Solvent-free microwave Michael addition between EMME and various nucleophiles

Article abstract of DOI:10.1081/SCC-200046503

Michael addition reaction between EMME and various O, S, N nucleophiles were investigated in the presence of catalysts such as KF, KOH, or K(OCCH ₃)₃ under solvent-free conditions either neat or on alumina as solid support. Compared

Full text of DOI:10.1081/SCC-200046503

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Solvent‐Free Microwave
Michael Addition Between
EMME and Various Nucleophiles
André Loupy a , Suk Jin Song b , Seong Jin Cho b ,
Dong Kyu Park b & Tae Woo Kwon b
a Laboratoire des Réactions Sélectives sur Supports,
associé au CNRS, UMR 8615‐ICMMO , Université
Paris‐Sud , Batiment, Orsay Cédex, France
b College of Science , Kyungsung University ,
Daeyoen‐dong, Busan, 608‐736, Korea
Published online: 05 Aug 2006.
To cite this article: André Loupy , Suk Jin Song , Seong Jin Cho , Dong Kyu Park
& Tae Woo Kwon (2005) Solvent‐Free Microwave Michael Addition Between EMME
and Various Nucleophiles, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 35:1, 79-87, DOI: 10.1081/
SCC-200046503
To link to this article: http://dx.doi.org/10.1081/SCC-200046503
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Synthetic Communicationsw, 35: 79–87, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200046503
Solvent-Free Microwave Michael Addition
Between EMME and Various Nucleophiles
´
Andre Loupy
´ ´
Laboratoire des Reactions Selectives sur Supports, associe au CNRS,
´
´
UMR 8615-ICMMO, Universite Paris-Sud, Batiment,
´
Orsay Cedex, France
Suk Jin Song, Seong Jin Cho, Dong Kyu Park, and Tae Woo Kwon
College of Science, Kyungsung University, Busan, Korea
Abstract: Michael addition reaction between EMME and various O, S, N nucleophiles
were investigated in the presence of catalysts such as KF, KOH, or K(OCCH3)3 under
solvent-free conditions either neat or on alumina as solid support. Compared to
low reactivity of alcohols (40 to 80% yields according to aliphatic chain), aniline or
thiophenol gave good to excellent yields (90–99%).
Keywords: Alumina, Michael addition, microwave irradiation, solvent-free reactions,
specific microwave effects
INTRODUCTION
The electron-deficient alkenes such as commercially available diethyl ethoxy-
methylenemalonate (EMME) 1 are valuable intermediates for the synthesis
of biologically important materials[1–4] and attractive acceptors for a
variety of Michael addition donors.[5–7] The applications of microwave
irradiation in organic chemistry have increased very rapidly. Intra- or inter-
molecular addition of a variety of primary[8,9] and secondary amines,[10,11]
Received in Japan August 18, 2004
Address correspondence to Tae Woo Kwon, College of Science, Kyungsung
University, Daeyoen-dong, Busan 608-736, Korea. E-mail: aloupy@icmo.u-psud.fr
or twkwon@star.ks.ac.kr

80
A. Loupy et al.
enamines,[12] imidazole,[13] and active carbon anions[14,15] have been used in
the microwave activated Michael additions. In a previous paper, we reported
that 1 may be unexpectedly converted into symmetrical dialkyl and diaryl-
methyl malonated derivatives 2 using Grignard reagent (RMgBr/reflux)
(2a). No a-b unsaturated products 3 were isolated. Addition of organocuprates
(R2CuLi) to 1 gave ethoxy substituted Michael adduct 3a. However, it was not
facile to introduce oxygen atoms in electro-deficient alkenes backbone. For
example, it required two or more steps to obtain 5 via unstable chlorinated
intermediate 4 in the presence of highly toxic thionyl chloride and pyridine
reagents.[16] In the hope that this troublesome step[16–18] can be replaced by
microwave irradiation (MWI) technique under mild conditions, we focused
on the environmentally benign Michael addition between various O, S, and
N nucleophiles leading to 5 (R ¼ n-butyl, isopentyl, cyclohexyl, n-octyl
alcohols) and 6 (X ¼ S or NH) and EMME for carbon-heteroatom bond
formation under MWI in the absence of solvent or toxic species (Scheme 1).
First we check the stability of 1 under microwave irradiation. EMME 1
was irradiated for 5 min in the absence of any nucleophile or catalyst and
was recovered as 99.9%. Then we examined the time and yields relationship
between EMME and various alcohols under MWI conditions in the absence of
catalyst.
When n-butyl alcohol was irradiated for 1 min, reaction did not take place
and only EMME was recovered (Table 1, entry 1). The best results were
obtained when the mixtures were irradiated for 10 min with all the aliphatic
alcohols examined affording the desired product as the major one within 40,
41, 57, and 80% yields, respectively, with R ¼ n-Bu, i-Pent, Cyclohexyl
and n-Oct (Table 1, entries 3, 6, 8, and 13). The specific (non-purely
thermal) microwave effects were clearly observed after accurate comparaisons
Scheme 1.

Microwave Michael Addition Between EMME and Nucleophiles
81
Table 1. Optimization of the reaction time in the solvent-free Michael Addition
between neat EMME and various alcohols ROH under MWI or conventional heating
in a thermostated oil bath under similar sets of conditions. (Scale ¼ 5.55 mmol,
mole ratio of 1 : ROH ¼ 1 : 3)
Time
(min)
Temperaturea
Yield
5 (%)
Recovered
EMME (%)
Entry
R
(8C)
1 (5a)
2 (5a)
3 (5a)
4 (5a)
5 (5b)
6 (5b)
7 (5b)
8 (5c)
n-Butyl
n-Butyl
1
5
—
—
0
17
99
82
59
57
93
45
42
40
65
37
34
33
16
99
n-Butyl
n-Butyl
10
20
1
—
40
40
101
—
i-Pentyl
i-Pentyl
i-Pentyl
5
41
10
30
10
10
30
40
50
10
22
—
—
52
57 (MW)
29 (Db)
54
51
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
n-Octyl
142
142
—
9 (5c)
10 (5c)
11 (5c)
12 (5c)
13 (5d)
14 (5e)
—
—
50
80
—
—
Phenyl
0
aTemperature of the reaction mixture was recorded with a digital thermometer just at
the end of MWI.
bConventional heating at the same temperature but using a thermostated oil bath.
between MWI and conventional heating under similar conditions (vessels,
reaction time, and temperature) (entries 8 vs. 9). Extension of reaction
times up to more than 10 min did not enhance the formation of the desired
Michael addition adduct (entries 10–12). Under these conditions, PhOH
was not a successful nucleophile toward 1 and did not give the desired
coupling product (Table 1, entry 14).
Within 10 min of MWI, the sequence of yields we obtained is tightly
connected to the boiling point of the alcohol involved (Table 2).
The effect of R group can be understood by considering the addition-
elimination mechanism of ROH on EMME (Scheme 2). The competitive
pathways a and b can be either driven by the relative leaving group ability
(EtOH should be surely close to ROH) or better by ROH volatility.
Pathway a will be therefore favored when a high boiling point ROH is

82
A. Loupy et al.
Table 2. Yields of reaction between EMME and ROH as a function of R and of their
boiling points
R
n-Butyl
i-Pentyl
Cyclohexyl
n-Octyl
Yield of 5 (%)
Boiling point of
ROH (8C)
40
116–118
41
118–119
57
160–161
80
196
involved. This consideration leads to the same sequence as for observed
yields.
We have next studied the effects of different basic species generally used
under solvent-free conditions: a supported base on solid mineral support (KF/
alumina) and a phase transfer catalysis system (KOH þ TBAB).
The main results are given in Table 3. In all cases, as reaction time
increased in the presence of KF/Al2O3 the yields were enhanced but
remained rather limited (entries 1–4 and 5–8). No base addition effect was
observed in the case of cyclohexyl alcohol (Table 3, entry 7 vs. Table 1
entry 8). Nonactivated phenol was totally inert (entries 11–12). This fact
can be explained by considering that phenol is a better leaving group than
ethanol. However, on another hand, the phenoxy compound was obtained
easily by reacting phenol with the diethyl chloromethylenemalonate 4
(Scheme 3).
The reactions between EMME and other nucleophiles were also investi-
gated (Table 4). In the case of aniline, the best yield (90%) was obtained
without using catalyst (entry 8). From the reaction between 1 and aniline,
only a small difference between microwave and thermal effect was
observed (entry 8 vs. 9). The presence of base or support did not significantly
increase the yields (entries 1, 3 and 6, 8).
In sharp contrast of low reactivity of phenol (Table 1, entry 14), treatment
of 1 with thiophenol under similar conditions afforded excellent yields of 8
(quantitative yield; 99%, entry 15). In this case, no solid support effects
were detectable (entries 11 vs. 12). The yield was significantly increased in
the presence of KF (entries 12 vs. 15, from 24 to 99% within 2 min).
Scheme 2. Addition-elimination mechanism of ROH to EMME.

Microwave Michael Addition Between EMME and Nucleophiles
83
Table 3. Use of different basic systems for the solvent-free reaction between 1 and
ROH under MWI
Recovered
EMME
yield(%)
Time
(min)
Yield(%)
(Microwave)
Entry
R
Basic system
1
2
n-butyl
n-butyl
KF/Al2O3
KF/Al2O3
KF/Al2O3
KF/Al2O3
KF/Al2O3
KF/Al2O3
KF/Al2O3
KF/Al2O3
KOH/TBABb
KOH/TBAB
KF/Al2O3
KOH/TBAB
1
5
8
26
90
65
58
56
93
67
43
39
70
65
85
32
3
n-butyl
n-butyl
10
20
1
30
30
4
5
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Phenyl
4
27
6
6
7
10
20
1
50
50
8
9
20
22
0 (NR)c
0 (NR)c
10
11
12
2
3 (898C)a
Phenyl
3
aTemperature of the reaction mixture was evaluated by a digital thermometer just at
the end of MWI.
bTetrabutylammonium bromide.
cNR ¼ no reaction.
A significant microwave effect was observed. When the reaction between
1 and PhSH was carried using classical heating in the absence of microwave
irradiation, the yield was only 7% (entry 16) when compared to 99% under
MWI (entry 15).
In summary, aniline and thiophenol gave good to excellent yields of
nucleophilic addition toward EMME. The order of nucleophilicity under
microwave irradiation without using any catalyst or solid support is aniline .
thiol . aliphatic alcohols ꢀ phenol. In the case of the reaction between
PhSH and EMME, a supported base such as KF/alumina increased the yield.
The most important microwave effect was observed in the case of thio-
phenol and was also rather significant with aliphatic alcohols that gave
Scheme 3. Solvent-free preparation of phenoxymethylenemalonate.

84
A. Loupy et al.
Table 4. Solvent-free Michael addition of other nucleophiles (PhNH2, PhSH) under
MWI (ratio of 7: PhNH2 ¼ 1 : 1.2, 7 : PhSH ¼ 1 : 1.2)
Recovered
EMME
(%)
Time
(min)
Temp.
(8C)
Entry
X
Base
Support
Yield (%)
1
2
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
S
none
none
K2CO3
K2CO3
KF
none
none
2
2
70
70
—
—
—
—
—
55
55
105
—
—
—
—
62
62
MW 86
D 73
89
3
—
—
—
6
3
none
2
4
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
bentonite
none
2
67
79
5
1
6
KF
2
86
82
—
2
7
none
none
none
none
none
none
none
KF
1
8
2
MW 90
D 79
65
—
—
24
52
30
6
9
2
10
11
12
13
14
15
16
8
12
2
25
24
S
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
S
7
52
90
S
1
—
—
—
S
KF
KF
2
MW 99
D 7
S
2
moderate yields but were strongly dependent on the chain length. Unfortu-
nately, no nucleophilic addition between inactivated PhOH toward 1 was
successful in our various MWI conditions.
The important specific MW effects observed here are consistent with the
consideration of mechanisms and with the assumption that the MW effects are
increased when the polarity of a system is enhanced. The rate-determining
step consists of the addition of nucleophile on the double bond of EMME.
The transition state is therefore more polar than ground state and consequently
more prone to electrostatic interactions of dipole-dipole type with the electric
field (Scheme 4). The more important stabilization of the transition state is
therefore responsible of reactivity by a decrease of the activation energy.
EXPERIMENTAL
Typical microwave procedure for 2-cyclohexyloxymethylene-malonic
acid diethyl ester, 5c (Table 1, entry 8) EMME (1.21 g, 5.55 mmol,

Microwave Michael Addition Between EMME and Nucleophiles
85
Scheme 4. Ground and transition states for the addition of thiophenol to EMME.
purchased from Aldrich) and cyclohexanol (1.68 g, 16.80 mmol, 3 eq.) were
mixed with Al2O3 (5.78 g) in the absence of any organic solvent and then
submitted for 10 min to microwave irradiation inside a domestic microwave
oven (Sam Sung, RE-555 TCW). The reaction mixture was dissolved in
ethyl acetate. Al2O3 was filtered off and the filtrate was concentrated by
rotary evaporator. The crude product was purified using column chromato-
1
graphy to give 5c (0.86 g, 3.19 mmol, 57%) as a colorless oil. H NMR
(300 MHz, CDCl3) 7.70 (1H, vinyl H, s), 4.23 (4H, two OCH2, q,
J ¼ 7.2 Hz), 4.01 (1H, cyclohexyl CH, quintet, J ¼ 3.8 Hz), 2.01–1.59
(10H, m, cyclohexyl CH2), 1.35(3H, CH2CH3, t, J ¼ 7.2 Hz), 1.31 (3H,
CH2CH3, t, J ¼ 7.2 Hz). 13C NMR (75 MHz, CDCl3) 164.5(C55O),
164.5(C55O), 163.2(Vinyl H), 106.3(.C55), 84.9 (cyclohexyl CH)
61.1(OCH2), 61.0(OCH2), 32.4(cyclohexyl CH2), 25.4(cyclohexyl CH2),
23.3 (cyclohexyl CH2), 14.6(ethoxy CH3), 14.5 (ethoxy CH3), Anal. Calcd
for C14H22O5 ¼ C62.20, H8.20; Found C61.17, H8.23.
2-Butoxymethylene-malonic acid diethyl ester, 5a. 1H NMR
(300 MHz, CDCl3) 7.60(1H, vinyl H, s), 4.46 (2H, OCH2, q, J ¼ 7.2 Hz),
4.20 (2H, OCH2 q, J ¼ 7.2 Hz), 4.12 (2H, OCH2CH2, t, J ¼ 6.6 Hz), 1.71
(2H, quintet, CH2CH2CH2, J ¼ 6.6 Hz), 1.45(2H, m, CH2CH2CH3), 1.31
(3H, OCH2CH3, t, J ¼ 7.2 Hz), 1.28 (3H, OCH2CH3, t, J ¼ 7.2 Hz), 0.92
(3H, t, CH2CH2CH3, J ¼ 6.6 Hz), 13C NMR (75 MHz, CDCl3)
165.5(C55O), 164.6(C55O), 164.4(Vinyl H), 106.5(.C55), 61.3–61.0(three
O CH2), 32.1(butyl CH2), 19.0 (butyl CH2), 14.5–14.0 (three CH3).
IR(neat); 3050.4, 2928.2, 2850.8, 1734.8, 1712.7, 1640.9, 1187.8 cm21
.
Anal. Calcd for C12H20O5 ¼ C59.00, H8.25; Found C58.93, H8.29.
2-(3-Methyl-butoxymethylene)-malonic acid diethyl ester, 5b. 1H
NMR (300 MHz, CDCl3) 7.59(1H, vinyl H, s), 4.31–4.20 (2H, OCH2CH3,
q, J ¼ 7.1 Hz), 4.12(2H, OCH2, t, J ¼ 6.7 Hz), 1.73(1H, CH(CH3)2, m,
J ¼ 6.8 Hz), 1.62 (2H, q, CH2CH2CH., J ¼ 6.7 Hz), 1.30 (two, OCH2CH3, t,
J ¼ 7.1 Hz), 0.94 (6H, d, CH(CH3)2, J ¼ 6.0 Hz). 13C NMR (75 MHz,
CDCl3) 164.5(C55O), 165.4(C55O), 162.3(Vinyl H), 106.6(.C55),

86
A. Loupy et al.
25.1(isopropyl CH),
61.3–61.1(three
OCH2),
38.7(OCH2CH2),
22.8(isopropyl CH3), 14.5(3H, t, OCH2CH3), 14.6(3H, t, OCH2CH3) IR
(neat); 3050.5, 2958.2, 1732.5, 1716.8, 1638.5, 1180.8 cm21 Anal. Calcd for
C13H22O5 ¼ C60.45, H8.58; Found C60.40, H8.59.
2-Octyloxymethylene-malonic acid diethyl ester, 5d. 1H NMR
(300 MHz, CDCl3) 7.59(1H, vinyl H, s), 4.25 (4H, two, OCH2, q,
J ¼ 7.1 Hz), 4.11 (one OCH2, t, J ¼ 6.7 Hz), 1.68 (2H, OCH2CH2, quintet,
J ¼ 6.7 Hz), 1.35–1.26 (10H, octyl, CH2), 1.32(6H, OCH2CH3, J ¼ 7.1 Hz),
0.88(3H, octyl CH3, t, J ¼ 6.9 Hz), 13C NMR (75 MHz, CDCl3)
165.4(C55O), 164.5(C55O), 164.4(Vinyl H), 106.5(.C55), 61.2–61.0(three
O CH2), 32.1(butyl CH2),30.1(butyl CH2), 29.5(butyl CH2), 29.5(butyl
CH2), 25.8(butyl CH2), 23,0(butyl CH2), 14.6(OCH2CH3), 14.6(OCH2CH3),
14.4 (octyl CH3). IR (neat); 3072.5, 2950.3, 2885.3, 1735.8, 1715.9, 1642.3,
1465.4, 1180.5 cm21. Anal. Calcd for C16H28O5 ¼ C63.97, H9.40; Found
C63.91, H9.43.
Typical microwave procedure for 2-phenylaminomethylene-malonic
acid diethyl ester, 13 (Table 4, entry 8) EMME (1.24, 5.73 mmol), aniline
(1.63 g, 16.87 mmol) were mixed with Al2O3 (3.68 g) in the absence of any
organic solvent and then submitted for 2 min to microwave irradiation
inside a domestic microwave oven (Sam Sung, RE-555 TCW). The reaction
mixture was dissolved in ethyl acetate. Al2O3 was filtered off and the
filtrate was concentrated by rotary evaporator. The crude product was
purified using column chromatography to give 13 (1.35 g, 5.15 mmol, 90%)
as a colorless oil. 1H NMR (300 MHz, CDCl3) 10.90 (1H, d, NH,
J ¼ 13.4 Hz), 8,56 (1H, vinyl H, d, J ¼ 13.7 Hz), 7.41(2H, aromatic ortho-
H, m),7.15(3H, m, aromatic meta and para H), 4.28 (4H, two OCH2, q,
J ¼ 7.1 Hz), 1.40–1.30 (6H, two CH3, t, J ¼ 7.1 Hz). 13C NMR (75 MHz,
CDCl3) 169.5(C55O), 165.1(C55O), 152.3(vinyl H), 139.2(Ar), 130.2(Ar),
125.3(Ar), 117.6(.C55), 60.8(OCH2), 60.5 (OCH2), 14.8(CH3), 14.7(CH3).
Anal. Calcd for C14H17NO455C63.87 H6.51; Found C63.81, H6.55.
Typical microwave procedure for 2-phenylsulfanylmethylene-
malonic acid diethyl ester, 14. (Table 4, entry 15) EMME (1.10 g,
5.09 mmol), thiophenol (0.67 g, 6.10 mmol, 1.2 eq.) and KF (0.29 g,
5.09 mmole) were mixed with Al2O3 (4.12 g) in the absence of any organic
solvent and then submitted for 2 min to microwave irradiation inside a
domestic microwave oven (Sam Sung, RE-555 TCW). The product was
isolated as described above and purified by column chromatography to give
1
14 (1.41 g, 5.03 mmol, 99 %) as a colorless oil. H NMR (300 MHz, CDCl3)
8.40 (1H, vinyl H, s), 7.47 (5H, aromatic H, m), 4.37 (2H, OCH2, q,
J ¼ 7.1 Hz), 4.23 (2H, OCH2, q, J ¼ 7.1 Hz), 1.38 (3H, CH3, t, J ¼ 7.1 Hz),
1.28 (3H, CH3, t, J ¼ 7.1 Hz). 13C NMR (75 MHz, CDCl3) 163.7(C55O),
165.0(C55O), 160.8(vinyl H), 135.4(Ar), 131.7(Ar), 130.0(Ar), 129.4(Ar),
119.0(.C55), 61.8(OCH2), 61.6 (OCH2), 14.7(CH3), 14.6 (CH3). Anal.
Calcd for C14H16O4S ¼ C59.98,H5.75; Found C59.82, H5.79.

Microwave Michael Addition Between EMME and Nucleophiles
ACKNOWLEDGMENTS
87
This work was supported by grant from the Kyungsung University research
foundation (2003) and Basic Research Program of the Korea Science &
Engineering Foundation (KOSEF R05-2003-000-11732-0).
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