Poly(N-vinylimidazole) as an efficient and recyclable catalyst of the aza-Michael reaction in water

Article abstract of DOI:10.1134/S1070428010040019

Poly(N-vinylimidazole) effectively catalyzed Michael addition of 1H-1,2,4-triazole, 3,5-dimethyl-1H-1,2,4-triazole, uracil, oxazolidin-2-one, and succinimide to but-3-en-2-one, cyclohex-2-en-1-one, methyl acrylate, and methyl vinyl sulfone in water at roo

Full text of DOI:10.1134/S1070428010040019

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 4, pp. 461–467. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.P. Beletskaya, E.A. Tarasenko, A.R. Khokhlov, V.S. Tyurin, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46,
No. 4, pp. 473–478.
Poly(N-vinylimidazole) as an Efficient and Recyclable Catalyst
of the Aza-Michael Reaction in Water
I. P. Beletskayaa, E. A. Tarasenkoa, A. R. Khokhlovb, and V. S. Tyurina
a Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
e-mail: beletska@org.chem.msu.ru
b Faculty of Chemistry, Moscow State University, Vorob’evy gory 1, Moscow, 119992 Russia
Received May 14, 2009
Abstract—Poly(N-vinylimidazole) effectively catalyzed Michael addition of 1H-1,2,4-triazole, 3,5-dimethyl-
1H-1,2,4-triazole, uracil, oxazolidin-2-one, and succinimide to but-3-en-2-one, cyclohex-2-en-1-one, methyl
acrylate, and methyl vinyl sulfone in water at room temperature. The catalyst can readily be regenerated and
repeatedly used at least five times without loss in activity, as shown in the reaction of 1H-1,2,4-triazole with
but-3-en-2-one as an example.
DOI: 10.1134/S1070428010040019
Organic polymers constitute the basis of all living
organisms; they play the role of construction materials
at both macro and micro levels and make cell organelle
space structured. Another function of organic polymers
as a part of enzymatic systems is to catalyze all
biochemical reactions and hence the life process as
a whole. The use of synthetic polymers is related pri-
marily to the design of different types of materials.
However, starting from the Merrifield solid-phase syn-
thesis in 1963 [1], organic polymers have found wide
application as supports for reagents and catalysts
[2, 3]. In the recent time, interest in such polymers
became stronger, and specific attention was given to
so-called “smart” polymers due to their ability to
change their physicochemical properties, primarily
solubility, depending on the conditions. Especially
promising is simulation of biopolymers by simple
synthetic polymers whose behavior is similar to the
behavior of polypeptides and that are capable of acting
as catalysts.
p-nitrophenyl acetate [6] and Michael addition of
thiols to electron-deficient alkenes [8], acting as base
catalysts.
An important advantage of polymeric catalysts is
that they can readily be separated from the products
due to considerable difference in the properties of
high- and low-molecular compounds. As a result, such
catalysts may be used repeatedly, which is profitable
from the economic viewpoint and is environmentally
benign. Thus the use of poly(N-vinylimidazole) is
promising from the viewpoint of “green chem-
istry” [9].
In the present work we examined the activity of
poly(N-vinylimidazole) with a molecular weight of
75300 [10] as base catalyst in the aza-Michael reac-
tion. The aza-Michael reaction is one of the most
general and widely used methods for building up new
carbon–nitrogen bonds, especially in the synthesis of
β-aminocarbonyl compounds. This reaction may be
catalyzed by various Lewis acids [11], combinations
BF3·OEt2–R4NX [12], MCl3–Me3SiCl (M = Ru, Fe)
[13], Brønsted acids [14], acidic clays [15], amines
[16, 17], N-methylimidazole [18], coordination com-
pounds of metals of the platinum group [19], ionic
liquids [20, 21], quaternary ammonium salts [20, 22]
and bases [23], KF–Al2O3 [24], borax [25], Amberlyst-
15 [26], tributylphosphine [27], R3P–Me3SiCl [28],
Cu(acac)2–[bmIm]BF4 [29], copper nanoparticles [30],
Imidazole ring is a structural fragment of the side
chain in the amino acid residue of histidine which
constitutes a part of almost all enzymes. Imidazole is
known to catalyze a number of biochemical reactions
[4, 5]; therefore, the catalytic activity of poly(N-vinyl-
imidazole) was studied while simulating some biologi-
cal processes [6, 7]. We previously found that poly-
mers having imidazole groups catalyze hydrolysis of
461

BELETSKAYA et al.
462
Hβ-SnA zeolite [31], silica gel [32], β-cyclodextrin
[33], sugars [34], sodium dodecyl sulfate [35], and in
the recent time by organic catalysts, e.g., of peptide
type [36]. Data were also reported on the aza-Michael
reactions performed in water in the absence of
a catalyst [37, 38]. However, these reactions occurred
only with fairly nucleophilic primary and secondary
amines. Only one example of the use of polymeric
bases as catalysts in the aza-Michael reactions was
reported: poly(N-vinylpyridine) catalyzed the addition
of secondary amines and carbamates to α,β-unsaturated
esters, nitriles, and ketones [39]. The reactions were
carried out under solvent-free conditions in hetero-
geneous medium. On the other hand, as noted above,
secondary amines are capable of reacting in the
absence of a catalyst. For example, the reactions of
piperidine and diethylamine with methyl acrylate in
water in the absence of catalyst [37] and in the pres-
ence of 5 wt % (with respect to amine) of poly(N-
vinylpyridine) in the absence of a solvent [39]
occurred under comparable conditions and afforded the
corresponding addition products in almost similar
yields. Secondary amines are much stronger bases than
poly(N-vinylpyridine); therefore, the use of the latter
as base catalyst in this case is likely to be redundant.
methyl vinyl ketone (run no. 1). In each cycle, when
the reaction was complete (according to the TLC data),
the mixture was evaporated, the residue was extracted
with ethyl acetate, the organic layer was removed from
the polymer, and water and reactants required for the
next cycle were added. The yields of 4-(1H-1,2,4-tri-
azol-1-yl)butan-2-one in five successive cycles were
88, 90, 85, 92, and 86% (according to the H NMR
data); thus almost no loss of catalytic activity was
observed.
1
Unlike 1H-1,2,4-triazoles, least nucleophilic nitro-
gen-containing heterocycles, such as uracil, oxazo-
lidin-2-one, and succinimide, readily reacted under
analogous conditions only with most reactive methyl
vinyl ketone (run nos. 8, 9, 11, 12). In the reaction with
uracil 1:1 and 1:2 adducts can be formed (run nos. 8,
9). The use of poly(N-vinylimidazole) as catalyst
allowed us to obtain 1:1 or 1:2 adduct, depending on
the amount of the alkene taken. Up to now, no catalyst
was found to ensure selective formation of the above
adducts. For example, the reactions catalyzed by
sodium dodecyl sulfate and NaHCO3 in water [35] or
by DABCO in acetonitrile [17] lead to preferential
formation of the 1:1 adduct, whereas the 1:2 adduct
was formed as the major product in the presence of
tributylphosphine [27] or benzyl(triethyl)ammonium
hydroxide [17]. In the reactions of methyl acrylate
with 1H-1,2,4-triazole and uracil, the yields of the
corresponding addition products were not satisfactory
even on prolonged heating (run nos. 3, 10).
In our study on the aza-Michael reaction catalyzed
by poly(N-vinylimidazole) we used as substrates aza
heterocycles (see table) that are weaker bases than
imidazole, otherwise the substrate itself can catalyze
its addition to electron-deficient alkenes. As Michael
acceptors we selected α,β-unsaturated ketones (methyl
vinyl ketone and cyclohex-2-en-1-one), methyl vinyl
sulfone, and methyl acrylate. The reactions were
carried out in water. 1H-1,2,4-Triazoles reacted with
the above alkenes in the presence of 10 mol % of poly-
(N-vinylimidazole) (PVI) under mild conditions (room
temperature), and the corresponding addition products
were obtained in high and good yields (Scheme 1; see
table, run nos. 1, 2, 4–7). An exception was less
reactive methyl acrylate (run no. 3).
Presumably, poly(N-vinylimidazole) as catalyst
favors polarization of the N–H bond in heterocyclic
substrates, thus increasing their nucleophilicity. This is
especially important for weakly nucleophilic substrates
(run nos. 8–12). Here, the polymer, which is not
a strong base, readily donates proton to the emerging
carbanion (Scheme 2). The role of water in the reac-
tions under study is essential. It also favors proton
transfer; therefore, reactions with even weakly basic
nitrogen-containing heterocycles may occur in the
absence of a catalyst, though at a considerably lower
rate. For example, the yields of the addition products
of 1H-1,2,4-triazole to methyl vinyl ketone (run no. 1)
and methyl vinyl sulfone (run no. 4) in the presence of
poly(N-vinylimidazole) are 82 and 87%, respectively,
and in the absence of catalyst (other conditions being
equal), 47 and 36%.
We examined the possibility for repeated use of
the catalyst in the reaction of 1H-1,2,4-triazole with
Scheme 1.
PVI (10 mol%)
H2O, 20–25°C
Z'
Z
NH
+
N
Z'
Z
I–XII
Thus we have shown that poly(N-vinylimidazole) is
a low-expensive, efficient, and (what is important)
readily recyclable organic catalyst for the addition of
Z = C(O)Me, SO2Me, CO2Me, Z′ = H;
ZZ′ = CH2CH2CH2C(O).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

POLY(N-VINYLIMIDAZOLE) AS AN EFFICIENT AND RECYCLABLE CATALYST
463
Addition of nitrogen-containing heterocycles to alkenes in the presence of poly(N-vinylimidazole) in water at 20–25°Ca
Run no. NH compound
Alkene
Reaction time, h
Product
Yield,b %
Reference
O
N
O
N
N
N
01
02
82 (47)
[18]
H2C
N
N
Me
O
N
H
N
N
Me
I
N
O
N
02
24
18 (60°C)
30
92
–
N
H
II
O
N
O
N
N
N
03
c20c
[18]
H2C
N
N
OMe
N
H
N
OMe
Me
III
O
O
S
N
O
O
N
04
05
87 (36)
-
H2C
S
Me
N
N
H
IV
Me
O
N
Me
O
N
N
N
05
48
91
90
-
Me
H2C
N
Me
Me
N
H
Me
V
Me
O
N
Me
O
N
N
N
N
06
–
N
Me
Me
N
H
Me
VI
Me
O
Me
N
N
O
O
O
S
N
H2C
S
07
08
24
04
94
–
Me
N
Me
N
H
Me
VII
O
O
O
O
HN
d83 (6)d0
[35]
HN
HN
N
H2C
O
Me
Me
Me
Me
O
O
N
H
VIII
Me
O
O
O
O
O
N
e09e
24
90
[27]
N
H2C
N
H
O
IX
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

BELETSKAYA et al.
464
(Contd.).
O
O
O
O
O
HN
10
11
16 (70°C)
c10c
75 (0)0
81
[18]
[40]
[41]
HN
O
N
H2C
O
O
OMe
OMe
O
N
H
X
O
O
O
N
08
24
H2C
N
H
Me
Me
XI
O
O
N
O
12
O
O
H2C
N
Me
H
O
Me
XII
a
Molar ratio NH-compound–alkene–poly(N-vinylimidazole) 1.0:1.2:0.1 (per monomer unit).
Yield of the isolated product; in parentheses is given the yield in the absence of catalyst.
According to the 1H NMR data using dimethyl fumarate as internal standard.
Apart from 1:1 adduct, 11% of 1:2 adduct was isolated.
b
c
d
e
Molar ratio NH-compound–alkene–poly(N-vinylimidazole) 1.0:2.4:0.1 (per monomer unit).
nitrogen-containing heterocycles to Michael acceptors.
was monitored by TLC on silica gel 60 F254 plates
(Merck). Silica gel Merck 60 (0.04–0.063 mm) was
used for column chromatography. Poly(N-vinylimid-
azole), M 75300, was synthesized according to the
procedure reported in [10].
The use of poly(N-vinylimidazole) is advantageous
due to experimental simplicity and economically safe
conditions: the reactions are carried out in water at
room temperature.
Addition of nitrogen-containing heterocycles to
alkenes in the presence of poly(N-vinylimidazole)
(general procedure). Water, 4 ml, was added to
14.1 mg (0.15 mmol per monomer unit) of poly(N-
vinylimidazole) and 1.5 mmol of nitrogen-containing
heterocycle, and the mixture was stirred for 10 min.
The corresponding alkene, 1.8 mmol, was then added,
EXPERIMENTAL
The H and 13C NMR spectra were recorded on
a Bruker AMX-400 spectrometer at 400.13 and
100.61 MHz, respectively, using CDCl3 as solvent. All
reactions were carried out under argon. Their progress
1
Scheme 2.
n
n
N
N
N
N
Z
N
H
N
NH
+
+
Z'
H
n
Z
N
N
Z
Z'
Z'
N
Z'
N
+
N
Z
n
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010

POLY(N-VINYLIMIDAZOLE) AS AN EFFICIENT AND RECYCLABLE CATALYST
465
the mixture was stirred at room temperature until the
reaction was complete (see table), evaporated to a min-
imal volume, and extracted with ethyl acetate, the ex-
tract was dried over Na2SO4, the solvent was distilled
off under reduced pressure, and the residue was sub-
jected to column chromatography using methylene
chloride–methanol as eluent. The products were iden-
tified by 1H and 13C NMR spectroscopy, and elemental
compositions were also determined for the newly
synthesized compounds.
3,5-Dimethyl-1-[2-(methylsulfonyl)ethyl]-1H-
1,2,4-triazole (VII). White solid, mp 118°C. H NMR
1
spectrum, δ, ppm: 2.32 s (3H, CH3), 2.48 s (3H, CH3),
2.64 s (3H, CH3S), 3.61 t (2H, CH2, J = 6.2 Hz), 4.46 t
(2H, CH2, J = 6.2 Hz). 13C NMR spectrum, δC, ppm:
11.67 (CH3), 13.71 (CH3), 41.52, 41.98, 53.36, 153.29
(C=N), 160.50 (C=N). Found, %: C 41.59; H 6.45;
N 20.76; S 15.86. C7H13N3O2S. Calculated, %:
C 41.36; H 6.45; N 20.67; S 15.78.
Reaction of 1H-1,2,4-triazole with but-3-en-2-
one with regeneration of the catalyst (see table, run
no. 1). Water, 0.5 ml, was added to a mixture of 1.9 mg
(0.02 mmol per monomer unit) of poly(N-vinylimida-
zole) and 13.8 mg (0.2 mmol) of 1H-1,2,4-triazole, and
the mixture was stirred for 10 min. But-3-en-2-one,
16.8 mg (0.24 mmol), was added, and the mixture was
stirred for 2 h at room temperature. The mixture was
then evaporated, the residue was extracted with ethyl
acetate, the extract was separated from the polymer,
dried over Na2SO4, and evaporated, dimethyl fumarate
was added as reference, and the mixture was analyzed
3-(1H-1,2,4-Triazol-1-yl)cyclohexan-1-one (II).
1
Colorless viscous liquid. H NMR spectrum, δ, ppm:
1.71–1.82 m (1H, CH2), 2.04–2.12 m (1H, CH2), 2.21–
2.29 m (2H, CH2), 2.38–2.49 m (1H, CH2), 2.83 d.d
(1H, CH2, J = 14.4, 4.3 Hz), 2.95 d.d (1H, CH2, J =
14.4, 9.9 Hz), 4.65 m (1H, 3-H), 7.94 s (1H, CH=N),
8.10 s (1H, CH=N). 13C NMR spectrum, δС, ppm:
21.46 (СH2), 31.22 (СH2), 40.38 (СH2), 46.94 (СH2),
57.80 (С3), 141.53 (C=N), 151.94 (C=N), 206.66
(C=O). Found, %: C 57.88; H 6.76; N 25.69.
C8H11N3O. Calculated, %: C 58.17; H 6.71; N 25.44.
1
1-[2-(Methylsulfonyl)ethyl]-1H-1,2,4-triazole
by H NMR. The polymer was washed with diethyl
1
(IV). White solid, mp 91°C. H NMR spectrum, δ,
ether and dried under reduced pressure, the above
indicated amounts of water and the reactants were
added, and the next reaction cycle was performed in
a similar way. The yields of 4-(1H-1,2,4-triazol-1-yl)-
butan-2-one in five successive cycles were 88, 90, 85,
92, and 86%.
ppm: 2.66 s (3H, CH3), 3.65 t (2H, CH2, J = 6.2 Hz),
4.70 t (2H, CH2, J = 6.2 Hz), 8.00 s (1H, CH=N),
8.23 s (1H, CH=N). 13C NMR spectrum, δC, ppm:
41.99, 43.10, 53.45, 144.27 (C=N), 152.82 (C=N).
Found, %: C 34.37; H 5.21; N 23.76; S 18.22.
C5H9N3O2S. Calculated, %: C 34.28; H 5.18; N 23.98;
S 18.30.
The authors thank the Chemistry and Materials
Science Department of the Russian Academy of
Sciences for financial support of this study (program
for basic research no. 3, “Design and Investigation of
Macromolecules and Macromolecular Structures of
New Generations”).
4-(3,5-Dimethyl-1H-1,2,4-triazol-1-yl)butan-2-
1
one (V). Colorless oily liquid. H NMR spectrum, δ,
ppm: 2.14 s (3H, CH3CO), 2.27 s (3H, CH3), 2.43 s
(3H, CH3), 3.03 t (2H, CH2, J = 6.3 Hz), 4.17 t (2H,
13
CH2, J = 6.3 Hz). C NMR spectrum, δC, ppm: 11.66
(CH3), 13.68 (CH3), 30.09 (CH3CO), 41.88 (CH2),
42.27 (CH2), 152.48 (C=N), 159.47 (C=N), 205.34
(C=O). Found, %: C 57.19; H 7.97; N 24.92.
C8H13N3O. Calculated, %: C 57.46; H 7.84; N 25.13.
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