Phase-transfer catalyzed Michael addition reaction using a new C 2-symmetric quaternary ammonium salt derived from l-proline

Article abstract of DOI:10.1007/s10562-011-0595-1

A new C₂-symmetric quaternary ammonium salt easily prepared from l-proline, was developed and used as an efficient phase-transfer catalyst (PTC) in Michael addition reaction of various active methylene compounds to aromatic enones. Malonate est

Full text of DOI:10.1007/s10562-011-0595-1

Catal Lett (2011) 141:1004–1008
DOI 10.1007/s10562-011-0595-1
Phase-Transfer Catalyzed Michael Addition Reaction Using
a New C -Symmetric Quaternary Ammonium Salt Derived From
2
L-Proline
Ce Su
•
Yi-Ming Xie Qing-Tang Zhang
•
Received: 31 January 2011 / Accepted: 29 March 2011 / Published online: 9 April 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A new C -symmetric quaternary ammonium
2
versatile applications in organic synthesis [2–4], it has also
salt easily prepared from L-proline, was developed and
used as an efficient phase-transfer catalyst (PTC) in
Michael addition reaction of various active methylene
compounds to aromatic enones. Malonate esters and ace-
tylacetone were reacted smoothly with various a,
b-unsaturated ketones in good to excellent yields, the
reaction conditions were optimized and the substrate scope
was also investigated. Thereby, a practical Michael addi-
tion methodology was established under phase-transfer
catalytic conditions with many advantages, including easy
availability of catalyst, mild reaction conditions, short
reaction times, simple workup procedures.
been found in multiple industrial applications [5, 6].
However, there are still some limits, such as long reaction
time, low yield or environment concerns.
Phase-transfer catalysis is one of the most important and
convenient methods in organic synthesis because of its
simple reaction procedures, mild conditions, inexpensive
and environmentally benign reagents [7, 8]. Based on these
advantages, the phase-transfer catalysis witnessed a rapid
development in recent years, especially in those phase-
transfer catalyzed asymmetric reactions [9–11]. This
methodology is still considered as one of the most potent
strategies for establishing green chemistry [8, 12]. Ever
since Dolling et al. [13] and O’Donnell and Bennett [14]
independently reported their successful results in phase-
transfer catalysis, many quaternary ammonium salts
derived from natural chiral amines such as cinchonine and
cinchonidine have been evaluated as chiral phase-transfer
catalysts (PTCs). The syntheses of non-naturally derived
PTCs have been attracted much attention, and numerous
efforts have been paid to develop new phase-transfer cat-
alytic methodology [8], which shows attractive advantages
both in the laboratory and in industry. Recently, Maruoka
and coworkers [15, 16], Belokon et al. [17] and Nagasawa
et al. [18] have reported the syntheses of non-natural PTCs
and their successful applications to versatile enantioselec-
tive reactions. Although many types of PTCs have been
synthesized and used, the major drawbacks of these cata-
lysts are the difficulty in modifying the structure of catalyst
to further improve catalytic activity and tedious preparation
of the catalysts. Therefore, the development of new method
for facile synthesis of novel PTCs with tunable structure
and high reactivity should still be a priority in this area.
In this work, we report the synthesis of a new PTC of
Keywords Michael addition Á Phase-transfer catalysis Á
C -symmetric Á Quaternary ammonium salt
2
1
Introduction
Michael addition reaction is an addition of active methy-
lene or methine compounds to electron-deficient olefins.
The mechanism for this reaction involves the deprotonation
of the active methylene (methine) compounds at methylene
(
methine) carbon by a base, and the conjugate addition of
the resulted carbanion to electron-deficient olefins, fol-
lowed by the acceptance of a proton. It is generally
regarded as one of the most efficient carbon–carbon bond
forming reactions and can be easily applied to construct
functionalized carbon framework [1]. Apart from its
C. Su (&) Á Y.-M. Xie Á Q.-T. Zhang
College of Petrochemical Engineering, Lanzhou University of
Technology, Lanzhou 730050, People’s Republic of China
e-mail: cesu1008@lut.cn
C -symmetrical quaternary ammonium salt prepared from
2
1
23

Phase-Transfer Catalyzed Michael Addition Reaction
1005
natural amino acid L-proline, and its application to the
Michael addition reaction of various active methylene
compounds to aromatic a, b-unsaturated ketones.
resulted reaction mixture was stirred at room temperature
for 1.5 h. When thin-layer chromatography (TLC) indi-
cated that chalcone was disappeared, water (10 mL) was
added, the organic phase was separated and the aqueous
phase was extracted with ethyl acetate (4 9 10 mL). The
organic layers were combined, washed with brine (10 mL)
and water (10 mL), dried over anhydrous MgSO4 for
30 min and then filtered. The filtrate was concentrated
under reduced pressure, and the residue was purified by
column chromatography on silica gel eluted with mixtures
of petroleum ether and ethyl acetate (13:1, v/v) to give the
desired product 1a (103 mg, 93%) as white solid. Data of
products are shown in Sects. 2.3.1 to 2.3.8.
2
Experimental
2
.1 General
Melting points were determined on an electrothermal
SGW X-4 micro) melting-point apparatus and the tem-
(
perature were not corrected. Infrared (IR) spectra were
recorded on a Nicolet AVATR 360FT spectrometer as KBr
-
1
pellets with absorption in cm . Nuclear magnetic reso-
nance (NMR) spectra were recorded on a Varian Mercury
2.3.1 Diethyl 2-(3-oxo-1,3-diphenylpropyl)malonate 1a
4
00 (400 MHz) spectrometer using CDCl as the solvent.
3
Chemical shifts are given in parts per million (ppm) (d)
relative to tetramethylsilane (TMS) (d 0.00 ppm). Ele-
mental analyses were performed on a Vario EL III ele-
mental analysis instrument. Thin layer chromatography
White solid, yield 93%; m.p. 71–72 °C (lit. 69–71 °C
[19]); IR (KBr): m = 3050, 2800, 1718, 1450, 1380, 1275,
-
1
1
728, 690 cm ; H NMR (400 MHz, CDCl , TMS), d:
3
7.89 (d, J = 7.2 Hz, 2H), 7.52 (t, J = 7.2 Hz, 1H), 7.42 (t,
J = 8.4 Hz, 2H), 7.25 (m, 5H), 4.20 (m, 3H), 3.98 (q,
J = 6.0 Hz, 2H), 3.82 (d, J = 9.6 Hz, 1H), 3.41–3.58 (m,
2H), 1.25 (t, J = 6.0 Hz, 3H), 1.01(t, J = 6.4 Hz, 3H).
(
TLC) was performed on silica plates and components
were visualized by phosphomolybdic acid. Column chro-
matography was carried out with silica gel (200–300 mesh)
using mixtures of petroleum ether and ethyl acetate as
eluent. All of the solvents and materials were reagent grade
and used without further purification.
2.3.2 Dimethyl 2-(3-oxo-1,3-diphenylpropyl)malonate 2a
White solid, yield 87%; m.p. 78–79 °C (lit. 78 °C [5]); IR
-
1
2
.2 Synthesis of C -Symmetric Quaternary
2
(KBr): m = 3100, 2800, 1725, 1380, 1275, 730, 690 cm ;
1
Ammonium Salt 2
H NMR (400 MHz, CDCl , TMS), d: 7.90 (d, J = 7.6 Hz,
3
2
H), 7.55 (t, J = 7.6 Hz, 1H), 7.44 (t, J = 7.6 Hz,1H),
7.18–7.25 (m, 6H), 4.20 (m, 1H), 3.84 (q, J = 9.6 Hz, 1H),
3.69 (m, 1H), 3.50 (m, 7H).
To a solution of 1 (166 mg, 1.0 mmol) in toluene (20 mL),
-(chloromethyl)naphthalene (441 mg, 2.5 mmol) was
1
added. The reaction mixture was stirred for 2 h at 120 °C.
Precipitation was formed and then collected by filtration,
washed with diethyl ether (3 9 20 mL) and dried under
vacuum at 110 °C for 12 h to give the product 2 (332 mg,
2.3.3 4-Acetyl-1,3-diphenyl-hexundion-(1,5) 3a
White solid, yield 56%; m.p. 144–145 °C (lit. 145–146 °C
[20]); IR (KBr): m = 2921, 1735, 1462, 1375, 689,
6
4%): Yellow solid, m.p. 218–219 °C; IR (KBr):
-1 1
;
-1
1
m = 2963, 1636, 1461, 812, 928 cm
H
NMR
760 cm ; H NMR (400 MHz, CDCl , TMS), d: 7.81
3
(
400 MHz, CDCl , TMS), d: 8.78 (d, J = 7.2 Hz, 2H),
(t, J = 9.6 Hz, 2H), 7.50 (d, J = 9.6 Hz, 1H), 7.38
(t, J = 10.0 Hz, 2H), 7.23 (m, 5H), 4.32 (d, J = 13.0 Hz,
1H), 4.24 (m, 1H), 3.31 (q, J = 11.2 Hz, 1H), 3.21 (d,
3
7
.91 (m, 2H), 7.65 (d, J = 6.8 Hz, 4H), 7.43 (m, 4H), 7.28
d, J = 6.0 Hz, 2H), 5.63 (s, 4H), 3.51 (m, 2H), 3.15 (m,
(
1
3
4
5
5
H), 2.80 (m, 4H), 2.12 (m, 4H), 1.88 (m, 4H); Mass m/z:
?
19 (M ). Anal. calc. for C H Cl N : C 73.99, H 6.94, N
J = 5.2 Hz, 1H), 2.27 (s, 3H), 1.90 (s, 3H); C-NMR
(400 MHz, CDCl ): d: 206.3, 205.5, 200.4, 146.0, 141.3,
129.0, 128.9, 128.8, 127.1, 126.8, 126.3, 68.4, 46.9, 42.2,
3
2
36
2
2
3
.39. Found: C 73.81, H 6.92, N 5.40%.
?
0.3, 26.8; Mass m/z: 308 (M ). Anal. calc. for C H O :
C 77.92, H 6.49. Found: C 77.76, H 6.48%.
3
20 20 3
2
.3 General Procedure for Michael Addition Reaction
in the Presence of PTC 2
2.3.4 Diethyl 2-(1-(4-methoxyphenyl)-3-oxo-3-
phenylpropyl)malonate 4a
Taking the Michael addition reaction of diethyl malonate to
chalcone as an example, to a solution of chalcone (62 mg,
0
.3 mmol) and PTC 2 (8 mg, 0.015 mmol) in toluene
5 mL), K CO (157 mg, 1.14 mmol) was added, followed
White solid, yield 84%; m.p. 61–63 °C (lit. 60–62 °C
[20]); IR (KBr): m = 3000, 2800, 1720, 1460, 1375, 1250,
(
2
3
-
1 1
by dimethyl malenate (0.068 mL, 0.45 mmol). The
1000, 850 cm ; H NMR (400 MHz, CDCl , TMS), d:
3
123

1
006
C. Su et al.
7
.88 (d, J = 10.8 Hz, 2H), 7.50 (d, J = 8.8 Hz, 1H), 7.42
t, J = 10.8 Hz, 2H), 7.17 (d, J = 11.2 Hz, 2H), 6.78
d, J = 11.2 Hz, 2H), 4.21 (m, 2H), 3.96 (q, J = 9.2 Hz,
(d, J = 7.2 Hz, 1H), 3.65 (m, 1H), 2.85 (q, J = 8.4 Hz,
2H), 2.04 (s, 3H), 1.24 (t, J = 7.2 Hz, 3H), 0.88
(
1
3
(
(t, J = 6.8 Hz, 3H); C-NMR (400 MHz, CDCl ): d:
3
2
H), 3.78 (d, J = 12.8 Hz, 1H), 3.73 (s, 3H), 3.52
q, J = 6.4 Hz, 1H), 3.40 (q, J = 6.4 Hz, 2H), 1.25
t, J = 9.6 Hz, 3H), 1.03 (t, J = 9.6 Hz, 3H).
206.0, 168.2, 167.6, 140.3, 128.4, 128.1, 127.2, 61.6, 61.3,
?
57.4, 47.4, 40.4, 30.2, 14.0, 13.7; Mass m/z: 306 (M ).
(
(
Anal. calc. For C H O : C 66.67, H 7.19. Found: C
17 22 5
66.57, H 7.21%.
2
.3.5 Dimethyl 2-(1-(4-nitrophenyl)-3-oxo-3-
phenylpropyl)malonate 5a
3
Results and Discussion
White solid, yield 90%; m.p. 111–112 °C (lit. 111–113 °C
[
21]); IR (KBr): m = 2900, 1720, 1530, 1465, 1375, 1300,
A new C -symmetric quaternary ammonium salt 2 was
2
-
1
1
7
8
7
3
30, 710 cm ; H NMR (400 MHz, CDCl , TMS), d:
conveniently prepared by simple dialkylation of a known
diamine 1, which was synthesized from L-proline according
to literature procedure [24] (Scheme 1). To investigate the
3
.12 (d, J = 8.8 Hz, 2H), 7.89 (d, J = 8.8 Hz, 2H), 7.45-
.57 (m, 5H), 4.30 (m, 3H), 4.00 (q, J = 7.2 Hz, 2H),
.84 (d, J = 9.6 Hz, 1H), 3.62–3.49 (m, 2H), 1.25
feasibility of this C -symmetric quaternary ammonium salt
2
(
t, J = 7.2 Hz, 3H), 1.05 (t, J = 7.2 Hz, 3H).
applying to phase-transfer catalysis, we carried out Michael
addition reactions of various active methylene compounds
to aromatic a, b-unsaturated ketones under PTC conditions.
Initial efforts sought to explore the optimal reaction
conditions, so the Michael addition of diethyl malonate to
chalcone catalyzed by quaternary ammonium salt 2, was
chosen as the model reaction to investigate the effects of
temperature, solvents, base dosage (K CO ) and the load-
2
.3.6 Diethyl 2-(1-(4-chlorophenyl)-3-oxo-3-
phenylpropyl)malonate 6a
White solid, yield 65%; m.p. 112–113 °C (lit. 113–115 °C
[
21]); IR (KBr): m = 2950, 1726, 1462, 1385, 1080,
-
1
1
8
60 cm ; H NMR (400 MHz, CDCl , TMS), d: 7.90
3
2
3
(
(
(
(
d, J = 7.6 Hz, 2H), 7.55 (t, J = 7.6 Hz, 1H), 7.42
t, J = 8.0 Hz, 2H), 7.22 (s, 4H), 4.21 (m, 3H), 3.98
q, J = 7.2 Hz, 2H), 3.78 (d, J = 10.0 Hz, 1H), 3.57–3.38
m, 2H), 1.25 (t, J = 6.8 Hz, 3H), 1.05(t, J = 7.2 Hz, 3H).
ing of catalyst on reaction rate and yields. The results are
summarized in Table 1.
As can be seen in Table 1, the reaction was susceptible
to reaction temperature. When the reaction of diethyl
malonate with chalcone in toluene under the influence of
K CO (380 mol %) and catalyst 2 (10 mol %) at 0 °C, the
2
.3.7 Diethyl 2-(3-(4-nitrophenyl)-3-oxo-1-
phenylpropyl)malonate 7a [22]
2
3
TLC indicated that there was no observable reaction even
after being stirred 48 h and starting material was recovered
quantitatively (entry 1). With the boost of temperature, the
reaction rate was enhanced dramatically (entry 2). The
rapid reaction rate and excellent yield was obtained when
the reaction temperature was raised up to 25 °C (entry 3).
However, when the temperature was above 25 °C, reaction
rate and yield had no noticeable improvement (entry 4).
With these initial results in hand, we investigated the effect
of solvent polarity on the reaction. When reaction medium
switched to halogenated solvents, such as chloroform and
dichloromethane, there was a sharp decrease in reaction
rate (entries 5 and 6). Particularly, diethyl malonate failed
to react with chalcone in chloroform due to its high polarity
(entry 6), while a good yield was obtained in dichloro-
methane (entry 5). Obviously, the solvents with lower
Yellow oil, yield 93%; IR (KBr): m = 2850, 1725,
1
-
1
1
530,1460, 1375, 1300, 730, 710 cm
;
H NMR
(
400 MHz, CDCl , TMS), d: 8.24 (d, J = 9.2 Hz, 2H),
3
8
.05 (d, J = 6.8 Hz, 2H), 7.26 (m, 5H), 4.12
(
(
(
q, J = 4.8 Hz, 3H), 3.98 (q, J = 6.8 Hz, 2H), 3.80
d, J = 9.6 Hz, 1H), 3.65 (d, J = 4.4 Hz, 1H), 3.51
m, 1H), 1.23 (t, J = 7.2 Hz, 3H), 1.01 (t, J = 6.8 Hz, 3H).
2
.3.8 Diethyl 2-(3-oxo-1-phenylbutyl)malonate 8a [23]
White solid, yield 83%; m. p. 41–42 °C; IR (KBr):
m = 3080, 2850, 1715, 1450, 1300, 740, 695 cm ; H
NMR (400 MHz, CDCl , TMS), d: 7.24 (m, 5H), 4.20
-
1
1
3
(
q, J = 7.2 Hz, 2H), 3.88 (d, J = 4.0 Hz, 2H), 3.86
Scheme 1 The dialkylation of
diamine 1
Ar Cl
H
H
N
N
N
H
1-(chloromethyl)naphthalene
toluene, reflux
Ar = α-Np
N
H
Cl
Ar
1
2
1
23

Phase-Transfer Catalyzed Michael Addition Reaction
1007
Table 1 Optimization of the reaction conditions
O
O
O
O
O
2
cat., K CO
2
3
solvent
EtO
EtO
EtO
OEt
O
a
Entry
Catalyst (mol%)
t (°C)
Solvent
2
K CO
3
(equiv.)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
10
10
10
10
10
10
10
10
5
0
10
25
35
25
25
25
25
25
25
25
PhCH
PhCH
PhCH
PhCH
3
3
3
3
3.8
3.8
3.8
3.8
3.8
3.8
1.9
0.24
3.8
3.8
3.8
48
3
No reaction
86
1.4
1.2
12
48
11
60
1.5
12
48
93
93
CH Cl
2
2
81
CHCl
PhCH
PhCH
PhCH
PhCH
PhCH
3
No reaction
3
3
3
3
3
90
82
93
91
43
1
1
0
1
1
0
All reactions were performed on a 0.3 mmol scale of chalcone and 0.45 mmol of diethyl malonate in 5 mL of solvent
a
Isolated yields obtained after column chromatography
polarity were favorable to this reaction, so toluene was a
preferred selection. The dosage of base was also critical to
the reaction. When the dosage of base was decreased to
likely to cause many side reactions as a result of more
nucleophilic activity, so a moderate yield was obtained
(entry 3). We found that a broad range of aromatic enones
bearing both electron-withdrawing and electron-donating
groups on aromatic ring can be reacted rapidly with diethyl
malonate in good to excellent yields (entries 1, 4–8).
However, the electronic effects of substituents on aromatic
ring are of important influence on the Michael addition.
The results demonstrated that the reactions of chalcones
with electron-withdrawing groups (entries 5, 6 and 7) were
faster than that of electron-donating group in para-position
at aromatic ring (entry 4). A prolonged reaction time was
required using benzylideneacetone as Michael acceptor,
although a good yield was obtained (entry 8). Unfortu-
nately, ethyl cinnamates are inert to ethyl malonate after
long time reaction under presented phase-transfer catalytic
conditions (entries 9 and 10).
1
7
90 mol%, the reaction rate was decreased markedly (entry
), further reducing dosage of base to 24 mol% resulted in
a very sluggish reaction, even though with good chemical
yield (entry 8). Thus, at least 380 mol% K CO is neces-
2
3
sary to get desirable reaction rate. Then, the catalytic
efficiency and catalyst loading was also evaluated. When
the loading of catalyst was decreased to 5 mol%, no
obvious changes in the reaction rate and yield were
observed (entry 9). Of course, further decreasing catalyst
loading to 1 mol%, the reaction turned out to be fairly slow
(
entry 10). In the absence of catalyst (entry 11), the
extremely slow reaction rate and obviously reduced yield
manifested that the quaternary ammonium salt 2 indeed
facilitated the Michael addition reaction of diethyl mal-
onate to chalcone substantially, thereby establishing opti-
mal reaction conditions for further exploration.
Under the optimized reaction conditions (room tem-
perature, toluene solvent, 380 mol% of K CO and
4 Conclusion
2
3
5
mol% of catalyst), we then investigated the generality of
In summary, a new C -symmetric quaternary ammonium
2
the reaction substrates. The results are showed in Table 2.
As shown in Table 2, various malonate esters and ace-
tylacetone were reacted smoothly with chalcone (entries 1,
salt easily prepared from L-proline was developed and used
as an efficient and practical PTC for Michael addition
reaction of various active methylene compounds to aro-
2
and 3). All malonate esters gave excellent chemical
matic enones in good to excellent yields. The C -symmetric
2
yields, though it seems that the diethyl malonate is a
superior Michael donor compared to dimethyl malonate in
this conjugate reaction (entries 1 and 2). Acetylacetone is
quaternary ammonium salt shows exciting phase-transfer
catalytic activity under very mild conditions. The presented
methodology highlights in facile synthesis of catalyst, mild
123

1
008
C. Su et al.
Table 2 Michael addition of active methylene compounds to various aromatic enones under phase-transfer catalytic conditions
R1
O
5
mol % 2,
O
O
O
O
3
.8 eq. K CO3
2
R2
R1
PhCH , rt
R3
R2
R3
R3
3
R3
O
a
Entry
R
1
R
2
R
3
Product
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
OEt
OMe
Me
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
1.5
2
93
87
24
3
56
4-MeO
OEt
OEt
OEt
OEt
OEt
OEt
OEt
84
4-NO
4-Cl
H
2
0.5
1
90
65
4-C
Me
6 4
H NO
2
0.7
10
48
48
93
H
83
H
OEt
OEt
No reaction
No reaction
1
0
3,4,5-MeO
All reactions were performed on a 0.3 mmol scale of a, b-unsaturated ketones, 0.45 mmol of active methylene compounds and 1.14 mmol of
CO in 5 mL of solvent in the presence of PTC 2 (5 mmol %) at room temperature
Isolated yields obtained after column chromatography
K
2
3
a
reaction conditions, short reaction times and simple workup
procedures. Though we did not observe any asymmetric
induction in this catalytic system, it provides some valuable
information on potential feasibility in asymmetric catalytic
conjugate additions of carbon nucleophiles to a, b-unsatu-
rated carbonyl compounds. Further investigations into chi-
ral induction of this type of PTCs are ongoing in our
laboratory. We anticipate that the present methodology will
find useful applications in asymmetric version.
8. Nelson A (1999) Angew Chem Int Ed 38:1583–1585
. Ooi T, Kameda M, Maruoka KJ (2002) Am Chem Soc
24:7640–7641
0. Shi M, Jiang J-K (2002) Tetrahedron Asymmetr 13:1941–1947
9
1
1
11. Arai S, Tsuge H, Shioiri
39:7563–7566
T (1998) Tetrahedron Lett
1
1
2. Kacprzak K, Gawronski J (2001) Synthesis 7:961–998
3. Dolling U-H, Davis P, Grabowski EJJJ (1984) Am Chem Soc
06:446–447
1
14. O’Donnell MJ, Bennett WD, Wu SJ (1989) Am Chem Soc
111:2353–2355
1
1
1
5. Ooi T, Kameda M, Maruoka KJ (1999) Am Chem Soc
21:6519–6520
6. Ooi T, Takeuchi M, Kameda M, Maruoka KJ (2000) Am Chem
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7. Belokon YN, Kochetkov KA, Churkina TD, Ikonnikov NS,
Larionov OV, Harutyunyan SR, Vyskocil S, North M, Kagan HB
1
Acknowledgments This project was supported by the Excellent
Young Teacher Fund of Lanzhou University of Technology (No.
Q200912).
(
2001) Angew Chem Int Ed 40:1948–1951
8. Kita T, Georgieva A, Hashimoto Y, Nakata T, Nagasawa K
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