Silver-catalyzed activation of internal propargylic alcohols in supercritical carbon dioxide: efficient and eco-friendly synthesis of 4-alkylidene-1,3-oxazolidin-2-ones

Article abstract of DOI:10.1016/j.tetlet.2008.10.078

The silver-catalyzed cycloaddition reactions of carbon dioxide with internal propargylic alcohols and primary amines under supercritical conditions give 4-alkylene-1,3-oxazolidin-2-ones in good to excellent yields. The optimized conditions are to use an a

Full text of DOI:10.1016/j.tetlet.2008.10.078

Tetrahedron Letters 50 (2009) 60–62
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Silver-catalyzed activation of internal propargylic alcohols
in supercritical carbon dioxide: efficient and eco-friendly
synthesis of 4-alkylidene-1,3-oxazolidin-2-ones
*
Huan-Feng Jiang , Jin-Wu Zhao
School of Chemistry and Chemical Engineering, South China University of Technology, 381 Wushan Road, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The silver-catalyzed cycloaddition reactions of carbon dioxide with internal propargylic alcohols and pri-
mary amines under supercritical conditions give 4-alkylene-1,3-oxazolidin-2-ones in good to excellent
yields. The optimized conditions are to use an alcohol (2 mmol), an amine (2 mmol), silver acetate
(0.1 mmol), and carbon dioxide (8 MPa) at 120 °C.
Received 17 May 2008
Revised 16 October 2008
Accepted 17 October 2008
Available online 22 October 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Carbon dioxide is a major greenhouse gas, and a great deal of
carbon dioxide has been ceaselessly emitted into atmosphere from
burning fossil fuel. The issue on recycling or removing CO2 from
industrial emissions has attracted increased attentions. On the
other hand, carbon dioxide is an abundant, cheap, and nontoxic
biorenewable resource, could potentially be an attractive raw
material to replace toxic chemicals such as phosgene, isocyanates,
or CO.1
different reaction conditions, and the results are summarized in
Table 1. CuI did not catalyze the reaction of internal propargylic
O
R1
scCO2/AgOAc
O
NR
R3
OH
+
RNH2
8MPa, 120°C
R2
R1
R2
R3
Oxazolidinones are useful heterocyclic compounds in organic
synthesis. They have a wide range of applications in asymmetric
syntheses as chiral synthons or chiral auxiliaries,2 and in medicinal
1
2
3
1
2
3
1a: R = n-Bu, R = Et, R = Ph
2a: R = n-Bu
2b: R = s-Bu
2c: R = Allyl
2d: R = Cy
1
1
2
2
3
3
1b: R , R =-C H -, R = Ph
5
10
10
chemistry because of their good antibacterial properties.2a,3
A
1c: R , R = -C H -, R = Me
5
1
1
2
2
3
3
1d: R = H, R = H, R = Ph
number of procedures to synthesize 4-methylene-1,3-oxazolidin-
2-ones have been developed, while few processes to produce 4-
substituted methylene ones have been reported.4,5 Schmalz et al.
reported that 4-alkylidene-1,3-oxazolidin-2-ones were prepared
from o-propargyl carbamates under catalysis of AuCl in MeCN,6
and Chandrasekaran’s group disclosed that o-propargyl carba-
mates were transformed into 4-alkylidene-1,3-oxazolidin-2-ones
catalyzed by base in DMF.7 However, the employed o-propargyl
carbamates are very expensive and not easily available, and vola-
tile organic chemicals (VOCs) are used. It was reported that termi-
nal propargylic alcohols smoothly reacted with carbon dioxide to
produce 4-methylene-1,3-oxazolidin-2-ones.5 However, the cyclo-
addition of internal propargylic alcohols with CO2 and amine has
not been reported. Recently, we found that internal propargylic
alcohols could be activated to form oxazolidinones in the presence
of silver salts in supercritical carbon dioxide (Scheme 1).
2e: R = n-C H
6
13
1e: R = H, R = H, R = Me
1f: R = H, R = Me, R = Ph
1g: R = H, R = Et, R = Et
1
1
2
2
3
3
Scheme 1. Cycloaddition reaction of internal propargylic alcohols with primary
amines in scCO2.
Table 1
Optimizing the reaction conditions for the cycloaddition of internal propargylic
a
alcohols with amines in scCO2
Entry
Catalyst
Temperature (°C)
Pressure (MPa)
Yieldb (%)
1
2
3
4
5
6
7
8
9
CuI
140
140
140
140
140
120
100
120
120
120
12
12
12
12
12
12
12
10
8
0
CuI/CNT
AgBF4
AgOAc
Ag2CO3
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
49
94
93
93
92
79
97
98
51
We first examined the cycloaddition reaction of 3-ethyl-1-
phenyl-1-heptyn-3-ol (1a) and n-butylamine (2a) in scCO2 under
10
6
a
Reaction conditions: 1a (2 mmol), 2a (2 mmol), cat. (0.1 mmol), 24 h.
Determined by GC analysis.
* Corresponding author. Tel.: +86 20 22236518; fax: +86 20 87112906.
E-mail address: jianghf@scut.edu.cn (H.-F. Jiang).
b
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.10.078

H.-F. Jiang, J.-W. Zhao / Tetrahedron Letters 50 (2009) 60–62
61
Table 2
alcohols with carbon dioxide and primary amine, which differed
from that of terminal propargylic alcohols (Table 1, entry 1).5a Even
though CuI was supported on carbon nanotube, it did not drive the
reaction satisfactorily (entry 2). When AgBF4 was added in the
reaction system, it was exciting that 4-benzylidene-3,5-dibutyl-
5-ethyloxazolidin-2-one (3a) was obtained in 94% yield (entry 3).
The further experiments showed that the counter ion of the silver
salt had little effect on the reaction (entries 4, 5). When the tem-
perature was reduced from 120 to 100 °C, the yield diminished
from 92% to 79% (entries 6, 7). The pressure of 8 MPa might be
the most suitable one as the highest yield was achieved (98%)
(entries 6, 8–10). Therefore, the best reaction conditions were 3-
ethyl-1-phenyl-1-heptyn-3-ol (2 mmol), n-butylamine (2 mmol),
and silver acetate (0.1 mmol); CO2 pressure, 8 MPa; temperature,
120 °C; time, 24 h.
Silver acetate-catalyzed cycloaddition reaction of internal propargylic alcohols with
primary amines in scCO2
a
O
R1
scCO2/AgOAc
O
NR
R3
OH
+
RNH2
8 MPa, 120 o
C
R2
R1
R3
R2
1
2
3
Entry
1
Alcohol
Amine
Product
Z:Eb
Yieldc (%)
O
O
N
1a
2a
50:50
50:50
55:45
95
Et
n-Bu
Ph
3a
As seen in Table 2, a series of primary amines such as n-butyl-
amine (2a), s-butylamine (2b), allylamine (2c), cyclohexylamine
(2d), and n-hexylamine (2e) were employed to go across the cyclo-
addition reaction with 3-ethyl-1-phenylhept-1-yn-3-ol (1a) in
scCO2, and the corresponding 4-alkylidene-1,3-oxazolidin-2-ones
were obtained in 95%, 93%, 90%, 85%, and 97% isolated yields,
respectively (Table 2, entries 1–5).8 Then, various internal pro-
pargylic alcohols were chosen to react with n-butylamine (2a)
in scCO2. 1-(Phenylethynyl)cyclohexanol (1b) and 1-(prop-1-
ynyl)cyclohexanol (1c) proceeded smoothly to give the desired
products in 96% and 91% yields (entries 6, 7). It was noteworthy
that primary internal propargylic alcohol 3-phenylprop-2-yn-1-ol
(1d) and secondary internal propargylic alcohol 4-phenylbut-3-
yn-2-ol (1f) could smoothly react to produce 4-alkylidene-1,3-
oxazolidin-2-ones in 73% and 80% yields (entries 8, 10). These
results did not coincide with those in our previous work.4a We con-
sidered that these products with exocyclic double bonds other than
endocyclic ones were formed because the newly formed double
bonds could conjugate with benzene rings. However, internal
O
O
N
2
3
1a
1a
2b
2c
93
90
Et
n-Bu
Ph
Ph
3b
O
O
N
Et
n-Bu
3c
O
O
N
4
1a
2d
55:45
85
Et
n-Bu
Ph
3d
O
O
N
propargylic alcohols with
a
-hydrogen whose R3 was alkyl, such
5
6
7
1a
1b
1c
2e
2a
2a
50:50
55:45
90:10
97
96
91
Et
as but-2-yn-1-ol (1e) and hept-4-yn-3-ol (1g), did not undergo
the cycloaddition reaction (entries 9, 11).
n-Bu
Ph
Ph
3e
In comparison with terminal propargylic alcohols,4a,9 internal
propargylic ones needed more active catalyst, such as silver ace-
tate, and higher reaction temperature. This indicated that the
internal propargylic alcohols were less reactive than terminal ones.
A proposed mechanism for the cycloaddition of internal propargy-
lic alcohols with amines in scCO2 is shown in Scheme 2. Ag salt
could promote the cycloaddition reaction of inert internal propar-
O
O
N
3f
O
O
N
gylic alcohol and CO2 to form
a-alkylene cyclic carbonate 5. The
nucleophilic addition of primary amine to 5 could afford 2-
oxoalkylcarbamate 6. 4-Hydroxy cyclic carbamate 7, a reaction
3g
O
O
N
R3
R3
8
9
1d
1e
2a
2a
70:30
—
73
0d
NH3R
R1
R2
-RNH2
-Ag
R1
R2
Ag
O
Ph
3h
RNH2
R3
CO2
O
+
OH
O
O
R1
R2
AgOAc
O
No product
1
5
O
O
4
O
N
RNH2
R1
10
1f
2a
2a
80:20
—
80
0e
O
O
Ph
3i
No product
O
O
O
NR
O
NR
OH
R3
11
1g
RHN
O
R3
R1
R2
a
R3
R2
R1
Reagents and conditions: alcohol
(0.1 mmol), Pco2 = 8 MPa, 120 °C.
1 (2 mmol), amine 2 (2 mmol), AgOAc
R2
b
3
7
6
Isolated yield.
Determined by GC.
1e Remained unchanged.
1g Remained unchanged.
c
d
Scheme 2. Proposed mechanism for cycloaddition reaction of internal propargylic
e
alcohols with primary amines.

62
H.-F. Jiang, J.-W. Zhao / Tetrahedron Letters 50 (2009) 60–62
(8), 41 (5). 4-Benzylidene-3-sec-butyl-5-butyl-5-ethyloxazolidin-2-one (3b, Z/E
mixture): IR (KBr,
/cmÀ1): 2968, 2934, 2875, 1760, 1666; 1H NMR (400 MHz,
intermediate formed via the intramolecular cyclization of 6, could
be alternatively eliminated, and Z/E ratio in the products almost
rested with stochastic process.
In conclusion, we have shown that internal propargylic alcohols
can be activated for the cycloaddition reaction with primary
amines and carbon dioxide under supercritical condition catalyzed
by silver salt to afford 4-alkylidene-1,3-oxazolidin-2-ones. Other
efficient chemical fixations of carbon dioxide into useful fine
chemicals are explored in our laboratory.
m
CDCl3) d (ppm): 0.85–0.89 (m, 3H), 0.94–0.99 (m, 6H), 1.36–1.45 (m, 7H), 1.63–
1.69 (m, 6H), 3.42–3.46 (t, J = 7.6 Hz, 1H), [3.91–3.95 (t, J = 7.8 Hz, 1H)], 5.32 (s,
1H), [5.94 (s, 1H)], 7.12–7.18 (m, 3H), 7.25–7.31 (m, 2H); 13C NMR (100 MHz,
CDCl3) d (ppm): 6.3, 10.4, 13.0, 16.0, 21.5, 23.8, 24.9, 31.1, 37.8, 50.6, 86.5, 98.5,
126.1, 127.1, 128.4, 134.3, 139.8, 154.9; MS (EI, 70 eV): m/z (%) = 315 [M+] (32),
259 (100), 244 (22), 224 (21), 202 (32), 180 (25), 145 (8), 117 (15), 91 (16), 57
(8), 41 (5). 3-Allyl-4-benzylidene-5-butyl-5-ethyloxazolidin-2-one (3c, Z/E
mixture): IR (KBr, m
/cmÀ1): 2959, 2931, 2873, 1742, 1673; 1H NMR (400 MHz,
CDCl3) d (ppm): 0.89–0.93 (m, 3H), 0.95–0.98 (m, 3H), 1.34–1.38 (m, 4H), 1.62–
1.70 (m, 3H), 3.93–3.97 (t, J = 7.8 Hz, 2H), 4.59–4.63 (q, J = 5.4 Hz, 1H), 4.89–4.92
(q, J = 5.4 Hz, 1H), 5.29–5.35 (m, 1H), 5.40 (s, 1H), [5.81 (s, 1H)], 7.16–7.22 (m,
3H), 7.25–7.30 (m, 2H); 13C NMR (100 MHz, CDCl3) d (ppm): 6.26, 13.0, 21.7,
24.0, 32.4, 39.1, 44.6, 86.8, 97.2, 116.9, 125.9, 126.9, 128.9, 130.4, 134.0, 138.9,
156.3; MS (EI, 70 eV): m/z (%) = 299 [M+] (34), 243 (100), 228 (22), 208 (16), 186
(8), 164 (14), 131 (8), 116 (15), 91 (12), 57 (15), 41 (12). 4-Benzylidene-5-butyl-3-
cyclohexyl-5-ethyloxazolidin-2-one (3d, Z/E mixture): IR (KBr, v/cmÀ1): 2957,
2931, 2858, 1761, 1665; 1H NMR (400 MHz, CDCl3) d (ppm): 0.83–0.91 (m, 6H),
1.32–1.38 (m, 8H), 1.57–1.85 (m, 10H), 3.15–3.19 (t, J = 7.8 Hz, 1H), [3.62–3.66
(t, J = 7.4 Hz, 1H)], 5.34 (s, 1H), [6.00 (s, 1H)], 7.12–7.19 (m, 3H), 7.25–7.30 (m,
2H); 13C NMR (100 MHz, CDCl3) d (ppm): 6.1, 13.0, 21.5, 23.9, 25.2, 27.6, 31.2,
37.7, 52.9, 86.4, 98.3, 126.1, 127.1, 128.5, 134.3, 139.7, 154.8; MS (EI, 70 eV): m/z
(%) = 341 [M+] (38), 285 (64), 260 (90), 230 (50), 203 (100), 168 (28), 124 (34), 91
(42), 57 (15), 55 (52), 41 (24), 28 (39). 4-Benzylidene-5-butyl-5-ethyl-3-
hexyloxazolidin-2-one (3e, Z/E mixture): IR (KBr, v/cmÀ1): 2958, 2931, 2861,
1767, 1671; 1H NMR (400 MHz, CDCl3) d (ppm): 0.72–0.76 (m, 3H), 0.82–0.89
(m, 6H), 1.30–1.36 (m, 10H), 1.63–1.65 (m, 6H), 3.24–3.29 (t, J = 7.2 Hz, 2H),
[3.50–3.54 (t, J = 7.8 Hz, 2H)], 5.32 (s, 1H), [5.94 (s, 1H)], 7.12–7.17 (m, 3H),
7.23–7.31 (m, 2H); 13C NMR (100 MHz, CDCl3) d (ppm): 7.1, 13.9, 22.5, 24.9,
26.1, 26.5, 31.5, 31.9, 33.3,41.3, 88.4, 99.0, 127.0, 128.1, 129.3, 134.9, 140.5,
156.3; MS (EI, 70 eV): m/z (%) = 343 [M+] (34), 287 (100), 252 (25), 230 (35), 202
(34), 188 (22), 131 (15), 117 (26), 91 (44), 55 (18), 43 (32), 28 (38). 4-
Benzylidene-3-butyl-5,5-pentamethyleneoxazolidin -2-one (3f, Z/E mixture): IR
(KBr, v/cmÀ1): 2964, 2935, 2866, 1761, 1686: 1H NMR (400 MHz, CDCl3) d
(ppm): 0.56–0.60 (m, 3H), 0.93–0.97 (m, 2H), 1.58–1.63 (m, 10H), 1.69–1.77 (m,
2H), 3.25–3.28 (m, 2H), [3.49–3.53 (t, J = 7.4 Hz, 2H)], 5.45 (s, 1H), [5.71 (s, 1H)],
7.13–7.19 (m, 3H), 7.21–7.32 (m, 2H); 13C NMR (100 MHz, CDCl3) d (ppm): 13.4,
19.2, 21.8, 24.7, 28.9, 37.3, 42.6, 83.9, 98.0, 126.7, 127.8, 129.6, 134.9, 143.2,
156.8; MS (EI, 70 eV): m/z (%) = 299 [M+] (100), 257 (22), 244 (54), 200 (16), 172
(26), 129 (10), 117 (15), 91 (22), 81 (14), 41 (6). 3-Butyl-4-ethylidene-5,5-
pentamethyleneoxazolidin-2-one (3g, Z/E mixture): IR (KBr, v/cmÀ1): 2961, 2934,
2864, 1764, 1671; 1H NMR (400 MHz, CDCl3) d (ppm): 0.88–0.92 (t, J = 7.4 Hz,
3H), 1.26–1.30 (t, J = 7.8 Hz, 3H), 1.48–1.50 (d, J = 7.6 Hz, 2H),1.62–1.90 (m,
12H), 3.33–3.37 (t, J = 7.4 Hz, 2H), [3.59–3.63 (t, J = 7.6 Hz, 2H)], 4.17–3.23 (t,
J = 7.6 Hz, 1H), [4.41–4.46 (t, J = 7.4 Hz, 1H)]; 13C NMR (100 MHz, CDCl3) d
(ppm): 11.5, 13.7, 19.7, 21.5, 24.7, 28.3, 34.1, 40.7, 83.5, 91.7, 141.6, 155.7; MS
(EI, 70 eV): m/z (%) = 237 [M+] (55), 208 (24), 195 (44), 182 (100), 164(22), 150
(28), 138 (32), 122 (32), 108 (18), 93 (14), 81 (16), 55 (14), 41 (12), 28(8).
4-Benzylidene-3-butyloxazolidin-2-one (3h, Z/E mixture): IR (KBr, v/cmÀ1): 2959,
2934, 2873, 1771, 1661; 1H NMR (400 MHz, CDCl3) d (ppm): 0.96–1.00 (t,
J = 7.4 Hz, 3H), 1.37–1.46 (m, 2H), 1.63–1.71 (m, 2H), 3.36–3.40 (t, J = 7.6 Hz,
2H), [3.56–3.960 (t, J = 7.4 Hz, 1H)], 4.46 (s, 2H), [5.14 (d, J = 2.8 Hz, 2H)], 5.65 (s,
1H), [6.46 (s, 1H)], 7.16–7.20 (m, 3H), 7.25–7.32 (m, 2H); 13C NMR (100 MHz,
CDCl3) d (ppm): 12.8, 19.1, 27.6, 40.6, 66.1, 98.7, 124.8, 126.0, 128.0, 134.5,
134.9, 155.9; MS (EI, 70 eV): m/z (%) = 231 [M+] (100), 201 (24), 174 (32), 161
(18), 130 (20), 118 (38), 91 (72), 78 (20), 41 (12). 4-Benzylidene-3-butyl-5-
methyloxazolidin-2-one (3i, Z/E mixture): IR (KBr, v/cmÀ1): 2960, 2934, 2873,
1770, 1667; 1H NMR (400 MHz, CDCl3) d (ppm): 0.96–0.99 (t, J = 7.4 Hz, 3H),
1.37–1.45 (m, 2H), 1.62–1.69 (m, 5H), 3.49–3.62 (m, 2H), 5.60 (d, J = 2.8 Hz, 1H),
5.64–5.69 (m, 1H), 7.14–7.19 (m, 3H), 7.25–7.33 (m, 2H); 13C NMR (100 MHz,
CDCl3) d (ppm): 12.8, 17.9, 19.1, 27.6, 40.3, 73.5, 98.3, 125.2, 126.8, 127.8, 134.2,
140.0, 155.3; MS (EI, 70 eV): m/z (%) = 245 [M+] (100), 190 (40), 145 (32), 130
(34), 117(60), 91 (75), 28 (20).
Acknowledgments
The authors thank the National Natural Science Foundation of
China (Nos. 20772034, 20625205, 20572027 and 20332030) and
Guangdong Natural Science Foundation (No. 07118070) for finan-
cial support of this work.
References and notes
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Chem. Soc. 2005, 127, 13118; (c) Ohnishi, Y. Y.; Matsunaga, T.; Nakao, Y.; Sato, H.;
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Schaad, D. R. Chem. Rev. 1996, 96, 835.
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4. (a) Jiang, H. F.; Zhao, J. W.; Wang, A. Z. Synthesis 2008, 5, 763; (b) Fournier, J.;
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8.
A
15 mL polytetrafluoroethylene (PTFE) reaction vessel was charged with
catalyst (0.1 mmol), internal propargylic alcohol (2 mmol), and amine
(2 mmol). The vessel was fixed into stainless autoclave in pressure
a
a
regulating system. The autoclave was sealed. Liquid carbon dioxide was
introduced from a cylinder, and it reacted at the selected temperature under
magnetic stir for the required reaction time. When the reaction was completed,
the vessel was cooled with an ice-bath, and the pressure was released slowly to
atmospheric pressure. The residual was flushed with 3 Â 10 mL diethyl ether.
The products were purified by column chromatography (gel, petroleum ether/
ethyl acetate, 6:1), and were characterized by 1H NMR, 13C NMR, and MS.
4-Benzylidene-3,5-dibutyl-5-ethyloxazolidin-2-one (3a, Z/E mixture): IR (KBr,
m
/cmÀ1): 2959, 2929, 2873, 1768, 1672; 1H NMR (400 MHz, CDCl3) d (ppm):
0.82–0.86 (m, 3H), 0.94–0.98 (m, 6H), 1.34–1.40 (m, 6H), 1.62–1.64 (m, 6H),
3.26–3.30 (t, J = 7.6 Hz, 2H), [3.50–3.56 (t, J = 7.4 Hz, 2H)], 5.40 (s, 1H), [5.79 (s,
1H)], 7.12–7.17 (m, 3H), 7.24–7.31 (m, 2H); 13C NMR (100 MHz, CDCl3) d (ppm):
7.1, 13.3, 13.9, 20.1, 22.4, 24.8, 28.9, 31.9, 38.4, 41.1, 88.4, 99.0, 127.0, 127.8,
128.1, 129.3, 129.7, 134.9, 140.5, 157.2; MS (EI, 70 eV): m/z (%) = 315 [M+] (32),
259 (100), 244 (22), 224 (21), 202 (32), 180 (25), 145 (8), 117 (15), 91 (16), 57
9. Yamada, W.; Sugawara, Y.; Cheng, H. M.; Ikeno, T.; Yamada, T. Eur. J. Org. Chem.
2007, 2604.