Synthesis of oxazolidinones by efficient fixation of atmospheric CO 2 with propargylic amines by using a silver/1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) dual-catalyst system

Article abstract of DOI:10.1002/chem.201203366

This'll fix it: Efficient fixation of atmospheric CO₂ has been achieved by the reaction of propargylic amines with a silver/DBU dual-catalyst system (see scheme). Various oxazolidinones were synthesized in moderate to good yields by using subst

Full text of DOI:10.1002/chem.201203366

DOI: 10.1002/chem.201203366
Synthesis of Oxazolidinones by Efficient Fixation of Atmospheric CO2 with
Propargylic Amines by using a Silver/1,8-Diazabicyclo
(DBU) Dual-Catalyst System
ACHTUNGTREN[NUNG 5.4.0]undec-7-ene
Masahiro Yoshida,* Tomotaka Mizuguchi, and Kozo Shishido[a]
Chemical fixation of CO2 has received much attention be-
reaction conditions. Herein, we report a practical methodol-
ogy for the fixation of atmospheric CO2, in which substitut-
ed oxazolidinones have been efficiently synthesized by con-
cause of the potential use of CO2 as an abundant carbon
source and the variety of organic molecules that can be syn-
thesized by the fixation of CO2.[1] Most of these transforma-
tions require an excess of CO2 and, therefore, large amounts
of CO2 are used annually for chemical synthesis on an indus-
trial scale. On the other hand, the concentration of CO2 in
the atmosphere has been increasing steadily, which is consid-
ered to have an impact on the global climate .[2] The fixation
of atmospheric CO2 thus represents an attractive area of
study in both organic and green chemistry. Various inorganic
and organic compounds, such as metal complexes,[3] N-heter-
ocyclic carbenes,[4] ureas,[5] and diamines,[6] have been utiliz-
ed for the purpose of capturing atmospheric CO2. We have
recently reported a synthesis of oxazolidinone by the 1,8-
ducting the reaction using
system.
a silver/DBU dual-catalyst
The reactions were initially attempted by using N-benzyl-
propargylamine (1a) (Table 1). Substrate 1a was treated
with of PtCl2 (0.5 mol%) and DBU (200 mol%) in DMSO/
Table 1. Optimization of the reaction conditions.
diazabicycloACHTUNGTRENNUNG[5.4.0]undec-7-ene (DBU)-promoted reaction of
a propargylic amine by bubbling air through the reaction
mixture (Scheme 1).[7,8] This result is the first example of the
Entry Catalyst
Solvent
DMSO/H2O[a] 200
DMSO/H2O[a] 200
DBU [mol%] Time [h] Yield [%]
1
2
3
PtCl2
CuI
CuG
240
120
114
24
18
16
17
33
–
69
63
78
86
90
92
95
94
N.R.
8
(OAc)2 DMSO/H2O[a] 200
4
5
6
AgOAc
AgOAc
Ag2O
DMSO/H2O[a] 200
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
200
200
200
10
0
10
7
8
9
10
11[b]
12[c]
AgNO3
AgNO3
AgNO3
none
AgNO3
AgNO3
48
27
20
10
10
95
95
Scheme 1. DBU-promoted fixation of atmospheric CO2. Bn=benzyl,
Bz=benzoyl.
[a] 10:1 ratio of DMSO/H2O was used as the solvent. [b] Reaction in
0.1m solution. [c] Reaction in 0.2m solution. N.R.=no reaction.
fixation of atmospheric CO2 into an organic molecule with
the concomitant formation of a covalent bond. However,
the reaction is an isolated example. Furthermore, a long re-
action time (2 weeks) and an excessive amount of DBU
(10 equiv) were required to complete the reaction on ac-
count of the low concentration of CO2 in air (0.04% v/v). To
increase the utility of this reaction, we investigated various
H2O (10:1) and the stirring was continued vigorously under
air at 608C for 240 h (Table 1, entry 1). The reaction success-
fully ran to completion, affording the desired oxazolidinone,
2a, in 69% yield. Further optimization reactions in which
various transition-metal catalysts (Table 1, entries 2–4) were
applied revealed that the reaction was complete in 24 h,
giving 2a in 86% yield in the presence of AgOAc[8j]
(Table 1, entry 4). A better result was obtained when the re-
action was conducted in DMSO (Table 1, entry 5), and the
yield was increased to 95% when AgNO3 was used as the
catalyst (Table 1, entry 7). Similar reactivity was observed
even in the presence of only 10 mol% DBU (Table 1,
entry 8). On the other hand, no reaction occurred in the ab-
sence of DBU (Table 1, entry 9). Similarly, the yield of 2a
[a] Prof. Dr. M. Yoshida, T. Mizuguchi, Prof. Dr. K. Shishido
Graduate School of Pharmaceutical Sciences
The University of Tokushima
1-78-1 Sho-machi, Tokushima 770-8505 (Japan)
Fax : (+81)88-633-7294
E-mail: yoshi@tokushima-u.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203366.
15578
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Chem. Eur. J. 2012, 18, 15578 – 15581

COMMUNICATION
was dramatically decreased to 8% when AgNO3 was not
added (Table 1, entry 10). These results indicate that, among
the candidates tested, both a silver complex and DBU are
necessary to promote the efficient fixation of atmospheric
CO2. The reaction rate was enhanced by increasing the con-
centration of the reactants in the solvent (Table 1, entries 11
and 12) and the best result was obtained when the reaction
was carried out in a 0.2m solution (Table 1, entry 12).
produce the corresponding products 2c–2 f in good yields
(Table 2, entries 2–5). When the reaction of substrate 1g,
containing a hydroxyethyl group, was conducted, the desired
oxazolidinone 2g was obtained in 33% yield together with
tetrahydrooxazinone 3g in 30% yield (Table 2, entry 6). The
reaction of the TMS-substituted propargylic amine 1h af-
forded the desilylated oxazolidinone 2a in 92% yield
(Table 2, entry 7). Substrates 1i and 1j, containing a siloxy-
and a hydroxymethyl group at the terminal position, were
stereoselectively converted to the oxazolidinones 2i and 2j
in 86 and 66% yields, respectively (Table 2, entries 8 and 9).
When the substrates 1k–1m, containing a methyl, an ethyl,
and a hydroxyethyl group, were subjected to the reaction
conditions, the corresponding products 2k–2m were ob-
tained in moderate yields (Table 2, entries 10–12). In these
Having identified a useful set of reaction conditions, we
subsequently examined reactions by using various propar-
gylic amines 1b–1m (Table 2). The reaction of N-(4-meth-
ACHTUNGTRENNUNGoxyACHTUNGTRENNUNGbenzyl)propargylamine (1b) successfully proceeded to
afford the oxazolidinone 2b in 89% yield (Table 2, entry 1).
The propargylic amines 1c–1 f, having a substituent at the
propargylic position, also reacted with atmospheric CO2 to
Table 2. Fixation of atmospheric CO2 by using various propargylic amines 1b–m.[a]
Entry
Substrate 1
Products
Yields
[%]
Entry
Substrate 1
Products
Yields
[%]
1[b]
89
87
7[b]
92
86
2[c]
8[c]
3[b]
89
78
9[d]
66
73 (2k)
9 (4k)
68 (2l)
14 (4l)
4[d]
10[d]
5[d]
87
11[d]
33 (2g)
30 (3g)
77 (2m)
13 (4m)
6[c]
12[d]
[a] The reactions were carried out in the presence of AgNO3 and DBU in DMSO (0.2m) at 608C. [b] 0.5 mol% AgNO3 and 200 mol% DBU were used.
[c] 0.5 mol% AgNO3 and 10 mol% DBU were used. [d] 2.0 mol% AgNO3 and 200 mol% DBU were used.
Chem. Eur. J. 2012, 18, 15578 – 15581
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M. Yoshida et al.
reactions, the dihydrooxazinones 4k–4m were also produced
as byproducts in low yields.
A plausible mechanism, which may account for the effi-
cient fixation of atmospheric CO2 by this process, is shown
in Scheme 2. Atmospheric CO2 is initially trapped by DBU
to form the DBU–CO2 complex 5 in situ that then reacts
Scheme 3. Attempted reaction of propargylic amine 1a with DBU–CO2
complex 5.
In conclusion, we have developed a methodology for the
synthesis of oxazolidinones by the fixation of atmospheric
CO2 with propargylic amines. Efficient fixation of CO2 has
been achieved by the use of a silver/DBU dual-catalyst
system. The reaction afforded a variety of substituted oxa-
ACHUTNGERNzNUG olAHCTUNGTRNENiUGN dinones in good yields, and the process provided a new
and practical protocol for the utilization of air as a source of
CO2. Further studies regarding this type of reaction and the
synthetic application of the resulting oxazolidinones are
now in progress.
Acknowledgements
This research was conducted as part of the Adaptable & Seamless Tech-
nology Transfer through Target-driven R&D (A-STEP) Program of the
Japan Science and Technology Agency (JST), and the Program for the
Promotion of Basic and Applied Research for Innovations in the Bio-ori-
ented Industry (BRAIN).
Keywords: amines · carbon dioxide fixation · organic bases ·
oxazolidinones · propargylic amines · silver
Scheme 2. Proposed reaction mechanism.
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Oxazolidinones by Efficient Fixation of Atmospheric CO2
COMMUNICATION
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Received: September 20, 2012
Published online: November 7, 2012
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