Atmospheric Pressure of CO2 as Protecting Reagent and Reactant: Efficient Synthesis of Oxazolidin-2-ones with Carbamate Salts, Aldehydes and Alkynes

Article abstract of DOI:10.1002/adsc.201500921

Carbon dioxide (CO₂) has been wildly employed as an environmentally benign C₁ resource for organic synthesis in the recent years. The capture of CO₂ with primary amines easily provides the corresponding carbamate salts. We described herein that carbamate salts are a useful reactant for the synthesis of oxazolidin-2-ones via the reaction with aromatic aldehydes and aromatic terminal alkynes. A variety of oxazolidin-2-ones with different functional groups were synthesized in 68-91% yields with only a 5 mol% amount of CuI as catalyst. It was found that the synergetic effect of iodide is important for the transformation. Notable, the captured CO₂ serves not only as a protecting reagent for electron-rich primary amine to avoid catalyst poisoning, but also as a reactant for the construction of oxazolidin-2-ones.

Full text of DOI:10.1002/adsc.201500921

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DOI: 10.1002/adsc.201500921
Atmospheric Pressure of CO2 as Protecting Reagent and
Reactant: Efficient Synthesis of Oxazolidin-2-ones with
Carbamate Salts, Aldehydes and Alkynes
Bing Yu,a Bin-Bin Cheng,a Wei-Qi Liu,a Wei Li,a Shan-Shan Wang,a Jie Cao,a
and Chang-Wen Hua,*
a
Key Laboratory of Cluster Science of Ministry of Education, College of Chemistry, Beijing Institute of Technology,
Beijing 100081, People’s Republic of China
Fax: (+86)-10-8138-1380; phone: (+86)-10-8138-1380; e-mail: cwhu@bit.edu.cn
Received: September 30, 2015; Published online: December 17, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500921.
Abstract: Carbon dioxide (CO2) has been wildly em- a 5 mol% amount of CuI as catalyst. It was found
ployed as an environmentally benign C1 resource for that the synergetic effect of iodide is important for
organic synthesis in the recent years. The capture of the transformation. Notable, the captured CO2
CO2 with primary amines easily provides the corre- serves not only as a protecting reagent for electron-
sponding carbamate salts. We described herein that rich primary amine to avoid catalyst poisoning, but
carbamate salts are a useful reactant for the synthesis also as a reactant for the construction of oxazolidin-
of oxazolidin-2-ones via the reaction with aromatic 2-ones.
aldehydes and aromatic terminal alkynes. A variety
of oxazolidin-2-ones with different functional groups Keywords: amines; carbon dioxide fixation; copper
were synthesized in 68–91% yields with only catalysis; oxazolidinone
Introduction
cyanates and epoxides.[9] Among the various methods
for oxazolidin-2-one synthesis, protocols such as the
Carbon dioxide (CO2) has gained increasing attention coupling of CO2 with aziridines,[10] amino alcohols,[11]
due to its continuous accumulation in the atmosphere amines/propargylic
alcohols,[12]
allenylmethyl-
which is thought to be causing global warming.[1] amines,[13] allylamines,[14] propargylic amines,[15] the
A
plethora of scientific effort has been devoted to the utilization of CO2 as a C1 resource with high atom ef-
development of various approaches for reducing CO2 ficiency is highly attractive. However, the substrates
emission, such as CO2 capture and storage/sequestra- or catalyst in those reactions were usually synthesized
tion (CCS).[2] Moreover, CO2 is also regarded as by tedious reaction procedures. In 2008, Li’s group
a ubiquitous, abundant, cheap, and non-toxic C1 re- developed the first multicomponent reaction for oxa-
source for the production of useful chemicals.[3] One zolidin-2-one synthesis via the coupling of a terminal
of the most attractive strategies for CO2 fixation is alkyne, an aldehyde, an amine and an atmospheric
[16]
CO2 capture and utilization (CCU), which circum- pressure of CO2. Amine hydrochlorides under basic
vents the energy consumption of the desorption step conditions were also employed for the multicompo-
in CCS.[4]
nent reaction.[17] Subsequently, the tandem decarboxy-
The oxazolidin-2-one framework has continued to lative/carboxylative cyclization using propiolic acid as
capture the interest of chemists worldwide due to its CO2 source was proven to be efficient for the synthe-
important applications in organic synthesis and phar- sis of oxazolidin-2-ones by Eycken et al.[18] Jiang et al.
maceutical chemistry.[5] Over the past decades, numer- developed a CuI/SnCl2 catalytic system for the similar
ous methods have been developed for the synthesis of reaction using a ketone instead of an aldehyde as re-
oxazolidin-2-one and its corresponding derivatives,[6] actant under 1.5 MPa of CO2.[19] Notably, all of these
for example, through the reaction of glycerol carbon- methodologies required a large amount of catalyst
ate or glycerol with urea,[7] the reaction of amino al- and additives (20–30 mol%), probably due to the fact
cohols and aryl iodides,[8] [2+3] cycloadditions of iso-
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Atmospheric Pressure of CO2 as Protecting Reagent and Reactant
that electron-rich primary amines poison the catalyst Results and Discussion
and lead to deactivation.
In our continuing study on CO2 utilization,[20] it is We initiated our studies using n-butylamine (1a) as
easy to find that nitrogen-containing compounds are a model amine for the optimization of the reaction
potential absorbents for CO2 capture. For instance, conditions. Firstly, the primary amine 1a was treated
aliphatic primary amines easily trap CO2 under mild with CO2 from a balloon, easily affording butan-1-
conditions generating the corresponding carbamate aminium butylcarbamate (2a) as a white solid. This
salts, which are stable and easily handled. Carbamate solid compound 2a was stable for months in a screw
salts have been employed as an organocatalyst for the cap tube on a shelf at ambient temperature without
Knoevenagel condensation. After reaction, the orga- any other protection. The multicomponent reaction of
nocatalyst could be removed under vacuum to give 2a, benzaldehyde (3a), and phenylacetylene (4a) was
the desired product without extraction, washing, or performed in a screw cap vial with a Teflon seal using
chromatography steps.[21] Carbamate salts were also EtOH as solvent. Screening of various copper cata-
used as stable alternatives for toxic liquid amines in lysts showed that the nature of the catalyst markedly
the reaction with aldehydes to produce imines.[22] Ad- affected the reaction (Table 1). A number of copper
ditionally, compressed CO2 can be applied as a tempo- catalysts (5 mol%), including CuI, CuCl, CuBr,
rary protecting group for the ring closing metathesis CuSCN, Cu2O, Cu(OTf)2, CuBr·DMS, CuTC, and
of an amine-containing diene[23] and hydroaminome- CuCl2·2H2O etc. were tested (entries 1–15). However,
thylation of N-ethylmethallylamine.[24] In the selective they displayed rather poor catalytic activity in the re-
Michael additions and acylations, an atmospheric action except for CuI, which provided the product ox-
pressure of CO2 was also used as a protecting group azolidin-2-one 5a in 69% yield.
to inhibit the reaction of primary amines.[25] In the
To improve the performance of the reaction, li-
previous reports, however, the protecting reagent CO2 gands[26] and Lewis acidic additives[19,27] were surveyed
was released as waste after the reaction. Inspired by with CuI as catalyst (Table 2). In this reaction, howev-
these achievements, we envisioned that the employ- er, Ph3P, l-proline, Ti(OEt)4, H3PW12O40 were proven
ment of CO2 as a protecting group and also as a reac-
tant for the synthesis should be feasible, which avoids
the emission of CO2.
Table 1. Optimization of the reaction conditions.[a]
Herein, we describe our results on the synthesis of
oxazolidin-2-ones via the CuI-catalyzed multicompo-
nent reaction of carbamate salts, aldehydes and termi-
nal alkynes (Scheme 1). The easily handled solid car-
bamate salts were generated from CO2 and primary
amines. In this procedure, the captured CO2 not only
acts as a reactant, but also acts as a protecting reagent
for the amine to avoid poisoning of the copper cata-
lyst under the reaction conditions. Importantly, a syn-
ergistic cooperation of copper and iodide was ob-
served in the reaction.
Entry
Catalyst
Yield [%][b]
1
2
3
CuI
CuBr
CuCl
69
19
5
4
CuSCN
8
5
6
7
8
Cu2O
<1
0
0
2
<1
2
<1
<1
<1
<1
<1
Cu(OTf)2
(CuOTf)2·toluene
CuBr·DMS
CuTC
CuCl2·2H2O
CuSO4
CuSO4·5H2O
CuCO3·Cu(OH)2
Cu(NO3)2·3H2O
Cu(OAc)2·H2O
9
10
11
12
13
14
15
[a]
Reaction conditions: carbamic acid ammonium salt
(1 mmol), aldehyde (2 mmol), alkyne (2 mmol), EtOH
(0.4 mL), Cu catalyst (5 mol% based on Cu), 808C, 12 h.
The yields were determined by GC with biphenyl as the
internal standard. DMS=dimethyl sulfide, CuTC=cop-
per(I) thiophene-2-carboxylate.
[b]
Scheme 1. Procedure for the construction of oxazolidin-2-
ones from carbamates.
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Table 2. Optimization of the reaction conditions.[a]
salts as white solids by bubbling CO2 gas into the
liquid amines. The carbamate salts were effective sub-
strates for reaction with benzaldehyde 3a and phenyl-
acetylene 4a to smoothly provide the products 5j–5l
in 74–85% yields under the standard conditions. How-
Entry
Solvent/Additives
Yield [%][b]
1
2
3
4
5
6
7
8
EtOH/Ph3P
EtOH/l-Proline
EtOH/Ti(OEt)4
EtOH/H3PW12O40
CH3OH
glycol
diethylene glycol
PhCl
DMF
EtOAc
PhCH3
PhCN
70
49
59
27
55
54
53
20
59
19
7
27
30
9
79
89
Table 3. Scope of aldehydes for the multicomponent reac-
tion.[a]
9
10
11
12
13
14
15
16[c]
THF
CH2Cl2
i-PrOH
i-PrOH
[a]
Reaction conditions unless otherwise specified: carbamic
acid ammonium salt (1 mmol), aldehyde (2 mmol),
alkyne (2 mmol), solvent (0.4 mL), CuI (5 mol%), 808C,
12 h.
[b]
[c]
The yields were determined by GC with biphenyl as the
internal standard.
18 h
to be ineffective (Table 2, entries 1–4). Further exami-
nation of solvents revealed that i-PrOH exhibits
somewhat higher performance (79%) than EtOH and
other solvents under identical conditions for the reac-
tion (Table 2, entries 5–15). In addition, an improved
yield (89%) was then observed when the reaction
time was extended to 18 h using i-PrOH as solvent
(Table 2, entry 16).
Having established the optimal conditions, we then
converted a variety of commercially available alde-
hydes 3 into the corresponding oxazolidin-2-ones 5 to
further explore the scope of this CO2 transformation
procedure. As showed in Table 3, aromatic aldehydes
bearing either electron-donating or electron-with-
drawing groups, including 4-Me, 4-MeO, 3-MeO, 2-
MeO, 4-Cl, 2-Cl, 4-OH, and 4-CN on the phenyl ring
were found to be reactive affording the isolated prod-
ucts 5a–5i with moderate to excellent yields (68–
91%). Substrate 3i was poorly soluble in i-PrOH and
thus gave the corresponding products 5i in lower yield
(entry 9). Unfortunately, aliphatic aldehydes, for ex-
ample, 1-octanal gave the corresponding oxazolidin-2-
one in poor yield (results not shown).
After having demonstrated that the protocol is
compatible with a wide range of aldehydes, an investi-
gation of the scope with respect to the primary
amines and terminal alkynes was undertaken
(Table 4). Primary amines such as cyclopentylamine
1b, cyclohexylamine 1c, and benzylamine 1d were
easily converted into the corresponding carbamate
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Atmospheric Pressure of CO2 as Protecting Reagent and Reactant
Table 4. Scope of amines and alkynes for the multicompo-
Table 3. (Continued)
nent reaction.[a]
[a]
Reaction conditions: carbamic acid ammonium salt 2a
(1 mmol), aldehyde 3 (2 mmol), alkyne 4a (2 mmol), i-
PrOH (0.4 mL), CuI (5 mol%), 808C, 18 h.
Isolated yields were given.
[b]
ever, phenylamine failed to afford the desired carba-
mate salt after bubbling CO2, which revealed that the
electron-rich amine is beneficial to our protocol (re-
sults not shown). Subsequently, the substituted phe-
nylacetylenes 4b–4d were briefly screened for the
construction of oxazolidin-2-ones. It was found that
phenylacetylenes with electron-withdrawing substitu-
ents and electron-donating substituents at the para-
position, including Me, MeO, F groups, showed good
reactivity, and the corresponding products 5m–5o
were obtained in 80–86% yields. However, only
a trace amount of 5p was detected by GC-MS when
the aliphatic alkyne 4e was used. A density functional
theory calculation [B3LYP/6–31G(d,p) level] indicat-
ed that the negative charge on the C-1 carbon of phe-
nylacetylene is À0.533 and that of 1-octyne is À0.468,
which suggested that the nucleophilicity of 1-octyne is
weaker.[28]
[a]
Reaction conditions: carbamic acid ammonium salt 2
(1 mmol), aldehyde 3a (2 mmol), alkyne 4 (2 mmol), i-
PrOH (0.4 mL), CuI (5 mol%), 808C, 18 h.
To gain insight into the effect of the unique CuI
catalysis, we performed some control experiments
using 5 mol% of CuBr as catalyst, 5 mol% of KI as
[b]
Isolated yields were given.
external iodide under otherwise identical conditions. further studies are required to clarify the precise
To our surprise, the product 5a was obtained in 84% mechanism of this CuI catalysis, it was revealed that
yield (Table 5, entry 1). However, 5 mol% of KI alone iodide has an excellent synergistic effect for promot-
does not catalyze this transformation (entry 2). On ing this copper-catalyzed reaction (Table 5, entry 1 vs.
the other hand, the reaction catalyzed by ZnBr2/KI Table 1, entry 2).
failed under the given reaction conditions, demon-
Based on the above experimental results, we pro-
strating the importance of copper (entry 3). Although pose a reaction pathway for this copper-catalyzed
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Bing Yu et al.
Table 5. Control experiments.[a]
of 2. To corroborate the reaction pathways outlined in
Scheme 2, we carried out a mass spectrometric (MS)
study. The GC-mass spectrum for the reaction shows
peaks of intermediates 8 and 9, in agreement with the
mechanism proposed by Li.[16] On the other hand, the
weak signal of a negative ion at m/z=222 was ob-
served in the ESI-MS, suggesting that the intermedi-
ate 6 was probably generated.
Entry
Catalyst/Additive
Yield [%][b]
1
2
3
CuBr/KI
–/KI
ZnBr2/KI
84
0
0
Conclusions
[a]
In summary, we have described an efficient catalyic
protocol using only 5 mol% of CuI as catalyst for the
reaction of carbamate salts, aromatic aldehydes, and
aromatic terminal alkynes to produce the important
oxazolidin-2-ones. In this work, CO2 captured by pri-
mary amines served as a protecting reagent to avoid
poisoning of the transition metal catalyst and simulta-
Reaction conditions: carbamic acid ammonium salt
(1 mmol), aldehyde (2 mmol), alkyne (2 mmol), catalyst
o
(5 mol%), KI (5 mol%), 80 C, 12 h in EtOH (0.4 mL).
[b]
The yields were determined by GC with biphenyl as the
internal standard.
transformation (Scheme 2). The carbamic acid ammo- neously as a reactant for the construction of the het-
nium salt 2 was easily formed by the capture of CO2 erocycles. By using this strategy, the multicomponent
with primary amine 1. Then two plausible pathways reaction can proceed smoothly without any other pro-
were postulated for the subsequent conversion. For tection. In addition, a series of oxazolidin-2-one deriv-
path a: carbamate salt 2 reacted with aldehyde 3 af- atives bearing different functional groups was synthe-
fording imine 8 with the release of one equivalent of sized in moderate to good yields. Further studies to
water and CO2. The imine 8 was attacked by the nu- expand the application of this concept are ongoing in
cleophilic terminal alkyne 4 under catalysis of CuI our laboratory.
giving propargylic amine 9 which then trapped the in
situ released CO2 and was followed by an intramolec-
ular cyclization to generate the heterocycle product 5. Experimental Section
For path b: as an alternative, the formation of 7 may
proceed by an addition of 2 and 3, followed by a nu- General Information
cleophilic addition of 4 without the decarboxylation
The starting materials are commercially available and were
used without further purification. The products were isolat-
ed by column chromatography on silica gel (200–300 mesh)
using petroleum ether (60–908C) and ethyl acetate. All com-
1
pounds were characterized by H NMR, 13C NMR and mass
spectroscopy (MS), and the results are consistent with those
reported in the literature. NMR spectra were determined on
1
a Bruker 400 MHz instrument in CDCl3. H NMR chemical
shifts were referenced to residual solvent as determined rel-
ative to CDCl3 (7.26 ppm). The 13C NMR chemical shifts
were reported in ppm relative to the carbon resonance of
CDCl3 (central peak is 77.0 ppm). 1H NMR peaks are la-
beled as singlet (s), doublet (d), triplet (t), and multiplet
(m). The coupling constants, J, are reported in Hertz (Hz).
GC-MS data were obtained on an Agilent 7890A. GC analy-
ses were performed on a Shimadzu GC-2014 equipped with
a capillary column (HP-5 30 m”0.25 mm) using a flame ioni-
zation detector.
Synthesis of Carbamate Salts from CO2 and Primary
Amines
To a reaction tube, liquid amine (10 mmol) was added. Then
CO2 gas was bubbled into the amine using a balloon. The re-
action is strongly exothermic. After about 5 min, the corre-
Scheme 2. Proposed reaction pathway for the reaction.
sponding carbamate salt was generated as white solid.
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Atmospheric Pressure of CO2 as Protecting Reagent and Reactant
128.3, 128.1, 126.4, 125.1, 120.9, 111.3, 102.6, 55.6, 41.4, 29.0,
19.7, 13.5; HR-MS (ESI): m/z=360.1593, calcd. for
C21H23NO3Na [M+Na]+: 360.1570; EI-MS: m/z (%)=
210.10 (100), 337.20 (47) [M+].
Typical Procedure for the Synthesis of Oxazolidin-2-
ones
To a 10-mL reaction tube, the copper catalyst (5 mol%), sol-
vent (0.4 mL), alkyne (2 mmol), aldehyde (2 mmol), and car-
bamate salt (1 mmol) were added. The reactions were car-
ried out in screw cap vials with a Teflon seal at 808C for
18 h. The reaction mixture was allowed to cool to room tem-
perature and the crude reaction mixture was further purified
by column chromatography (silica gel, petroleum ether/
EtOAc) to afford the desired product oxazolidinones.
(Z)-5-Benzylidene-3-butyl-4-(4-chlorophenyl)oxazolidin-
2-one (5f): 1H NMR (CDCl3, 400 MHz): d=7.55–7.50 (m,
2H), 7.40–7.38 (m, 2H), 7.33–7.25 (m, 4H), 7.20–7.16 (m,
1H), 5.35 (s, 1H), 5.22 (s, 1H), 3.51–3.47 (m, 1H), 2.82–2.79
(m, 1H), 1.46–1.40 (m, 2H), 1.29–1.26 (m, 2H), 0.88 (t, 3H,
J=7.6 Hz); 13C NMR (CDCl3, 100.6 MHz): d=154.7, 147.1,
135.8, 135.2, 133.1, 131.6, 129.4, 129.0, 128.2, 126.9, 104.7,
63.0, 41.5, 28.8, 19.6, 13.5; HR-MS (ESI): m/z=364.1095,
calcd. for C20H20ClNO2Na [M+Na]+: 364.1075; EI-MS: m/z
(%)=214.10 (100), 341.20 (36) [M+].
(Z)-5-Benzylidene-3-butyl-4-(2-chlorophenyl)oxazolidin-
2-one (5g): 1H NMR (CDCl3, 400 MHz): d=7.78–7.76 (m,
1H), 7.51–7.25 (m, 8H), 5.25 (s, 1H), 5.07 (s, 1H), 3.37–3.33
(m, 1H), 2.63–2.61 (m, 1H), 1.44–1.40 (m, 2H), 1.29–1.26
(m, 2H), 0.89 (t, 3H, J=7.8 Hz); 13C NMR (CDCl3,
100.6 MHz): d=155.03, 146.28, 137.87, 133.16, 131.64,
129.67, 129.21, 128.92, 128.34, 128.29, 127.03, 122.92, 104.06,
51.74, 41.65, 31.90, 19.71, 13.52; HR-MS (ESI): m/z=
364.1104, calcd. for C20H20ClNO2Na [M+Na]+: 364.1075;
EI-MS: m/z (%)=179.10 (100), 341.10 (43) [M+].
Characterization Data of Oxazolidin-2-ones
(Z)-5-Benzylidene-3-butyl-4-phenyloxazolidin-2-one
(5a):
1H NMR (CDCl3, 400 MHz): d=7.53–7.51 (m, 2H), 7.44–
7.42 (m, 3H), 7.35–7.28 (m, 4H), 7.20–7.17 (m, 1H), 5.38 (d,
1H, J=2.0 Hz), 5.25 (d, 1H, J=2.0 Hz), 3.55–3.48 (m, 1H,),
2.86–2.80 (m, 1H), 1.46–1.44 (m, 2H), 1.29–1.25 (m, 2H),
0.88 (t, 3H, J=7.4 Hz); 13C NMR (CDCl3, 100.6 MHz): d=
155.1, 147.7, 137.3, 133.5, 129.4, 129.3, 128.4, 128.3, 127.8,
126.9, 104.5, 63.9, 41.6, 29.0, 19.8, 13.6; HR-MS (ESI): m/z=
330.1471, calcd. for C20H21NO2Na [M+Na]+: 330.1465; EI-
MS: m/z (%)=180.10 (100), 307.20 (41) [M+].
(Z)-5-Benzylidene-3-butyl-4-(p-tolyl)oxazolidin-2-one
(Z)-5-Benzylidene-3-butyl-4-(4-hydroxyphenyl)oxazolidin-
2-one (5h): 1H NMR (CDCl3, 400 MHz): d=9.84 (s, 1H),
7.81–7.79 (m, 2H), 7.50–7.48 (m, 2H), 7.29–7.20 (m, 2H),
7.18–7.17 (m, 3H), 5.36 (s, 1H), 5.27 (s, 1H), 3.49–3.44 (m,
1H), 2.85–2.81 (m, 1H), 1.29–1.27 (m, 2H), 1.26–1.25 (m,
2H), 0.87 (t, 3H, J=7.4 Hz); 13C NMR (CDCl3, 100.6 MHz):
d=156.9, 155.5, 147.8, 132.5, 129.4, 128.4, 128.3, 127.0, 116.1,
116.2, 104.7, 63.5, 41.5, 28.9, 19.7, 13.6; HR-MS (ESI): m/z=
346.1433, calcd. for C20H21NO3Na [M+Na]+: 346.1414; EI-
MS: m/z (%)=196.10 (100), 323.20 (21) [M+].
(Z)-4-(5-Benzylidene-3-butyl-2-oxooxazolidin-4-yl)-benzo-
nitrile (5i): 1H NMR (CDCl3, 400 MHz): d=7.78–7.77 (m,
2H), 7.48–7.45 (m, 4H), 7.29–7.24 (m, 2H), 7.18–7.16 (m,
1H), 5.43 (s, 1H), 5.20 (s, 1H), 3.54–3.52 (m, 1H), 2.80–2.81
(m, 1H), 1.46–1.40 (m, 2H), 1.29–1.26 (m, 2H), 0.87 (t, 3H,
J=7.4 Hz); 13C NMR (CDCl3, 100.6 MHz): d=154.9, 146.1,
142.4, 133.5, 132.4, 128.4, 128.3, 128.3, 127.0, 117.7, 113.2,
104.7, 63.5, 41.5, 28.9, 19.7, 13.6; HR-MS (ESI): m/z=
355.1426, calcd. for C21H21NO2Na [M+Na]+: 355.1418; EI-
MS: m/z (%)=205.10 (100), 332.20 (56) [M+].
(5b): 1H NMR (CDCl3, 400 MHz): d=7.50–7.48 (m, 2H),
7.24–7.11 (m, 7H), 5.29 (s, 1H), 5.21 (s, 1H), 3.47–3.44 (m,
1H), 2.81–2.77 (m, 1H), 2.33 (s, 3H), 1.43–1.38 (m, 2H),
1.28–1.21 (m, 2H), 0.87 (t, 3H, J=7.6 Hz); 13C NMR
(CDCl3, 100.6 MHz): d=154.7, 147.8, 139.0, 134.0, 133.3,
129.7, 128.1, 128.0, 127.5, 126.5, 104.0, 63.3, 41.2, 28.6, 20.9,
19.5, 13.3; HR-MS (ESI): m/z=344.1636, calcd. for
C21H23NO2Na [M+Na]+: 344.1621; EI-MS: m/z (%)=
194.10 (100), 321.20 (34) [M+].
(Z)-5-Benzylidene-3-butyl-4-(4-methoxyphenyl)oxazoli-
din-2-one (5c): 1H NMR (CDCl3, 400 MHz): d=7.52–7.50
(m, 2H), 7.30–7.28 (m, 3H), 7.23–7.18 (m, 1H), 7.17–7.15
(m, 1H), 6.94–6.92 (m, 2H), 5.34 (d, 1H, J=2.0), 5.24 (d,
1H, J=2.0), 3.81 (s, 1H), 3.48–3.43 (m, 1H), 2.83–2.79 (m,
1H), 1.46–1.42 (m, 2H), 1.29–1.25 (m, 2H), 0.87 (t, 3H, J=
7.8 Hz); 13C NMR (CDCl3, 100.6 MHz): d=160.2, 154.8,
148.0, 133.4, 129.1, 129.0, 128.3, 128.2, 126.7, 114.5, 104.2,
63.3, 55.2, 41.4, 28.8, 19.7, 13.5; HR-MS (ESI): m/z=
360.1595, calcd. for C21H23NO3Na [M+Na]+: 360.1570; EI-
MS: m/z (%)=210.10 (100), 337.20 (18) [M+].
(Z)-5-Benzylidene-3-cyclopentyl-4-phenyloxazolidin-2-one
(5j): 1H NMR (CDCl3, 400 MHz): d=7.59–7.57 (m, 1H),
7.48–7.35 (m, 2H), 7.29–7.24 (m, 6H), 7.18–7.16 (m, 1H),
5.38 (s, 1H), 5.17 (s, 1H), 3.83–3.79 (m, 1H), 1.90–1.88 (m,
2H), 1.76–1.71 (m, 2H), 1.47–1.43 (m, 4H); 13C NMR
(CDCl3, 100.6 MHz): d=154.5, 148.0, 139.1, 133.5, 131.6,
129.1, 128.3, 128.2, 127.5, 126.7, 104.1, 64.2, 55.9, 29.6, 24.1;
HR-MS (ESI): m/z=342.1482, calcd. for C21H21NO2Na [M+
Na]+: 342.1465; EI-MS: m/z (%)=180.10 (100), 319.10 (42)
[M+].
(Z)-5-Benzylidene-3-cyclohexyl-4-phenyloxazolidin-2-one
(5k): 1H NMR (CDCl3, 400 MHz): d=7.56–7.54 (m, 2H),
7.42–7.39 (m, 3H), 7.36–7.31 (m, 5H), 7.22–7.19 (m, 1H),
5.43 (s, 1H), 5.20 (s, 1H), 3.61–3.55 (m, 1H), 1.82–1.75 (m,
3H), 1.71–1.66 (m, 3H), 1.36–1.23 (m, 5H); 13C NMR
(CDCl3, 100.6 MHz): d=154.5, 148.2, 139.4, 133.4, 131.6,
129.0, 128.4, 128.1, 127.6, 126.6, 104.0, 63.0, 54.5, 31.0, 25.5,
24.9; HR-MS (ESI): m/z=356.1642, calcd. for C22H23NO2Na
(Z)-5-Benzylidene-3-butyl-4-(3-methoxyphenyl)oxazoli-
din-2-one (5d): 1H NMR (CDCl3, 400 MHz): d=7.53–7.51
(m, 2H), 7.36–7.26 (m, 3H), 7.20–7.18 (m, 1H), 6.95–6.91
(m, 2H), 6.84–6.83 (m, 1H), 5.35 (d, 1H, J=2.0), 5.28 (d,
1H, J=2.0), 3.82 (s, 3H), 3.55–3.51 (m, 1H), 2.86–2.82 (m,
1H), 1.49–1.45 (m, 2H), 1.33–1.26 (m, 2H), 0.89 (t, 3H, J=
7.8 Hz); 13C NMR (CDCl3, 100.6 MHz): d=160.3, 155.0,
147.4, 138.8, 133.4, 130.3, 128.4, 128.3, 126.9, 120.0, 114.6,
113.1, 104.4, 63.7, 55.3, 41.6, 28.9, 19.8, 13.6; HR-MS (ESI):
m/z=360.1595, calcd. for C21H23NO3Na f[M+Na]+:
360.1570; EI-MS: m/z (%)=210.10 (100), 337.20 (18) [M+].
(Z)-5-Benzylidene-3-butyl-4-(2-methoxyphenyl)oxazoli-
din-2-one (5e): 1H NMR (CDCl3, 400 MHz): d=7.54–7.52
(m, 2H), 7.38–7.34 (m, 1H), 7.29–7.22 (m, 3H), 7.17–7.14
(m, 1H), 7.00–6.93 (m, 2H), 5.71 (s, 1H), 5.31 (s, 1H), 3.84
(s, 1H), 3.54–3.46 (m, 1H), 2.77–2.73 (m, 1H), 1.46–1.45 (m,
2H), 1.30–1.26 (m, 2H), 0.87 (t, 3H, J=7.8 Hz); 13C NMR
(CDCl3, 100.6 MHz): d=157.8, 155.4, 147.6, 133.8, 130.4,
Adv. Synth. Catal. 2016, 358, 90 – 97
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Bing Yu et al.
[M+Na]+: 356.1621; EI-MS: m/z (%)=180.10 (100), 333.20
Thauer, G. L. Waldrop, Chem. Rev. 2013, 113, 6621–
6658; b) M. Aresta, A. Dibenedetto, A. Angelini,
Chem. Rev. 2013, 114, 1709–1742.
(39) [M+].
(Z)-3-Benzyl-5-benzylidene-4-phenyloxazolidin-2-one (5l):
1H NMR (CDCl3, 400 MHz): d=7.61–7.60 (m, 2H), 7.41–
7.39 (m, 3H), 7.32–7.29 (m, 8H), 7.26–7.24 (m, 2H), 5.17 (s,
1H), 5.12 (s, 1H), 3.99 (s, 2H); 13C NMR (CDCl3,
100.6 MHz): d=155.0, 147.4, 140.2, 139.7, 136.7, 134.7, 133.3,
131.7, 129.3, 128.8, 128.4, 127.6, 127.0, 123.0, 104.7, 62.7,
45.4; HR-MS (ESI): m/z=364.1335, calcd. for C23H19NO2Na
[M+Na]+: 364.1308; EI-MS: m/z (%)=91.10 (100), 341.10
(36) [M+].
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(Z)-3-Butyl-5-(4-methylbenzylidene)-4-phenyloxazolidin-
1
2-one (5m): H NMR (CDCl3, 400 MHz): d=7.42–7.25 (m,
7H), 7.11–7.09 (m, 2H), 5.37 (s, 1H), 5.21 (s, 1H), 3.54–3.47
(m, 1H), 2.85–2.80 (m, 1H), 2.31 (s, 3H), 1.47–1.43 (m, 2H),
1.31–1.25 (m, 2H), 0.87 (t, 3H, J=7.4 Hz); 13C NMR
(CDCl3, 100.6 MHz): d=155.1, 146.9, 137.4, 136.7, 130.6,
129.3, 129.2, 129.1, 128.2, 127.8, 104.4, 63.8, 41.6, 28.9, 21.2,
19.8, 13.6; HR-MS (ESI): m/z=344.1666, calcd. for
C21H23NO2Na [M+Na]+: 344.1621; EI-MS: m/z (%)=
194.10 (100), 321.20 (49) [M+].
(Z)-3-Butyl-5-(4-methoxybenzylidene)-4-phenyloxazoli-
din-2-one (5n): 1H NMR (CDCl3, 400 MHz): d=7.59–7.57
(m, 1H), 7.47–7.36 (m, 3H), 7.33–7.31 (m, 2H), 6.84–6.82
(m, 3H), 5.36 (s, 1H), 5.19 (s, 1H), 3.78 (s, 1H), 3.52–3.46
(m, 1H), 2.85–2.79 (m, 1H), 1.46–1.43 (m, 2H), 1.30–1.26
(m, 2H), 0.87 (t, 3H, J=7.8 Hz); 13C NMR (CDCl3,
100.6 MHz): d=158.4, 155.1, 145.9, 137.5, 133.0, 129.6, 129.2,
127.7, 126.2, 113.8, 104.0, 63.7, 55.2, 41.5, 28.9, 19.7, 13.6;
HR-MS (ESI): m/z=360.1587, calcd. for C21H23NO3Na for
[M+Na]+: 360.1570; EI-MS: m/z (%)=210.10 (100), 337.20
(38) [M+].
(Z)-3-Butyl-5-(4-fluorobenzylidene)-4-phenyloxazolidin-2-
one (5o): 1H NMR (CDCl3, 400 MHz): d=7.50–7.42 (m,
5H), 7.39–7.31 (m, 2H), 6.98–6.94 (m, 2H), 5.37 (s, 1H),
5.21 (s, 1H), 3.52–3.47 (m, 1H), 2.86–2.81 (m, 1H), 1.48–
1.40 (m, 2H), 1.30–1.22 (m, 2H), 0.87 (t, 3H, J=7.8 Hz);
13C NMR (CDCl3, 100.6 MHz): d=162.7, 160.2, 154.8, 147.3,
137.1, 133.5, 129.9, 129.3, 128.5, 127.7, 115.3, 103.3, 63.7,
41.5, 28.8, 19.7, 13.5; HR-MS (ESI): m/z=348.1383, calcd.
for C20H20FNO2Na [M+Na]+: 348.1370; EI-MS: m/z (%)=
198.10 (100), 325.10 (39) [M+].
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Acknowledgements
We thank the Natural Science Foundation of China
(21173021, 21231002, 21276026, 21501010), 973 Program
(2014CB932103) for financial support. B.Y. is grateful for the
financial support from China Postdoctoral Science Founda-
tion funded project (2015M570939) and BIT Basic Research
Foundation (20141942004).
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