Efficient catalyst-free chemical fixation of carbon dioxide into 2-oxazolidinones under supercritical condition

Article abstract of DOI:10.1016/j.cclet.2011.04.004

4-Methylene-1,3-oxazolidin-2-ones can be synthesized from propargylic alcohols, primary amines and carbon dioxide under supercritical condition in the absence of any additional catalyst and solvent. Various propargylic alcohols and primary amines were exa

Full text of DOI:10.1016/j.cclet.2011.04.004

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1063–1066
www.elsevier.com/locate/cclet
Efficient catalyst-free chemical fixation of carbon dioxide into
2-oxazolidinones under supercritical condition
*
Jing Xiu Xu , Jin Wu Zhao, Zhen Bin Jia
School of Pharmacy, Guangdong Medical College, Dongguan 523808, China
Received 20 December 2010
Available online 25 June 2011
Abstract
4-Methylene-1,3-oxazolidin-2-ones can be synthesized from propargylic alcohols, primary amines and carbon dioxide under
supercritical condition in the absence of any additional catalyst and solvent. Various propargylic alcohols and primary amines were
examined.
# 2011 Jing Xiu Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Catalyst-free; Carbon dioxide; Supercritical; 2-Oxazolidinone
Oxazolidinones are useful heterocyclic compounds in organic synthesis. They can be used as chiral synthons or
chiral auxiliaries in asymmetric syntheses, and they usually exist as necessary moiety in pharmaceutical chemistry
owing to their good antibacterial properties [1]. Thanks to the exocyclic double bond, 4-methylene-1,3-oxazolidin- 2-
ones can be further transformed [2]. In our previous work, 4-methylene-1,3-oxazolidin-2-ones were prepared via the
cycloadditon of propargylic alcohols with amines and carbon dioxide (CO2) catalyzed by transition metal salt cuprous
iodide [3]. It was reported that the reaction of propargylic alcohols, primary amines and CO2 to construct the
oxazolidinones could be catalyzed by tri-n-butylphosphine which is expensive and toxic [4]. Deng’s group disclosed
that the three-component reaction could proceed under the catalysis of the costly ionic liquid with cuprous chloride as
co-catalyst [5], or without [6]. These approaches to 4-methylene-1,3-oxazolidin-2-ones all suffer the drawback of
needing expensive, toxic or metal catalysts.
CO2 is the most important greenhouse gas produced by human activities, primarily through the combustion of fossil
fuels. On the other hand, CO2 is an abundant, cheap, and nontoxic biorenewable C1 building block in organic
synthesis. Therefore, from the viewpoint of green chemistry and carbon reduction, chemical fixation of CO2 into
useful organic compounds has been an essential issue in synthetic organic chemistry during the last two decades [7]. In
addition, supercritical carbon dioxide (scCO2, Tc = 31.1 8C, Pc = 7.39 MPa) has been emerged as an environmentally
benign alternative to organic solvents because of its advantages in terms of nonflammability, easy separation from
reaction mixtures, as well as eco-compatibility, low cost, and availability. Hence, it is quite significant that CO2 could
be used both as an attractive raw material and as a green reaction medium [8]. Herein, we wish to report an efficient and
* Corresponding author.
E-mail address: jingxiuxu@sohu.com (J.X. Xu).
1001-8417/$ – see front matter # 2011 Jing Xiu Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.04.004

1[(Schme_1)TD$FIG] 064
J.X. Xu et al. / Chinese Chemical Letters 22 (2011) 1063–1066
O
1
R
scCO
2
R
N
O
OH
+
RNH
2
14 MPa, 120 ºC
2
R
1
R
2
R
Scheme 1. Catalyst-free chemical fixation of carbon dioxide into 2-oxazolidinones under supercritical condition.
Table 1
Optimizing the reaction conditions for the chemical fixation of CO2 into 4-methyleneoxazolidin-2-ones with propargylic alcohols and primary
amines.a
[TD$LINE]
O
CO
2
Bu
N
OH
O
+
H N Bu
2
.
Entry
Pressure (MPa)
Temperature (8C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
5
5
120
120
120
120
120
120
120
140
100
10
24
48
48
48
48
48
48
48
Trace
20
5
49
8
72
11
14
17
14
14
76
84
73
84
70
a
Reagents and conditions: 2-methylbut-3-yn-2-ol (2 mmol), n-butylamine (4 mmol).
b
Determined by GC analysis.
eco-friendly process for conversion of CO2 into 4-methyleneoxazolidin-2-ones in the absence of any additional
catalyst and solvent (Scheme 1).
We first optimized the the reaction conditions for the chemical fixation of CO2 with 2-methylbut-3-yn-2-ol and n-
butylamine as model substrates, and the results are summarized in Table 1. When the cycloaddition reaction proceeded
at 120 8C under 5 MPa for 10 h [6], only trace amounts of the desired 3-butyl-5,5-dimethyl-4- methyleneoxazolidin-2-
one a was detected (entry 1). When the reaction time was lengthened from 10 h to 48 h the yields rose from trace to
49% (entries 2, 3). When CO2 pressure was increased from 5 MPa to 8 MPa, the yield soared from 50% to 72% (entries
3, 4). Presumedly, CO2 under this pressure became scCO2, playing the role of the reaction medium to improve the
three-component assembly. When CO2 pressure was further raised to 11 MPa and 14 MPa, the yield of the
cycloaddition reaction was bettered to 76% and 84%, respectively (entries 5, 6). However, when the pressure was
elevated to 17 MPa, the yield of the corresponding 2-oxazolindinone decreased to 73% (entry 7). It was also found that
the further raise of the reaction temperature could not promote the yield (entry 8), while the decline of the temperature
resulted in an inferior yield (entry 9). Therefore, the best reaction conditions were the factors depicted in entry 6.
We next probed the generality and the limitation of the chemical fixation of CO2. The results are tabulated in Table 2
[9]. Under the optimal conditions, 2-methylbut-3-yn-2-ol and a variety of primary amines went across the
cycloaddition reaction in scCO2, As seen in Table 2, along with n-butylamine, allylamine and cyclohexylamine
undergo three-component assembly smoothly to afford the desired products b and c in respectively in 72% and 87%
yields, respectively (entries 2, 3). Unfortunately but expectedly, aniline could not undergo the cycloaddition owing to
its poor nucleophilicity (entry 4). Our study suggested that the steric hindrance of the substituents on the primary
amines had strong impact on the chemical fixation of CO2. sec-Butylamine carrying a bulkier substituent gave lower
yield than n-butylamine (entry 5), and tert-butylamine could not produce the desired product at all (entry 6). n-
Butylamine was then treated with various propargylic alcohols. 2-Phenylbut-3-yn-2-ol furnished the expected product
g in excellent 88% yield (entry 7), and the product h was obtained in 84% yield from 1-ethynylcyclohexanol (entry 8),

J.X. Xu et al. / Chinese Chemical Letters 22 (2011) 1063–1066
1065
Table 2
Chemical fixation of CO2 into 4-methyleneoxazolidin-2-ones with the corresponding propargylic alcohols and primary amines under supercritical
condition.a
[TD$LINE]
O
1
2
R
R
scCO
R
2
N
O
OH
+
RNH
2
o
14 MPa, 120 C
1
R
2
R
.
Entry
R1
R2
R
Yield (%)b
1
2
Me
Me
Me
Me
Me
Me
Me
Me
n-Bu
Allyl
Cy
80 (a)
72 (b)
87 (c)
0c (d)
70 (e)
0d (f)
88 (g)
84 (h)
70 (i)
65 (j)
Me
3
Me
4
Me
Ph
5
Me
sec-Bu
t-Bu
n-Bu
n-Bu
n-Bu
n-Bu
6
Me
7
Ph
8
–C5H10
–
9
i-Pr
Me
Me
10
n-C6H13
a
Reagents and conditions: alcohol (2 mmol), amine (4 mmol), Pco2 = 14 MPa, 120 8C.
Isolated yield.
b
c
d
No desired product detected.
2-Methylbut-3-yn-2-ol remained unchanged.
[(Schme_2)TD$FIG]
H
NH R
1
R
1
2
1
2
2
R
R
R
R
R
O
C
2
RNH
2
CO
+
OH
O
A
O
O
2
RNH
3
O
O
O
- RNH
2
O
1
R
O
D
R
2
1
2
R
R
O
RNH
2
RN
O
RN
HO
O
RHN
O
O
O
1
1
R
R
2
2
R
R
O
B
C
Scheme 2. Proposed mechanism for the catalyst-free chemical fixation of carbon dioxide into 2-oxazolidinone.
3,4-dimethylpent-1-yn-3-ol and 3-methylnon-1-yn-3-ol afforded the corresponding products i and j in yields of 70%
and 65%, respectively (entries 9, 10).
Based on the above experimental results, a proposal mechanism is illustrated in Scheme 2. Ammonium carbonate A
is firstly formed by the reaction of propargylic alcohol, amine and CO2, which may undergoes cyclization with the help
of a proton to furnish the a-methylene cyclic carbonate B [10]; then amine attacks the carbonyl group of the a-
methylene cyclic carbonate to generate the 2-oxoalkyl carbamate C. Its nitrogen atom launches intramolecular attack
on the carbonyl to give 4-hydroxy cyclic carbamate D whose 4-hydroxy is eliminated with the hydrogen atom of 4-
methyl to afford the corresponding 4-methylene-2-oxazolidinone [3].
In conclusion, we have developed an efficient and eco-friendly process to fix CO2 into 4-methyleneoxazolidin- 2-
ones with propargylic alcohols and primary amines under supercritical condition, dispensing with any additional
catalyst and solvent. In this method, carbon dioxide was employed not only as reaction medium, but also as starting
material.

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J.X. Xu et al. / Chinese Chemical Letters 22 (2011) 1063–1066
Acknowledgments
This work was supported financially by Youth Foundation of Guangdong Medical College (No. XQ1029) and
Science and Technology Planning Project of Zhanjiang city (No. 2009c3103024).
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6H), 1.26–1.36 (m, 2H), 1.10–1.18 (m, 1H); 13C NMR (100 MHz, CDCl3): d 154.9, 150.6, 81.3, 80.1, 53.9, 33.2, 28.6, 28.2, 25.5; MS (EI,
70 eV): m/z = 209 (M+), 128, 112, 84, 55, 41; compound g (Table 2 entry 7): IR (KBr, n/cmÀ1): 2939, 2870, 1758; 1H NMR (400 MHz, CDCl3):
d 7.29–7.44 (m, 5H), 4.20 (d, 1H, J = 3.2 Hz), 4.09 (d, 1H, J = 2.8 Hz), 3.40 À 3.52 (m, 2H), 1.83 (s, 3H), 1.55–1.62 (m, 2H), 1.30–1.35 (m,
2H), 0.88–0.95 (m, 3H); 13C NMR (100 MHz, CDCl3): d 155.7, 149.5, 141.1, 128.7, 127.9, 125.0, 91.5, 82.3, 28.4, 27.3, 20.4 13.9; MS (EI,
70 eV): m/z = 245 (M+), 190, 158, 144, 129, 97, 77, 41.
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