Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by MgCl2

Article abstract of DOI:10.1246/cl.170252

Magnesium chloride (MgCl₂), a stable and cheap salt, works as an active catalyst for the synthesis of cyclic carbonates from epoxides and atmospheric-pressure carbon dioxide (CO₂). Various epoxides are converted to the corresponding cyclic carbonates in good to high yields.

Full text of DOI:10.1246/cl.170252

Advance Publication Cover Page
Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide Catalyzed by MgCl
2
Tetsuaki Fujihara,* Masaki Inokuchi, Taiga Mizoe, Keisuke Nogi, Jun Terao, and Yasushi Tsuji*
Advance Publication on the web April 15, 2017
doi:10.1246/cl.170252
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2017 The Chemical Society of Japan
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1
Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide Catalyzed by MgCl
2
†
‡
Tetsuaki Fujihara,* Masaki Inokuchi, Taiga Mizoe, Keisuke Nogi, Jun Terao and Yasushi Tsuji*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University
Nishikyo-ku, Kyoto 615-8510
E-mail: tfuji@scl.kyoto-u.c.jp, ytsuji@scl.kyoto-u.ac.jp
2
Magnesium chloride (MgCl ), a stable and cheap salt,
Table 1. Optimization of Reaction Conditions for MgCl
catalyzed Synthesis of Cyclic Carbonate from 1a and CO .
2
2
-
works as an active catalyst for synthesis of cyclic carbonates
from epoxides and an atmospheric pressure of carbon
a
2
dioxide (CO ). Various epoxides are converted to the
corresponding cyclic carbonates in good to high yields.
b
Entry
1
Catalyst
Solvent
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DMA
NMP
Yield of 2a (%)
Carbon dioxide (CO
2
) is abundant, non-toxic, and easily
available C1 source. Therefore, an efficient catalyst is
indispensable for conversion of CO into useful products.
Recently, we developed C-C bond forming reactions with
c
1
MgCl
2
2
90 (91)
d
2
MgCl
71
88
0
2
3
4
5
6
7
8
9
MgBr
2
2
CO
2
in the presence of a transition-metal catalyst. For CO
are also
important. Among them, carboxylation of epoxides with
2
MgF
2
fixation, C-O bond forming reactions with CO
2
3
Mg(OTf)2
LiBr
trace
65
21
9
3
2
CO is a straightforward method to afford cyclic carbonates
as well as polycarbonates.
4
Bu
AlCl
ZnCl
4
NBr
Regarding a catalyst for the synthesis of cyclic
3
3
carbonate with CO
2
, in 1993 Endo and co-workers found
5
that simple inorganic salts such as LiBr were active. More
recently, metal complexes catalysts with various ligands
were developed to improve catalytic activity and selectivity.
Namely, Ema and co-workers synthesized elaborated
bifunctional metalloporphyrin catalysts showing very high
2
65
71
0
1
1
1
0
1
2
ZnBr
2
none
MgCl
MgCl2
MgCl
2
90
86
78
6
turnover number frequency (TOF). Kleij designed active Al
13
7
catalysts bearing a suitable tetradentate ligand. Jamison
1
4
2
reported bromine catalyzed cyclic carbonates synthesis with
8
a
CO
2
by using a flow reaction system.
Reaction conditions: 1,2-epoxydecane (1a, 0.50 mmol), catalyst (0.025
mmol, 5.0 mol %) in DMF (0.50 mL) at 100 °C for 18 h under CO (1
2
In the present study, we found that MgCl is highly
2
b
atm). Determined by GC analysis using an internal standard method.
active catalyst among simple inorganic salts to catalyze the
carboxylation of epoxides using CO . Shim and co-workers
reported that a combination of MgBr and phosphines
alone did not show
c
d
Isolated yield with 2.0 mmol scale. MgCl
2
(30 mol %) at 25 °C for 72
2
h.
2
9
showed good reactivity, while MgBr
any catalytic activity.
2
Under the optimum reaction conditions, various
epoxides (1: 2.0 mmol) afforded the corresponding cyclic
carbonates (2) (Table 2). In the reactions, all the substrates
were fully consumed. With 1b, the corresponding product
(2b) was isolated in 93% yield (entry 1). Epoxides bearing
butoxy (1c), benzyloxy (1d), and phenoxy (1e) substituents
gave 2c, 2d, and 2e in good to high yields (entries 2-4). A
bromo functionality on an aromatic ring was tolerated in the
reaction (entry 5). An alkenyl (1g) and alkynyl (1h) moieties
were intact, giving the corresponding 2g and 2h in good
yields (entries 6 and 7). Styrene oxide derivatives (1i and 1j)
also provided 2i and 2j in good yields (entries 8 and 9). A
substrate with an acrylate moiety (1k) afforded the product
(2k) at 40 °C for 5 h. Besides mono-substituted epoxides,
cyclohexene oxide (1l) gave the corresponding carbonate (2l)
in moderate yield with 10 mol % catalyst loading after 72 h
(entry 11).
First, the reaction of 1,2-epoxydecane (1a) was carried
out with 5.0 mol % of MgCl in DMF at 100 °C under an
atmospheric pressure of CO (Table 1). Under the reaction
2
2
conditions, the corresponding cyclic carbonate (2a) was
obtained in 90% GC yield (entry 1). Employing 2.0 mmol of
1
a, 2a was isolated in 91% yield. With 30 mol % of MgCl
the reaction proceeded even at 25 °C, affording 2a in 71%
yield after 72 h (entry 2). As for a catalyst, MgBr was also
effective, giving 2a in 88% yield (entry 3), while MgF and
Mg(OTf) were not efficient at all (entries 4 and 5). Other
salts such as LiBr, Bu
2
,
2
2
2
5
a
5a
4
3 2 2
NBr, AlCl , ZnCl and ZnBr
afforded 2a in moderate yields (entries 6–10). Without a
catalyst, the reaction did not proceed at all (entry 11).
Regarding the solvent, dimethylsulfoxide (DMSO), N,N-
dimethylacetamide (DMA), and N-methylpyrolidone (NMP)
provided 2a in good yields (entries 12–14).

2
Table 2. Scope of Substratesa
Entry
1
Product 2
Isolated Yield (%)
93
2
b
2
85
72
78
2
c
b
3
2
d
4
2
e
Scheme 1. A possible reaction mechanism
This work was supported by a Grant-in-Aid for Young
Scientists (A) (No. 25708017) from JSPS, Japan.
b
5
65
2
f
Supporting
Information
is
available
on
6
7
86
70
http://dx.doi.org/10.1246/cl.******.
2
g
References and Notes
†
Present address: Department of Chemistry, Graduate School of
Science, Kyoto University, Kyoto 606-8502
Present address: Department of Basic Science, Graduate School
2
h
‡
of Art and Sciences, The University of Tokyo, Tokyo 153-8902.
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Carbon Dioxide, ed. By S. L. Suib, Elsevier: Amsterdam, 2013. b)
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Angelini, Chem. Rev. 2014, 114, 1709–1742.
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i
b
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016, 138, 5547–5550. b) Y. Tani, T. Fujihara, J. Terao, Y. Tsuji,
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c
1
0
1
64
53
3
4
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1
2
k
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l
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a
Reaction conditions: epoxide (1, 2.0 mmol), MgCl
2
(0.10 mmol, 5.0
(1 atm).
Reaction was carried out with 0.50 mmol scale. Substrate 0.50 mmol
Chem. Rev. 2010, 110, 4554–4581.
mol %), in DMF (2.0 mL), at 100 °C, for 18 h, under CO
2
a) C.-Y. Yu, H.-J. Chuang, B.-T. Ko, Catal. Sci. Technol, 2016, 6,
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b
c
d
scale, MgCl
2
(0.050 mmol, 10 mol%), at 40 °C, for 5 h. 1l (0.50 mmol),
MgCl (0.050 mmol, 10 mol%), in DMF (0.50 mL) at 100 °C, 72 h.
2
A possible catalytic cycle is shown in Scheme 1. First,
epoxide 1 is activated by the coordination of MgCl to form
A (step 1). Then, the chloro anion attacks a sterically less
hindered site of A, generating B (step 2). The reaction of
CO
carbonate 2 via D and MgCl
In conclusion, we found that MgCl
cheap and easy-to-handle reagent, catalyzed the reaction of
epoxides with CO . The reaction afforded various cyclic
carbonates in good to high yields under an atmospheric
pressure of CO
2
5
6
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2
with B provides C (step 3). Finally, C affords cyclic
is regenerated (steps 4 and 5).
, a stable, abundant,
2
1
34–138.
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