Ionic tagged DABCO grafted on magnetic nanoparticles: A water-compatible catalyst for the aqueous aza-Michael addition of amines to α,β- unsaturated amides

Article abstract of DOI:10.1039/c4cy00232f

Ionic tagged 1,4-Diazabicyclo[2.2.2]octane (DABCO) grafted on magnetic nanoparticles (MNPs) was prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) and thermal gravimetric analysis (TGA). The resulting magnetic solid supported DABCO catalyst with an ionic moiety was efficient for aza-Michael addition of aliphatic amines to various α,β-unsaturated amides in water at room temperature, affording the desired products in good to excellent yields. Gratifyingly, the catalyst could be readily recovered by an external magnet and reused ten times without any significant loss of activity. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c4cy00232f

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Ionic tagged DABCO grafted on magnetic nanoparticles: a
waterꢀcompatible catalyst for aqueous azaꢀMichael addition of
amines to α,βꢀunsaturated amides
Anguo Ying a *, Shuo Liu b, Yuxiang Nib, Fangli Qiu a, Songlin Xu b *, Wenyuan Tanga
(a School of Pharmaceutical and Chemical Engineering, Taizhou University, Taizhou
318000)
(b School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072)
Abstract Ionic tagged 1,4ꢀDiazabicyclo[2.2.2]octane (DABCO) grafted on magnetic
nanoparticles (MNPs) was prepared and characterized by Xꢀray diffraction (XRD), transmission
electron microscopy (TEM), Fourier transform infrared spectroscopy (FTꢀIR), vibrating sample
magnetometer (VSM) and thermal gravimetric analysis (TGA). The resulting magnetic solid
supported DABCO catalyst with ionic moiety was efficient for azaꢀMichael addition of aliphatic
amines to various α,βꢀunsatuated amides in water at room temperature, affording the desired
products in good to excellent yields. Gratifying, the catalyst could be readily recovered by an
external magnet and reused for ten times without significant loss of activity.
Keywords Magnetic nanoparticles, immobilization, azaꢀMichael addition, unsaturated amide,
recyclability.
Introduction
βꢀAmino amides as well as their derivatives are found in many natural and pharmaceutical
compounds that express potential biological activities[1]. For example, dual acetylcholinesterase
(AChE) inhibitor 1 have been approved by FDA for the treatment of Alzheimer’disease (AD)[2].
* Corresponding authors. Tel/fax: +86 576 88660359.
Eꢀmail address:yinganguo@163.com or agying@tzc.edu.cn (A. Ying), slxu@tju.edu.cn (S. Xu).
Electronic supplementary information (ESI) available: detailed NMR spectra of IS and unknown addition
products.
1

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The ethyl sulfide 2 with an IC50=100nM against MetAP2 show growth inhibition property against
HUVECs[1b]. Triazolopiperazine 3 is a DPPꢀ4 inhibitor for the treatment of the type 2
diabetes[1e]. αꢀHydroxyꢀβꢀamino amides 4 is a key intermediate for the preparation of
P1ꢀαꢀketoamides, which demonstrate potent inhibition of aminopeptidases and prolyl
endopeptidases[3].
H
N
O
N
NH2
O
OEt
CCH2CH2N
R1
N
S
H
O
R2
O
HO
2
1
2
F
F
F
R2
O
O
NH2
NHR1
N
N
PGHN
N
CF3
HO
N
3
4
Fig.1 Representative examples of biologically active products containing βꢀamino amide moiety
In view of excellent pharmaceutical activities of βꢀamino amides based compounds, much
attention has been attracted to the construction and synthesis of these analogues[3,4]. As an
atomꢀeconomic, simply and highly efficient synthetic method, Michael addition has been widely
utilized in organic transformations. Accordingly, the conjugated addition of amines to
α,βꢀunsaturated amides has been frequently exploited as fascinating protocol to prepare βꢀamino
amides. Several procedures have been reported to construct βꢀamino amides over the past few
years using a variety of catalysts such as boric acid[5a], bromodimethylsulfonium bromide[5b],
KF/Al2O3[5c], LiClO4[5d], Cu(acac)2 immobilized in ionic liquids[5e], polymer supported
2

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gadolinium triflate[5f], phosphate impregnated titania[5g], ionic liquids[5h,5i] and silica gel[5j].
Very recently, Cooks presented a novel CꢀN bond formation reaction occurring in thin films
deposited on ambient surfaces, providing an alternative method for the rapid synthesis of reaction
product on a small scale[6]. Despite the remarkable success of the protocols mentioned above,
however, most of them suffered from one or some drawbacks, for example, substrateꢀselective and
airꢀsensitive for some catalysts, large amount catalyst loading, utilization of heavy metal salts
coupled with volatile and harmful organic solvents, as well as tedious workꢀup and difficult
recovery of catalyst. Thus, the development of a novel, efficient catalyst for azaꢀconjugate
reaction of amines with α,βꢀunsaturated amides is highly desirable.
Magnetic nanoparticles (MNPs) as catalyst supports have been attracting more and more
attention because they are not only readily dispersed in reaction solution with intrinsically high
surface area rending the efficient accessibility of substrates to the surface bound to the active
catalytic sites, but also they are superꢀparamagnetic and can be easily recovered from the reaction
mixture using an external magnet[7]. Thus, a lot of MNPs supported catalysts with excellent
catalytic activities, have been developed and applied in versatile organic synthesis, including
coupling reactions[8aꢀc], Ritter reaction[8d], cyanosilylation of carbonyl compounds[8e],
Friedlander reaction[8f], reduction of α,βꢀepoxy ketones[8g], and some enantioselective
reactions[8hꢀj]. Very recently, to combine the magnetic nanoꢀsupport features and unique
properties of ionic moiety which usually facilitates accessibility of reactant to active site on the
surface of the catalysts, as well as stabilizes the formed intermediates during reaction process[9],
MNPs supported acidic[10] and chiral catalysts[11] with ionic tags were successfully prepared and
exploited to promote the oneꢀpot synthesis of benzoxanthenes and the direct asymmetric aldol
3

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reaction, respectively. Herein, we present MNPs supported 1,4ꢀDiazabicyclo[2.2.2]octane
(DABCO) with ionic tag and its application as catalyst for azaꢀMichael addition of amines to
α,βꢀunsaturated amides.
Results and discussion
Preparation and characterization of the catalyst
The magnetic nanoparticle supported DABCO with ionic tag (ITꢀDABCO@MNPs) was
prepared following the procedure depicted in Scheme 1. The first step was to prepare Fe3O4
nanoparticles, starting from commercially available ferric chloride hexahydrate and ferrous
chloride tetrahydrate[12]. To prevent the aggregation of the Fe3O4 particles and provide numerous
surface SiꢀOH groups for further modifications, silica as a protecting shell was utilized to coat the
naked particles to form a coreꢀshell structure (SiO2@Fe3O4) by a chemical coꢀprecipitating
method according with the reported literature 13. Ionic salt 5 was synthesized by quaternization of
DABCO with triethoxyꢀ3ꢀ(chloropropyl)ꢀsilane in dry toluene refluxing for 48 hours. Then MNPs
(SiO2@ Fe3O4) with abundant surface hydroxyl groups were selected as carriers to graft the ionic
salt 5 to give the desired catalyst ITꢀDABCO@MNPs as grey solid.
Cl
(EtO)3Si
N
+
N
(EtO)3Si
ꢀ
N
N
Cl
Dry toluene, reflux for 2 days
5, Ionic Salt
DABCO
OH
SiO2
O
5
SiO2
+
N
TEOS
OH
OH
O
Si
ꢀ
N
Dry ethanol
Reflux for 48h
Cl
O
Fe3O4
SiO2@Fe3O4(MNPs)
ITꢀDABCO@MNPs
4

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Scheme 1 Synthesis of ionic tagged DABCO grafted on MNPs
The XRD patterns of carrier SiO2@ Fe3O4 (MNPs) and catalyst ITꢀDABCO@MNPs show the
typical peaks at 30.07°, 35.52°, 43.12°, 53.36°, 57.19°, 62.79° with the corresponding reflections
of (220), (311), (400), (422), (511), (440) crystal planes as indicated in Fig. 2. Comparing the
XRD pattern of MNPs and catalyst ITꢀDABCO@MNPs, immobilization of IS 5 on the surface of
the MNPs did not significantly affect the structure of Fe3O4 nanoparticles and they both match
well with the data for standard Fe3O4 sample[14]. A broad peak in the XRD pattern of
ITꢀDABCO@MNPs at 2θ=22ꢀ26° is the characteristics of amorphous silica shell of the silica
coated nanoparticles (SiO2@ Fe3O4) [15].
Fig.2 Powder Xꢀray diffraction patterns of MNPs and ITꢀDABCO@MNPs
The transmission electron microscop (TEM) images of bare Fe3O4, silica coated nanoparticles
(MNPs) and ITꢀDABCO@MNPs were confirmed that three samples have uniformꢀsized magnetic
nanoparticles with almost spherical morphology. The silica shell on the bare Fe3O4 is 3ꢀ5 nm
thick(Fig.3a). For comparison with SiO2@Fe3O4 (Fig.3a), the grey shell in Fig.3b and Fig.3c
5

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exhibits thickness of 5ꢀ15 nm, demonstrating the successful immobilization of ionic salt 5 on the
nanoparticles. The loading of IS 5 per g was determined to be 1.41 mmol gꢀ1 by elemental analysis
of nitrogen.
(a)
(b)
(c)
Fig.3 Transmission electron microscope (TEM) images of SiO2@Fe3O4(a), fresh ITꢀ
DABCO@MNPs (b), ITꢀDABCO@MNPs after ten times reused(c).
Successful functionalization of the MNPs with DABCO based salt 5 was further confirmed by
Fourier transform infrared spectroscopy (FTꢀIR) analysis. The blank MNPs, ionic salt 5 and
ITꢀDABCO@MNPs were intensively investigated (Fig.4). As shown in Fig.4, the spectrum for the
MNPs along exhibits a peak at 575 cmꢀ1 and stretching vibration at 1080 cmꢀ1 which are attributed
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to the FeꢀO vibration and SiꢀOꢀSi modes of the silica shell, respectively. The two characteristic
vibrations can also be observed in the spectrum of immobilized catalyst ITꢀDABCO@MNPs,
proving that surface modification on the particles has not bring change regarding the properties of
magnetic core at all. Both IS 5 and ITꢀDABCO@MNPs shows typical peaks at 1472 cmꢀ1, 2887
cmꢀ1, 2972 cmꢀ1, which can be assigned to the alkyl chain stretching and deformation
vibrations[10]. The presence of CꢀN bond at the DABCO structure was evident from characteristic
band at 1210 cmꢀ1.
Fig.4 FTꢀIR spectra of ITꢀDABCO@MNPs, ionic salt 5 and SiO2@Fe3O4.
The magnetism of samples was characterized by vibrating sample magnetometer (VSM) at
room temperature. As shown in Fig.5, the two examples both present excellent paramagnetism and
can be completely saturated at high fields of up to 2.0 T. When the IS 5 was grafted on the surface
of the carrier MNPs (SiO2@Fe3O4), the saturated magnetism was decreased from 59.2 to 34.6 emu
gꢀ1. The efficient magnetization of catalyst ITꢀDABCO@MNPs can also be verified by simple
attraction with external magnetic forces during the reaction workup process (Fig.8b).
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Fig.5 Magnetic curves of MNPs and ITꢀDABCO@MNPs
The stability of the supported catalyst ITꢀDABCO@MNPs was investigated by the
thermogravimetric (TG) analysis, which is also one indication of bond formation between MNPs
and catalyst. As shown in Fig.6, an initial loss from room temperature to 238 ℃ was detected due
to the removal of surface absorbed water and structural water within amorphous SiO2[16]. The
second weigh loss at 239ꢀ400 ℃ was assigned to complete cleavage of DABCO moiety grafted
on the shell around the nanoparticles and the amount of the organic DABCO was approximately
16.5 % against the total solid catalyst. The last weigh loss was at the temperature range of from
401 ℃ to 540 ℃, probably due to the decomposition of trialkoxysilane moiety[11,17]. The peak
in DTG curve demonstrates that the most fastest weigh loss occurred between 239 ℃ and
323 ℃. Thus, the rational and safe temperature for its catalytic performance is around or below
239 ℃.
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Fig.6 Thermogravimetric (TG) and different thermogravimetric (DTG) analysis of catalyst
ITꢀDABCO@MNPs
ITꢀDABCO@MNPs catalyzed azaꢀMichael addition of amines to α,βꢀunsaturated amides
We tested the catalytic activity of supported catalyst ITꢀDABCO@MNPs using azaꢀMichael
addition of morpholine to 4ꢀacryloylmorpholine as model reaction. In an effort to establish a better
catalytic system, the effects of solvent, catalyst, amount of catalyst on azaꢀMichael addition were
thoroughly evaluated on the model reaction at room temperature. As shown in Table 1, solvent is a
crucial factor for the reaction results in terms of reaction rate and yield. Protic solvents including
methanol and water gave good reaction yields within 3 hours while aprotic solvents gave
significantly lower yields (Table 1, entries 1ꢀ4). From both viewpoint of environmentally benign
green chemistry and reaction results, water was finally selected as the suitable medium for further
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examinations. Then, a serious of catalysts were exploited to promote the reaction of morpholine
and 4ꢀacryloylmorpholine (Table 1, entries 4ꢀ7). Organic base triethylamine was found to be
effective for the reaction affording the desired product in 65 % yield in 4 hours. Very interestingly,
ionic tagged DABCO grafted on MNPs (ITꢀDABCO@MNPs) show much better catalytic activity
than its corresponding organic base DABCO (Table 1, entries 4 and 5). When the reaction was
catalyzed by MNPs or in absence of any catalyst, almost no reaction product was detected
(Table 1, entries 6 and 7). With the increasing amount of the catalyst from 1.0 mol % (Table 1,
entries 4 and 11ꢀ12), the desired product yield does not further increase while reducing the amount
of the catalyst leads to the obviously decreased yield (Table 1, entries 4 and 9ꢀ10). Therefore, 1.0
mol % of ITꢀDABCO@MNPs with water as solvent was enough to push the reaction to
completion.
Table 1 Conjugated addition of morpholine (5 mmol) to 4ꢀacryloylmorpholine (6 mmol) under
different reaction conditions
O
O
O
Catalyst
rt
N
N
O
+
N
O
O
N
H
Entry
Catalyst (mol %)
Solvent b
CH2Cl2
Toluene
methanol
Water
Time (h)
Yield (%)a
1
2
3
4
5
6
ITꢀDABCO@MNPs (1.0)
ITꢀDABCO@MNPs (1.0)
ITꢀDABCO@MNPs (1.0)
ITꢀDABCO@MNPs (1.0)
DABCO (2.0)
5
5
3
2
4
4
13
8
69
84
76
65
Water
Et3N (2.0)
Water
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7
8
SiO2@Fe3O4 (MNPs) (150 mg)
Water
Water
Water
Water
Water
Water
8
24
3
Trace
ꢀ
NRc
65
9
ITꢀDABCO@MNPs (0.5)
ITꢀDABCO@MNPs (0.1)
ITꢀDABCO@MNPs (1.5)
ITꢀDABCO@MNPs(3.0)
10
11
12
3
38
2
84
2
85
a Isolated yield based on morpholine. b The volume of solvent is 10 mL. c NR: no reaction.
With the optimal reaction conditions in hand as well as to study the generality of this procedure,
we then proceeded to explore a wide range of aliphatic amines and α,βꢀunsatuated amides (Table
2). As shown in Table 2, the reaction of various aliphatic amines and Nꢀsubstituted acrylamides
underwent smoothly to yield the desired adducts in good to excellent yields. Pyrrolidine,
Nꢀmethylꢀpeperidine and Nꢀethylꢀpiperazine were efficient donors to react with
4ꢀacryloylmorpholine to generate the conjugated products in the yields of 75 %ꢀ89 % (Table 2,
entries 1ꢀ3). It has been observed that the reaction is greatly influenced by the steric hindrance. In
other word, the larger the substituent on N position of the acrylamide is, the lower the reaction rate
is (Table 2, entries 5,6,9,11). To our pleasure, Nꢀhydroxymethyl acrylamide and diacetone
acrylamide are also efficient Michael acceptors to give the corresponding products with
reasonable yields (Table 2, entries 13ꢀ17). Finally, chemꢀselectivity of ITꢀDABCO@MNPs was
examined in the reaction of 4ꢀacryloylmorpholine and Nꢀ(2ꢀhydroxyethyl)piperazine (Scheme 2).
85 % Yield of adduct formed by nitrogen nucleophile attack was obtained while no side product
formed via oxygen nucleophile addition was detected, demonstrating the excellent
chemꢀselectivity of ITꢀDABCO@MNPs.
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Table 2 azaꢀMichael reaction catalyzed by ITꢀDABCO@MNPs in water a
Entr
y
α,βꢀUnsaturated
Time
(h)
Yield
Amine
Product
Ref.
18a
ꢀ
amide
(%)b
O
O
N
N
1
2
2
2
89
N
O
N
H
O
O
O
O
N
89
75
N
N
O
N
H
O
O
N
N
N
N
O
N
3
3
ꢀ
O
N
H
O
O
4
5
6
7
1
1
2
3
92
87
83
91
5j
5j
N
NH2
N
H
NH2
O
O
O
O
O
N
NH2
NH2
N
H
O
O
N
N
ꢀ
N
N
N
H
O
O
O
O
18b
N
N
H
N
N
O
N
N
N
8
9
1
3
88
75
ꢀ
ꢀ
N
N
H
O
O
O
N
N
N
H
N
H
O
H
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O
O
O
O
10
11
12
3
3
3
93
ꢀ
18c
ꢀ
N
H
N
N
H
N
H
O
O
N
H
N
70
86
N
H
N
H
O
O
N
N
N
H
H
N
H
O
O
N
OH
N
N
N
H
13
1
92
ꢀ
N
OH
OH
H
N
H
O
O
O
N
OH
N
H
14
15
16
1
5
2
91
65
91
ꢀ
18c
ꢀ
N
H
N
H
NH2
O
N
OH
O
HN
N
H
OH
O
H
O
O
N
H
N
N
N
N
H
N
H
O
O
O
O
O
N
N
N
H
H
17
5
70
ꢀ
O
N
H
a Reactions were carried out on 5.0 mmol scale of amine with 1.2 equiv of α,βꢀunsaturated amide
b
in the presence of 1.0 % mol of ITꢀDABCO@MNPs in water (10 mL) at room temperature.
Isolated yield based on amine.
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O
N
O
O
N
HN
OH
O
Side product, 3h, yield: 0
O
N
IT-DABCO@MNPs
H2O, rt
+
N
O
N
H
N
N
O
N
HO
Product, 3 h, yield: 85 %
Scheme 2 Investigation of chemꢀselectivity of catalyst ITꢀDABCO@MNPs
A plausible mechanism for the azaꢀMichael reaction between amine and α,βꢀunsaturated amide
is depicted in Fig.7. The reaction proceeds via the initial formation of hydrogen bond (in state B)
between catalyst A and amine, which is favorable to produce nitrogen anion (state C).
Subsequently, the nucleophile reacts with unsaturated amide to give the final target product and
release the catalyst ITꢀDABCO@MNPs. The catalyst ITꢀDABCO@MNPs (A) has two domains.
One is the functional domain, in which nitrogen provides a hydrogen bond acceptor. The remained
domain as well as OH group on the surface of the silica coated magnetic nanoparticles makes the
catalyst compatible with water and being applied in environmental benign aqueous conditions.
Moreover, the “ionic environment” present electrosteric activation to stabilize the transitionꢀstate
[9b]. All of these novel features as well as high surface area of the MNPsꢀsupported catalyst
facilitate the reaction efficiently.
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SiO2
SiO2
Fe3O4
Fe3O4
O
O
O
O
O
O
Si
Si
ꢀ
SiO2
ꢀ
C
+ Cl
+ Cl
Fe3O4
N
N
B
N
H
NH
O
O
O
N
Si
N
O
N
ꢀ
hydrophilic
domain
+ Cl
N
N
functional domain
A
SiO2
Fe3O4
O
O
O
Si
H
N
ꢀ
+ Cl
N
N
A
O
N
N
Product
Fig.7 A plausible mechanism for azaꢀMichael addition of aliphatic amine to α,βꢀunsaturated amide
One of the key characteristics of magnetic nanoparticles supported catalysts is their practical
recovery and reuse in the presence of appropriate magnetic field. To investigate this issue, the
recyclability of the catalyst ITꢀDABCO@MNPs was examined in the model reaction of
morpholine and 4ꢀacryloylmorpholine. As shown in Fig.8, the catalyst was highly dispersed in the
reaction system. Upon completion of the reaction, the catalyst can be readily recovered from the
reaction mixture with assistance of external magnet. The decanted solution was extracted with
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ethyl acetate to obtain crude product, followed by column flash chromatography for further
purification. The recovered catalyst was washed with methanol, dried under vacuum and subjected
to the next run.. For comparison, the reuse of free base DABCO was also tested in the same model
reaction. The ITꢀDABCO@MNPs could be recycled up 10 times without any significant loss of
activity while remarkably decrease in the yield was observed using DABCO as catalyst (Fig.9).
The reason is that after the ten usage, the ionic tagged DABCO moiety has not degraded from the
magnetic carrier, judging from the FTꢀIR spectra (Fig.10) and the TEM observation of the
recovered catalyst (Fig.3c). Moreover, the loading of DABCO residue subjected ten recycle
reaction is 1.28 mmol gꢀ1, slightly lower than that of fresh catalyst ITꢀDABCO@MNPs (1.41
mmol gꢀ1). On the contrary, DABCO was greatly washed away during the workup process of
extraction, leading to its bad recyclability.
(a)
(b)
Fig.8 Photographs of the dispersion of the catalyst ITꢀDABCO@MNPs in water (a) and the
separation with an external magnet (b).
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IT-DABCO@MNPs
DABCO
100
80
60
40
20
0
1 2 3 4 5 6 7 8 9 10
Run number
Fig.9 Reuse of the catalyst ITꢀDABCO@MNPs (reaction time: 2h) and DABCO (reaction time:
4h) in the aqueous reaction of morpholine and 4ꢀacryloylmorpholine.
Fig.10 FTꢀIR spectra of fresh catalyst ITꢀDABCO@MNPs and catalyst subjected to reused ten
times.
Conclusions
In conclusion, a magnetically recoverable DABCO catalyst with ionic tag (ITꢀDABCO@MNPs)
was successfully prepared and was subsequently used in aqueous azaꢀMichael addition of various
amines to a wide range of α,βꢀunsaturated amides at room temperature with success. The presence
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of the ionic tag or ionic environment in the supported catalyst make it waterꢀcompatible and
effective for the type of reaction. In addition, the catalyst is reusable for ten cycles without any
significant loss of its catalytic activity. Further applications of the catalyst to other organic
transformations are undergoing in our laboratory.
Experimental
Materials and instruments
All chemical reagents were purchased without further purification. The reaction monitoring was
accomplished by thin layer chromatography (TLC) on gel F254 plates. Powder Xꢀray diffraction
data were obtained Cu Kα radiation. Fourier transform infrared spectroscopy (FTꢀIR) were
recorded on a spectrometer using KBr pellets. Transmission electron microscopy (TEM) was
performed with a instrument operating at 40ꢀ100 kV. The magnetic measurements were carried out
in a vibrating sample magnetometer (VSM) at room temperature. 1H and 13C NMR were recorded
on a spectrometer at 400 MHz and 100 MHz in CDCl3, respectively. Chemical shifts were reported
in parts per million (δ), relative to the internal standard of tetramethylsilane (TMS).
Preparation of silica coated magnetic nanoparticleꢀSiO2@ Fe3O4 (MNPs)
Magnetic (Fe3O4) nanoparticles were prepared by the coprecipitation [12]. FeCl3ꢁ6H2O (8.1 g,
0.03 mmol) and FeCl2ꢁ4H2O (4.97 g, 0.025 mmol) were dissolved in distilled water (100 mL). The
resulting transparent solution was heated at 85 ℃ with vigorous mechanically stirring under N2
atmosphere for 1 h. The pH value was then adjusted to 9 using the concentrated aqueous ammonia
(25 wt %). After the color of the bulk solution turned to back, the magnetic precipitates were
separated and washed several times with deionized water until the pH value of the eluent
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decreased to 7. The coating of a layer of silica on the surface of the naked Fe3O4 was conducted
through solꢀgel method [13]. The naked Fe3O4 (1.0 g) was dispersed in ethanol (200 mL) by
ultrasonic irradiation. The concentrated NH3ꢁH2O (6 mL) and TEOS (2 mL) were successively
added into the solution. With continuous strring for 24 h at room temperature. The resulting MNPs
was collected by an external magnet and washed three times with ethanol, followed by drying in
vacuum.
Synthesis of the catalyst ITꢀDABCO@MNPs
To
a
solution of DABCO (5.6 g, 50 mmol) in dry toluene (50 mL),
3ꢀchloropropyltriethoxysilane (12.0 mL, 50 mmol) was added and the mixture was refluxed for 48
h under nitrogen atmosphere. TLC showed the completion of the reaction. The reaction mixture
was evaporated under reduced pressure, followed by dried under vacuum for 6 h to give
intermediate ionic salt 5 as a white solid in 96 % yield.
The obtained MNPs powder (2 g) was dispersed in 30 mL toluene by sonication for 1 h., and
then ionic salt 5 (0.5 g) was added to the mixture. After mechanical stirring in reflux under
nitrogen atmosphere for 48 h, the suspended solid was separated by an external magnet and rinsed
with ethanol for three times and then dried under vacuum for 8 h to afford the final catalyst as grey
solid (2.28 g).
NMR data for ionic salt 5
1H NMR (400MHz, D2O): δ 3.82ꢀ3.87(m, 3H), 3.55ꢀ3.61(m, 3H), 3.32ꢀ3.36(m, 6H), 3.19ꢀ3.23(m,
2H), 3.11ꢀ3.15(m, 6H), 1.76ꢀ1.85(m, 2H), 1.18(t, 4H), 1.12(t, 5H), 0.56ꢀ0.73(m, 2H); 13C NMR
(100MHz, D2O): δ 66.4, 57.5, 52.2, 44.3, 16.9, 15.4.
General procedure for the ITꢀDABCO@MNPs catalyzed ambient azaꢀMichael addition of
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amines to α,βꢀunsaturated amides in water
A mixture of amine (5 mmol), α,βꢀunsatuated amide (6 mmol), water (20 mL) and
ITꢀDABCO@MNPs (35 mg) was stirred at room temperature. Upon the completion of the reaction
(monitored by TLC), the catalyst, separated from the reaction solution by external magnet, washed
with ethanol and ethyl acetate, followed by drying under vacuum, was reused for subsequent runs.
The decanting solution was directly filtrated and the remained residue was extracted with ethyl
acetate. The resulting crude product was purified by column chromatography using petroleum
1
ether/ethyl acetate as the eluent. The products were characterized by H NMR, 13C NMR and
elemental analysis.
NMR data for nonꢀpublished products
3ꢀ(4ꢀMethylpiperidinꢀ1ꢀyl)ꢀ1ꢀmorpholinopropanꢀ1ꢀone (Table 2, entry 2)
1H NMR (400 MHz, CDCl3) (ppm): 3.71(d, 1H, J=2.8Hz), 3.65(d, 4H, J=3.6Hz), 3.59(s, 3H),
3.47(s, 2H), 3.01(d, 2H, J=11.6Hz), 2.83(t, 2H, J=7.6Hz), 2.64(t, 2H, J=7.6Hz), 2.15(t, 2H,
J=7.6Hz), 1.96(s, 1H), 1.65(d, 2H, J=12.8Hz), 0.92(d, 3H, J=6.0Hz); 13C NMR (100 MHz, CDCl3)
(ppm): 170.0, 72.5, 66.8, 66.6, 61.6, 53.7, 53.6, 45.9, 41.9, 33.2, 30.2, 30.0, 21.5. Anal. Calcd for
C13H24N2O2: C, 64.97; H, 10.07; N, 11.66; O, 13.31. Found: C, 64.83; H, 10.23; N, 11.55; O,
13.39.
3ꢀ(4ꢀEthylpiperazinꢀ1ꢀyl)ꢀ1ꢀmorpholinopropanꢀ1ꢀone (Table 2, entry 3)
1H NMR (400 MHz, CDCl3) (ppm): 3.49ꢀ3.55(m, 6H), 3.36(s, 2H), 2.63(d, 2H, J=8.0Hz),
2.33ꢀ2.46(m, 12H), 0.98(t, 3H, J=7.2Hz); 13C NMR (100 MHz, CDCl3) (ppm): 170.2, 66.7, 66.5,
53.8, 52.7, 52.2, 52.0, 45.9, 41.8, 30.4, 11.6. Anal. Calcd for C13H25N3O2: C, 61.15; H, 9.87; N,
16.46; O, 12.53. Found: C, 61.10; H, 9.91; N, 16.43; O, 12.56.
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N, Nꢀdimethylꢀ3ꢀmorpholinopropanamide (Table 2, entry 6)
1H NMR (400 MHz, CDCl3) (ppm):3.68(t, 4H, J=4.8Hz), 2.98(s, 3H), 2.91(s, 3H), 2.67ꢀ2.72(m,
2H), 2.51(d, 2H, J=8.0Hz), 2.46ꢀ2.48(m, 4H); 13C NMR (100 MHz, CDCl3) (ppm):171.5, 66.7,
54.3, 53.6, 37.2, 35.4, 30.5. Anal. Calcd for C9H18N2O2: Found: C, 58.04; H, 9.74; N, 15.04; O,
17.18. C, 57.99; H, 9.85; N, 14.93; O, 17.23.
3ꢀ(4ꢀEthylpiperazinꢀ1ꢀyl)ꢀN,Nꢀdimethylpropanamide (Table 2, entry 8)
1H NMR (400 MHz, CDCl3) (ppm): 5.04(s, 2H), 2.91(s, 3H), 2.82(s, 3H), 2.63ꢀ2.67(m, 2H),
2.49(s, 4H), 2.44(d, 4H, J=8.4Hz), 2.37(d, 2H, J=7.2Hz), 0.99(t, 3H, J=7.2Hz); 13C NMR (100
MHz, CDCl3) (ppm): 171.4, 72.5, 61.3, 53.6, 52.4, 52.0, 51.9, 37.1, 35.3, 30.5, 11.4. Anal. Calcd
for C11H23N3O: C, 61.93; H, 10.87; N, 19.70; O, 7.50. Found: C, 61.86; H, 10.95; N, 19.64; O,
7.55.
Nꢀisopropylꢀ3ꢀmorpholinopropanamide (Table 2, entry 9)
1H NMR (400 MHz, CDCl3) (ppm):7.95(s, 1H), 3.99ꢀ4.08(m, 1H), 3.73(d, 4H, J= 3.6Hz), 2.62(t,
2H, J=6.4Hz), 2.51(s, 4H), 2.35(t, 2H, J=6.4Hz), 1.16(t, 3H, J=2.4Hz), 1.14(t, 3H, J=2.4Hz); 13
C
NMR (100 MHz, CDCl3) (ppm):171.2, 67.0, 54.4, 52.9, 40.8, 32.0, 22.9. Anal. Calcd for
C10H20N2O2: C, 59.97; H, 10.07; N, 13.99; O, 15.98. Found: C, 59.86; H, 10.20; N, 13.89; O,
16.05.
Nꢀisopropylꢀ3ꢀ(pyrrolidinꢀ1ꢀyl)propanamide (Table 2, entry 10)
1H NMR (400 MHz, CDCl3) (ppm): 8.10(s, 1H), 3.95ꢀ4.04(m, 1H), 2.76(t, 2H, J=6.4Hz), 2.59(s,
4H), 2.37(t, 3H, J=6.4Hz), 1.78ꢀ1.81(m, 4H), 1.10(d, 6H, J=6.4Hz); 13C NMR (100 MHz, CDCl3)
(ppm): 171.4, 53.2, 51.6, 40.7, 34.2, 23.5, 22.7. Anal. Calcd for C10H20N2O: C, 65.18; H, 10.94; N,
15.20; O, 8.68. Found: C, 65.14; H, 10.99; N, 15.16; O, 8.71.
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Nꢀ(tertꢀbutyl)ꢀ3ꢀ(4ꢀmethylpiperidinꢀ1ꢀyl)propanamide (Table 2, entry 12)
1H NMR (400 MHz, CDCl3) (ppm): 8.59(s, 1H), 2.91(d, 2H, J=11.6Hz), 2.55(t, 2H, J=6.0Hz),
2.27(t, 2H, J=6.0Hz), 2.18(s, 1H), 1.94ꢀ2.00(m, 2H), 1.69(d, 2H, J=12.8Hz), 1.34(s, 9H),
1.12ꢀ1.22(m, 2H), 0.94(d, 3H, J=6.4Hz); 13C NMR (100 MHz, CDCl3) (ppm): 172.0, 54.4, 53.1,
50.3, 34.5, 33.2, 30.7, 28.9, 21.8. Anal. Calcd for C13H26N2O: C, 68.98; H, 11.58; N, 12.38; O,
7.06. Found: C, 68.93; H, 11.63; N, 12.35; O, 7.09
Nꢀ(hydroxymethyl)ꢀ3ꢀ(4ꢀethylpiperazinꢀ1ꢀyl)propanamide (Table 2, entry 13)
1H NMR (400 MHz, CDCl3) (ppm): 8.83(s, 1H), 4.68(d, 2H, J=6.4Hz), 4.58(s, 2H), 3.57ꢀ3.69(m,
1H), 2.63(d, 3H, J=6.4Hz), 2.52(s, 5H), 2.37ꢀ2.43(m, 4H), 1.06(t, 3H, J=7.2Hz); 13C NMR (100
MHz, CDCl3) (ppm): 173.9, 63.8, 53.5, 52.5, 52.4, 52.2, 52.1, 52.0, 32.3, 11.6. Anal. Calcd for
C10H21N3O2: C, 55.79; H, 9.83; N, 19.52; O, 14.86. Found: C, 55.63; H, 10.02; N, 19.40; O, 14.95.
Nꢀ(hydroxymethyl)ꢀ3ꢀ(4ꢀmethylpiperidinꢀ1ꢀyl)propanamide (Table 2, entry 14)
1H NMR (400 MHz, CDCl3) (ppm): 8.98(s, 1H), 4.69(d, 1H, J=6.0Hz), 3.70(d, 1H, J=3.2Hz),
3.58(d, 1H, J=3.2Hz), 3.09(d, 2H, J=11.6Hz), 2.82(s, 2H), 2.52(s, 2H), 2.19ꢀ2.24(m, 2H), 1.96(s,
1H), 1.68(d, 2H, J=13.2Hz), 1.44(s, 1H), 1.30ꢀ1.43(m, 2H), 0.92(q, 3H, J=6.4Hz); 13C NMR (100
MHz, CDCl3) (ppm): 173.2, 72.4, 63.7, 61.4, 53.4, 53.0, 33.3, 32.9, 31.9, 29.9, 21.4. Anal. Calcd
for C10H20N2O2: C, 59.97; H, 10.07; N, 13.99; O, 15.98. Found: C, 59.88; H, 10.16; N, 13.93; O,
16.03.
3ꢀ(4ꢀEthylpiperazinꢀ1ꢀyl)ꢀNꢀ(2ꢀmethylꢀ4ꢀoxopentanꢀ2ꢀyl)propanamide (Table 2, entry 16)
1H NMR (400 MHz, CDCl3) (ppm): 8.57(s, 1H), 3.68(t, 1H, J=4.4Hz), 3.55(t, 1H, J=4.4Hz),
2.96(s, 2H), 2.65ꢀ2.75(m, 2H), 2.53(t, 4H, J=6.0Hz), 2.37ꢀ2.43(m, 4H), 2.14(t, 2H, J=6.0Hz),
2.04(s, 3H), 1.31(s, 6H), 1.05(t, 3H, J=7.2Hz); 13C NMR (100 MHz, CDCl3) (ppm): 207.6, 172.0,
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72.5, 61.4, 53.7, 52.7, 52.2, 52.0, 51.2, 50.5, 32.7, 31.5, 27.8, 11.8. Anal. Calcd for C15H29N3O2: C,
63.57; H, 10.31; N, 14.83; O, 11.29. Found: C, 63.52; H, 10.37; N, 14.79; O, 11.32.
Nꢀ(2ꢀmethylꢀ4ꢀoxopentanꢀ2ꢀyl)ꢀ3ꢀmorpholinopropanamide (Table 2, entry 17)
1H NMR (400 MHz, CDCl3) (ppm):8.42(s, 1H), 3.74(t, 4H, J=4.8Hz), 3.00(s, 2H), 2.58(t, 2H,
J=6.0Hz), 2.53(s, 4H), 2.26(t, 2H, J=6.0Hz), 2.08(s, 3H), 1.36(s, 6H); 13C NMR (100 MHz,
CDCl3) (ppm): 207.5, 171.8, 66.9, 54.3, 52.7, 51.2, 50.4, 32.5, 31.5, 27.8. Anal. Calcd for
C13H24N2O3: C, 60.91; H, 9.44; N, 10.93; O, 18.72. Found: C, 60.79; H, 9.57; N, 10.86; O, 18.78.
3ꢀ(4ꢀ(2ꢀHydroxyethyl)piperazinꢀ1ꢀyl)ꢀ1ꢀmorpholinopropanꢀ1ꢀone (Scheme 2)
1H NMR (400 MHz, CDCl3) (ppm): 3.69ꢀ3.71(m, 1H), 3.61ꢀ3.68(m, 4H), 3.60(s, 1H),
3.55ꢀ3.58(m, 3H), 3.44(t, 4H, J=4.4Hz), 2.68ꢀ2.72(m,2H), 2.51ꢀ2.54(t, 8H, J=4.4Hz), 2.49(t, 2H,
J=4.4Hz); 13C NMR (100 MHz, CDCl3) (ppm): 170.3, 72.4, 66.8, 66.6, 61.5, 59.5, 57.8, 53.8, 53.0,
52.7, 45.9, 41.9, 30.5. Anal. Calcd for C13H25N3O3: C, 57.54; H, 9.29; N, 15.49; O, 17.69. Found:
C, 57.41; H, 9.42; N, 15.41; O, 17.76.
Acknowledgements
We are grateful for the financial supports for this research by the National Natural Science
Foundation of China (Grant 21106090 and 21176170), Foundation of Low Carbon Fatty Amine
Engineering Research Center of Zhejiang Province (2012E10033), and Zhejiang Provincial
Natural Science Foundation of China (No. LY12B02004).
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Ionic tagged DABCO grafted on magnetic nanoparticles: a
water-compatible catalyst for aqueous aza-Michael addition of
amines to α,β-unsaturated amides
Anguo Ying a *, Shuo Liu b, Yuxiang Nib, Fangli Qiu a, Songlin Xu b *, Wenyuan Tanga
SiO2
Fe3O4
O
O
O
Si
H
N
-
+Cl
O
hydrophilic
domain
N
N
O
N
N
functional domain
N
Product
A water compatible DABCO grafted on magnetic nanoparticles with ionic tag has been developed
and used to catalyze the aza-Michael addition.
* Corresponding authors. Tel/fax: +86 576 88660359.
E-mail address:yinganguo@163.com or agying@tzc.edu.cn (A. Ying), slxu@tju.edu.cn (S. Xu).
Electronic supplementary information (ESI) available: detailed NMR spectra of IS and unknown addition
products.