Nano polypropylenimine dendrimer (DAB-PPI-G1): As a novel nano basic-polymer catalyst for one-pot synthesis of 2-amino-2-chromene derivatives

Article abstract of DOI:10.1039/c5ra04458h

The nano polypropylenimine dendrimer (DAB-PPI-G₁) Lewis base catalyst was found to be a highly efficient and recoverable catalyst for the rapid and convenient synthesis of 2-amino-2-chromene derivatives through the three-component condensation of aromatic aldehydes, malononitrile or ethyl cyanoacetate and phenols under solvent-free conditions in excellent yields and short reaction times.

Full text of DOI:10.1039/c5ra04458h

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Nano polypropylenimine dendrimer (DAB-PPI-G1):
as a novel nano basic-polymer catalyst for one-pot
synthesis of 2-amino-2-chromene derivatives†
Cite this: RSC Adv., 2015, 5, 42997
Received 13th March 2015
Accepted 16th April 2015
*
Behrooz Maleki and Safoora Sheikh
DOI: 10.1039/c5ra04458h
www.rsc.org/advances
The nano polypropylenimine dendrimer (DAB-PPI-G1) Lewis base ethyl cyanoacetate and phenols is particularly popular. Catalysts
catalyst was found to be a highly efficient and recoverable catalyst for that have been used for this conversion include a basic ionic
the rapid and convenient synthesis of 2-amino-2-chromene deriva- liquid [1-(n-butyl)-3-methylimidazolium hydroxide ([bmim]-
tives through the three-component condensation of aromatic alde- OH)],13 p-dimethylaminopyridine (DMAP),14 Triton B,15 K2CO3,16
hydes, malononitrile or ethyl cyanoacetate and phenols under MCM-41-NH2,17 cetyltrimethylammonium chloride (CTACl),18
solvent-free conditions in excellent yields and short reaction times.
cetyltrimethylammonium bromide (CTABr),19 K3PO4$3H2O,20
piperazine,21 tetramethylguanidine,22 H14[NaP5W30O110],23
CuSO4$5H2O,24 methanesulfonic acid,25 KF-Al2O3,26 potassium
phthalimide-N-oxyl,27 the nanostructured diphosphate Na2-
CaP2O7,28 DBU,29 and Ca(OH)2.30 However, most of the reported
methods suffer from one or more of the following drawbacks:
low yields, long reaction times, harsh reaction conditions,
tedious work-up leading to the generation of large amounts of
toxic waste, and the use of unrecyclable, hazardous, catalysts.
Therefore, the use of eco-friendly and non-toxic catalysts with
high efficiency in the synthesis of these compounds is highly
regarded.
Introduction
Dendrimers are monodisperse and usually highly symmetric,
spherical compounds. Nano polypropylenimine is an important
class of dendrimer. In fact, dendrimers are polymer nano-
structures with unique capabilities. First generation poly-
propylenimine dendrimers consist of four free terminal NH2
groups.1 These groups make polypropylenimine (PPI) den-
drimers polyvalent and also increase their basic properties.
Polypropylenimine dendrimers are used as agents for targeted
drug delivery and gene transfer.2 The physical characteristics of
dendrimers, including their monodispersity, water solubility,
encapsulation ability, and large number of functionalizable
peripheral groups, make these macromolecules appropriate
candidates for evaluation as drug delivery vehicles (Fig. 1).
2-Amino-2-chromen derivatives have attracted extensive
interest owing to their biological activity.3 There is a widespread
interest in the synthesis of chromene and its derivatives owing
to their diverse range of biological properties such as their
antimicrobial,4 TNF-a inhibitory,5 antifungal,6 estrogenic,7
anticancer,8 anti-HIV,9 and anti-bacterial properites.10 Such
compounds have also been applied in pigments,11 pesticides
and insecticides.12 Among the several methods reported for the
synthesis of 2-amino-2-chromen derivatives, the three-
component reaction between aldehydes, malononitrile or
Results and discussion
During the course of our recent studies directed toward the
development of practical, safe and environmentally friendly
procedures for some important transformations,31 we hoped to
report a simple and efficient procedure for the synthesis of 2-
Department of Chemistry, Hakim Sabzevari University, Sabzevar 96179-76487, Iran.
E-mail: b.maleki@hsu.ac.ir; Fax: +9844010300; Tel: +985144013324
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra04458h
Fig. 1 Schematic representation of dendrimeric structures.
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amino-chromenes using the nano polypropylenimine den-
drimer (DAB-PPI-G1) under solvent-free conditions (Scheme 1).
The core of PPI is a diamine (commonly 1,4-diaminobutane).
The reaction began with the addition of four molecules of
acrylonitrile to the central 1,4-diaminobutane core, and
produced the generation 0.5 polypropylenimine dendrimer with
four terminal nitrile groups. In the next step, we reduced the
nitrile groups using NaBH4 in the presence of anhydrous cobalt
chloride catalyst and produced the generation 1 nano poly-
propylenimine dendrimer with four terminal amine groups
(Scheme 2).
Scanning electron microscopy images of the nano poly-
propylenimine dendrimer are shown in Fig. 2A. The
morphology indicates agglomeration of the dendrimer particles
and a porous structure. The images shown in Fig. 2B have been
prepared by an optical microscope with nano focus, they show
the approximate size of particles of PPI dendrimer that have
been sprayed onto the glass through the use of a color scale
(Fig. 2B).
The size dispersion of the PPI synthesized by the proposed
method was investigated by dynamic light scattering (DLS) and
shown in Fig. 2C. As it can be seen, the nanoparticle size is
between 13–53 nm and the mean diameter is 24 nm.
Creation of molecular functionality and diversity32 from
common starting materials while combining economic33 and
environmental34 aspects constitutes a great challenge in modern
organic chemistry.35 In these contexts, multicomponent reactions
Scheme 2 Synthesis of the nano polypropylenimine dendrimer (DAB-
PPI-G1).
(MCRs) under solvent-free conditions are valuable procedures in
organic synthesis because a multistep reaction may produce
considerable amounts of environmentally unfavorable wastes
mainly due to a series of complex isolation procedures, which
oen need expensive, toxic, and hazardous solvents aer each
step. Malononitrile is one of the most versatile reagents to be used
in MCRs because of the high reactivity of both the methylene and
the cyano groups.36 From this perspective, we used malononitrile
(1.5 mmol) as the active reagent to react with benzaldehyde (1
mmol) and 1-naphthol (1 mmol) to optimize the reaction
Scheme 1 One-pot synthesis of 2-amino-2-chromene derivatives.
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Fig. 2 (A) Scanning electron microscopy images of dendrimer PPI G1 (i and ii); (B) optical microscopy nano focus images of dendrimer PPI G1: (i)
dendrimer PPI sprayed on glass (a film of PPI G1) and (ii) an image obtained from the particle sizes within the PPI G1 film on glass; (C) particle size
dispersion of PPI by a dynamic light scattering method (DLS).
conditions at rst. A summary of the optimization experiments is (entries 7–8). Aerwards, the loading of PPI was selected, and 15
provided in Table 1.
mol% of PPI was established as the optimal amount (entries 9–
Initially, we performed the three-component reaction using 10). To evaluate the effect of PPI, the reaction was examined in
ꢀ
the nano polypropylenimine dendrimer (PPI) as the catalyst the absence of PPI under solvent-free conditions at 110 C; no
ꢀ
under solvent-free conditions at 110 ꢀC, and exhilaratingly product was formed aer 20 min at 110 C (entry 11).
obtained the target product in 95% yield aer 3 min (Table 1,
In recent years, various nano-materials have been used as
entry 1). To further optimize the reaction conditions, a series of suitable catalysts for the synthesis of various organic
catalysts such as ethylenediamine (EDA), 1,4-diamino butane compounds.37 They increase the efficiency of time consuming
(DAB), triethanolamine (TEA), diethanolamine (DEA), and reactions compared to regular catalysts. One efficient approach
poly(amido amine) (PAMAM) dendrimers were investigated to enhance the catalytic activity of catalysts is their nano-
(entries 2–6). Compared with other catalysts, PPI was the best structure construction. Favorable properties of nano poly-
catalyst in terms of the yield and reaction time (entry 1). Next, propylenimine dendrimers (PPI) including increased surface
we screened the proper temperature for the model reaction area, saving of material, and cost efficiency, make them more
efficient catalysts than their counterparts. In our quest to prove
the efficiency of nano polypropylenimine dendrimers (PPI),
where nanostructures play an important role in the catalytic
Table 1 Optimization of reaction conditions
properties, the synthesis of 6a was investigated using similar
Entry Catalyst
Conditions
Time (min) Yielda (%)
non nanostructures (Table 1, entries 2–6). As it can be seen,
better efficiency for the nano polypropylenimine dendrimer
(PPI) is found in the synthesis of 6a.
1
2
3
4
5
6
7
8
PPI (15 mol%)
Solvent-free/110 ꢀ
Solvent-free/110 ꢀ
Solvent-free/110 ꢀ
C
C
C
3
3
95
70
EDA (5 drops)
DAB (5 drops)
TEA (5 drops)
DEA (5 drops)
Based on the optimized reaction conditions, the reactions of
1 or 2-naphthol or resorcinol, malonitrile, and various aromatic
(heterocyclic) aldehydes were investigated. As shown in Table 2,
aromatic aldehydes carrying either electron-withdrawing or
electron-donating substituents afforded excellent yields of
product with high purity at 110 ꢀC under solvent-free
conditions.
3
7
5
3
3
3
3
3
45
85
86
Trace
90
Solvent-free/110 ꢀC
Solvent-free/110 ꢀ
C
C
C
PAMAM (5 drops) Solvent-free/110 ꢀ
PPI (15 mol%)
PPI (15 mol%)
PPI (10 mol%)
PPI (20 mol%)
—
Solvent-free/120 ꢀ
Solvent-free/100 ꢀC
74
86
9
10
11
Solvent-free/110 ꢀ
Solvent-free/110 ꢀ
Solvent-free/110 ꢀ
C
C
C
89
b
20
—
A possible reaction mechanism is proposed in Scheme 3. We
presume that the reaction proceeds via initial formation of I
a
Isolated yields. b No reaction.
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Table 2 One-pot synthesis of 2-amino-2-chromene derivatives
Entry
R
Phenols
R1
Products
Time (min)
Yielda (%) (ref.)
1
C6H5
CN
3
95 (ref. 24)
6a
2
2-ClC6H5
CN
4
95 (ref. 24)
6b
3
3-NO2C6H5
CN
12
94 (ref. 24)
6c
4
4-ClC6H5
CN
4
96 (ref. 24)
6d
5
3-NO2C6H5
CO2Et
20
88 (ref. 25)
6e
6
4-FC6H5
CN
15
78 (ref. 26)
6f
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Table 2 (Contd.)
Entry
R
Phenols
R1
Products
Time (min)
Yielda (%) (ref.)
7
4-ClC6H5
CO2Et
30
95 (ref. 26)
7g
8
4-BrC6H5
4-OHC6H5
4-ClC6H5
CO2Et
CO2Et
CN
30
50
15
89 (new)
88 (new)
92 (ref. 27)
7h
9
7i
10
7j
11
4-NO2C6H5
CO2Et
20
89 (new)
7k
12
3-NO2C6H5
CO2Et
20
90 (ref. 15)
7l
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Table 2 (Contd.)
Entry
R
Phenols
R1
Products
Time (min)
Yielda (%) (ref.)
13
C6H5
CN
20
82 (ref. 27)
8m
14
4-BrC6H5
CN
25
85 (ref. 27)
8n
15
2-Furyl
CN
30
76 (ref. 27)
8o
16
4-ClC6H5
CN
20
87 (ref. 27)
8p
17
2-ClC6H5
CN
20
89 (ref. 27)
8q
a
Isolated yields.
through a Knoevenagel condensation of the aryl aldehyde and is better and in all cases much more efficient for this
malononitrile. Then, 1-naphthol loses a hydrogen atom under reaction than the other catalysts (including acidic and basic
the action of PPI. Subsequently, Michael addition between II catalysts).
and I produces intermediate III, followed by intramolecular
cyclization to form IV. The isomerization of IV gives the nal
product 6.
Experimental
General
Table 3 summarizes the results and compares them with
results obtained by other groups. Based on this comparison,
our method is simpler and more efficient for the synthesis
of 2-amino-2-chromene derivatives. These results clearly
demonstrate that the polypropylenimine dendrimer catalyst
All the chemicals required were purchased from Merck or
Aldrich. Melting points were determined using Electrothermal
9100 apparatus. FT-IR spectra were recorded on a Shimadzu FT
IR-8400S instrument (with the samples as KBr disks for the
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Scheme 3 Proposed mechanism.
range 400–4000 cmÀ1). 1H and 13C NMR spectra were deter-
mined on a Bruker DRX-300 Avance spectrometer in DMSO-d6
or CDCl3, and shis are given in d downeld from tetrame-
thylsilane (TMS) as an internal standard. Optical microscopy
was performed with a nano focus AG lindner strabe 98 D-46149
Oberhausen.
1. Synthesis of nano polypropylenimine dendrimer (PPI)
1.1. Synthesis of polypropylenimine dendrimer generation 0.5
(DAB-PPI-G0.5). To a mixture of 1,4-diaminobutane (10 mL) was
added dropwise acrylonitrile (35 mL) at 0 C for 30 min. Then,
the excess acrylonitrile was removed by rotary vacuum at 0.1
ꢀ
Table 3 Comparison of methods for the synthesis of 2-amino-2-chromene including acidic and basic catalysts
Entry
Compounds
Conditions
Time (min)
Yield (%)
Solvent-free/110 ꢀC/PPI (present work)
MCM-41-NH2/H2O/70 ꢀC (ref. 17)
CTABr/H2O/ultrasonic/rt (ref. 19)
Piperazine/MWI/solvent-free (ref. 21)
CuSO4$5H2O/water/reux (ref. 24)
Methanesulfonic acid/CH3CN/reux (ref. 25)
Na2CaP2O7/water/reux (ref. 28)
3
95
69
92
88
95
90
81
30
150
7
60
180
300
1
7a
7b
7c
Solvent-free/110 ꢀC/PPI (present work)
DMAP/solvent-free/MWI (ref. 14)
CTABr/H2O/ultrasonic/rt (ref. 19)
CuSO4.5H2O/water/reux (ref. 24)
KF-Al2O3/EtOH/80 ꢀC/reux (ref. 26)
4
95
95
80
85
86
60
150
30
300
2
Solvent-free/110 ꢀC/PPI (present work)
CTABr/H2O/ultrasonic/rt (ref. 19)
12
40
60
240
300
94
93
77
90
84
K3PO4$3H2O/100 ꢀC/solvent-free (ref. 20)
Methanesulfonic acid/CH3CN/reux (ref. 25)
Na2CaP2O7/water/reux (ref. 28)
3
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ꢀ
mm and a temperature of 45 C. The polypropylenimine den-
drimer generation 0.5 (DAB-PPI-G0.5) was obtained as an oily
viscous light yellow solution in 95% yield.
3.5. Polypropylenimine dendrimer generation 1. Yellow solid.
IR (KBr, cmÀ1): 3400 (N–H), 1668 (N–H), 1219, 1315 (C–N), 1130
(C–C).
1.2. Synthesis of polypropylenimine dendrimer generation 1
(DAB-PPI-G1). To a mixture of polypropylenimine dendrimer
generation 0.5 (10 g) in methanol (35 mL) at 0 ꢀC, was added
NaBH4 (6.23 g) and anhydrous cobalt chloride (0.0002 g). The
reaction mixture was stirred for 60 min at this temperature. Then,
the mixture was ltered, washed with methanol (30 mL), and then
dried at room temperature to give polypropylenimine dendrimer
generation 1 (DAB-PPI-G1) as a white powder (92% yield).
2. General procedure for synthesis of 2-amino-2-chromene.
PPI (15 mol%) was added to a mixture of the aromatic aldehyde
(1 mmol), active methylene (malononitrile or ethyl cyanoacetate)
(1 mmol), and phenol (a or b-naphthol or resorcinol) (1 mmol) in
a 10 mL ask at room temperature. The temperature was then
raised to 110 ꢀC and maintained for the appropriate time (see
Table 2) with stirring. Aer the completion of the reaction as
indicated by TLC (hexane–ethyl acetate, 4 : 1), hot EtOH (96%,
5 mL) was added and the mixture was stirred for 2 min.
Next, the resulting crude product was poured onto a mixture
of crushed ice and cold water to get the pure 2-amino-2-
chromene derivative as a solid product, which was separated,
ltered, and recrystallized from EtOH (3 mL).
Conclusion
In conclusion, we have reported a green and eco-friendly synthesis
of 2-amino-2-chromene derivatives using a highly efficient poly-
meric nanomaterial PPI catalyst. PPI is classied as a dendrimer
with special properties such as being antimicrobial, antibacterial,
non-toxic, and environmentally friendly. The most important
advantages of this reaction include a mild, green synthesis;
avoidance of the use of toxic organic solvents, excellent yield,
short reaction times and a simple work up procedure.
Acknowledgements
We are thankful to the University of Hakim Sabzevari Research
Council for the partial support of this research.
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