Communication
3
4 H, CH2), 2.14 (sept, JH,H = 6.8 Hz, 2 H, CH), 0.91 (d, 3JH,H = 6.7 Hz,
12 H, CH3) ppm. 13C{1H} NMR (D2O): δ = 164.3 (C11), 135.6 (C2),
122.7 (C4), 56.5 (C5), 28.9 (C6), 18.5 (C7) ppm. HRMS (ESI-MS): calcd.
for C11H21N2 [M]+ 181.16993; found 181.16998. C13H23N2O4 (271.34):
calcd. C 57.55, H 8.54, N 10.32; found C 57.41, H 8.58, N 10.61.
Conclusions
In this paper, we showed for the first time that alkali and imid-
azolium hydrogen carbonate salts were efficient catalysts for
the conversion of amino alcohols and diethyl carbonate into
the corresponding cyclic oxazolidinones. Whereas imidazolium
hydrogen carbonate is more expensive and less abundant than
its KHCO3 analogue, it was the only catalyst able to convert a
[iBu2IM](HCO3): [iBu2IM](HC2O4) (1.000 g, 3.67 mmol) was dissolved
M TBAPF6, 65 mL). The electrolysis was performed
in a one-compartment cell with under bubbling of carbon dioxide
in acetonitrile (0.1
nonactivated N-aryl amino alcohol into the related oxazol- (atmospheric pressure) with two carbon-felt electrodes at an ap-
plied current of 30.0 mA. Electrolysis was stopped after an uptake
of 3.0 F mol–1 of imidazolium salt. The solvent was removed under
vacuum. Acetonitrile (a few mL) was added, following by THF (10
to 20 mL) to precipitate the expected product. [iBu2IM](HCO3) was
filtered and dried under vacuum (0.551 g, 2.27 mmol, 61 %). M.p.
idinone in high yield in a catalytic and selective manner. Be-
sides, this catalyst could be recovered and reused at the end of
the catalytic runs without any loss in catalytic performance. It
is therefore a very promising catalyst for the development of
continuous-flow processes in reply to industrial demands.
1
150 °C. H NMR (D2O): δ = 8.84 (s, 1 H, H2), 7.54 (s, 2 H, H4), 4.08
3
(d, 3JH,H = 7.2 Hz, 4 H, CH2), 2.20 (sept, JH,H = 6.8 Hz, 2 H, CH), 0.97
3
(d, JH,H = 6.7 Hz, 12 H, CH3) ppm. 13C{1H} NMR (D2O): δ = 160.3
Experimental Section
(HCO3), 135.4 (C2), 122.7 (C4), 56.5 (CH2), 28.9 (CH), 18.6 (CH3) ppm.
C
12H22N2O3 (242.32): calcd. C 59.48, H 9.15, N 11.56; found C 59.10,
Reagents and Instrumentation: Diethyl carbonate (TCI, 98 %), 2-
(isopropylamino)ethanol (TCI, 99 %), 2-(ethylamino)ethanol (Alfa
Aesar, 98 %), N-(2-hydroxyethyl)aniline (Sigma Aldrich, 98 %), and
Et2O (Sigma Aldrich, 99 %, with BHT stabilizer) were used as re-
ceived. Acetonitrile (Carlo Erba, HPLC PLUS-Gradient) was distilled
from CaH2. Isobutylamine was procured from Alfa Aesar (99 %) or
H 9.13, N 11.79.
Synthesis and Characterization of Oxazolidinones
General Procedure: A 25 mL Schlenk tube was charged with the
catalyst (0.41 mmol), the ꢀ-amino alcohol (8.1 mmol), and diethyl
carbonate (1.5 mL, 12.4 mmol). The Schlenk was closed by a cap
pierced with a needle. The mixture was stirred and heated at 100 °C
in a preheated oil bath for 24 h. The purification method is given
below for each compound.
was obtained from L
-valine.[20] The [BMMIM](BF4) ionic liquid was
prepared by the conventional method based on an alkylation of
1,2-dimethylimidazolium with an excess amount of bromobutane,
following by anion exchange with KBF4 in acetone and dried over-
night under vacuum at 80 °C. NMR spectra were recorded by using
a Bruker 300 MHz Bruker Avance III spectrometer. 1H NMR and
13C{1H} NMR spectra were calibrated to the deuterated solvent on
the basis of the relative chemical shift of the solvent as an internal
standard. Mass spectra were obtained by using a Bruker Micro-ToF
Q instrument in ESI mode. Elemental analyses were performed with
an Analyzer CHN Thermo Electron Flash EA 1112 Series.
For Et-OX and iPr-OX: The solvent was evaporated under vacuum.
A precipitate was formed by adding Et2O (10 mL). The mixture was
cooled overnight at –30 °C. The solution was removed, and the
solvent was evaporated. A yellow liquid was obtained (917 mg,
6.3 mmol. 98 %). Data for Et-OX: 1H NMR (CDCl3): δ = 1.17 (t, 3JH,H
=
3
7.2 Hz, 3 H), 3.32 (q, JH,H = 7.2 Hz, 2 H), 3.55 (m, 2 H), 4.31 (m, 2
H) ppm. 13C{1H} NMR (CDCl3): δ = 12.5, 38.8, 43.9, 61.6, 158.2 ppm.
C5H9NO2 (115.13): calcd. C 55.16, H 7.88, N 12.17; found C 50.43, H
Electrosynthesis: All manipulations were performed by using
Schlenk techniques at room temperature. The supporting electro-
lyte {[TBA](PF6): tetrabutylammonium hexafluorophosphate} was
degassed under vacuum before use and was then dissolved in
1
3
8.10, N 12.44. Data for iPr-OX: H NMR (CDCl3): δ = 1.17 (d, JH,H
=
3
6.8 Hz, 6 H), 3.49 (m, 2 H), 4.09 (hept., JH,H = 6.8 Hz, 1 H), 4.29 (m,
2 H) ppm. 13C{1H} NMR (CDCl3): δ = 19.6, 39.5, 44.7, 61.8, 157.6 ppm.
C6H11NO2 (129.16): calcd. C 55.80, H 8.58, N 10.84; found C 56.15, H
8.74, N 11.60.
acetonitrile to a concentration of 0.1 M. Bulk electrolyses were per-
formed in a one-compartment cell with an Amel 552 potentiostat
coupled with an Amel 721 electronic integrator. Carbon felts (l =
5 cm, L = 3 cm, thickness = 5 mm) were used as working and
counter electrodes.
For Ph-OX: Evaporation of the solvent led to a solid that was solu-
bilized in EtOH (4 mL) and water (2 mL). After heating for a few
minutes, water (2 mL) was introduced, which led to the formation
of a precipitate. The mixture was cooled overnight at 5 °C. The
resulting crystalline product was filtered and washed with cold wa-
ter (2 × 2 mL) and Et2O (2 × 3 mL). The solid was then dissolved in
CH2Cl2, and the resulting organic phase was dried with MgSO4 and
filtered. A white solid was obtained after removal of the solvents
Synthesis of Imidazolium Catalysts[20]
[iBu2IM](HC2O4): Isobutylamine (10 mL, 0.101 mol) was added to
a suspension of paraformaldehyde (3.05 g, 0.102 mol) in toluene
(0.1 L), which was cooled to 0 °C with a water bath. Afterwards, the
mixture was stirred for 30 min and then cooled to 0 °C. Another
equivalent of isobutylamine (10 mL, 0.101 mol) was added, followed
by oxalic acid (9.06 g, 0.101 mol) and water (25 mL). The cooling
bath was removed, and the solution was stirred for 2 h. Then, gly-
oxal (40 wt-% solution in water, 11.5 mL, 0.100 mol) was added.
The mixture was stirred for 2 h at 110 °C and water was removed
by a Dean–Stark apparatus. The resulting dark brown solution was
1
under vacuum (1.142 g, 7.0 mmol. 86 %). H NMR (CDCl3): δ = 4.06
(m, 2 H), 4.48 (m, 2 H), 7.14 (m, 1 H), 7.38 (m, 2 H), 7.55 (m, 2 H)
ppm. 13C{1H} NMR (CDCl3): δ = 45.3, 61.4, 118.4, 124.2, 129.2, 138.4,
155.4 ppm. C9H9NO2 (163.18): calcd. C 66.25, H 5.56, N 8.58; found
C 66.08, H 5.55, N 8.81.
Catalysis Experiments
stirred overnight. All volatile material was removed in vacuo, and Performed in an Ionic Liquid: A 25 mL Schlenk tube was charged
the brown residue was dissolved in a minimum amount of aceto-
nitrile, filtered to remove the solids, and precipitated with diethyl
ether. This resulting brown solid was purified by recrystallization
with [BMMIM](BF4) (3 g, 12.5 mmol), the catalyst (0.41 mmol), 2-
(ethylamino)ethanol (0.79 mL, 8.1 mmol), and diethyl carbonate
(1.5 mL, 12.4 mmol). The Schlenk tube was closed by a cap pierced
(chloroform/THF) to afford an off-white powder (12.5 g, 0.101 mol, with a needle. The mixture was stirred and heated at 100 °C in a
1
68 %). M.p. 129 °C. H NMR (CDCl3): δ = 10.65 (s, 1 H, COOH), 8.77
preheated oil bath for 48 h. The catalytic activities are summarized
4
3
(s, 1 H, H2), 7.30 (d, JH,H = 1.5 Hz, 2 H, H4), 4.14 (d, JH,H = 7.3 Hz, in Table 3.
Eur. J. Org. Chem. 2016, 3514–3518
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim