Passerini three-component cascade reactions in deep eutectic solvent: an environmentally benign and rapid system for the synthesis of α-acyloxyamides

Article abstract of DOI:10.1007/s11164-015-2390-x

Abstract: A greener synthesis of α-acyloxyamides was achieved by one-pot three component cascade Passerini reactions in a deep eutectic solvent (DES). Reactions proceeded rapidly and afforded the corresponding α-acyloxyamides by a variety of aldehydes, acids and isocyanides in excellent yields. The DES has the advantages of easy workup, high yield, and an environmentally benign and, moreover, shortened time as the greatest exclusivity of this system compared with previously reported methods. Graphical Abstract: Passerini three-component cascade reaction in a deep eutectic solvent: an environmentally benign and rapid system for the synthesis of α-acyloxyamides.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-015-2390-x

Res Chem Intermed
DOI 10.1007/s11164-015-2390-x
Passerini three-component cascade reactions in deep
eutectic solvent: an environmentally benign and rapid
system for the synthesis of a-acyloxyamides
Ahmad Shaabani1 Ronak Afshari1
•
•
Seyyed Emad Hooshmand1
Received: 30 August 2015 / Accepted: 11 December 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A greener synthesis of a-acyloxyamides was achieved by one-pot three
component cascade Passerini reactions in a deep eutectic solvent (DES). Reactions
proceeded rapidly and afforded the corresponding a-acyloxyamides by a variety of
aldehydes, acids and isocyanides in excellent yields. The DES has the advantages of easy
workup, high yield, and an environmentally benign and, moreover, shortened time as the
greatest exclusivity of this system compared with previously reported methods.
Graphical Abstract Passerini three-component cascade reaction in a deep eutectic
solvent: an environmentally benign and rapid system for the synthesis of
a-acyloxyamides.
&
Ahmad Shaabani
a-shaabani@sbu.ac.ir
1
Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran, Iran
123

A. Shaabani et al.
Keywords Deep eutectic solvents Á Passerini reaction Á Isocyanide Á
a-Acyloxycarboxamide Á Green chemistry
Introduction
What makes a solvent green? The prevalent opinion is that the ideal green solvent is
safe for both the human beings and the environment and its use and manufacture are
sustainable [1]. Environmental and health issues are quickly emerging as a major
challenge for the twenty-first century with the basic aspects of efficiency and
economy being relevant to all aspects of science. From a synthetic chemist’s
viewpoint, this emphasis on environmental and health issues is leading to an
increased focus on developing green efficient strategies for the synthesis of
materials without using any hazardous solvents or reagents. For this inspiration,
scientists have tried to replace toxic solvents with eco-friendly materials.
A closely related class of solvents with physical properties and phase behaviors
very similar to those of room temperature ionic liquids (RTILs) are deep eutectic
solvents (DESs), which were developed by Abbott et al. [2, 3]. The most common
DESs are based on choline chloride (ChCl) and hydrogen-bond donors such as urea,
citric acid, sugar, and glycerol. DESs are attractive alternatives to RTILs, as they are
less expensive, more synthetically accessible, nontoxic and biodegradable [4, 5].
For instance, the preparation of DES in a pure state is considerably easier and
economically viable as it shows 100 % atom economy with satiety to post-synthesis
purification that was used for the ILs.
Heretofore so much chemical processing such as extraction [6], polymerizations
[7], biomass processing [8], materials synthesis [9], and organic reactions [10–18]
have been applied in DES medium. Quite recently a review has reported
information about Deep Eutectic Solvents (DESs) and their applications in metal
electrodeposition, metal extraction, synthesis of nanoparticles, gas adsorption, and
synthesis applications [19].
Multicomponent reactions (MCRs) are useful and powerful tools in which three
or more different starting materials react to form novel and complex molecules in a
one-pot strategy with great efficiency and atom economy. The development of such
processes in which several bonds are formed without isolation of intermediates
receives considerable attention for the preparation of structurally diverse libraries of
drug-like poly-functional compounds [20–24]. Isocyanides have emerged as a
magic compound in organic and medicinal chemistry, allowing the formation of
different molecular architectures from readily accessible precursors in a convergent
manner and also have recently gained attention in macromolecular synthesis [25–
27]. The ability of isocyanides to undergo facile addition with both nucleophiles and
electrophiles makes it a popular reactant class for the development of novel MCRs.
Because of the unique reactivity of the isocyanide functional groups, isocyanide-
based multi-component reactions (IMCRs) are among the most versatile, in terms of
number and variety of compounds that can be generated [28–30]. One of particular
importance in this area is the Passerini three-component reaction (P-3CR) involving
the condensation of an isocyanide, an aldehyde, and a carboxylic acid followed by
123

Passerini three-component cascade reactions in deep…
Mumm’s rearrangement, leading to a-acyloxyamide scaffolds [31]. The Passerini
reaction broadly has been used in synthetic and medicinal chemistry [36–40]. The a-
acyloxycarboxamide scaffold is a frequent motif in many natural products as well as
in pharmacologically active depspeptides thus making the Passerini reaction a
particularly valuable method by which highly diverse libraries of these compounds
can be constructed fast and screened for biological activity. For example, compound
A exhibits inhibitory activity for the RNase H function of HIV-1 reverse
transcriptase [32] and compound B is reported to have herbicidal activity (Fig. 1)
[33].
Various strategies, reagents, and catalysts have been used over the past decades
due to the profound biological activity, synthetic utility, and diverse structural
variety of new compounds [34, 35]. The Passerini reaction is generally performed in
an organic solvent such as CH2Cl2, toluene or MeOH and long reaction times are
often required. However, several optimizations have been achieved to improve the
yield, reduce the cost, the ecological impact, and the reaction times of this reaction.
Thus, processes have been described in aqueous solution [36], ionic liquid [37, 38],
without using solvents either at room temperature [39], or under microwave
irradiation activation [40]. Recently, this reaction has been performed under high
temperature (180 °C) under solvent free conditions [41]. Therefore, developing a
more efficient and environmentally friendly methodology for the Passerini reaction
is highly desirable.
Results and discussion
As part of our studies on MCRs [42–46], herein we wish to report an efficient, fast,
and environmentally compatible procedures for the synthesis of a-acyloxyamide
derivatives with a Passerini three-component cascade reaction in various choline
chloride-based deep eutectic solvents. It was found that simple mixing of an
aldehyde, a carboxylic acid, and an isocyanide in DES without using any catalysts
afforded products in excellent yield. In order to obtain the best medium, the
catalytic activities of various DESs were evaluated. The model reaction of
F
F
F
F
O
O
H
N
H
N
NC
O
O
O
O
O
O2N
A
B
F
Fig. 1 Examples of a-acyloxyamide-based drugs
123

A. Shaabani et al.
benzaldehyde (0.20 mmol), benzoic acid (0.20 mmol), and cyclohexyl isocyanide
(0.20 mmol) was investigated in various choline chloride-based DESs systems at
different temperatures. Furthermore, the utilization of some DESs based on ChCl
such as ethylene glycol and resorcinol/urea provided the desired product in trace
yields at ambient temperature, but, at 60 °C, ChCl-based ethylene glycol was
observed at about 50 %. Likewise, utilization of organic acids on DESs such as
malonic acid, PTSA ,and citric acid indicated the moderate yield, while also for this
optimization ZnCl2 as a Lewis acid has been used.
As indicated in Table 1, the best conditions for this reaction were observed while
the starting materials were heated at 60 °C in choline chloride and urea.
After optimization, the scope of this reaction was examined using different
carboxylic acids, aldehydes, and isocyanides in 1 mL of DES (ChCl:Urea). The
results of these reactions are summarized in Table 2. Various carboxylic acids such
as benzoic acid, 4-methyl benzoic acid, 4-bromo benzoic acid, 2-naphthoic acid, and
trans-styryl acetic acid were used in this process. Our literature survey at this stage
revealed that there was no report yet available on the use of 2-naphthoic acid in the
Passerini reactions (4p). Aliphatic acids such as propionic acid (4k) were applied
successfully in this reaction and afforded the corresponding a-acyloxyamides in
excellent yields. Also, aromatic aldehydes containing both electron-donating and
withdrawing groups on the phenyl ring reacted equally well in this protocol.
Heteroaromatic aldehydes such as pyridine-4-carbaldehyde and furfural are
suitable substrates in this reaction (4j, 4p). In addition, aliphatic aldehyde such as
Table 1 Passerini reaction in various choline chloride-based DESsa
Entry
DES (molar ratio)
T (°C)
Yield (%)
1
Choline chloride:malonic acid (1:1)
Choline chloride:malonic acid (1:1)
Choline chloride:citric acid (2:1)
Choline chloride:citric acid (2:1)
Choline chloride:PTSA (1:1)
25
60
25
60
25
60
25
60
25
60
25
60
25
60
80
35
2
60
3
46
4
75
5
20
6
Choline chloride:PTSA (1:1)
66
7
Choline chloride:ZnCl2 (1:2)
35
8
Choline chloride:ZnCl2 (1:2)
63
9
Choline chloride:ethylene glycol (1:2)
Choline chloride:ethylene glycol (1:2)
Choline chloride:urea:resorcinol (1:2:3)
Choline chloride:urea:resorcinol (1:2:3)
Choline chloride:urea (1:2)
Trace
50
10
11
12
13
14
15
a
Trace
10
65
Choline chloride:urea (1:2)
90
Choline chloride:urea (1:2)
92
Reaction conditions: benzaldehyde (0.20 mmol), benzoic acid (0.20 mmol) and cyclohexyl isocyanide
(0.20 mmol)
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Passerini three-component cascade reactions in deep…
Table 2 Passerini reaction in DES conditions
Entry
R1
R2
R3
Time (min)
Product
Yield (%)a
1
C6H5
C6H5
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
tert-butyl
7
20
15
10
20
12
10
7
(4a)
(4b)
(4c)
(4d)
(4e)
(4f)
90
85
82
94
85
88
90
90
85
88
85
65
84
90
92
89
2
C6H5
o-NO2C6H4
m-NO2C6H4
p-NO2C6H4
o-CH3C6H4
p- CH3C6H4
p-BrC6H4
p-ClC6H4
p-CH3C6H4
4-Pyridine
p-BrC6H4
Isopropyl
Piperonal
p-ClC6H4
2-Naphthyl
2-Furan
3
C6H5
4
C6H5
5
C6H5
6
C6H5
7
C6H5
(4g)
(4h)
(4h)
(4j)
8
C6H5
9
p-BrC6H4
p-CH3C6H4
Propionic
C6H5
15
12
18
25
20
15
10
12
10
11
12
13
14
15
16
a
(4k)
(4l)
C6H5
(4m)
(4n)
(4o)
(4p)
C6H5
tert-butyl
p-CH3C6H4
2-Naphthyl
tert-butyl
tert-butyl
Isolated yield
isopropyl carbaldehyde reacted with moderate yield. Likewise we found that the
reactions proceeded very efficiently with alkyl isocyanides such as cyclohexyl
isocyanide and tert-butyl isocyanide.
In addition, for completing library compounds, our research conducted the
Passerini reaction with activated carbonyl group compounds such as alloxsans [47]
and isatin [48] instead of aldehydes. The scope of the reaction was investigated and
the results summarized in Table 3.
DES may play a dual role in this reaction as a solvent and a catalyst, which, in the
latter case, was activated by the carbonyl group via hydrogen bonding. Also, one of
the advantages of DES is their ability to perform as a recyclable reaction media. The
DES was dissolved in water, and the crude product was obtained by extraction with
EtOAc. The DES was recovered by evaporating water at 80 °C under vacuum and
recycled for the next batch. Afterward, it was reused for subsequent reactions
(Fig. 2).
The results of our reaction conditions were compared with previous reports for
the synthesis of a-acyloxyamides with respect to their yields, temperatures, and the
times required for the reaction. As shown in Table 4, in the case of DES, the
123

A. Shaabani et al.
Table 3 Synthesis of a-acyloxyamides by alloxsans and isatin
O
O
O
R
O
R
O
+
+
or
R3 NC
O
N
N
R1
OH
N
H
O
R: H, CH3
O
O
N
O
O
NH
O
NH
N
HN
O
O
O
O
N
H
O
O
O
5b:3h, 72%
5a:2h, 80%
NH
NH
O
O
O
O
O
O
O
O
N
H
N
H
5d:2.5h, 70%
5c:3h, 75%
100
80
60
40
20
0
Fig. 2 Reusability of DES
1
2
3
4
Run
reaction yield is increased at the shorter reaction times under mild conditions and
avoids problems associated with such as handling, safety, pollution, corrosiveness,
harsh reaction conditions, toxicity of metal-containing waste, tedious work-up, and
catalyst recovery.
123

Passerini three-component cascade reactions in deep…
Experimental section
Melting points were measured on an Electrothermal 9100 apparatus and are
uncorrected. IR spectra were recorded on a Shimadzu IR-470 spectrometer. The
elemental analyses were performed with an Elementar Analysensysteme GmbH
VarioEL. 1H and 13C NMR spectra were recorded on a BRUKER DRX-300
AVANCE spectrometer at 300.13 and 75.47 MHz. NMR spectra were obtained in
DMSO-d6. The chemicals used were purchased from Merck and Fluka Chemical
Companies.
Preparation of choline chloride based deep eutectic solvents (DESs)
Choline chloride-based deep eutectic solvent was prepared according to the
literature [2, 3]; choline chloride and the second component were mixed on the basis
of reported relationships as in Table 1 and heated until a liquid appeared. The
obtained DES was used without any further purification.
General procedure for the synthesis of a-acyloxyamides
A mixture of an aldehyde (0.25 mmol), a carboxylic acid (0.25 mmol), and an
isocyanide (0.25 mmol) were placed in choline chloride–urea-based deep eutectic
solvent (1 mL) and vigorously stirred at 60 °C for a certain period of time as
indicated in Table 1. After completion of the reaction, as indicated by TLC (5:5
EtOAc:Hexane), water (10 mL) was added. The solid was separated by filtration
and washed twice with a saturated aqueous solution of NaHCO3. In most of the
cases, the pure products were obtained without further purification. If necessary, the
purification was performed by recrystallization from ethyl acetate or ethanol.
Table 4 Comparison of the results of the Passerini reaction using different systems with those obtained
by reported conditions
Conditions
T (°C)
Time
Yield (%)
Ref.
Water
25
3.5 h
72–95
64–92
20–89
35–91
60–92
40–92
78
[42]
Solvent free
180
25
4 min
24 h
[47]
Solvent free
[45]
Ionic liquid [bmim][PF6]
PEG 400
r.t
2–14 h
1–6 h
5–9 h
15 h
[44]
r.t
[43]
Ionic liquid [bmim][BF4]
CH2Cl2
60
[43]
Reflux
60
[44]
Toluene
10 h
77
[44]
MeOH
Reflux
60
18 h
32
[44]
Microwave
3–5 min
7–25 min
61–82
65–94
[46]
DES (choline chloride:urea)
60
This work
123

A. Shaabani et al.
Selected data of new compounds
(Cyclohexylcarbamoyl)(4-bromophenyl)methylbenzoate (4g)
White powder; m.p. 210 °C (dec). IR (KBr) cm-1: 3368, 3330, 2913, 2850, 1647,
1
1615, 1511, 1440. H NMR (300 MHz, DMSO-d6): d (ppm) 1.08–1.24 (m, 5H),
1.56–1.77(m, 5H), 3.37 (m, 1H), 6.07 (s, 1H), 7.57–7.85 (m, 7H), 8.03 (d, 2H,
J = 7.8 Hz), 8.32 (brs, 1H); 13C NMR (75 MHz, DMSO-d6): d (ppm) 24.8, 24.9,
25.5, 32.4, 32.6, 48.1, 75.2, 122.3, 129.3, 129.5, 129.7, 129.9, 131.9, 134.1, 135.9,
165.3, 166.9 Anal. Calcd for C21H22BrNO3: C, 60.59; H, 5.33; N, 3.36; found C,
60.22; H, 5.64; N, 3.45.
(Cyclohexylcarbamoyl)(4-bromophenyl)methyl propionate (4k)
Cream powder; m.p. 102–104 °C. IR (KBr) cm-1: 3335, 2927, 2840, 1651, 1531,
1435. 1H NMR (300 MHz, DMSO-d6): d (ppm) 1.02–1.07(t, 3H, J = 7.5 Hz),
1.13–1.20(m, 5H), 1.54–1.69 (m, 5H), 2.41–2.44 (q, 2H, J = 2.4 Hz), 3.12 (m, 1H),
5.81 (s, 1H), 7.35–7.43 (m, 2H), 7.57–7.60 (m, 2H), 8.20 (brs, 1H); 13C NMR
(75 MHz, DMSO-d6): d (ppm) 25.1, 25.5, 25.7, 27.1, 32.4, 32.6, 48.0, 53.6, 74.5,
122.1, 129.7, 131.7, 136.0, 167.0, 173.3; Anal. Calcd for C17H22BrNO3: C, 55.44;
H, 6.02; N, 3.80; found C, 55.22; H, 5.95; N, 3.93.
(Tert-butylcarbamoyl)(naphthalen-2-yl)methyl 4-methylbenzoate (4o)
White powder; m.p. 142–143 °C. IR (KBr) cm-1: 3335, 2907, 2838, 1662, 1531,
1435. 1H NMR (300 MHz, DMSO-d6): d (ppm) 1.23 (m, 9H), 2.40 (m, 3H),
7.39–7.44 (m, 2H), 7.58 (m, 3H), 7.73–7.76 (m, 1H), 7.89–7.98 (m, 3H), 7.99 (brs,
1H), 8.08–8.11 (m, 2H); 13C NMR (75 MHz, DMSO-d6): d (ppm) 26.4, 33.5, 55.7,
80.7, 130.1, 131.0, 131.6, 131.8, 132.6, 132.8, 134.7, 137.4, 138.0, 139.0, 149.1,
162.8, 170.1; Anal. Calcd for C24H25NO3: C, 76.77; H, 6.71; N, 3.73; found C,
76.97; H, 6.50; N, 3.45.
(Tert-butylcarbamoyl)(furan-2-yl)methyl 2-naphthoate (4p)
Cream powder; m.p. 168–171 °C. IR (KBr) cm-1: 3348, 2910, 2843, 1657, 1625,
1
1511, 1480. H NMR (300 MHz, DMSO-d6): d (ppm) 1.27 (m, 9H), 4.14 (s, 1H),
5.93 (m, 1H), 6.40 (m, 1H), 6.50 (m, 1H), 7.43–7.59 (m, 5H), 7.73 (brs, 1H). 13C
NMR (75 MHz, DMSO-d6): d (ppm) 33.5, 55.1, 75.9, 107.1, 108.3, 111.7, 131.2,
132.8, 134.7, 137.4, 138.0, 139.0, 149.1, 162.8, 170.1. Anal. Calcd for C21H21NO4:
C, 71.78; H, 6.02; N, 3.99; found C, 71.57; H, 5.64; N, 4.45.
3-(Cyclohexylcarbamoyl)-2-oxoindolin-3-yl benzoate (5e)
Yellow powder; m.p. 199–204 °C. IR (KBr) cm-1: 3345, 2923, 2845, 1725, 1724,
1668, 1627, 1518, 1441. 1H NMR (300 MHz, CDCl3): d (ppm) 0.92–1.20 (m, 10H),
123

Passerini three-component cascade reactions in deep…
3.70 (brs, 1H), 6.80–6.82 (m, 2H), 7.15–7.22 (m, 4H), 7.73–7.79 (m, 2H), 7.82 (brs,
1H). C22H22N2O4: C, 69.83; H, 5.86; N, 7.40; found C, 69.22; H, 5.64; N, 8.45.
Conclusion
In summary, we have described a green, effective, and rapid strategy for use of the
Passerini reaction with an eco-friendly and biodegradable deep eutectic solvent
based in a mixture of choline chloride and urea. Advantages of this system are
simplicity, easy separation, reusability of DES, short reaction times, and high yields.
Acknowledgments We gratefully acknowledge financial support from the Iran National Science
Foundation (INSF), the Research Council of Shahid Beheshti University, and Catalyst Center of
Excellence (CCE) at Shahid Beheshti University.
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