[bmim]OH-promoted one-pot, three-component synthesis of β-nitro sulfides in water

Article abstract of DOI:10.1080/10426507.2016.1146272

A task-specific ionic liquid, [bmim]OH, has been found to be a highly efficient catalyst for one-pot, three-component coupling of aryl aldehydes, nitromethane, and thiols for the synthesis of β-nitro sulfides in water. The main advantages of the present p

Full text of DOI:10.1080/10426507.2016.1146272

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
[bmim]OH-Promoted one-pot three-component
synthesis of β-nitro sulfides in water
Ali Yousefi & Barahman Movassagh
To cite this article: Ali Yousefi & Barahman Movassagh (2016): [bmim]OH-Promoted one-pot
three-component synthesis of β-nitro sulfides in water, Phosphorus, Sulfur, and Silicon and the
Related Elements, DOI: 10.1080/10426507.2016.1146272
To link to this article: http://dx.doi.org/10.1080/10426507.2016.1146272
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[bmim]OH-Promoted one-pot three-component synthesis of β-nitro sulfides in water
Ali Yousefia,b,* and Barahman Movassagha
a Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315-1618,
Tehran, Iran
b Department of Chemistry, Faculty of Sciences, Shahid Rajaee Teacher Training University, P.
O. Box 16785-163, Tehran, Iran
E-mail address: nmryousefi@yahoo.com
Abstract
A task-specific ionic liquid, [bmim]OH, has been found to be a highly efficient catalyst for one-
pot three-component coupling of aryl aldehydes, nitromethane, and thiols for the synthesis of β-
nitro sulfides in water. The main advantages of the present protocol include the use of
inexpensive simple substrates and an ionic liquid as a basic catalyst.
RS
[bmim]OH (20 mol%)
ArCHO
NO2
+
RSH
CH3NO2
+
H2O, 100 oC
Ar
Keywords
β-Nitro sulfides; ionic liquids; thiols; aldehydes; nitromethane; water
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Introduction
Water has attracted considerable attention in recent years as a versatile solvent in organic
chemistry because of its power to minimizing toxic organic solvent disposal and waste
production.1-3 Water as a solvent is non-toxic, non-inflammable and has high heat capacity,
possibility of controlling pH, isolating insoluble solid products by filtration and recycling
inorganic catalysts.1
Due to the fact that organic products can be proposed directly in a single step and diversity
can be achieved simply by varying the reaction substrates,4 the multi-component reactions
(MCRs) were utilized to synthesize novel chemicals, drug-like scaffolds, and natural product
compounds has pervaded in organic transformation.5,6
Ionic liquids (ILs) have attracted increasing interest in organic synthesis owing to their great
potential not only as alternative green reaction media but also as new catalysts and reagents, and
because they are also easy to recycle.7-14
Nitro olefins have been recognized as versatile building blocks and synthetic intermediates
due to their easy conversion into a variety of diverse functionalities.15-21 These compounds are
markedly electron-deficient and powerful dienophiles in the Diels-Alder reaction.18
Alternatively, these electrophilic alkenes readily undergo Michael addition with many different
nucleophiles because of the strong electron-withdrawing nature of the nitro group.
Heteroatom-centered nucleophiles such as sulfur, oxygen, nitrogen, and phosphorous anions
are good nucleophiles for the Michael addition to nitroalkenes, which provides a useful method
for the introduction of two heteroatoms on vicinal positions, in which the nitro group can be
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readily converted into other functional groups such as keto (the Nef reaction), cyano, and amino
groups.18, 22-27
The reaction of thiols with nitroalkenes in the presence of a base is the most common method
for the preparation of β-nitro sulfides.28-36 The treatment of β-nitro acetals with thiols in the
presence of triethylamine has also been reported for the preparation of β-nitro sulfides.37
Recently, ionic liquids such as n-Bu4NBr,38 and Me4NF39 have been introduced as efficient
catalyst for the Michael addition of thiols to α,β-unsaturated carbonyl compounds, as well as
limited numbers of nitroolefins. Several other procedures for the preparation of β-nitro sulfides
from thiols and β-nitrostyrenes have been introduced, using ammonium chloride as a catalyst,40
and catalyst-free reaction under neat condition41 or in water42 as medium.
Results and Discussion
In recent years, basic ionic liquids (BILs) have been used as environmentally friendly
solvents and catalysts with high activity and selectivity and easily recoverable materials
which can replace traditional bases such as KOH, H2CO3, NaOAc, and Et3N. 1-Butyl-3-
methylimidazolinium hydroxide, [bmim]OH, is one such BIL which acts as a reaction
medium as well as a basic catalyst and has varied applications in the field of synthetic
methodology development.43-47
To the best of our knowledge, there is no report of constructing β-nitro sulfides by a
one-pot, three-component reaction of an aryl aldehyde, nitromethane, and thiols.
Considering the above points along with our ongoing efforts to develop new one-pot
synthetic processes,48-55 we report herein the first ionic liquid [bmim]OH-promoted
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synthesis of β-nitro sulfides using a three-component coupling reaction of aromatic
aldehydes, nitromethane, and thiols in water at 100 ºC.
To find the optimal conditions, a mixture of benzaldehyde (1.0 mmol), nitromethane
(1.0 mmol), and thiophenol (1.0 mmol) was examined under various conditions (Table 1);
the effect of different solvents, temperatures, basic catalysts as well as ionic liquids were
examined. The best result (86%) was obtained by carrying out the reaction in the presence
of [bmim]OH ionic liquid. The use of other organic and inorganic basic catalysts such as
Et3N, DABCO, K3PO4 and Cs2CO3 resulted in a considerable drop in yields (under 45%).
Also, optimization of the solvent was investigated and it was found that among
acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, toluene, water, and even
solvent-free conditions, the best result in terms of yield was obtained with water (Table 1,
Entries 4-10).
The effect of the reaction temperature was also checked, and the best performance was
observed at 100 ºC. The optimum catalyst loading for the ionic liquid [bmim]OH was
found to be 20 mol% (Table 1, Entry 5); however, a catalyst loading lower than 20 mol%
gave decreased yield (Table 1, Entry 6), while an increase in the catalyst concentration to
40 mol% did not appreciably increase the yield (Table 1, Entry 7). Therefore, it was
decided to use [bmim]OH as the catalyst, H2O as the solvent, and 20 mol% of the catalyst
at 100 ºC as the optimum conditions in further studies.
To survey the generality of the catalytic protocol, we studied this thia-Michael reaction
using various aryl and heteroaryl aldehydes as well as different thiols including aromatic
thiols and alkyl thiols under the optimized reaction conditions. The results are listed in
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Table 2, and β-nitro sulfides could be obtained in good to excellent yields (75-96%).
Generally, the reaction rate of aromatic thiols was found to be faster than that of alkyl
thiols (Table 2, Entrie 1-6). The reaction was almost equally facile with both electron-donating
and moderate electron-withdrawing substituents on the aldehydes (Table 2, Entries 7, 10 and 13).
Heteroaryl aldehydes such as furfural and thiophene-2-carbaldehyde also reacted with thiols to
give the products in good to high yields (Table 2, Entries 12 and 14).
Conclusion
In summary, a simple and very efficient one-pot three-component procedure for the synthesis
of β-nitro sulfides starting from aldehydes, nitromethane, and thiols in water using a task-specific
ionic liquid, [bmim]OH, has been developed. This method offers marked improvements with
regard to operational simplicity, greenness of procedure, avoiding hazardous organic solvents
and toxic catalysts, general applicability, reaction conditions, high isolated yields, and thus it
provides a better and practical alternative to the existing procedures.28-42
Experimental
All chemicals were purchased from Merck and Fluka chemical companies. Melting points were
determined on a Büchi melting point B-540 apparatus. Fourier transform infrared (FT-IR)
spectra were recorded on an ABB Bomem Model FTLA 2000 spectrophotometer. Nuclear
magnetic resonance (NMR) spectra were recorded at 300 (1H) and 75.4 (13C) MHz, on a
commercial Bruker DMX-300 instrument using CDCl3 as solvent. Chemical shifts were
determined by reference to residual CHCl3 in CDCl3. The Supplemental Materials contains
sample 1H and 13C NMR spectra for the known products (Figures S 1 -- S 16)
General procedure
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A mixture of an aromatic aldehyde (1.0 mmol), nitromethane (1.0 mmol), thiol (1.0 mmol),
and [bmim]OH (20 mol%) in water (2 mL) was stirred at 100 C for an appropriate time of 5-12
h (Table 2). The course of the reaction was monitored by thin layer chromatography (TLC) until
the starting materials disappeared completely. Then, water (8 mL) was added to the reaction
mixture, and extracted with diethyl ether (2 × 10 mL). The combined organic layer was dried
(Na2SO4) and the solvent was evaporated under reduced pressure, and the crude product thus
obtained was purified by preparative TLC (silica gel, eluent EtOAc/n-hexane = 1:10) to obtain
pure products. The remaining ionic liquid was rinsed with ether (5 mL), dried under vacuum at
90 C for 2 h to eliminate any water trapped and reused for subsequent runs.45
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Table 1. Optimization of the base-catalyzed one-pot reaction of benzaldehyde,
nitromethane, and thiophenola
SPh
Base
PhCHO + CH3NO2 + PhSH
NO2
Ph
Base (mol Temp. Yield
Entry Solvent
%)
(°C)
(%)b
40
[bmim]BF4
(20)
1
2
CH3CN
CH3CN
CH3CN
85
[bmim]OH
(20)
85
75
60
54
86
70
87
63
10
45
[bmim]OH
(20)
3
75
[bmim]OH
(20)
4
100
100
100
100
100
100
100
[bmim]OH
(20)
5
H2O
H2O
[bmim]OH
(15)
6
[bmim]OH
(40)
7
H2O
[bmim]OH
(20)
8
DMSO
PhCH3
DMF
[bmim]OH
(20)
9
[bmim]OH
(20)
10
aReaction conditions: benzaldehyde (1.0 mmol), nitromethane (1.0 mmol), thiophenol (1.0
mmol), base, solvent (2 ML), 6 h.
bYield of isolated and purified product.
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Table 2 One-pot three-component [bmim]OH-promoted synthesis of β-nitro sulfidesa
RS
[bmim]OH (20 mol%)
ArCHO
NO2
RSH
+
CH3NO2
+
H2O, 100 oC
Ar
3
2
1
Time Yield
(h)
Entry
Aldehyde
PhCHO
PhCHO
Thiol
PhSH
Product
3a
(%)b,c
8641
1
2
6
SH
6
6
9534
9134
3b
Me
SH
3
PhCHO
3c
Me
SH
4
5
6
PhCHO
PhCHO
PhCHO
6
9041
8441
8556
3d
3e
3f
SH
SH
12
12
CHO
7
8
PhSH
6
5
9441
9634
3g
3h
MeO
MeO
CHO
SH
Me
OMe
CHO
9
PhSH
PhSH
6
6
8356
8741
3i
3j
CHO
10
Cl
CHO
11
12
PhSH
PhSH
8
8441
7541
3k
3l
12
O
CHO
12
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Cl
CHO
SH
SH
13
12
6
7857
8557
3m
3n
Cl
14
S
CHO
aReaction conditions: aldehyde (1.0 mmol), nitromethane (1.0 mmol), and thiol (1.0 mmol),
catalyst (20 mol%), H2O (2 ML), 100 ºC.
bYield of isolated and purified product.
cReferences are provided for known compounds.
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