AgI/TMG-Promoted Cascade Reaction of Propargyl Alcohols, Carbon Dioxide, and 2-Aminoethanols to 2-Oxazolidinones

Article abstract of DOI:10.1002/cphc.201700297

Chemical valorization of CO₂ to access various value-added compounds has been a long-term and challenging objective from the viewpoint of sustainable chemistry. Herein, a one-pot three-component reaction of terminal propargyl alcohols, CO₂, and 2-aminoethanols was developed for the synthesis of 2-oxazolidinones and an equal amount of α-hydroxyl ketones promoted by Ag₂O/TMG (1,1,3,3-tetramethylguanidine) with a TON (turnover number) of up to 1260. By addition of terminal propargyl alcohol, the thermodynamic disadvantage of the conventional 2-aminoethanol/CO₂ coupling was ameliorated. Mechanistic investigations including control experiments, DFT calculation, kinetic and NMR studies suggest that the reaction proceeds through a cascade pathway and TMG could activate propargyl alcohol and 2-aminoethanol through the formation of hydrogen bonds and also activate CO₂.

Full text of DOI:10.1002/cphc.201700297

Accepted Article
Title: Ag(I)/TMG-Promoted Cascade Reaction of Propargyl Alcohols,
Carbon Dioxide, and 2-Aminoethanols to 2-Oxazolidinones
Authors: Xue-Dong Li, Qing-Wen Song, Xian-Dong Lang, Liang-Nian
He, and Yao Chang
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10.1002/cphc.201700297
ChemPhysChem
ARTICLE
Ag(I)/TMG-Promoted Cascade Reaction of Propargyl Alcohols,
Carbon Dioxide, and 2-Aminoethanols to 2-Oxazolidinones
Xue-Dong Li,[a] Qing-Wen Song,[a] Xian-Dong Lang,[a] Yao Chang,[a] and Liang-Nian He*[a,b]
Abstract: Chemical valorization of CO2 to access various value-
added compounds has been a long-term and challenging object from
the viewpoint of sustainable chemistry. Herein, a one-pot three-
component reaction of terminal propargyl alcohols, CO2, and 2-
aminoethanols was developed for the synthesis of 2-oxazolidinones
and equal amount of α-hydroxyl ketones promoted by Ag2O/TMG
(1,1,3,3-tetramethylguanidine) with the TON (turnover number) up to
1260. By addition of terminal propargyl alcohol, thermodynamic
disadvantage of the conventional 2-aminoethanol/CO2 coupling was
ketones simultaneously, which also are of great importance as
synthetic intermediates.[13] Initially the reaction of propargyl
alcohol with CO2 gives α-alkylidene cyclic carbonate
intermediate, which then undertakes a nucleophilic ring-opening
reaction by a 2-aminoalcohol to generate the corresponding β-
oxopropylcarbamate species, followed by further intramolecular
nucleophilic cyclization to afford 2-oxazolidinones and α-
hydroxyl ketones. In addition, propargyl alcohols have been
widely employed to produce valuable compounds such as α-
alkylidene cyclic carbonate,[8c-8f] α-hydroxyl ketone,[13] β-
oxopropylcarbamate[14], 1,3-oxazolidin-2-one[8] and so on. Based
on the aforementioned reports, silver compounds are known as
efficient catalysts for CO2 conversion with various alkynes due to
robust activation ability towards carbon-carbon triple bond.[15]
Particularly, bifunctional basic silver complex bearing Lewis
acidic and Lewis basic sites is reported to efficiently activate
both carbon-carbon triple bond and hydroxyl group.[16] Indeed,
silver compounds in combination with organic bases e.g. DBU
(2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine) or nitrogen-
containing ligands effectively catalyzed the carboxylative
cyclization of propargyl alcohols with CO2.[17] Furthermore, N-
heterocyclic olefins can also be used as an robust
organocatalyst, rendering the reaction proceed under mild
conditions.[8f] Inspired by these precedent reports, we herein
would like to report an effective bifunctional Ag2O/TMG-catalytic
system, which could promote the three-component reaction of
terminal propargyl alcohols, CO2, and 2-aminoethanols/glycols
under mild conditions. Moderate to high yields and excellent
functional group tolerance are also secured. Notably, this
catalytic system showed high efficiency. Besides, mechanistic
ameliorated.
Mechanistic
investigations
including
control
experiments, DFT calculation, kinetic and NMR studies suggest that
the reaction proceeds through a cascade pathway and TMG could
activate propargyl alcohol and 2-aminoethanol through the formation
of hydrogen bonding and also activate CO2.
Introduction
During the past few decades, chemical utilization of CO2 as a
sustainable carbonyl source is of great significance for the
production of chemical products through the formation of C-O/C-
N bond.[1] Among all the CO2-based products, oxazolidinone
motifs have attracted considerable attention which are kind of
heterocyclic compounds and have found widespread
applications as chemical intermediates[2] and chiral auxiliaries[3]
in organic synthesis, and as antibacterial drugs[4] in
pharmaceutical chemistry. Conventional preparation methods of
oxazolidinones involve toxic and gaseous carbonyl reagents
such as phosgene or carbon monoxide.[5] Recently, a series of
processes using CO2 as an alternative to carbon monoxide and
phosgene have been developed,[6] including carboxylative
cyclization of propargyl amines and CO2,[7] coupling reaction of
propargyl alcohols, primary amines with CO2,[8] direct
condensation of amino alcohols with CO2,[9] cycloaddition of
aziridines with CO2.[10]
1
investigations using H NMR, 13C NMR spectra, DFT calculation
disclosed the synergistic effect of between Ag2O and TMG, and
the role of TMG in the activation of CO2, propargyl alcohol and
2-aminoethanol through the formation of hydrogen bonding. This
protocol represents a practical approach for chemical fixation of
CO2 with the utilization of in situ generated silver complex from
readily accessible Ag2O/TMG as a robust and efficient catalytic
species.
Aqueous amino alcohols are usually utilized to absorb CO2 in
carbon capture process. In this aspect, direct condensation of
amino alcohols with CO2 is most promising, which utilizes bulky
commodity and green-house gas to afford valuable products.
However, the thermodynamic limitation in the condensation
reaction of amino alcohols with CO2 represents a major hurdle.
On the other hand, because CO2 is highly stable and difficult to
[9a]
activate,[11] the TON
and TOF (turnover frequency) [9b] of the
reaction are exigently required to improve. To address this issue,
we have recently developed a novel access to 2-oxazolidinones
and α-hydroxyl ketones promoted by Ag2CO3/xantphos as
shown in Scheme 1,[12] along with the formation of α-hydroxyl
Scheme 1. Chemical fixation of CO2 with propargyl alcohols and (a) amines (b)
amino alcohols.
[a] X.-D. Li, Q.-W. Song, X.-D. Lang, Y. Chang, Prof. L.-N. He
State Key Laboratory and Institute of Elemento-Organic Chemistry
College of Chemistry, Nankai University
Tianjin, 300071, P. R. China
Results and Discussion
E-mail: heln@nankai.edu.cn
[b] Prof. L.-N. He
2.1. Optimization of the reaction conditions
Collaborative Innovation Center of Chemical Science and Engineering
Nankai University
Tianjin, 300071, P. R. China.
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10.1002/cphc.201700297
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ARTICLE
We initially launched our study by exploring the simultaneous
synthesis of 3-benzyloxazolidin-2-one (3a) and 3-hydroxy-3-
methylbutan-2-one (4a) from 2-(benzylamino)ethanol (1a), 2-
methylbut-3-yn-2-ol (2a) with CO2 to validate our hypothesis
5
Ag2O(2.5)
Ag2O(2.5)
Ag2O(2.5)
Ag2O(2.5)
Ag2O(2.5)
Ag2O(2.5)
Ag2O(2.5)
Ag2O(5)
Ag2O(5)
Ag2O(5)
Ag2O(5)
Ag2O(5)
-
TMG(10)
DBU(10)
DBN(10)
2,2’-bipy(10)
TMEDA(10)
K2CO3(10)
TBD(10)
TMG(30)
TMG(30)
TMG(30)
TMG(30)
-
30
5
27
5
6
7
23
11
14
5
25
12
11
5
o
under 1 MPa CO2 at 60 C for 12 h as summarized in Table 1
(for detailed optimization results, see Table S1-S3 in Supporting
Information). To begin with, a variety of silver salts such as
Ag2CO3, AgNO3, AgCl, AgOAc and Ag2O were screened in the
presence of TMG (1,1,3,3-tetramethylguanidine) (entries 1-5).
Among them, Ag2O was found to be the best one, and gave
equal amount of 3a and 4a in 30% yield (entry 5). It is also worth
mentioning that, the anion did not have significant influence on
the reaction outcome. To promote the efficiency, several organic
and inorganic bases such as TMG, DBU, DBN (1,5-
8
9
10
11
4
5
12
79
86
96
99
8
78
85
97
99
7
13[d]
14[d,e]
15[d,f]
16[d,f]
17[d,f]
18[d,f]
19[d,f]
20[d,f]
21[d,f]
diazabicyclo[4.3.0]non-5-ene),
2,2’-bipy
(2,2’-bipyridine),
TMEDA (N,N,N',N'-tetramethylethylenediamine), K2CO3 and
TBD (2,3,4,6,7,8-hexaydro-1H-pyrimido[1,2-a]pyrimidine), were
evaluated in the presence of Ag2O (entries 5-11). Obviously,
strong organic base TMG gave the most promising result with
30% yield of 3a (entry 5). The reason could be that the
guanidine may serve as a suitable ligand and meanwhile
stabilize the reactive intermediate i.e. α-alkylidene cyclic
carbonate significantly. In addition, with further modulating the
loading of Ag2O and TMG, the molar ratio of 1a and 2a, and
reaction temperature (entries 12-15), quantitative yields for both
products 3a and 4a were obtained (entry 15). On the other hand,
5 mol% Ag2O or 30 mol% TMG alone exhibited exceedingly low
activity under the given conditions (entries 16, 17). Further effect
of the molar ratio of Ag2O/TMG on the reaction outcome (entries
15, 18-19 vs 20), indicating the in situ formed silver complex with
1:2 molar ratio of Ag2O/TMG as the active catalytic species. In
comparison, Ag2CO3 was found to be less effective than Ag2O
(entry 21 vs. 15).
TMG(30)
TMG(20)
TMG(10)
TMG(10)
TMG(30)
33
87
78
14
83
34
91
76
11
83
Ag2O(5)
Ag2O(5)
-
Ag2CO3(5)
[a] Reaction conditions: 2-(benzylamino)ethanol 1a (75.6 mg, 0.5 mmol), 2-
methylbut-3-yn-2-ol 2a (42.1 mg, 0.5 mmol, 1.0 equiv.), [Ag] (5 mol%), base
(10 mol%), CH3CN (1 mL), CO2 1 MPa, 60 oC, 12 h. [b] Determined by 1H
NMR with 1,1,2,2-tetrachloroethane as the internal standard. [c] 4a yield
based on 1a. [d] 80 oC. [e] 2a (0.75 mmol, 1.5 equiv.). [f] 2a (1.0 mmol, 2.0
equiv.).
To further validate the efficaciousness of this three-
component reaction, gram-scale and TON experiments were
performed as depicted in Scheme 2. As a result, 1a was almost
quantitatively -transformed to the product 3a (Scheme 2a).
Further improving the amount of 1a (4 mmol to 60 mmol), a high
TON up to 1260 was obtained (Scheme 2b).
Table 1. Optimization of the reaction conditions.[a,b]
Scheme 2. Evaluation of the catalyst activity (a) gram-scale experiment, (b)
TON experiment.[18]
Entry
Catalyst (mol%)
Base
(mol%)
3a
(%)
Yield
4a Yield[c]
(%)
2.2. Substrate scope
With the established protocol in hand, we next explored the
substrate scope. As shown in Table 2, the reaction of a wide
range of aromatic 2-aminoalcohols proceeded well (Table 2,
entries 1-4). The benzyl-substituted substrate with strong
electron-withdrawing nitro group 1e showed reduced reactivity
(entry 5), perhaps because the electron-withdrawing group
weakens the nucleophilicity of the NH group.8c,8d Interestingly,
1
2
3
4
Ag2CO3(2.5)
AgNO3(5)
AgCl(5)
TMG(10)
TMG(10)
TMG(10)
TMG(10)
23
24
28
27
23
22
29
27
AgOAc(5)
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10.1002/cphc.201700297
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ARTICLE
bis(2-ethanolamine) 1g with dual functional group was
successfully transformed into the corresponding functionalized
2-oxazolidinone derivative in excellent yield (entry 7). To our
delight, glycols (1h-1j), instead of amino alcohols, were also
effective to afford cyclic carbonates in high yields (3h-3j) (entries
8-10). In addition, propargyl alcohols with alkyl or phenyl
substituents at the propargylic position (2b-2d) were
demonstrated to be credible substrates to give the
corresponding 2-oxazolidinone 3a and α-hydroxyl ketones (4b-
4d) in moderate to good yields (entries 11-13). To our surprise,
for ethisterone (2e), a natural product containing propargyl
alcohol motifs, Ag2O/TMG system was still effective to produce
the corresponding α-hydroxyl ketone (4e) in 63% yield with no
interference to the chiral and other functional groups (entry 14).
This result suggested this catalytic protocol would be a credible
and practical method for the synthesis of complicated
oxazolidinones which have potential application in drug
discovery.
8
9
95
58
97
57
4a
4a
3h
3i
10
11
94
98
3j
4a
4b
93(91)[c]
82(78)[c]
3a
3a
12
13
14
99
70
61
99
65
63
Table 2. Substrate scope.[a,b]
4c
4d
3a
3a
Entry
1
Product 3
Product 4
3 Yield/%
4 Yield/%
99
99
4a
3a
4e
2
3
89
85
89
82
[a] Reactions were carried out with 0.5 mmol 2-aminoalcohol 1, 1.0 mmol
propargyl alcohol 2, Ag2O (5.8 mg, 5 mol%), TMG (17.6 mg, 30 mol%) under
1.0 MPa CO2 at 80 oC in CH3CN (1.0 mL) for 12 h. [b] Determined by 1H
NMR analysis by using 1,1,2,2-tetrachloroethane as an internal standard. [c]
Isolated yield.
4a
4a
3b
2.3 Mechanistic studies
To understand the mechanism of this three-component reaction,
a series of control experiments were carried out as shown in
Scheme 3 and Scheme 4. Firstly, propargyl alcohol 2a reacted
with CO2 under the optimal conditions to produce 4,4-dimethyl-5-
methylene-1,3-dioxolan-2-one (5a) in 62% yield (Scheme 3a). In
this step, TMG is indispensable to the carboxylative cyclization
(Scheme 3b, 3c vs 3a). The formation of 5a requires a base to
activate the hydroxyl of 2a in order to enhance the
nucleophilicity of oxygen atom to promote the carboxylative
cyclization between 2a and CO2. While in the present system,
the alkalinity of Ag2O is too weak to activate hydroxyl. To
investigate this interaction, 1H NMR study was conducted as
shown in Figure 1. After the addition of TMG, the signal of
hydroxyl at δ = 3.44 ppm disappeared, which indicates the
hydroxyl is activated by TMG. As reported, TMG is able to
activate CO2.[19] Further 13C NMR study indicated the effect of
Ag2O (Figure 2). As a result, Ag2O alone could not active 2a
since no change could be observed between Figure 2b and 2a.
However, after the addition of TMG, the peaks of the C-C triple
bond in 2a shifted obviously, which indicated the activation of
triple bond by [Ag][12] and a possible complex formed by Ag2O
3c
3d
4
5
82
24
80
23
4a
4a
3e
6
7
99
93
99
92
4a
4a
3f
3g
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10.1002/cphc.201700297
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ARTICLE
and TMG (Figure 2c). Upon the activation of Ag2O and TMG, the
carboxylative cyclization of propargyl alcohol with CO2 gave 5a.
Then, 5a reacted with 1.0 equivalent of 2-aminoalcohol 1a under
the standard conditions and almost equal amount of 3a and 4a
was obtained (Scheme 4a). These results suggested that α-
alkylidene cyclic carbonate is the intermediate, being well in
agreement with previous study.[12] TMG is also essential to the
intramolecular cyclization step (Scheme 4b, 4c vs 4a) to activate
the hydroxyl of 2-aminoethanol, which could be beneficial for the
intramolecular cyclization between 2-aminoethanol and α-
alkylidene cyclic carbonate 5a.
Figure 1. 1H NMR (400 MHz, CD3CN) spectra (a) 2-methylbut-3-yn-2-ol (2a)
(b) TMG (c) the mixture of 2a (24.0 mg, 0.3 mmol) and TMG (34.5 mg, 0.3
mmol).
Scheme 3. The control experiments between propargyl alcohol and CO2.
Standard conditions: 2-methylbut-3-yn-2-ol 2a (84.1 g, 1 mmol), Ag2O (5.8 mg,
2.5 mol%), TMG (17.6 mg, 15 mol%), CH3CN (1 mL), CO2 1 MPa, 80 oC, 12 h.
Figure 2. 13C NMR (100.6 MHz, CDCl3) spectra (a) 2-methylbut-3-yn-2-ol (2a)
(b) the mixture of 2a (24.0 mg, 0.3 mmol) and Ag2O (0.23 g, 0.1 mmol) (c) the
mixture of 2a (24.0 mg, 0.3 mmol), Ag2O (23.1 mg, 0.1 mmol) and TMG (11.5
mg, 0.1 mmol).
To gain further insight into the reaction pathway, the kinetic
study was conducted as depicted in Figure 3. During the whole
process, almost equal amount of 3a and 4a were obtained, while
5a was not detected. It is easy to be inferred that the rate of the
intramolecular cyclization step in Scheme 4a is much faster than
the carboxylative cyclization step in Scheme 3a, and the
carboxylative cyclization of propargyl alcohol with CO2 is the
rate-determining step in this study.
Scheme 4. The control experiments between α-alkylidene cyclic carbonate
and 2-aminoethanol. Standard conditions: 2-(benzylamino)ethanol 1a (75.6
mg, 0.5 mmol), 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one 5a (64.1 mg, 0.5
mmol), Ag2O (5.8 mg, 5 mol%), TMG (17.6 mg, 30 mol%), CH3CN (1 mL), 80
oC, 12 h.
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10.1002/cphc.201700297
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ARTICLE
Figure 3. Kinetic curves of the three-component cascade reaction of 2-
methylbut-3-yn-2-ol (2a), CO2, and 2-(benzylamino)ethanol (1a) to prepare 3-
benzyloxazolidin-2-one (3a) and 3-hydroxy-3-methylbutan-2-one (4a).
Reaction conditions: 2-(benzylamino)ethanol 1a (75.6 mg, 0.5 mmol), 2-
methylbut-3-yn-2-ol 2a (84.1 mg, 1.0 mmol, 2.0 equiv.), Ag2O (5.8 mg, 5
mol%), TMG (17.6 mg, 30 mol%), CO2 (1.0 MPa), 80 oC in CH3CN (1.0 mL).
Figure 4. 1H NMR (400 MHz, CD3CN) spectra (a) TMG (b) the reaction
between Ag2O (0.23 g, 1 mmol) and TMG (0.12 g, 1 mmol) in CH3CN (1 mL)
at 80 oC for 12 h.
To investigate the interaction between Ag2O and TMG, NMR
study was run as shown in Figure 4 and Figure 5. It could be
1
found in the H NMR spectra that the signal of methyl in TMG
shifted to 2.74 ppm from 2.65 ppm (Figure 4), indicating possible
interaction between Ag2O and TMG. There are two kinds of
methyl in the 13C NMR study (Figure 5), suggesting a possible
interaction between Ag2O and TMG in Scheme 5, being in
accordance with the experimental results in Table 1 and
previous reports.[20] To further study the interaction between
Ag2O and TMG, quantum chemical calculations were performed
using the program Gaussian 09.[21] The thermodynamic
calculation showed that favorable formation of a complex with a
1:1 molar ratio of Ag to TMG as shown in Scheme 5. The results
of Mulliken atomic charges suggested that the carbon atoms (Ca,
Cb in Scheme 5) of methyl in TMG are inequivalent (for detail
result, see the supporting information). Furthermore, 3a and 4a
were obtained in 89% yield from the reaction with freshly-
prepared clear solution of equal mole of Ag2O and TMG in
CH3CN as a catalyst, also demonstrating the homogeneous
nature of the reaction.
Figure 5. 13C NMR (100.6 MHz, CDCl3) spectra (a) TMG (b) the reaction
between Ag2O (0.23 g, 1 mmol) and TMG (0.12 g, 1 mmol) in CH3CN (1 mL)
at 80 oC for 12 h.
On the basis of the control experiments, NMR studies, kinetic
curves, DFT calculation and published results,[8,12,13] a plausible
mechanism for the silver-promoted three-component reaction is
proposed as shown in Scheme 6. The carboxylative cyclization
of propargyl alcohol with CO2 initially gives the α-alkylidene
cyclic carbonate as an intermediate catalyzed by the complex
shown in Scheme 5. The complex formed with 1:1 molar ratio of
Ag(I)/TMG could activate the triple bond of propargyl alcohol,
while the free TMG could activate the hydroxyl through hydrogen
bonding and activate CO2 too. Then, α-alkylidene cyclic
Scheme 5. Possible complex formed from Ag2O and TMG.
carbonate undertakes
a
nucleophilic addition by
a
2-
aminoalcohol to form the corresponding β-oxopropylcarbamate
species.[12] An intramolecular cyclization affords the 2-
oxazolidinone and α-hydroxyl ketone, and regenerates the
catalyst, upon the activation of carbonyl by Ag(I)/TMG complex
and hydroxyl by and TMG.
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10.1002/cphc.201700297
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ARTICLE
extracted with CH2Cl2 (3 × 20 mL), washed with water (20.0 mL), and
dried with Na2SO4. The CH2Cl2 solution was concentrated under vacuum
and the residue was purified by column chromatography on silica gel
using petroleum ether/ethyl acetate (v/v, 10:1-1:2) as eluent to give the
desired products.
General procedure for the synthesis of 2-oxazolidinones and α-
hydroxyl ketones
The reactions were conducted in a 25-mL oven-dried autoclave with a
glass tube inside equipped with magnetic stirring. Ag2O (5.8 mg, 5 mol%),
TMG (17.6 mg, 30 mol%), propargylic alcohols (1.0 mmol), 2-
aminoethanols (0.5 mmol), CH3CN (1.0 mL), and CO2 (1 MPa) were
successively introduced and heated at 80 °C for 12 h. When the reaction
completed, the vessel was cooled with an ice-bath, and the pressure was
released slowly to atmospheric pressure. The residue was flushed with
2×3 mL CH2Cl2 and purified by column chromatography on silica gel (n-
butylamine saturation) using petroleum ether/ethyl acetate (v/v, 50:1-1:1)
as eluent to give the desired products.
Scheme 6. Plausible mechanism.
Conclusions
In summary, we have developed an alternative synthetic
strategy for the synthesis of 2-oxazolidinones through the
Ag2O/TMG-catalyzed three-component cascade reaction of
propargyl alcohols, CO2, and 2-aminoethanols under mild
reaction conditions. A wide range of propargyl alcohols and 2-
aminoethanols, even complicated molecules (e.g. natural
product ethisterone), are suitable for the catalytic system
affording various 2-oxazolidinones and α-hydroxyl ketones in
excellent yield and selectivity. Based on control experiments,
NMR studies, kinetic curve and DFT calculation, we found TMG
as strong organic base is able to activate hydroxyl of propargyl
alcohols and 2-aminoethanols through hydrogen bonding, and
also synergistic effect of between Ag2O and TMG. This method
is efficient with the TON up to 1260, and especially productive
with valuable products featuring with high atom-economy.
Acknowledgements
This work was financially supported by National Key Research
and Development Program (2016YFA0602900), National
Natural Science Foundation of China (21472103, 21421001,
21421062, 21672119), the Natural Science Foundation of
Tianjin Municipality (16JCZDJC39900), Specialized Research
Fund for the Doctoral Program of Higher Education (project
20130031110013), and MOE Innovation Team (IRT13022) of
China.
Keywords: carbon dioxide chemistry • C1 building blocks •
cyclization • homogeneous catalysis • synthetic methods
Experimental Section
[1]
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J. Katz, S. C. Bergmeier, Tetrahedron Lett. 2002, 43, 557-559.
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General analytic methods. 1H NMR spectra was recorded on 400 MHz
spectrometers using CDCl3, CD3CN or DMSO-d6 as solvent referenced
to CDCl3 (7.26 ppm), CD3CN (1.96 ppm) or DMSO-d6 (2.50 ppm). 13C
NMR was recorded at 100.6 MHz in CDCl3 (77.00 ppm) or DMSO-d6
(39.52 ppm). Multiplets were assigned as singlet, doublet, triplet, doublet
of doublet, multiplet and broad singlet. Mass spectra were recorded on a
Shimadzu GCMS-QP2010 equipped with a RTX-5MS capillary column at
an ionization voltage of 70 eV. The data are given as mass units per
charge (m/z). High resolution mass spectrometry was conducted using a
Varian 7.0 T FTICR-MS by ESI technique.
[2]
[3]
[4]
[5]
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Materials. Unless otherwise noted, carbon dioxide (99.99%),
commercially available propargyl alcohols. All starting materials were
obtained from Aladdin or Alfa Aesar and used as received. All reactions
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General procedure for the synthesis of 2-aminoethanol derivatives
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[18] a) Reaction conditions: 2-(benzylamino)ethanol 1a (0.60 g, 4 mmol), 2-
methylbut-3-yn-2-ol 2a (0.64 g, 8 mmol), Ag2O (2.3 mg, 0.01 mmol),
TMG (6.9 mg, 0.06 mmol), CH3CN (1 mL), CO2 2 MPa, 80 oC, 24 h; b)
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methylbut-3-yn-2-ol 2a (9.7 g, 120 mmol), Ag2O (2.3 mg, 0.01 mmol),
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Layout 2:
ARTICLE
Xue-Dong Li, Qing-Wen Song, Xian-
Dong Lang, Yao Chang, and Liang-Nian
He*
Page No. – Page No.
Ag(I)/TMG-Promoted Cascade
Reaction of Propargyl Alcohols,
Carbon Dioxide, and 2-
An Ag2O/TMG -promoted substrate-driven and divergent route leads to a variety of
heterocycles from propargyl alcohols, CO2, and 2-aminoethanols with the TON up
to 1260. The reaction proceeds through a cascade pathway with α-alkylidene cyclic
carbonate as the intermediate and TMG could activate propargyl alcohol and 2-
aminoethanol through the formation of hydrogen bonding.
Aminoethanols to 2-Oxazolidinones
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