Indirect conversion of ambient pressure CO2 into oxazolidin-2-ones by a copper-based magnetic nanocatalyst

Article abstract of DOI:10.1039/c6ra15857a

An efficient, practical and magnetically recyclable Cu-based catalytic system for the synthesis of oxazolidin-2-ones via the multicomponent reaction of carbamate salts, aromatic aldehydes and aromatic terminal alkynes was developed. The magnetic nanocatalyst, namely FeDOPACu, could efficiently promote the construction of oxazolidin-2-ones with different functional groups in good to excellent yields. Importantly, the catalyst can be easily recovered by applying an external magnet, which rendered this protocol economic and environmentally begin. This method represents an attractive heterogeneous protocol for indirect transformation of CO₂ into value-added heterocyles as the carbamate salts are easily obtained by capturing CO₂ with primary amines.

Full text of DOI:10.1039/c6ra15857a

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DOI: 10.1039/C6RA15857A
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Indirect Conversion of Ambient Pressure of CO2 into
Oxazolidin-2-ones by A Copper-Based Magnetic Nanocatalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Bin-Bin Cheng, Bing Yu* and Chang-Wen Hu*
An efficient, practical and magnetically recyclable Cu-based catalytic system for the synthesis of oxazolidin-2-ones via the
multicomponent reaction of carbamate salts, aromatic aldehydes and aromatic terminal alkynes was developed. The
magnetic nanocatalyst, namely FeDOPACu, could efficiently promote the construction of oxazolidin-2-ones with different
functional groups in good to excellent yields. Importantly, the catalyst can be easily recovered by applying an external
magnet, which rendered this protocol economic and environmentally begin. This method represents an attractive
heterogeneous protocol for indirect transformation of CO2 into value-added heterocyles as the carbamate salts are easily
obtained by capturing CO2 with primary amines.
DOI: 10.1039/x0xx00000x
www.rsc.org/
utilize CO2 as C1 resource, are extremely attractive due to their
high atom economy. Despite their indisputable success of the
reactions mentioned above, these methods generally suffer from
some limitations, such as tedious synthesis processes for their
substrates or catalysts, high-pressure apparatus. Therefore,
strategies using readily available starting materials and efficient
catalytic system for the synthesis of oxazolidin-2-one scaffold
from low-pressure CO2 (ideally 1 atm) under mild conditions
are highly desired.
In 2008, the first multicomponent reaction for oxazolidin-2-
ones synthesis was developed by Li’s group through the
copper-catalysed coupling of terminal alkynes, aldehydes,
primary amines and CO2.18 It has been demonstrated that the
reaction proceeded via a tandem A3-coupling/carboxylative
cyclization. In 2012, Eycken and co-workers reported a tandem
decarboxylative/carboxylative cyclization of propiolic acid,
aldehyde, amine for oxazolidin-2-ones synthesis. In this
procedure, it was believed that decarboxylation of propiolic
acid provided CO2 for the subsequently cyclization.19 However,
it is worth pointing out that a large amount of catalysts or
additives20 (20-30 mol%) were needed for an ideal reactivity in
those reports, probably because the electron-rich nature of
primary amines may poison and deactivate the catalysts. In this
context, we recently reported that carbamate salts generated
from primary amines and CO2 are useful reactants for the
construction of oxazolidin-2-ones via the reaction with
aldehydes and terminal alkynes with only 5 mol% of CuI as
catalyst.21 In this work, the captured CO2 served as a protecting
reagent to avoid poisoning of the transition metal catalyst and
simultaneously as a reactant for the construction of the
heterocycles.
Introduction
In the recent decades, carbon dioxide (CO2) is regarded as the
main greenhouse gas, rendering the greenhouse effect an urgent
worldwide environment issue due to the continuous
accumulation of CO2 in atmosphere.1 On the other hand, CO2 is
an ideal C1 building block for chemical synthesis due to its
ubiquitous, cheap and nontoxic nature.2 Numerous efforts have
been devoted to the development of efficient methods for
reducing the accumulation of CO2, such as CO2 capture and
storage/sequestration (CCS),3 CO2 capture and utilization
(CCU).4 Importantly, CCU can avoid the energy consumption
of the desorption step in CCS, which makes CCU one of the
most attractive strategies of CO2 fixation.
As a useful heterocycle, the oxazolidin-2-one moiety can not
only be applied in pharmaceutical chemistry,5 but also served as
synthons in a variety of organic transformations,6 especially in
the formation of bioactive compounds or the related synthetic
intermediates.7 Decades of efforts toward exploring strategies
for the construction of oxazolidin-2-one and its corresponding
derivatives have allowed numerous methods to realize it.8 The
latest of these methods includes the reaction of glycerol
carbonate or glycerol with urea,9 the [2+3] cycloaddition of
isocyanates and epoxides,10 the reaction of amino alcohols and
aryl iodides.11 While from the point view of green chemistry,
protocols such as the coupling of CO2 with aziridines,12 amino
alcohols,13 amines/propargylic alcohols,14 allenylmethyl-
amines,15 allylamines,16 propargylic amines17 which directly
Given the high catalytical activity and excellent recyclability
from the reaction mixture of magnetically separable
nanocatalysts (MSNCs), functionalizing the surfaces of nano-
sized magnetic materials has opened the door for the design of
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novel nanocatalysts.22 One of the most important way to
prepare MSNCs is directly functionalization of the naked
magnetic nanoparticles.23 Notably, MSNCs have been
extensively applied in a variety of catalytic organic reactions
such as Suzuki reaction,24 Heck reaction,25 Sonogashira
reaction,26 Hiyama reaction,27 A3 coupling,28 arylation
reaction,29 oxidative coupling30 and aerobic oxidation.31 These
new-designed MNPCs possess an additional advantage of being
easily separable by an external magnet, which could overcome
the inconvenience of separating traditional heterogeneous
nanocatalysts by filtration or centrifugation after reactions.
magnet, washed with water and methanol respectively, dried
DOI: 10.1039/C6RA15857A
under vacuum at 60 C for 8 hours subsequently (Scheme 2).
As described in Fig. 1, it clearly shows a spherical
morphology and a 10~25 nm size range of the three kinds of
View Article Online
o
Scheme 2 The synthetic route of the catalyst FeDOPACu.
Engaged in the continuous research about the CO2 utilization
32
and heterogeneous catalysis,21,
we would like to present
particles, i.e. nano-Fe3O4, FeDOPA and FeDOPACu, from
transmission electron microscopy (TEM) images and the
scanning electron microscopy (SEM) images (see the
Supporting Information). Additionally, those particles were
characterized using powder X-ray diffraction (XRD) (Fig. 2).
According to the JCPDS data (JCPDS File Card No. 19-0629),
the peaks at 30.62, 35.92, 43.48, 54.00, 57.62, and 63.36 were
attributed to the (220), (311), (400), (422), (511), and (440)
faces of nano-Fe3O4, respectively, which indicates the
formation of single-phase Fe3O4. After further functionalization
of nano-Fe3O4, no significant change of those characteristic
peaks was observed, suggesting that this magnetic nanoparticle
is a stable supporter.
herein our investigation on the use of a copper-based
magnetically separable nanocatalyst, namely FeDOPACu, as an
efficient and reusable catalyst for the synthesis of oxazolidin-2-
ones via the multicomponent reaction of carbamate salts,
aldehydes and terminal alkynes (Scheme 1). The solid state
carbamate salts were obtained by the capture of CO2 with liquid
primary amines, which can provide CO2 to serve as both
reactant and protecting reagent for the catalyst to avoid catalyst
poisoning during the reaction process.33
Scheme 1 Procedure for the construction of oxazolidin-2-ones from carbamates with
FeDOPACu as the catalyst.
Fig. 1 The transmission electron microscopy (TEM) image of: (a) nano-Fe3O4, (b)
FeDOPA, (c) FeDOPACu, (d) recovered FeDOPACu.
Results and discussion
Preparation and characterization of FeDOPACu
The magnetic nanoparticle catalyst was synthesized using a
modified literature procedure.34 For a typical preparation, the
inert support nano-Fe3O4 were synthesized by a co-precipitation
method with ferrous sulfate and ferric sulfate as precursors. The
synthesized nano-ferrites was sonicated with dopamine
hydrochloride (DOPA) in water for 2 h giving FeDOPA. To the
FeDOPA containing aqueous solution, CuCl2 was added; then
the pH was adjusted to 9 followed by addition of hydrazine
monohydrate solution, and NaBH4 subsequently. After being
stirred at room temperature for 24 h, the black copper-based
nanomaterial FeDOPACu was separated with an external
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reaction conditions were surveyed using various heterogeneous
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Cu-based magnetic catalysts and KI as adDdiOtiI:v1e0..1A03s9c/Can6RbAe15s8e5e7nA
in Table 1, a moderate yield (74%) of desired oxazolidin-2-one
product 5a was found when FeDOPACu (5 mol%) and KI (5
mol%) were added simultaneously (entry 1). Nevertheless, the
control reactions almost did not proceed with neither KI (5
mol%) nor FeDOPACu (5 mol%) alone (entries 2 and 3). This
result confirmed that the synergistic effect between copper and
iodide was critical for this reaction. Subsequently, several
copper-based magnetic nanoparticle catalysts including
RecoveredFeDOPACu
FeDOPACu
FeDOPA
nano-Fe3O4
38
CuFeO2,36 CuFe2O4,37 Cu(OH)x-Fe3O4 were synthesized and
JCPDS-19-0629
tested for this reaction in the presence of KI as additive.
However, they displayed rather poor catalytic activity under the
identical reaction conditions (entries 4-6). Furthermore, a
number of iodides, such as LiI, NaI, NIS, TBAI and I2, were
surveyed as additives with FeDOPACu as catalyst. Among
these, LiI, NaI, and NIS had shown good activities for the
reaction (63%-71% yields), while TBAI and I2 gave much
lower yield of 5a (35% and 38%). However, none of these
iodides can surpass the catalytic ability of KI in the presence of
FeDOPACu as catalyst (entries 7-11 vs. entry 1). According to
HSAB theory, Li+, Na+, K+ are hard ions which is beneficial to
the synergetic effect of iodide. While the bulky alkyl chains and
covalent bonding in TBAI and I2 may prevent the activity of
iodide.
20
30
40
50
60
70
2degree
Fig. 2 Powder X-ray diffraction (XRD) pattern of the synthesized nano-Fe3O4, FeDOPA,
FeDOPACu and the recovered FeDOPACu after reaction. The bottom of the image
indicates the JCPDS data (JCPDS File Card No. 19-0629) for nano-Fe3O4.
Table 1 Optimization of the reaction conditions. a
Entry
Catalyst/Additive
FeDOPACu/KI
FeDOPACu/-
-/KI
Yieldb (%)
Fig. 3 FT-IR spectra of a: bare nano-Fe3O4; b: FeDOPA; c: FeDOPACu.
1
2
74
< 1
0
The nanoparticles were further characterized by FT-IR. As
shown in Fig. 3, the characteristic signals of Fe–O stretching
(570 cm-1) and O–H bending (1620 cm-1) vibrations were
observed in the spectra of bare nano-Fe3O4, FeDOPA and
FeDOPACu. The signal of C-C stretching vibration (1487 cm-1)
of benzene ring is found both in FeDOPA and FeDOPACu,
indicating that the DOPA was anchored successfully on the
surface of bare nano-Fe3O4. Additionally, a slight blue shift of
the typical N-H stretching (3380-3450 cm-1) was found in
FeDOPACu comparing with FeDOPA. This may be caused by
the coordination effect between copper and the –NH2 groups in
DOPA. Moreover, inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) analysis revealed that the weight
percentage of copper was 3.82%.
3
4
CuFeO2/KI
5
5
CuFe2O4/KI
3
6
Cu(OH)x-Fe3O4/KI
FeDOPACu/LiI
FeDOPACu/NaI
FeDOPACu/NIS
FeDOPACu/TBAI
FeDOPACu/I2
35
63
71
65
35
38
7
8
9
10
11
a
Reaction conditions: Carbamate salts 2a (1 mmol), alkyne 3a (2 mmol),
aldehyde 4a (2 mmol), EtOH (0.4 mL), catalyst (5 mol% based on Cu), additive
(5 mol%), 80 oC, 12 h. TBAI = tetrabutylammonium iodide, NIS = N-
iodosuccinimide. b Yields were determined by GC with biphenyl as the internal
standard.
Optimization of the reaction conditions
Table 2 Optimization of the reaction solvents. a
First of all, n-butylamine (1a) was used to trap CO2 affording
butan-1-aminium butylcarbamate (2a) as a white solid.35 The
model reaction between 2a
, phenylacetylene (3a), and
benzaldehyde (4a) was conducted in 8 mL screw-cap vial with
a Teflon seal using EtOH as solvent without any other
protection. Based on the previously reported synergistic
cooperation between copper and iodide in this reaction,21
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Entry
Solvent
MeOH
EtOH
Yieldb (%)
Table 3 Scope of synthesized oxazolidin-2-ones from different aldehydes.a
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DOI: 10.1039/C6RA15857A
1
2
64
74
42
65
53
49
47
39
12
25
6
3
i-PrOH
CH3CN
diethyl ether
THF
4
5
6
7
EtOAc
DMF
8
9
glycol
CH2Cl2
H2O
10
11
12
13 c
14 d
PhCl
16
95
99
EtOH
EtOH
a Reaction conditions unless otherwise specified: Carbamate salts 2a (1 mmol),
alkyne 3a (2 mmol), aldehyde 4a (2 mmol), solvent (0.4 mL), FeDOPACu (5
o
mol%), KI (5 mol%), 80 C, 12 h. b Yields were determined by GC with biphenyl
as the internal standard. c 100 oC, 10 h. d FeDOPACu (10 mol%), KI (10 mol%),
100 oC, 5 h.
In addition of catalyst and additive, we also screened various
solvent for the reaction. It turns out that the solvent can impact
the efficiency of the reaction dramatically. As delineated in
Table 2, EtOH exhibited best performance among solvents like
MeOH, i-PrOH, CH3CN, diethyl ether, THF, EtOAc, DMF, etc
(entries 1-12). Moreover, an excellent yield (95%) of 5a was
o
observed when the reaction was conducted at 100 C for 10 h
(entry 13). More importantly, the reaction time can be further
shortened by increasing the catalyst/additive loadings to 10
o
mol% at 100 C (entry 14). Therefore, EtOH was chosen as the
optimized solvent for further investigation by using 10 mol% of
FeDOPACu/KI catalytic system at 100 oC for 5 h.
Synthesis of oxazolidin-2-ones catalysed by FeDOPACu
Having established a standard set of reaction conditions, we
then converted a range of commercially available aldehydes
4
into the corresponding oxazolidin-2-ones
the
5 to further explore
a
Reaction conditions: Carbamate salts 2 (1 mmol), alkyne 3 (2 mmol),
aldehyde 4 (2 mmol), EtOH (0.2 mL), FeDOPACu (10 mol%), KI (10 mol%),
100 oC, 5 h. b Isolated yields were given.
applicability and the reactivity of the catalytic system for this
CO2 transformation reaction. As listed in Table 3, aromatic
aldehydes with electron-donating (4a-4f), including 4-iPr, 4-
Me, 4-MeO, 3-MeO and 2-MeO, can deliver the corresponding
products 5a-5f with high to excellent yields (92%-98%) (Table
3
, entries 1-6). However, aldehyde 4g with electron-
withdrawing substituents at the para position showed lower
reactivity, and the corresponding product 5g was obtained in
lower yield (85%). Unfortunately, aliphatic aldehyde i.e. 1-
octanal did not convert into the corresponding oxazolidin-2-one
under the optimized conditions (results not shown).
As for exploring the scope of terminal alkyne, 3b-3d were
examined briefly. In contrast with the scope of aldehydes,
electron withdrawing and donating substituents at the para-
position of phenylacetylene, including –F, –OMe and –Me were
surveyed. It turned out that the alkynes with electron donating
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groups showed higher yields than those with electron
withdrawing groups, indicating that the electronic effect would
affect the efficiency of this reaction (Table 4, entries 1-3).
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DOI: 10.1039/C6RA15857A
On the other hand, when carbamate salts 2b and 2c
,
generated from benzylamine 1b and cyclohexylamine 1c, were
employed as substrates under the identical reaction condition,
quite different yields for oxazolidin-2-ones 5k and 5l (89% and
54%) were observed, probably owing to the steric effect of the
groups on amines constraints the cyclization efficiency of
corresponding oxazolidin-2-ones (entries 4 and 5). Only a trace
amount of oxazolidin-2-one was detected on GC-MS when
aliphatic alkyne 1-octyne was used as reactant.
Based on the experimental results and previous reports,18-21
possible mechanism is proposed as illustrated in Scheme 3. The
carbamate salt was generated from primary amine and CO2.
a
2
Then the reaction of
carbamate intermediate
2
8
and
3, 4 afforded corresponding
under the catalysis of copper with
inorganic iodide as ligand,42 followed by an intramolecular
cyclization to give the desired oxazolidin-2-one product
regenerate the copper-contained catalyst.
5 and
Table 4 Scope of synthesized oxazolidin-2-ones from different alkynes and amines.a
Scheme 3 The proposed reaction pathway.
Recycling use of catalyst FeDOPACu
In order to confirm if the Cu species dissolved from the
nanocatalyst which could contribute to the synthesis of
oxazolidin-2-ones, a control experiment was conducted. The
a Reaction conditions: Carbamic acid ammonium salts 2 (1 mmol), alkyne 3 (2
mmol), aldehyde 4 (2 mmol), EtOH (0.2 mL), FeDOPACu (10 mol%), KI (10
mol%), 100 oC, 5 h. b Isolated yields were given.
mixture of 3a, 4a, EtOH (0.2 mL), KI (10 mol%), FeDOPACu
(10 mol%) was stirring at 100 oC for 1 h, then the solid catalyst
was hot filtered from the reaction. The reaction was continued
with the filtrate by adding the carbamate salt 2a as
carboxylative reagent for an additional 4 h. However, it did not
exhibit any further reactivity, suggesting that the reaction
proceeds on the heterogeneous surface. Furthermore, ICP-AES
analysis of the filtrate confirmed that only traces of Cu were
detected in the solution (93 ppm).
It is well known that propargylamines can be widely applied
as synthesis intermediates for a wide range of bioactive
compounds and natural products.39 The three-component
reaction of ketones, amines and alkynes, namely KA2 reaction
has been proved as an efficient approach to propargylamines.
But some limitations still remain unsolved in KA2 reaction,40
for example, the primary amines are challenging substrates for
the reaction in contrast with secondary amines.41 Remarkably,
when our catalytic system was applied to the reaction of
The recovery and reusability is of great importance for
practical applications of heterogeneous catalytic systems,
especially for the concern of industrial utilization. The
recyclability of the FeDOPACu used in this work was
investigated in the model reaction. After the completion of the
reaction, the catalyst was simply separated from the reaction
mixture by an external magnet. Subsequently, the recovered
cyclohexanone 6a, carbamate salt 2a and phenylacetylene 3a
,
the corresponding propargylamine 7a was obtained as product
in excellent yield (96%) [Eq. (1)]. Herein, the indirectly
application of n-butylamine for KA2 reaction to synthesize
corresponding propargylamine was successfully achieved with
high efficiency by our protocol.
o
catalyst was washed with diethyl ether, and dried at 60 C for
30 min. The dried catalyst can be reused directly with KI as
additive for the next run. The catalyst can be reused at least
three times providing good to excellent yields of the
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corresponding oxazolidin-2-one. However, only 17% yield of The synthesized FeDOPA (1 g) was dispersed in water-
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DOI: 10.1039/C6RA15857A
product was observed in the second run without additional KI, methanol mixture (1:1). CuCl2·2H2O (0.1 g) solution in water
demonstrating that the synergistic effects of KI is dramatically was added to the reaction mixture. Hydrazine monohydrate
important for the reaction (See the Supporting Information).
solution in water was added dropwise to bring the pH of this
Furthermore, the recovered FeDOPACu was characterized mixture to 9, followed by the addition of 0.1 g of NaBH4. Then
by TEM and XRD after first run of the reaction. As shown in the reaction mixture was stirred for 24 h at room temperature.
Fig. 1d and Fig. 2, no obvious changes in morphology or size The product was allowed to settle, washed several times with
of FeDOPACu were found, and no other signals were observed water and acetone, and dried under vacuum at 60 oC for 2 h.34
in the XRD pattern either. Therefore, the slight decrease of the
Typical route for the synthesis of oxazolidin-2-ones
catalytic ability probably be caused by the inevitable loss of the
The copper catalyst (10 mol%), additive (10 mol%), solvent
(0.2 mL), alkyne (2 mmol), aldehyde (2 mmol), and carbamate
salt (1 mmol) were added to a 8 mL reaction tube equipped
with magnetic stir bar. The reactions were carried out in screw
catalyst during the regenerating procedure.
Conclusions
o
cap vials with a Teflon seal at 100 C for certain time. The
In summary, we have established a highly effective, easily
recoverable and practical copper-based magnetically separable
nanocatalyst FeDOPACu for the synthesis of oxazolidin-2-ones
via a one-pot multicomponent reaction of carbamate salts,
aldehydes, and terminal alkynes. In this work, the captured CO2
by primary amines served as not only a reactant, but also a
protecting reagent to prevent the transition metal catalyst from
being poisoned by electron-rich amines, which enabled the
heterogeneous catalyst can be reused. Additionally, a variety of
oxazolidin-2-one derivatives bearing different substitutions
were synthesized in moderate to excellent yields. Moreover,
this catalytic system can also work well for the construction of
propargylamine from ketones, primary amines and alkynes
(KA2 reaction).
reaction mixture was settled to cool to room temperature and
the catalyst was separated by an external magnetic. The crude
reaction mixture was further purified by column
chromatography (silica gel, petroleum ether/EtOAc) to afford
the desired product oxazolidin-2-ones.
Characterization Data of Oxazolidin-2-ones
(Z)-5-Benzylidene-3-butyl-4-phenyloxazolidin-2-one (5a):
1H NMR (CDCl3, 400 MHz): δ = 7.53–7.51 (m, 2H), 7.44–7.42
(m, 3H), 7.35–7.28 (m, 4H), 7.20–7.17 (m, 1H), 5.38 (d, 1H, J
= 2.0 Hz), 5.25 (d, 1H, J = 2.0 Hz), 3.55–3.48 (m, 1H,), 2.86–
2.80 (m, 1H), 1.46–1.44 (m, 2H), 1.29–1.25 (m, 2H), 0.88 (t,
3H, J = 7.4 Hz); 13C NMR (CDCl3, 100.6 MHz): δ = 155.1,
147.7, 137.3, 133.5, 129.4, 129.3, 128.4, 128.3, 127.8, 126.9,
104.5, 63.9, 41.6, 29.0, 19.8, 13.6; HRMS (ESI): m/z, calcd. for
C20H21NO2Na [M+Na]+ requires 330.1465, found 330.1471;
EI-MS: m/z (%) = 180.10 (100), 307.20 (41) [M+].
Experimental
Synthesis of carbamic acid ammonium salts
(Z)-5-Benzylidene-3-butyl-4-(p-tolyl)oxazolidin-2-one (5b):
1H NMR (CDCl3, 400 MHz): δ = 7.50–7.48 (m, 2H), 7.24–7.11
(m, 7H), 5.29 (s, 1H), 5.21 (s, 1H), 3.47–3.44 (m, 1H), 2.81–
2.77 (m, 1H), 2.33 (s, 3H), 1.43–1.38 (m, 2H), 1.28–1.21 (m,
2H), 0.87 (t, 3H, J = 7.6 Hz); 13C NMR (CDCl3, 100.6 MHz): δ
= 154.7, 147.8, 139.0, 134.0, 133.3, 129.7, 128.1, 128.0, 127.5,
126.5, 104.0, 63.3, 41.2, 28.6, 20.9, 19.5, 13.3; HRMS (ESI):
m/z, calcd. for C21H23NO2Na [M+Na]+ requires 344.1621,
found 344.1636; EI-MS: m/z (%) = 194.10 (100), 321.20 (34)
[M+].
(Z)-5-Benzylidene-3-butyl-4-(4-methoxyphenyl)oxazolidin-
2-one (5c): 1H NMR (CDCl3, 400 MHz): δ = 7.52–7.50 (m,
2H), 7.30–7.28 (m, 3H), 7.23–7.18 (m, 1H), 7.17–7.15 (m, 1H),
6.94–6.92 (m, 2H), 5.34 (d, 1H, J = 2.0 Hz), 5.24 (d, 1H, J =
2.0 Hz), 3.81 (s, 1H), 3.48–3.43 (m, 1H), 2.83–2.79 (m, 1H),
1.46–1.42 (m, 2H), 1.29–1.25 (m, 2H), 0.87 (t, 3H, J = 7.8 Hz);
13C NMR (CDCl3, 100.6 MHz): δ = 160.2, 154.8, 148.0, 133.4,
129.1, 129.0, 128.3, 128.2, 126.7, 114.5, 104.2, 63.3, 55.2,
41.4, 28.8, 19.7, 13.5; HRMS (ESI): m/z, calcd. for
C21H23NO3Na [M+Na]+ requires 360.1570, found 360.1595;
EI-MS: m/z (%) = 210.10 (100), 337.20 (18) [M+].
The gaseous CO2 in a balloon was bubbled into the liquid
amine (20 mmol) in a reaction tube. The reaction is slightly
exothermic. After about 5 min, the corresponding carbamic acid
ammonium salt was synthesized as white solid.
Synthesis of magnetic nano-ferrites
In a 1000 mL beaker, FeSO4·7H2O (13.9 g) and Fe2(SO4)3 (20
g) were dissolved in water (500 mL). The pH of the solution
was adjusted to 10 by slowly added ammonium hydroxide (25
wt%). The reaction mixture was then continually stirred for 1 h
at 60 oC. The generated precipitated were separated
magnetically, and washed with water until the pH reached 7,
o
and then dried under vacuum at 60 C for 2 h. This magnetic
nano-ferrite (Fe3O4) was then used for further surface chemical
modification.
Synthesis of magnetic FeDOPA
Nano-Fe3O4 (2 g) was dispersed in water (25 mL) by sonication
for 30 min. The solution of dopamine hydrochloride (1 g) in
water (5 mL) was added and sonicated for another 2 h. The
amine-functionalized nanomaterial FeDOPA was then
precipitated using acetone, isolated by centrifugation, and dried
under vacuum at 60 oC for 2 h.
(Z)-5-Benzylidene-3-butyl-4-(3-methoxyphenyl)oxazolidin-
2-one (5d): 1H NMR (CDCl3, 400 MHz): δ = 7.53–7.51 (m,
2H), 7.36–7.26 (m, 3H), 7.20–7.18 (m, 1H), 6.95–6.91 (m, 2H),
6.84–6.83 (m, 1H), 5.35 (d, 1H, J = 2.0 Hz), 5.28 (d, 1H, J =
Synthesis of the catalyst FeDOPACu
6 | J. Name., 2013, 00, 1-3
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2.0 Hz), 3.82 (s, 3H), 3.55–3.51 (m, 1H), 2.86–2.82 (m, 1H), calcd. for C21H23NO3Na [M+Na]+ requires 360V.1ie5w7A0rt,iclefoOunlninde
+
DOI: 10.1039/C6RA15857A
1.49–1.45 (m, 2H), 1.33–1.26 (m, 2H), 0.89 (t, 3H, J = 7.8 Hz); 360.1587; EI-MS: m/z (%) = 210.10 (100), 337.20 (38) [M ].
13C NMR (CDCl3, 100.6 MHz): δ = 160.3, 155.0, 147.4, 138.8, (Z)-3-Butyl-5-(4-fluorobenzylidene)-4-phenyloxazolidin-2-
133.4, 130.3, 128.4, 128.3, 126.9, 120.0, 114.6, 113.1, 104.4, one (5j): 1H NMR (CDCl3, 400 MHz): δ = 7.50–7.42 (m, 5H),
63.7, 55.3, 41.6, 28.9, 19.8, 13.6; HRMS (ESI): m/z, calcd. for 7.39–7.31 (m, 2H), 6.98–6.94 (m, 2H), 5.37 (s, 1H), 5.21 (s,
C21H23NO3Na [M+Na]+ requires 360.1570, found 360.1595; 1H), 3.52–3.47 (m, 1H), 2.86–2.81 (m, 1H), 1.48–1.40 (m, 2H),
EI-MS: m/z (%) = 210.10 (100), 337.20 (18) [M+].
(Z)-5-Benzylidene-3-butyl-4-(2-methoxyphenyl)oxazolidin-
1.30–1.22 (m, 2H), 0.87 (t, 3H, J = 7.8 Hz); 13C NMR (CDCl3,
100.6 MHz): δ = 162.7, 160.2, 154.8, 147.3, 137.1, 133.5,
2-one (5e): 1H NMR (CDCl3, 400 MHz): δ = 7.54–7.52 (m, 129.9, 129.3, 128.5, 127.7, 115.3, 103.3, 63.7, 41.5, 28.8, 19.7,
2H), 7.38–7.34 (m, 1H), 7.29–7.22 (m, 3H), 7.17–7.14 (m, 1H), 13.5; HRMS (ESI): m/z, calcd. for C20H20FNO2Na [M+Na]+
7.00–6.93 (m, 2H), 5.71 (s, 1H), 5.31 (s, 1H), 3.84 (s, 1H), requires 348.1370, found 348.1383; EI-MS: m/z (%) = 198.10
3.54–3.46 (m, 1H), 2.77–2.73 (m, 1H), 1.46–1.45 (m, 2H), (100), 325.10 (39) [M+].
1.30–1.26 (m, 2H), 0.87 (t, 3H, J = 7.8 Hz); 13C NMR (CDCl3, (Z)-3-Benzyl-5-benzylidene-4-phenyloxazolidin-2-one (5k):
100.6 MHz): δ = 157.8, 155.4, 147.6, 133.8, 130.4, 128.3, 1H NMR (CDCl3, 400 MHz): δ = 7.61–7.60 (m, 2H), 7.41–
128.1, 126.4, 125.1, 120.9, 111.3, 102.6, 55.6, 41.4, 29.0, 19.7, 7.39 (m, 3H), 7.32–7.29 (m, 8H), 7.26–7.24 (m, 2H), 5.17 (s,
13.5; HRMS (ESI): m/z, calcd. for C21H23NO3Na [M+Na]+ 1H), 5.12 (s, 1H), 3.99 (s, 2H); 13C NMR (CDCl3, 100.6 MHz):
requires 360.1570, found 360.1595; EI-MS: m/z (%) = 210.10 δ = 155.0, 147.4, 140.2, 139.7, 136.7, 134.7, 133.3, 131.7,
(100), 337.20 (47) [M+].
129.3, 128.8, 128.4, 127.6, 127.0, 123.0, 104.7, 62.7, 45.4;
(Z)-5-Benzylidene-3-butyl-4-(4-isopropylphenyl) oxazolidin- HRMS (ESI): m/z, calcd. for C23H19NO2Na [M+Na]+ requires
2-one (5f): 1H NMR (CDCl3, 400 MHz): δ = 7.53–7.51 (m, 364.1308, found 364.1335; EI-MS: m/z (%) = 91.10 (100),
2H), 7.31–7.26 (m, 4H), 7.24–7.22 (d, 2H), 7.19–7.16 (t, 1H, J 341.10 (36) [M+].
= 7.4 Hz), 5.36 (d, 1H, J = 1.8 Hz), 5.26 (d, 1H, J = 1.9 Hz), (Z)-5-Benzylidene-3-cyclohexyl-4-phenyloxazolidin-2-one
3.54–3.47 (m, 1H), 2.95–2.92 (m, 1H), 2.85–2.80 (m, 1H), (5l): 1H NMR (CDCl3, 400 MHz): δ = 7.56–7.54 (m, 2H),
1.48–1.44 (m, 2H), 1.27–1.24 (m, 8H), 0.92–0.86 (m, 3H); 13C 7.42–7.39 (m, 3H), 7.36–7.31 (m, 5H), 7.22–7.19 (m, 1H), 5.43
NMR (CDCl3, 100.6 MHz): δ = 155.0, 150.2, 147.9, 134.6, (s, 1H), 5.20 (s, 1H), 3.61–3.55 (m, 1H), 1.82–1.75 (m, 3H),
133.6, 131.7, 128.4, 127.7, 127.3, 104.3, 63.6, 41.5, 33.9, 29.0, 1.71–1.66 (m, 3H), 1.36–1.23 (m, 5H); 13C NMR (CDCl3,
23.9, 19.8, 13.6; HRMS (ESI): m/z, calcd. for C23H28NO2 100.6 MHz): δ = 154.5, 148.2, 139.4, 133.4, 131.6, 129.0,
[M+H]+ requires 350.2115, found 350.2115; EI-MS: m/z (%) = 128.4, 128.1, 127.6, 126.6, 104.0, 63.0, 54.5, 31.0, 25.5, 24.9;
207.20 (100), 349.30 (38) [M+].
(Z)-5-Benzylidene-3-butyl-4-(4-chlorophenyl)oxazolidin-2-
one (5g): 1H NMR (CDCl3, 400 MHz): δ = 7.55–7.50 (m, 2H), 333.20 (39) [M+].
HRMS (ESI): m/z, calcd. for C22H23NO2Na [M+Na]+ requires
356.1621, found 356.1642; EI-MS: m/z (%) = 180.10 (100),
7.40–7.38 (m, 2H), 7.33–7.25 (m, 4H), 7.20–7.16 (m, 1H), 5.35 N-butyl-1-(phenylethynyl)cyclohexanamine (7a): 1H NMR
(s, 1H), 5.22 (s, 1H), 3.51–3.47 (m, 1H), 2.82–2.79 (m, 1H), (CDCl3, 400 MHz): δ = 7.43–7.41 (m, 2H), 7.30–7.25 (m, 3H),
1.46–1.40 (m, 2H), 1.29–1.26 (m, 2H), 0.88 (t, 3H, J = 7.6 Hz); 2.80 (t, 2H, J = 7.2 Hz), 1.95 (s, 1H), 1.92 (s, 1H), 1.70–1.65
13C NMR (CDCl3, 100.6 MHz): δ = 154.7, 147.1, 135.8, 135.2, (m, 5H), 1.42–1.37 (m, 7H), 1.24 (d, J = 10.4 Hz, 1H), 0.95–
133.1, 131.6, 129.4, 129.0, 128.2, 126.9, 104.7, 63.0, 41.5, 0.92 (t, 3H, J = 7.3 Hz); 13C NMR (CDCl3, 100.6 MHz): δ =
28.8, 19.6, 13.5; HRMS (ESI): m/z, calcd. for C20H20ClNO2Na 131.6, 128.2, 127.7, 123.8, 93.7, 84.4, 55.0, 43.0, 38.3, 32.8,
[M+Na]+ requires 364.1075, found 364.1095; EI-MS: m/z (%) 26.0, 23.1, 20.6, 14.0. HRMS (ESI): m/z, calcd. for C18H26N
= 214.10 (100), 341.20 (36) [M+].
[M+H]+ requires 256.2060, found 256.2078; EI-MS: m/z (%) =
212.20 (100), 255.30 (19) [M+].
(Z)-3-Butyl-5-(4-methylbenzylidene)-4-phenyloxazolidin-2-
one (5h): 1H NMR (CDCl3, 400 MHz): δ = 7.42–7.25 (m, 7H),
7.11–7.09 (m, 2H), 5.37 (s, 1H), 5.21 (s, 1H), 3.54–3.47 (m,
1H), 2.85–2.80 (m, 1H), 2.31 (s, 3H), 1.47–1.43 (m, 2H), 1.31–
1.25 (m, 2H), 0.87 (t, 3H, J = 7.4 Hz); 13C NMR (CDCl3, 100.6
MHz): δ = 155.1, 146.9, 137.4, 136.7, 130.6, 129.3, 129.2,
129.1, 128.2, 127.8, 104.4, 63.8, 41.6, 28.9, 21.2, 19.8, 13.6;
HRMS (ESI): m/z, calcd. for C21H23NO2Na [M+Na]+ requires
344.1621, found 344.1666; EI-MS: m/z (%) = 194.10 (100),
321.20 (49) [M+].
Acknowledgements
We thank the Natural Science Foundation of China (21173021,
21231002,
21276026,
21501010),
973
Program
(2014CB932103) for financial support. B. Y. is grateful for the
financial support from China Postdoctoral Science Foundation
(2015M570939) and BIT Basic Research Foundation
(20151942001).
(Z)-3-Butyl-5-(4-methoxybenzylidene)-4-phenyloxazolidin-
2-one (5i): 1H NMR (CDCl3, 400 MHz): δ = 7.59–7.57 (m,
1H), 7.47–7.36 (m, 3H), 7.33–7.31 (m, 2H), 6.84–6.82 (m, 3H),
5.36 (s, 1H), 5.19 (s, 1H), 3.78 (s, 1H), 3.52–3.46 (m, 1H),
2.85–2.79 (m, 1H), 1.46–1.43 (m, 2H), 1.30–1.26 (m, 2H), 0.87
(t, 3H, J = 7.8 Hz); 13C NMR (CDCl3, 100.6 MHz): δ = 158.4,
155.1, 145.9, 137.5, 133.0, 129.6, 129.2, 127.7, 126.2, 113.8,
104.0, 63.7, 55.2, 41.5, 28.9, 19.7, 13.6; HRMS (ESI): m/z,
Notes and references
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This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C6RA15857A
Table of Content
Indirect Conversion of Ambient Pressure of CO2 into Oxazolidin-2-ones by A
Copper-Based Magnetic Nanocatalyst
Bin-Bin Cheng, Bing Yu* and Chang-Wen Hu*
Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry and Chemical Engineering,
Beijing Institute of Technology, Beijing 100081, P. R. China.
CO2
(1 atm)
R1-NH
+
2
oxazolidin-2-ones
+ High catalytic activity
+ Magnetically recyclable
carbamate salts
+
+
A magnetically recyclable Cu-based catalytic system was developed for the indirect conversion of
ambient presure of CO2 into oxazolidin-2-ones.