A mild, efficient, and green procedure for Michael addition of active methylene compounds to chalcones under microwave irradiation

Article abstract of DOI:10.1081/SCC-200048473

A simple, rapid, and highly efficient method has been developed for the Michael addition of active methylene compounds to chalcones using potassium carbonate and water under microwave irradiation. The method is totally exempt of organic solvents, and pure

Full text of DOI:10.1081/SCC-200048473

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A Mild, Efficient, and Green
Procedure for Michael
Addition of Active Methylene
Compounds to Chalcones Under
Microwave Irradiation
Satya Paul a , Monika Gupta a , Parvinder Pal Singh a
, Rajive Gupta a & André Loupy b
a Department of Chemistry, University of Jammu,
Jammu, 180 006, India
b Laboratoire des Réactions Sélectives sur Supports,
CNRS UMR 8615, ICMMO, Université Paris‐Sud, Orsay
Cedex, France
Available online: 28 Jul 2007
To cite this article: Satya Paul, Monika Gupta, Parvinder Pal Singh, Rajive Gupta &
André Loupy (2005): A Mild, Efficient, and Green Procedure for Michael Addition of
Active Methylene Compounds to Chalcones Under Microwave Irradiation, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:2, 325-332
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Synthetic Communicationsw, 35: 325–332, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048473
A Mild, Efficient, and Green Procedure for
Michael Addition of Active Methylene
Compounds to Chalcones Under
Microwave Irradiation
Satya Paul, Monika Gupta, Parvinder Pal Singh, and Rajive Gupta
Department of Chemistry, University of Jammu, Jammu, India
†
´
Andre Loupy
´
Laboratoire des Reactions Selectives sur Supports, CNRS UMR 8615,
´
´
ICMMO, Universite Paris-Sud, Orsay Cedex, France
Abstract: A simple, rapid, and highly efficient method has been developed for the
Michael addition of active methylene compounds to chalcones using potassium
carbonate and water under microwave irradiation. The method is totally exempt of
organic solvents, and pure products were obtained in good to excellent yields. This
method can be used for the parallel synthesis and further scale-up to 50 mmol of
substrate.
Keywords: Michael reaction, chalcones, active methylene compounds, water,
potassium carbonate, microwave activation
INTRODUCTION
Michael addition of active methylene compounds to a,b-unsaturated ketones
is a highly useful method for the formation of C22C bonds. The reaction is
Received in the UK June 10, 2004
Address correspondence to Satya Paul, Department of Chemistry, University of
Jammu, Jammu 180 006, India. Fax: þ91-191-2505086; E-mail: paul7@rediffmail.
com
†Fax: 33 1 69 15 46 79; E-mail: aloupy@icmo.u-psud.fr

326
S. Paul et al.
usually catalyzed by strong bases such as NaOH, KOH, Ba(OH)2, and NaOEt.
But these drastic conditions often cause some side reactions, including
rearrangement, bis-addition, auto-condensation, subsequent condensation,
retro-Michael reaction and so on.[1–5] These undesirable side reactions
decrease the yield and make the purification of products very difficult. It
has been reported[6] that when weaker bases such as piperidine and tertiary
amines are used, then better results can be obtained. There have been
reports on Michael reaction catalyzed by K2CO3 in organic solvent,[7] in
water and in the presence of surfactant,[8] and under phase transfer catalysis
conditions.[9–11] To some extent, these mild conditions can minimize the
reversibility of Michael addition reaction[12] and other side reactions;
thus, improved yields can be achieved. However, there were still some dis-
advantages due to long reaction time or tedious workup in these methods.
Recently, Michael addition reaction in solvent-free conditions using high-
speed vibration milling was reported.[13,14] Although this is quite a good
method, it still has the disadvantage of experimental setup because one has
to first make a capsule and then be fitted in the vibration mill. Furthermore,
the method has been described only for 1 mmol of substrates, and the
authors are silent about the scaling up of the procedure for larger amounts.
Thus, to circumvent the above problems, a safe, mild, simple, environment-
friendly, and general method needs to be developed.
The use of microwaves for carrying out organic reactions is a well-
established procedure because the reactions are clean, fast, and economical,
and the workup procedure becomes very simple. Work in this direction has
recently been reviewed.[15–21]
The use of water as a solvent in organic chemistry was rediscovered in the
1980s by Breslow et al., who showed that hydrophobic effects can strongly
enhance the rate of several organic reactions.[22,23] Previously, the scant solu-
bility of the reactants was the main reason that ruled out this solvent from
studies. Furthermore, reasons that make water unique among solvents are
that it is cheap, not flammable, and, more importantly, it is not toxic.
Organic reactions using water under microwave irradiation[24,25] is an actual
field that has shown excellent results, leading to the development of many
reaction procedures which are environment-friendly and falling in the
domain of Green Chemistry. There are some reports on Michael reaction
under microwave irradiation.[26–32]
Keeping in view the importance of Michael reaction in academia,
industry, and our continued interest[34–37] in devising environment friendly
procedures for organic reactions, we report here a simple, efficient, rapid,
and environment-friendly procedure for the Michael addition of active
methylene compounds to chalcones using water as energy transfer medium
and K2CO3 as base under microwave irradiation (Scheme 1).
The Michael reaction of chalcone 1a with diethylmalonate 2 was first
examined by using K2CO3 as base and water as solvent. The molar ratios of

Michael Addition of Active Methylene Compounds
327
Scheme 1.
reagents, irradiation times, and microwave power levels were optimized to
achieve higher yields in an environment-friendly way. Optimum conditions
(Table 1) used a 1 : 1 molar ratio of chalcone 1a and diethylmalonate 2 with
K2CO3 (2 eq) and water (2 mL for 5 mmol of the substrate). Power level
corresponding to 480 W was found to be an efficient power level for the
reaction to proceed safely. All reactions were performed by using 5 mmol
of chalcone 1, 5 mmol of active methylene compound 2, 10 mmol of
Table 1. Microwave-induced Michael reaction of chalcones with active methylene
compounds using K2CO3/H2O (power ¼ 480 W)
Product
Timea (min)
Reaction temp.b (8C)
Yieldc (%)
3a
3b
3c
3d
3e
3f
1
82–84
85–87
84–86
75–78
88–91
88–92
85–88
89–92
88–91
91–93
88–90
87–90
92
93
91
92
87
92
90
85
99
95
92
96
1.25
3
2.75
0.5
0.75
1
3g
3h
3i
3
1.75
1.25
3
3j
3k
3l
1
aReactions were carried out with pulse of 30 s (10 s cooling time).
bFinal temperature was measured by immersing a glass thermometer in the reaction
mixture at the end of exposure during the MW experiment and was an approximate
temperature range.
cIsolated yield from 3 runs.

328
S. Paul et al.
K2CO3, and 2 mL of water. In each case, almost pure products (on the basis of
TLC) were obtained and hence no need for further purification.
To describe the general applicability of the procedure, different chalcones
(1a–l) were reacted with different active methylene compounds 2 (diethyl-
malonate, ethylcyanoacetate, and ethylacetoacetate). In all cases, our protocol
is highly successful and leads to pure products in nearly quantitative yields.
To show the feasibility of using microwave irradiation for the parallel
Michael addition reaction of chalcones with active methylene compounds,
four reaction vessels containing the appropriate mixtures of chalcones
1a–d, diethylmalonate 2, K2CO3, and water were simultaneously placed
inside the oven and irradiated. After workup, the products were obtained in
good to excellent yields. Furthermore, to explore the possibility of scaling
up of our procedures for larger amounts, reaction in chalcone 1a (50 mmol)
with diethylmalonate 2 (50 mmol), K2CO3 (75 mmol), and water (25 mL)
was carried out under MW irradiation. It has been found that the reaction
works equally well for 5 mmol, and finally product 3a (17 g, 85%) was
obtained.
EXPERIMENTAL
General
Melting points were determined on a Buchi melting point apparatus and are
1
uncorrected. H NMR spectra were obtained on a Bruker DPX-200 NMR
spectrometer (200 MHz) in CDCl3/CDCl3 þ DMSO-d6 using tetramethyl-
silane as internal standard, and IR spectra were recorded by using KBr disc
on Hitachi 270–30 spectrophotometer. The mass spectral data were
obtained on a JEOL D-300 spectrometer. The reactions were monitored by
TLC. For the microwave irradiation experiments described below, a conven-
tional (unmodified) household microwave oven equipped with a turntable was
used (LG Little Chef MS 192 W operating at 2450 MHz having maximum
output of 800 W).
General Procedure for Michael Reaction of Chalcones 1 with
Active Methylene Compounds 2
Single-compound Method
The appropriate chalcone 1 (5 mmol), active methylene compound 2
(5 mmol), K2CO3 (10 mmol), and distilled water (2 mL) were taken in a
borosil beaker (50 mL) and mixed properly with the help of a glass rod
(15 s). The beaker was then introduced into a microwave oven (LG Little

Michael Addition of Active Methylene Compounds
329
Chef MS 192 W operating at 2450 MHz having maximum output of 800
Watt), and the mixture was irradiated at 480 W for an appropriate time
(Table 1). After irradiation, ice-cold water (5 mL) was added, and the
product so obtained was filtered, washed with excess water, and dried.
It was crystallized from EtOAc: pet. ether.
Parallel Synthesis Method (in Products 3a–d)
The appropriate chalcone 1 (5 mmol), diethylmalonate 2 (5 mmol), K2CO3
(10 mmol), and water (2 mL) were placed in four individual beakers
(25 mL). The mixture in all four beakers was mixed separately (15 s each).
The beakers were then introduced inside the MW oven and irradiated simul-
taneously six times at 480 W for 30 s with 1 min cooling time. After workup as
above, products 3a–d (Table 2) were obtained in good to excellent yields.
1
The structures of the products were confirmed by IR, H NMR, mass
spectroscopy, and by comparison with authentic samples prepared according
to literature methods.
Spectral and Analytical Data of Some Selected Compounds
Compound 3c
Mp 116–1188C (lit. Mp 1228C).[2] IR (KBr): 1754, 1730, 1685 cm21
.
1H NMR (300 MHz, CDCl3): d 1.12 (t, J ¼ 7.2 Hz, 3H), 1.25 (t, J ¼ 7.1 Hz,
3H), 3.40 (d, J ¼ 16.7, 9.10 Hz, 1H), 3.52 (dd, J ¼ 16.2, 4.7 Hz, 1H), 3.75
(d, J ¼ 9.75 Hz, 1H), 4.01 (q, J ¼ 7.4 Hz, 2H), 4.10 (td, J ¼ 9.35,
4.7 Hz, 1H), 4.22 (q, J ¼ 7.1 Hz, 2H), 7.44 (dd, J ¼ 7.1 Hz, 1H), 7.50
(d, J ¼ 9.0 Hz, 2H), 7.76 (td, J ¼ 7.6, 1.5 Hz, 1H), 7.95 (dd, J ¼ 7.8 Hz,
2H), 8.10 (d, J ¼ 9.0 Hz, 2H), 8.50 (d, J ¼ 4.0 Hz, 1H). m/z (Mþ): 413.15.
Table 2. Parallel Michael reaction of chalcones with diethylmalonate using
K2CO3/H2O under microwave irradiation (power ¼ 480 W)
Reaction
temp.a (8C)
Chalcone
Product
Time (min)
Yieldb (%)
1a
1b
1c
1d
3a
3b
3c
3d
3
3
3
3
88–90
89–92
88–91
75–78
92
91
89
93
aThe final temperature was measured by immersing a glass thermometer in the
reaction mixture at the end of exposure during the MW experiment and was an approxi-
mate temperature range.
bIsolated yield from 3 runs.

330
S. Paul et al.
Compound 3d
1
Mp 57–588C (lit. Mp 58–608C).[13] IR (KBr): 1752, 1730, 1682 cm21. H
NMR (300 MHz, CDCl3): d 1.08 (t, J ¼ 7.1 Hz, 3H), 1.23 (t, J ¼ 7.1 Hz,
3H), 3.38 (dd, J ¼ 16.5, 9.25 Hz, 1H), 3.50 (dd, J ¼ 16.4, 4.5 Hz, 1H), 3.75
(d, J ¼ 9.7 Hz, 1H), 4.01 (q, J ¼ 7.4 Hz, 2H), 4.10 (td, J ¼ 9.4, 4.6 Hz, 1H),
4.20 (qd, J ¼ 7.0 Hz, 2H), 5.83 (s, 2H), 6.67 (d, J ¼ 8.0 Hz, 1H), 6.70 (dd,
J ¼ 8.0, 1.1 Hz, 2H), 6.77 (d, J ¼ 1.1 Hz, 1H), 7.43 (t, J ¼ 7.68 Hz, 2H),
7.54 (t, J ¼ 7.3 Hz, 1H), 7.92 (d, J ¼ 7.3, 1.2 Hz, 1H). m/z (Mþ): 393.45.
Compound 3g
Mp 132–338C. IR (KBr): 2223, 1750, 1722, 1688 cm21. 1H NMR (300 MHz,
CDCl3): d 1.15 (t, J ¼ 7.2 Hz, 3H), 3.48 (dd, J ¼ 17.1, 9.1 Hz, 1H), 3.64
(dd, J ¼ 16.8, 4.7 Hz, 1H), 3.85 (d, J ¼ 9.6 Hz, 1H), 3.98 (q, J ¼ 7.5 Hz,
2H), 4.12 (td, J ¼ 9.6, 4.7 Hz, 1H), 7.47 (dd, J ¼ 7.0 Hz, 1H), 7.52
(d, J ¼ 8.9 Hz, 2H), 7.75(td, J ¼ 7.6, 1.5 Hz, 1H), 7.92 (dd, J ¼ 7.8 Hz, 2H),
8.10 (d, J ¼ 8.5 Hz, 2H), 8.60 (d, J ¼ 4.2 Hz, 1H).m/z (Mþ): 366.23.
Compound 3h
Mp 104–1068C (lit. Mp 1078C).[38] IR (KBr): 2220, 1748, 1717, 1685 cm21
.
1H NMR (300 MHz, CDCl3): d 1.15 (t, J ¼ 7.3 Hz, 3H), 3.42 (dd, J ¼ 17.0,
9.3 Hz, 1H), 3.50 (dd, J ¼ 16.7, 4.4 Hz, 1H), 3.75 (d, J ¼ 10.0 Hz, 1H), 4.12
(tq, J ¼ 9.3, 4.7 Hz, 1H), 4.17 (q, J ¼ 7.5 Hz, 2H), 5.85 (s, 2H), 6.69
(d, J ¼ 8.1 Hz, 1H), 6.73 (dd, J ¼ 8.0, 1.1 Hz, 2H), 6.78 (d, J ¼ 1.1 Hz, 1H),
7.43 (t, J ¼ 7.71 Hz, 2H), 7.57 (t, J ¼ 7.4 Hz, 1H), 7.92 (d, J ¼ 7.4, 1.2 Hz,
1H). m/z (Mþ): 365.82.
Compound 3i
1
Mp 62–638C. IR (KBr): 1750, 1721, 1688, 1273 cm21. H NMR (300 MHz,
CDCl3): d 1.19 (t, J ¼ 7.4 Hz, 3H), 2.44 (s, 3H), 3.56 (dd, J ¼ 17.4, 4.0 Hz,
1H), 3.77 (d, J ¼ 10.2 Hz, 1H), 3.95 (dd, J ¼ 17.7, 9.6 Hz, 1H), 3.98
(s, 3H), 4.03 (q, J ¼ 7.0 Hz, 2H), 4.17 (td, J ¼ 9.7, 4.5 Hz, 1H), 7.0
(d, J ¼ 8.0 Hz, 2H), 7.12 (d, J ¼ 8.0 Hz, 2H), 7.40 (dd, J ¼ 7.0, 5.0 Hz, 1H),
7.60 (t, J ¼ 7.5 Hz, 1H), 7.72 (d, J ¼ 7.5 Hz, 2H), 7.90 (d, J ¼ 4.4 Hz, 1H).
m/z (Mþ): 367.13.
Compound 3j
Mp 91–928C (lit. Mp 948C).[39] IR (KBr): 1752, 1730, 1682 cm21. 1H NMR
(300 MHz, CDCl3): d 1.17 (t, J ¼ 7.3 Hz, 3H), 2.41 (s, 3H), 3.54 (dd, J ¼ 17.7,
4.1 Hz, 1H), 3.76 (d, J ¼ 10.4 Hz, 1H), 3.92 (dd, J ¼ 17.9, 9.7 Hz, 1H), 4.03

Michael Addition of Active Methylene Compounds
331
(q, J ¼ 7.0 Hz, 2H), 4.15 (td, J ¼ 9.7, 4.6 Hz, 1H), 7.21 (d, J ¼ 8.1 Hz, 2H),
7.28 (dd, J ¼ 8.2 Hz, 2H), 7.47 (dd, J ¼ 7.0, 5.0 Hz, 1H), 7.78
(t, J ¼ 7.6 Hz, 1H), 7.90 (d, J ¼ 7.5 Hz, 2H), 8.60 (d, J ¼ 4.4 Hz, 1H). m/z
(Mþ): 372.64.
Compound 3l
Mp 87–898C. IR (KBr): 1755, 1728, 1685 cm21 1H NMR (300 MHz,
.
CDCl3): d 1.14 (t, J ¼ 7.2 Hz, 3H), 2.47 (s, 3H), 3.50 (dd, J ¼ 17.1, 4.0 Hz,
1H), 3.70 (d, J ¼ 9.8 Hz, 1H), 3.88 (dd, J ¼ 17.1, 9.6 Hz, 1H), 4.07
(q, J ¼ 7.1 Hz, 2H), 4.16 (td, J ¼ 9.8, 4.7 Hz, 1H), 5.83 (s, 2H), 6.66
(d, J ¼ 7.8 Hz, 1H), 6.71 (dd, J ¼ 8.1, 1.0 Hz, 2H), 6.78 (d, J ¼ 1.1 Hz, 1H),
7.40 (t, J ¼ 7.6 Hz, 2H), 7.52 (t, J ¼ 7.21 Hz, 1H), 7.95 (d, J ¼ 7.32, 1.2 Hz,
1H). m/z (Mþ): 382.56.
In conclusion, we have developed an efficient procedure for Michael
reaction of a,b-unsaturated carbonyl compounds with active methylene
compounds using K2CO3 as base and water as nontoxic, cheap, and non-
flammable solvent and using a cheap and universal domestic MW oven
under very safe conditions in open vessels. The salient features of our method
is that it is simple, rapid, economical, general, environment-friendly, and
can be used for parallel synthesis and scaledup for larger amounts (e.g.,
50 mmol) of substrates. This method could be very efficient alternative to
existing methods.
ACKNOWLEDGMENT
One of the authors (MG) is thankful to Council of Scientific and Industrial
Research (CSIR), New Delhi, for awarding Junior Research Fellowship (JRF).
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