Naturally occurring α-amino acid: a simple and inexpensive catalyst for the selective synthesis of 5-aryl-2-oxazolidinones from CO2 and aziridines under solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2009.12.031

Naturally occurring α-amino acid successfully catalyzed cycloaddition of aziridine with carbon dioxide to afford 5-aryl-2-oxazolisinones under mild conditions without the need of any additives. The scope of this reaction is very general, providing the corresponding products in good yields and excellent regioselectivity (87:13-100:0) regardless of the α-amino acid examined and a wide variety of N-substituted aziridines employed. Two possible reaction pathways for the reaction were also discussed.

Full text of DOI:10.1016/j.tetlet.2009.12.031

Tetrahedron Letters 51 (2010) 928–932
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Naturally occurring
a-amino acid: a simple and inexpensive catalyst
for the selective synthesis of 5-aryl-2-oxazolidinones from CO2 and aziridines
under solvent-free conditions
*
Huan-Feng Jiang , Jin-Wu Ye, Chao-Rong Qi, Liang-Bin Huang
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Naturally occurring a-amino acid successfully catalyzed cycloaddition of aziridine with carbon dioxide to
afford 5-aryl-2-oxazolisinones under mild conditions without the need of any additives. The scope of this
reaction is very general, providing the corresponding products in good yields and excellent regioselectiv-
Received 4 August 2009
Revised 2 December 2009
Accepted 8 December 2009
Available online 11 December 2009
ity (87:13–100:0) regardless of the
a-amino acid examined and a wide variety of N-substituted aziridines
employed. Two possible reaction pathways for the reaction were also discussed.
Ó 2009 Published by Elsevier Ltd.
Within the space of a few years, development of highly efficient
methods for chemical fixation of carbon dioxide has been drawing
intensive interest in organic synthesis and chemical industry. This
is due to the fact that carbon dioxide, main greenhouse gas, can be
used as a safe and cheap C1 building block to produce useful organ-
ic compounds.1 One of the attractive methods to fix CO2 is the cou-
pling of CO2 with aziridines to form oxazolidinones, which are
widely available in organic synthesis as chiral auxiliaries or as bio-
logically active pharmaceutical agents.2 In this respect, numerous
catalysts have been reported for this reaction, such as nickel com-
plexes,3 iodine,4 alkali metal halide,5–7 salen Cr(III)/DMAP,8 phenol/
DMAP,9 and PEG6000(NBu3Br)2.10 However, most catalysts cannot
meet the current industrial demands because of some drawbacks,
such as the need for a cosolvent or cocatalyst, and their high cost.
Therefore, development of efficient catalysts for this transforma-
tion using cheap and non-toxic reagents and conducting the reac-
tions under solvent-free conditions is still desirable.
cheaper, and ecological catalyst system would have great potential
in industrial application for chemical fixation of carbon dioxide.
At first, L-histidine, which is one of the most effective catalysts
for the cycloaddition of CO2 with epoxides, was employed as the
catalyst for the reaction of 1-propyl-2-phenylazirdine (1a)12 with
CO2.13 Results in Table 1 showed that
L
-histidine was very active
for this transformation. Hence, experiments with -histidine as a
L
catalyst were examined carefully to study the carboxylation of 1a
under a variety of reaction conditions, which included changes in
catalyst loading (0.2–0.8 mol %), temperature (70–130 °C), CO2
pressure (3–11 MPa), reaction time (12–48 h).
As is easily seen from Table 1, the activity of our catalytic sys-
tem is strongly dependent on reaction temperature. In the lower
temperature region (70–110 °C), the total yields of oxazolidinone
2a and 3a increased rapidly with increasing temperature, while
no significant change observed from 110 to 130 °C (Table 1, entries
1–5). In an attempt to determine the suitable dosage of L-histidine
As our ongoing interest in CO2 incorporation into fine organic
used, we found that even when the catalyst loading was as low as
0.2 mol %, the coupling reaction still proceeded smoothly to give
oxazolidinones in 70% yield (Table 1, entries 6, 9, and 10). At
8 MPa of CO2 pressure and 110 °C, 1a could be completely con-
verted into oxazolidines after 36 h (Table 1, entries 2, 6–8). When
the reaction time was shortened to 12 h, the total yield of oxazolid-
inones was decreased from 99% to 32%. It is worth mentioning that
5-phenyl-3-propyloxazolidin-2-one (2a) was predominately
formed in all cases which resulted from the opening of the aziri-
dine ring at the most substituted carbon.
chemicals,11 we recently reported the use of naturally occurring
a
-amino acid in the cycloaddition of CO2 with epoxides to form
carbonates.11b Herein, we have successfully extended the scope
of this catalytic system to aziridines without the need of any toxic
organic solvents or cocatalysts. To the best of our knowledge, this
is the first work to use this natural catalyst system to chemical fix-
ation of CO2 with aziridines. Furthermore, a-amino acids are very
active for both epoxides and aziridines. Comparing to the majority
of reported catalysts for the carboxylation of CO2 with aziridines,
a
-amino acids have many advantages, such as natural, simple,
Figure 1 illustrates CO2 pressure dependence on the yield and
regioselectivity of oxazolidinones. The yield of oxazolidinones also
strongly depended on CO2 pressure, while variation of pressure
had no influence on the regioselectivity of 2a. The maximum yield
reached 99% at about 8 MPa near the critical pressure of CO2 and a
further increase in pressure to 12 MPa led to a depression in yield.
accessible, inexpensive, and non-toxic. We believe that this simple,
* Corresponding author. Tel./fax: +86 20 87112906.
E-mail address: jianghf@scut.edu.cn (H.-F. Jiang).
0040-4039/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2009.12.031

H.-F. Jiang et al. / Tetrahedron Letters 51 (2010) 928–932
929
Table 1
Carboxylation of aziridine into oxazolidinone
O
O
N
L-histidine
N
O
O
N
CO2
+
+
solvent-free
Ph
Ph
Ph
1a
3a
2a
Entry
Catalyst (mol %)
Temperature (°C)
Time (h)
Yield (%)
2a:3a (%)
1
2
3
4
5
6
7
8
9
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.4
0.2
130
110
100
90
48
48
48
48
48
36
24
12
36
36
99
99
88
65
8
99
83
32
84
70
95:5
94:6
94:6
92:8
93:7
93:7
93:7
92:8
92:8
93:7
70
110
110
110
110
110
10
Yield: the total yield of 2a and 3a; regioselectivity: molar ratio of 2a:3a; reaction conditions: 1a (322 mg, 2 mmol), L-histidine (1.9 mg, 0.012 mmol), 36 h, 110 °C.
72 h, although it gave 3-tert-butyl-5-phenyloxazolidin-2-one (2i)
as the sole product (Table 3, entry 8). Table 3 also showed that azir-
idines with either electron-donating group or electron-withdraw-
ing group on the C1-aryl group could smoothly react with CO2
and give oxazolidinones in high yield and regioselectivity (Table
3, entries 9–11). It can be suggested from the above-mentioned re-
sults in Tables 2 and 3 that the product yields and regioselectivity
depends on the catalyst structure, the electron nature of the sub-
100
90
80
70
60
50
40
30
Table 2
Yield
Regioselectivity
Coupling of CO2 with 1-n-propyl-2-phenylaziridine (1a) catalyzed by various
a
-amino acida
O
O
2
4
6
8
10
12
N
alpha-amino acid
solvent-free
CO2 pressure (MPa)
N
O
O
N
CO2
+
+
Ph
Figure 1. CO2 pressure-yield and regioselectivity plots in the reaction of 1a with
Ph
Ph
1a
CO2.
3a
2a
Entry
a
-Amino acid
-Glycine
-Alanine
Yieldb (%)
2a:3ac (%)
1
2
96
48
99
94
99
84
99
99
99
83
82
86
88
99
96
74
62
99
87
99
92:8
89:11
91:9
87:13
91:9
94:6
93:7
92:8
90:10
92:8
91:9
89:11
96:4
93:7
95:5
96:4
95:5
92:8
91:9
92:8
This interesting phenomenon is almost certainly due to the phase
behavior in this set of experiments and is in general agreement
with previous report.14
Encouraged by the successful results of CO2-fixation using L-his-
tidine as the catalyst, we next examined the cycloaddition reac-
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
3
-Leucine
4
-Isoleucine
-Valine
5
6
tions of 1-propyl-2-phenylazirdine (1a) with CO2 using various
-Serine
7
common
a-amino acids as catalysts under the given conditions.
-Threonine
-Cysteine
8
The results were summarized in Table 2. Almost all of the amino
acids examined could catalyze the reaction to give oxazolidinones
in good to excellent yields with a large excess of the 5-substituted
isomer over the 4-substituted one (from 87:13 to 96:4).
9
-Methionine
-Tyrosine
10
11
12
13
14
15
16
17
18
19
20
-Phenylalanine
-Tryptophan
-Arginine
The reaction was then extended to the carboxylation of several
monosubstituted aziridines 1b–1l which were primarily varied as
to their N-substitution in the catalysis of
were listed in Table 3. -Histidine was a highly effective catalyst
L
-histidine.15 The results
-Histidine
-Lysine
L
for the conversion of various monosubstituted aziridines into
oxazolidinones under the optimal conditions. Substrate 1b and 1c
afforded a relatively low yield of the desired product because self-
oligomers were formed during the reaction (Table 3, entries 1 and
2). The substrates 1d–1h bearing alkyl groups or cyclohexyl at the
nitrogen atom afforded corresponding oxazolidinones in good to
excellent yields, and 5-substituted oxazolidinones were the major
isomer (Table 3, entries 3–7). However, substrate 1i with a tert-bu-
tyl substitution at nitrogen atom afforded lower yield (42%) after
-Aspartic acid
-Glutamic acid
-Asparagine
-Glutamine
-Proline
a
Reaction conditions: 1a (322 mg, 2 mmol); 36 h, CO2 8 MPa, 110 °C.
The total yield of 2a and 3a, determined by GC with biphenyl as an internal
b
standard.
c
Molar ratio of 2a to 3a.

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H.-F. Jiang et al. / Tetrahedron Letters 51 (2010) 928–932
Table 3
Substrate scope of L-histidine in the reaction of CO2 and N-substituted aziridinesa
O
O
R'
R'
R'
N
L-histidine
N
O
O
N
CO2
+
+
solvent-free
R
R
R
3
1
2
Entry
1
Substrate
Conversionb (%)
>99
Isolated yieldc (%)
54
2:3d (%)
1b
1c
87:13
NH
N
2
3
4
>99
>99
>99
79
97
97
94:6
98:2
95:5
1d
N
1e
1f
N
N
5
6
>99
>99
97
95
99.5:0.5
98:2
1g
1h
N
N
7
8e
9
>99
45
96
42
94
100:0
100:0
99:1
1i
N
Cl
1j
>99
N
1k
10
11
>99
>99
96
92
99:1
N
O
1l
100:0
N
a
b
c
Reaction conditions: substrates (2 mmol) L-histidine (1.9 mg, 0.012 mmol), 36 h, CO2 8 MPa, 110 °C.
Determined by GC with biphenyl as an internal standard.
The total yield of 2 and 3.
d
e
Molar ratio of 2 to 3, determined by 1H NMR.
The reaction time is 72 h.
strates, and the steric hindrance of the substituent group at the
nitrogen atom. These regiospecific results are similar to those of
the reaction of aziridines in the presence of salen Cr(III)/DMAP8 or
PEG6000(NBu3Br)2.10
amino acid which activated the aizridine ring through hydrogen
bonding according to the Baldwin’s rule.18 Thus, the activated
ring was nucleophilic attacked by the carboxylate ion of another
amino acid. Since the bond dissocaiation energy of ArCH–NR is
lower than that of ArCHCH2–NHR in aziridine ring,19 the inter-
mediate 5 was favorably formed via Path A although ring-open-
ing reaction occurred at the more sterically hindered side of the
aziridine ring. Regioselectivity in this ring-opening reaction re-
sults in the regioselective formation of oxazolidinones. Then,
the interaction was occurred between the zwitterion 5 and CO2
to form intermediate 7. Finally the intramolecular cyclization
via nucleophilic attack led to the final product and regenerated
the catalyst. Path B is a difavorable route on energy, however if
intermediate 6 was formed, regioisomer 3 could be obtained
through a similar way.
It has been suggested that hydrogen binding can activate the
ring-opening reaction of epoxides.16 In our catalytic system,
there was a hydrogen bond donor from amino acids. On the basis
of the special structure of amino acid17 and our experimental re-
sults, we proposed a plausible reaction mechanism for the forma-
tion of oxazolidinones involving Lewis acid activation and Lewis
base nucleophilic attack of the aziridines by different amino
acids, which was shown in Scheme 1. Firstly, the aziridine ring
was activated by an amino acid through hydrogen bond to form
the intermediate 4. Next, it has been reported that the nucleo-
philic attack would not occur by the carboxylate ion of the same

H.-F. Jiang et al. / Tetrahedron Letters 51 (2010) 928–932
931
O
O
R'
N
R'
R'
N
O
O
N
OOCCHR''NH3
OOCCHR''NH3
R
R
R
3
1
NH3CHR'COO
2
Path B
Path A
O
O
R'
a
R'
R
O
N
R'
O
N
8
7
N H NH2CHR''COO
NH3CHR''COO
R
4
R
OOCCHR''NH3
b
OOCCHR''NH3
O
C
O
C
R'
N
R'
N
O
O
R
R
OOCCHR''NH3
OOCCHR''NH3
CO2
6
5
a
R'
R
R'
R
N H NH2CHR''COO
NH3CHR''COO
N H NH2
CHR''
favoured
O
R'
O
R
N H NH2CHR''COO
NH3CHR''COO
disfavoured
b
disfavoured
Scheme 1. A proposed mechanism for the coupling of CO2 and aziridines by the a-amino acids catalyst system.
7. Sudo, T.; Morioka, Y.; Sanda, F.; Endo, T. Tetrahedron Lett. 2004, 45, 1363.
8. Miller, A. W.; Nguyen, S. T. Org. Lett. 2004, 6, 2301.
9. Shen, Y. M.; Duan, W. L.; Shi, M. Eur. J. Org. Chem. 2004, 3080.
10. Du, Y.; Wu, Y.; Liu, A. H.; He, L. N. J. Org. Chem. 2008, 73, 4709.
In conclusion, a novel catalytic system for incorporation of CO2
into aziridines for the synthesis of oxazolidinones was developed.
Almost all the naturally occurring
a-amino acids were efficient
11. (a) Qi, C. R.; Jiang, H. F. Green Chem. 2007, 9, 1284; (b) Qi, C. R.; Jiang, H. F.;
Wang, Z. Y.; Zou, B. Synlett 2007, 2, 255; (c) Qi, C. R.; Jiang, H. F.; Wang, Z. Y.;
Zou, B. Chin. J. Chem. 2007, 25, 1051; (d) Qi, C. R.; Jiang, H. F.; Liu, H. L.; Yang, S.
R.; Zou, B. Chem. J. Chin. Univ. 2007, 28, 1084; (e) Yuan, G. Q.; Jiang, H. F.; Lin, C.;
Liao, S. J. Electrochim. Acta. 2007, 53, 2170; (f) Jiang, H. F.; Zhao, J. W.; Wang, A.
Z. Synthesis 2008, 5, 763; (g) Yuan, G. Q.; Jiang, H. F.; Lin, C. Tetrahedron 2008,
64, 5866; (h) Yuan, G. Q.; Shan, Y. J.; Jiang, H. F.; Qi, C. R. Chin. J. Chem. 2008, 26,
947; (i) Jiang, H. F.; Wang, A. Z.; Liu, H. L.; Qi, C. R. Eur. J. Org. Chem. 2008, 13,
2309; (j) Jiang, H. F.; Yuan, B. Z.; Qi, C. R. Chin. J. Chem. 2008, 26, 1305; (k) Jiang,
H. F.; Zhao, J. W. Tetrahedron Lett. 2009, 50, 60.
catalysts for the reaction of CO2 with aziridines to obtain the cor-
responding oxazolidinones in excellent yield and high regio-
selectivity. This CO2-fixation method can be operated under
supercritical conditions without any additives. The hopeful meth-
od for chemical fixation of CO2 will be further improved in order
to develop more environmentally benign progress.
Acknowledgments
12. All of the aziridines were synthesized according to the following literatures (a)
Capriati, V.; Florio, S.; Luisi, R.; Musio, B. Org. Lett. 2005, 7, 3749; (b) Ref. 10.
We thank the National Natural Foundation of China (Nos.
20625205, 20772034, and 20932002) and Guangdong Natural Sci-
ence Foundation (No. 07118070) for financial support.
13. General procedure for carboxylation of aziridine with CO2: Aziridine (2 mmol),
L-
histidine (1.9 mg, 0.012 mmol) was added to 15 mL stainless autoclave
a
reactor with a magnetic stirrer. CO2 was introduced into the autoclave and
then the pressure was generally adjusted to 8 MPa at 110 °C. The mixture was
stirred continuously at 110 °C for 36 h, and the pressure was kept constant
during the reaction. After the reaction, the reactor was cooled in ice-water and
extra CO2 was vented slowly. An aliquot of sample was taken from the
resultant mixture and dissolved in CH2Cl2 for GC analysis. The residue was
purified by flash silica gel chromatography using petroleum ether/ethyl
acetate = 10:1 to 1:1 as eluant to afford the product. The products were
further identified by NMR and MS.
References and notes
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Chem. Rev. 2007, 107, 2365.
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Bergmeier, S. C. Tetrahedron Lett. 2002, 43, 557; (d) Sim, T. B.; Kang, S. H.; Lee, K.
S.; Lee, W. K. J. Org. Chem. 2003, 68, 104; (e) Watson, R. J.; Batty, D.; Baxter, A.
D.; Hannah, D. R.; Owen, D. A.; Montana, J. G. Tetrahedron Lett. 2002, 43, 683; (f)
Aurelio, L.; Brownlee, R. T. C.; Hughus, A. B. Chem. Rev. 2004, 104, 5823; (g)
Makhtar, T. M.; Wright, G. D. Chem. Rev. 2005, 105, 529; (h) Andreou, T.; Costa,
A. M.; Esteban, L.; Gonzalez, L.; Mas, G.; Vilarrasa, J. Org. Lett. 2005, 7, 4083.
3. Tascedda, P.; Dunach, E. Chem. Commun. 2000, 449.
4. Kawanami, H.; Ikushima, Y. Tetrahedron Lett. 2002, 43, 3841.
5. Hancock, M. T.; Pinhas, A. R. Tetrahedron Lett. 2003, 44, 5457.
6. Sudo, A.; Morioka, Y.; Koizumi, E.; Sanda, F.; Endo, T. Tetrahedron Lett. 2003, 44,
7889.
14. Zhang, H. F.; Han, B. X.; Hou, Z. S.; Liu, Z. M. Fluid Phase Equilib. 2001, 179, 131.
15. Spectroscopic data of the 5-aryl-2-oxazolidinones: 5-Phenyl-3-propyloxazolidin-2-
one (2a): 1H NMR (400 MHz, CDCl3) d 0.91 (t, 3J = 7.2 Hz, 3H), 1.52–1.61 (m,
2H), 3.18–3.31 (m, 2H), 3.40 (t, 3J = 8.0 Hz, 1H), 3.90 (t, 3J = 8.8 Hz, 1H), 5.46 (t,
3J = 8.0 Hz, 1H), 7.32–7.39 (m, 5H); 13C NMR (100 MHz, CDCl3) d 11.0, 20.5,
45.7, 52.0, 74.2, 125.4, 128.6, 128.7, 138.8, 157.9; MS (EI) m/z (%): 205, 144,
132, 105, 91, 70, 43.
5-Phenyloxazolidin-2-one (2b): 1H NMR (400 MHz, CDCl3) d 3.53 (t, 3J = 8.4 Hz,
1H), 3.97 (t, 3J = 8.4 Hz, 1H), 5.60 (t, 3J = 8.2 Hz, 1H), 6.68 (s, 1H), 7.36–7.41 (m,
5H); 13C NMR (100 MHz, CDCl3) d 48.2, 77.7, 125.5, 128.7, 138.3, 160.1; MS (EI)
m/z (%): 163, 107, 91, 79, 77, 32.
3-Methyl-5-phenyloxazolidin-2-one(2c): 1H NMR (400 MHz, CDCl3) d 2.91 (s,
3H), 3.43 (t, 3J = 8.4 Hz, 1H), 3.91 (t, 3J = 8.8 Hz, 1H), 5.46 (t, 3J = 8.0 Hz, 1H),

932
H.-F. Jiang et al. / Tetrahedron Letters 51 (2010) 928–932
7.35–7.41 (m, 5H); 13C NMR (100 MHz, CDCl3) d 30.9, 54.2, 74.0, 125.4, 128.6,
(100 MHz, CDCl3) d 48.3, 51.5, 74.5, 125.5, 128.0, 128.1, 128.7, 128.8, 135.6,
138.5, 157.9; MS (EI) m/z (%): 253, 165, 118, 104, 91, 65.
128.7, 138.5, 158.0. MS (EI) m/z (%): 177, 132, 91, 77, 43.
3-Ethyl-5-phenyloxazolidin-2-one (2d): 1H NMR (400 MHz, CDCl3) d 1.05 (t,
3J = 7.2 Hz, 3H), 1.29–1.38 (m, 2H), 1.48–1.56 (m, 2H), 3.21–3.35 (m, 2H), 3.40
(t, 3J = 8.0 Hz, 1H), 3.89 (t, 3J = 8.8 Hz, 1H), 5.45 (t, 3J = 8.0 Hz, 1H), 7.32–7.39 (m,
5H); 13C NMR (100 MHz, CDCl3) d 13.6, 19.7, 29.2, 43.7, 52.0, 74.2, 125.4, 128.6,
128.7, 138.8, 157.8; MS (EI) m/z (%): 191, 146, 130, 91, 57.
5-(4-Chlorophenyl)-3-cyclohexyloxazolidin-2-one (2j): 1H NMR (400 MHz,
CDCl3) d 1.05–1.83 (m, 10H), 3.34 (t, 3J = 8.0 Hz, 1H), 3.69–3.76 (m, 1H), 3.89
(t, 3J = 8.7 Hz, 1H), 5.44 (t, 3J = 8.0 Hz, 1H), 7.27–7.38 (m, 4H); 13C NMR
(100 MHz, CDCl3) d 25.2, 25.3, 30.0, 30.4, 48.2, 52.6, 73.8, 126.8, 129.0, 134.5,
137.6, 156.8; MS (EI) m/z (%): 279, 267, 236, 198, 192, 180, 154, 138, 110, 103,
55.
3-Butyl-5-phenyloxazolidin-2-one (2e): 1H NMR (400 MHz, CDCl3) d 0.92 (t,
3J = 7.2 Hz, 3H), 1.29–1.38 (m, 2H), 1.48–1.56 (m, 2H), 3.21–3.35 (m, 2H), 3.40
(t, 3J = 8.0 Hz, 1H), 3.89 (t, 3J = 8.8 Hz, 1H), 5.45 (t, 3J = 8.0 Hz, 1H), 7.32–7.39 (m,
5H); 13C NMR (100 MHz, CDCl3) d 13.6, 19.7, 29.2, 43.7, 52.0, 74.2, 125.4, 128.6,
128.7, 138.8, 157.8; MS (EI) m/z (%): 219, 176, 132, 105, 91, 84.
3-Cyclohexyl-5-p-tolyloxazolidin-2-one (2k): 1H NMR (400 MHz, CDCl3) d 1.02–
1.82 (m, 10H), 2.36 (s, 3H), 3.38 (t, 3J = 8.0 Hz, 1H), 3.71–3.75 (m, 1H), 3.85 (t,
3J = 8.7 Hz, 1H), 5.43 (t, 3J = 8.0 Hz, 1H), 7.17–7.26 (m, 4H); 13C NMR (100 MHz,
CDCl3) d 21.1, 25.2, 25.3, 25.4, 30.1, 30.5, 48.3, 52.5, 74.5, 125.5, 129.5, 136.0,
138.6, 157.3; MS (EI) m/z (%): 259, 220, 214, 172, 158, 134, 118, 105, 91, 55.
3-Cyclohexyl-5-(4-methoxyphenyl)oxazolidin-2-one (2l): 1H NMR (400 MHz,
CDCl3) d 0.86–1.86 (m, 10H), 3.39 (t, 3J = 8.0 Hz, 1H), 3.72–3.87 (m, 5H), 5.41
(t, 3J = 8.0 Hz, 1H), 6.91 (d, J = 8.8 Hz, 2H), 7.27 (d, J = 8.8 Hz, 2H); 13C NMR
(100 MHz, CDCl3) d 25.2, 25.3, 30.0, 30.5, 48.2, 52.4, 55.3, 74.5, 114.1, 127.1,
130.8, 157.2, 159.8; MS (EI) m/z (%): 275, 230, 188, 148, 134, 121, 110, 83.
16. Huang, J. W.; Shi, M. J. Org. Chem. 1993, 58, 6198.
17. (a) Bonaccorsi, R.; Palla, P.; Tomasi, J. J. Am. Chem. Soc. 1984, 106, 1945; (b)
Furic, K.; Mohacek, V.; Bonifacic, M.; Stefanic, I. J. Mol. Struct. 1992, 267, 39; (c)
Jensen, J. H.; Gordon, M. S. J. Am. Chem. Soc. 1995, 117, 8159.
18. (a) Baldwin, J. E. J. Chem. Soc., Chem, Commun. 1976, 734; (b) Baldwin, J. E.;
Cutting, J.; Dupont, W.; Kruse, L.; Silberman, L.; Thomas, R. C. J. Chem. Soc.,
Chem. Commun. 1976, 736.
3-tert-Butyl-5-phenyloxazolidin-2-one (2f): 1H NMR (400 MHz, CDCl3) d 1.41 (s,
9H), 3.45 (t, 3J = 8.4 Hz, 1H), 3.95 (t, 3J = 8.6 Hz, 1H), 5.36 (t, 3J = 8.2 Hz, 1H),
7.32–7.41 (m, 5H); 13C NMR (100 MHz, CDCl3) d 27.3, 50.9, 53.4, 73.3, 125.4,
128.5, 128.7, 138.9, 156.6; MS (EI) m/z (%): 219, 204, 160, 91, 57.
3-Hexyl-5-phenyloxazolidin-2-one (2g): 1H NMR (400 MHz, CDCl3) d 0.79 (t,
3J = 6.6 Hz, 3H), 1.20–1.24 (m, 6H), 1.43–1.47 (m, 2H), 3.13–3.23 (m, 2H), 3.31
(t, 3J = 8.0 Hz, 1H), 3.82 (t, 3J = 8.8 Hz, 1H), 5.37 (t, 3J = 8.0 Hz, 3H), 7.25–7.31 (m,
5H); 13C NMR (100 MHz, CDCl3) d 13.6, 22.1, 25.9, 26.9, 31.0, 43.7, 51.7, 73.9,
125.1, 128.3, 128.5, 138.7, 157.5; MS (EI) m/z (%): 247, 176, 156, 132, 104, 91,
77.
3-Cyclohexyl-5-phenyloxazolidin-2-one (2h): 1H NMR (400 MHz, CDCl3) d 1.0–
1.9 (m, 10H), 3.39 (t, 3J = 8.0 Hz, 1H), 3.71–3.78 (m, 1H), 3.88 (t, 3J = 8.6 Hz, 1H),
5.46 (t, 3J = 8.0 Hz, 1H), 7.33–7.41 (m, 5H); 13C NMR (100 MHz, CDCl3) d 25.1,
29.9, 30.4, 48.2, 52.4, 74.4, 125.3, 128.6, 128.7, 138.9, 157.1; MS (EI) m/z (%):
245, 200, 164, 110, 104, 91, 55.
19. (a)Handbook of Bond Dissociation Energies in Organic Compounds; Luo, Y. R., Ed.;
Science Press: Beijing, China, 2005; (b)Handbook of Bond Dissociation Energies in
Organic Compounds; Luo, Y. R., Ed.; CRC Press: USA, 2002. The bond dissociation
energy data of similar bonds: C6H5CH2–NHCH3, 68.7 2 kcal/mol; C2H5–
NHCH3, 79.8 2 kcal/mol.
3-Benzyl-5-phenyloxazolidin-2-one (2i): 1H NMR (400 MHz, CDCl3) d 3.29 (t,
3J = 8.2 Hz, 1H), 3.75 (t, 3J = 8.8 Hz, 1H), 4.46 (ABq, JAB = 15.0 Hz,
Dm
AB = 36.0 Hz, 2H), 5.45 (t, 3J = 8.0 Hz, 1H), 7.26–7.36 (m, 10H); 13C NMR