Facile synthesis of oxazolidinones catalyzed by n-Bu4NBr 3/n-Bu4NBr directly from olefins, chloramine-T and carbon dioxide

Article abstract of DOI:10.1016/j.catcom.2010.04.003

A binary catalyst systemcomposed of n-Bu4NBr3/n-Bu4NBrwas developed for facile synthesis of 5-substituted 2-oxazolidinoneswith perfect regioselectivity in a single operation directly fromolefins, chloramine-T and CO₂. The choice of efficient binary catalysts for two steps, i.e. aziridination and cycloaddition, and the optimization of reaction condition are keys to the one-pot synthesis of 5-substituted 2-oxazolidinones. A possiblemechanismfor the present one-pot synthesis of oxazolidinones was also proposed.

Full text of DOI:10.1016/j.catcom.2010.04.003

Catalysis Communications 11 (2010) 992–995
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Facile synthesis of oxazolidinones catalyzed by n-Bu4NBr3/n-Bu4NBr directly from
olefins, chloramine-T and carbon dioxide
⁎
De-Lin Kong, Liang-Nian He , Jin-Quan Wang
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A binary catalyst system composed of n-Bu4NBr3/n-Bu4NBr was developed for facile synthesis of 5-substituted 2-
oxazolidinones with perfect regioselectivity in a single operation directly from olefins, chloramine-T and CO2. The
choice of efficient binary catalysts for two steps, i.e. aziridination and cycloaddition, and the optimization of
reaction condition are keys to the one-pot synthesis of 5-substituted 2-oxazolidinones. A possible mechanism for
the present one-pot synthesis of oxazolidinones was also proposed.
Received 5 January 2010
Received in revised form 26 March 2010
Accepted 1 April 2010
Available online 13 April 2010
© 2010 Elsevier B.V. All rights reserved.
Keywords:
Carbon dioxide
Chloramine-T
Olefin
Oxazolidinone
Binary catalyst
1. Introduction
work, we would like to report a binary catalyst system comprising n-
Bu4NBr3/n-Bu4NBr for highly regioselective synthesis of 5-substituted 2-
Carbon dioxide is the most abundant greenhouse gas and can be also
regarded as a typical renewable natural resource. The chemical fixation
of CO2 received much attention from the viewpoint of resources
utilization and green chemistry [1]. In this context, one of the major
successes is the utilization of CO2 as the starting materials to prepare the
five-membered cyclic compounds. 2-Oxazolidinones are an important
class of five-membered cycles [2] showing a plethora of applications as
intermediates [3] and chiral auxiliaries [4] in organic synthesis.
oxazolidinones in a single operation via the three-component reaction of
olefin, chloramine-T (sodium p-toluenesulfonchloramide, TsNClNa, a
practical nitrogen source) with CO2.
2. Experimental
2.1. General procedure for the synthesis of tetrabutylammonium tribromide
according to the published procedure
Currently, there are four main synthetic strategies for 2-oxazolidinones
starting from CO2 as C1 resources: (i) direct addition of CO2 to 1, 2-
aminoalcohols; [5–7] (ii) reaction of propargylamines with CO2; [8–10]
(iii) reaction of amine/aminoalcohol with cyclic carbonate from CO2
[11,12] and (iv) insertion of CO2 into the aziridines. Among them, cyclo-
addition of CO2 with aziridines is one of the most promising methods for
synthesis of oxazolidinones. Several catalyst systems have been explored
for this reaction [13–17]. However, such a cycloaddition generally involves
the initial synthesis of aziridine from olefin and a nitrogen source, [18–31]
which requires a tedious workup for separation and involves metal
catalysts in most cases. In other words, this two-step manipulation is one
of the main drawbacks of this process. So it is more desirable to synthesize
an oxazolidinone directly from olefin, a nitrogen source and CO2.
To a solution of tetrabutylammonium bromide (3.2 g, 10 mmol) and
sodium bromate (0.5 g, 3.3 mmol) in water (20 mL) was added
dropwise hydrobromic acid (40%, 4 mL) under stirring at r.t. After the
mixture was stirred for 15 min, the immediate orange precipitate was
filtered and recrystallized from petroleum ether-dichloromethane (4:1)
to give tetrabutylammonium tribromide as orange crystals; yield 4.65 g
(96.5%); m.p. 72–73 °C (lit. 70–72 °C)[32,33].
2.2. General procedure for the synthesis of oxazolidinones from olefins,
chloramine-T and CO2
A 50 mL autoclave reactor was charged with olefin (3 mmol),
chloramine-T (4 mmol, the commercially available chloramine-T
trihydrate was dried to constant weight at ca. 80 °C for 12 h in a drying
pistol [34,35]), n-Bu4NBr (0.3 mmol), n-Bu4NBr3 (0.3 mmol), hydro-
quinone (0.15 mmol), biphenyl (100 mg, as internal standard) and
CH3CN (10 mL). CO2 was introduced into the autoclave and then the
We have developed an effective catalytic process for the synthesis of
5-substituted 2-oxazolidinone from aziridine and CO2 [14,15]. In this
⁎
Corresponding author. Tel./fax: +86 22 2350 4216.
E-mail address: heln@nankai.edu.cn (L.-N. He).
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.04.003

D.-L. Kong et al. / Catalysis Communications 11 (2010) 992–995
993
Table 1
mixture was stirred at desired temperature (for instance 100 °C) for
Catalyst effect on one-pot process for the synthesis of 5-phenyl 2-oxazolidinonea.
15 min to allow equilibration. Finally, the pressure was adjusted to the
reaction pressure (e.g. 8 MPa) and the mixture wasstirred continuously.
When the reaction finished, the reactor was cooled in ice-water and CO2
was ejected slowly. An aliquot of sample was taken from the resultant
mixture for GC analysis. The residue was purified by column
chromatography on silica gel (200–300 mesh, eluting with 5:1 to 20:1
petroleum ether/ethyl acetate) to afford the desired product. The
products were further identified by 1H NMR and 13C NMR spectroscopy,
ESI-MS and IR, which are consistent with those reported in the literature
and in good agreement with the assigned structures. The polymeric
side-product was purified by reprecipitation from THF/H2O to remove
low-molecular-weight products, and finally, the product was dried in
vacuo. Molecular weights and molecular weight distributions of the
oligomers were measured using Agilent Technologies 1200 Series GPC-
SEC Analysis System (concentration, 1 mg/mL; eluent, THF; flow rate,
1 mL/min; temperature, 23 °C). Calibration was made with monodis-
persed polystyrenes as standards (see Electronic supplementary
information).
b
Entry
Cat. I
Cat. II
Yield /%
2
3
4
1
2
3
–
–
0
0
2.8
11.3
9.0
9.9
11.4
3.3
0
0
0
0
4.1
11.1
3.8
3.2
9.6
2.4
22.1
2.1
0.28
0.82
3.7
4.7
1.8
3.7
6.5
–
n-Bu4NBr
–
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NBr3
n-Bu4NI3
Me4NBr3
n-Pr4NBr3
n-CetMe3NBr3
27.0
31.0
10.8
31.5
49.6
14.9
27.9
31.1
0
0
35.1
4.9
12.6
20.3
25.6
c
4
–
5
6
7
8
9
n-Bu4NF
n-Bu4NCl
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NI
I2
LiBr
Bu4NI
Me4NBr
n-Pr4NBr
n-CetMe3NBr
d
e
4.9
f
10
12.2
0.86
0.77
0.56
0.56
0.69
6.1
11
12
13
14
15
16
g
17
1.7
a
All the reaction were performed with styrene (3 mmol), chloramine-T (4 mmol,
1.33 equiv.), Cat. I (0.3 mmol, 10 mol%), Cat. II (0.3 mmol, 10 mol%), hydroquinone
(0.15 mmol, 5 mol%, as polymerization inhibitor) and CH3CN (10 mL) at 8 MPa CO2,
100 °C for 24 h unless otherwise noted.
3. Results and discussion
b
Determined by GC using biphenyl as internal standard.
3.1. One-pot binary catalytic process for the synthesis of 5-phenyl 2-
oxazolidinone
c
Cat. I (0.9 mmol, 30 mol%).
d
Without hydroquinone 0.3526 g of oligomer (Mn=6.6869×102 g/mol, Mw=6.7158×
102 g/mol, Mz=6.7452×102 g/mol) was obtained.
e
PhMe3NBr3 was found to be active towards the aziridination of
olefins and n-Bu4NBr was effective for the cycloaddition reaction of
aziridine and CO2, in well agreement with the published results. [13,21]
We reasoned the binary catalysts comprising n-Bu4NBr3/n-Bu4NBr
could be effective for synthesis of 5-substituted 2-oxazolidinones in a
single operation directly from olefins, chloramine-T and CO2 as depicted
in Scheme 1. Styrene was selected as a model substrate for further
investigation.
Table 1 summarizes experimental results on catalyst effect on one-
pot process for the synthesis of 2-oxazolidinones. Neither product 2, 3
nor 4 was detected at all without any catalyst (entry 1, Table 1). And n-
Bu4NBr alone was also inactive for this process (entry 2). On the other
hand, n-Bu4NBr3 itself showed poor active to afford the desired product
3 in 27% yield (entry 3) and increasing its amount enhanced formation
of aziridine 2 (entry 4), so Br−3 is necessary for the generation of 2-
oxazolidinones 3. Interestingly, addition of n-Bu4NBr could improve the
activity (entry 3 vs.7). Notably, the anion of catalyst II has great influence
on reactivity. The yield of 3 was found to be n-Bu4NBrNn-Bu4NClNn-
Bu4NF (entries 5–7), being presumably correlated with nucleophilicity
and leaving ability of the anions. However, both n-Bu4NI and I2 gave no
desired product (entry 11 and 12), which could be ascribed to possible
oxidation of n-Bu4NI or I2 by Br-3. Indeed, n-Bu4NI3 in place of n-Bu4NBr3
produced product 3 even low yield (entry 14 vs. 10), also supporting this
hypothesis. Subsequently, a series of tetraalkylammonium tribromide
Chloramine-T trihydrate (4 mmol).
Cat. I (0.15 mmol, 5 mol%), Cat. II (0.15 mmol, 5 mol%).
n-CetMe3NBr: cetyl trimethylammonium bromide.
f
g
and tetraalkylammonium bromide with various alkyl chain lengths
were also investigated (entries 15–17). The oxazolidinone yield
increased in the order of n-Bu4N+Nn-Pr4N+NMe4N+ (entries 7, 15,
16), n-CetMe3N+NMe4N+ (entries 15, 17). The LiBr which has been
reported [13] to be active for the coupling of aziridine and CO2, also gave
relatively good yield (entry 13). All the results demonstrated a
homogeneous binary catalyst system of n-Bu4NBr3/n-Bu4NBr was the
most effective for the present one-pot process to regioselectively afford
5-phenyl 2-oxazolidinone 3 in 49.6% yield without the formation 4-
phenyl isomer, alongside with 11.4% yield of aziridine 2 and 9.6%
hydrolyzed product 4. In addition, the influence of the amount of
catalyst was also evaluated. The yield of 3 was 31.1% when 5 mol%
catalyst was used; and increased to 49.6% with 10 mol% of catalyst
loading (entries 7 and 10). Moreover, more polymerized products were
detected without hydroquinone (entry 8). And the use of the trihydrate
of chloramine-T gave more hydrolytic product 4 (entry 9).
3.2. The effects of the reaction parameters
The reaction conditions were also carefully examined for the
reaction of styrene with chloramine-T and CO2 using the n-Bu4NBr3/n-
Bu4NBr binary catalyst system, and the results are summarized in
Table 2. The yield of 2-oxazolidinone 3 increased with reaction time
within 24 h (entries 1–5, Table 2). On the other hand, the yield of 3
increased rapidly with reaction temperature up to 100 °C, whereas,
further increase in the temperature caused a decrease in the yield
(entries 4, 6–9), possibly due to the decomposition of chloramine-T.
[32,33] The influence of CO2 pressure on the reaction was also
investigated, the most proper pressure was around 8 MPa. The yield of
the target product 3 increased with CO2 pressure up to 8 MPa (entry 4,
10–13, Table 2). This enhancement would be ascribed to less mass
transfer limitation under near critical CO2 conditions. Whereas, further
increase in the CO2 pressure caused a decrease in the yield. This
presumably is owing to CO2 diluent effect, which could decrease the
polarity of the reaction medium. So the appropriate reaction conditions
are at 100 °C under 8 MPa CO2 pressure and 24 h.
Scheme 1. One-pot synthesis of 5-phenyl-2-oxazolidinone via the three-component
coupling of styrene, chloramine-T and CO2.

994
D.-L. Kong et al. / Catalysis Communications 11 (2010) 992–995
Table 2
Screening reaction conditionsa.
Entry
Temp./°C
Pressure
/MPa
Time/
h
Yield /%b
2
3
4
Scheme 2. Substrate scope.
1
2
3
4
5
6
7
8
9
10
11
12
13
100
100
100
100
100
25
8
8
8
8
8
8
8
8
8
6
12
18
24
48
24
24
24
24
24
24
24
24
13.9
11.2
11.1
11.4
8.07
8.13
12.7
8.25
0.39
18.4
14.2
25.5
49.4
49.6
48.0
0
5.2
8.5
9.4
9.6
9.2
1.5
1.6
6.0
11.5
4.1
6.9
9.7
9.4
c
However, cyclohexene showed no 2-oxazolidinone other than 39.8%
isolated yield of the aziridine (entry 1 vs 5), probably because of
inactivity of its corresponding aziridine originating from the steric effect
of the internal olefin. Notably, the electron-donating group at benzene
ring is likely to be more favorable than electron-deficient counterpart
(entries 6–10) to improve the reaction, presumably owing to the
electronic influence (see Scheme 3). In particular, the electron-
withdrawing group gave just 4% yield of the aziridine without formation
of the 2-oxazolidinone, whereas electron-donating group showed
higher reactivity in comparison with electron-withdrawing group
affording the 2-oxazolidinone with full conversion of the aziridine and
a moderate yield (entry 9 vs. 10). Accordingly, electronic effect could
have greater impact on generation of 2-oxazolidinone than aziridine.
Interestingly, phenyl substituted aliphatic olefins and a diene showed
better activities among the tested substrates (entries 11–13). It is also
worth noting that only one carbon–carbon double bond was converted
to the oxazolidinone (entry 13). Its structure could be proved by NMR
spectra (see Supporting Information).
50
80
6.7
15.3
36.7
0
19.7
22.5
43.3
120
100
100
100
100
0.1
2
6
5.66
3.01
8.77
13
a
Reactions wereconducted with styrene(3 mmol), chloramine-T(4 mmol, 1.33equiv.),
n-Bu4NBr (0.3 mmol, 10 mol%), n-Bu4NBr3 (0.3 mmol, 10 mol%), hydroquinone
(0.15 mmol, 5 mol%, as polymerization inhibitor), and CH3CN (10 mL).
b
Determined by GC using biphenyl as internal standard.
The polymeric side-product was purified by reprecipitation from THF/H2O. 0.0919 g of
c
oligomers (Mn=5.5245×102 g/mol, Mw=5.8025×102 g/mol, Mz=6.1788×102 g/mol)
was isolated.
3.3. Solvent effect
3.5. Possible mechanism
The effect of solvent on the reaction was evaluated as shown in
Table 3. As a result, catalytic activity is strongly dependent on the solvent
(entries 1–9, Table 3). Among the solvents, acetonitrile showed the best
results under the otherwise identical conditions (entry 1), possibly due
to the polarity and the solvent power for dissolving chloramine-T.
Particularly, CCl4 is a bifunctional initiator to initiate atom transfer
radical polymerization of styrene. Indeed, it gave polymers as major
product. [36]
On the basis of the literature [13,21] and experiment results, a
possible mechanism for the present n-Bu4NBr3/n-Bu4NBr catalyzed
one-pot process of forming 5-substituted 2-oxazolidinone via the
three-component reaction of olefin, chloramine-T and CO2 is shown in
Scheme 3. For the first step, the olefin (1) reacts with a Br+ source
(Br−3 , Br–Cl) to give the bromonium ion (5), which then undergoes
benzylic opening by TsNCl− forming the β-bromo-N-chloro-N-
toluenesulfonamide (6). Attack of Br− on the N–Cl group in putative
intermediate (6) generates the anion (7). Expulsion of Br− from the
anion (7) obtained the aziridine (2). [21] For the second step, the
mechanism involves three steps: the nucleophilic species Br−initiates
the ring-opening of the aziridine (2), followed by reacting with the
activated CO2 and subsequent cyclization via an intramolecular
nucleophilic attack leading to the target product 5-substituted 2-
oxazolidinone (3) and regeneration of the catalyst. On the other hand,
3.4. Synthesis of various carbamates
To demonstrate the utility and generality of this approach to
formation of 5-substituted 2-oxazolidinones, we examined the reac-
tions of various olefins with chloramine-T and CO2 by performing the
reaction under the identical conditions (Scheme 2).
The results are listed in Table 4. The substrates with different alkyl
chain lengths were investigated (entries 1–4, Table 4), which gave
relative different reactivity, presumably owing to the sterically hindered
influence interms of reactionmechanisticconsideration (seeScheme3).
Table 4
Substrate scope of this approacha.
Entry
Olefin
Isolated yield of
aziridines /%
Isolated yield of
oxazolidinones /%
Table 3
Solvent effecta.
1
2
1-hexene
1-heptene
1-octene
1-dodecene
cyclohexene
Styrene
2-methylstyrene
3-methylstyrene
4-methylstyrene
4-chlorostyrene
3-phenyl-1-propene
4-phenyl-1-butene
1,5-hexadiene
6.0
8.8
12.6
18.2
39.8
11.4
4.6
0
63.7
55.9
38.2
14.6
0
47.6
36.9
47.1
42.7
0
Entry
solvent
Yield /%b
2
3
4b
5
3
4
1
2
3
4
5
6
7
8
9
CH3CN
–
11.4
3.86
2.06
5.06
0.60
4.12
8.36
2.64
2.55
49.6
9.6
0
4.7
2.2
0
7.2
1.9
2.8
0.59
6
7
8
9
10
11
12
13
0.96
THF
26.1
15.2
0
DMF
NMP
CH2Cl2
CHCl3
Toluene
CCl4
0
4.0
6.4
5.8
6.8
19.5
52.1
53.0
56.4
3.34
28.3
2.21
a
All the experiments were conducted at 8 MPa CO2, 100 °C for 24 h in a 50 mL stainless
steel autoclave containing olefin (3 mmol), chloramine-T (4 mmol, 1.33 equiv.), n-Bu4NBr
(0.3 mmol, 10 mol%), n-Bu4NBr3 (0.3 mmol, 10 mol%), hydroquinone(0.15 mmol, 5 mol%,
as polymerization inhibitor), and CH3CN (10 mL).
a
Reaction conditions: styrene (3 mmol), chloramine-T (4 mmol, 1.33 equiv.), n-Bu4NBr
(0.3 mmol, 10 mol%), n-Bu4NBr3 (0.3 mmol, 10 mol%), hydroquinone (0.15 mmol, 5 mol%,
as polymerization inhibitor), and solvent (10 mL), 8 MPa CO2, 100 °C for 24 h.
b
b
Determined by GC using biphenyl as internal standard.
48 h.

D.-L. Kong et al. / Catalysis Communications 11 (2010) 992–995
995
Scheme 3. A putative mechanism.
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In conclusion, we developed a simple and effective process catalyzed
by n-Bu4NBr3/n-Bu4NBr in a single operation for the synthesis of 5-
substituted 2-oxazolidinones with perfect regioselectivity directly from
olefins, chloramine-T, and CO2. The choice of efficient binary catalysts
for two steps, i.e. aziridination and cycloaddition, and the optimization
of reaction condition are keys to the one-pot synthesis of 5-substituted
2-oxazolidinones. The present protocol could show an additional
example for efficiently utilizing CO2 as a carbon source in the field of
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Acknowledgments
We are grateful to the National Natural Science Foundation of China
(grant nos. 20672054, 20872073) and the 111 project (B06005), and the
Committee of Science and Technology of Tianjin for financial support.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.catcom.2010.04.003.
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