Cycloaddition of tertiary aziridines and carbon dioxide using a recyclable organocatalyst, 1,3-di-tert-butylimidazolium-2-carboxylate: Straightforward access to 3-substituted 2-oxazolidones

Article abstract of DOI:10.1039/c2gc36414j

Imidazolium-2-carboxylates derived from N-heterocyclic carbenes (NHCs) and CO₂ serve as efficient catalysts for CO₂-carboxylation of tertiary aziridines bearing various substituents such as halogens, ether, olefin, ester, acetal, and nitro groups on the aziridine ring in 2-propanol, leading to 3-substituted-2-oxazolidones in good to excellent yields and with high selectivity. The NHC-CO₂ adducts facilitate nucleophilic attack of the CO₂ moiety on the aziridines, in which the substituents are intact during the carboxylation. The catalyst is successfully recycled up to five times with no apparent loss in activity.

Full text of DOI:10.1039/c2gc36414j

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PAPER
Cycloaddition of tertiary aziridines and carbon dioxide
using a recyclable organocatalyst, 1,3-di-tert-
butylimidazolium-2-carboxylate: straightforward
access to 3-substituted 2-oxazolidones†
Cite this: Green Chem., 2013, 15, 425
Atsushi Ueno, Yoshihito Kayaki and Takao Ikariya*
Imidazolium-2-carboxylates derived from N-heterocyclic carbenes (NHCs) and CO2 serve as efficient
catalysts for CO2-carboxylation of tertiary aziridines bearing various substituents such as halogens,
ether, olefin, ester, acetal, and nitro groups on the aziridine ring in 2-propanol, leading to 3-substituted-
2-oxazolidones in good to excellent yields and with high selectivity. The NHC–CO2 adducts facilitate
nucleophilic attack of the CO2 moiety on the aziridines, in which the substituents are intact during the
carboxylation. The catalyst is successfully recycled up to five times with no apparent loss in activity.
Received 6th September 2012,
Accepted 25th October 2012
DOI: 10.1039/c2gc36414j
www.rsc.org/greenchem
1. Introduction
Over the last few decades, there has been great interest in util-
ization of carbon dioxide (CO2) as a ubiquitous C1 source in
terms of synthetic challenge and environmental issues.1 The
straightforward CO2 fixation into valuable compounds offers
practical advantages in organic synthesis because of its non-
toxic, abundant, and inexpensive properties. 2-Oxazolidones
have been perceived as versatile intermediates for production
of pharmaceuticals and fine chemicals as well as chiral auxili-
aries,2 and thus dehydrative carboxylation of amino alcohol,3
carboxylative cyclization of propargylamines,4 and cyclo-
addition of aziridines5 have been explored for construction of
the five-membered urethane ring structure. The ring-opening
reaction of secondary protic aziridines with CO2 in the pres-
ence of various catalysts or additives has been demonstrated to
give 2-oxazolidones, and oligomeric or polymeric products
containing urethane and amine units were also obtainable
depending on the reaction conditions using high pressure or
supercritical CO2 systems.5a,f,6,7 Recently, some advances have
been made for the cycloaddition of tertiary aziridines and CO2
promoted by several halide salts or natural α-amino acids,
leading to selective formation of N-substituted 2-oxazolido-
nes.5l–w However, the reaction scopes are mostly limited to
Scheme 1 Carboxylative cyclization of propargyl alcohols catalyzed by imida-
zolium-2-carboxylates.
substrates bearing simple aliphatic and aromatic groups on
the nitrogen atom.8 We have recently developed the imidazo-
lium-2-carboxylates (1; NHC–CO2) catalyzed carboxylative cycli-
zation of propargylic alcohols and cycloaddition of epoxides to
CO2, producing cyclic carbonates as shown in Scheme 1.9 The
NHC–CO2 adducts derived from NHCs and CO2 are utilized as
a convenient CO2 carrier10 to accomplish CO2 fixation through
the nucleophilic incorporation of the OvCvO unit.9,11 These
results inspired us to apply further this CO2 fixation protocol
to the synthesis of urethane using CO2. Herein we report that
the NHC–CO2 adducts serve as efficient catalysts for cyclo-
addition of aziridines to CO2 to afford the corresponding
2-oxazolidones with a variety of functional groups. Further-
more, it is successfully demonstrated that the organocatalyst
can be simply recovered by precipitation and reused without a
significant loss of activity.
Graduate School of Science and Engineering, Tokyo Institute of Technology,
2-12-1-E4-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan.
E-mail: tikariya@apc.titech.ac.jp; Fax: +81 3 5734 2637; Tel: +81 3 5734 2636
†Electronic supplementary information (ESI) available: Synthetic procedure for
new aziridine substrates, NMR spectra of aziridines (2) and 2-oxazolidones (3)
and crystal structure determination of 3a. CCDC 896141. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c2gc36414j
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Table 1 Cycloaddition of N-benzylaziridine 2a and CO2 with catalyst 1aa
Entry
Solvent
Cat
% Yieldb
1
2
3
4
5
6
7
8
9
(CH3)2CHOH
(CH3)2CHOH
(CH3)2CHOH
(CH3)2CHOH
CH3CH2OH
(CH3)3COH
Benzene
1a
1b
1c
1d
1a
1a
1a
1a
1a
92
70
68
63
50
26
1
DMF
THF
66
23
a Reaction conditions: 2 (1.0 mmol), 1 (0.05 mmol), solvent (2.0 mL),
Fig. 1 Temperature effect on the yield of 3a. Reaction conditions: 1a
(0.05 mmol), 2a (1.0 mmol), 2-propanol (2.0 mL) under 5.0 MPa of CO2 for 15 h.
5.0 MPa, 90 °C, 20 h. b Determined by 1H NMR spectroscopy.
2. Results and discussion
The carboxylation reaction was performed using N-benzylaziri-
dine (2a) as a model substrate with 5.0 MPa of CO2 at 90 °C for
20 h in the presence of an organocatalyst, 1,3-bis(tert-butyl)-
imidazolium-2-carboxylate (1a) (5 mol%). The halide free cata-
lyst 1a was obtained by treatment of CO2 (0.1 MPa) with the
parent NHC generated from imidazolium tetrafluoroborate in
THF containing an equimolar amount of KOC(CH3)3.12 In the
absence of any catalysts and additives, 2a was hardly converted
to give the cycloaddition product in less than 16% yield, and a
mixture of oligomers was formed. The outcome of the reaction
is highly influenced by the structure of the NHC catalysts and
reaction conditions. Table 1 lists some representative results of
the reaction. Catalyst screening tests revealed that the catalyst
1a promoted the carboxylation of 2a in 2-propanol under
the standard conditions to give the desired urethane product,
3-benzyl-2-oxazolidone (3a), in 92% yield (entry 1), whereas
1,3-diisopropyl- and diaryl-substituted NHC–CO2 adducts
(1b–1d) exhibited somewhat lower catalytic activity (63–70%)
(entries 2–4). A protic solvent 2-propanol is the best solvent for
the reaction. In ethanol, the substrate 2a was all consumed to
yield the product 3a in addition to the oligomeric byproducts
determined by the 1H NMR spectrum (entry 5). The reaction
Fig. 2 CO2 pressure effect on the yield of 3a. Reaction conditions: 1a
(0.05 mmol), 2a (1.0 mmol), 2-propanol (2.0 mL) at 90 °C for 20 h.
catch-and-release phenomenon of the NHC catalyst exists in
the reaction phase, and the reaction will be retarded by un-
favorable decarboxylation of NHC–CO2 at an elevated temp-
erature above 90 °C. Although the reaction did not take place
at all under an atmospheric pressure of CO2 at 90 °C for 20 h,
an increase in the pressure of CO2 caused a positive effect
on the urethane formation reaching 92% yield under 5.0 MPa
(Fig. 2), indicating preferable formation of the NHC–CO2
adduct at a higher pressure.13
The substrate scope was then examined by using catalyst 1a
under the optimized conditions of 5.0 MPa of CO2 at 90 °C in
2-propanol. As listed in Table 2, the reaction of 2b having a
tert-butyl group gave the product in a good yield (entry 2;
t
in BuOH gave 3a in 26% yield without formation of the un-
desired products (entry 6). In contrast to alcoholic solvents,
the reaction in benzene was strongly retarded to give the
product in less than 1% yield (entry 7). An aprotic polar
solvent, DMF, gave a satisfactory chemical yield (66%) in the
carboxylation of 2a (entry 8).
Catalytic performance was markedly influenced by the reac-
tion temperature and pressure. On increasing the temperature
from 60 °C to 100 °C under 5.0 MPa for 15 h, the chemical
yield of 3a showed the maximum at around 90 °C as shown
in Fig. 1. It can be reasonably assumed that a dynamic CO2
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a
Table 2 Carboxylation of N-substituted aziridines catalyzed by NHC–CO2
Entry Aziridine R1
Product % Yieldb,c
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
CH2C6H5
C(CH3)3
CH2CH2OH
CH2CH2OCH2C6H5
CH2CH2OCH2CHvCH2
3a
3b
3c
3d
3e
92(85)
74
40
81(72)
95(88)
90(85)
91(82)
82(78)
90(78)
75(70)
82(78)
82(75)
80(75)
94(88)
60(55)
CH2CH2OSi(CH3)2[C(CH3)3] 3f
CH2CH2OC(vO)C6H5
CH2CH2OCH2-3-C6H4F
CH2CH2OCH2-3-C6H4Cl
CH2CH2OCH2-3-C6H4Br
CH2CH2OCH2-3-C6H4I
CH2CH2OCH2-3-C6H4NO2
CH2CH2OCH2-3-C6H4OCH3 3m
CH2CH2OCH2C6H3(OCH2O) 3n
CH2CH2OCH2-2-thienyl
3g
3h
3i
3j
3k
3l
9
10
11
12
13
14
15
Fig. 3 Possible mechanisms of cycloaddition of tertiary aziridines with CO2.
3o
performance of 1a was well maintained during the catalyst
reuse six times, leading to 3a in a range of 90–92% yields.
While the precise mechanism of the present reaction still
remains obscure, the key step is probably nucleophilic attack
of the CO2 unit on the distorted aziridine ring of the substrate,
as proposed in our previous work on carboxylation of propar-
gyl alcohols and epoxides catalyzed by NHC–CO2 adducts.9 As
shown in Fig. 3, the zwitterionic CO2 adduct would promote
the C–N bond cleavage to give an intermediate where the elec-
trophilic carboxyl group is susceptible to attack by the nitro-
gen, and then the product urethane and the regenerated NHCs
are released (cycle A). The positive effect on the urethane yield
observed with the catalyst 1a bearing electron donating alkyls
rather than the less basic catalysts 1c and 1d seems to be con-
sistent with the nucleophilic attack mechanism. Because the
possible ionic intermediates are influenced by the polarity of
the reaction medium, the urethane formation was significantly
retarded in less polar solvents as mentioned above (Table 1,
entry 7).
a Reaction conditions: 2 (1.0 mmol), 1a (0.05 mmol), 2-propanol
(2.0 mL), 5.0 MPa, 90 °C, 20 h. b Determined by 1H NMR spectroscopy.
c Isolated yields in parenthesis.
a
Table 3 Reusability of catalyst 1a in cycloaddition of 2a and CO2
Cycle
% Recovery
% Yieldb
1
2
3
4
5
6
99.5
99.2
99.2
99.4
99.5
99.1
92
91
92
90
90
90
a Reaction conditions: 2 (9.0 mmol), 1a (0.45 mmol), 2-propanol
(18.0 mL), 5.0 MPa, 90 °C, 20 h. b Determined by 1H NMR
spectroscopy.
In an alternative mechanism (cycle B), zwitterionic aziridi-
nium-1-carboxylate, generated from the tertiary aziridine and
CO2, acts as a catalyst to promote the ring-opening of other
aziridine molecules via the nucleophilic attack. In the absence
of NHC–CO2 adducts, this catalytic cycle could provide the
undesired oligomeric byproducts (vide supra). These results
strongly suggest that the NHC–CO2 catalyst accelerates the car-
boxylation by suppressing formation of oligomer in 2-propanol
leading to the selective CO2 fixation.
74%). Although commercially available 1-(2-hydroxyethyl)aziri-
dine 2c resulted in a moderate yield of 40% (entry 3), the cata-
lyst system tolerates a broad range of other functional groups.
In the reaction of 2d–o containing various substituents on the
nitrogen atom, the desired urethanes were obtained in the
range of 60–95% and successfully isolated in 55–88% yields
after column chromatographic purification (entries 4–15). For
example, carboxylation of 1-aziridineethanol derivatives pro-
tected by benzyl ether (2d), allyl (2e), and silyl (2f) groups
efficiently proceeded to give cyclic urethane up to 95% yield.
Other polar substituents including ester, halides, nitro, ether,
and acetal groups as well as a heteroaromatic ring remained
intact during the cycloaddition.
3. Conclusions
In conclusion, we demonstrated that the cycloaddition of
Potential practicability of the present carboxylation was tertiary aziridines with CO2 can be efficiently promoted by imi-
demonstrated by a simple catalyst recovery and reuse pro- dazolium-2-carboxylates in 2-propanol. The NHC–CO2 adduct
cedure in a scale-up reaction using 1.2 g of 2a. The imidazo- facilitates incorporation of the CO2 molecule to provide access
lium-2-carboxylate catalyst 1a was successfully recovered by to synthetically useful 2-oxazolidones selectively. Notably, the
precipitation from the reaction mixture by addition of diethyl present organocatalysis tolerates various functional groups
ether under a CO2 atmosphere followed by filtration. More and heteroatoms on the substrate, leading to substituted
than 99% of the NHC–CO2 adduct based on the amount of 2-oxazolidones with high efficiency, and offers the promising
loading catalyst was successfully isolated after drying under product/catalyst separation method that permits catalyst reuse
reduced pressure as shown in Table 3. The catalytic without a significant loss of catalytic activity.
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(m, 2H), 3.58–3.61 (m, 2H), 3.67–3.71 (m, 2H), 3.96–3.98 (m,
4. Experimental section
2
3
2H), 4.27–4.31 (m, 2H), 5.17 (ddt, 1H, JHH = 1.8 Hz, JHH
=
CAUTION: The experiments described here could involve risk of 10.4 Hz, 4JHH = 1.5 Hz; HCvCH2), 5.22 (ddt, 1H, 2JHH = 1.8 Hz,
4
an explosion and were conducted using equipment and safety pre- 3JHH = 17.3 Hz, JHH = 1.6 Hz; HCvCH2), 5.81–5.92 (m, 1H;
cautions suitable for high pressure CO2 conditions.
HCvCH2); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.2, 46.0, 61.9,
68.6, 71.8, 117.0, 134.3, 158.5 (CvO); HRMS (ESI) calcd for
C8H14NO3 172.0968 (M + H+), found 172.0966.
General methods
Solvents were dried by refluxing over sodium benzophenone
3-[2-(TERT-BUTYLDIMETHYLSILYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3F).
ketyl (THF, ether, benzene) or CaH2 (2-propanol, ethanol, tert- Colorless liquid; 85% yield (208.3 mg); 1H NMR (399.8 MHz,
butyl alcohol) and distilled under argon. Carbon dioxide CDCl3) δ 0.05 (s, 6H; Si(CH3)2C(CH3)3), 0.88 (s, 9H; Si-
(99.999%) was purchased from Showa Tansan. Imidazolium- (CH3)2C(CH3)3), 3.36 (m, 2H), 3.70 (m, 2H), 3.76 (m, 2H), 4.29
2-carboxylates (1a–1d) were prepared according to the reported (m, 2H); 13C{1H} NMR (100.5 MHz, CDCl3) δ −5.56, 18.0, 25.7,
method using Schlenk techniques under an argon atmos- 46.2, 46.7, 61.8, 61.9, 158.5 (CvO). Anal. Calcd for
1
phere.14 The H and 13C NMR spectra were acquired on JEOL C11H23NO3Si: C, 53.84; H, 9.52; N, 5.71. Found: C, 53.44;
JNM-LA300 and JNM-ECX400 spectrometers as solutions in H, 9.52; N, 5.62.
CDCl3. The NMR chemical shifts were referenced to SiMe4
3-[2-(BENZOYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3G). Pale yellow
by using residual proton impurities in the deuterated solvent. liquid; 82% yield (197.2 mg); 1H NMR (399.8 MHz, CDCl3)
Elemental analyses were carried out using a PE2400 Series II δ 3.68 (m, 4H), 4.32 (m, 2H), 4.48 (m, 2H), 7.42–8.03 (m, 5H;
CHNS/O Analyzer (Perkin Elmer). High-resolution mass COC6H5); 13C{1H} NMR (100.5 MHz, CDCl3) δ 43.5, 45.2, 61.8,
spectra were obtained on a TOF MS instrument with an ESI 62.3, 128.5, 129.5, 129.6, 133.2, 158.3 (NCO), 166.2(COO). Anal.
source (JEOL JMS-T100LC mass spectrometer).
Calcd for C13H15NO5: C, 58.86; H, 5.70; N, 5.28. Found:
C, 58.73; H, 5.62; N, 5.25.
3-[2-(3-FLUOROPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3H).
Typical procedure for the cycloaddition
The reaction was carried out in a 50 mL stainless steel auto- Colorless liquid; 78% yield (187.2 mg); 1H NMR (399.8 MHz,
clave equipped with a stirring bar. The autoclave containing CDCl3) δ 3.49–3.50 (m, 2H), 3.65–3.72 (m, 4H), 4.29–4.33
the catalyst (0.05 mmol) was purged with argon gas to remove (m, 2H), 4.51 (s, 2H; OCH2C6H4F), 6.95–7.35 (m, 4H;
oxygen. Aziridines (1.00 mmol) and 2-propanol (2.0 mL) were OCH2C6H4F); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.2, 46.0,
introduced into the autoclave with a syringe while the vessel 61.9, 68.8, 72.2, 114.0, 114.3 (J = 21.08), 114.4, 114.6 (J = 21.09),
was purged with argon. The vessel was charged with CO2 to 122.81, 122.83 (J = 1.92), 129.9, 130.0 (J = 8.62), 140.4, 140.5
the required pressure through a cooling apparatus with an (J = 6.70), 158.5 (CvO), 161.6, 164.1 (1JCF = 246.3 Hz). Anal.
HPLC pump (JASCO SCF-Get). After stirring the reaction Calcd for C12H14FNO3: C, 60.24; H, 5.90; N, 5.85. Found:
mixture under the predetermined conditions, the autoclave C, 60.44; H, 5.70; N, 5.58.
was cooled in an ice bath to room temperature within a few
3-[2-(3-CHLOROPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3I).
minutes, and CO2 was slowly vented. The reaction mixture was Colorless liquid; 78% yield (199.7 mg); 1H NMR (399.8 MHz,
1
concentrated in vacuo and analyzed by H NMR spectroscopy CDCl3) δ 3.46–3.49 (m, 2H), 3.64–3.72 (m, 4H), 4.29–4.33
with Durene (11.2 mg, 0.08 mmol; an internal standard) after (m, 2H), 4.49 (s, 2H; OCH2C6H4Cl), 7.15–7.31 (m, 4H;
filtration through a PTFE filter (0.45 μm). The crude products OCH2C6H4Cl); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.2, 46.0,
were purified by column chromatography on silica gel 61.9, 68.8, 72.2, 125.5, 127.5, 127.8, 129.7, 134.3, 139.9, 158.4
(hexane–ethyl acetate = 5 : 1) and Kugelrohr distillation except (CvO). Anal. Calcd for C12H14ClNO3: C, 56.37; H, 5.52;
the urethanes, 3b and 3c.
N, 5.48. Found: C, 56.75; H, 5.40; N, 5.28.
3-BENZYL-1,3-OXAZOLIDIN-2-ONE (3A). White solid; 85% yield
3-[2-(3-BROMOPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3J).
Colorless liquid; 70% yield (210.7 mg); 1H NMR (399.8 MHz,
1
3
(148.8 mg); H NMR (399.8 MHz, CDCl3) δ 1.28 (t, 2H, JHH
=
3
2.1 Hz), 1.83 (t, 2H, JHH = 2.1 Hz), 3.39 (s, 2H; CH2C6H5), CDCl3) δ 3.47–3.50 (m, 2H), 3.64–3.70 (m, 4H), 4.30–4.34
7.26–7.38 (m, 5H; CH2C6H5); 13C{1H} NMR (100.5 MHz, CDCl3) (m, 2H), 4.49 (s, 2H; OCH2C6H4Br), 7.19–7.47 (m, 4H;
δ 43.9, 48.4, 61.7, 127.9, 128.1, 128.8, 135.7, 158.5 (CvO); OCH2C6H4Br); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.2, 46.0,
HRMS (ESI) calcd for C10H11NNaO 200.0682 (M + Na+), found 61.9, 68.8, 72.1, 122.3, 125.9, 130.0, 130.4, 130.8, 140.2, 158.5
200.0687.
(CvO). Anal. Calcd for C12H14BrNO3: C, 48.02; H, 4.70; N,
3-[2-(BENZYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3D). Colorless liquid; 4.67. Found: C, 47.93; H, 4.55; N, 4.63.
1
72% yield (159.8 mg); H NMR (399.8 MHz, CDCl3) δ 3.48 (m,
3-[2-(3-IODOPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE
(3K).
2H), 3.64–3.98 (m, 4H), 4.29 (m, 2H), 4.52 (s, 2H; CH2C6H5), Colorless liquid; 78% yield (273.0 mg); 1H NMR (399.8 MHz,
7.29–7.37 (m, 5H; CH2C6H5); 13C{1H} NMR (100.5 MHz, CDCl3) CDCl3) δ 3.46–3.49 (m, 2H), 3.63–3.70 (m, 4H), 4.29–4.33
δ 44.2, 45.9, 61.9, 68.6, 73.0, 76.6, 127.6, 127.7, 128.4, 137.8, (m, 2H), 4.45 (s, 2H; OCH2C6H4I), 7.06–7.68 (m, 4H;
158.4 (CvO). Anal. Calcd for C12H15NO3: C, 65.14; H, 6.83; N, OCH2C6H4I); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.1, 46.0,
6.33. Found: C, 64.66; H, 6.70; N, 6.29.
61.9, 68.8, 72.0, 94.3, 126.6, 130.1, 136.4, 136.7, 140.2, 158.5
3-[2-(ALLYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3E). Colorless liquid; (CvO). HRMS (ESI) calcd for C12H14INO3 369.9916 (M + Na+),
88% yield (147.8 mg); 1H NMR (399.8 MHz, CDCl3) δ 3.43–3.46 found 369.9929.
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3-[2-(3-NITROPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE
(3L). dai Center, Technical Department, Tokyo Institute of Technol-
Orange liquid; 75% yield (201.3 mg); 1H NMR (399.8 MHz, ogy, for HRMS analysis.
CDCl3) δ 3.48–3.51 (m, 2H), 3.67–3.71 (m, 4H), 4.29–4.33
(m, 2H), 4.60 (s, 2H; OCH2C6H4NO2), 7.49–8.16 (m, 4H;
OCH2C6H4NO2); 13C{1H} NMR (100.5 MHz, CDCl3) δ 44.2, 46.1,
62.1, 69.2, 71.8, 122.1, 122.8, 129.6, 133.3, 140.3, 148.5,
Notes and references
158.7 (CvO); HRMS (ESI) calcd for C12H14N2O5Na 289.0800
(M + Na+), found 289.0800.
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3-[2-(3-METHOXYPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE (3M).
Colorless liquid; 75% yield (191.3 mg); 1H NMR (399.8 MHz,
CDCl3) δ 3.46–3.50 (m, 2H), 3.63–3.69 (m, 4H), 3.80 (s, 3H;
CH3O), 4.27–4.31 (m, 2H), 4.49 (s, 2H; OCH2C6H4OCH3),
6.82–7.28 (m, 4H; OCH2C6H4OCH3); 13C{1H} NMR (100.5 MHz,
CDCl3) δ 44.2, 45.9, 55.1, 61.9, 68.5, 72.9, 113.1, 119.8, 129.4,
139.4, 158.5 (CvO), 159.7 (CH3OC). Anal. Calcd for
C13H17NO4: C, 62.14; H, 6.82; N, 5.57. Found: C, 62.03; H, 6.70;
N, 5.32.
3-[2-(3,4-METHYLENEDIOXYPHENYLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-
2-ONE (3N). Colorless liquid; 88% yield (234.1 mg); 1H NMR
(399.8 MHz, CDCl3) δ 3.46 (m, 2H), 3.60 (m, 2H), 3.67 (m, 2H),
4.29 (m, 2H), 4.41 (s, 2H; CH2C6H3OCH2O), 5.95 (s, 2H;
CH2C6H3OCH2O), 6.76–6.80 (m, 3H; CH2C6H3OCH2O); 13C{1H}
NMR (100.5 MHz, CDCl3) δ 44.2, 45.9, 61.9, 68.3, 72.9, 101.0,
108.0, 108.3, 121.2, 131.6, 147.2, 147.7, 158.5 (CvO). Anal.
Calcd for C13H15NO5: C, 58.86; H, 5.70; N, 5.28. Found:
C, 58.73; H, 5.62; N, 5.25.
3-[2-(THIOPHEN-2-YLMETHYLOXY)ETHYL]-1,3-OXAZOLIDIN-2-ONE
(3O).
Orange liquid; 52% yield (119.6 mg); 1H NMR (399.8 MHz,
CDCl3) δ 3.45 (m, 2H), 3.63–3.71 (m, 4H), 4.29 (m, 2H), 4.67
(s, 2H; CH2C4H3S), 6.96–7.29 (m, 3H; CH2C4H3S); 13C{1H} NMR
(100.5 MHz, CDCl3) δ 44.1, 46.0, 125.9, 126.4, 126.7, 140.5,
158.5 (CvO). Anal. Calcd for C10H13NO3S: C, 52.85; H, 5.77;
N, 6.16. Found: C, 52.95; H, 5.74; N, 6.09.
CRYSTAL STRUCTURE DETERMINATION OF 3A. Single crystals suitable
for X-ray diffraction were grown by slow diffusion of hexane
into an ethyl acetate saturated solution of 3a. Crystal data:
C10H11NO2 M = 177.20, orthorhombic, a = 5.955(3) Å, b = 7.460
(3) Å, c = 19.878(8) Å, V = 883.1(6) Å3, T = 93 K, space group
P212121 (no. 19), Z = 4, Dc = 1.333 g cm−3, λ(MoKα) = 0.71070 Å,
7147 reflections measured, 2023 unique (Rint = 0.029), which
were used in all calculations. The structure was solved by
the direct method (SIR92) and refined by the full-matrix
least-squares methods on F2 with 130 parameters. R1 = 0.030
(I > 2σ(I)) and wR2 = 0.092, GOF 1.00; max/min residual density
0.27/−0.28 e Å−3. The details of the refinement are described
in a cif file (CCDC 896141).
Acknowledgements
This work was supported by JSPS KAKENHI Grant Numbers
22225004 and 24350079, and partly supported by the GCOE
Program. Y. K. gratefully acknowledges financial support from
Research Seeds Quest Program, Japan Science and Technology
Agency (JST). The authors thank Material Analysis Suzukake-
This journal is © The Royal Society of Chemistry 2013
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430 | Green Chem., 2013, 15, 425–430
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