N-Tosylaziridine, a new substrate for chemical fixation of carbon dioxide via ring expansion reaction under atmospheric pressure

Article abstract of DOI:10.1016/j.tetlet.2003.12.052

N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane, N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosylaziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism.

Full text of DOI:10.1016/j.tetlet.2003.12.052

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 1363–1365
N-Tosylaziridine, a new substrate for chemical fixation of carbon
dioxide via ring expansion reaction under atmospheric pressure
Atsushi Sudo,a Yosuke Morioka,b Fumio Sandac and Takeshi Endod,*
aMolecular Engineering Institute, Kinki University, 11-6 Kayanomori, Iizuka, Fukuoka 820-8555, Japan
bChemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan
cDepartment of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku,
Kyoto 606-8501, Japan
dDepartment of Polymer Science and Engineering, Faculty of Engineering, Yamagata University, Jonan, Yonezawa,
Yamagata 992-8510, Japan
Received 17 November 2003; revised 6 December 2003; accepted 11 December 2003
Abstract—N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction
was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane,
N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosyl-
aziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism.
Ó 2003Elsevier Ltd. All rights reserved.
CO2 will be an inexhaustible and nontoxic C1 resource if
its highly efficient chemical fixation process is available.
For this goal, various reactions of CO2 to convert it into
useful compounds have been studied.1–4 Among them,
cycloaddition of CO2 with epoxide has been most
intensively studied and has become one of the most
promising methods for chemical fixation of CO2.5–8 We
have developed highly efficient CO2–epoxide cycload-
dition catalyzed by alkali-metal halide or quaternary
ammonium salt, which enables facile fixation of gaseous
CO2 under atmospheric pressure.9;10 The obtained
products, cyclic carbonates, have been proved to be
useful monomers for polymer synthesis.11 Recently, we
have found that N–H aziridines react with CO2 under
atmospheric pressure, affording the corresponding cyclic
urethanes, 1,3-oxazolidin-2-ones.12 The reaction can be
efficiently catalyzed by alkali-metal halide or quaternary
ammonium salt, similarly to the analogous reaction of
epoxide.
idine has appeared to be of our great interest. From
scientific viewpoints, its reactivity would be much dif-
ferent from that of N–H aziridines by the presence of
highly electron-withdrawing sulfonyl group on the
nitrogen atom, and thus worth challenging as a new
target. From much practical viewpoints, its structural
diversity and availability is guaranteed by a versatile
N-sulfonylaziridination reaction of various olefins.13
This paper describes a new reaction of N-(p-toluene-
sulfonyl)aziridine (N-tosylaziridine, 1) with CO2, using
our simple and inexpensive catalytic system.
The reaction system is depicted in Scheme 1. As a cat-
alyst, lithium bromide (LiBr) was used, since it is the
most efficient one in the previously studied cycloaddi-
tion reaction of N–H aziridine with CO2, and is stable
under a wide range of reaction conditions. The sub-
strates, 2-decyl-N-tosylaziridine (1a) and N-tosylaziri-
dines having aromatic substituent at 2-position (1b–e),
In the course of our seeking for a new family of sub-
strates for fixation of gaseous CO2, N-sulfonylated azir-
O
Ts
N
LiBr (20 mol%)
Ts
O
N
CO2
+
R
Keywords: Aziridine; Cycloaddition; Carbon dioxide; Atmospheric
pressure; Carbon disulfide.
(1 atm)
R
1
2
* Corresponding author. Tel.: +81-948-227267; fax: +81-238-263092;
e-mail: tendo@yz.yamagata-u.ac.jp
Scheme 1.
0040-4039/$ - see front matter Ó 2003Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.12.052

1364
A. Sudo et al. / Tetrahedron Letters 45 (2004) 1363–1365
Table 1. Cycloaddition of CO2 with N-tosylaziridine 1 catalyzed by LiBra
Entry
Aziridine
R
Solvent
Temperature
Product
Yield/%b
1
2
3
4
5
6
1a
1b
1b
1c
1d
1e
Desyl
Ph
Ph
THF
THF
NMP
NMP
NMP
NMP
rt
2a
42
0
rt
100 °C
100 °C
100 °C
100 °C
2b
2c
2d
2e
70
42
76
79
4-ClC6H4
4-MeC6H4
4-MeOC6H4
a Conditions: ½1Š ¼ 1:0 M, in NMP at 100 °C for 24 h.
0
b Determined by GC.
were synthesized from the corresponding olefins by az-
iridination reactions with chloramine-T.13 The reaction
of aziridine 1a, which has an alkyl substituent, was
performed in tetrahydrofuran (THF) at ambient tem-
perature (entry 1 in Table 1). CO2 was supplied to a
reaction vessel from an equipped balloon with atmo-
spheric pressure. GC analysis of the reaction mixture
revealed that the reaction proceeded slowly, and the
corresponding cyclic urethane, 4-decyl-3-(4-toluene-
sulfonyl)-1,3-oxazolidin-2-one (2a) formed in 42% yield.
The corresponding regioisomer, 5-alkyl substituted one,
100
1b
1c
1d
1e
80
60
40
1
20
0
was not detected at all by GC and 300 MHz H NMR
analyses of the crude mixture. The other aziridines 1b–e
can also be used as a substrate for the present reaction
system, if the reaction conditions were chosen appro-
priately. Although these aziridines did not react with
CO2 at ambient temperature, they did at 100 °C (entries
2–6 in Table 1). In order to elevate the reaction tem-
perature, N-methylpyrrolidone (NMP) was employed as
a less volatile solvent. In all cases, only the corre-
sponding cyclic urethane and the aziridine were detected
by GC and 1H NMR, indicating that decomposition of
the aziridine and other side reactions such as alternate
copolymerization were negligible. No regioisomer was
detected by NMR analysis.
0
6
12
18
24
time/h
Figure 1. Time-conversion plots for the reactions of N-tosylaziridines
1b (R ¼ Ph), 1c (R ¼ 4-ClC6H4), 1d (R ¼ 4-MeC6H4) and 1e (R ¼ 4-
MeOC6H4) with CO2 in NMP at 100 °C, catalyzed by 20 mol % LiBr.
1.6
1b
1c
1d
1e
1.4
1.2
1.0
The time-conversion dependence was analyzed in the
reactions of the aziridines having several aromatic sub-
stituents 1b–e by GC in order to investigate how the
substituent effects on the reaction rate. In all cases, the
time-conversion curve reached saturation before com-
plete conversion. The reason for this tendency is not
clear at present but it should not be caused by side
reactions. As shown in Figure 1, the order of the reac-
tion rate is roughly 1e > 1d > 1b > 1c, if the induction
periods of the reaction are neglected. This order suggests
that the reactivity of N-tosylaziridine increases when the
substituent X at para-position of the aromatic sub-
stituent is an electron-donating one. The fact that the
aziridine 1a having a relatively electron-donating alkyl
substituent reacted with CO2 without heating is in good
accordance with the order. It is noteworthy that this
order is opposite to that found in the reaction of epoxide
with CO2, indicating that the rate-determining step in
the present reaction is different to that in the analogous
reaction of epoxide (vide infra).10
0.8
0.6
0.4
0.2
0
0
3
6
9
12
time/h
Figure 2. First order time-conversion plots for the reactions of
N-tosylaziridines 1b (R ¼ Ph), 1c (R ¼ 4-ClC6H4), 1d (R ¼ 4-MeC6H4)
and 1e (R ¼ 4-MeOC6H4) with CO2 in NMP at 100 °C, catalyzed by
20 mol % LiBr.
due to the presence of the induction period, the rate
constants k were calculated based on the equation
ꢀd½1Š=dt ¼ k½1Š0t, in order to obtain more detailed
information on the reaction behavior. The calculated
constants for 1b, 1c, 1d, and 1e were 1.3, 0.6, 1.8, and 2.1
(L molꢀ1 minꢀ1), respectively. Based on these values,
Figure 2 shows the first order time-conversion rela-
tionships of the reactions of 1b–e, based on the afore-
mentioned time-conversion plots. Although some plots
were deviated from the approximated first order kinetics

A. Sudo et al. / Tetrahedron Letters 45 (2004) 1363–1365
1365
five-membered cyclic urethane. In the case of the reac-
tion of epoxide, this step is considered to be the rate-
determining step, because the reactivity of epoxide is
enhanced by electron-withdrawing substituent. On the
other hand, since the reactivity of N-tosylaziridine is
suppressed by electron-withdrawing group, this ring-
opening step should not be the rate-determining one.
The next step is reaction of anionic nitrogen with CO2 to
form the intermediate B, whose intramolecular cycliza-
tion gives the product. Since this step might be in
equilibrium between A and B, the final cyclization
step might be the rate-determining one in the reaction of
N-tosylaziridine, which is accelerated by electron-
donating substituent. The possible reason for this
acceleration can be inductive effect by the neighboring
aromatic group.
ln(kX/kH)
0.8
0.6
0.4
0.2
X=OMe
-0.3
X=Me
σx
-0.2
-0.1
0
0.1
0.2
0.3
X=H
-0.2
-0.4
-0.6
-0.8
X=Cl
In summary, N-tosylaziridine was found to be a useful
substrate for cycloaddition with CO2. The reaction can
be easily operated under atmospheric pressure by
employing lithium bromide as a catalyst. This hopeful
method for chemical fixation of CO2 will be further
studied to clarify its mechanism in order to develop
further efficient chemical transformation of CO2 into
valuable products.
Figure 3. Hammett plots for the reactions of N-tosylaziridines 1.
Li+
-N Ts
Li+
R
Ts
N
Br
R
Br-
A
References and notes
O
O
-O
CO2
Li+
Br
Ts
1. Verdecchia, M.; Marta, F.; Palombi, L.; Rossi, L. J. Org.
Chem. 2002, 67, 8287–8289.
N Ts
R
O
N
LiBr
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3. Saito, S.; Nakagawa, S.; Koizumi, T.; Hirayama, K.;
Yamamoto, Y. J. Org. Chem. 1999, 64, 3975–3978.
4. Takimoto, M.; Mori, M. J. Am. Chem. Soc. 2002, 124,
10008–10009.
R
B
Scheme 2.
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1559–1562.
6. Darensbourg, D. J.; Lewis, S. J.; Rodgers, J. L.; Yar-
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Tetrahedron Lett. 2003, 44, 7889–7891.
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Sharpress, K. B. J. Am. Chem. Soc. 1998, 120, 6844.
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Scientific & Technical: Northern Ireland, 1987; p 129.
relative ratios of the rate constants are plotted against
the HammettÕs r values of para-substituents14 to find a
virtually linear relationship as shown in Figure 3.
As shown in the Hammett plot, the reactivity of
N-tosylaziridine in its reaction with CO2 is increased by
introduction of electron-donating substituent. This ten-
dency is opposite to that found in the reaction of
epoxide with CO2.10 Scheme 2 depicts a plausible
mechanism for the present reaction, which is convenient
for us to understand the difference in the electronic effect
of substituent between the reaction of N-tosylaziridine
and that of epoxide. The first step of the reaction of
N-tosylaziridine would be ring-opening reaction by
nucleophilic attack of bromide anion from the catalyst
to give the intermediate A, analogously to the reaction
of epoxide. Regioselectivity in this ring-opening reaction
leads to the regioselective formation of the final product,