling of 2-haloquinoxalines with triphenylaluminum two[Cu2(O)OH(phen)2]+ cations only through two Ot and two Ob
(triphenylbismuthane, phenylboronic acid and etc.).12 Because atoms. This kind of four-connection coordination mode of the
the limitation of the reaction substrates, the dehydrogenation hexatungstate in compound 1 is rare and may play an important
reactions of 2-phenyl-1,2,3,4-tetrahydroquinoxaline or 2- role in the stabilization of the whole skeleton. 17
phenyl-1,2-dihydroquinoxaline are also rare.13
In the above perspective, the use of catalysts based on cheap
copper and POMs in the organic reactions is especially
beneficial for large-scale and industrial applications. Thus,
design and synthesis of one-component Cu-POMs is highly
desirable for investigating novel organic reactions, in particular
the construction of heterocyclic compounds owing to their
excellent biological activities. Importantly, as a simple and
easily-handling
precursor
for
constructing
2-
phenylquinoxalines, vinyl azides is not frequently used as the
raw materials thus far. In continuation of our ongoing efforts to
synthesis functional POMs and assemble heterocycles,6, 14 we
reported
two
copper-polyoxometalates
(Cu-POMs:
[Cu2(O)OH(phen)2]2[W6O19]·6H2O
1
and [Cu2(phen)4Cl]
[HW6O19]·2H2O 2) (Fig. 1-2), and the catalytic performance of
[Cu2(O)OH(phen)2]2[W6O19].6H2O
has showed higher
1
Fig. 1 The simplified representation of the controlling synthesis of 1-
efficiency for the preparation of 2-phenylquinoxalines via the
one-pot coupling and oxidation reactions of 2-haloanilines with
vinyl azides or 3-phenyl-2H-azirines in good yield under mild
conditions (scheme 1).
2
Results and discussion
The reaction of Na2WO4·2H2O, CuCl2 2H2O, NaVO3 and phen
.
at 160 °C for 120 h under pH = 8.9 afforded green-crystals of
.
compound 1, the reaction of Na2WO4·2H2O, CuCl2 2H2O,
NH4VO3 and phen at 160 °C for 120 h under pH = 8.0 afforded
black-crystals of compound 2 (Fig. 1 and Table S1). Interestingly,
compounds 1-2 consisted of identical [W6O19] unit and similar
copper-phen complexes, the two units are bonded via four Cu-
O chemical bonds in compound 1, however, compound 2 is
discreted and stabilized by intermolecular electrostatic
interactions. All of the W atoms in 1-2 are in the +6 oxidation
state, however, the copper oxidation state in compounds 1-2
are +2 and +1, respectively, as revealed from bond valence sum
(BVS) values (Table S3)15.
Single crystal X-ray diffraction indicates that 1 crystallize in
the triclinic space group P-1. 1 is assembled of two dinuclear
copper counter cations [Cu2(O)OH(phen)2]+, one Lindqvist
shaped polyanion [W6O19]2- and six free lattice H2O molecules.
The two [Cu2(O)OH(phen)2]+ cations are bridged with [W6O19]2-
by O(1)t (terminal oxygen, connected to one W atom), O(2)b
(bridging oxygen, connecting edge-shared WO6 octahedra) and
form the[Cu2(O)OH(phen)2]2[W6O19] molecule. In the unit of
[Cu2(O)OH(phen)2]+, the Cu(II) atoms is coordinated by two N
atoms from two bidentate phen ligands, one μ2-O hydroxyl
oxygen atom, one μ2-O oxygen atom and one Ot or Ob from the
polyanion in a distorted square pyramidal geometry, and the
bond lengths around Cu atoms lie in the range 1.697 (10)-1.733
(8) Å (average 1.713 Å ) for Cu-N 1.895 (9)-1.949 (7) Å (average
1.923 Å ) for Cu-O, which are similar with those of reported
Fig. 2 (a) the polyhedron structure of compound 1; (b): the
polyhedron structure of compound 2; (c) the thermal ellipsoidal
plots of compound 1; (d): the thermal ellipsoidal plots of
compound 2. For clarity, the hydrogen atoms and free water
molecules are omitted, thermal ellipsoids are drawn at the 30%
probability level.
Table 1 Optimization of the reaction conditionsa
N3
I
N
Copper catalyst
Base, Solvent
NH2
T oC, Air
N
1b
1a
1c
T
Yield
(%)b
26
Entry
1
Catalyst
Cu-POMs 1
Base
Solvent
DMF
(oC)
100
Cs2CO3
2 | J. Name., 2012, 00, 1-3
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ARTICLE
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Cu-POMs 2
Cu-POMs 1
Cu-POMs 2
Cu-POMs 1
Cu-POMs 2
Cu-POMs 1
Cu-POMs 1
Cu-POMs 1
Cu-POMs 1
Cu-POMs 1
Cu-POMs 1
/
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3 dioxane
Cs2CO3 dioxane
K2CO3
K3PO4
DBU
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
toluene
toluene
100
100
100
100
100
100
100
100
100
90
110
100
100
100
100
100
19
67
54
23
20
60
59
9
compounds 1 and 2 were observed at 522 nmVaienwdArt5icl1e2Onnlmine,
respectively.
DOI: 10.1039/D0DT02625E
Then 2-iodoaniline 1a and (1-azidovinyl)benzene 1b were
selected as the model substrates to identify and optimize the
reaction parameters. The reaction was firstly carried out in DMF
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
o
with Cu-POMs 1 (3 mol%), Cs2CO3 (2.0 equiv.) at 100 C under
air. 24 h later, the reaction was stopped and the anticipated
product 1c was detected in 26% yield (Table 1, entry 1). Then
Cu-POMs 2 was tested and 19% of 1c was detected (Table 1,
entry 2). The two catalysts were also examined in other solvents
(dioxane and toluene), Cu-POMs 1 and toluene was found to be
the best choice (Table 1, entries 3-6). During the study of bases,
Cs2CO3 showed the best efficiency (Table 1, entries 7-9). From
the TLC monitoring of the reactions, it was found that the
starting material 1b was consumed completely and 1a was still
left. Then the reaction was repeated with Cu-POMs 1 (3 mol%),
1a (0.5 mmol), 1b (1.0 mmol) and Cs2CO3 (1.0 mmol) in toluene
(2.0 mL) under air atomsphere for 12 h, then another 0.5 mmol
1b was added in two portions at 6 h intervals via syringe. To our
delight, the starting substrate of 1a was consumed and the
reaction yield of 1c was detected in 84% (Table 1, entry 10). The
reaction at lower (90oC) temperatures evidently decreased the
reaction yields (Table 1, entry 11). When the reaction was
carried out at 110 oC, the yield of 1c was not changed obviously
(Table 1, entry 12). Without the catalyst or only using CuCl2 as
the catalyst, no product of 1c was detected (Table 1, entries 13-
14). Some other simple cuprous salts (CuI and CuBr) were used
to repeat the reaction, and the product yields were not high
(Table 1, entries 15-16). Other catalyst systems were also
surveyed (CuCl2/1,10-phen, CuCl2/1,10-phen/Na2WO4 and
CuCl2/1,10-phen/O2), but the yields did not improve (Table 1,
entries 17-19). From the above experiments, entry 10 shows the
best reaction conditions.
84c
61c
66c
0c,d
0c,d
45c
38c
23c
CuCl2
CuI
CuBr
CuCl2/phen
CuCl2/phen/Na2
WO4
18
Cs2CO3
toluene
100
33c,e
19
CuCl2/phen/O2
Cs2CO3
toluene
100
28c,f
a Reaction conditions: catalyst (0.015 mmol), 1a (0.5 mmol), 1b (1.0
b
mmol) and base (1.0 mmol) in solvent (2.0 mL) under air for 24 h.
The yield was determined by 1H NMR analysis of crude products
using 1, 3, 5-trimethoxybenzene as the internal standard. c Reaction
conditions: catalyst (0.015 mmol) or copper salt (0.015 mmol), ligand
(0.03 mmol), 1a (0.5 mmol), 1b (1.0 mmol) and base (1.0 mmol) in
toluene (2.0 mL) under air atomsphere for 12 h, then 0.5 mmol 1b
was added in two portions at 6 h intervals via syringe. d No catalyst
was used. e 0.03 mmol Na2WO4 was used. f Oxygen balloon was used.
For [W6O19]2-, the polyanion comprises six edge-shared WO6
octahedra and exhibits approximate Oh point symmetry (Fig.
2a). The O atoms can be divided into three groups: Ot, Ob and Oc
(the central O atom, common to all six WO6 octahedra). The W-
O distances are comparable with those found in the reported
compounds.18 In addition, the supramolecular structure of 1
was stabilized by intermolecular strong hydrogen-bonding
interactions [O3···O8 (-x+1/2, -y+1/2, -z+2): 2.741(7) Å; O10···
O4 (-x-1, -y, -z): 2.713(7) Å; O5···O11(-x+1/2, -y+1/2, -z+2):
2.720(6) Å] (Table S2) forming a 3D network (Fig. S1).
Table 2 Scope of the one-pot Cu-POMs -catalyzed coupling reaction
for the synthesis of 2-phenylquinoxalines.a
Single-crystal X-ray diffraction analysis reveals that
compound (2) comprises a twofold-symmetric dicopper(I)
cation, [Cu2(phen)4Cl]+, a centrosymmetric Lindqvist polyanion
[HW6O19]- and with two free water (Fig. 1), which is similar with
the reported compound. 19 In the [Cu2(phen)4Cl]+ cation, two Cu
(I) atoms adopt the square pyramidal coordination geometry
(Fig. 2b), coordinated by two phen ligands and one bridging
chloride (Table S1). In the compound 2, the copper oxidation
state is +1, we inferred that phenanthroline or the NH4+ group
in NH4VO3 might be used as reducing agent in the synthesis of
compound 2.20 The supramolecular structure of 2 was stabilized
by intermolecular electrostatic attraction and strong hydrogen-
bonding interactions [O3···O8 (-x+1/2, -y+1/2, -z+2): 2.741(7) Å;
O10··· O4 (-x-1, -y, -z): 2.713(7) Å; O5···O11(-x+1/2, -y+1/2, -
z+2): 2.720(6) Å] (Table S2) and forming a 3D network (Fig. S2).
The electronic absorption spectra for the compounds 1 and 2
were conducted and the results were illustrated in Fig. S8.
Because the copper atoms of compounds 1-2 are d9 system, d10
system, respectively, the diffuse reflectance spectra of
compounds 1 and 2 are slightly different.21 The broad valley of
N3
R2
NH2
N
1
Cu-POMs
Cs2CO3, toluene
100 o
R1
R1
R2
I
N
a
b
c
C
N
N
N
N
1c, 84%
2c, 82%
Cl
N
N
N
N
N
N
t-Bu
N
F
Cl
Cl
N
3c, 82%
4c, 78%
5c, 79%
6c, 75%
Cl
F
N
N
N
N
Cl
Cl
N
N
N
N
7c, 71%
8c, 79%
9c, 80%
10c, 83%
t-Bu
t-Bu
N
N
N
N
N
Cl
N
N
N
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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expansion of the substrate scope was focused on V3ie-wphAretincleylO-2nlHine-
azirines d, it can be synthesized by (1-azidovinyl)benzenes b in
toluene under reflux condition (Scheme 2). The reactions of a
with d were got in good yields under the optimized reaction
conditions (Scheme 2, 1c, 14c and 12c).
11c, 81%
12c, 82%
13c, 80%
1c, 35%c
DOI: 10.1039/D0DT02625E
a Reaction conditions: Cu-POMs 1 (0.015 mmol), a (0.5 mmol), b (1.0
mmol) and Cs2CO3 (1.0 mmol) in toluene (2.0 mL) under air for 12 h,
then 0.5 mmol b was added in two portions at 6h intervals via
syringe. b Isolated yield after flash chromatography based on a. c 2-
bromoaniline was used.
From the X-ray crystallography we confirmed the structure of
the products, the reactions of 2-haloanilines with vinyl azides or
3-phenyl-2H-azirines could react smoothly and get the
corresponding products c, but not c’ (Scheme 1). 2-
Phenylquinoxalines d can be synthesized by the oxidation
reaction of 1h via the standard condition (Scheme 3). On the
basis of the above results, a possible mechanism was proposed
in Scheme 4. The intermediate species e and f could be formed
under the optimized reaction conditions, and then the obtained
intermediates e and f proceeded the nucleophilic attack
reaction to get the intermediate g as the graphic shown,22 which
translated to the final product h after the classic copper-
catalyzed coupling reaction and elimination reaction, the
intermediate h could be detected by the GC-MS ((M-1)+= 207.4)
and HPLC-MS ((M-1)+=207.0943, (M+1)+ =209.1097) (Fig. S7).
The products c could be got after the oxidation reaction.
N3
N
toulene. reflux
eq 1
eq 2
1d
1b
N
NH2
I
N
N
1
Cu-POMs
Cs2CO3, toluene, 100 o
C
1d
2d
3d
1a
1c 83%
,
N
NH2
N
eq 3
1
Cu-POMs
Cs2CO3, toluene, 100 o
C
I
N
14c
, 85%
1a
N
NH2
N
1
Cu-POMs
eq 4
I
Cs2CO3, toluene, 100 o
C
N
12c
, 80%
2a
Scheme 2 Synthesis of 2-phenylquinoxalines by Cu-POMs 1
Catalyzed Coupling of 2-iodoanilines with 3-phenyl-2H-azirines.
Experimental
Materials and instruments
N
N
N
Standard condition
N
All reagents and solvents were pure analytical grade
materials purchased from commercial sources and were used
without further purification, if not stated otherwise. All melting
points are uncorrected. All starting substrates were prepared
according to the known literatures. The NMR spectra were
recorded in CDCl3 on a 400 MHz (Agilent) or 500 MHz (Bruker)
instrument with TMS as internal standard. High-resolution mass
spectra (HRMS) were obtained with a Q-TOF Premier (ESI). TLC
was carried out with 0.2 mm thick silica gel plates (GF254). The
FT-IR spectra were recorded as KBr pellets in the range of 4000-
400 cm−1 on a Nicolet 170 SXFT/IR spectrometer. The powder X-
ray diffraction pattern was collected by using a Rigaku D/max-
2550 diffractometer with CuKα radiation. The diffuse
reflectance measurements were collected using Cary 5000 UV-
Vis-NIR Spectrophotometer. Visualization was accomplished by
UV light. Column chromatography was hand packed with silica
gel (200-300 mesh).
H
1d (91%)
1h
Scheme 3 Synthesis of 2-phenylquinoxaline by 3-phenyl-1,2-
dihydroquinoxaline via the standard condition.
N
N
NH
N
I
C
HC
NH
I
R2
R2
R1
base H
I
base
NH2
I
R1
e
R1
HN
g'
f
d
b
N
g
toulene
reflux
N3
Copper-catalyzed
coupling reaction
base.HI
R2
I
R1
base H
a
R2
R2
N
N
N
Cu-POMs
O2
R1
N
R1
H
c
h
Scheme 4 Proposed mechanism of the reaction.
Typical
procedure
for
the
synthesis
of
With the optimized reaction conditions in hand, the scope of
substrates was further investigated (Table 2). Firstly, we used
the substituted 2-iodoanilines a to react with 1b. The substrates
of a with electron-donating groups (CH3, i-Pr and t-Bu) and
electron-withdrawing groups (F, Cl and CF3) could generated the
desired products in good yields (Table 2, 2c-6c). The structure
of 2c was unambiguously elucidated by X-ray crystallography
(CCDC No. 2008846). When 2-(2-chlorophenyl)-2H-azirine was
used to repeat the reaction, the yield decreased obviously
because of the steric effect (Table 2, 7c). Other substituted (1-
azidovinyl)benzenes (0.5 mmol) b were also investigated, the
products were got in moderate yields (Table 2, 7c-11c). Then we
carried out the cross-reaction experiment, the results did not
change obviously (Table 2, 12c and 13c). Finally, 2-bromoaniline
was used to repeat the reaction, only 15% of 1c was got. Further
[Cu2(O)OH(phen)2]2[W6O19].6H2O 1.
A mixture of Na2WO4·2H2O (0.18 mmol), NaVO3 (0.014
mmol), CuCl2 2H2O (0.02mmol), 1, 10’-phenanthroline (0.02
.
mmol) and H2O (18 mL) was stirred for half an hour in air. Then
the mixture transferred to a Teflon-lined autoclave (23 mL) and
kept at 160 oC for 120 h. After the autoclave was slowly cooled
to room temperature, green crystals were filtered out, washed
with distilled water and dried in a desiccator at room
temperature yield 32%. IR (KBr pellet, cm-1): 3429(s), 2922(w),
1582(s), 1412(m), 1087(w), 908(m), 866(m), 812(m), 716(m),
646(m), 476(w). Elemental analysis for C48H44Cu2N8O25W6 (1)
Calcd C, 24.40; H, 1.88; N, 4.74 (%); found: C, 24.57; H, 1.89; N,
4.81 (%).
4 | J. Name., 2012, 00, 1-3
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ARTICLE
Typical procedure for the synthesis of [Cu2(phen)4Cl]
[HW6O19]·2H2O 2.
Notes and references
1
View Article Online
For reviews see: (a) D. L. Long, E. BurDkOhoI:l1d0e.1r0a39n/dD0LD. TC0r2o6n2i5nE,
Chem. Soc. Rev., 2007, 36, 105; (b) L. Vilà-Nadal and L. Cronin,
Nat. Rev. Mater., 2017, 2, 17054; (c) A. V. Anyushin, A.
A mixture of Na2WO4·2H2O (0.18 mmol), NH4VO3 (0.014
.
mmol), CuCl2 2H2O (0.02mmol), 1, 10’-phenanthroline (0.02
mmol) and H2O (18 mL) was stirred for half an hour in air. Then
the mixture was adjusted to pH = 8.0 with dilute HCl and stirred
for half an hour in air. Finally, the resulting mixture was
transferred to a Teflon-lined autoclave (23 mL) and kept at 160
oC for 120 h. After the autoclave was slowly cooled to room
temperature, black crystals were filtered out, washed with
distilled water and dried in a desiccator at room temperature
yield 46 %. IR (KBr pellet, cm-1): 3436(s), 3016(w), 1580(s),
1476(m), 1083(w), 912(m), 872(m), 817(m), 723(m), 652(w),
485(m). Elemental analysis for C48H46Cu4N8O29W6 (2) Calcd C,
22.55; H, 1.81; N, 4.38; found: C, 22.35; H, 1.71; N, 4.23 (%).
General procedure for the synthesis of 2-phenylquinoxalines
1c-14c.
An oven-dried round flask was charged with a magnetic stir
bar, Cu-POMs 1 (0.015 mmol), 2-iodoanilines a (0.5 mmol), (1-
azidovinyl)benzenes b or 3-phenyl-2H-azirines d (1.0 mmol),
Cs2CO3 (1.0 mmol) and toluene (2.0 mL). The reaction mixture
was stirred at 100 oC for 12 h, then another amount of 0.5 mmol
b or d was added in two portions at 6h intervals via syringe. The
reaction was monitored by TLC. When 2-iodoanilines a
consumed completely, the reaction was stopped and cooled to
room temperature, then the resulting suspension was filtered
through a pad of filter paper with 20 mL of ethyl acetate for 3
times. After evaporating the solvent under reduced pressure,
the residue was purified by column chromatography on silica
gel using petrol/EtOAc (10:1, v:v) as eluent to give c.
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In conclusion, one bonded- and one discreted- Linqvist
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synthesized and routinely characterized. Importantly, these Cu-
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preparation of 2-phenylquinoxalines via the one-pot coupling
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Conflicts of interest
There are no conflicts to declare.
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This work was financially supported by the Shandong Provincial
Natural Science Foundation (ZR2019QB022 and ZR2019MB043)
and the National Natural Science Foundation of China
(21871125).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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DOI: 10.1039/D0DT02625E
Bonded- and Discreted- Linqvist Hexatungstate-Based Copper
hybrids as Heterogeneous Catalysts for One-pot Synthesis of
2-Phenylquinoxalines via 2-Haloanilines with Vinyl Azides or
3-Phenyl-2H-azirines
Guodong Shen,*a Zeyou Wanga, Xianqiang Huang,*a Shuwen Gong,a Jiangong
Zhang,a Zhenfei Tang,a Manman Sun,b Xin Lvc
aSchool of Chemistry and Chemical Engineering, Shandong Provincial Key Laboratory of
Chemical Energy Storage and Novel Cell Technology, Liaocheng University, 1 Hunan Avenue,
Liaocheng 252000, Shandong, P. R. China
bAdvanced Research Institute and Department of Chemistry, Taizhou University, 1139 Shifu
Avenue, Taizhou 318000, Zhejiang, P. R. China.
cKey Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of
Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, P. R. China.
N
N3
R1
N
R2
R2
R2
R2
NH2
I
b
1
Cu-POMs
c'
or
N
R1
Cs2CO3, toluene
100 o
N
N
C
a
d
R1
c
One bonded- and one discreted- Linqvist hexatungstate-based copper hybrids
(Cu-POMs) (1) and [Cu2(phen)4Cl]
([Cu2(O)OH(phen)2]2[W6O19].6H2O
[HW6O19]·2H2O (2) (phen= 1,10-phenanthroline) ) were controllably synthesized and
routinely characterized. Cu-POMs 1-2 consisted of identical [W6O19] unit and similar
copper-phen complexes, the two units are bonded via four Cu-O chemical bonds in
compound 1, however, compound 2 is discreted and stabilized by intermolecular
electrostatic interactions. Importantly, these Cu-POMs catalysts were first applied in
the novel reaction for preparation of 2-phenylquinoxalines via the one-pot coupling
and oxidation reactions of 2-haloanilines with vinyl azides or 3-phenyl-2H-azirines
under mild conditions, and Cu-POMs 1 showed higher catalytic performance in good
yields (79-84%). The reactions exhibit some functional group tolerance and allow for
the preparation of a number of 2-phenylquinoxalines.