Nano-Co-[4-chlorophenyl-salicylaldimine-pyranopyrimidine dione]Cl2 as a new Schiff base complex and catalyst for the one-pot synthesis of some 4H-pyrimido[2,1-b]benzazoles

Article abstract of DOI:10.1007/s11164-020-04279-5

Abstract: Nano-Co-[4-clolorophenyl-salsylaldimine-pyranopyrimidine dione]Cl₂ {Nano-[Co-4CSP]Cl₂} was prepared and fully characterized as a new nano-Schiff base complex. Nano-[Co-4CSP]Cl₂ was successfully used as an efficie

Full text of DOI:10.1007/s11164-020-04279-5

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04279-5
Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑
pyranopyrimidine dione]Cl2 as a new Schif base
complex and catalyst for the one‑pot synthesis of some
4H‑pyrimido[2,1‑b]benzazoles
Ahmad Reza Moosavi‑Zare1 · Hamid Goudarziafshar1 · Parva Fashi1
Received: 8 May 2020 / Accepted: 18 September 2020
© Springer Nature B.V. 2020
Abstract
Nano-Co-[4-clolorophenyl-salsylaldimine-pyranopyrimidine dione]Cl2 {Nano-[Co-
4CSP]Cl2} was prepared and fully characterized as a new nano-Schif base complex.
Nano-[Co-4CSP]Cl2 was successfully used as an efcient catalyst for the synthesis
of some 4H-pyrimido[2,1-b]benzazoles such as 4H-pyrimido[2,1-b]benzothiazoles
and 4H-pyrimido[2,1-b]benzimidazoles.
Keywords Nano-[Co-4CSP]Cl2 · Pyrano[2,3-d]pyrimidine dione ·
4H-pyrimido[2,1-b]benzazole · Schif base
Introduction
4H-pyrimido[2,1-b]benzazole derivatives such as 4H-pyrimido[2,1-b]benzothia-
zoles and 4H-pyrimido[2,1-b]benzimidazoles are important biological fused hetero-
cyclic compounds which are prepared by the multi-component Biginelli-type reac-
tion [1]. In this kind reaction, Biginelli-like compounds such as 4H-pyrimido[2,1-b]
benzazoles were prepared by the condensation reaction of ethyl acetoacetate with
various aldehyde and 2-aminobenzothiazole or 2-aminobenzimidazole, like thio-
urea or urea in Biginelli reaction, to prepare 4H-pyrimido[2,1-b]benzothiazoles
and 4H-pyrimido[2,1-b]benzimidazoles, respectively [1]. This condensation as a
multi-component reaction through the direct synthesis of target product, without the
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04279-5) contains supplementary material, which is available to authorized users.
*
*
Ahmad Reza Moosavi-Zare
moosavizare@yahoo.com
Hamid Goudarziafshar
hamid_gafshar@yahoo.com
1
Sayyed Jamaleddin Asadabadi University, Asadabad 6541861841, Islamic Republic of Iran
Vol.:(0123456789)
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A. R. Moosavi-Zare et al.
preparation of side products, has some important advantages such as increasing of
the yield and decreasing of reaction time, waste of energy, materials and solvents
[2–6].
4H-pyrimido[2,1-b]benzazoles have the ability to prepare the various drugs
and applied as anti-tumor [7], anti-infammatory [8], anti-bacterial [9] and anti-
fungal compounds [10]. Various methods have been reported for the preparation of
4H-pyrimido[2,1-b]benzazole derivatives in the presence of diferent catalysts such
as Fe3O4@nano-cellulose/TiCl [11], TMGT [1], iron fuoride [12], nano-Fe3O4@
SiO2–TiCl3 [6], chitosan [13], nano-TiCl2/cellulose [14], H3PO4–Al2O3 [15] and
acetic acid [16]. But, according to the importance of these compounds, new and use-
ful methods are still needed to prepare these signifcant compounds.
Pyrano[2,3-d]pyrimidine diones have important biological properties such as
antitumor [17], antibacterial [18], antihypertensive [19], bronchodilators [20] and
antiallergic [21, 22]. Because of the signifcant biological properties of these com-
pounds, in continuous to our previous researches on the synthesis of new Schif
base complexes based on pyranopyrazole derivatives as amine [21, 23–28], we have
synthesized a derivative of pyrano[2,3-d]pyrimidine diones, namely 7-amino-5-(4-
chlorophenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d]pyrimidine-6-carboni-
trile and reacted with salicylaldehyde and Co(Cl)2·6H2O to give nano-Co-[4-clolo-
rophenyl-salsylaldimine-pyranopyrimidinedione]Cl2 {Nano-[Co-4CSP]Cl2} as a
new Schif base complex (Fig. 1) and successfully applied as a catalyst for the syn-
thesis of some 4H-pyrimido[2,1-b]benzazole derivatives (Scheme 1).
Experimental
Procedure for the synthesis of [4CSP]
A mixture of 7-amino-5-(4-chlorophenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano
[2,3-d]pyrimidine-6-carbonitrile as an amine (1 mmol), salicylaldehyde (1.2 mmol) and
Fig. 1 The proposed structure of
nano-[Co-4CSP]Cl2
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Scheme 1 The preparation of 4H-pyrimido[2,1-b]benzazoles using nano-[Co-4CSP]Cl2
acetic acid glacial as a catalyst (13 mol%) was added in a 25-mL round-bottomed fask
connected to a refux condenser and stirred at 110 °C for 48 h. After completion of the
reaction, as monitored by TLC, the reaction mixture was washed with ethylacetate and
hexane (7/3) (10 mL) for three times to purify (7E)-7-(2-hydroxybenzylideneamino)-
5-(4-chlorophenyl)-2,3,4,5-tetrahydro-2,4-dioxo-1H pyrano[2,3-d]pyrimidine-6-car-
bonitrile (4CSP) as a Schif base from excess salicylaldehyde.
Spectral data for [4CSP]
Yellow Solid; M.p.: 233–235°°C; M.p.: 235–237 °C; Yield: 80%; IR (KBr, cm−1):
1
3155, 3018, 2856, 1715, 1659, 1618, 756,550; H-NMR (400 MHz, DMSO-d6): δ
(ppm) 5.43 (s, 1H), 7.069, (t, J=7.60 Hz, 1H), 7.16–7.22 (m, 2H), 7.31–7.38 (m, 3H),
7.61 (dd, J=6.40, 1.2 Hz,1H), 7.69 (dd, J=6.00, 1.60 Hz, 1H), 10.08 (s,1H), 11.09
(d, J=6.80 Hz, 1H), 11.37 (s,1H), 12.06 (s, 1H); 13CNMR (100 MHz, DMSO-d6): δ
(ppm) 31.3, 86.7, 116.1, 119.8, 121.2, 123.7, 125.4, 128.3, 129.3, 131.9, 133.6, 136.3,
148.2, 149.6, 154.8, 157.6, 163.1, 191.3, 197.1.
Procedure for the synthesis
of nano‑Co‑[4‑clolorophenyl‑salsylaldimine‑pyranopyrimidine dione]Cl2
{Nano‑[Co‑4CSP]Cl2}
7-Amino-5-(4-chlorophenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d] pyrimi-
dine-6-carbonitrile as an amine (1 mmol) and Co(Cl)2·6H2O (1 mmol) were added to a
25-mL round-bottomed fask containing salicylaldehyde (1.2 mmol) which connected
to a refux condenser and stirred at 100 °C for 72 h. After this time, the reaction mix-
ture was washed by ethylacetate and hexane (7/3) (10 mL) for three times to purify
nano-Co-[4-clolorophenyl-salsylaldimine-pyranopyrimidine dione]Cl2 {Nano-[Co-
4CSP]Cl2} in 80% of yield (Scheme 2).
General procedure for the synthesis of 4H‑pyrimido[2,1‑b]benzazole derivatives
A mixture of aromatic aldehyde, (1 mmol), ethyl acetoacetate (1 mmol, 0.13 g),
2-aminobenzothiazole (1 mmol, 0.15 g) or 2-aminobenzimidazole (1 mmol,
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A. R. Moosavi-Zare et al.
Scheme 2 The preparation of nano-[Co-4CSP]Cl2
0.133 g) and nano-[Co-4CSP]Cl2 (0.164 g, 3 mol%) as a catalyst was added to
25-mL round-bottomed fask connected to a refux condenser and stirred at 70 °C
under solvent-free conditions. After the completion of the reaction, as monitored
by TLC, the reaction mixture was extracted with warm ethanol (10 mL) and sep-
arated from the catalyst by simple fltration. Finally, the desired product was
purifed by the recrystallization in ethanol (90%). Note: Compound 1 was puri-
fed by plate chromatography. The spectral data of some prepared compounds
are given in supporting information.
Selected spectral data of compounds
Ethyl‑2‑methyl‑4‑(phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzothiazole‑3‑carboxylate (1)
Yellow Solid; M.p.: 179–181 °C; Yield: 87%; IR (KBr, cm−1): 3043, 2968,
1
1670, 1589, 1462, 1244, 744, 543; H-NMR: (250 MHz, DMSO-d6): δ (ppm)
1.17 (s, 3H), 2.30 (s, 3H), 4.02 (s, 2H), 5.74 (s, 1H), 7.16–7.28 (m, 4H), 7.50 (d,
J = 6.75 Hz, 1H), 7.60 (d, J = 6.75 Hz, 1H), 7.71 (d, J = 6.75 Hz, 1H); 13CNMR:
(62.5 MHz, DMSO-d6): δ (ppm) 14.5, 23.6, 57.0, 59.9, 103.1, 112.7, 123.2,
124.4, 127.2, 127.4, 128.7, 129.0, 142.0, 154.5.
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Ethyl‑2‑methyl‑4‑(2,4 dichloro‑phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzothia‑
zole‑3‑carboxylate (2)
Yellow Solid; M.p.: 114–117 °C; Yield: 80%; IR (KBr, cm−1): 3067, 2981,
1
1689, 1584, 1073, 1016, 746, 579; H-NMR: (250 MHz, DMSO-d6): δ (ppm)
1.08 (s, 3H), 3.30 (s, 3H), 4.01 (s, 2H), 6.77 (s, 1H), 7.16–7.28 (m, 4H), 7.50 (d,
J = 6.75 Hz, 1H), 7.60 (d, J = 6.75 Hz, 1H), 7.71 (d, J = 6.75 Hz, 1H); 13CNMR:
(62.5 MHz, DMSO-d6): δ (ppm) 14.5, 23.8, 56,0, 59.9, 101.8, 111.8, 122.9,
123.4, 124.7, 127.3, 129.3, 130.0, 131.1, 132.7, 137.9, 141.6, 155.3, 163.1, 165.6.
Ethyl‑2‑methyl‑4‑(3‑hydroxy‑phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzothiazole‑3‑car‑
boxylate (3)
White Solid; M.p.: 260–261 °C; Yield: 85%; IR (KBr, cm−1): 3048, 2980, 2864,
1
2933, 1686, 1510, 1100,754, 552; H-NMR: (250 MHz, DMSO-d6): δ (ppm)
1.18 (s, 3H), 2.28 (s, 3H), 4.04 (s, 2H), 6.34 (s, 1H)), 6.57 (d, J = 6.75 Hz, 1H),
6.77–6.84 (m, 2H), 7.02 (d, J = 6.75 Hz, 1H) 7.16 (d, J = 6.00 Hz 1H), 7.31 (s,
3H), 7.70 (d, J = 7.00 Hz, 1H), 9.40 (s,1H); 13CNMR: (62.5 MHz, DMSO-d6):
δ (ppm) 14.5, 23.6, 56.9, 59.9, 103.2, 112.7, 114.0, 115.7, 118.1, 123.2, 124.4,
127.2, 129.8, 138.0, 143.2, 154.2, 158.0, 163.0, 166.0.
Ethyl‑2‑methyl‑4‑(2,4‑dichloro‑phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzoimida‑
zole‑3‑carboxylate (12)
White Solid; M.p.: 280 °C; Yield: 72%; IR (KBr, cm−1): 3235, 2931, 1698, 1656,
1618, 729, 465; 1H-NMR (500 MHz, DMSO-d6): δ (ppm) 1.13 (t, J=6.85 Hz, 3H),
2.53(s, 3H), 4.03 (s, 2H), 6.76 (s, 1H), 7.00 (d, J=7.90 Hz, 1H), 7.09 (t, J=7.30 Hz,
2H), 7.18 (d, J=7.80 Hz, 1H), 7.40 (d, J=7.50 Hz, 1H), 7.51–7.58 (m, 1H), 11.04
(s, 1H); 13CNMR (125 MHz, DMSO-d6): δ (ppm) 14.0, 18.7, 53.2, 59.3, 109.1,
117.0, 120.4, 122.0, 128.0, 128.9, 131.5, 132.6, 133.2, 142.1, 145.1, 147.6, 164.8.
Ethyl‑2‑methyl‑4‑(3‑nitro‑phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzoimidazole‑3‑car‑
boxylate (15)
White Solid; M.p.: 261–262 °C; Yield: 68%; IR (KBr, cm−1): 3232, 2978, 1706,
1659, 1617, 1528, 1236, 737; 477; 1H-NMR (500 MHz, DMSO-d6): δ (ppm) 1.18
(t,, J = 7.00 Hz,3H), 2.52 (s, 3H), 4.04 (q, J = 5.50 Hz, 2H), 6.68 (s, 1H), 6.97
(t, J = 7.65 Hz, 1H), 7.07(t, J = 7.35 Hz, 1H), 7.33 (d, J = 7.85 Hz, 1H), 7.38 (d,
J = 7.90 Hz, 1H), 7.59 (t, J = 7.80 Hz, 1H), 7.77 (d, J = 7.40 Hz, 1H), 8.08 (d,
J = 8.15 Hz, 1H), 8.30(s, 1H), 10.99 (s, NH); 13CNMR (125 MHz, DMSO-d6):
1 3

A. R. Moosavi-Zare et al.
δ (ppm) 13.9, 18.7, 55.1, 59.8, 97.0, 109.8, 116.9, 120.4, 121.8, 122.0, 122.8,
130.2, 131.3, 133.5, 142.2, 144.2, 145.3, 147.5, 147.6, 164.9.
Ethyl‑2‑methyl‑4‑(4‑chloro‑phenyl)‑4H‑pyrimido[2,1‑b] [1,3] benzoimidazole‑3‑car‑
boxylate (16)
White Solid; M.p.: 290–292 °C; Yield: 85%; IR (KBr, cm−1): 3235, 3103, 2928,
1695, 1656, 1617, 701, 517; 1H-NMR (250 MHz, DMSO-d6): δ (ppm) 1.11 (s, 3H),
2.44 (s, 3H), 4.00 (s, 2H), 6.41 (s, 1H), 6.57 (d, J=6.75 Hz, 1H), 6.89–7.34 (m, 9H),
10.88 (s,1H); 13CNMR (125 MHz, DMSO-d6): δ (ppm) 14.4, 19.0, 55.7, 59.8, 97.9,
110.2, 117.2, 120.6, 122.3, 128.8, 129.4, 131.8, 132.7, 141.4, 142.7, 145.8, 147.2,
165.5.
Results and discussion
7-Amino-5-(4-chlorophenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d]pyrimi-
dine-6-carbonitrile as a pyrano[2,3-d]pyrimidine dione compound was synthesized
by the reaction of barbituric acid, 4-chlorobenzaldehyde, malononitrile using isoni-
cotinic acid as a catalyst. Then, the prepared compound as an amine was reacted
with salicylaldehyde and Co(Cl)2·6H2O at 100 °C for 72 h to give nano-Co-[4-clolo-
rophenyl-salsylaldimine-pyranopyrimidine
dione]Cl2
{Nano-[Co-4CSP]Cl2}
(Scheme 2). The structure of nano-[Co-4CSMP]Cl2 was studied by various analyses
such as FT-IR, TGA, DTG, SEM, BET and mass to confrm the chemical structure,
available chemical elements, thermal stability, morphology, size of particles and
active surface area of the synthesized nano-Schif base complex.
To investigate the structure of Schif base compound (4CSP), at frst, by the reac-
tion of 7-amino-5-(4-chlorophenyl)-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d]
pyrimidine-6-carbonitrile as an amine with salicylaldehyde in the presence of acetic
acid as a mild catalyst, (7E)-7-(2-hydroxybenzylideneamino)-5-(4-chlorophenyl)-
2,3,4,5-tetrahydro-2,4-dioxo-1H pyrano[2,3-d]pyrimidine-6-carbonitrile (4CSP) as
a Schif base was prepared individually at 110 °C after 48 h (Scheme 3). To show
and confrm the preparation of Schif base ligand, the structure of it was studied by
Scheme 3 The preparation of [4CSP]
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
1
FT-IR, H-NMR and 13CNMR spectra. The related spectra are given in supporting
information.
In another procedure, to direct preparation of the Schif base complex, by the
reaction of the prepared pyrano[2,3-d]pyrimidine dione derivative with salicylalde-
hyde and CoCl2·6H2O, nano-[Co-4CSP]Cl2 prepared in one step, the mass spectra of
the complex, to show the preparation of nano-[Co-4CSP]Cl2, were recorded and the
exact mass of it was appeared at 549 m/z.
FT-IR spectrum of nano-[Co-4CSP]Cl2 was studied, and a broad peak appeared
at 3250–3500 cm−1 which could be related to O–H stretching and another peak at
1656 cm−1 could be corresponded to stretching mode of C=N bond in the structure
of nano-[Co-4CSP]Cl2 which coordinated with Cobalt (II) chloride (Fig. 2). The
peak at 1710 cm−1 is related to stretching of C=O group in the structure of nano-
[Co-4CSP]Cl2. The peak related to cyano group (CN) is displayed in the structure
of ligand (4CSP), due to interaction of nitrogen with cobalt in complex, weakened
and appeared in 2237 cm−1. According to that, the existence of important functional
groups in nano-[Co-4CSP]Cl2 was approved by FT-IR spectrum.
To illustrate the presence of the desired elements in the structure of complex,
energy-dispersive X-ray spectroscopy (EDX) from nano-[Co-4CSP]Cl2 was studied
and the expected elements in the complex were approved (Fig. 3). As it is shown in
Fig. 3, it indicates that carbon, oxygen, nitrogen, chlorine and cobalt were presented
in nano-[Co-4CSP]Cl2.
To fnd the morphology and the particle size of nano-[Co-4CSP]Cl2, the scan-
ning electron microscope (SEM) micrographs of nano-[Co-4CSP]Cl2 was checked
out and showed that the synthesized particles were prepared in size less than 100 nm
(Fig. 4).
Fig. 2 FT-IR spectrum of nano-[Co-4CSP]Cl2
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A. R. Moosavi-Zare et al.
Fig. 3 Energy-dispersive X-ray spectroscopy (EDX) of nano-[Co-4CSP]Cl2
Fig. 4 SEM micrograph of nano-[Co-4CSP]Cl2
Table 1 Specifc surface area (BET), mean pore diameter and total pore volume of nano-[Co-4CSP]Cl2
Sample
Specifc surface area
Mean pore diameter (nm)
Total pore volume
(m2 g−1
11.64
)
(cm3 g−1
0.13
)
Nano-[Co-4CSMP]Cl2
45.71
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Fig. 5 N2 adsorption–desorption isotherms of nano-[Co-4CSP]Cl2
Fig. 6 Thermal gravimetric analysis (TGA) of nano-[Co-4CSP]Cl2 at range of 25–800 °C
1 3

A. R. Moosavi-Zare et al.
Because of the porous structure of catalyst particles, to display the efective sur-
face of complex for the catalysis of the reactions, the volume and size of the cavities
included in nano-[Co-4CSP]Cl2 were studied. The specifc surface area, mean pore
diameter and total pore volume of nano-[Co-4CSP]Cl2 are 11.64 m2 g−1, 45.71 nm
and 0.13 cm3 g−1, respectively (Table 1, Fig. 5).
To indicate the temperature range for the application of nano-[Co-4CSP]Cl2
in the chemical reactions and thermal stability of it, thermal gravimetric analysis
(TGA) and diferential thermal gravimetric (DTG) of the complex were investi-
gated and displayed that it could be used in the temperature range up to 200 °C
without no particular changes in its structure (Fig. 6).
After the preparation and identifcation of nano-[Co-4CSP]Cl2, the reaction of
2-aminobenzothiazole, benzaldehyde and ethyl acetoacetate was considered as a
model reaction. This reaction was examined in the presence of various amounts
of nano-[Co-4CSP]Cl2 at range of 50–100 °C under solvent-free condition which
the best result was obtained using 3 mol% of the catalyst at 70 °C (Table 2). Also,
the model reaction was tested in some various solvents such as ethyl acetate, chlo-
roform, dichloromethane and n-hexane in comparison with solvent-free condition
which did not modify the yield of product and reaction time (Table 2). Moreover,
the model reaction was tested in the presence of CoCl2 as a catalyst in compari-
son with nano-[Co-4CSP]Cl2 which did not have no acceptable result.
After the optimization of the reaction condition, to display the generality of
the catalyst, a wide range of various aldehydes was used for the preparation of
4H-pyrimido[2,1-b]benzazoles. For this purpose, ethyl acetoacetate was reacted
with various aldehyde and 2-aminobenzothiazole or 2-aminobenzimidazole to
give 4H-pyrimido[2,1-b]benzothiazoles and 4H-pyrimido[2,1-b]benzimidazoles,
respectively. The expected products were synthesized with high yields in good
reaction times (Table 3).
In the purposed mechanism, which is supported by the previous literature
[9–15, 29–31], ethyl acetoacetate reacted with aldehyde which was activated
by the catalyst to give Knoevenagel product. Then, 2-aminobenzothiazole was
Table 2 Efect of catalyst
Mol% of Solvent
catalyst
Temp. (°C) Time (min) Yielda (%)
amounts, temperature and
solvents on the reaction
between 2-aminobenzothiazole,
benzaldehyde and ethyl
acetoacetate
1
3
5
3
3
3
3
3
3
–
–
–
–
70
60
60
60
60
60
60
60
60
60
60
87
87
80
87
75
50
60
10
70
70
50
–
100
Refux
Refux
Ethyl acetate
Chloroform
Dichloromethane Refux
n-Hexane Refux
aIsolated yield
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Table 3 The preparation of 4H-pyrimido[2,1-b]benzazoles
Entry
Product
Time (min)
Yielda (%)
87
M.p. °C (Lit.)ref
1
60
179–181 (175–178)9
2
120
80
114–117 (112–116)9
3
4
5
90
150
120
85
81
79
260–261 (259–261)9
110–114 (107–109)9
138–140 (140–142)9
6
7
120
120
78
79
174–177 (–)13
164–165 (164–166)9
1 3

A. R. Moosavi-Zare et al.
Table 3 (continued)
Entry
Product
Time (min)
60
Yielda (%)
86
M.p. °C (Lit.)ref
8
128–130 (130–132)30
9
40
70
76
85
220–223 (218–222)9
152–154 (153–156)9
10
11
12
45
86
72
161–163 (160–164)9
280 (>300)31
100
13
14
120
110
82
79
230 (225)1 (dec)
259–261(261.3–261.9)29
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Table 3 (continued)
Entry
Product
Time (min)
10
Yielda (%)
68
M.p. °C (Lit.)ref
15
291–292 (294–297)31
16
90
85
290–292 (291.4–292.2)29
The reaction was carried out at 70 °C under solvent-free conditions
aIsolated yield
reacted with Knoevenagel product to furnish intermediate (I). Afterward, by the
intranucleophilic attack to carbonyl group in intermediate (I) which was activated
by the catalyst and removing of one molecule of H2O in the last step, the desired
product was prepared (Scheme 4).
To investigate the reusability of the catalyst, the reaction of 2-aminobenzothia-
zole, benzaldehyde and ethyl acetoacetate, as a model reaction, was studied in the
presence of the reuse catalyst. In this regard, after the completion of the reaction,
the reaction mixture was extracted by warm ethanol and separated from the cata-
lyst by simple fltration. The separated catalyst was washed with ethyl acetate,
dried and successfully reused for four times (Fig. 7).
Conclusions
In summary, nano-Co-[4-clolorophenyl-salsylaldimine-pyranopyrimidinedione]Cl2
{Nano-[Co-4CSP]Cl2} as a novel Schif base complex and catalyst was synthesized
and identifed by various techniques such as IR, SEM, EDX, TGA, DTA and BET
as well as mass analysis. The prepared nano-Schif base complex and catalyst were
successfully used for the synthesis of some 4H-pyrimido[2,1-b]benzazoles including
4H-pyrimido[2,1-b]benzothiazoles and 4H-pyrimido[2,1-b]benzimidazoles.
1 3

A. R. Moosavi-Zare et al.
Scheme 4 The ofered mechanism for the synthesis of 4H-pyrimido[2,1-b]benzazoles
1 3

Nano‑Co‑[4‑chlorophenyl‑salicylaldimine‑pyranopyrimidine…
Fig. 7 The condensation of 2-aminobenzothiazole with benzaldehyde and ethyl acetoacetate in the pres-
ence of reused catalyst
Funding Funding was provided by Sayyed Jamaleddin Asadabadi University.
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