Salicyldimine-based Schiff's complex of copper(II) as an efficient catalyst for the synthesis of nitrogen and oxygen heterocycles

Article abstract of DOI:10.1039/c4nj02391a

In the present paper, we have reported the synthesis of an imine-based silica-functionalized copper(II) catalyst using salicyldehyde as a ligand. Furthermore, the catalyst is characterized through various spectroscopic techniques, namely FTIR, XRD, TGA, E

Full text of DOI:10.1039/c4nj02391a

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Salicyldimine-based Schiff’s complex of copper(II)
as an efficient catalyst for the synthesis of
nitrogen and oxygen heterocycles†
Cite this:DOI: 10.1039/c4nj02391a
a
a
b
b
Manjulla Gupta, Monika Gupta,* Rajnikant and Vivek K. Gupta
In the present paper, we have reported the synthesis of an imine-based silica-functionalized copper(II) catalyst
using salicyldehyde as a ligand. Furthermore, the catalyst is characterized through various spectroscopic
techniques, namely FTIR, XRD, TGA, EDX, XPS, SEM, TEM and AAS. Herein, we have studied its applications in
the synthesis of the oxygen-containing heterocyclic 2-amino-4H-chromenes and the nitrogen-containing
heterocyclic acridinones. A single crystal X-ray analysis of 2-amino-4-(4-chlorophenyl)-6,6,8,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile has revealed that the compound crystallizes in a monoclinic
Received (in Victoria, Australia)
2
4th December 2014,
Accepted 3rd February 2015
DOI: 10.1039/c4nj02391a
www.rsc.org/njc
1
crystal system with space group P2 /n.
7
CoFe
2 4
O nanoparticles as well as DABCO. Although these proce-
1
. Introduction
dures are suitable for the synthesis of 4H-chromenes and 4H-pyrans,
The development of useful organic transformations that provide many of these approaches suffer a range of limitations, such as the
maximum structural diversity and with few synthetic steps to use of hazardous solvents, prolonged reaction times, tedious workup
unite compounds with interesting properties is of a great deal procedures, the use of expensive catalysts, lack of general applic-
1
8
of interest in modern drug discovery. The multicomponent ability and the use of specialized apparatus.
coupling reaction (MCR) is a powerful tool in the synthesis of
biologically active compounds. Their atom economics, one-pot activity, such as antibacterial, antimalarial, anticancer and
procedure, numerous structural variations, easy access to complex fungicidal properties, and DNA-binding moieties etc. They also
Acridine derivatives possess a wide spectrum of biological
2
9
10
molecules and both time- and cost-effective approach are among the have been used as pigments and dyes. The synthesis of acridine
3,4
desired features of multicomponent reactions. Aminochromenes derivatives is an important and principal task in organic chemistry
are an important class of compounds as they are present in many because as industrially produced synthetic fuels contain nitrogen
natural compounds, as a precursor of cosmetics, pigments and analogues of polycyclic aromatic hydrocarbons (PAH), the acridine
5
11
potentially biodegradable agrochemicals, and they possess phar- derivatives are becoming of increasing concern. A literature
6
macological properties. Various types of homogeneous or hetero- survey for the synthesis of acridines reveals that various catalysts
geneous catalysts have been applied in this transformation, such as such as poly-phosphoric acid, cetyltrimethylammoniumbromide
silica nanoparticles, MgO, ferric hydrogen sulphate, meglumine, (CTAB), L-proline, zeolites, N-propyl sulphamic acid and ionic
[
bmim]OH, lithium bromide, the ionic liquid choline chloride- liquids, as well as microwave irradiation and ultrasound irradia-
1
2
urea, 4-(dimethylamino)pyridine (DMAP), silica gel-supported tion catalyse this organic transformation, but they suffer from
polyphosphoric acid (PPA-SiO ), Ba(OTf) , tetrabutyl ammonium several drawbacks, such as long reaction times, harsh reaction
2
2
bromide (TBAB), amino acids, potassium phthalimide-N-oxyl conditions, expense, need for specialized apparatus, toxicity and
POPINO), nanosized ZnO, nanocrystalline MgO, NH Al(SO difficulty in product separation, which limits their use in the
2H O (Alum), hydrotalcite, tungstic acid functionalized SBA-15, synthesis of acridines.
(
1
4
4
)
2
Á
9c
2
Nowadays, the use of heterogeneous catalysts for multi-
component reactions is of keen interest to chemists due to their
recyclable and reusable nature. To the best of our knowledge, a
silica-functionalised copper(II) catalyst has not so far been used in
these organic transformations. Keeping in mind these observa-
tions, we have prepared a salicyldimine-based Schiff’s complex of
copper(II) and studied its applications in the synthesis of 2-amino-
a
b
Department of Chemistry, University of Jammu, Jammu-180 006, India.
E-mail: monika.gupta77@rediffmail.com
Post-Graduate Department of Physics & Electronics, University of Jammu,
Jammu Tawi - 180 006, India
†
Electronic supplementary information (ESI) available: XRD graph of SiO
2
–Cu(II).
1
The spectral data as well as H NMR of all the compounds are enclosed. The
original compound and spectra are available from the authors and can be
provided free of cost for reference purposes. CCDC 1038945. For ESI and crystal-
lographic data in CIF or other electronic format see DOI: 10.1039/c4nj02391a
4H-chromenes (Scheme 1) and acridinones (Scheme 2) in ethanol
(as a green reaction medium).
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was removed using Dean–Stark apparatus. The imine formed
was filtered and washed thoroughly with xylene to remove any
physical compounds present on the silica, followed by drying in
an oven for 8 h at 110 1C.
The mixture of Schiff’s base (4 g) and copper(II) acetate
(2 mmol) was stirred in acetonitrile (80 mL) at room temperature
for 24 h. The solid was filtered off and washed with acetonitrile
until the washings were colourless, and finally dried in an oven
at 100 1C. The conditioning of the catalyst was done for a total
of 6 h (2 h refluxing in each of water, ethanol and toluene). The
conditioned catalyst was dried in an oven for 6 h at 100 1C.
Scheme 1 SiO
2
–Cu(II)-catalysed one pot synthesis of 2-amino-4H- 2.3 General procedure for the synthesis of 2-amino-4H-
chromenes in ethanol.
chromenes
To a 100 mL round bottom flask, a mixture of 1,3-dicarbonyl
compound (1 mmol), malononitrile (1 mmol), aromatic aldehyde
2
(1 mmol) and SiO –Cu(II) (0.2 g) in ethanol (5 mL) was added. The
reaction mixture was stirred at 80 1C in open air. After the comple-
tion of the reaction, as determined through TLC, the reaction
mixture was cooled to room temperature and filtered off to remove
the catalyst. The residue was washed with water followed by EtOAc
2
Scheme 2 SiO –Cu(II)-catalysed one pot synthesis of acridinones in
ethanol.
(
3 Â 10 mL). The product was obtained after the removal of solvent
under reduced pressure followed by crystallization from pet
ether or EtOAc–pet ether or by passing through a column of
silica and subsequent elution with EtOAc–pet ether.
2. Experimental
2.1 Materials and instrumentation
Crystal structure determination and refinement. Three-
Silica gel was purchased from ACROSS Organics and 3-amino- dimensional X-ray intensity diffraction data for a block-shaped
propyl(trimethoxy)silane and salicyldehyde were purchased single crystal of the title compound were collected on an X’calibur
from Sigma Aldrich and were used without further purification. Computer-Controlled Single Crystal X-ray Diffractometer equipped
IR spectra of the catalyst and the synthesized compounds were with a CCD Camera. The diffractometer provides reflections of a
À1
recorded in the range of 4000–300 cm on a Shimadzu Prestige-21 large number of individual planes, and their corresponding inten-
spectrophotometer. TGA of the catalyst was obtained on a Linesis sities were recorded electronically with the help of a CCD camera.
Thermal Analyser. X-ray diffractograms were recorded over 2 h with
All non-hydrogen atoms of the molecule were located using the
a range of 10–801 on a Panalytical X’pert Pro X-ray diffraction best E-map. Atoms H30 and H40 attached to N21 were located using
spectrometer using CuKa radiation. XPS spectra of the catalyst a difference Fourier map and refined isotropically. All remaining
were recorded on a KRATOS ESCA model AXIS 165 (Resolution). hydrogen atoms were geometrically fixed and allowed to ride on
SEM was recorded on a JSM-7600F and TEM was recorded on a their parent C atoms with C–H = 0.93–0.98 Å, and U (H) = 1.5 Â
iso
Hitachi (H-7500) 120 kV with CCD camera. The atomic absorp- U (C) of the attached C atoms for methyl H atoms and 1.2 Â U
eq
eq
tion spectrometric analysis (AAS) was performed on an Avanta-M for other H atoms. Finally, the R-factor converged to 0.0472 for
1
13
atomic absorption spectrometer. H NMR and C NMR of the 2093 observed reflections. The residual electron density in the final
À3
compounds were obtained on a Bruker Avance III (400 MHz) difference Fourier map ranges from À0.271 to 0.238 e Å . Atomic
spectrometer. Mass spectra of the products were obtained on a scattering factors were taken from the International Tables for X-ray
Bruker Daltonics Esquire 3000 spectrometer.
crystallography (1992, vol. C, Tables 4.2.6.8 and 6.1.1.4). The
geometry of the molecule was calculated using the PLATON
2.2 Preparation of the silica-functionalized copper(II) catalyst
(Spek, 2009) and PARST (Nardelli, 1995) software. The crystallo-
Silica (K60, 0.060–0.200 mm) was activated by refluxing it in a graphic data are summarized in Table 1.
mixture of conc. HCl and distilled water (1 : 1) for 12 h. The
2
.4 General procedure for the synthesis of acridinones
activated silica was washed thoroughly with water and finally dried
in an oven at 110 1C for 7–8 h. To a solution of 3-aminopropyl- A mixture of aromatic aldehyde (1 mmol), dimedone (1 mmol),
trimethoxy)silane (1.79 g, 10 mmol) in dry toluene, 10 g of ammonium acetate (1 mmol) and SiO –Cu(II) (0.1 g) in ethanol
(
2
activated silica was added and refluxed for 24 h. The 3-amino- (5 mL) was stirred in a 100 mL round bottom flask at 80 1C for
propylsilica (AMPS) was filtered off, washed with xylene and dried an appropriate time. The progress of the reaction was deter-
in an oven at 110 1C for 7 h. The 3-aminopropylsilica (AMPS, 5 g) mined through TLC. On completion (monitored by TLC), the
was added to a solution of salicyldehyde (1 mL) in sodium-dried reaction mixture was cooled to room temperature and filtered. The
toluene (250 mL) in a round bottom flask. The reaction mixture residue was washed with water followed by EtOAc (3 Â 10 mL).
was refluxed at 110 1C and water formed during the reaction The product was obtained after the removal of solvent under
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Table 1 Crystal and experimental data
reduced pressure followed by crystallization from pet ether or
EtOAc–pet ether or by passing through a column of silica and
subsequent elution with EtOAc–pet ether.
Crystal description
Crystal size
White, block
0.30 Â 0.20 Â 0.20 mm
‘C18 17ClN
328.79
Empirical formula
Formula weight
H
2 2
O ’
Radiation, wavelength
Unit cell dimensions
MoKa, 0.71073 Å
a = 9.3992(8) Å, b = 16.8270(11) Å,
c = 10.9101(9) Å, b = 112.042(10)1
Monoclinic
3
. Results and discussion
Crystal system
Space group
3.1 Characterisation of SiO –Cu(II)
2
P2
1599.4(2) Å
1.365 Mg m
4
1
/n
3
2
SiO –Cu(II) was prepared according to the outlined scheme by the
chemical modification of silica with 3-aminopropylsilane followed by
linking with a suitable ligand i.e. salicyldehyde which provides
binding sites for metal complexation. Finally, SiO –Cu(II) was pre-
pared by the coordination of copper(II) acetate with the salicyldimine-
based Schiff’s complex to form a salen complex. The general
2
preparation procedure for SiO –Cu(II) is outlined in Scheme 3.
Characterization of the catalyst was carried out by Fourier
transform infrared spectroscopy (FTIR), thermogravimetric analysis
Unit cell volume
Density (calculated)
No. of molecules per unit cell, Z
Temperature
Absorption coefficient
F(000)
Scan mode
y range for entire data collection
Range of indices
À3
293(2) K
0.250 mm
À1
2
688
o
3.81 to 26.001
À11 r h r 11, À20 r k r 20,
À13 r l r 13
6916/3128
2093
0.0315
0.0505
Direct methods
Full-matrix least-squares on F
216
Reflections collected/unique
Reflections observed (I 4 2s(I))
(TGA), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy
R
R
int
sigma
(XPS), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), atomic absorption spectroscopic analysis (AAS)
and EDX study. The FTIR of 3-aminopropylsilica displays CH
stretching bands at 2932 and 2863 cm and aliphatic deformation
bands at 1449 cm . The FTIR of chemically modified silica (imine)
Structure determination
Refinement
2
No. of parameters refined
Final R
2
À1
0.0472
0.1209
2
wR(F )
À1
2
2
2
Weight
o
1/[s (F ) + (0.0508P) + 0.1663P]
2 2
À1
shows a sharp peak at 1632 cm due to the CQN bond, which on
where P = [F
o c
+ 2F ]/3
Goodness-of-fit
1.028
0.000
complexation with copper disappears and appear as a band at
(
D/s)max
À1
À3
1625 cm . The lowering in frequency of the CQN peak is indicative
Final residual electron density
Measurement
À0.271 o Dr o 0.238 e Å
14
of the formation of the metal–ligand bond (Fig. 1).
X’calibur system
[
Oxford Diffraction, 2013]
The TGA curve showed an initial weight loss of 1.75% (attributed
to the loss of residual solvent and water which may be trapped on
the surface of the catalyst) at 100 1C followed by the loss of approx.
4% at 200 1C and then approx. 10.5% at 250 1C. Thus, the
catalyst is stable up to 225 1C and hence it is safe to carry out
1
3
Software for structure solution
Software for refinement
Software for molecular plotting
SHELXS97 (Sheldrick, 2008)
SHELXL97 (Sheldrick, 2008)
ORTEP-3 (Farrugia, 2012)
1
3
1
5
18
PLATON (Spek, 2009)1
8
Software for geometrical
calculations
PLATON (Spek, 2009)
17
PARST (Nardelli, 1995)
2
the reaction at 80 1C using SiO –Cu(II) (Fig. 2).
2
Scheme 3 Synthesis of silica-functionalized copper(II) [SiO –Cu(II)].
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2
Fig. 1 FTIR spectrum for SiO –Cu(II).
The amount of copper loaded onto the silica surface
The oxidation state of copper in SiO
2
–Cu(II) was determined
was determined by AAS analysis. The catalyst was stirred from the measurements of binding energies using XPS spectra.
2
+
in dilute HNO
3
solution and then subjected to AAS The XPS spectra of the Cu 2p3/2 photoelectrons confirms Cu
analysis. SiO
catalyst.
2
–Cu(II) contained 0.0144 g of copper per gram of as the dominant oxidation state in SiO
peak at 932.54 eV) (Fig. 3).
2
–Cu(II) (due to a strong
2
Fig. 2 TGA curve for SiO –Cu(II).
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2
Fig. 3 XPS spectra for SiO –Cu(II).
2
Fig. 4 SEM images of SiO –Cu(II).
Scanning electron microscopy and transmission electron
microscopy are useful techniques for imaging the surface
topography and internal structure of the catalyst. SEM images
of SiO –Cu(II) reveal the porous and homogeneous structure of
2
the catalyst and TEM images show that the copper(II) particles
are uniformly distributed on the surface of the silica with a
mean diameter of 8 nm (Fig. 4 and 5).
The EDX spectrum reveals the presence of C, N, O, Si and Cu
2
in SiO –Cu(II), which is consistent with the outlined preparation
scheme of the catalyst (Fig. 6).
2
Fig. 5 TEM images of SiO –Cu(II).
3
.2 Catalyst testing for the synthesis of 2-amino-4H-
chromenes
In order to optimize the reaction conditions for the synthesis of Solvents of different polarities were tested using the model
-amino-4H-chromenes, we have selected dimedone, 4-chloro- substrates and SiO –Cu(II) as the catalyst (Table 2). From the
the catalyst is sufficient to carry out the reaction to completion.
2
2
benzaldehye and malononitrile as model substrates. First, we table, it can be concluded that ethanol serves as the best solvent
carried out the reaction between the model substrates using for this organic transformation with respect to polarity, clean
SiO –Cu(II) as the catalyst at different temperatures (25 1C, work-up procedure and green nature.
2
40 1C, 60 1C, 80 1C and 100 1C). The results are presented in
Using these optimized conditions, the reaction using different
Table 2. It has been observed that the best results are obtained substrates containing electron donating as well as electron
at 80 1C and no change in the percent yield of product is releasing groups was investigated. It was found that the reac-
observed beyond 80 1C. The reaction using different molar ratios tions for all of the different substrates proceeded smoothly to
2
of SiO –Cu(II) was performed and this showed that 2.5 mol% of give 2-amino-4H-chromenes (Table 3). To determine the role of
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Table 3 SiO
ethanol at 80 1C
2
–Cu(II)-catalysed synthesis of 2-amino-4H-chromenes in
a
b
1,3-Dicarbonyl
Time Yield
R
compound
(min) (%) M.p./lit. m.p.
1
9
1
2
3
4
1
92
235/232–234
20
19
19
70 94
75 92
209–210/210–215
201–202/198–200
205–207/206–208
2
Fig. 6 EDX spectrum of SiO –Cu(II).
120 88
SiO
H-chromenes, the reaction using the model substrates was
also done with silica, imine, Cu(OAc) and without the catalyst
2
–Cu(II) as a catalyst for catalyzing the synthesis of 2-amino-
4
2
1
9
9
5
80 91
200/198–200
2
Table 2 Effect of solvent, temperature and catalyst on the SiO –Cu(II)-
catalysed synthesis of 2-amino-4H-chromenes and synthesis of acridinones
1
6
7
8
9
70 92
50 90
45 94
55 90
216/216–218
224/223–226
214/212–214
Synthesis of 2-amino-
a
b
4H-chromenes
Synthesis of acridinones
f
f
Time (h) Yield (%) Time (min)
Yield (%)
c
19
19
Solvent
Acetonitrile
Toluene
Ethanol
3.5
4
1
2.5
2
1.5
75
60
94
60
45
85
30
45
15
60
50
25
85
60
95
55
68
87
Water
Dichloromethane
Methanol
d
Temperature
25 1C
40 1C
60 1C
80 1C
100 1C
5
3.5
3
1
1
60
78
82
94
94
60
40
30
15
15
40
60
75
95
95
21
290–291/292–293
e
Catalyst
No catalyst
SiO
19
4.5
4.5
2.5
2
50
55
70
20
94
80
80
55
30
12
65
65
75
78
95
10
60 94
166/165–168
2
Imine
Cu(OAc)
2
2
SiO –Cu(II)
1
a
Dimedone (0.140 g, 1 mmol), 4-chlorobenzaldehye (0.140 g, 1 mmol)
19
11
75 89
178–179/176–177
b
and malononitrile (0.066 g, 1 mmol). Dimedone (0.280 g, 2 mmol),
4
-nitrobenzaldehye (0.151 g, 1 mmol) and NH
4
OAc (0.077 g, 1 mmol).
Optimised reaction conditions for the synthesis of 2-amino-4H-
chromenes: SiO –Cu(II) (0.2 g) and solvent (5 mL) at refluxing tempera-
ture; for acridinones: SiO –Cu(II) (0.1 g) and solvent (5 mL) at refluxing
temperature. Optimised reaction conditions for the synthesis of 2-amino-
H-chromenes: SiO –Cu(II) (0.2 g) and ethanol (5 mL); for acridinones:
SiO –Cu(II) (0.1 g) and ethanol (5 mL). Optimised reaction conditions
c
2
2
1
9
d
12
75 85
65 88
212–215/213–214
235–256/234–238
4
2
e
2
for the synthesis of 2-amino-4H-chromenes: catalyst (0.2 g), ethanol (5 mL)
f
at 80 1C; for acridinones: catalyst (0.1 g), ethanol (5 mL) at 80 1C. Yields
7
h
13
based on either product obtained from crystallization or by separation
through column chromatography.
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Table 3 (continued)
b
1,3-Dicarbonyl
Time Yield
R
compound
(min) (%) M.p./lit. m.p.
2
0
14
15
16
45 92
120 92
120 85
228–229/230
22
189/190–192
23
179–181/178–181
Fig. 7 ORTEP view of the molecule with displacement ellipsoids drawn at
4
0%. H atoms are shown as small spheres of arbitrary radii.
2
3
1
1
7
8
100 89
120 85
141/141–143
Crystal structure of 2-amino-4-(4-chlorophenyl)-6,6,8,8-tetra-
hydro-7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile. An ORTEP
23
15
174–175/174–177
view of the compound with atomic labeling is shown in Fig. 7.
16
The geometry of the molecule was calculated using the WinGX,
17
18
PARST and PLATON software. Selected bond lengths and bond
23
1
9
120 80
182/180–181
Table 4 Selected bond lengths [Å] and bond angles [1]
Cl1–C13
O1–C2
O1–C5A
C3–C2
C3–C16
C3–C4
O9–C9
C2–N20
N20–H30
N20–H40
C4–C5
C4–C10
C4–H4
1.741(2)
1.375(2)
1.379(2)
1.347(3)
1.414(3)
1.510(3)
1.226(3)
1.339(3)
0.87(2)
C13–C12
C13–C14
C7–C17
C7–C18
C7–C8
C9–C8
C16–N19
C12–C11
C12–H12
C15–C14
C15–H15
C14–H14
1.365(3)
1.372(3)
1.523(3)
1.526(3)
1.531(3)
1.505(3)
1.148(3)
1.391(3)
0.9300
2
3
2
2
2
0
1
100 86
110 88
170–171/172–173
189–191/191–192
2
0.83(3)
1.381(3)
0.9300
0.9300
1.512(3)
1.541(3)
0.9800
C11–H11
0.9300
22
2
2
3
120 88
100 85
176–177/175–176
C5–C5A
C5–C9
C5A–C6
C10–C11
C10–C15
C6–C7
C6–H6A
C6–H6B
C2–O1–C5A
C2–C3–C16
C2–C3–C4
C16–C3–C4
N20–C2–C3
N20–C2–O1
C3–C2–O1
C2–N20–H30
C2–N20–H40
H30–N20–H40
C3–C4–C5
C3–C4–C10
C5–C4–C10
C3–C4–H4
C5–C4–H4
C10–C4–H4
C5A–C5–C9
C5A–C5–C4
1.332(3)
1.467(3)
1.481(3)
1.377(3)
1.388(3)
1.528(3)
0.9700
C8–H8A
C8–H8B
0.9700
0.9700
0.9600
0.9600
0.9600
0.9600
0.9600
0.9600
109.6(2)
110.48(19)
107.10(18)
120.6(2)
121.28(19)
118.1(2)
178.6(3)
119.3(2)
120.3
120.3
121.4(2)
119.3
119.3
119.7(2)
120.1
C17–H17A
C17–H17B
C17–H17C
C18–H18A
C18–H18B
C18–H18C
C17–C7–C8
C18–C7–C8
C6–C7–C8
O9–C9–C5
O9–C9–C8
C5–C9–C8
N19–C16–C3
C13–C12–C11
C13–C12–H12
C11–C12–H12
C14–C15–C10
C14–C15–H15
C10–C15–H15
C13–C14–C15
C13–C14–H14
C15–C14–H14
C10–C11–C12
C10–C11–H11
22
2
2
187/187–188
0.9700
117.69(16)
118.71(19)
122.18(18)
119.07(19)
128.9(2)
109.55(19)
121.55(17)
121.6(16)
118.3(17)
116(2)
107.42(16)
113.90(16)
111.49(16)
107.9
1
1
75–177/177.5–
78.5
4
5
100 82
90 70
22
22
2
202/203–204
a
Optimised reaction conditions: dimedone (0.140 g, 1 mmol), 4-chloro-
2
benzaldehye (0.140 g, 1 mmol), malononitrile (0.066 g, 1 mmol), SiO –
b
Cu(II) (0.2 g) and ethanol (5 mL) at refluxing temperature. Yields based
on either product obtained from crystallization or by separation through
column chromatography.
107.9
107.9
117.25(18)
121.82(17)
under the same conditions as applied for SiO
inferred that the best results with respect to time and yield of the
product was obtained using SiO –Cu(II) as the catalyst (Table 2).
2
–Cu(II). It was clearly
120.1
121.7(2)
119.1
2
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Table 4 (continued)
Table 5 SiO
2
–Cu(II)-catalysed synthesis of acridinones in ethanol at
a
8
0 1C
C9–C5–C4
120.74(18)
122.39(18)
126.71(18)
110.90(17)
117.4(2)
121.63(19)
120.96(18)
112.42(18)
109.1
109.1
109.1
109.1
107.9
120.4(2)
119.73(19)
119.82(19)
109.7(2)
111.11(19)
108.81(19)
C12–C11–H11
C9–C8–C7
C9–C8–H8A
C7–C8–H8A
C9–C8–H8B
119.1
114.62(18)
108.6
108.6
108.6
108.6
107.6
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
b
C5–C5A–O1
C5–C5A–C6
O1–C5A–C6
C11–C10–C15
C11–C10–C4
C15–C10–C4
C5A–C6–C7
C5A–C6–H6A
C7–C6–H6A
C5A–C6–H6B
C7–C6–H6B
H6A–C6–H6B
C12–C13–C14
C12–C13–Cl1
C14–C13–Cl1
C17–C7–C18
C17–C7–C6
C18–C7–C6
Aldehyde
Time (min)
8
Yield (%)
92
M.p./lit. m.p.
24
1
2
275/277–278
C7–C8–H8B
H8A–C8–H8B
C7–C17–H17A
C7–C17–H17B
H17A–C17–H17B
C7–C17–H17C
H17A–C17–H17C
H17B–C17–H17C
C7–C18–H18A
C7–C18–H18B
H18A–C18–H18B
C7–C18–H18C
H18A–C18–H18C
H18B–C18–H18C
24
10
12
20
94
94
80
4300/4300
24
3
4
269–271/272–273
24
4300/4300
angles are given in Table 4. The packing view of the molecules in
the unit cell viewed down the a-axis is shown in Fig. 8.
2
5
5
6
7
12
15
13
92
88
95
295/292–294
3.3 Catalyst testing for the synthesis of acridinones
The reaction conditions for the synthesis of acridinones were
optimized using dimedone, 4-nitrobenzaldehyde and ammonium
acetate as model substrates. The reaction using the model
substrates and SiO –Cu(II) was carried out to confirm the choice
2
of solvent and range of temperature. All the results have been
presented in Table 2.
24
265/265–267
24
294–295/294–296
The reaction with dimedone, ammonium acetate and different
aldehydes using SiO –Cu(II) as the catalyst were carried out and all
2
the reactions proceeded very efficiently to give the desired products
9
c
8
9
14
12
91
90
213/215–217
in good yields (Table 5). To establish the catalytic role of SiO
in the synthesis of acridinones, the reaction using the model
substrates was carried out with silica, imine, Cu(OAc) and without
the catalyst under the same conditions as applied for SiO –Cu(II) and
it was found that SiO –Cu(II) catalyses the reaction very efficiently
and afforded the products in good to excellent yields (Table 2).
2
–Cu(II)
2
26
4300/4300
2
2
25
10
12
92
310/308–313
4
. Recyclability of the silica-
functionalized copper(II) catalyst
9
c
For quantifying the heterogeneity and recyclability of SiO –Cu(II), 11
a series of six consecutive runs was carried out for entry 8,
12
10
95
93
287/283–285
288/287–289
2
24
12
a
Optimised reaction conditions: dimedone (0.280 g, 2 mmol), 4-nitro-
OAc (0.077 g, 1 mmol), SiO –Cu(II)
0.1 g) in ethanol (5 mL) at 80 1C. Yields based on either product obtained
benzaldehye (0.151 g, 1 mmol), NH
(
4
2
b
from crystallization or by separation through column chromatography.
Table 3 and entry 11, Table 5 under the respective optimised
conditions. It was observed that there is almost no change in the
activity of the catalyst for up to six uses. The results are presented
Fig. 8 The packing arrangement of the molecules viewed down the a-axis. in the form of a graph (Fig. 9).
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4
5
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Fig. 9 Recyclability of SiO –Cu(II) for the synthesis of 2-amino-4H-
chromenes and the synthesis of acridinones.
4
6, 1145; ( f ) W. B. Sun, P. Zhang, J. Fan, S. H. Chen and Z. H.
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. Conclusion
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In conclusion, we have reportedthe synthesis of a silica-
functionalized copper(II) catalyst from easily available starting
materials using a simple methodology and with thorough
characterization. The significance of this work lies in the fact
that copper(II) acetate, which is an active catalyst, coordinates
to the support with a homogenous distribution, which makes it
recyclable and more active than its native form. The catalyst
can be easily reproduced by simple work-up procedures and
can be reused in consecutive reactions. The application of the
catalyst has been studied for multicomponent reactions in the
synthesis of 2-amino-4H-chromenes and acridinones. Moreover,
aminochromenes and acridinones are important compounds in
agrochemical and medicinal fields, which makes this research
more applicable and interesting.
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(
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4
2
Acknowledgements
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for TEM and XRD and also to the Head, SAIF, IIT Bombay for
recording SEM images and also EDX measurements. We are also
thankful to the Head, SAIF, IIT Roorkee for thermogravimetric
analysis. We extend our sincere thanks to UGC, New Delhi
for financial support to purchase FTIR and awarding Major
Research Project (F 41-281/2012 (SR). One of the authors
3
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(
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