Cycloaddition of COto epoxides catalyzed by N-heterocyclic carbene (NHC)-ZnBrsystem under mild conditions

Article abstract of DOI:10.1055/s-0031-1290957

A very simple and convenient method toward coupling of COwith epoxides catalyzed by NHC/ZnBrhas been developed. This catalytic system exhibits excellent activity and selectivity in the cycloaddition reactions of COto terminal epoxides. The reactions can e

Full text of DOI:10.1055/s-0031-1290957

LETTER
▌1343
lCettyercloaddition of CO2 to Epoxides Catalyzed by N-Heterocyclic Carbene
(NHC)–ZnBr2 System under Mild Conditions
Cycloaddition of CO2 to Epoxides Catalyzed by NHC–ZnBr2 System
Xiang Liu,a Changsheng Cao,*a Yunfei Li,a Pei Guan,a Longguang Yang,a Yanhui Shi*a,b
a
College of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Xuzhou
Normal University, Xuzhou, Jiangsu 221116, P. R. of China
Fax +86(516)83500349; E-mail: yhshi@xznu.edu.cn
b
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. of China
Received: 17.02.2012; Accepted after revision: 12.03.2012
the typical NHC–CO2 adducts (Figure 1).6 Later, more
NHC–CO2 adducts7 were prepared, and their application8
was studied. Recently, they have shown great potential as
catalyst for CO2 coupling with epoxides.9 However,
Abstract: A very simple and convenient method toward coupling
of CO2 with epoxides catalyzed by NHC/ZnBr2 has been developed.
This catalytic system exhibits excellent activity and selectivity in
the cycloaddition reactions of CO2 to terminal epoxides. The reac-
tions can even be carried out under CO2 pressure as low as 0.05 MPa NHC–CO2 adducts are relatively unstable, and the forcing
and give carbonates in high yields.
conditions, such as high pressure and high temperature
(2–10 MPa of CO2 and 40–120 °C)9 are still required for
Key words: N-heterocyclic carbenes, NHC–CO2 adducts, carbon
dioxide, epoxides, cyclic carbonates
the reactions. As we know that air- and moisture-sensitive
NHC can be generated in situ by deprotonation of the cor-
responding imidazol(in)ium salts with a base. Thus, dur-
ing our studies on chemical fixation of CO2, very stable
imidazol(in)ium salts have been selected as NHC precur-
sors (Figure 2). Herein, we reported an efficient and sim-
ple approach for the synthesis of cyclic carbonates under
one (0.1 MPa) or even 0.5 atmosphere pressure (0.05
MPa) of carbon dioxide at 80 °C. The reaction was cata-
lyzed by NHC generated in situ with ZnBr2 as cocatalyst.
The utilization of CO2 as the ideal C1 feedstock for the
production of value-added chemical products becomes an
active area of research because CO2 is a renewable, abun-
dant, low cost, and nontoxic source of functional carbon
unit.1 As an environmentally benign process with 100%
atom efficiency, the transformation of CO2 into cyclic car-
bonates by the coupling reaction with epoxides has re-
ceived much attention.2,3 Cyclic carbonates are excellent
aprotic polar high-boiling solvents, electrolytes, and fuel
additives, and used extensively as intermediate in the pro-
duction of fine chemicals, engineering plastics, and phar-
maceuticals.2 A wide range of catalysts have been
explored for the generation of cyclic carbonates,2,4 how-
ever, most catalytic processes suffer from low catalytic
activity, high CO2 pressure, and high reaction tempera-
ture, and/or the using of expensive metallic compounds is
often required. So development of more efficient, readily
available, and low-cost catalyst and mild protocol is still
highly desired.
In the first stage of our work, we tested whether NHC
formed in situ could catalyze the cycloaddition of 2-
phenyloxirane with CO2 using 2 mol% of 4,5-dihydro-
1,3-bis(2,4,6-trimethylphenyl)-1H-imidazolinium chlo-
ride (2) and CsCO3 as base. To our delight, when the re-
action was carried out in DMSO at 80 °C for 24 hours
under 0.1 MPa of CO2, 21% of 4-phenyl-1,3-dioxolan-2-
one was obtained with 100% selectivity (Table 1, entry 1).
It has been reported that the presence of an electrophile as
cocatalyst could remarkably enhance the catalytic activity
in the coupling reaction of CO2 with epoxides.4d,9a,10
Therefore, we performed the screening of a series of wide-
ly used Lewis acids as cocatalyst to promote the CO2 ad-
dition under the identical conditions. The results (Table 1,
entries 2–4) demonstrated that the reaction rate signifi-
cantly increased with FeCl3 (82%) or ZnCl2 (88%) as co-
catalyst and did not change with a relatively stronger
Lewis acid AlCl3 (21%). Furthermore, we investigated
several NHC with different steric hindrances and elec-
tronic properties (Figure 2). Screening tests, using a series
of imidazol(in)ium chlorides (Table 1, entries 5–12) with
a cheaper base (K2CO3) under the same conditions, re-
vealed that 1) the NHC with a C4–C5 saturated imidazole
ring (Table 1, 1–4, entries 5–8) were better than their anal-
ogous unsaturated ones (Table 1, 5–8, entries 9–12); 2)
generally, the NHC with an N-aryl group (Table 1, entries
6–8 and 10–12) showed good activities compared to those
with an N-alkyl group (Table 1, entries 5 and 9); 3) sub-
stituents on the phenyl groups of NHC influenced the cat-
O
N
O
N
Ar(alkyl)
(alkyl)Ar
Figure 1 Imidazol(in)ium carboxylates
N-Heterocyclic carbenes (NHC) have been widely ap-
plied in catalysis and in coordination chemistry, where
they serve as extremely strong σ-donor after Arduengo
and co-workers first isolated the stable NHC in 1991.5
Louie first used the σ-donor character of NHC to capture
CO2 leading to imidazolium-2-carboxylates, identified as
SYNLETT 2012, 23, 1343–1348
Advanced online publication: 08.05.2012
DOI: 10.1055/s-0031-1290957; Art ID: ST-2012-W0146-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

1344
X. Liu et al.
LETTER
N+
N
N
N+
N+
N+
N
N
Cl–
Cl–
Cl–
Cl–
1
2
3
4
N+
N
N+
N
N+
N
N+
N
Cl–
Cl–
Cl–
Cl–
5
8
6
7
Figure 2 Structure of imidazol(in)ium chlorides
alytic activities (Table 1, entries 6–8 and 10–12). It seems As this catalytic system is very effective, it is interesting
that both steric issues and electronic properties play im- to examine if this reaction could be conducted under less
portant roles in the cycloaddition. The best yield was at- than 0.1 MPa of CO2 (Table 4). The results showed that
tained by using the diethyl-substituted saturated the good yield could be reached with a partial pressure of
imidazolinium chloride 4. A couple of control experi- 0.05 MPa of CO2 (Table 4, entries 2 and 3). To the best of
ments are worthy of note. The reaction does not occur our knowledge, no reaction has been reported to carry out
without the imidazol(in)ium salt (Table 1, entry 13) or efficiently under 0.05 MPa CO2 so far.
without the base (Table 1, entry 14). Consequently NHC
In order to better understand the reaction mechanism and
formed in situ must be present for the reaction to take
determine the catalytic active species, Zn–NHC complex
place. The solvent has also an effect on the reaction (Table
(3–ZnCl2)12 and NHC–CO2 (3–CO2)6,9 were prepared ac-
cording to the literature procedure, however, the attempt
1, entries 7, 15–17). The reaction was conducted in a more
polar solvent providing a higher yield, and the best solvent
tested for the reaction is DMSO. In addition, we investi-
gated if the halide ions from ZnX2 (X= Cl, Br, I) would
have effect on the catalyst activity (Table 1, entries 7, 18,
and 19). Interestingly, there is a big improvement in the
on making NHC–ZnBr2 failed. The performance of 3–
ZnCl223 and 3–CO224 was investigated in the reaction of 2-
phenyloxirane under 0.1 MPa of CO2. The comparable re-
sults were achieved by using 3–ZnCl2 complex, 3–CO2
adduct with ZnCl2, or 3, K2CO3, and ZnCl2 (Table 5, en-
tries 1–3). It is also true for the 3–ZnBr2 catalytic system
yield with ZnBr2 or ZnI2 as cocatalyst. The reason proba-
bly is that the Br– or I– anion takes part in the
(Table 5, entries 4 and 5). Consequently, both the Zn–
cycloaddition11 or they would influence the electrophilic
NHC complex and the NHC–CO2 adduct could play roles
in the cycloaddition reaction.
ability of Zn. As 3–ZnBr2, 3–ZnI2 and 4–ZnBr2 showed
similar activity (Table 1, entries 18–20), and 3 is easier to
prepare than 4 and ZnBr2 is cheaper than ZnI2, catalyst 3–
ZnBr2 is a good choice of catalytic system to use.
A further NMR experiment indicated that the treatment of
the Zn–NHC complex (3–ZnCl2) with CO2 at elevated
temperature led to the NHC–CO2 adduct. The NMR spec-
tra are shown in Figure 3. The formation of the 3–CO2 ad-
duct from the reaction of 3–ZnCl2 with CO2 was evident
from the distinctive peak of NCH2CH2N of the imidazole
ring, which appeared at δ = 4.88 ppm for the 3–CO2 ad-
duct. After the reaction of 3–ZnCl2 with CO2 at 50 °C for
To determine the optimum reaction conditions, catalyst
loading and reaction temperature were tested in the cyclo-
addition reaction of 2-phenyloxirane to CO2 as well (Ta-
ble 2). The results showed that the reaction went well with
2 mol% of catalyst at 80 °C for 24 hours (Table 2, entry
2). Therefore, in the following studies, all the reactions
were carried out with 2 mol% of 3–ZnBr2 as catalyst,
K2CO3 as base, and DMSO as a solvent at 80 °C for 24
hours under 0.1 MPa of CO2.
three hours, the peak changed from δ = 4.81 ppm (3–
ZnCl2) to δ = 4.88 ppm. The formation of NHC–CO2 was
To further probe the scope of the catalysis, a larger selec-
tion of epoxides was screened under the optimum condi-
tions (Table 3). The reactions with these terminal
epoxides were very clean and totally completed within 24
hours, and no chromatography was required for the puri-
fication. The pure carbonate products were obtained by
filtration of the reaction mixture over a plug of SiO2, so
the workup was very simple. Unfortunately, the reaction
with a sterically hindered disubstituted epoxide, for exam-
1
ple, 1,2-cyclohexene oxide, leads to an unclean reaction
with less than 10% of desired carbonate.
Figure 3 H NMR spectra in CDCl3. a) 3–CO2 adduct; b) 3–ZnCl2
complex; c) treatment of 3–ZnCl2 complex with CO2.
Synlett 2012, 23, 1343–1348
© Georg Thieme Verlag Stuttgart · New York

LETTER
Cycloaddition of CO2 to Epoxides Catalyzed by NHC-ZnBr2 System
1345
Table 1 Screening of Various Catalysts, Solvents, Bases and Lewis
Acids for the Cycloaddition Reaction of CO2 to 2-Phenyloxirane
Table 2 Screening of Catalyst Loading and Temperature for the Cy-
cloaddition Reaction of CO2 to 2-Phenyloxirane
Ph
cat. NHC (2 mol%)
Ph
O
O
O
3, K2CO3, ZnBr2 (2 mol%)
O
salt, base
O
O
Ph
+ O
C
O
Ph
+
O
C
O
O
DMSO, 24 h
solvent, 80 °C, 24 h
O
0.1 MPa
0.1 MPa
Entrya
Loading of 3 (mol%) Temp (°C)
Entrya
GC yield (%)b
Catalyst Solvent
Base
Lewis
acid
GC yield
(%)b
1
2
3
4
5
5
2
1
2
2
80
80
99
98
60
50
70
1
2
2
2
2
2
1
2
3
4
5
6
7
8
–
3
3
3
3
3
3
4
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
–
21
21
82
88
20
35
58
68
10
15
53
55
0
AlCl3
FeCl3
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnBr2
ZnCl2
ZnCl2
ZnCl2
ZnBr2
ZnI2
80
3
50
4
100
5
a Reaction conditions: The reaction was carried out in a 50 mL round-
bottom flask containing 2-phenyloxirane (2 mL, 17.5 mmol), Lewis
acid (0.35 mmol), and base (0.35 mmol).
6
b Using dodecane as internal standard and the average of two runs.
7
8
Table 3 Cycloaddition of CO2 to Epoxides by 3–ZnBr2 Catalyst15
R
9
O
O
3 (2 mol%), K2CO3, ZnBr2
O
Ph
+ O
C
O
O
10
11
12
13
14
15
16
17
18
19
20
DMSO, 80 °C, 24 h
0.1 MPa
Entrya
1
Isolated yield (%)b
97
R
Product
Et
O
O
O
0
O
2
3
4
5
6
7
8
9
n-Bu
ClCH2
BrCH2
Ph
96
90
92
95
96
98
95
97
K2CO3
K2CO3
53
0
O
O
toluene
O
Cl
1,4-dioxane K2CO3
0
O
O
O
DMSO
DMSO
DMSO
K2CO3
K2CO3
K2CO3
98
99
99
Br
O
O
ZnBr2
Ph
O
O
a Reaction conditions: The reaction was carried out in a 50 mL round-
bottom flask containing 2-phenyloxirane (2 mL, 17.5 mmol), catalyst
(0.35 mmol), Lewis acid (0.35 mmol), and base (0.35 mmol).
b Using dodecane as internal standard and the average of two runs.
O
O
Bn
O
Ph
Ph
O
O
further proofed by the characteristic absorption at 1681
cm–1 in FTIR experiments.
PhOCH2
O
O
O
O
From the established mechanism for the catalytic cycload-
dition of CO2 to epoxides9,13 and our current results, we
suggested that NHC is the catalytic active species, and
there are two ways for NHC involving in the catalytic cir-
cle. The proposed mechanism is shown in Scheme 1. In
circle i, NHC generated in situ directly reacts with CO2 to
form the NHC–CO2 adduct A. In circle ii, NHC reacts
with ZnX2 to form the Zn–NHC complex B, which would
further react with CO2 to generate the NHC–CO2 adduct
A. Then the nucleophilic addition of zwitterionic adduct
A to the epoxide, which is activated through its coordina-
O
O
Ph
PhCH2OCH2
PhCOOCH2
O
O
O
Ph
O
O
O
a Reaction conditions: The reaction was carried out in a 50 mL round-
bottom flask containing epoxide (17.5 mmol), 2 mol% of catalyst 3
(0.149 g, 0.35 mmol), 2 mol% of K2CO3 (0.048 g, 0.35 mmol), and
2 mol% of ZnBr2 (0.079 g, 0.35 mmol).
b The average of two runs.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1343–1348

1346
X. Liu et al.
LETTER
Table 4 Cycloaddition Reaction of CO2 to 2-Phenyloxirane under
Different Partial Pressure of CO2
N
O
N
O
N
O
N
Ar
Ar
Ar
Ar
Ph
O
3 (2 mol%), base, ZnBr2
O
O–
Ph
+ O
C
O
O
A
DMSO, 80 °C, 24 h
O
(CO2 + Ar = 0.1 MPa)
ZnX2
CO2
R2
Entrya
GC yield (%)b
Base
VCO2/VAr PCO2 (atm)
O
1
2
3
4
K2CO3
K2CO3
Cs2CO3
K2CO3
1:0
1:1
1:1
1:2
1
98
88
89
20
N
N
Ar
Ar
ZnX2
0.5
0.5
0.33
ZnX2
O
sol
R2
B
a Reaction conditions: the reaction was carried out in a 50 mL round-
bottom flask containing 2-phenyloxirane (2 mL, 17.5 mmol), catalyst
(0.35 mmol), Lewis acid (0.35 mmol), and base (0.35 mmol).
b Using dodecane as internal standard and the average of two runs.
ZnX2
N
(i)
(ii)
N
N
Ar
Ar
N
Ar
O
O
Ar
••
X2Zn
O–
Table 5 Using Different Catalytic Systems for the Cycloaddition
Reaction of CO2 to 2-Phenyloxirane
C
R2
K2CO3
Ph
catalytic system
O
O
O
N+
O
O
N
Ph
+ O
C
O
O
Ar
Ar
O
DMSO, 80 °C, 24 h
Cl–
R2
0.1 MPa
Entrya
GC yield (%)b
Scheme 1 Plausible mechanism of the carboxylation catalyzed by the
NHC–Lewis acid
Catalytic system (2 mol%)
1
2
3
4
5
3–ZnCl2 complex
52
57
58
97
98
were achieved using this catalytic system under mild con-
ditions, and the workup was very simple. Further mecha-
nistic and reactivity studies of this and related catalyst
systems in various CO2 fixation reaction are ongoing in
our laboratories, and we hope to discover an efficient cat-
alyst system in the recycling and reusing of CO2 in indus-
try.
3–CO2 adduct + ZnCl2
3 + K2CO3 + ZnCl2
3–CO2 adduct + ZnBr2
3 + K2CO3 + ZnBr2
a Reaction conditions: The reaction was carried out in a 50 mL round-
bottom flask containing 2-phenyloxirane (2 mL, 17.5 mmol).
b Using dodecane as internal standard and the average of two runs.
Acknowledgment
This work was supported by Qing Lan Project (08QLT001 and
08QLD006) of Jiangsu Education Committee, SRF for ROCS,
SEM, 333 project for the cultivation of high-level talents
(33GC10002), PAPD and NSFC (21172188, 21071121).
tion to the electrophilic Lewis acid, to generate intermedi-
ate C. Subsequent intramolecular cyclization of C
regenerates NHC and releases cyclic carbonate as prod-
uct.
Compared to the previously reported NHC-catalyzed
system9a and the ZnCl2–imidazolium system,14 this new
NHC–ZnBr2 binary catalyst system required much milder
conditions. For example, the ZnCl2–imidazolium system
required 1.5 MPa of CO2, and 100 °C to make the reaction
happened. In our catalyst system, the reaction can be car-
ried out under 0.1 MPa of CO2, 80 °C leading to high yield
of product.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.onmornifIatngonimSorfniturItagponiSutpor
References and Notes
(1) (a) Jessop, P. G.; Joó, F.; Tai, C.-C. Coord. Chem. Rev.
2004, 248, 2425. (b) Yoshida, S.; Fukui, K.; Kikuchi, S.;
Yamada, T. J. Am. Chem. Soc. 2010, 132, 4072.
(c) Minakata, S.; Sasaki, I.; Ide, T. Angew. Chem. Int. Ed.
2010, 49, 1309. (d) Zhang, W.-Z.; Li, W.-J.; Zhang, X.;
Zhou, H.; Lu, X.-B. Org. Lett. 2010, 12, 4748. (e) Lee, B.;
Kang, S. H.; Kang, D.; Lee, K. H.; Cho, J.; Nam, W.; Han,
O. H.; Hur, N. H. Chem. Commun. 2011, 47, 11219.
(f) Watile, R. A.; Bagal, D. B.; Patil, Y. P.; Bhanage, B. M.
Tetrahedron Lett. 2011, 52, 6383.
In summary, we have developed an efficient catalyst for
the cycloaddition of CO2 to epoxides. In the present work,
the fixation of CO2 by epoxides can be carried out using
NHC–ZnBr2 as catalyst under one or even half of atmo-
sphere pressure of CO2 (0.1 or 0.05 MPa). High conver-
sions with good selectivity towards cyclic carbonates
Synlett 2012, 23, 1343–1348
© Georg Thieme Verlag Stuttgart · New York

LETTER
Cycloaddition of CO2 to Epoxides Catalyzed by NHC-ZnBr2 System
1347
(2) (a) Sakakura, T.; Choi, J.-C.; Yasuda, H. Chem. Rev. 2007,
107, 2365. (b) Decortes, A.; Castilla, A. M.; Kleij, A. W.
Angew. Chem. Int. Ed. 2010, 49, 9822. (c) Liu, X.-B.;
Darensbourg, D. J. Chem. Soc. Rev. 2012, 41, 1462.
(3) (a) Kim, H. S.; Kim, J. J.; Lee, B. G.; Jung, O. S.; Jang,
H. G.; Kang, S. O. Angew. Chem. Int. Ed. 2000, 39, 4096.
(b) Kim, H. S.; Kim, J. J.; Lee, S. D.; Lah, M. S.; Moon, D.;
Jang, H. G. Chem. Eur. J. 2003, 9, 678. (c) Wu, S.-S.; Zhang,
X.-W.; Dai, W.-L.; Yin, S.-F.; Li, W.-S.; Ren, Y.-Q.; Au,
C.-T. Appl. Catal., A 2008, 341, 106. (d) Xiong, Y.; Wang,
H.; Wang, R.; Yan, Y.; Zheng, B.; Wang, Y. Chem.
Commun. 2010, 46, 3399.
(4) (a) Yamaguchi, K.; Ebitani, K.; Yoshida, T.; Yoshida, H.;
Kaneda, K. J. Am. Chem. Soc. 1999, 121, 4526. (b) Kim, Y.
J.; Varma, R. S. J. Org. Chem. 2005, 70, 7882. (c) Jiang,
J.-L.; Gao, F.; Hua, R.; Qiu, X. J. Org. Chem. 2005, 70, 381.
(d) Meléndez, J.; North, M.; Pasquale, R. Eur. J. Inorg.
Chem. 2007, 3323. (e) Darensbourg, D. J. Chem. Rev. 2007,
107, 2388. (f) Dai, W.-L.; Luo, S.-L.; Yin, S.-F.; Au, C.-T.
Appl. Catal., A 2009, 366, 2. (g) Riduan, S. N.; Zhang, Y.
Dalton Trans. 2010, 39, 3347. (h) North, M.; Pasquale, R.;
Young, C. Green Chem. 2010, 12, 1514. (i) Decortes, A.;
Castilla, A. M.; Kleij, A. W. Angew. Chem. Int. Ed. 2010, 49,
9822.
(5) (a) Arduengo, A. J. III.; Harlow, R. L.; Kline, M. J. Am.
Chem. Soc. 1991, 113, 361. (b) Arduengo, A. J. III. Acc.
Chem. Res. 1999, 32, 913. (c) Bourissou, D.; Guerret, O.;
Gabbaïe, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39.
(d) Methot, J. L.; Roush, W. R. Adv. Synth. Catal. 2004, 346,
1035. (e) N-Heterocyclic Carbenes in Synthesis; Nolan, S.
P., Ed.; Wiley-VCH: Weinheim, 2006. (f) N-Heterocyclic
Carbenes in Transition Metal Catalysis; Glorius, F., Ed.;
Springer: Berlin, 2007. (g) Hahn, F. E.; Jahnke, M. C.
Angew. Chem. Int. Ed. 2008, 47, 3122. (h) Díez-González,
S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612.
(i) Melaimi, M.; Soleilhavoup, M.; Bertrand, G. Angew.
Chem. Int. Ed. 2010, 49, 8810. (j) Chiang, P.-C.; Bode, J. W.
Org. Lett. 2011, 13, 2422.
three times. Then epoxide (17.5 mmol) and DMSO (10 mL)
were injected into the flask by syringe, and CO2 was
provided by a balloon. The reaction was stirred at 80 °C for
24 h. After the reaction was cooled down, H2O (200 mL) was
added to the reaction mixture. The organic layer was
extracted with CH2Cl2 (3 × 20 mL), and filtered through a
silica plug. The products were collected by evaporating
volatiles and dried under vacuum. Using high-purity or low-
grade CO2 had no impact on the results.
4-Ethyl-1,3-dioxolan-2-one16
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 4.69–4.62 (m,
1 H), 4.52 (t, J = 8.0 Hz, 1 H), 4.08 (t, J = 7.6 Hz, 1 H), 1.87–
1.68 (m, 2 H), 1.02 (t, J = 7.6 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): δ = 155.1 (C=O), 78.0, 69.0, 26.9, 8.5. IR: ν = 1799
(CO) cm–1.
4-Butyl-1,3-dioxolan-2-one17
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 4.72–4.65 (m,
1 H), 4.51 (t, J = 8.0 Hz, 1 H), 4.05 (t, J = 8.0 Hz, 1 H), 1.82–
1.61 (m, 2 H), 1.46–1.27 (m, 4 H), 0.89 (t, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 155.0 (C=O), 69.3, 53.4,
33.4, 26.3, 22.1, 13.7. IR: ν = 1790 (CO) cm–1.
4-(Chloromethyl)-1,3-dioxolan-2-one18
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 4.99–4.93 (m,
1 H), 4.59 (app. t, J = 8.4 Hz, 1 H), 4.41 (dd, J = 6.0, 8.8 Hz,
1 H), 3.78 (dd, J = 12.0, 5.6 Hz, 1 H), 3.73 (dd, J = 12.0, 4.0
Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 154.0 (C=O),
74.2, 66.9, 43.5. IR: ν = 1790 (CO) cm–1.
4-(Bromomethyl)-1,3-dioxolan-2-one19
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 4.97–4.90 (m,
1 H), 4.60 (app. t, J = 8.4 Hz, 1 H), 4.36 (dd, J = 6.0, 9.0 Hz,
1 H), 3.61–3.52 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ =
154.2 (C=O), 73.9, 68.0, 31.7. IR: ν = 1794 (CO) cm–1.
4-Phenyl-1,3-dioxolan-2-one18
White solid. 1H NMR (400 MHz, CDCl3): δ = 7.47–7.35 (m,
5 H), 5.68 (t, J = 8.0 Hz, 1 H), 4.80 (t, J = 8.4 Hz, 1 H), 4.35
(t, J = 8.4 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 154.8
(C=O), 135.8, 129.7, 129.2, 125.8, 77.9, 71.1. IR: ν = 1775
(CO) cm–1.
(6) Duong, H. A.; Tekavec, T. N.; Arif, A. M.; Louie, J. Chem.
Commun. 2004, 112.
(7) Van Ausdall, B. R.; Glass, J. L.; Wiggins, K. M.; Aarif,
A. M.; Louie, J. J. Org. Chem. 2009, 74, 7935.
4-Benzyl-1,3-dioxolan-2-one20
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 7.36–7.21 (m,
5 H), 4.96–4.89 (m, 1 H), 4.44 (t, J = 8.0 Hz, 1 H), 4.17 (t, J
= 7.2 Hz, 1 H), 3.15 (dd, J = 14.0, 6.4 Hz, 1 H), 2.99 (dd, J
= 14.2, 6.4 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 154.8
(C=O), 133.8, 129.3, 128.9, 127.5, 76.7, 68.4, 39.5. IR: ν =
1791 (CO) cm–1.
(8) (a) Tommasi, I.; Sorrentino, F. Tetrahedron Lett. 2005, 46,
2141. (b) Gu, L.-Q.; Zhang, Y.-G. J. Am. Chem. Soc. 2010,
132, 914. (c) Van Ausdall, B. R.; Poth, N. F.; Kincaid, V. A.;
Arif, A. M.; Louie, J. J. Org. Chem. 2011, 76, 8413.
(9) (a) Zhou, H.; Zhang, W.-Z.; Liu, C.-H.; Qu, J.-P.; Lu, X.-B.
J. Org. Chem. 2008, 73, 8039. (b) Kayaki, Y.; Yamamoto,
M.; Ikariya, T. Angew. Chem. Int. Ed. 2009, 48, 4194.
(10) (a) Lu, X.-B.; Feng, X.-J.; He, R. Appl. Catal., A 2002, 234,
25. (b) Lu, X.-B.; Liang, B.; Zhang, Y.-J.; Tian, Y.-Z.;
Wang, Y.-M.; Bai, C.-X.; Wang, H.; Zhang, R. J. Am. Chem.
Soc. 2004, 126, 3732.
(11) Lu, X.-B.; Zhang, Y.-J.; Liang, B.; Li, X.; Wang, H. J. Mol.
Catal. A: Chem. 2004, 210, 31.
(12) Wang, D.; Wurst, K.; Buchmeiser, M. R. J. Organomet.
Chem. 2004, 689, 2123.
(13) Ajitha, M. J.; Suresh, C. H. Tetrahedron Lett. 2011, 52,
5403.
(14) Li, F.; Xiao, L.; Xia, C.; Hu, B. Tetrahedron Lett. 2004, 45,
8307.
4-(Phenoxymethyl)-1,3-dioxolan-2-one21
White solid. 1H NMR (400 MHz, CDCl3): δ = 7.31 (t, J = 7.6
Hz, 2 H), 7.02 (t, J = 7.2 Hz, 1 H), 6.91 (d, J = 8.4 Hz, 2 H),
5.06–5.00 (m, 1 H), 4.62 (t, J = 8.8 Hz, 1 H), 4.54 (dd, J =
8.4, 6.0 Hz, 1 H), 4.24 (dd, J = 10.0, 4.0 Hz, 1 H), 4.15 (dd,
J = 10.4, 3.2 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ =
157.7, 154.6 (C=O), 129.7, 121.9, 114.5, 74.1, 66.8, 66.2.
IR: ν = 1803 (CO) cm–1.
4-(Benzyloxymethyl)-1,3-dioxolan-2-one20
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 7.39–7.30 (m,
5 H), 4.85–4.79 (m, 1 H), 4.60 (dd, J = 22.8, 12.0 Hz, 2 H),
4.49 (app. t, J = 8.4 Hz, 1 H), 4.39 (dd, J = 8.4, 6.0 Hz, 1 H),
3.71 (dd, J = 10.8, 3.6 Hz, 1 H), 3.62 (dd, J = 10.8, 3.6 Hz, 1
H). 13C NMR (100 MHz, CDCl3): δ = 154.8 (C=O), 137.0,
128.6, 128.1, 127.7, 74.9, 73.7, 68.8, 66.3. IR: ν = 1790 (CO)
cm–1.
(15) General Procedure for the Cycloaddition Reaction of
Epoxides with CO2
(2-Oxo-1,3-dioxolan-4-yl)methyl Benzoate22
Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 8.02 (d, J = 8.0
Hz, 2 H), 7.60 (t, J = 7.2 Hz, 1 H), 7.47 (t, J = 7.6 Hz, 2 H),
5.09–5.03 (m, 1 H), 4.65–4.57 (m, 2 H), 4.51 (dd, J = 12.8,
4.0 Hz, 1 H), 4.43 (dd, J = 8.4, 5.6 Hz, 1 H). 13C NMR (100
An oven-dried 50 mL of round-bottom flask containing 2
mol% of catalyst 3 (0.149 g, 0.35 mmol), 2 mol% of K2CO3
(0.048 g, 0.35 mmol), and 2 mol% of ZnBr2 (0.079 g, 0.35
mmol) was purged with CO2 under atmosphere pressure
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1343–1348

1348
X. Liu et al.
LETTER
(22) Dibenedetto, A.; Angelini, A.; Aresta, M.; Ethiraj, J.;
Fragale, C.; Nocito, F. Tetrahedron 2011, 67, 1308.
(23) Zn–NHC Complex (3c–ZnCl2)
MHz, CDCl3): δ = 165.9 (C=O), 154.4 (C=O), 133.7, 129.8,
128.6, 128.4, 73.8, 66.0, 63.6. IR: ν = 1793 (CO) cm–1.
(16) (a) Zhou, H.; Wang, Y. M.; Zhang, W. Z.; Qu, J. P.; Lu,
X. B. Green Chem. 2011, 13, 644. (b) Ulusoy, M.; Kilic, A.;
Durgun, M.; Tasci, Z.; Cetinkaya, B. J. Organomet. Chem.
2011, 696, 1372.
(17) Tsutsumi, Y.; Yamakawa, K.; Yoshida, M.; Ema, T.; Sakai,
T. Org. Lett. 2010, 12, 5728.
(18) Huang, J. W.; Shi, M. J. Org. Chem. 2003, 68, 6705.
(19) Sit, W. N.; Ng, S. M.; Kwong, K. Y.; Lau, C. P. J. Org.
Chem. 2005, 70, 8583.
(20) Davies, S. G.; Fletcher, A. M.; Kurosawa, W.; Lee, J. A.;
Poce, G.; Roberts, P. M.; Thomson, J. E.; Williamson, D. M.
J. Org. Chem. 2010, 75, 7745.
1H NMR (400 MHz, CDCl3): δ = 7.28 (t, J = 8.0 Hz, 2 H),
7.08 (d, J = 8.0 Hz, 4 H), 4.81 (s, 4 H), 2.95 (sext, J = 6.8 Hz,
4 H), 1.21 (d, J = 6.8 Hz, 12 H), 1.02 (d, J = 6.8 Hz, 12 H).
13C NMR (100 MHz, CDCl3): δ = 156.6, 146.5, 131.3, 129.4,
124.9, 55.7, 28.9, 25.4, 23.8. Anal. Calcd (%) for
C27H38Cl2N2Zn (526.9 g/mol): C, 61.55; H, 7.27; N, 5.32.
Found: C, 61.41; H, 7.57; N, 5.27.
(24) 1,3-Bis(2,6-diisopropylphenyl)imidazolinium-2-
carboxylate (3–CO2)
1H NMR (400 MHz, CDCl3): δ = 7.48 (t, J = 8.0 Hz, 2 H),
7.28 (d, J = 7.6 Hz, 4 H), 4.88 (s, 4 H), 3.02 (sext, J = 6.8 Hz,
4 H), 1.40 (d, J = 6.8 Hz, 12 H), 1.25 (d, J = 6.8 Hz, 12 H).
IR: ν = 1681 (CO) cm–1.
(21) Jiang, J.-L.; Gao, F.; Hua, R.; Qiu, X.-Q. J. Org. Chem.
2005, 70, 381.
Synlett 2012, 23, 1343–1348
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