Flower-shaped ZnO nanoparticles as an efficient, heterogeneous and reusable catalyst in the synthesis of N-arylhomophthalimides and benzannelated isoquinolinones

Article abstract of DOI:10.1007/s11164-012-0511-3

A simple and green protocol, developed utilizing an efficient, heterogeneous and recyclable catalyst, i.e. zinc oxide nanoparticles (ZnO NPs)-mediated synthesis of N-arylhomophthalimides and benzannelated isoquinolinones, is reported. The structures of th

Full text of DOI:10.1007/s11164-012-0511-3

Res Chem Intermed (2012) 38:1881–1892
DOI 10.1007/s11164-012-0511-3
Flower-shaped ZnO nanoparticles as an efficient,
heterogeneous and reusable catalyst in the synthesis
of N-arylhomophthalimides and benzannelated
isoquinolinones
•
Varadhan Krishnakumar Kesarla Mohan Kumar
•
•
Badal Kumar Mandal Fazlur-Rahman Nawaz Khan
Received: 9 December 2011 / Accepted: 16 February 2012 / Published online: 18 April 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A simple and green protocol, developed utilizing an efficient, hetero-
geneous and recyclable catalyst, i.e. zinc oxide nanoparticles (ZnO NPs)-mediated
synthesis of N-arylhomophthalimides and benzannelated isoquinolinones, is repor-
1
ted. The structures of the desired products were characterized by FTIR, H NMR,
13C NMR, and HRMS techniques. The ZnO NPs exhibited excellent catalytic
activity and the proposed methodology is capable of providing the desired products
in good yield and purity.
Keywords Homophthalic acid Á N-arylhomophthalimide Á
Benzannelated isoquinolinones Á ZnO nanoparticles Á Reusable
Introduction
In recent decades, nano-crystalline metal oxides have found numerous applications
including hazardous materials destruction [1], as active gas adsorbents [2], and in
oxidation of volatile organic compounds [3]. In addition, great attention has been
focused towards nanoparticle-mediated organic transformations [4, 5] with
enhanced reactions potency due to their larger surface area to volume ratio [6].
Electronic supplementary material The online version of this article (doi:
10.1007/s11164-012-0511-3) contains supplementary material, which is available to authorized users.
V. Krishnakumar Á F.-R. N. Khan (&)
Organic and Medicinal Chemistry Research Laboratory, Organic Chemistry Division, School
of Advanced Sciences, VIT-University, Vellore 632 014, Tamil Nadu, India
e-mail: nawaz_f@yahoo.co.in
V. Krishnakumar Á K. M. Kumar Á B. K. Mandal
Trace Elements Speciation Research Laboratory, Environmental and Analytical Chemistry Division,
School of Advanced Sciences, VIT-University, Vellore 632 014, Tamil Nadu, India
e-mail: badalmandal@vit.ac.in
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Isoquinolines have demonstrated widespread biological activities and constitute a
large number of naturally occurring alkaloids [7, 8]. Fused isoquinolines were used
as anti-inflammatory, anti-pyretic [9], and anti-cancer agents [10]. Similarly, the
benzannealated oxazoles, thiazoles, and diazoles are known to exhibit a broad range
of biological and pharmaceutical properties, e.g., anti-microbial [11], anti-oxidant
[12], anti-tubercular [13], anti-mycobacterial [14], anti-inflammatory [15], anti-
cancer [16], and anti-HIV [11] activities. They have also been used as fluorescent
brighteners [17].
Benzene fused with isoquinoline-1,3-diones produces good spectral properties
and numerous applications, including light-emitting diodes [18], fluorescence
switchers [19], fluorescence markers in biology [20], liquid crystal displays [21],
electroluminescent materials [22], potential photosensitive biological units [23],
laser active media [24], photo-induced electron sensors [25], and in optical materials
[26].
The isoquinoline-1,3-diones have been prepared either by amination of
homophthalic anhydride or by pTSA-mediated reaction of homophthalic acid with
anilines under reflux conditions using Dean-strap apparatus or through the silica
gel adsorbed homophthalic acid and anilines under microwave irradiation [27].
The benzannelated benzoxazole and benzothiazole have been produced in two steps
involving longer reaction times [27, 28] or through the reaction of homophthalic
acid and anilines under refluxing acetic anhydride followed by acetic acid [29].
However, the above methods include drawbacks such as longer reaction times,
larger number of steps, use of large amounts of catalyst or adsorbents, and use of
hazardous reagents. In continuation of our earlier work involving different synthetic
methodologies [30–34] using heterogeneous, reusable metal oxide nanoparticles as
catalysts, we here report an efficient, green, inexpensive and reusable heterogeneous
catalyst-mediated synthesis of N-arylhomophthalimide and benzannelated isoquin-
olinones in good yield and purity.
Results and discussion
Numerous methodologies have been developed for the synthesis of ZnO NPs [35–
37]. However, ZnO NPs preparation from aqueous solutions is the most promising
method because of its simplicity, low operating temperature, and high yields of pure
products [38]. Nowadays, the synthesis of ZnO crystals from aqueous solutions has
attracted researchers [39]. The surface area and pore volume of nano-sized ZnO
materials, respectively, *38.8–48.23 and 0.099–0.189 ,were larger than those of
commercial ones at *3.1–18.45 and 0.046, respectively, which may derive from the
great differences in surface morphology [38, 40, 41]. The ZnO NPs required for the
present investigation were obtained in high purity and yield from the corresponding
zinc acetate solution [42]. The X-ray diffraction (XRD) pattern of ZnO NPs
suggested discrete diffraction peaks at 31.90, 34.40, 36.37, 47.67, 56.71, 62.98,
66.51, 68.05, and 69.21 assigned to (100), (002), (101), (102), (110), (103), (200),
(112), and (201) confirming hexagonal ZnO NPs (Fig. 1), and were in good
agreement with the standard card (JCPDS no. 00-0361451). Scanning electron
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Flower shaped ZnO nanoparticles
1883
Fig. 1 XRD pattern of ZnO nanoparticles
Fig. 2 SEM image of synthesized ZnO nanoparticles
microscopic (SEM) images showed that the particles were flower-shaped and
uniformly distributed (Fig. 2). Similarly, transmission electron microscope (TEM)
images of ZnO NPs revealed that the particles were flower-shaped and that the
average flower size was less than 500 nm (Fig. 3). The selected area electron
diffraction (SAED) pattern showed that the synthesized ZnO was crystalline and
could be indexed to hexagonal ZnO NPs. The EDS spectrum of the nano-sized
sample also confirmed the presence of Zn and O atoms (Fig. 4).
In the reported microwave-assisted synthesis of isoquinolinones from homoph-
thalic acid [27, 28], the methodology involved impregnating the solid support with
homophthalic acid and then reacting with the substituted anilines; however, this
required large amounts of solid support (3–5 g).
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V. Krishnakumar et al.
Fig. 3 TEM image of synthesized ZnO nanoparticles
Fig. 4 EDX spectrum of ZnO nanoparticles
Moreover, microwave-irradiated reaction was completed in shorter reaction times
with less yield compounds compared to the conventional method. However, the
reactions between homophthalic anhydride and anilines or benzylamines were carried
out in the presence of p-toluenesulfonic acid, and longer reaction times (22–24 h) were
required to get the desired products, 3 and 6.
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Flower shaped ZnO nanoparticles
1885
R
O
O
NH2
COOH
N
5 mol % nano ZnO
N
5 mol % nano ZnO
Toluene, reflux
Toluene, reflux
X
O
4a-c
X = O, S, NH
R
3a-h
COOH
H2N
2a-k
1
5 mol % nano ZnO
Toluene, reflux
O
N
5
O
6
R = H, 2-Cl, 3-Cl, 4-Cl, 4-F, 4-Br, 4-Me, 4-Et (3a-h)
R = 2-OH, 2-SH, 2-NH2 (4a-c)
In the present investigation, in order to get an efficient yield of the desired
products 3, 4, and 6 from homophthalic acid with high purity, optimization of the
reaction has been carried out (Tables 1, 2 and 3). The optimized reaction condition
has been achieved by varying the catalyst (Table 1), the catalyst loading (Table 2),
and the solvent (Table 3). From Table 1, entry 10, it is evident that, among the
tested catalysts, the synthesized ZnO Nps gave good yield and that 5 mol% of
catalyst is sufficient to carry out the reaction (Table 2, entry 1), while the catalyst
can be reused for successive runs of the reactions without any significant loss of the
catalyst and product yield. The reaction works well with toluene solvent (Table 3,
entry 4). Having established the optimized condition, the scope of the reaction has
been tested by varying the different anilines to give the desired products 3a–h. It
should be noted that, when the reaction is carried out with different orthosubstituted
anilines, the desired products 4a–c were obtained. Also, the reaction was found to
be effective with benzyl amines to form the desired product 6 (Table 4).
Table 1 Performance
of various catalysts
Entry
Catalyst
% of yield
1
2
3
4
5
6
7
8
8
9
10
None
Traces
32
Zn2CO3
ZnCl2
Zn(OAc)2
ZnO
45
30
50
MgO
45
CaO
30
ZrO2
42
TiO2
35
Al2O3
ZnO (nano)
40
72
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V. Krishnakumar et al.
Yield (%)
Table 2 Optimization of the
ZnO (nano) catalyst loading
S. no.
Mol%
1
2
3
5
72a, 72b, 70c, 69d
10
15
72
73
a
c
d
Fresh, b1st run, 2nd run, 3rd
run
Table 3 Effect of the solvent
S. no.
Solvents
Yield
1
2
3
4
5
THF
Nil
DMF
Traces
Traces
72%
Nil
Ethanol
Toluene
Acetonitrile
Table 4 ZnO nanoparticles
(5 mol% mediated condensation
of anilines or benzylamine with
homophthalic acid
Compound
R
Time in h
Yield (%)
3a
3b
3c
3d
3e
3f
H
12
12
12
14
14
14
14
14
8
72
75
70
75
68
76
79
78
45
48
55
72
4-CH3
4-CH2CH3
2-Cl
3-Cl
4-Cl
3g
3h
4a
4b
4c
6
4-F
4-Br
2-OH
2-SH
8
2-NH2
aBenzyl amine
8
a
Starting material used was
benzyl amine
12
The synthesized products were purified and characterized by various spectral and
analytical techniques. The IR spectra of compounds 3a–h and 6 showed the C1-
carbonyl group around 1,600 cm-1 and the C3-carbonyl group around 1,700 cm-1
.
1
In the H NMR spectra of compound 3a, geminal coupling was observed for C4-
CH2 protons with J = 22.5 Hz at d 4.2 ppm, while in the remaining compounds, the
J value could not be determined, because the splitting pattern was not resolved. The
C8-aromatic protons of 3a–h and 6 showed doublet at d 8.2 ppm due to the
deshielding effect of the C1-carbonyl group. The 13C NMR peaks at d 169 and
164 ppm indicated the C3 and C1 carbonyl groups of the desired product. In the case
of compound 4a, the d value has been shifted from upfield (d = 4.2 ppm) to
downfield (d = 6.4 ppm) in 1H NMR, and for the 13C NMR the C3-carbonyl group,
it disappeared from the range of 169 ppm which confirmed the formation of the
compound 4a (Mechanism II).
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Flower shaped ZnO nanoparticles
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ZnO
OH
O
O
COOH
H2N
ZnO
R
O
-H2O
O
H
N
O
COOH
R
1
H
O
3
O
OH
N
R
N
R
-H2O
O
O
Mechanism 1 Possible mechanism for the formation of N-arylhomophthalimide, 3
In the case of 4a–c, the N-arylhomophthalimides were expected; however, the
benzannelated isoquinolinones 4a–c were obtained. In the literature, homophthalic
acid 1 when treated with 2-hydroxy aniline 4a formed benzoxazole nucleophile, is
not sufficient to attack the carbonyl moiety present in the carboxylic group. In this
case, benzoxazole intermediate converted into its anhydride on warming at 40 °C in
acetic anhydride, which had a carbonyl group with increased electrophilicity and a
better leaving group (OAc2) than (OH2). But in the presence of nano-ZnO, the
electrophilicity of the carboxylic carbonyl group increased (see Mechanism II) and
favored the cyclized product 4a–c.
The reusability of the catalyst was investigated by conducting the model reaction
between 1 and 2a to afford the desired product 3a. The catalyst was recovered from
the reaction mixture by filtration after the first run. Then, it was washed with
distilled water and thrice with ethyl alcohol, and dried in a hot-air oven for 1 h. The
recovered catalyst was reused thrice to obtain the desired product without significant
loss of yield at 72, 70, and 69%, respectively. It is noteworthy that the yields of the
product in the first, second, and third run were almost the same compared to the
yield obtained with the fresh catalyst.
ZnO
O
O
NH2
N
OH
COOH
COOH
OH
O
O
N
4a
1
2i
Mechanism 2 Possible mechanism for the formation of benzannelated isoquinolinones
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Experimental section
Materials and methods
Melting points were recorded with an open capillary tube and corrected with
benzoic acid. Infrared (IR) spectra were measured on a Bruker Infrared spectrom-
eter, with samples analyzed as KBr disks. High resolution mass spectra (HRMS)
1
were obtained using JEOL GC MATE II HRMS (EI) mass spectrometry. H-NMR
and 13C-NMR spectral analyses were carried out on a Bruker-Avance Digital 500
and 125 MHz spectrometer in CDCl3 using TMS as an internal standard.
Chromatographic separations were done using silica gel (60–120 mesh). Thin layer
chromatography (TLC) was performed using glass plates coated with silica gel G,
and the spots visualization were done by iodine vapor. The pH of the suspension
was monitored by a Digital pH meter MK VI (Systronics, Naroda, Ahmedabad,
India).
Chemicals purchased from Sigma-Aldrich, India, Sd-fine Chemicals, India, and
Central Drug House, India, were used without further purification. Toluene was
purchased from SRL and dried over anhydrous calcium chloride. Other AR grade
solvents purchased from Sd-fine Chemicals were used directly without further
purification.
Synthesis and characterization of ZnO nanoparticles
Flower-shaped ZnO NPs were prepared using the method described elsewhere [42].
In brief, ZnO NPs were synthesized by dissolving 4 mM Zinc acetate dihydrate in
300 ml of milli-Q water. An appropriate amount of NaOH was dissolved in 50 ml of
milli-Q water. Then, the NaOH solution was added dropwise into zinc acetate
solution using a peristaltic pump (Revotek, India) and stirred vigorously using a
magnetic stirrer for half an hour. The pH of the solution was maintained between 8
and 9. The resulting turbid solution was placed in a temperature-controlled water
bath (Guna water bath, BMQR, ISO 9001 certified) at 75 °C for 1 h, and the white
powder that was formed was separated by filtration, washed twice with milli-Q
water followed by ethanol.
Purified ZnO NPs were subjected to X-ray diffraction analysis (Bruker D8
˚
Advance diffractometer with Cu Ka radiation, k = 1.54 A). The scanning range
was between 10° and 90°. The size and morphology of the synthesized ZnO NPs
were determined by a high resolution transmission electron microscope (HR-TEM).
The TEM images were recorded by placing a drop of sample dispersion (1 ml
samples added to 5 ml of propanol and sonicated for few minutes) on a carbon-
coated copper grid and dried in vacuum. The HR-TEM images were taken using
JEOL 3010, 300 kV instrument. SEM/EDS analysis was carried out using a Carl
Zeiss SEM instrument attached to an EVO MA 15 (Oxford Instruments, UK). The
solid samples were sprinkled on the adhesive carbon tape which was supported on a
metallic disk. The sample images were taken at different magnifications.
Simultaneously, the EDS spectrum was recorded at selected areas on the solid
surface to obtain elemental composition.
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Flower shaped ZnO nanoparticles
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General procedure for the synthesis of N-aryl/aralkylhomophthalimides (3a–h/6)
benzannelated isoquinolinones (4a–c)
A mixture of homophthalic acid (1) and substituted anilines (2a–k) or benzyl amine
(5) (1:1 ratio) in dry toluene, and 5 mol% nano-ZnO were amended to the
suspension. The reaction mixture was heated under reflux condition. The progress of
the reaction was monitored by thin layer chromatography. After the completion of
the reaction, the catalyst was separated by filtration. The solvent was removed under
vacuum, and then a crude sample was purified by silica gel column chromatography
using ethyl acetate and n-hexane mixture as an eluant.
1
The obtained products were characterized by FTIR, H NMR, 13C NMR and
HRMS techniques. The spectral data of compounds (3a–h), (4a–c) and 6 are given
below.
2-Phenylisoquinoline-1,3 (2H,4H)-dione, 3a white solid, mp 146–147 °C, IR
(KBr) 1,718 (C3 CO), 1,665 (C1-CO) cm-1 1H NMR (500 MHz, CDCl3) d 4.24 (s,
2H, C4-CH2), 7.23–7.25 (m, 2H), 7.36 (d, J = 7.5 Hz, 1H), 7.47–7.55 (m, 4H), 7.65
(t, J = 6.5 Hz,1H), 8.26 (d, J = 8.0 Hz, 1H, C8–H), 13C NMR (125 MHz, CDCl3)
d 36.98, 125.48, 127.34, 127.89, 128.52, 128.72, 129.35, 129.49, 133.99, 134.26,
135.11, 165.05 (C1-CO), 169.92 (C3-CO) ppm, HRMS [EI, M?] calcd for
C15H11NO2 m/z 237.2533, found 237.4283.
2-p-Tolylisoquinoline-1,3 (2H,4H)-dione, 3b white solid, mp 154–156 °C, IR
(KBr) 1,721 (C3 CO), 1,679 (C1-CO) cm-1 1H NMR (500 MHz, CDCl3) d 2.44 (s,
3H, CH3), 4.24 (s, 2H, C4-CH2), 7.11 (d, J = 6.5 Hz, 2H), 7.32–7.51 (m, 3H), 7.48
(t, J = 7.0 Hz, 1H), 7.64 (t, J = 7.5 Hz, 1H), 8.26 (d, J = 6.5 Hz, 1H, C8-H), 13C
NMR (125 MHz, CDCl3) d 21.27, 36.97, 125.52, 127.29, 127.86, 128.13, 129.52,
130.10, 132.35, 133.93, 134.21, 138.67, 165.12 (C1-CO), 170.04 (C3-CO) ppm,
HRMS [EI, M?] calcd for C16H13NO2 m/z 251.2799, found 251.9947.
2-(4-Ethylphenyl)isoquinoline-1,3 (2H,4H)-dione, 3c off-white solid, mp
112–114 °C, IR (KBr) 1,718 (C3 CO), 1,670 (C1-CO) cm-1 1H NMR (500 MHz,
CDCl3) d 1.29 (t, J = 7.5 Hz, 3H, –CH3), 2.72 (q, J = 7.5 Hz, 2H, –CH2), 4.24 (s,
2H, C4-CH2), 7.13 (d, J = 8.0 Hz, 2H), 7.35–7.37 (m, 3H), 7.48 (t, J = 7.5 Hz,
1H), 7.64 (t, J = 7.5 Hz, 1H), 8.26 (d, J = 8.0 Hz, 1H, C8-H), 13C NMR
(125 MHz, CDCl3) d 15.19, 28.57, 36.99, 125.55, 127.27, 127.81, 127.86, 128.16,
128.87, 129.52, 132.48, 133.91, 134.22, 165.13 (C1-CO), 170.02 (C3-CO) ppm,
HRMS [EI, M?] calcd for C17H15NO2 m/z 265.3065, found 265.3064.
2-(2-Chlorophenyl)isoquinoline-1,3 (2H,4H)-dione, 3d white solid, mp
116–118 °C, IR (KBr) 1,720 (C3 CO), 1,679 (C1-CO) cm.-1 1H NMR (500 MHz,
CDCl3) d 4.25 (s, J = 22.5 Hz, 1H, C4-CH2), 4.32 (s, J = 22.5 Hz, 1H, C4-CH2),
7.28-7.32 (m, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.41–7.45 (m, 2H), 7.49 (t,
J = 7.5 Hz, 1H), 7.56–7.59 (m, 1H), 7.37 (t, J = 7.5 Hz, 1H), 8.25 (d,
J = 8.0 Hz, 1H, C8-H), 13C NMR (125 MHz, CDCl3) d 36.87, 125.17, 127.47,
127.81, 127.94, 129.54, 130.23, 130.28, 130.46, 132.70, 133.19, 134.17, 134.33,
164.29 (C1-CO), 169.17 (C3-CO) ppm, HRMS [EI, M?] calcd for C15H10ClNO2 m/
z 271.6984, found 237.4283.
2-(3-Chlorophenyl)isoquinoline-1,3 (2H,4H)-dione, 3e white solid, mp
148–150 °C, IR (KBr) 1,718 (C3 CO), 1,674 (C1-CO) cm.-1 1H NMR (500 MHz,
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V. Krishnakumar et al.
CDCl3) d 4.24 (s, 2H, C4-CH2), 7.13–7.15 (m, 1H), 7.25 (t, J = 2.0 Hz, 1H), 7.36
(d, J = 7.5 Hz, 1H), 7.45–7.46 (m, 2H), 7.49 (t, J = 7.5 Hz,1H), 7.66 (t,
J = 6.5 Hz, 1H), 8.25 (d, J = 8.0 Hz, 1H, C8-H), 13C NMR (125 MHz, CDCl3)
d 36.93, 125.20, 126.98, 127.38, 128.01, 129.06, 129.09, 129.54, 130.21, 134.10,
134.20, 134.34, 136.12, 164.79 (C1-CO), 169.65 (C3-CO) ppm, HRMS [EI, M?]
calcd for C15H10ClNO2 m/z 271.6984, found 237.4283.
2-(4-Chlorophenyl)isoquinoline-1,3 (2H,4H)-dione, 3f white solid, mp
160–162 °C, IR (KBr) 1,720 (C3 CO), 1,679 (C1-CO) cm-1 1H NMR (500 MHz,
CDCl3) d 4.24 (s, 2H, C4-CH2), 7.17–7.67 (m, 7H, Ar–H), 8.25 (d, J = 5.5 Hz, 1H,
C8-H), 13C NMR (125 MHz, CDCl3) d 36.92, 125.24, 127.35, 127.99, 129.59,
129.79, 129.93, 133.46, 134.17, 134.70, 136.34, 164.91 (C1-CO), 169.77 (C3-CO)
ppm, HRMS [EI, M?] calcd for C15H10ClNO2 m/z 271.6984, found 273.7347.
2-(4-Bromophenyl)isoquinoline-1,3 (2H,4H)-dione, 3 g off-white solid, mp
154–156 °C, IR (KBr) 1,722 (C3 CO), 1,679 (C1-CO) cm-1 1H NMR (500 MHz,
CDCl3) d 4.23 (s, 2H, C4-CH2), 7.12 (d, J = 8.5 Hz, 2H), 7.36 (d, J = 7.5 Hz, 1H),
7.50 (t, J = 7.5 Hz, 1H), 7.64 (m, 3H), 8.26 (d, J = 8.5 Hz, 1H, C8-H), 13C NMR
(125 MHz, CDCl3) d 36.92, 125.31, 127.35, 127.97, 129.53, 130.26, 130.29,
130.33, 130.78, 130.81, 134.12, 164.82 (C1-CO), 169.72 (C3-CO) ppm, HRMS [EI,
M?] calcd for C15H10BrNO2 m/z 316.1494, found 316.1494.
2-(4-Fluorophenyl)isoquinoline-1,3 (2H,4H)-dione, 3h light yellow solid, mp
196–197 °C, IR (KBr) 1,720 (C3 CO), 1,679 (C1-CO) cm-1 1H NMR (500 MHz,
CDCl3) d 4.24 (s, 2H, C4-CH2), 7.20 (d, J = 6.5 Hz, 4H), 7.36 (d, J = 8.0 Hz, 1H),
7.49 (t, J = 7.0 Hz, 1H), 7.66 (t, J = 6.5 Hz 1H), 8.25 (d, J = 7.0 Hz, 1H, C8-H),
13C NMR (125 MHz, CDCl3) d 36.94, 125.43, 127.44, 127.46, 129.28, 129.97,
130.23, 130.52, 130.78, 130.97, 134.13, 165.03 (C1-CO), 169.91 (C3-CO) ppm,
HRMS [EI, M?] calcd for C15H10FNO2 m/z 255.2438, found 255.0741.
11H-Benzo[4, 5]oxazolo[3,2-b]isoquinolin-11-one, 4a yellow solid, mp
206–207 °C, IR (KBr) 1,720 (C3 CO), 1,678 (C1-CO) cm-1 1H NMR (500 MHz,
CDCl3) d 6.46 (s, 1H), 7.36–7.38 (m, 3H), 7.41 (t, J = 8.0 Hz, 1H), 7.59 (d,
J = 8.0 Hz, 1H), 7.65 (t, J = 8.0 Hz, 1H), 8.50 (d, J = 8.0 Hz, 1H), 8.55 (d,
J = 5.5 Hz, 1H), 13C NMR (125 MHz, CDCl3) d 81.86, 109.86, 116.41, 121.49,
124.17, 124.44, 125.90, 126.11, 127.76, 127.80, 132.79, 137.66, 147.19, 149.88,
159.29 (C = O) ppm, HRMS [EI, M ?] calcd for C15H9NO2 m/z 235.2375, found
235. 2791.
Compounds 4b and 4c were crossed checked and confirmed using melting point
as reported in the literature.
11H-benzo[4, 5]thiazolo[3,2-b]isoquinolin-11-one, 4b yellow solid, mp
186–188 °C, (lit29, 186–186.5 °C).
Benzo[4, 5]imidazo[1,2-b]isoquinolin-11(5H)-one, 4c yellow solid, mp [ 300 °C,
(lit29,[320 °C).
2-Benzylisoquinoline-1,3 (2H,4H)-dione, 6 off white solid, mp 106–107 °C, IR
(KBr) 1,713 (C3 CO), 1,670 (C1-CO) cm-1 1H NMR (500 MHz, CDCl3) d 4.07 (s,
2H, C4-CH2), 5.20 (s, 2H, benzilic-CH2), 7.26 (d, J = 7.5 Hz, 2H), 7.30–7.33 (m,
2H), 7.42 (t, J = 8.0 Hz, 1H), 7.49 (d, J = 7.0 Hz, 2H), 7.58 (t, J = 6.5 Hz, 1H),
8.26 (d, J = 8.5 Hz, 1H, C8-H), 13C NMR (125 MHz, CDCl3) d 36.51, 43.29,
125.38, 127.13, 127.53, 127.74, 128.43, 128.99, 129.28, 133.68, 134.11, 137.09,
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Flower shaped ZnO nanoparticles
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164.82 (C1-CO), 169.88 (C3-CO) ppm, HRMS [EI, M?] calcd for C16H13NO2
m/z 251.2799, found 251.2798.
Conclusion
In conclusion, a green chemistry protocol for the synthesis of N-arylhomophthal-
imide and benzannelated isoquinolinones in shorter reaction times, mild condition,
and high percentage of yield and purity is reported. In addition, the catalyst utilized
in the present methodology is reusable, low cost, and non-toxic.
Acknowledgments The author Varadhan Krishnakumar is grateful to VIT University for the Research
Associateship. Also, the authors thank VIT University for analysis of XRD and providing laboratory
facilities, and heartly acknowledge the help of SAIF, IIT Madras, Chennai, for providing the NMR,
HRMS, SEM, and TEM facilities.
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