Solvent-free synthesis of β-amino ketones using carboxyl-functionalized poly(ionic liquid) at room temperature

Article abstract of DOI:10.1007/s11164-017-3134-x

Abstract: Carboxyl-functionalized poly(ionic liquid) (CFPIL) was easily synthesized from its starting material and characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis and elemental analysis. The synthesized CFPIL was use

Full text of DOI:10.1007/s11164-017-3134-x

Res Chem Intermed
DOI 10.1007/s11164-017-3134-x
Solvent-free synthesis of b-amino ketones using
carboxyl-functionalized poly(ionic liquid) at room
temperature
Avinash Ganesh Khiratkar1 Kamlesh Rudreshwar Balinge1
•
•
Karan Jivanlal Bhansali1 Pundlik Rambhau Bhagat1
•
Received: 13 June 2017 / Accepted: 28 August 2017
Ó Springer Science+Business Media B.V. 2017
Abstract Carboxyl-functionalized poly(ionic liquid) (CFPIL) was easily synthesized
from its starting material and characterized by Fourier transform infrared spectroscopy,
thermal gravimetric analysis and elemental analysis. The synthesized CFPIL was used as
an efficient heterogeneous catalyst for the synthesis of b-amino ketones by three-com-
ponent one-pot Mannich reaction between various aromatic aldehydes with amines and
acetophenone at room temperature under solvent-free condition. The effect of the
amount of catalyst and reaction time were investigated. The results showed that CFPIL
has good to moderate catalytic activity and reusability. The catalytic process was simple
and the catalyst could be easily recovered by filtration and washed with ethanol to reuse
for the next experiment without significant loss of catalytic activity.
Electronic supplementary material The online version of this article (doi:10.1007/s11164-017-3134-x)
contains supplementary material, which is available to authorized users.
&
Pundlik Rambhau Bhagat
drprbhagat111@gmail.com
1
Department of Chemistry, School of Advanced Sciences, VIT University, Vellore,
Tamil Nadu 632014, India
123

A. G. Khiratkar et al.
Graphical Abstract
Keywords Poly(ionic liquid) Á Solvent-free Á Mannich reaction Á Room
temperature Á Carboxyl-functionalized
Introduction
Mannich reaction is one of the most significant C–C bond=forming reactions in
organic transformation for the synthesis of secondary and tertiary amine derivatives.
These b-amino carbonyl compounds are found to be important building blocks for
the synthesis of numerous biologically attractive natural products such as amino
alcohols, peptides, and lactams, and as precursors to optically active amino acids as
well as pharmaceuticals, alkaloids and polyketides [1].
In recent decades, various catalysts have been used for the preparation of b-
amino carbonyl compounds including Lewis acids [2, 3], heteropoly acids [4, 5],
Brønsted acids [6], rare metal salts [7, 8], lipase [9] proline [10] and hydrophobic
polystyrene-supported sulfonic acids (PS-SO3H) [11].
Scandium tris(dodecylsulfate) and scandium tris(dodecanesulfonate); copper
triflate [12] and HBF4 [13, 14] have also been recognized to catalyze these reactions
in good yields with the help of just a surfactant. They normally suffer from the
problems of long duration and harsh reaction conditions, toxicity and trproblem-
souble in product separation which limit the process to obtain complex molecules.
As there is an increasing demand for the improvement of organic reactions in
environmentally friendly conditions, there is a need to minimize the use of
hazardous chemicals by substituting the traditional organic solvents in reactions and
their successive work-up with other non-toxic solvents like water or avoiding
solvents during the synthesis.
In recent years, ionic liquids (ILs) have received widespread research interest as
environmentally benign solvents and catalysts due to their promising properties
such as high thermal stability, non-inflammability, negligible vapor pressure and
reusability [15–18]. Acidic ionic liquids are widely used in various organic reactions
such as esterification, alkylation, condensation and many more. Brønsted acidic
ionic liquids have drawn special attention of researchers as efficient catalysts for the
synthesis of valuable chemicals [19, 20]. In the past few years, ILs-based
123

Solvent-free synthesis of b-amino ketones using…
homogeneous catalysts have been plagued by a number of serious disadvantages
like the leaching of the catalyst, side reactions and efforts in the isolation of
products [21, 22]. These difficulties could be overcome by introducing the polymer
moiety in ILs, as a heterogeneous catalyst [23]. Poly(ionic liquid)s (PILs) are a class
of polymer compounds which is composed of ILs as repeating units and could be
acting as a supporting material. Recently, PILs have been used as a catalyst for
various catalytic transformations with better stability as well as better recoverability
and recyclability [24–26]. Combining these unique properties of PILs, they are
evolving as green heterogeneous catalysts.
To the best of our knowledge, there is no report on solvent-free synthesis of b-
amino carbonyl compounds at room temperature (RT) via the Mannich reaction
between aromatic aldehydes, aromatic ketone, and aromatic amines involving
catalytic amounts of carboxyl-functionalized poly(ionic liquid). The reaction
progressed with moderate yield of the preferred Mannich base using a catalytic
amount of CFPIL-1. The effect of anions of the ionic liquid on the reaction rate has
also been investigated. Furthermore, the optimizations of catalyst dose, duration and
reusability have also been examined.
Experimental section
Materials and instruments
4-vinylbenzyl chloride (90%) and 3-bromopropionic acid (97%) were obtained
from Sigma-Aldrich, India. Azobisisobutyronitrile (98%) was procured from Avra
synthesis and recrystallized from methanol before use. Sodium hydride (60%
suspension in paraffin oil), benzimidazole (LR) and all the substituted aromatic
aldehydes, amines and acetophenone were procured from S D Fine Chemicals,
India. Commercial grade solvents and reagents were used as received unless
specified othterwise. NMR spectra were recorded in deuterated solvents such as
DMSO-d6 and CDCl3 on a 400 MHz Bruker spectrometer with TMS as an internal
reference. Thermal stability of the CFPIL was confirmed using thermogravimetric
analyzer (TGA; (SDT Q600; USA). Fourier-transform Infrared (FT-IR) spectra of
CFPIL-1 and synthesized b-amino ketones were recorded in a Shimadzu IR affinity-
1 spectrometer with an attenuated total reflectance set-up in the range of
4000–400 cm-1 with a resolution of 4 cm-1. The elemental analysis (C, H and
N) was performed on an Elementar Vario EL III instrument.
Synthesis of carboxyl-functionalized poly(ionic liquids) (CFPIL)
Synthesis of 1-(4-vinylbenyl)-1H-benzimidazole (VBBim)
1-(4-vinylbenyl)-1H-benzimidazole was synthesized according to our previously
reported procedure [27] and the detailed process is given in the supporting
1
information. Yield: 9.36 g, 80%. H NMR (400 MHz, CDCl3) d: 7.92 (s, 1H),
7.83–7.81 (d, 2H), 7.36–7.34 (d, 2H), 7.25–7.23 (d, 2H), 7.12–7.10 (d, 2H)
123

A. G. Khiratkar et al.
6.70–6.63 (dd, 1H), 5.74–5.69 (d, 1H), 5.30 (s, 2H), 5.26–5.23 (d, 1H). 13C NMR
(400 MHz, CDCl3) d: 144.02, 143.26, 137.72, 136.09, 134.90, 133.98, 127.40,
126.88, 123.19, 122.39, 120.48, 114.70, 110.13, 48.68. GC–MS; Calcd. Mass
234.29, found: 234.30.
Synthesis of carboxyl-functionalized ionic liquid monomer (CFILM)
1-(4-vinylbenyl)-1H-benzimidazole (7.02 g, 30 mmol) and 3-bromopropionic acid
(4.56 g, 30 mmol) were dissolved in 100 mL chloroform and the reaction mixture
was stirred for 48 h at 70 °C. The solid mass of the product was filtered and washed
with chloroform (3 9 50 mL) to obtain the pure, white amorphous carboxyl-
functionalized ionic liquid monomer. Yield: 5.8 g, 50.08%.
1H NMR (400 MHz, DMSO-d6) d: 12.67 (s, 1H), 9.99 (s, 1H), 8.15–8.13 (d, 2H),
7.94–7.92 (d, 2H),7.67–7.65 (d, 2H) 7.49–7.47 (d, 2H), 6.75–6.68 (dd, 1H), 5.87 (d,
1H), 5.83–5.78 (s, 2H), 5.29–5.27 (d, 1H), 4.73–4.70 (t, 2H), 3.04–3.01 (t, 2H).13C
NMR (100 MHz, DMSO-d6) d: 171.79, 143.06, 137.47, 135.90, 133.41, 131.18,
130.65, 128.62, 126.64, 126.59, 115.23, 114.00, 113.89, 49.57, 42.80, 32.75.
Synthesis of carboxyl-functionalized poly(ionic liquid) (CFPIL-1)
Synthesis of carboxyl-functionalized poly(ionic liquid) was prepared according to
the published procedure [28] and spectral analysis data were found consistent with
the proposed structure.
1
Yield: 3.56 g, 79.11%). H NMR (400 MHz, DMSO-d6) d: 10.52 (s, 1H), 10.04
(s, 1H), 8.14 (s, 2H), 7.94 (s, 2H), 7.69 (s, 2H) 7.63 (s, 2H), 5.87 (s, 2H), 4.72 (s,
2H), 3.02 (s, 2H), 1.54 (s, 1H), 1.42 (s, 2H).13C NMR (100 MHz, DMSO-d6) d:
171.83, 143.04, 135.90, 133.37, 131.20, 130.68, 128.58, 126.61, 115.27, 113.98,
51.79, 49.59, 42.78, 32.70, 22.03. Anal. Calcd for C21H25BrN2O2 (%): C, 60.44, H,
6.04, N, 6.71. Found: C, 55.84, H, 5.76, N, 6.93.
Synthesis of carboxyl-functionalized poly(ionic liquid) containing mesylate/tosylate
counteranion
The synthesis of carboxyl-functionalized poly(ionic liquid) containing mesylate/to-
sylate counter anion was carried out according to the published procedure [29] with
slight modifications. Methane sulphonic acid (1.935 g, 5.5 mmol) and anhydrous
methanol (10 mL) were charged into a 50-mL round-bottom flask and stirred at
0 °C for 10 min. The solid, CFPIL-1 (1.496 g, 5 mmol) was added gradually with
constant stirring for 30 min at this temperature. The reaction mixture was stirred for
1 h at RT and stirring continued at 60 °C for 24 h until a negative silver nitrate test
was confirmed. The methanol was removed using a rotational evaporator followed
by washing with ethyl acetate to gobtainet desired pure product. Finally, CFPIL-2
was dried in vacuum at 45 °C for 24 h to obtain a yellowish solid compound.
Yield: 89%. 1H NMR (400 MHz, DMSO-d6) d: 10.20 (s, 1H), 10 (s, 1H), 8.14 (s,
2H), 7.93 (s, 2H), 7.64 (s, 2H) 7.47 (s, 2H), 7.33 (s, 2H), 7.05 (s, 2H), 5.77 (s, 2H),
4.72 (s, 2H), 3.03 (s, 2H), 2.21 (s, 3H), 2.07 (s, 1H), 1.06 (s, 2H). 13C NMR
123

Solvent-free synthesis of b-amino ketones using…
(100 MHz, DMSO-d6) d: 171.76, 147.94, 145.03, 143.11, 138.10, 135.94, 131.20,
128.62, 128.21, 128.01, 125.85, 125.48, 113.99, 67.70, 49.59, 42.78, 32.70, 25.87,
20.77.
The CFPIL-3 was synthesized using a similar procedure to that of CFPIL-2.
CFPIL-3: yellowish solid. Yield: 87%. 1H NMR (400 MHz, DMSO-d6) d: 10.02 (s,
1H), 10.00 (s, 1H), 8.14 (s, 2H), 7.94 (s, 2H), 7.65 (s, 2H) 7.63 (s, 2H), 5.77 (s, 2H),
4.72 (s, 2H), 3.85 (s, 2H), 2.37 (s, 3H), 2.07 (s, 1H), 1.22 (s, 2H). 13C NMR
(100 MHz, DMSO-d6) d: 172.27, 143.59, 131.67, 131.14, 130.44, 129.18, 129.09,
128.89, 127.14, 114.48, 56.50, 49.89, 43.26, 33.16, 21.55, 19.00, 14.38 (Scheme 1).
General synthesis procedure of b-amino ketones
In a typical procedure, aromatic aldehydes (2 mmol), acetophenone (2 mmol),
aromatic amines (2 mmol) and the catalyst (15 wt% 32 mg) were stirred in a 50-mL
single-neck round-bottom flask equipped with a magnetic stirrer under solvent-free
condition at RT (Scheme 2). The reaction progress was monitored by TLC using
ethyl acetate and n-hexane solvent (2:8) as a mobile phase and, upon completion;
the product separated at ambient temperature. The resulting precipitate was
dissolved in a minimum quantity of an ethanol and acetone (1:1) mixture by gentle
Scheme 1 Synthesis scheme of CFPIL-1, 2 and 3
123

A. G. Khiratkar et al.
Scheme 2 CFPIL-catalyzed Mannich reactions of aromatic aldehydes, aromatic amines and
acetophenone
heating. The separated catalyst was filtered off using a sintered funnel, washed with
acetone and dried in an oven at 50 °C for 10 h to reuse for the next experiment. The
filtrate was cooled to ice-cold temperature to afford the pure b-amino ketone
derivatives (4a–4l) which did not required further purification. The structural
elucidation of b-amino ketones was carried out using 1H, 13C NMR, and FT-IR, and
their physical data (m.p.) were identified with those reported in literature.
Spectral data for selected b-amino ketone
1,3-Diphenyl-3-phenylamino-propan-1-one (4a): white solid; Yield: 70%; mp
1
132–136 °C. H NMR (400 MHz, CDCl3): d 3.47 (m, 2H), 4.96 (d, 1H), 6.48 (t,
1 H, J = 7.27 Hz), 6.61 (d, 2H, J = 8.02 Hz), 7.24 (t, 1H, J = 7.35 Hz), 7.37 (t,
2H, J = 7.6 Hz), 7.39 (t, 2H, J = 7.80 Hz), 7.47 d, (2H, J = 7.64 Hz), 7.51 (t, 1H,
J = 7.2 Hz), 7.85 (d, 2H, J = 7.49 Hz). 13C NMR (100 MHz, CDCl3): 198.29,
147.01, 142.99, 136.72, 133.44, 129.12, 128.84, 128.72, 128.22, 127.37, 126.39,
117.80, 113.83, 54.82, 46.33. (KBr, m/cm-1): 3383, 3022, 1741, 1668. HRMS (EI):
m/z calculated for [M]? [C21H19NO]? 301.1467, Found 301.1465.
Results and discussion
Characterization of the CFPIL-1
1
Figure 1 shows the H NMR spectrum of synthesized VBBim, CFILM monomer
1
and CFPIL-1 polymer. The H NMR spectrum of VBBim shows all the expected
peaks of the corresponding structure. The peak at 7.92 ppm is attributed to the C2-H
of the benzimidazole ring in the VBBim (Fig. 1A).
The 1H NMR spectrum of CFILM (Fig. 1B) exhibited the one unique absorption
at 12.67 (broad) expected for the –OH group. Also, the peak has shifted from 7.92 to
10.11 ppm to the deshielding region, confirming the successful formation of the
CFILM monomer.
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Solvent-free synthesis of b-amino ketones using…
(C)
CFPIL-1
(B)
CFILM
(A)
VBBim
Fig. 1 Comparative NMR spectra of (A) VBBim, (B) CFILM monomer and (C) CFPIL-1 polymer
C
-OH Stre.
-1
C=O 1724 cm
-1
2978 cm
B
A
-1
-OH stre. 2821 cm
-1
C=O 1712 cm
CFPIL
CFILM
VBBim
4000
3500
3000
2500
2000
1500
-1
1000
500
Wavenumber cm
Fig. 2 Comparative FT-IR spectra of (A) VBBim, (B) CFILM monomer and (C) CFPIL polymer
After polymerization, the absorption at 0.5–1.5 ppm can be attributed to the alkyl
end-group of the polymer. Moreover, broadening of peaks can be endorsed the
formation of CFPIL-1 polymer (Fig. 1C).
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A. G. Khiratkar et al.
Figure 2 shows the comparative FT-IR spectra of VBBim, CFILM and CFPIL-1.
The –OH stretching frequency of the –COOH group in CFILM (B) and CFPIL-1
(C) appeared at 2821 and 2978 cm-1, respectively.
Also, the carbonyl group (C=O) of the CFILM and CFPIL-1 was found at 1712
and 1724 cm-1, respectively. This confirms the successful formation of the CFPIL-
1 polymer. However, –OH and –COOH stretching frequencies are absent in the
VBBim (A) spectrum.
Initially, we optimized the catalytic efficacy of different CFPIL catalysts for
solvent free one-pot three-component reaction of aromatic aldehydes, acetophe-
none, and aromatic amines with a catalyst (5 wt%) at RT as a model reaction with
benzaldehyde (0.212 g, 2 mmol), acetophenone (0.240 g, 2 mmol) and aniline
(0.186 g, 2 mmol).
Among them, CFPIL-1 showed the best catalytic activity toward the reaction
when compared to other polymeric catalysts (Table 1, entries 1–3).
First, we performed the reaction without a catalyst at RT for 5 h. There was little
yield indicated that, the catalyst played a key role in the reaction (Table 2, entry 1).
We tested the reaction with 5 wt% of the CFPIL-1 to obtain 25% yield (Table 2,
entry 2). By increasing the loading of the CFPIL-1 from 10 to 15 wt%, an
improvement in yield up to 70% in 5 h of reaction time was observed (Table 2,
entries 3, 4). It is significant that no progress was perceived in the case of the
reaction rate and yield by increasing the amount of the catalyst up to 20 wt%
(Table 2, entry 5). Based on these results, 15 wt% of the CFPIL-1 is appropriate for
the reaction.
The duration played an important role in the Mannich reaction catalyzed by
CFPIL-1. The reaction was carried out at different intervals, with the reaction at 5 h
affording the products in high selectivity with nearly complete conversion with a
maximum yield of 70% (Table 3, entries 1–5).
Increasing the period of the reaction from 6 to 7 h (Table 3, entries 6, 7)
produced no substantial increase in the yield of the reaction. Therefore, 5 h was
selected as the time for the further investigations.
Having recognized the optimal reaction conditions, we sought to assess the
possibility and efficacy of the reaction. For this purpose, a wide range of aldehydes,
substituted anilines and acetophenone were selected to accomplish the Mannich
reaction, and the results were displayed in Table 4.
Table 1 The effect of various CFPIL on Mannich reactions
Entry
CFPIL
Catalyst (wt%)
Time (h)
Yieldsa (%)
1
2
3
CFPIL-1
CFPIL-2
CFPIL-3
5
5
5
5
5
5
25
15
13
Reaction conditions: benzaldehyde (2 mmol), acetophenone (2 mmol) and aniline (2 mmol) solvent-free,
RT
aIsolated yield
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Solvent-free synthesis of b-amino ketones using…
Table 2 Effect of catalyst amount on Mannich reactions
Entry
Catalyst amount (CFPIL-1) (wt%)
Time (h)
Yieldsa (%)
1
2
3
4
5
0
5
5
5
5
5
5
9
25
50
70
70
10
15
20
Reaction conditions: benzaldehyde (2 mmol), acetophenone (2 mmol) and aniline (2 mmol) solvent-free,
RT
aIsolated yield
Table 3 Optimization of reaction time
Entry
Catalyst amount (CFPIL) (wt%)
Temperature
Time (h)
Yielda (%)
1
2
3
4
5
6
7
15
15
15
15
15
15
15
RT
RT
RT
RT
RT
RT
RT
1
2
3
4
5
6
7
35
38
55
62
70
69
68
Reaction conditions: Benzaldehyde (2 mmol), acetophenone (2 mmol) and aniline (2 mmol), CFPIL-1
(15 wt%); solvent-free, RT
aYields refer to the isolated pure products after recrystallization with 1:1 mixture of ethanol and acetone
With regard to the various aldehydes bearing both electron-donating and -
withdrawing substituents, they can be competently converted into b-amino ketones
in good to moderate yields as shown in Table 4, entries 1–12. All the Mannich bases
1
were characterized by H, 13C NMR and IR spectroscopy. Moreover, the yields
obtained for CFPIL-1 towards the Mannich reactions is better than or comparable to
the literature reports with respect to catalyst loading, temperature and duration
(Table 5).
Recyclability and stability of the CFPIL-1
In addition, we have examined the reusability of CFPIL-1 for the model reaction
under optimized conditions. At the end of the reaction, the catalyst was simply
filtered in hot conditions from an acetone–ethanol mixture, washed with ethanol,
and dried at 50 °C for 12 h in an oven. Catalyst reutilizing experiments were carried
out with repeated use for further three consecutive reactions between benzaldehyde,
aniline and acetophenone to yield the Mannich base, i.e. 1, 3-diphenyl-3-
phenylamino-propan-1-one. As shown in Fig. 3, the first reaction using recovered
123

A. G. Khiratkar et al.
Table 4 Multicomponent Mannich reactions of aromatic aldehydes, amines and acetophenone catalyzed
by CFPIL
Entry
R1
R2
Product
Time (h)
Yielda (%)
1
C6H5
H
4a
4b
4c
4d
4e
4f
5
10
10
5
70
68
67
68
71
57
67
60
68
65
64
69
2
4-ClC6H4
4-MeO C6H4
4-MeOC6H4
4-CH3C6H4
4-BrC6H4
4-OMeC6H4
4-OMeC6H4
4-ClC6H4
4-CH3C6H4
4-CH3
H
3
H
4
4-Cl
H
5
14
9
6
H
7
4-OH
4-F
4-Cl
4-Cl
4-F
H
4g
4h
4i
5
8
8
9
5
10
11
12
4j
5
4k
4l
5
C6H5
4
Reaction conditions: aromatic aldehydes (2 mmol), acetophenone (2 mmol) and aromatic amines
(2 mmol), CFPIL-1 (15 wt%); solvent-free, RT
aYields refer to the isolated pure products after recrystallization from 1:1 mixture of ethanol:acetone
Table 5 Comparison of the different solid acid catalyst for the synthesis of b-amino ketones
Entry Catalyst
Catalyst loading Temperature Time
(g)
Yield
(%)
Ref.
(h)
1
2
3
PS-SO3H
0.080
30 °C
RT
24
18
10
75
76
83
[30]
[31]
[32]
H3PW12O30
0.691
Yttria–zirconia based
Lewis acid
10 mol%
65 °C
4
5
WOx–ZrO2 solid acid
catalyst
0.05
RT
RT
8
5
80
70
[33]
CFPIL-1
0.032
Present
work
CFPIL-1 afforded a yield similar to that achieved in the first run. In the second and
third runs, the yields steadily decreased.
TGA of the CFILM monomer as well as the CFPIL-1 polymer have been studied
to discover the thermal stability (Fig. 4a, b). TGA of the CFILM and CFPIL-1 was
studied in the range of 30–800 °C with the temperature increasing at the rate of
10 °C min-1 in a N2 atmosphere. The thermogram of CFILM shows an initial
weight loss of 64.07% which started from 180 to 380 °C. Another weight loss of
24.12% started from 380 to 548 °C. However, the thermogram of CFPIL-1 shows
an initial weight loss of 50.41% which started from 239 to 403 °C. Another weight
loss of 30.85% started from 380 to 640 °C.
From the above TGA results, it can be concluded that the weight loss of the
monomer starts from 180 °C, but this initial weight loss in the polymer was
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Solvent-free synthesis of b-amino ketones using…
70
67
66
80
60
40
20
0
1
2
3
4
Runs
Fig. 3 Recyclability of CFPIL-1 for the synthesis of b-amino ketones
CFILM (A)
CFPIL-1 (B)
A
100
B
80
60
40
20
0
0
200
400
600
800
Temperature (°C)
Fig. 4 TGA thermogram of (A) CFILM monomer and (B) CFPIL-1 polymer
exhibited at 239 °C and hence it clearly indicates that the stability of the CFPIL-1
polymer is better as compared to the CFILM monomer.
Conclusions
We have developed a CFPIL-1 catalyst and used it in a Mannich reaction between
aromatic aldehydes, aromatic ketone and aromatic amines to prepare b-amino
carbonyl compounds in good to moderate yieldsof up to 70%. Owing to the
combination of –COOH functional groups and the poly(ionic liquid), the Mannich
reactions can be conducted effectively. In addition, mild reaction conditions, easy
123

A. G. Khiratkar et al.
work-up, low catalyst loading, non-requirement of column chromatography purifi-
cation, and the recoverability and reusability of the catalyst up to three cycles are
the prominent features of this method. Besides the synthesis of b-amino carbonyl
compounds, such an environmentally benign catalyst should find a wider application
in various acid-catalyzed reactions, which is a continuing project. Furthermore, the
good yields, mild conditions and suitable operation, as well as straightforward path,
confirmed that our method would play a vital role in synthesis of corresponding
pharmaceuticals and natural products.
Acknowledgements We gratefully acknowledge SIF DST-VIT-FIST, VIT University, Vellore for
providing NMR, FT-IR as well as other required facilities. The authors are also grateful for financial help
provided by RGEMS, VIT University, Vellore and other facilities provided by ‘‘Smart Materials
Laboratory for Bio-sensing and Catalysis.’’
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