Microwave assisted one pot three component synthesis of propargylamine, tetra substituted propargylamine and pyrrolo[1,2-: A] quinolines using CuNPs@ZnO-PTh as a heterogeneous catalyst

Article abstract of DOI:10.1039/c8nj00410b

The present work deals with the investigation and catalytic activity analysis of copper nanoparticles (CuNPs) supported on a zinc oxide-polythiophene (ZnO-PTh) nanocomposite. CuNPs@ZnO-PTh was prepared using a simple impregnation method and characterized

Full text of DOI:10.1039/c8nj00410b

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The role of atropisomers on the photo-reactivity and fatigue of
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Microwave assisted one pot three component synthesis of propargylamine,
tetra substituted propargylamine and pyrrolo[1,2-a]quinolines using
CuNPs@ZnO-PTh as a heterogeneous catalyst
Akshara P. Shaha, Anuj S. Sharmab, Shilpa Jaina and Navinchandra G Shimpi a,*
aDepartment of Chemistry University of Mumbai, Santacruz (East), Mumbai-400098, India
bDepartment of Chemistry, School of Sciences, Gujarat University, Ahmedabad-380009, India
Abstract
The present work deals with the investigation and catalytic activity of copper nanoparticles
(CuNPs) supported on Zinc oxideꢀpolythiophene (ZnOꢀPTh) nanocomposite. CuNPs@ZnOꢀPTh
was prepared using simple impregnation method and characterized using various techniques
(XRD, XPS, FTꢀIR, SEM, ICPꢀAES, TEM, TEMꢀEDS and EDAX). HRꢀTEM indicates that
CuNPs supported on ZnOꢀPTh were of spherical in shape and distributed uniformly over the
nanocomposite with particle size ~2ꢀ8 nm. Further, synthesized CuNPs@ZnOꢀPTh was used as a
heterogeneous catalyst for the synthesis of propargylamine, tetra substituted propargylamine (A3
and KA2 coupling reactions) and pyrrolo[1,2ꢀa]quinoline (A3 coupling reactions) using
microwave technique in ethylene glycol as a recyclable, green and biodegradable solvent with
98% yield. The high catalytic activity of CuNPs@ZnOꢀPTh was due to the high surface area and
synergetic effect of both CuNPs and ZnOꢀPTh nanocomposite, which makes it cost effective,
environmentally benign with high atom economy. Considering all above facts, this protocol was
found to be more efficient and sustainable as compared to available commercial methods.
Keywords: CuNPs@ZnOꢀPTh, KA2 and A3 coupling, Heterogeneous catalyst and Reusability
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
*Corresponding author:
Dr. Navinchandra G. Shimpi(navin_shimpi@rediffmail.com)
Phone No: +91ꢀ22ꢀ265435

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Introduction
With increasing environmental concerns and economic considerations, there is a huge demand
for inexpensive and abundant base metals among novel catalytic materials in replacement of
expensive precious metals.1 Among baseꢀmetal nanoparticles, copper nanoparticles (CuNPs)
display unique catalytic reactivity in a wide range of organic transformations such as
hydrogenation2, crossꢀcoupling reactions3, reduction4, azideꢀalkyne cycloaddition5 and oxidation
reactions.6ꢀ7 Copper metal can exists in various possible oxidation states such as Cu0, Cu+1 and
Cu+2 etc. which enables one and two electron transfer mechanism.8 The CuNPs display several
advantages such as highly accessible surface areas and unique quantum effects which are
significant for any catalytic reactions. Generally, CuNPs with smaller sizes are preferred since
particle size of less than 10 nm with a narrow size distribution is believed to be most beneficial
for catalytic efficiency. However, the increase in surface energy with decreasing particle size
certainly causes serious aggregation, thereby leading to inferior performance in practical
applications. The major problem is to stabilize copper nanoparticles and prevent its oxidation and
agglomeration.9 Thus, need of the hour is to develop various support materials which can
stabilize the copper nanocatalyst and also shows higher stability, selectivity and are costꢀ
effective.10 Considering this, ZnOꢀPTh nanocomposite was prepared as support material using
simple impregnation method. Synergistic effect in catalytic activities of ZnOꢀPTh with Cu are
the main reasons for enhancement in catalytic activity along with high surface area.11
Microwave (MW) are known as nonꢀionizing radiations, namely electromagnetic waves that are
composed of mutually perpendicular electric and magnetic fields. MW heating is nonꢀcontact
energy transfer process that alters electromagnetic energy into thermal energy at certain
frequencies, comprising fast heating rates. In addition, electromagnetic energy is effectively
absorbed by the materials under microwave irradiation. In heterogeneous catalyzed organic
reactions, the uses of MW is increasing significantly and playing a crucial role which provides
environmentally benign approach in terms of sustainable chemistry among scientific community.
The main advantages associated with MW are remarkably reduced reaction time, reduced
formation of by products and improved yield with purity of the desired product.12ꢀ13
Presently, the multicomponent coupling reactions became a powerful synthetic tool for the
synthesis of valuable organic compounds by using supported heterogeneous catalyst.14ꢀ15

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However, it was challenging to develop such sustainable and green tool for the synthesis of
multicomponent reaction which follows the green metrics factor such as the higher atom
economy with lowꢀE factor. Environmental factor (Eꢀfactor) is the most important principle in
green chemistry that calculates the total waste amount produced after purification of desired
product. Therefore, researchers have put efforts to design such catalyst, which shows higher
activity, selectivity in green and reusable solvents with excellent reusability up to several cycles
without loss in activity.
Amongst the available multicomponent reactions, significant efforts have been made for the one
pot A3 and KA2 coupling reaction of secondary amine, aldehyde or cyclic ketone and alkyne to
synthesize propargylamines and tetraꢀsubstituted propargylamine.16 Propargylamines were
synthesized traditionally by the amination of propargylic halides, propargylic phosphonates,
propargylic triflates and the nucleophilic addition of in situ generated metal acetylides to imines
and enamines.17ꢀ19 This method had several disadvantages such as poor atom economy,
corrosive, generation of large amounts of waste after the completion of reaction, use of
stoichiometric amounts of reagents which are highly sensitive towards the moisture and it
requires tedious workup procedure during the reaction. Propargylamines has wide applications
and plays a crucial role in various biologically active compounds such as oxazoles, isosters,
oxotremorine analogues and conformational restricted peptides. In addition, it is also used as
intermediate for the production of natural products such as βꢀlactams, herbicides and fungicides.
Propargylamines are useful in synthesis of various drug molecules for treatment of Parkinson’s
and Alzheimer’s disease. Moreover, it shows remarkable biological activity and has been
successfully applied in drugs such as rasagiline which is a potent cardiovascular drug.20ꢀ22
Additionally, among the various propargylamines, amines functional groups present on
propargylamine intermediates were found to be most versatile precursors to develop biologically
important heterocycles such as quinolines, aminoindolizines, pyrrolo[1,2ꢀa]quinolines etc.23 It
was found that the pyrrolo[1,2ꢀa]quinolines is a tricyclic heterocyclic compound mainly found in
natural products with a wide range of biological activities such as antibacterial, antifungal,
apoptosis, anticonvulsant, antiꢀinflammatory, antiꢀleukemic, histamine H3 receptor antagonist
activity, neurological activities and tumour inhibitor against P388 leukaemia (Figure 1).24

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Figure 1 Biologically important pyrrolo[1, 2-a]quinoline containing natural product and
pharmaceuticals
The yield of propargylamine has been improved using various homogenous catalysts such as
Cu(I) pybox complex25, dicopper (I) complex26, FeꢀI2ꢀCuBr27, CuꢀPF6 ligand28, CuCl2 , CuBr30,
29
CuI31 and CuCl.32ꢀ33 However poor reusability, lower stability and water contamination reduces
its applicability in various industries as well as academics. To overcome this limitation, various
heterogeneous catalysts such as CuꢀCMC34, SiO2ꢀNHCꢀCu(I)35, CuNPs@ MS36, CuNPs/TiO2 ,
37
39ꢀ40
Cu(II)/HM38,
CuO/GNS(graphene)43ꢀ44
CuO/Fe2O3
,
Cu(I)ꢀN2S2ꢀsalen/MCMꢀ4141,
CuNPs@Fe3O4NPs/GO45,
Cu(I)ꢀUSY
CuNPs/Montmorllonite46,
(zeolite)42,
,
CuI/TrititanateNanotube47, Cu2O/ZnO48 and Cu/Alꢀoxide49 etc. are used for A3 as well as KA2
coupling reactions. Xiong et al. developed oyster shell waste supported CuCl2 catalyst and
investigated its activity towards A3 coupling under the microwave irradiations.50 Nevertheless,
the issues of recyclability reduced its applicability. Recently, Ermolatev et al. reported
microwave assisted decarboxylative coupling of 2ꢀoxaacetic acid, an amine and alkyne to form
polyꢀsubstituted propargylamine using CuBr as catalyst. However, both methods required high
amount of catalyst loading (15 mol%) and recyclability issues, which makes this protocol less
sustainable and accessible.51 Tu et al. reported an efficient tool to synthesize propargylamine
under microwave irradiation using CuI catalyst.52 Similarly, Kaur et al. reported microwave
assisted synthesis of propargylamine by employing CuNPs supported on nitroꢀfunctionalized

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polystyrene resin (NPS). This catalyst gave higher yield of propargylamine in sorter reaction
time. However, the utilization of toluene as solvent and higher copper loading was required for
higher yield of product.53
Herein, we report, synthesis and catalysis of CuNPs@ZnOꢀPTh nanocomposite for A3 and KA 2
coupling reactions for the synthesis of propargylamines, tetra substituted propargylamine and
pyrrolo[1,2ꢀa]quinolines using microwave technique. This synthetic protocol may offer potential
route using catalytic amount as well as acts as a versatile, heterogenous and recyclable catalyst,
which shows higher yield and high atom economy.
Experimental
Materials and method
All chemicals and reagents were purchased from commercial sources and used without further
purification. Reactions were performed in a microwave at 100ºC. Column chromatography was
carried out using silica gel (230ꢀ400 mesh). Thin layer chromatography was performed using
Merck silica gel 60 F254 plates (TLC) and components were visualized using UV (254 nm).
Melting points were taken in open capillaries and are uncorrected. The crystalline or amorphous
nature of ZnO, ZnOꢀPTh and CuNPs@ZnOꢀPTh was analysed using powder Xꢀray
diffractometer (Shimadzu, Maxima 7000 S) using CuKα (λ=1.5418 Å and1.6 kW Xꢀray tube
with applied voltage of 40 kV and current values of 40 mA) radiation from 10 to 80º 2θ range at
scanning speed of 5º minꢀ1. Diffraction peaks of crystalline phases were compared with standard
JCPDS data files. XPS data was obtained using monochromatic aluminium with an Al Kα
(1486.6 eV) with Xꢀray source operating at a vacuum of 10ꢀ7 Pa. All the binding energy values
were calibrated using C1 s line of 284.7 eV. Isolated products were confirmed using Fourier
transform infrared (FTIR) spectroscopy recorded on Perkin Elmer, Frontier equipment.
Morphology and particle size of the samples were investigated on field emission scanning
electron microscope (FESEM, Hitachi Sꢀ4800, Japan). Inductively coupled plasma atomic
emission spectroscopy (ICPꢀAES) analysis was carried out on a HJY Ultimaꢀ2 instrument: 1000
W, nebulizer pressure 2.96, nebulizer flow 1.29, wavelength 242.795 nm. A JEOL JEM 2100
instrument was used for particle size measurements through transmission electron microscopy
1
13
(TEM) as well as energy dispersive atomic Xꢀray analysis (EDAX). H and CNMR (300Hz)

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was recorded on Bruker ADVANCE II using TMS as internal standard in CDCl3. ESI Mass
spectra of representative compounds were recorded on a Waters UPLCꢀTQD Mass spectrometer.
Synthesis of ZnO nanorods
Zinc chloride (ZnCl2) (1.0 M), NaOH (4.0 M) and sodium dodecyl sulphate (SDS) (0.2 M)
solutions were prepared in deionized water respectively. According to the molar ratio of
Zn2+/OH−, NaOH (4M) was added dropꢀwise into 1M ZnCl2 (20mL) aqueous solution with
intense magnetic stirring at 3°C. Further, 5mL SDS (0.2 M) and 40mL distilled water were
introduced into the above mixture to get a 100mL clear solution. Thereafter, the solution was
kept at room temperature for 1.5 hours under vigorous stirring to obtain white precipitate.
Subsequently, the solution was transferred to groundꢀglass stopped conical flask and aged at
85°C for 5h. The precipitate deposited on the bottom of the conical flask were collected by
centrifugation and repeatedly washed with water and ethanol. Precipitates obtained were dried at
60°C in vacuum oven54.
Synthesis of ZnO- PTh nanocomposite
ZnO NRs (1 gm) were dispersed in chloroform (20 ml) and sonicated for 30 min. Further 1.6 ml
(0.02 mol) of thiophene was added in ZnO NRs solution and stirred for 30 min with dropꢀwise
addition of FeCl3 solution prepared in chloroform. The ratio of FeCl3 to thiophene was taken as
3:1. Further the solution kept for next 24 h at room temperature under controlled stirring. The
obtained composite was filtered and washed multiple times with water to remove unreacted
oxidising agent. Further, composite was washed with methanol to convert it into reduced state
(black to red). The obtained precipitate was dried in hot air vacuum oven at 50°C for 4 h.55
Synthesis of CuNPs@ZnO-PTh
ZnOꢀPTh nanocomposite (1.0 g) was dissolved in deionised water (20 ml) with constant stirring.
CuNO3.3H2O (1.0 mmol) solution prepared in deionised water was added dropꢀwise to the
solution of ZnOꢀPTh. While stirring, hydrazine hydrate (2.0 mmol) was added slowly and
solution was kept under constant magnetic stirring for 4 h. The resulting colloidal suspension
was centrifuged and washed multiple times using deionised water. Further, the as obtained
catalyst was dispersed in water (10 ml) and stored under inert condition.

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General reaction procedure for A3 and KA2 coupling catalyzed by Cu NPs@ ZnO-
PTh
A mixture of aldehydes (1.0 mmol) or cyclic ketones (1.0 mmol), secondary amines (1.0 mmol),
acetylenes (1.0 mmol), CuNPs@ ZnOꢀPTh (20 mg) and ethylene glycol (2ml) were added to a
10ml CEM vial and stirred at 80oC for 15 minutes. After completion of reaction (monitored by
TLC) reaction mixture was centrifuged and filtered. Then, the reaction mass was dissolved in
ethyl acetate. The ethyl acetate layer was washed with water (3 x 10ml) and brine (1 x10 ml) and
treated with dried anhydrous Na2SO4. The reaction mixture was concentrated under vacuum and
crude reaction mass was purified by column chromatography using hexaneꢀethyl acetate as the
eluent.
Results and discussion
Characteristics of ZnO-PTh
ZnOꢀPTh nanocomposite was selected as support for deposition of CuNPs. Polymeric materials
have been effectively used as a promising support for the stabilization of metal nanoparticles
with control over size distribution. The purpose of using support of ZnOꢀPTh is to make the
CuNPs free from aggregation, as aggregation leads to decrease in surface to volume ratio, which
ultimately decreases its catalytic properties.56 Polythiophene is an organic conducting polymer
with good chemical stability, mechanical strength and bioꢀcompatibility. While, ZnO is a wellꢀ
known nꢀtype semiconductor with band gap of 3.37 eV. This inorganicꢀorganic hybrid structure
exhibits excellent physicochemical properties resulting from synergistic effect of individual
properties of semiconducting metal oxide (ZnO) and conducting polymer (PTh). Interactions
occurring at molecular levels and nanoꢀmeter size control of these hybrid materials leads to an
efficient electronꢀtransfer reaction which is crucial for any catalytic process. The wellꢀdispersed
ZnOꢀPTh nanocomposites were produced in a single reaction step. This method has several
advantages over existing techniques as it does not require templates and large amount of organic
solvents. Synthesized composites were used as a support for Cu nanoparticle as shown in Figure
2.

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Figure 2 Schematic representation for the synthesis of CuNPs@ZnO-PTh
Characterization of CuNPs@ZnO-PTh
The synthesized CuNPs@ZnOꢀPTh catalyst was thoroughly characterized by various
sophisticated analytical techniques such as, XRD,XPS, FTꢀIR, FESEM, TEM, EDS and EDAX.
XRD of ZnO NRs shows similar diffraction peaks, which corresponds to hexagonal wurtzite
phase (JPCDS 36ꢀ1451, Figure 3a).57 Average particle size was calculated using Scherrer’s
formula and found to be ~25 nm. However, diffraction peak of ZnO was absent in ZnOꢀPTh
nanocomposite and only broad diffraction peak was observed at 2θ= 15ꢀ25º(Figure 3b).The ZnO
peak gets disappeared completely in ZnOꢀPTh nanocomposite since ZnO gets embedded into
PTh chains, thus affecting the detection of crystal diffraction.54 Figure 3c shows the diffraction
pattern of CuNPs@ZnOꢀPTh, peaks observed at 43.52°, 50.64º and 74.35° corresponds to (111),
(200), and (220) planes of fcc structure of pure Cu (JCPDS no. 71ꢀ4610), while peaks of lesser
intensity before 43.52o matches with ZnOꢀPTh (Figure 3c).58ꢀ59 This suggests that CuNPs were
decorated over the surface of ZnOꢀPTh support.

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Figure 3 XRD of (a)ZnO, (b)ZnO-PTh and (c) CuNPs@ZnO-PTh
The oxidation state and surface property of copper nanoparticles supported on ZnOꢀPTh
nanocomposite and its elemental composition was investigated by Xꢀray photoelectron
spectroscopy. The survey spectra revealed the presence of Cu 3p, O 1s, C 1s, Zn 2p and S 2p
with binding energies at 932.05 eV, 530.6 eV, 286 eV and 163.2 eV respectively. (Figure S1,
See ESI). The deconvoluted C1s binding energy spectrum was fitted into three peaks at around
284.6 eV, 286.2 eV and 288 eV, which can be attributed to CꢀC, CꢀS, C=C bonding, respectively
(Figure S2,See ESI). The XPS spectrum for Zn 2p coreꢀlevel consisting of Zn 2p3/2 and 2p1/2
peaks at 1021.28 eV and 1044.45eV, attributed to Zn2+ valance state (Figure S3, See ESI).60 The
O1s peak appeared at 530.10 eV was due to the presence of CuꢀO bond (Figure S4, See ESI). In
addition, peak observed at 531.53 eV was due to oxide ions that are surrounded by Zn atoms.

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The Zn 2p XPS spectrum was broad and asymmetric. The deconvoluted S 2p peak indicates the
presence of 2p3/2 (164.1 eV) and 2p1/2 (165.3 eV) with a separation of 1.2 eV and the relatively
high energy broad tail produced by positively charged sulphur within the thiophene ring (Figure
S5, ESI). Further studies on XPS confirmed the presence of both Cu2+ and Cu reduced species as
clearly visualized in Cu 2p XPS experiment (Figure 4). The presence of a shakeꢀup peak (about
940ꢀ945 eV) was characteristic of Cu2+ species, particularly of CuO (in the absence of Cu2+)
61
species, no shakeꢀup peaks can be visualized , which is in good agreement with XRD results.
The presence of lower Cu 2p3/2 binding energy peaks (932.05 eV) indicates the existence of
reduced copper species.62 However, the distinction between Cu+ and Cu0 species (that appear at
very similar binding energies) was only feasible through examination of the Auger spectra.63
Figure 4 Deconvoluted XPS spectrum of Cu 2p
Figure 5 represents FTꢀIR spectra of a) ZnO, b) ZnOꢀPTh and c) CuNPs@ZnOꢀPTh respectively.
The peaks observed at 3200ꢀ3600 cmꢀ1 corresponds to OꢀH mode of vibration. Between 1566 and
1547 cmꢀ1, strong asymmetric stretching mode of vibration of C=O was observed (Figure 5a). In
ZnOꢀPTh nanocomposite, a broad band appears ~ 3423 cmꢀ1 which corresponds to the OꢀH
stretching vibration. The bands observed at 2923 cmꢀ1 corresponds to CꢀH stretching vibration
while bands at 1640 cmꢀ1 and 1426 cmꢀ1 indicate asymmetric and symmetric stretching vibrations

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of thiophene units, respectively. The band at 1167 cmꢀ1 and 790 cmꢀ1 can be assigned to CꢀH (inꢀ
plane) and CꢀH (outꢀofꢀplane) bending vibration of thiophene units, which indicates the αꢀ
position linkage between the thiophene rings. Moreover, the bands observed at 830 cmꢀ1 and 692
cm−1 may be assigned to CꢀS stretching and CꢀSꢀC bending vibrations indicating the presence of
thiophene rings.55 Figure 5b indicates the presence of ZnO in hybrid material indicated by a new
band centred at 488 cmꢀ1 which associates with ZnꢀO stretching. Similar peaks were observed in
CuNPs@ZnOꢀPTh nanocomposite.
Figure 5 FT-IR of (a) ZnO, (b)ZnO-PTh and (c)CuNPs@ZnO-PTh
To evaluate the specific surface area, the nitrogen sorption measurement was carried out.
Specific surface area was found to be 19.26, 35 and 71.03 m2g−1 respectively for ZnO, ZnOꢀPTh
and CuNPs@ZnOꢀPTh nanocomposite. In BET equation, when P/P0 ≪ 1 and c ≫ 1, it leads to
monolayer formation and Type I adsorption isotherm was obtained. The sorption exhibits type I
isotherm, which indicated monolayer adsorption in our case. High surface area of CuNPs@ZnOꢀ
PTh nanocomposite leads to more active sites per unit volume, which increases catalytic
efficiency. Thermal stability study was done using TGA (Figure S6, See ESI). As indicated by
thermogram, thermal stability of nanocomposite increased with incorporation of CuNPs into

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ZnOꢀPTh matrix. Catalyst doesn’t show any air or moisture sensitive nature, therefore no extra
care was taken in order to store or handle the catalyst in recovery process. 64ꢀ65
Figure 6 shows FESEM images of a) ZnOꢀPTh and b) CuNPs@ZnOꢀPTh with sheet like
structure with size in range ~200 nm (ZnOꢀPTh) and ~50 nm (CuNPs@ZnOꢀPTh) respectively.
It was observed that size of nanocomposite decreases significantly with impregnation of CuNPs,
which leads to increase number of active sites per unit area. Therefore, it’s catalytic activity
increases effectively. FESEM indicates that CuNPs have been distributed uniformly over the
ZnOꢀPTh support, which can also be reflected from XRD pattern (Figure 3c). The amount of
CuNPs loaded into the ZnOꢀPTh material was investigated using ICPꢀAES analysis. In this
proces, CuNPs@ZnOꢀPTh(500 mg) was incinerated in a crucible at 550 ˚C for 2h. Further, the
obtained residue was dissolved in aqua regia (1 ml) and diluted using distilled water (5 ml). The
average concentration of copper (3 trials) as determined from ICPꢀAES was found to be 0.13
mol% of copper.
Figure 6 SEM images of (a) ZnO-PTh and (b) CuNPs@ZnO-PTh
Figure 7 represents TEM and HRꢀTEM of CuNPs@ZnOꢀPTh catalyst, respectively. It was
observed that CuNPs were spherical in shape and dispersed uniformly into ZnOꢀPTh support.
The size was observed to be ∼2ꢀ8 nm. HRꢀTEM also supports the results of TEM i.e. CuNPs
dispersed uniformly over the ZnOꢀPTh support. Moreover, lattice fringes with the crystal lattice

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spacing of CuNPs having size 0.207 nm. The presene of Cu with uniform distribution of CuNPs
into ZnOꢀPTh was observed on EDS mapping as well as EDAX spectra (Figure 8 and 9).
Figure 7 TEM and HR-TEM images of CuNPs@ZnO-PTh
Figure 8 TEM-EDS mapping of C, O, S, Cu and Zn present in CuNPs@ZnO-PTh material

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Figure 9 EDX spectra of CuNPs@ZnO-PTh
Catalytic performance of CuNPs@ZnO-PTh as a heterogeneous catalyst for one pot
three component A3coupling reactions
The intial evaluation of the catalytic activity was started with the coupling reaction of aldehydes,
secondary amines and terminal acetylenes under microwave irradiation to afford
propargylamines as shown in Scheme1. The performance of supported metal nanocatalyst in
organic reactions mainly depends upon the accessibility of the available catalytic sites, which
mostly depends on the nature of support material, polarity of substrate as well as solvents. To
study the optimized reaction conditions, a model reaction of benzaldehyde, piperidine and phenyl
acetylene was performed under microwave using CuNPs@ZnOꢀPTh catalyst in the presence of
various solvents at 80°C to afford the corresponding propargylamine as shown in Table 1.
Scheme 1 Cu NPs@ZnO-PTh Catalyzed Synthesis of Propargylamines via A3 Coupling
Reaction.
The obtained product shows lower yield in polar solvents such as ethanol, acetone (47ꢀ54%)
(Entries 1ꢀ2, Table 1). However, yield increased up to 64ꢀ87% in case of DMF, acetonitrile,
Toluene and 1,4ꢀdioxane solvents (Entries 3ꢀ6, Table 1). Further the reaction was carried out in

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solvent free conditions, which showed poor conversion (25%). This can be attributed to the fact
that most of catalyst material was stuck on the surface of microwave vials (Entry 8, Table 1).
Interestingly, the desired product was obtained with 98% yield in ethylene glycol (EG) (Entry 7,
Table 1). With these interesting observations, we studied the effect of temperature (entry 9ꢀ12,
Table 1) and CuNPs@ZnOꢀPTh catalyst dose (Entry 14ꢀ16, Table 1) on the yield of product. In
absence of catalyst, trace conversion was observed (Entry 13, Table 1). The present model
reaction was carried out with copper nanoparticles alone as a catalyst. However, the lower yield
of product was observed. This is mainly due to the unstability and agglomeration of the
nanoparticles during the reaction (Entry 17, Table 1). Furthermore, the reaction was also
performed in the presence of ZnOꢀPTh support material alone as a catalyst. However, the trace
yield of product was obtained (Entry 18, Table 1). The results shows that the usage of 20mg of
CuNPs@ZnOꢀPTh catalyst at 80˚C in EG was sufficient to obtained the highest yield of desired
product in minimum reaction time (98 %, 15 min) (Entry 12, Table 1).
Table 1 Optimization reaction condition for CuNPs@ZnO-PTh catalyzed A3 coupling
reactiona
Entry Catalyst (mg)
Solvent
Time (min) Temp( ˚C) Yield (1)(%)

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1
2
20
20
20
20
20
20
20
20
20
20
20
20
ꢀ
EtOH
Acetone
DMF
Acetonitrile
Toluene
1,4ꢀdioxane
EG
15
15
15
15
15
15
15
15
30
30
25
15
15
15
15
15
15
30
80
80
80
80
80
80
80
80
50
60
70
80
80
80
80
80
80
80
54
47
3
64
4
75
5
85
6
87
7
8b
98
ꢀ
25
9
EG
47
10
11
12
13c
14
15
16
17d
18e
EG
62
EG
75
EG
98
EG
Trace
45
05
10
15
20
20
EG
EG
61
EG
85
EG
25
EG
Trace
a Reaction conditions: Benzaldehyde (1.0 mmol), Piperidine (1.0 mmol), Phenyl acetylene
b
c
d
(1.0 mmol), Catalyst (mol %), = Solvent free conditions, = Absence of catalyst,
Presence of Cu NPs, e = Presence of ZnOꢀPTh.
=
The scope of the present protocol for the synthesis of propargylamine was also investigated. The
different derivatives of propargylamine were synthesized (Table 2). It was observed that the
reaction was uniform, irrespective of the nature of the substituents (electron withdrawing or
electron donating) on the aromatic ring. A wide range of aldehyde substituents having functional
groups –X (Br, Cl, I), ꢀOH, –CH3, ꢀOCH3, ꢀNO2 and ꢀN(CH3)2 were found to be compatible with
this procedure. Almost all screened substrates undergone A3 coupling easily and effectively to
obtain the corresponding yield of products. Moreover, the furfuraldehyde (Entry 10, Table 2) and
vaniline (Entry 6, Table 2) gave an excellent product in minimal reaction time. Different amines
such as piperidine (Entry1, Table 2), pyrrolidine (Entry 11, Table 2) and morpholine (Entry 12,
Table 2) were gave higher yield of propargylamines. Acetylenes derivatives (electron

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withdrawing and electron donating) were also tried for the synthesis of propargylamine, which
gave the corresponding products yield of 95ꢀ99% (Entry 13ꢀ15, Table 2). Cyclopropane also
1
gave good yield (Entry 16, Table 2). All the products were characterized using H NMR and 13C
NMR spectra. Some of the products were also characterized by Mass Spectra, which are
summarized in supporting information.
Table 2 Scope of the CuNPs@ZnO-PTh catalyst for the synthesis of Propargylamines
Entry R (Benzaldehyde)
R1 (Amine)
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Pyrrolidine
Morpholine
Piperidine
Piperidine
Piperidine
Piperidine
R2 (Alkyne)
Yield (%)
99
1
Ph
4ꢀBrꢀC6H4
4ꢀClꢀC6H4
4ꢀOHꢀC6H4
4ꢀNO2ꢀC6H4
4ꢀOHꢀ3ꢀOMeꢀC6H3
4ꢀIꢀC6H4
4ꢀOCH3ꢀC6H4
4ꢀN(CH3)2ꢀC6H4
C4H3O
Ph
2
Ph
98
3
Ph
97
4
Ph
95
5
Ph
98
6
Ph
99
7
Ph
71
8
Ph
Ph
74
9
96
10
11
12
13
14
15
16
Ph
96
Ph
Ph
95
Ph
Ph
92
Ph
4ꢀBrꢀC6H4
4ꢀNO2ꢀC6H4
4ꢀCH3OꢀC6H4
C3H5
99
Ph
97
Ph
95
Ph
78
Reaction conditions: Aldehyde (1.0 mmol), Acetylene (1.0 mmol), Secondary amine (1.0
mmol), Catalyst (20 mg), 5 mL Ethylene Glycol, 15 min, 100W.

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Catalytic performance of CuNPs@ZnO-PTh towards one pot three component KA2
coupling reactions
Next, we investigated the catalytic activity of the CuNPs@ ZnOꢀPTh catalyst for the coupling
reaction of cyclic ketone, secondary amines and terminal acetylenes under microwave irradiation
to afford tetrasubtituted propargylamines as shown in Scheme 2. To study the optimized reaction
conditions, a model reaction of cyclohexanone, piperidine and phenyl acetylene was performed
under microwave using CuNPs@ZnOꢀPTh catalyst in the presence of various solvents at 80°C to
afford the tetrasubstituted propargylamine (2) shown in Table 3.
Scheme 2 Cu NPs@ZnO-PTh Catalyzed synthesis of tetrasubstituted propargylamines via
KA2 Coupling Reaction
It was observed that the polar solvents such as ethanol, methanol and water gave poor yield of
product (25ꢀ47%) (Entries 1ꢀ3, Table 3). The yield of product was increased up to 55ꢀ82% in
DMF, acetonitrile and 1,4ꢀdioxane (Entries 4ꢀ6, Table 3). However, the reaction was also carried
out in solvent free conditions, which shows poor yield of products (Entry7, Table 3). The best
yield (98%) of the desired product was achieved in ethylene glycol (EG) (Entry 8, Table 3). The
effect of various parameters such as temperature (Entries 9ꢀ12, Table 3) and catalyst
concentration (Entries 14ꢀ17, Table 3) were well studied. However, in the absence of the
catalyst, only trace conversion was found (Entry 13, Table 3). The model reaction was also
carried out with Cu NPs. However, poor yield was observed (Entry18, Table 3). In addition, the
support material such as ZnOꢀPTh alone use as a catalyst; the trace yield of product was
observed (Entry 19, Table 3). Thus, the results shows that the usage of 25mg of CuNPs@ZnOꢀ
PTh catalyst dose at 80˚C in EG was sufficient to obtained highest yield of tetrasubstituted
propargylamine in minimum period of time (98 %, 15 min) (Entry 8).

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Table 3 Optimization reaction conditions for CuNPs@ZnO-PTh catalyzed KA2 coupling
reactiona
Entry
1
Catalyst (mg)
Solvent
EtOH
MtOH
H2O
DMF
Acetonitrile
1,4ꢀdioxane
ꢀ
Time (min)
T ( ˚C)
80
80
80
80
80
80
80
80
50
60
70
80
80
80
80
80
80
80
80
Yield (2) (%)
25
25
25
25
25
25
25
25
25
25
25
25
ꢀ
05
10
15
20
25
25
15
15
15
15
15
15
15
15
35
30
20
15
15
15
15
15
15
15
30
43
47
25
55
67
82
15
98
45
71
80
98
Trace
42
62
85
90
32
2
3
4
5
6
7b
8
EG
EG
EG
EG
EG
EG
EG
EG
EG
EG
EG
EG
9
10
11
12
13c
14
15
16
17
18d
19e
Trace
aReaction conditions: Cyclohexanone (1.0 mmol), Piperidine (1.0 mmol), Phenyl acetylene (1.0
mmol), Catalyst (mol %), b = Solvent free conditions, c = Absence of catalyst, d = Presence of Cu
NPs, e = Presence of ZnOꢀPTh.
We expanded the scope of present catalyst CuNPs@ZnOꢀPTh for the synthesis of
tetrasubstituted propargylamines from the reaction using various substrates such as
cyclohexanone, cyclopentanone and secondary amines including piperidine, morpholine,
pyrrolidine with various substituted phenyl acetylene in our optimization reaction conditions. It
was also found that almost all screened secondary amine underwent KA2 coupling smoothly to

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afford the corresponding products in 95ꢀ98% yields. Further, the substituted phenyl acetylene
gave higher yield of product (94ꢀ96%). However, the reaction proceeded slowly in case of
cyclopropyl acetylene (Entry 9, 11, Table 4).
Table 4 Scope of the CuNPs@ZnO-PTh catalyst for the synthesis of tetra substituted
Propargylamines
Entry
Cyclic Ketone
Cyclohexanone
Cyclohexanone
Cyclohexanone
Cyclopentanone
Cyclopentanone
Cyclopentanone
Cyclopentanone
Cyclohexanone
Cyclohexanone
R1 (Amine)
Piperidine
Pyrrolidine
Morpholine
Piperidine
Pyrrolidine
Morpholine
Piperidine
Piperidine
Piperidine
R2 (Alkyne)
Yield (%)
1
2
3
4
5
6
7
8
9
Ph
96
94
95
96
95
94
96
95
85
Ph
Ph
Ph
Ph
Ph
4ꢀCH3OꢀC6H4
4ꢀCH3ꢀC6H4
C3H5
10
Cyclopentanone
Piperidine
4ꢀCH3ꢀC6H4
97
11
12
Cyclopentanone
Cyclopentanone
Piperidine
Piperidine
C3H5
78
95
4ꢀCH3OꢀC6H4
Reaction conditions: Cyclic ketone (1.0 mmol), Secondary amine (1.0 mmol), Alkyne (1.0
mmol), Catalyst (25 mg), 5 mL Ethylene Glycol, 15 min, 100W.
Catalytic performance of CuNPs@ZnO-PTh towards the synthesis of pyrrolo[1, 2-a]
quinoline
To achieved the excellent catalytic performance of the present catalyst towards the A3 and KA2
coupling reaction, we further extended the versatility of CuNPs@ZnOꢀPTh catalyst for the

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synthesis of pyrrolo[1, 2ꢀa]quinoline as represented in Scheme 3. A model reaction of quinolineꢀ
2ꢀcarboxaldehyde, piperidine, phenyl acetylene was used to synthesized pyrrolo[1, 2ꢀa]
quinoline. To optimize the reaction condition, various solvents were screened at 100˚C in a
model reaction as shown in Table 5.
Scheme 3 Cu NPs@ZnO-PTh Catalyzed Synthesis of Pyrrolo[1, 2a]quinoline via A3
Coupling Reaction.
In the presence of acetone, methanol, ethanol, a mixture of pyrrolo[1, 2ꢀa]quinoline (A) and
chalcone (B) were obtained (entries 2ꢀ4, Table 5). However, the chalcone formed more
exclusively in case of solvent free conditions and H2O in 55% and 50% yield respectively
(Entries 1, 6, Table 5). To our delight, the selectivity in formation of desired product (A) was
observed in the presence of DMF, acetonitrile, 1,4ꢀdioxane and EG (Entries 5, 7ꢀ9, Table 5). The
presence of catalyst was necessary for the progress of the reaction, as in its absence no reaction
occurred (Entry 15, Table 5). The model reaction was performed with Cu NPs. However, poor
conversion was observed (Entry 19, Table 5). In addition, the following reaction was also
performed with ZnOꢀPTh, the trace amount of chalcone was obtained along with moderate yield
of pyrrolo[1, 2ꢀa]quinoline formation under optimized condition (Entry 20, Table 5).

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Table 5 Optimization reaction conditions of synthesis of pyrrolo[1, 2-a]quinoline catalyzed
by CuNPs@ZnO-PTha
Entry Catalyst(mg)
Solvent
ꢀ
Time (min) Temp (˚C) Yield (%) (3) Yield (%) (4)
1b
20
20
20
20
20
20
20
20
20
20
20
20
20
20
ꢀ
30
30
30
30
30
30
30
30
30
45
40
40
30
30
30
30
30
30
30
40
100
100
100
100
100
100
100
100
100
60
ꢀ
15
55
45
19
15
ꢀ
2
Acetone
MeOH
EtOH
DMF
H2O
3
54
4
58
5
64
6
ꢀ
50
ꢀ
7
Acetonitrile
1,4ꢀdioxane
EG
75
8
87
ꢀ
9
98
-
10
11
12
13
14
15c
16
17
18
19d
20e
EG
42
ꢀ
EG
70
65
ꢀ
EG
80
72
ꢀ
EG
90
87
ꢀ
EG
100
100
100
100
100
100
100
98
ꢀ
EG
Trace
45
ꢀ
05
10
15
20
20
EG
ꢀ
EG
64
ꢀ
EG
82
ꢀ
EG
24
ꢀ
EG
Trace
ꢀ
aReaction conditions: Quinoline 2ꢀcarboxaldehyde (1.0 mmol), Piperidine (1.0 mmol), Phenyl
acetylene (1.0 mmol), Catalyst (mol %), b = Solvent free conditions, c= Absence of catalyst.
d = Presence of Cu NPs, e = Presence of ZnOꢀPTh.

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The generality of CuNPs@ZnOꢀPTh catalytic system was studied for the synthesis of variety of
pyrrolo[1,2ꢀa]quinoline derivatives from the reaction among various substrates such as
quinolineꢀ2ꢀcarboxaldehyde, phenyl acetylenes and secondary amines under optimized reaction
conditions as summarized in Table 6. The results indicates that the all screened substrates
underwent smooth cycloisomerization to afford the pyrrolo[1, 2ꢀa]quinoline with excellent yield
(85ꢀ99%) (Table 6).
Table 6 Scope of the CuNPs@ZnO-PTh catalyst for the synthesis of pyrrolo[1, 2-a]
quinoline
Entry
R1 (Amine)
R2 (Alkyne)
Yield (%)
1
2
3
4
15
6
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Pyrrolidine
Morpholine
Ph
4ꢀBrꢀC6H4
4ꢀNO2ꢀC6H4
C3H5
4ꢀOCH3ꢀC6H4
4ꢀCH3ꢀC6H4
Ph
98
90
85
90
99
99
95
92
7
8
Ph
9
4ꢀCyclohexyl Piperidine
Ph
94
Reaction conditions: Quinoline 2ꢀcarboxaldehdye (1.0 mmol), Acetylene (1.0 mmol),
Secondary amine (1.0 mmol), Catalyst (20 mg), 5 mL EG, 30 min, 100 W.
Proposed reaction mechanism for CuNPs@ZnO-PTh catalyzed synthesis of pyrrolo
[1,2a]quinolines
Based on the literature reports, we proposed the mechanism for three component one pot
synthesis of propargylamine over CuNPs@ZnOꢀPTh nanocomposite. The probable reaction
mechanistic scheme was pictorially illustrated in Scheme 4. In step I, it was proposed that Cu

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nanoparticles on ZnOꢀPTh support activate the C–H bond of the acetylenic substrate to generate
a copperꢀacetylide complex on the surface of ZnOꢀPTh support23. This was indeed a very
favourable step because copper is well known to exhibit high alkynophilicity for terminal
alkynes. In step II, the copperꢀacetylide complex reacts with iminium ions that were generated
in-situ from the reaction between aldehyde and secondary amine, to give corresponding 2ꢀ
quinolinyl propargylamine intermediate. The cycloꢀisomerization of intermediate (III) can be
promoted by copper active sites of CuNPs@ZnOꢀPTh to afford the desired product. The catalytic
activity of CuNPs@ZnOꢀPTh may be due to the synergistic effect of both Cu nanoparticle and
ZnOꢀPTh active site. The CuNPs@ZnOꢀPTh catalyst gets regenerated which further enabled
catalytic cycles to continue till the completion of the reaction. Moreover, the synergistic effect of
both the ZnOꢀPTh and CuNPs was responsible for its excellent catalytic activity.
Scheme 4 Plausible reaction mechanism for the one pot synthesis of propargylamines using
CuNPs@ZnO-PTh catalyst
Green chemistry metrics
The green chemistry metrics are the important parameter for the evaluation of green and
sustainable reaction. The green chemistry metrics for all three model reactions to form
propargylamine (1), tetra substituted propargylamine (2) and pyrrolo[1, 2ꢀa]quinoline (3) were
calculated and the results were represented in Table 4 (Calculation provided in ESI). The results

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indicated that the values of green chemistry metrics such as Eꢀfactor, process mass intensity
(PMI), reaction mass efficiency (RME), atom economy (AE), and carbon efficiency (CE) were
almost close to their ideal values.66ꢀ67
Table 7 Quantification of Green chemistry metrics for the product (1), (2) and (3)
No
1
Green Chemistry Metrics
Eꢀfactor
Ideal value Product (1) Product (2)
Product (3)
0.075
0
0.0892
1.089
92 %
94%
0.087
1.087
92 %
94 %
98 %
2
Process mass intensity (PMI)
Reaction mass efficiency (RME)
Atom economy (AE)
1
1.075
3
100 %
100 %
100 %
93 %
4
95 %
5
Carbon efficiency (CE)
98 %
98 %
Recyclability
The catalyst separation and its reusability were the most important parameters for an ideal
heterogeneous catalytic system that made the protocol more economical and sustainable over
homogeneous catalysts. The recyclability of CuNPs@ZnOꢀPTh catalysts has been evaluated for
the synthesis of propargylamine (A3 coupling) under the optimised reaction conditions. (Figure
10).

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Figure 10 Recycling of CuNPs@ZnO-PTh catalyst in the A3 coupling
The catalyst was recovered after the completion of reaction by using centrifugation method and
washed with hot distilled water and methanol to remove the absorbed products. After that, it was
dried under vacuum and further reused to check its catalytic activity. The catalytic property of
nanocomposite was studied for five consecutive cycles without any significant loss in product
yield. It has been noted that in first four cycles, the loss of its activity was negligible. After the
fifth cycle, there was a slight reduction of 3 % from the initial catalytic activity which indicates
sustainability of nanocomposites. TEM analysis of the recycled catalyst was another important
technique to ascertain the particle size of metal nanoparticles after the reaction.TEM images of
the recovered catalyst after the fifth cycles shows that most of the particles were still in the size
range of 2ꢀ7 nm. However, some bigger particles and slight agglomeration of copper
nanoparticles was also found within the size range of 10ꢀ15 nm (Figure 11). This implies that,
growth occurs by copper nanoparticles migration and coalescence that was mostly viable at the
exposed surface of ZnOꢀPTh nanocomposite.

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Figure 11 TEM and HR-TEM images of recycled CuNPs@ZnO-PTh catalyst
Comparison of catalytic activity of supported copper nanoparticles towards the synthesis of
Propargylamine
The catalytic activities of CuNPs@ZnOꢀPTh for the synthesis of propargylamine with that of
previous work related to copper based catalyst with different supports are compared (Table 8). It
was observed that the yield of propargylamine achieved using this catalyst was comparable to
those reported earlier in literature. The solvent used for this protocol was biodegradable and
reusable. Furthermore, the minimum reaction time was required to afford higher yield of
propargylamine. Present work reports only 0.0052 % of Cu (25 mg of Cu NPs/ZnOꢀPTh) which
is substantially low as compared to other catalysts.
Table 8 Comparison of catalytic activity of copper nanoparticles deposited on different
supports
Entry
Catalyst
Cu
(Mol %)
0.3
Solvent
Temp
(ºC)
60
70
82
100
110
60
110
70
Time Yield
(%)
Ref.
1
2
3
4
5
6
7
8
Cu NPs/MS
Cu NPs/TiO2
CuO/GNS
THF
Neat
Acetonitrile
Toluene
Toluene
CHCl3
20 h
7 h
96
98
89
98
96
97
98
85
36
37
43
53
68
69
46
70
0.5
0.7
5 h
Cu/Nitro Resin
Cu NPs/MOFꢀ5ꢀC
Cu/PMOꢀIL
Cu/Montmorillonite
Cu/NCNTs
0.0037
9.7
0.15
0.05
0.004
25 min
6 h
24 h
3 h
Toluene
THF
4ꢀ6 h

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9
10
Cu/Graphene
Cu NPs/ZnO-PTh
2.6
0.0052
Toluene
100
80
24 h
15 min
96
98
71
Present
Work
EG
MS = Starch Microparticles, GNS = Graphene Nano sheet, NCTs = Nitrogenꢀdoped carbon
nanotubes
Study of catalytic leaching is another important parameter to determine the recyclability of
heterogeneous catalyst. Leaching of active metal species mostly depends upon number of
circumstances such as type of solvent and stabilizing agents that used during the reaction. To
estimate the leaching of copper from the catalyst material, the filtrate was analyzed by ICPꢀAES
after the removal of catalyst from the reaction mixture. No trace of copper was observed above
the detectable limit. This indicates that there were no stable catalytic species in the reaction
mixture. In addition, it was revealed that the concentration of copper present in fresh catalyst was
similar as compared to reused catalyst at fifth cycle.
Conclusion
The present work develops an efficient protocol for the synthesis of CuNPs@ZnOꢀPTh via a
simple impregnation method using inexpensive starting material, which is an important criteria
for large scale industrial productions. The catalytic properties of CuNPs@ZnOꢀPTh was
investigated for the synthesis of propargylamine, tetra substituted propargylamine (A3 and KA2
coupling reactions) and pyrrolo[1, 2ꢀa]quinoline (A3 coupling reactions). CuNPs@ZnOꢀPTh
catalyst with loading (20ꢀ25 mg) shows highest yield of desired product in minimum reaction
time (98%, 15 min) at 80˚C in ethylene glycol as green solvent. The high surface area and
synergistic effect of both the ZnOꢀPTh and CuNPs was responsible for its excellent catalytic
performance along with wide substrate scope, mild reaction conditions, recyclability without
significant loss in activity, short reaction time, easy workꢀup procedure, green solvent free
conditions with higher yield. Further, applications in drug design of synthesized molecules are
currently ongoing with collaboration.
Acknowledgement
One of the authors (A. Shah) is thankful to the University Grants Commission, New Delhi, India
for providing financial support under the MANF (Maulana Azad National Fellowship). Also

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thankful to NCNNUM, University of Mumbai, PRL, Ahmedabad and MNIT Jaipur for providing
characterization facilities.
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