Copper(I)-Catalyzed Four-Component Coupling Using Renewable Building Blocks of CO2 and Biomass-Based Aldehydes

Article abstract of DOI:10.1002/ejoc.201800461

Both carbon dioxide- (CO₂) and biomass-based molecules have recently been regarded as renewable, abundant, environmentally benign, and attractive carbon feedstocks for organic synthesis. Therefore, a mild and efficient method for the synthesis

Full text of DOI:10.1002/ejoc.201800461

A Journal of
Accepted Article
Title: Copper(I)-Catalyzed Four-Component Coupling Using
Renewable Building Blocks of CO2 and Biomass-Based
Aldehydes
Authors: Qiumin Wu, Jinzhu Chen, Xuhong Guo, and Yisheng Xu
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10.1002/ejoc.201800461
European Journal of Organic Chemistry
Copper(I)-Catalyzed Four-Component Coupling Using Renewable
Building Blocks of CO2 and Biomass-Based Aldehydes
Qiumin Wu,[a,b] Jinzhu Chen,*,[b] Xuhong Guo[a] and Yisheng Xu*,[a]
[a] State-Key Laboratory of Chemical Engineering, East China University of Science and Technology.
130 Meilong Rd., Shanghai 200237, P.R. China.
[b] College of Chemistry and Materials Science, Jinan University. No. 601 Huangpu Avenue West,
Tianhe District, Guangzhou 510632, P.R. China.
*Corresponding author. E-mail address: chenjz@jnu.edu.cn (J. Chen), yshxu@ecust.edu.cn (Y. Xu);
Tel./Fax: (+86)-20-8522-0223.
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European Journal of Organic Chemistry
Abstract: Both carbon dioxide (CO2) and biomass-based molecules are recently regarded as
renewable, abundant, environmentally benign, and attractive carbon-based feedstocks for organic
synthesis. Therefore, a mild and efficient method for a synthesis of 1,3-oxazolidin-2-ones was
developed through a green four-component coupling reaction by using CO2, biomass-based aldehydes
such as furfural and 5-hydroxymethylfurfural (HMF), terminal aromatic alkynes, and primary
aliphatic amines with copper iodide as a catalyst. Twenty-four examples of furyl-substituted 1,3-
oxazolidin-2-ones were obtained in 29–84% yields from the four-component coupling reaction.
Moreover, the coupling reaction was applicable for the syntheses of furyl-containing bis-
oxazolidinone and poly-oxazolidinone under mild conditions.
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European Journal of Organic Chemistry
1. INTRODUCTION
The growing carbon dioxide (CO2) emissions has recently received much attentions due to global
warming effect. It poses one of the opportunities for the transformation of CO2 from industrial sources
and the atmosphere to basic chemicals, together with a reduction of fossil fuel usage.[1-5] In other
words, as a renewable, inexpensive, abundant, non-toxic and C1 building block on earth, CO2 has
gained considerable concerns in the conversion into various significantly important chemicals and
organic intermediates, such as cyclic carbonates,[6-7] dimethyl carbonates,[8-9] polycarbonates,[10-11]
polyurethane,[12-13] methanol,[14-15] formic acid,[16-17] formats,[18] formamides,[18] carbamic
acid(ester),[19] oxazolidinones[20] and others.[21]
Among these CO2-derived chemicals, the oxazolidinone framework constitutes a significant
class of biological and pharmaceutical compounds. Therefore, oxazolidinone compounds are widely
used in pharmaceutical chemistry and fine chemicals as versatile intermediates and chiral
auxiliaries.[22-23] Typically, oxazolidinones were employed as monoamine oxidase inhibitors,[24]
cholesteryl ester transfer protein inhibitors,[25] and anticonvulsant drugs such as ethadione,
paramethadione, and trimethadione.[26] The preparation of oxazolidinones has been extensively
investigated by using various reagents and catalytic system as shown in Scheme 1.[27] From the
perspective of green chemistry, the cycloaddition procedure for oxazolidinone preparation using CO2
as a C1 source is more attractive in comparison with other processes. For example, the synthesis of
oxazolidinone from CO2 and propargylic amines through carboxylative cyclization were
systematically examined by using various catalysts including transition metal catalysts of Pd,[28]
Ag,[29] Au,[30] Zn,[31] and metal-free catalysts such as protic ionic liquids,[32] superbases,[33] N-
heterocyclic carbene.[34] Moreover, it is very inspiring for oxazolidinone synthesis by a three-
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European Journal of Organic Chemistry
component coupling between CO2, propargylic alcohol and primary amine with transition-metal
catalysts such as Ag,[35] Cu,[36] Ru,[37] and tertiary phosphine,[38] CuCl/ionic liquids,[39] ionic liquids.[40]
Due to the fact that propargylamine can be prepared by a three-component coupling reaction between
alkyne, amine and aldehyde (Scheme 1). Li and his co-workers reported the 1,3-oxazolidin-2-one
synthesis from a multi-component coupling by using benzaldehyde and CO2.[41,42]
Scheme 1. Various methods for synthesis of oxazolidinone
In addition to CO2, biomass is regarded as a renewable, abundant and attractive carbon-based
feedstock as well as a promising alternative for fossil source.[43] Typically, Yan and co-workers
recently reported renewable heterocyclic compound synthesis from biomass-based carbohydrates,
chitin and waste shrimp shells.[44-45] In addition, both furfural and 5-hydroxymethylfurfural (HMF)
are biomass-based versatile platform chemicals with high potential for the syntheses of bio-fuels and
biomass-based fine chemicals such as levulinic acid,[46-47] -valerolactone, 3,5-
dihydroxymethylfurfural, 2,5-furandicarboxylic acid, 2,5-diformylfuran and so on.[48] We thus
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European Journal of Organic Chemistry
believe it should be very promising in term of green and high atomic efficiency for a four-component
coupling reaction by using renewable building blocks of CO2 and biomass-based furfural or HMF for
the preparation of furyl-containing 1,3-oxazolidin-2-ones. However, compared with benzaldehyde,
the presence of furan ring in the furfural and HMF makes them more reactive and unstable, and
various complicated furan ring-related reactions such as Diels-Alder reaction,[49] hydrolytic ring
opening,[50] hydrogenolytic ring opening,[51] ring hydrogenation,[52] furan ring polymerization,[53-54]
and humins formation[55-56] were observed during their transformations. Furthermore, the presence of
activated hydroxymethyl group in HMF makes it more difficult to become the desired product.[56] It
is thereby an urgent need but still a significant challenge to develop methodology for furfural- and
HMF-related transformations. As far as we know, the synthesis of furyl-substituted 1,3-oxazolidin-
2-ones via four-component coupling reaction by using biomass-based aldehydes such as furfural and
HMF is barely reported and no systematic research has ever been described.
Scheme 2. CuI-promoted four-component coupling and three-component coupling reactions
Herein, we demonstrated the copper-promoted four-component coupling reactions by using
renewable building blocks of CO2 and biomass-based furfural or HMF for the preparation of furyl-
substituted 1,3-oxazolidin-2-ones (Scheme 2). Our research revealed that the four-component
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European Journal of Organic Chemistry
coupling reaction between terminal aromatic alkyne, primary aliphatic amine, CO2, and biomass-
based aldehyde afforded the desired 1,3-oxazolidin-2-one. In the case of aldehyde substrates, both
furfural and HMF were applicable for the coupling reactions. For primary aliphatic amine reagents,
even tert-butylamine with strong steric hindrance afforded the corresponding oxazolidinone.
Moreover, we also reported the synthesis of furyl-substituted bis-oxazolidinone from dialkyne, as
well as furyl-containing poly-oxazolidinone from dialkyne and diamine by using the coupling
reactions. In terms of aromatic amine and secondary aliphatic amine, a three-component coupling
between aromatic alkyne, amine and biomass-based aldehyde was observed to give furyl-substituted
propargylamine without the participation of CO2 (Scheme 2).
2. RESULTS & DISCUSSION
Initially, the optimization process was performed by using various copper salts for the model
reaction of a four-component coupling reaction between phenylacetylene 1a, biomass-based furfural
2a, and cyclohexylamine 3a under pressurized CO2 to give furyl-substituted 1,3-oxazolidin-2-one
4a (Table 1). Screening of various investigated copper salts indicates that CuI is the most effective
catalyst for the coupling by producing the desired 4a in 73% yield under the investigated conditions
(Table 1, entries 1-5) with trace amount of 1,4-diphenylbuta-1,3-diyne (Supporting Information) as
by-product. Evidently, the anion of cuprous salt catalyst (CuX, X = Cl, Br, I) plays an important role
in the reaction and the promotion effect of the anion increases with the order of Cl− < Br− < I−, which
is in line with the tendency of its leaving ability and nucleophilicity. Therefore, the leaving tendency
of anion may presumably accelerate the formation of active Cu+ complex.[32,57] Moreover, our
control experiment demonstrates that 4a was unobserved in the absence of any catalysts, further
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Table 1. Optimization for the copper-promoted four-component coupling reaction between
phenylacetylene, furfural, CO2 and cyclohexylaminea
Catalyst
[mol%]
T
[C]
75
75
75
75
75
75
75
75
55
65
85
95
75
75
75
75
75
75
75
75
75
75
75
75
75
PCO2
[MPa]
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.1
1.0
1.5
2.0
2.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
t
4a Yieldb
[%]
0
Entry
Solvent
[h]
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
8
1
CuSCN (30)
Cu(OTf)2 (30)
CuCl (30)
CuBr (30)
CuI (30)
CuI (10)
CuI (20)
CuI (40)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
CuI (30)
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
Toluene
H2O
2
3
3
27
54
73
44
70
63
10
18
65
63
59
76
70
71
71
64
73
60
72
18
34
55
63
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
10
14
16
12
12
12
12
EtOAc
THF
aReaction conditions: 1a (102 mg, 1.0 mmol), 2a (192 mg, 2.0 mmol), 3a (198 mg, 2.0 mmol), catalyst
(10-40 mol% relative to 1a), CO2 (0.1-2.5 MPa), solvent (0.11 mL), reaction temperature (55-75 C),
reaction time (8-16 h). bBased on 1a and determined by HPLC using external standard method with
mobile phase of CH3OH and H2O (VCH3OH:VH2O = 1:1).
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European Journal of Organic Chemistry
indicating the excellent promotion effect of the CuI on the coupling reaction. The influence of
catalyst loading level on the coupling reveals that 4a yields are smoothly increased to a maximum
with an optimum CuI loading amount of 30 mol% relative to the 1a (Table 1, entries 5-8). As
expected, the effect of reaction temperature was observed to dramatically raise the 4a yield from 10%
at 55 C to 73% at 75 C under the investigated conditions (Table 1, entries 5, 9-10), reflecting a
remarkable promotion effect of temperature on the coupling reaction. However, a further increase
of temperature leads to a slightly reduced 4a yield (Table 1, entries 5, 11-12). The influence of initial
CO2 pressure on the reaction reveals that an enhancement of CO2 pressure from atmospheric
pressure to 0.5 MPa improve the 4a yield from 59% to 76% (Table 1, entries 5, 13-14), showing a
requirement of higher CO2 concentration to promote the coupling reaction. When the CO2 pressure
is high enough to smoothly accomplish the coupling reaction, a further increased CO2 pressure above
0.5 MPa shows very limited effect on the coupling reaction (Table 1, entries 5, 13-17). The influence
of reaction time on the coupling shows an optimum of 12 h for the reactions (Table 1, entries 5, 18-
21). Besides, the reaction is strongly dependent on the reaction media in which ethanol is the best
for the reaction. Generally, the 4a yields obtained from polar solvents such as EtOH, THF, EtOAc
and H2O are much higher than that obtained from nonpolar solvents such as toluene (Table 1, entries
5, 22-25).
To probe the scope of the coupling reaction, various aromatic alkynes 1, amines 3 and biomass-
based aldehydes 2 were systematically investigated under the optimized conditions. In general, both
biomass-based furfural 2a and HMF 2b were converted smoothly into the corresponding products by
using the optimized conditions at hand (Table 2). In the case of the coupling of para-substituted
phenylacetylene 1a with furfural 2a, cyclohexylamine 3a and CO2, the yields of target oxazolidinones
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European Journal of Organic Chemistry
Table 2. Synthesis of various 1,3-oxazolidin-2-one via CuI-promoted four-component coupling
reaction between alkyne, amine, CO2, and biomass-based aldehyde.a
aReaction conditions: alkyne 1 (1.0 mmol), amine 3 (2.0 mmol), aldehyde 2 (2.0 mmol), CuI (57 mg,
0.3 mmol), EtOH (0.11 mL), CO2 (0.5 MPa), 75 C, 12 h. Isolated oxazolidinone yields based on 1.
bReaction conditions: 1,3-diethynylbenzene (1.0 mmol), 2 (4.0 mmol), cyclohexylamine (4.0 mmol),
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CuI (0.3 mmol), EtOH (0.11 mL), CO2 (1.0 MPa), 75 C, 36 h.
decreases with the complexity of substituted groups on the phenylacetylene molecule. Notably, both
the electron-donating groups, including methyl 4c, ethyl 4g and methoxyl 4e, and electron-
withdrawing groups such as chlorine 4i are well-tolerated in the reaction system. Similar results were
also observed in the coupling of para-substituted phenylacetylene 1a with HMF 2b, cyclohexylamine
3a and CO2. Notably, the methyl-substituted phenylacetylene with methyl group on meta-position of
the benzene 4k gives the same yield when compared with the para-substituted product 4a, which
demonstrates that the coupling yield is presumably not affected by the position of the methyl group
when furfural 2a participates in the reaction. In addition to phenylacetylene and substituted
phenylacetylene, 2-ethynylthiophene and 2-ethynylpyridine are applicable for the coupling reactions,
yielding thiophene-substituted oxazolidinone 4m and pyridine-substituted oxazolidinone 4p,
respectively. Moreover, the coupling reaction was performed very well with 1,3-diethynylbenzene to
give the desired furyl-containing bis-oxazolidinone products 5a and 5b, further suggesting the
widespread applicability of the coupling towards aromatic terminal alkyne substrates. However,
aliphatic terminal alkyne of 1-octyne was inapplicable to the coupling reactions under the investigated
condition, presumably due to its low acidity.[58-59] Notably, the four-component coupling reactions
between phenylacetylene 1a, butylamine, CO2 with biomass-based aldehydes including both furfural
and HMF show relatively low yields of furyl-containing 1,3-oxazolidin-2-ones (32−50%, 4u−v,
Table 2) if compared with the 1,3-oxazolidin-2-one yields from the coupling reactions with
benzaldehyde (85%).[41] Moreover, the variation of the yields of furyl-substituted 1,3-oxazolidin-2-
one products (4a−z, Table 2) are irregular when compared with those of benzaldehyde-participated
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1,3-oxazolidin-2-one syntheses.[41] Finally, the furfural- and HMF-participated CO2-fixation
reactions generally show low yields of target products than those from high reactive substrates such
as epoxide, aziridine, 2-aminoethanol and terminal alkyne or those through a domino reaction
substrate including terminal propargyl alcohol, propargylic amine, o-alkynylaniline derivatives
etc.[60-62] These results can presumably be attributed to the instability of furan ring.[63] According to
the reported references, the furan ring opening reactions,[51] furan ring polymerization,[53-54] and
polymeric humins formations[55-56] occurred constantly in the furfural- and HMF-involved reactions.
Particularly, polymeric humins can neither be analyzed by HPLC nor be quantified according to their
composition.[64-65] In addition to biomass-based furfural and HMF, aldehydes including 5-methyl-2-
furaldehyde, 5-ethyl-2-furaldehyde and 5-chloro-2-furaldehyde were investigated for the four-
component coupling with moderate to low yield of the desired 1,3-oxazolidin-2-ones 5c-e as shown
in Table 2.
Encouraged by the wide scope of alkynes, we further investigated the effect of amine substrate
on the 1,3-oxazolidin-2-one preparation. Not surprisingly, the coupling reactions show a very broad
substrate scope to primary amines regardless of the participation of furfural 2a or HMF 2b. Typical
primary aliphatic amines, such as n-propylamine, n-butylamine and n-octylamine give the
corresponding 1,3-oxazolidin-2-ones in 32~70% yields (4q-v, Table 2), presumably owing to the
strong adsorption of primary amines towards CO2 under mild conditions. [66] The coupling reaction
with benzylamine was also performed smoothly with decent yields of the corresponding target
products (4w-x, Table 2). Notably, tert-butylamine, with strong steric-hindrance effect, shows limited
effect on the coupling by producing the corresponding oxazolidin-2-one with reasonable yields (4y-
z, Table 2). However, in the case of aniline, propargylic amine products 6a-b (Table 3) were observed
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Table 3. Synthesis of various propargylamines via CuI-promoted three-component coupling between
phenylacetylene, amine and biomass-based aldehyde.a
aReaction conditions: 1a (1.0 mmol), 2 (2.0 mmol), 3 (2.0 mmol), CuI (57 mg, 0.3 mmol), EtOH
b
(0.11 mL), 75 C, 12 h. Isolated propargylamine yields based on 1a. Reaction conditions: 1,3-
diethynylbenzene (1.0 mmol), 2 (4.0 mmol), aniline (4.0 mmol), CuI (0.3 mmol), EtOH (0.11 mL),
75 C, 36 h. Isolated bis-propargylic amine yields based on 1,3-diethynylbenzene.
by CuI-promoted three-component coupling of phenylacetylene 1a, aniline and biomass-based
aldehydes 2. We speculated that low pKa of propargylic amine 6a-b inhibits the nucleophilic attack
of nitrogen atom in the 6a-b to CO2 and prohibits the subsequent hydrogen transfer from NH group
in 6a-b to the oxygen atom of CO2. [67-70] From the point of view, the pKa and the number of activated
hydrogen atoms are the most important factors, jointly determining the types of the coupling reaction.
Besides, the furyl-containing bis-propargylic amines 6c-d were successfully synthesized by the
coupling of 1,3-diethynylbenzene, aniline and aldehyde 2. Finally, secondary aliphatic amines,
including diethyl amine and pyrrolidine, undergoes a three-component assembly with
phenylacetylene and biomass-based aldehydes 2 to give the corresponding furyl-containing
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European Journal of Organic Chemistry
propargylic amines 6e-h under the investigated conditions (Table 3).
Previously, phenyl-substituted bis-oxazolidinone was prepared copper-catalyzed four-
component coupling between phenylacetylene, benzaldehyde, diamine hydrochloride salt and CO2;
while, phenyl-containing poly-oxazolidinone was synthesized from 1,3-diethynylbenzene,
benzaldehyde, diamine hydrochloride salt and CO2.[42] In our case, in addition to the synthesis of
furyl-containing bis-oxazolidinone products 5a and 5b, we further investigated the preparation of
furyl-containing poly-oxazolidinone 7 by the CuI-coupling of 1,3-diethynylbenzene furfural, 1,6-
hexanediamine and CO2 (Scheme 3). It is worth mentioning that various attempts were made to
dissolve the black and hard solid of furyl-containing poly-oxazolidinone 7 with solvents such as H2O,
CH2Cl2, THF and DMF but without any success. Figure 1 shows a solid state 13C-NMR spectrum of
the 7. The characteristic signal of carbonyl in the oxazolidinone ring was observed at 154 ppm.[41,42]
While, the free carbons on the benzene ring of 7 shows specific peaks at 126 and 130 ppm. Besides,
three signals at 112, 144 and 151 ppm are ascribed to the carbon atoms on the furan rings.[42] The
symmetric carbons on the hexyl bridge show signal at 27 ppm and the peak at 44 ppm is assigned to
the terminal carbon atoms of hexyl bridge bonded to the nitrogen on the oxazolidinone ring. Therefore,
our above experimental results demonstrate that CuI can efficiently promote four-component
coupling reaction between aromatic terminal alkyne 1, primary aliphatic amine 3, CO2 and biomass-
based aldehyde such as furfural 2a and HMF 2b to give furyl-substituted 1,3-oxazolidin-2-one 4
(Table 2). In addition, furyl-containing bis-oxazolidinone 5a, 5b and poly-oxazolidinone 7 were
synthesized by the investigated catalytic system under the optimized reaction conditions. While, CuI-
promoted three-component coupling reaction was observed between aromatic terminal alkyne 1,
primary aromatic amine or secondary aliphatic amine 3 and biomass-based aldehyde 2 to yield furyl-
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Scheme 3. Synthesis of furyl-containing poly-oxazolidinone
126
154
27
O
N
O
N
44
144
O
O
n
151
56
130
O
O
112
144
150
100
ppm
50
0
Figure 1. The solid state 13C CP/MAS NMR spectrum of furyl-containing poly-oxazolidinone 7
recorded at a MAS rate of 75 MHz.
substituted propargylic amine. Besides, the furyl-substituted bis-propargylic amines 6c-d were
obtained by the CuI-promoted three-component coupling system. Notably, the isolated furyl-
substituted 1,3-oxazolidin-2-ones and furyl-substituted propargylic amines are quite stable although
they were prepared from unstable furfural or HMF, indicating their potential applications in the
productions of various organic chemicals and stable intermediates.
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Scheme 4. Proposed reaction mechanisms
Two tentative reaction pathways for the copper-promoted four-component coupling were
proposed in Scheme 4.[41,67,71-72] For the path a, Cu(I) species initially reacts with a terminal alkyne
to give a terminal copper-acetylide intermediate 8 presumably with the help of amine. Evidently, the
leaving tendency of anion for cuprous salt (CuX, X = Cl, Br, I) may promote the formation of the
intermediate 8. This assumption is in accord with our experimental observations (Table 1, entries
3−5). The imine 9, forms by aldehyde 2 and primary aliphatic amine 3, is attacked by the intermediate
8 to yield copper-complex which then undergoes demetallation to release secondary propargylamine
10. A subsequent carboxylation of 10 under the atmosphere of CO2 gives intermediate 11, again, with
the help of amine. While, Cu(I) species-promoted cyclization of intermediate 11 results in the
formation of heterocyclic oxazolidinone product 4. In the case of path b, the carbamic acid ammonium
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European Journal of Organic Chemistry
salt 12, obtained from the amine 3 and CO2, attacks aldehyde group of furfural 2a or HMF 2b to give
intermediate 13. A subsequent capture of 13 by copper-acetylide 8 promotes the generation of
intermediate 11; while, the product 4 is obtained by Cu-promoted cyclization of 11.
To prove the reaction pathways outlined in Scheme 4, control experiments were performed as
shown in Scheme 5. To examine the path a mechanism, we repeated the coupling reaction between
phenylacetylene 1a, furfural 2a and cyclohexylamine 3a under optimized conditions with N2 instead
of CO2 and, to our expectation, the secondary propargylamine 14 was obtained with a moderate
isolated yield of 63% (Scheme 5). However, a CuI-promoted direct carboxylative cyclization of 14
leads to a low yield of 59% for the target product 4a (Scheme 5a). While, an enhanced 4a yield up to
83% was observed only when cyclohexylamine was employed to the carboxylative cyclization
reaction (Scheme 5b). The above results suggest that the amine presumably catalyzes the
carboxylation step of the 14 as an organic base and/or participated in the formation of active Cu
species to promote the subsequent cyclization step. Previously, He and co-workers reported 2-
oxazolidinone syntheses from propargylic amines and CO2 at atmospheric pressure by using Cu(II)-
substituted polyoxometalate-based ionic liquids.[73] The bifunctional Cu(II) catalyst simultaneously
activate both two substrates of propargylic amine and CO2, thus effectively promoting the
carboxylative cyclization. Therefore, the combination of cyclohexylamine and CuI may promote
carboxylative cyclization of 14 in our case (Scheme 5b). In the case of the investigation of path b
mechanism (Scheme 4), we obtained a 91% yield of carbamic acid ammonium salt 15 from CO2 and
cyclohexylamine (Scheme 5), which promotes the chemical fixation of CO2 and accordingly increases
13
the CO2 concentration in the reaction system. The quantitative formation of 15 was proved by C
{H} NMR analysis due to the presence of the characteristic signal of carbonyl at 159 ppm (Figure
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European Journal of Organic Chemistry
S38, Supporting Information). CuI-promoted three-component coupling of 15, phenylacetylene 1a,
and furfural 2a gives the target product 4a with a yield of 73% (Scheme 5c). Therefore, both path a
and b may competitively occur depending on the reaction conditions.
Scheme 5. Control experiments for 4a synthesis
a)
b)
Cu 2p XPS
Cu LMM
916.0 eV
2p
3/2
932.7 eV
913.5 eV
2p
1/2
910.8 eV
918.5 eV
952.5 eV
930
935
940
945
950
955
960
906
909
912
915
918
921
924
Binding Energy / eV
Kinetic Energy / eV
Figure 2. a) Cu 2p XPS and b) Cu LMM of the recovered catalyst
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To investigate the active species of the Cu catalyst, the catalyst was collected and recovered after
the reaction and further analyzed by X-ray photoelectron spectra (XPS). As showed in Figure 2a,
Cu2p XPS shows two peaks centered at the binding energies of 932.7 eV and 952.5 eV without any
satellite peaks, indicating the absence of Cu2+ species.[74] Due to the overlap of Cu0 and Cu+ in the
Cu2p XPS spectra, the Cu LMM spectra was carried out for further characterization. The peaks with
kinetic energy located at 918.5 and 916.0 eV were assigned to metallic copper and Cu+ species,
respectively,[75] thus suggesting the presence of both Cu0 and Cu+ species during the catalytic cycle
as described in the Scheme 4.[76] The Cu+ species can be assigned to copper-acetylide intermediate 8
(Scheme 4); while, Cu0 species can presumably attributed to the Cu0 complex or Cu0
nanoparticles.[77,78] Notably, Cu0-nanoparticles were reported for propargylamine synthesis through
three-component coupling of aldehyde, amine and alkyne.[78] To investigate the catalytic activity of
the recovered Cu-containing materials, the catalyst residue was isolated from reaction medium by
filtration, washed thoroughly with ethanol, dried under the vacuum, and then applied to the next run
of the four-component coupling reaction. To our surprise, the desired 1,3-oxazolidi-2-one 4a was
obtained with the yield of 21%, which is low if compared with the 76% yield of 4a in the first run.
3. CONCLUSION
In summary, we demonstrated a CuI-promoted four-component coupling for 1,3-oxazolidin-2-one
synthesis by using terminal aromatic alkyne, primary aliphatic amine, and renewable building blocks of
CO2 and biomass-based aldehyde under a green and mild conditions. A series of furyl-containing 1,3-
oxazolidin-2-ones, bis-oxazolidinones and poly-oxazolidinone were prepared by the coupling reaction.
Two reaction pathways were proposed and further proved by control experiments. Moreover, a three-
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10.1002/ejoc.201800461
European Journal of Organic Chemistry
component coupling was observed between terminal aromatic alkyne, aromatic amine or secondary
aliphatic amine, and biomass-based aldehyde to give furyl-substituted propargylamine without the
participation of CO2.
4. EXPERIMENTAL SECTION
4.1. Synthetic procedure
Synthesis of 1,3-oxazolidin-2-one 4
The coupling reaction was carried out in a 25 mL-stainless steel autoclave. The autoclave reactor
was successively loaded with a magnetic stir bar, CuI (57 mg, 0.3 mmol), phenylacetylene (102 mg,
1.0 mmol), furfural (192 mg, 2.0 mmol), cyclohexylamine (198 mg, 2.0 mmol) and EtOH (0.11 mL).
After flushing the autoclave with CO2 three times, the CO2 pressure was kept at 0.5 MPa at ambient
temperature. The reaction was carried out in an oil bath at 75 C for 12 h with a stirring speed of 600
rpm. The reaction vessel was then cooled down to ambient temperature conditions and the reaction
mixture was filtered with filter membrane (0.45 m). The resulting filtrate was concentrated by
rotavapor and the crude product was further purified by a flash column chromatography on silica gel
(v/v, cyclohexane/EtOAc = 25:1) to afford 4a as a white flaked solid with the yield of 76% (246 mg).
1H NMR (400 MHz, 25 °C, CDCl3, Figure S1, Supporting Information) δ 7.54 (d, J = 7.6 Hz, 2H),
7.43 (s, 1H), 7.30 (t, J = 7.6 Hz, 2H), 7.19 (t, J = 7.3 Hz, 1H), 6.49–6.38 (m, 2H), 5.53 (s, 1H), 5.34
13
(s, 1H), 3.69–3.57 (m, 1H), 1.84–1.55 (m, 6H), 1.08 (dddt, J = 25.8, 16.6, 13.3, 8.4 Hz, 4H). C
NMR (101 MHz, 25 °C, CDCl3, Figure S1, Supporting Information) δ154.17, 150.39, 144.63, 143.51,
133.45, 128.50, 128.45, 127.01, 110.88, 110.09, 103.87, 55.95, 54.16, 30.43, 29.63, 25.78, 25.75,
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10.1002/ejoc.201800461
European Journal of Organic Chemistry
25.18). MS (ESI, Figure S37, Supporting Information): Anal. Calcd. for C20H21NO3: m/z = 324.1600
[MH+], Found: m/z = 324.1595 [MH+].
Synthesis of bis-oxazolidinone 5
The bis-oxazolidinone 5a was obtained similarly as depicted above in the production of 4a by
using CuI (57 mg, 0.3 mmol), furfural (384 mg, 4.0 mmol), cyclohexylamine (396 mg, 4.0 mmol),
1,3-diethynylbenzene (126 mg, 1.0 mmol), CO2 (1.0 MPa) and EtOH (0.11 mL). The product 5a was
obtained as orange solid with the yield of 43% by flash column chromatography (cyclohexane/EtOAc
1
= 10:1). H NMR (400 MHz, 25 °C, CDCl3, Figure S25, Supporting Information) δ 7.55 (s, 1H),
7.51–7.47 (m, 2H), 7.45 (d, J = 1.1 Hz, 2H), 7.31–7.27 (m, 1H), 6.49 (dd, J = 3.2, 0.5 Hz, 2H), 6.42
(dd, J = 3.2, 1.9 Hz, 2H), 5.54 (d, J = 1.8 Hz, 2H), 5.37 (d, J = 1.8 Hz, 2H), 3.64 (ddd, J = 12.2, 10.3,
3.8 Hz, 2H), 1.72 (dtd, J = 34.4, 30.5, 13.0 Hz, 10H), 1.45 (s, 2H), 1.36–1.18 (m, 4H), 1.07–0.85 (m,
13
4H). C NMR (101 MHz, 25 °C, CDCl3, Figure S25, Supporting Information) δ 154.21, 150.29,
144.71, 143.52, 133.58, 128.74, 128.41, 127.09, 110.94, 110.20, 103.88, 55.99, 54.18, 30.44, 29.65,
27.01, 25.80, 25.78, 25.21. MS (ESI, Figure S61, Supporting Information): Anal. Calcd. for
C34H36N2O6: m/z = 569.2652 [MH+], Found: m/z = 569.2651 [MH+].
Synthesis of propargylamine 6
The propargylamine 6a was obtained similarly as depicted above in the production of 4a by
using CuI (57 mg, 0.3 mmol, 30 mmol% relative to alkyne), furfural (192 mg, 2.0 mmol), aniline
(186 mg, 2.0 mmol), phenylacetylene (102 mg, 1.0 mmol) and EtOH (0.11 mL) under nitrogen
atmosphere. The desired propargylamine 6a was obtained as orange oil with the yield of 66% (v/v,
cyclohexane/EtOAc = 25:1). 1H NMR (400 MHz, 25 °C, CDCl3, Figure S27, Supporting Information)
δ 7.50–7.47 (m, 2H), 7.42 (s, 1H), 7.33–7.31 (m, 3H), 6.49 (d, J = 3.2 Hz, 1H), 6.35 (dd, J = 3.1, 1.9
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10.1002/ejoc.201800461
European Journal of Organic Chemistry
Hz, 1H), 5.08 (s, 1H), 2.77–2.54 (m, 4H), 1.11 (t, J = 7.2 Hz, 6H). 13C NMR (101 MHz, 25 °C, CDCl3,
Figure S27, Supporting Information) δ 152.65, 142.55, 131.94, 128.41, 128.35, 123.13, 110.17,
109.07, 85.90, 84.49, 52.04, 45.07, 13.44. MS (ESI, Figure S63, Supporting Information): Anal.
Calcd. for C19H15NO: m/z = 274.1232 [MH+], Found: m/z = 274.1225 [MH+]
Synthesis of poly-oxazolidinone 7
The poly-oxazolidinone 7 was obtained similarly as depicted above in the production of 4a by
using CuI (57 mg, 0.3 mmol), furfural (384 mg, 4.0 mmol), 1,6-hexanediamine (232 mg, 2.0 mmol),
1,3-diethynylbenzene (126 mg, 1.0 mmol), CO2 (3 MPa) and EtOH (0.11 mL) at 75 C for 2 days in
the autoclave. The poly-oxazolidinone 7 was obtained as hard and black solid after filtration and
washed thoroughly with H2O, CH2Cl2, THF, DMF by Soxhlet extractions.
4.2. Characterization techniques
1H and 13C{1H} NMR spectra were recorded on a Bruker Advance 300 at 400 MHz for 1H and
101 MHz for 13C with CDCl3 and DMSO-d6 as the solvent and tetramethylsilane (TMS) as the internal
standard. Chemical shifts were showed in parts per million (ppm,  scale) downfield from TMS at
0.00 ppm and referenced to the CDCl3 at 7.26 ppm for 1H, and 77.16 ppm for 13C, respectively. In the
case of DMSO-d6, chemical shifts referenced to 2.50 ppm for 1H and 39.52 ppm for 13C. The solid-
13
state C NMR spectra were recorded on a Bruker Advance III at 75 MHz. High-resolution mass
spectra were obtained by ESI on a SCIEX X500R QTOF. X-ray photoelectron spectra (XPS) and
Auger electron spectroscopy were performed on a Kratos Ultra system using an Al Kα radiation
source. The binding energies for each spectrum were calibrated with a C 1s spectrum of 284.6 eV.
5. ASSOCIATED CONTENT
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10.1002/ejoc.201800461
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Supporting Information
The Supporting Information is available free of charge on the Wiley Publications website at DOI:
XXXX. 1H and 13C {1H} NMR spectra, high-resolution mass spectra of the products (PDF).
6. AUTHOR INFORMATION
Corresponding Author
*E-mail address: chenjz@jnu.edu.cn. Tel.: (+86)-20-8522-0223, Fax: (+86)-20-8522-0223 (J. Chen),
*E-mail address: yshxu@ecust.edu.cn (Y. Xu)
ORCID
Jinzhu Chen: 0000-0002-6475-1431
Yisheng Xu: 0000-0001-8245-9787
Notes
The authors declare no competing financial interest.
7. ACKNOWLEDGEMENTS
We are grateful for the financial support from National Natural Science Foundation of China
(21472189, 21676089 and 21172219), Shanghai Talent Development Fund (2017038), and the
Fundamental Research Funds for the Central Universities (21617431 and 222201717013). We thank
Meng Zhang from Hebei University of Science and Technology for the assistance with the previous
research.
Keywords: biomass·carbon dioxide fixation·copper·multi-component coupling·oxazolidinone
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For Table of Contents Use Only
Copper(I)-Catalyzed Four-Component Coupling Using Renewable Building Blocks of CO2
and Biomass-Based Aldehydes
Qiumin Wu, Jinzhu Chen, Xuhong Guo and Yisheng Xu
Furyl-containing oxazolidinone, bis-oxazolidinone and poly-oxazolidinone were obtained by copper-
promoted four-component coupling using renewable building blocks of CO2 and biomass-based
aldehydes.
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