Reduced graphene oxide supported copper oxide nanocomposites: An efficient heterogeneous and reusable catalyst for the synthesis of ynones, 1,3-diynes and 1,5-benzodiazepines in one-pot under sustainable reaction conditions

Article abstract of DOI:10.1002/aoc.5646

A greener and efficient method for the synthesis of ynones and 1,3-diynes using copper oxide nanoparticles (CuONPs) doped reduced graphene oxide (CuO@rGO) catalyst under palladium, ligand and solvent free conditions have been developed. The catalyst was s

Full text of DOI:10.1002/aoc.5646

Received: 7 August 2019
DOI: 10.1002/aoc.5646
Revised: 3 December 2019
Accepted: 16 December 2019
F U L L P A P E R
Reduced graphene oxide supported copper oxide
nanocomposites: An efficient heterogeneous and reusable
catalyst for the synthesis of ynones, 1,3-diynes and
1,5-benzodiazepines in one-pot under sustainable reaction
conditions
Rajib Sarkar
| Ajay Gupta | Ramen Jamatia | Amarta Kumar Pal
Department of Chemistry, Centre for
Advanced Studies, North-Eastern Hill
University, Shillong, 793022, India
A greener and efficient method for the synthesis of ynones and 1,3-diynes
using copper oxide nanoparticles (CuONPs) doped reduced graphene oxide
(CuO@rGO) catalyst under palladium, ligand and solvent free conditions have
been developed. The catalyst was subsequently utilized for the synthesis of bio-
logically active 1,5-benzodiazepines in one pot via sequential addition of acyl
chlorides, terminal alkynes and o-phenylenediamines. The methodology ini-
tially involves in situ formation of ynones which react with o-
phenylenediamines in presence of ethanol to afford a wide variety of benzodi-
azepines. Mild reaction conditions, good to an excellent yield of the products,
cheap and recyclable catalyst make this methodology environmentally benign
and sustainable.
Correspondence
Amarta Kumar Pal, Department of
Chemistry, Centre for Advanced Studies,
North-Eastern Hill University, Shillong,
793022, India.
Email: amartya_pal22@yahoo.com;
akpal@nehu.ac.in
Funding information
Science and Engineering Research Board,
Grant/Award Number: EMR/2016/005089
dated 30.6.2017; North-Eastern Hill
University; University Grant Commission
(UGC)
K E Y W O R D S
1,5-benzodiazepines, cross-coupling, one-pot synthesis, CuO@rGO nanoparticles, homo-
coupling, ynones
1 | INTRODUCTION
easy accessibility to such ynones. C. Zhang and co-
workers reported the palladium catalyzed carbonylative
Synthesis of α,β-acetylenic carbonyl derivatives
(ynones) and 1,3-diynes has been extensively studied
over the years due to their wide application in the
synthesis of natural products, pharmaceutical and het-
reaction for the development of ynones.13 However,
the disadvantage of this methodology is the use of
toxic CO gas in the reaction. M. Cui and co-workers
reported Pd (PPh3)2Cl2 catalyzed cross-coupling of
amide derivatives with terminal alkynes to yield
ynones, but the reaction proceeds in the presence of
solvent like THF and requires a much longer time to
2
erocyclic compounds.1, Several classical methods for
their synthesis are cited in the literature.3–12 In recent
years, palladium-catalyzed Sonogashira type of cross-
coupling reaction among acyl chloride and terminal
alkynes has received much attention because of its
complete.14 In fact, uses of Cu and Pd complexes in
these reactions are well reported.15,
However, most
16
Appl Organometal Chem. 2020;e5646.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.5646

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SARKAR ET AL.
of these catalysts are homogeneous and unrecyclable.
Various other catalysts containing copper and palla-
dium have also been reported in the literature for the
coupling of acyl chlorides and terminal alkynes. But
the use of such costly palladium and CuI as co-cata-
lyst, limits their application for such transformations.17,
oxidation,22 hydrogenation,23 C-C coupling24 etc. How-
ever, due to higher surface energy, nanoparticles tend
to agglomerate themselves which in-turn reduces cata-
lytic activity.25 In this regard, heterogeneous solid
supported with a large surface area, which inhibits
nanoparticle agglomeration and thereby increasing its
catalytic activity will be desirable. Graphene oxide or
reduced graphene oxide nanosheets with a very large
surface area containing various oxygenated functional
groups tend to anchor metal nanoparticles on its sur-
face effectively.26 Therefore, we wish to develop
reduced graphene oxide supported copper oxide
nanocomposites as a reusable catalyst for the aforemen-
tioned synthesis. Further ynones are versatile bifunc-
tional synthons for the synthesis of pharmacologically
18
On the other hand, bimetallic catalysts such as
Pd/Cu, Ni/Cu and other heterogeneous Cu catalysts
20
have been used for the synthesis of 1,3-diynes.19,
Biswas and group reported the coupling of alkynes
using copper oxide supported on manganese oxide in
the presence of toluene at a higher temperature of
21
ꢀ
105 C.
Recently, metal nano-catalysts because of their
higher catalytic activity have been employed for various
organic transformation reactions such as selective
and
biologically
active
heterocycles
like
FIGURE 1 Some biologically and
pharmacologically active benzodiazepine
compounds
SCHEME 1 Synthesis of 1.5-benzodiazepines

SYNTHESIS OF YNONES, 1,3-DIYNES AND 1,5-BENZODIAZEPINES
3 of 12
benzodiazepines. These benzodiazepines have immense
biological activities such as anti-inflammatory, anti-
depressive, anticonvulsant, analgesic, hypnotic and
sedation.27 Some of the biologically and pharmacologi-
2 | RESULT AND DISCUSSIONS
Graphite Oxide (GO) and CuO@rGO were prepared by
the reported procedure (Scheme 2).31, 32 CuO@rGO was
synthesized by the mixing of GO (30 mg) with 200 ml
aqueous solution of CuCl2 (9% w/v), and the mixture was
then ultrasonicated for 1 hr. To the resulting suspension,
NaBH4 (10 ml, 1%) was added slowly which was then
heated at 100 ꢀC for 24 hr, and cooled to 50 ꢀC, separated
by centrifugation, washed with DI water (3 × 10 ml),
methanol (3 × 10 ml) and finally diethyl ether
(3 × 10 ml). The resulting CuO@rGO nanocomposites
were dried at 100 ꢀC under vacuum.32 After synthesis, the
catalyst was characterized by transmission electron
microscopy (TEM), electron dispersive X-ray spectroscopy
(EDX), powder XRD, FT-IR, inductively coupled plasma
atomic emission spectroscopy (ICP-AES) and Barrett–
Joyner–Halenda (BET) analysis.
cally
active
benzodiazepines
e.g.
triflubazam,
lofendazam, CP-141PS, clobazam, chlordiazepoxide are
shown in Figure 1. Agnes Solan et al and S.-G. Huang
group demonstrated the use of ynones derivatives for
the synthesis of benzodiazepines using microwave irra-
28
ꢀ
diation at 50–80 C or expensive and moisture sensi-
tive Ga (OTf)3 as a catalyst29 respectively. K. V.
Srinivasan and co-workers reported30 the one-pot syn-
thesis of benzodiazepines utilizing Pd (OAc)2 as a cata-
ꢀ
lyst at 100 C (Scheme 1). However, this methodology
suffers the drawback of the use of costly and non-
recyclable catalyst. Therefore, we decided to develop a
protocol for the synthesis of ynones, 1,3-diynes and
benzodiazepines (Scheme 1, present work) which is
cheap, environmental friendly and sustainable. There-
fore, we herein report CuO@rGO catalyzed synthesis
of said compounds under palladium, ligand and solvent
free reaction conditions.
Powder XRD analysis was used to investigate the
formation of GO and CuO@rGO nanocomposites. It is
clearly observed that the GO (Figure 2a) has diffrac-
tion peaks at 9.33ꢀ and 42.20ꢀ due to distinctive [001]
SCHEME 2 Synthesis of CuO@rGO nanocomposites
FIGURE 2 PXRD pattern of (a) GO and (b) CuO@rGO nanocomposites

4 of 12
SARKAR ET AL.
FIGURE 3 TEM image of CuO@rGO nanocomposites at 100 nm (a), SAED pattern (b) and EDX spectrum (c) of CuO@rGO
nanocomposites
and [100] planes which display the oxidation of graph-
ite to graphite oxide (GO).33 The XRD pattern of
CuO@rGO nanocomposites (Figure 2b) exhibits new
diffraction peak at 2θ = 24.4ꢀ (002) which indicates a
high degree of reduction of GO to rGO during the
FIGURE 5 N2-sorption isotherm CuO@rGO nanocomposites
FIGURE 4 Comparative FT-IR spectra of GO and CuO@rGO
SCHEME 3 Model reaction for CuO@rGO catalyzed cross
nanocomposites
coupling of acyl chloride and terminal alkyne

SYNTHESIS OF YNONES, 1,3-DIYNES AND 1,5-BENZODIAZEPINES
5 of 12
TABLE 1
Screening of Reaction Conditions
Entry
1
Catalyst (mol %)
Free
Base (equiv.)
Solvent
Free
Temp.(ꢀC)
RT
80
Product
3a
Yield%aa
Free
ND
ND
ND
ND
ND
96
2
Free
Free
Free
3a
3
CuO@rGO (0.8)
CuO@rGO (0.8)
Free
Free
Free
RT
80
3a
4
Free
Free
3a
5
Et3N(5)
Et3N(5)
Et3N(4)
Et3N(3)
Et3N(3)
Et3N(2)
Et3N(3)
Et3N(3)
Et3N(3)
Et3N(3)
Et3N(3)
K2CO3(3)
Cs2CO3(3)
BZA(3)
Pyridine (3)
DIPEA(3)
Et3N(3)
Et3N(3)
Et3N(3)
Et3N(3)
Et3N(3)
Free
80
3a
6
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (1.2)
Pd (OAc)2 (0.8)
PdCl2 (0.8)
Free
60
3a
7
Free
60
3a
96
8
Free
60
3a
96
9
Free
30
3a
3a
96
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Free
30
89
Free
30
3a
96
Free
30
3a
92
Free
30
3a
90
Pd/C (0.8)
Free
30
3a
93
Pd (PPh3)2Cl2(0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
Free
30
3a
90
Free
30
3a
ND
ND
ND
ND
48
Free
30
3a
Free
30
3a
Free
30
3a
Free
30
3a
Dichloromethane
Toluene
Ethanol
Acetonitrile
Dimethylformamide
30
3a
52
30
3a
83
30
3a
87
30
3a
16
30
3a
12
Reaction conditions: Reactions were carried out using 1a (1.2 mmol), 2a (1 mmol) in presence of Et3N (3 equiv.) and 0.8 mol % of catalyst,
CuO@rGO.
aYields of isolated pure products.
FIGURE 6 (a) Solvent Standardization and (b) Catalyst standardization forcross coupling of acyl chlorides and terminal alkynes

6 of 12
SARKAR ET AL.
incorporation process of CuO nanoparticles (NPs). The
spectrum (Figure 3c) reveal the presence of Cu species in
CuO@rGO nanocomposites (Supporting Information,
Figure S2). The loading of Cu was then estimated by ICP-
AES analysis, which shows only 12.8 wt % of Cu exist in
the catalyst.
The comparative FT-IR spectrum of GO and
CuO@rGO nanocomposites is given in (Figure 4). The
FT-IR spectrum of GO shows various characteristic
absorption peaks at 3444, 1725, 1396, 1224 and
1046 cm−1 corresponding to the hydroxyl (C-OH), car-
other new diffraction peaks at 2θ = 32.4ꢀ (110), 35.3ꢀ (
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1 11), 38.05 (111), 48.4 ( 2 02), 53.8 (020), 58.1 (202),
ꢀ
ꢀ
ꢀ
ꢀ
61.3 ( 1 13), 64.4 (311) and 68.1 (220) arises due to CuO
nanoparticles.34 The additional peak observed at
2θ = 44.1ꢀ (111) could be because of the presence trace
amount of Cu nanoparticles present in the prepared cata-
lyst (Supporting Information, Figure S1).35
The TEM image (Figure 3a) of CuO@rGO clearly
indicates that the highly monodisperse nature of CuO
nanoparticles, having average diameter~5–15 nm have
anchored on the surface of rGO. SAED image (Figure 3b)
reflects the crystalline nature of CuO@rGO and the EDX
boxyl (O=C-OH), epoxy and alkoxy (C-O) functional
34
groups.33,
The peak at 1622 cm−1 corresponds to
skeletal vibrations of the graphitic domains.34 In the
TABLE 2
Screening of the effects of various copper salts as catalyst
Entry
[Cu] catalysts (mol %)
CuCl2 (0.8)
Product
Yield%aa
trace
1
2
3
4
5
6
3a
3a
3a
3a
3a
3a
CuI (0.8)
trace
Cu (OAc)2 (0.8)
Cu (NO3)2 (0.8)
CuSO4 (0.8)
trace
trace
trace
CuBr (0.8)
trace
a: Isolated yield of pure product.
SCHEME 4 Substrate
scope for CuO@rGO catalyzed
cross coupling of acyl chlorides
and terminal alkynes. Reaction
conditions: 1 (1.2 nmol),
2 (1 mmol), CuO@rGO
(0.8 mol %), Et3N (3 equiv.),
were stirred at 30 ꢀC. b Yields
of isolated pure products

SYNTHESIS OF YNONES, 1,3-DIYNES AND 1,5-BENZODIAZEPINES
7 of 12
SCHEME 5 Homo-coupling of different
terminal alkynes for the synthesis of symmetrical
1,3-diynes. Reaction conditions: 2 (2 nmol), base
(3 equiv.), and CuO@rGO (1.2 mol) were
allowed to react in a 25 ml round bottom flask
under O2 atmosphere. dYields of isolated pure
products
TABLE 3
Screening of reaction conditions for homo-coupling of phenyl acetylene
Entry
Catalyst (mol %)
CuO@rGO
Base
Condition
Temp.(ꢀC)
Time (hr)
Product
4a
Yield (%)cc
1
Free
air
O2
O2
air
O2
O2
O2
O2
O2
O2
O2
O2
RT
RT
50
40
40
40
30
40
40
40
40
40
24
24
4
ND
ND
98
2
Free
BZA(3)
BZA(3)
BZA(3)
BZA(4)
BZA(3)
BZA(3)
DBU
4a
3
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (1.2)
CuO@rGO (1.2)
CuO@rGO (1.2)
CuO@rGO (1.2)
CuO@rGO (1.2)
CuO@rGO (1.2)
CuO@rGO (1.2)
4a
4
4
4a
72
5
4
4a
98
6
4
4a
98
7
4
4a
90
8
4
4a
ND
ND
ND
12
9
K2CO3
Cs2CO3
Et3N
4
4a
10
11
12
4
4a
4
4a
Pyridine
4
4a
32
Reaction conditions: 2a (2 mmol), base (3 equiv.) and CuO@rGO (1.2 mol %) were allowed to react in a 25 ml round bottom flask under
O2 atmosphere.
cYields of the pure products. BZA = benzyl amine.
FT-IR spectrum of CuO@rGO, the absorption peaks at
1382 cm−1, 1211 cm−1 and 537 cm−1 are due to the
epoxy and alkoxy and Cu-O stretching vibration
respectively.34 The disappearance of the carboxylic acid
peak at 1734 cm−1 also indicates the reduction of GO
to rGO functionalities (Supporting Information,
Figure S3).36
The N2-sorption analysis was performed to investigate
the surface area of the CuO@rGO nanocomposites and is
shown in Figure 5. The as-synthesized CuO@rGO
nanocomposites found to have large BET surface area of
about 337 m2/g respectively (Supporting Information,
Figure S4).34
After the successful preparation of CuO@rGO, its cat-
alytic activity was investigated for the synthesis of ynones
(Scheme 3). Initially, p-nitrobenzoyl chloride and phenyl
acetylene were chosen as the model substrates. At first,
the model reaction was carried out without any catalyst
FIGURE 7 Ortep diagram of compound 4c (CCDC 1881184)

8 of 12
SARKAR ET AL.
TABLE 4
Screening of reaction conditions for hetero-coupling of terminal alkynes catalyzed by CuO@rGO
Entry
2a (mmol)
2c (mmol)
Base (equiv.)
BZA(3)
4a (yield %)
5a (yield %)
4e (yield %)
1
2
3
4
5
1
1
1
2
3
1
2
34
23
12
52
67
45
61
82
32
26
24
32
26
18
12
BZA(3)
3
BZA(3)
`1
1
BZA(3)
BZA(3)
in the presence of a base like triethyl amine (Et3N) and
stirred at RT for 24 hr under solvent free reaction condi-
tion (SFRC). Reaction failed to produce the desired prod-
uct and only starting materials were witnessed. Then the
poor conversion (Figure 6a). Bases like benzylamine,
Cs2CO3 and K2CO3 performed very inefficiently, furnish-
ing lower yield (Table 1) but triethyl amine afforded the
best result. Heteroaromatic bases like pyridine showed
inadequacy in producing the desired product (Table 1).
The fate of reaction was then examined with various
readily available copper catalysts (0.8 mol %) like CuI2,
CuCl2, Cu (NO3)2, Cu (OAc)2, CuSO4 and CuBr. They
furnished only trace amount of the desired product 3a
(Table 2). After fixing the optimum condition, the gen-
erality of the procedure was explored. Variety of acyl
chlorides and acetylenes bearing electron donating and
electron withdrawing groups were tested, which
resulted good to excellent yield of the desired product.
It was observed that both aromatic and aliphatic termi-
nal alkynes were well tolerated in this reaction
(Scheme 4).
ꢀ
reaction was heated at 80 C for 24 hr. The same result
was encountered. Again, when the model reaction was
performed in the presence of catalyst CuO@rGO (0.8 mol
ꢀ
%, with respect to CuO) at 30 C, 96% conversion of the
product was observed within just 20 min. Further increas-
ing the temperature, the yield remains constant. There-
ꢀ
fore, 30 C is the optimum temperature of this reaction
(Table 1). It was observed that lowering the catalyst con-
centration from 0.8 mol % to 0.1 mol %, product yield
decreases but higher catalyst loading (0.8 mol %) did not
have any effect on product yield (Figure 6b). So, 0.8 mol
% is the minimum catalyst concentration for getting the
maximum yield.
Next, to check the solvent effect, the model reaction
was performed with various solvents like ethanol, tolu-
ene, dichloromethane, acetonitrile and dimethyl-
formamide. In EtOH and toluene, the good conversion
was achieved but DCM, CH3CN and DMF showed very
After the successful synthesis of ynones, the catalyst
was further utilized for the Glaser oxidative coupling
for the preparation of 1,3-diynes. Initially, homo-
coupling of phenylacetylene was considered as the
model reaction catalyzed by CuO@rGO in presence of
SCHEME 6 Cross-coupling of
different terminal alkynes for the
synthesis of unsymmetrical 1,3-diynes.
Reaction conditions: e6 (2 nmol) and
7 (1 mmol). f6 (1 mmol) and 7 (1 mmol).
Y=Isolated yield of pure products

SYNTHESIS OF YNONES, 1,3-DIYNES AND 1,5-BENZODIAZEPINES
9 of 12
benzylamine as a base under SFRC and O2 atmosphere.
The reaction proceeds well and produced an excellent
yield of the homocoupling product 4a. Then various
aromatic terminal alkynes containing both electron-
donating and electron withdrawing groups were applied
and irrespective of the natures of the substituent, excel-
lent yield (95–98%, Scheme 5) of the desired products
(4a-e) were obtained. It is clear from Table 3 that the
best result was obtained with 1.2 mol % of catalyst. Var-
ious other bases such as K2CO3, Cs2CO3, Et3N and pyri-
dine were tested (Table 3) but benzyl amine which is
cheap and commercially available found to be most effi-
cient in this transformation 4a (Table 3, entry 6).
Details screening of the reaction parameters are given
in Table 3. Furthermore, the structure of the compound
4c was confirmed by X-ray crystallography analysis
(Supporting Information, Table S1). Figure 7 shows the
ortep diagram of compound 4c.
The catalyst was then successfully utilized for the
synthesis of unsymmetrical 1,3-diynes via cross-
coupling of two different terminal alkynes. First, phe-
nyl acetylene (2a) and cyclohexylacetylene (2c) were
taken as model substrates. The maximum yield 82% of
the desired product 5a was obtained by taking 1:3
molar ratio of 2a and 2c (Table 4). From the experi-
mental result (Table 4), it can be concluded that
alkyne containing electron donating group requires
much more molar ratio than electron withdrawing or
neutral counterpart. When the reaction was conducted
with 4-ethynylanisole and simple phenyl acetylene or
1-ethynyl-4-fluorobenzene, (2:1) molar ratio furnished
the excellent yields (86% and 83%) of the final prod-
ucts 5b and 5c respectively (Scheme 6).
Due to the huge biological and pharmaceutical appli-
cation of benzodiazepines, we aimed to synthesize this
moiety via one pot multicomponent reaction. Along with
this line of thinking, benzoylchloride, phenyl acetylene
and triethyl amine were reacted in the presence of
CuO@rGO at 30 ꢀC for a period of 15–20 min under
SFRC. Then o-phenylenediamine and ethanol were added
to the same vessel and the reaction was continued for at
least 2.0–3.0 hr at 60 ꢀC. Various conditions were applied
to the model reaction to get the best yield and combina-
tion of 0.8 mol % catalyst, triethyl amine (3 equiv.) and
EtOH (3 ml) was found to be most efficient to produce
the maximum yield of the desired product 6a (Table 5,
entry 3). A little deviation from the standard condition,
the lower yield of the expected product 6a (Table 5) was
obtained. After that, various coupling partners like acyl
chlorides and terminal acetylenes bearing electron donat-
ing and with drawing groups were tested with o-phe-
nylenediamines. It was of note that the desired products
TABLE 5
Screening of reaction conditions for the synthesis of 1,5-benzodiazepines
Entry
Catalyst (mol %)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
CuO@rGO (0.8)
Solvent
Temp. (ꢀC)
RT
Time (hr)
24 hr
Product
Yield (%)gg
1
2
3
4
5
6
7
8
9
Free
6a
6a
6a
6a
6a
6a
6a
6a
6a
ND
63
Free
60
2.20 hr
2.20 hr
2.20 hr
2.20 hr
2.20 hr
2.20 hr
2.20 hr
2.20 hr
Ehanol
60
82
Ethanol
70
82
Ethanol
80
82
Water
reflux
reflux
reflux
reflux
56
Dichloromethane
Acetonitrile
Dimethylformamide
27
12
ND
Reaction conditions: Reactions were carried out using 1c (1.2 mmol), 2a (1 mmol), diamine (1.3 mmol), 0.8 mol % of catalyst, CuO@rGO
and ethanol (3 ml).
gYield of isolated pure products.

10 of 12
SARKAR ET AL.
SCHEME 7 Substrate scope for the
preparation of 1,5-benzodiazepines catalyzed
by CuO@rGO. Reaction conditions:
1 (1.2 mmol), 8 (mmol) diamine (1.3 mmol),
were stirred at 60 ꢀC in presence of 0.8 mol %
of catalyst, CuO@rGO and EtOH (3 ml). h
Yieids of isolated pure products
were obtained in good to excellent yield and functional
groups have no effect on the yield of the products
(Scheme 7). The structure of the compound 6a was fur-
ther confirmed by X-ray crystallography (Supporting
Information, Table S1). Figure 8 shows the ortep diagram
of compound 6a.
The leaching test was carried out for the cross cou-
pling of acyl chloride and phenylacetylene (Scheme 3).
The reaction was initially stirred for 10 min. After that,
the reaction mixture was dissolved in chloroform and the
catalyst was removed by filtration. The solvent was then
removed from the reaction mixture and the residue was
stirred again for another 20 min under the same reaction
condition. It was observed that after removing the cata-
lyst product yield was not increased, which in turn
proved that there was no or very negligible leaching of
the catalyst.
The reusability of heterogeneous catalysts plays a
key role in its practical application in many organic
transformations over the homogeneous catalysts. There-
fore, the performance of the recovered catalyst was
investigated and it was observed that the activity of
recovered CuO@rGO remains almost unchanged up to
seventh consecutive runs. The histogram chart of the
reused catalyst showing the corresponding yield of the
reaction up to seven consecutive runs is shown in
Figure 9.
FIGURE 8 Ortep diagram of compound 6a (CCDC 1916396)

SYNTHESIS OF YNONES, 1,3-DIYNES AND 1,5-BENZODIAZEPINES
11 of 12
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3 | CONCLUSION
In conclusion, we have developed new avenues for the
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ACKNOWLEDGMENTS
We thank Science and Engineering Research Board
(SERB, EMR/2016/005089 dated 30.6.2017), Department
of Chemistry of North-Eastern Hill University
(NEHU) and University Grant Commission We are
grateful to Sophisticated Analytical and Instrumenta-
tion Facility (SAIF) and Department of nanotechnology
of North-Eastern Hill University and Department
of CSS,Indian Association of Cultivation of Science
(IACS), Kolkata. We also take this opportunity to
thank Dr. Snehadrinarayan Khatua, Department of
Chemistry, North-Eastern Hill University, Shillong.
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Omega 2018, 3, 7288.
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19, 1576.
ORCID
Rajib Sarkar https://orcid.org/0000-0001-7838-3804
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How to cite this article: Sarkar R, Gupta A,
Jamatia R, Pal AK. Reduced graphene oxide
supported copper oxide nanocomposites: An
efficient heterogeneous and reusable catalyst for
the synthesis of ynones, 1,3-diynes and 1,5-
benzodiazepines in one-pot under sustainable
reaction conditions. Appl Organometal Chem. 2020;
e5646. https://doi.org/10.1002/aoc.5646
SUPPORTING INFORMATION
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in the Supporting Information section at the end of this
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