Microwave-assisted base-catalysed rearrangement of 3-aryl(arylalkyl)-4- iminooxazolidin-2-ones into 4-arylimino- and 4-arylalkyliminooxazolidin-2-ones

Article abstract of DOI:10.1055/s-2006-942352

The microwave-assisted base-catalysed Dimroth rearrangement of 3-aryl(arylalkyl)-4-iminooxazolidin-2-ones into 4-arylimino- and 4-arylalkyliminooxazolidin-2-ones is described. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942352

PAPER
1803
Microwave-Assisted Base-Catalysed Rearrangement of 3-Aryl(arylalkyl)-
4-iminooxazolidin-2-ones into 4-Arylimino- and 4-Arylalkyliminooxazolidin-
2-ones
M
icrowave-Ass
h
iste
d
Synthe
o
sis of 4-Subs
m
titute
d
Iminooxazol
aidin-2-oness Kurz,* Khalid Widyan, Mehdi Khankischpur
Institute of Pharmacy, University of Hamburg, Bundesstraße 45, 20146 Hamburg, Germany
Fax +49(40)428386573; E-mail: kurz@chemie.uni-hamburg.de
Received 4 October 2005; revised 13 January 2006
We now describe the microwave-assisted synthesis of
4-arylimino- and 4-arylalkyliminooxazolidin-2-ones
starting from 3-substituted 4-iminooxazolidin-2-ones 4.
Abstract: The microwave-assisted base-catalysed Dimroth re-
arrangement of 3-aryl(arylalkyl)-4-iminooxazolidin-2-ones into
4-arylimino- and 4-arylalkyliminooxazolidin-2-ones is described.
Substrates 4 have been prepared in a novel one-pot reac-
tion by stepwise treatment of cyanohydrins 1 with 1,1¢-
carbonyldiimidazole (CDI) and primary amines via the
open chained intermediates 2 and 3 (Scheme 1, Table 1).
The formation of compounds 4 was readily monitored by
IR spectroscopy. 4-Iminooxazolidin-2-ones 4 are charac-
terised by two sharp IR absorption bands at 1670–1685
(C=N) cm–1 and 1760–1791 (C=O) cm–1.
Key words: heterocycles, ring closure, rearrangements, amidines,
microwave chemistry
The structural modification of bioactive heterocycles us-
ing microwave-assisted chemistry represents an important
challenge for organic and medicinal chemists.1 4-Arylimi-
no- and 4-arylalkyliminooxazolidin-2-ones I (Figure 1)
are regioisomers of N-substituted 4-iminooxazolidin-2-
ones II, a class of compounds that attracted interest in ag-
ricultural chemistry, especially due to their fungicidal ac-
tivity.2 Compounds II (Figure 1) are commonly prepared
by reactions of cyanohydrins with isocyanates via a-cy-
anocarbamates in the presence of a base.2
O
N
N
OH
CN
O
CDI
H2NR2
R1
R1
CN
CH2Cl2
2
1
O
O
H
O
O
O
R2
Et3N
O
R1
N
R2
N
O
N
R3
NH
O
N
O
N
H
O
R1
CN
NH
4a–g
R1
R1
R1
NH
R2
III
R2
R2
II
3
N
R3
Scheme 1 Synthesis of 3-substituted 4-iminooxazolidin-2-ones 4.
Table 1 Synthesis of 3-Substituted 4-Iminooxazolidin-2-ones 4
I
Figure 1
4
a
b
c
d
e
f
R1
R2
Yield (%)
To the best of our knowledge only a few examples of the
title compounds I are known and no general synthetic
method has yet been established for their preparation.
Kauffman reported the synthesis of two 4-(p-tolylimi-
no)oxazolidin-2-ones by mild acidic hydrolysis of
2-ethoxy-4-(p-tolylimino)-2-oxazolines.3 Stronger acidic
reaction conditions afforded the corresponding oxazoli-
din-2,4-diones. Wu described one example of I in the
course of the structural modification of a-benzoxazolyl-
carbamates with herbicidal activity.4 L’abbé suggested a
tautomeric structure III for the title compounds (I).5
Again, the acidic hydrolysis of III (Figure 1) led to the
corresponding oxazolidin-2,4-diones.
1-Naphthyl
Cyclopropyl
1-Naphthyl
2-Naphthyl
CH3
3-FPh
65
72
70
68
75
73
50
4-CNPh
4-CNPh
4-FPh
4-CH3Bn
4-FBn
2-ClBn
CH3
g
Ph
In two previous publications we described the sodium
methoxide supported decarbonylation of O-substituted
3-hydroxy-4-iminooxazolidin-2-ones into a-hydroxyami-
doximes as well as their triethylamine-catalysed Dimroth
rearrangement into 4-alkoxy(aralkoxy)iminooxazolidin-
2-ones.6,7 These results encouraged us to investigate the
behaviour of compounds 4 under similar reaction condi-
SYNTHESIS 2006, No. 11, pp 1803–1806
Advanced online publication: 05.05.2006
DOI: 10.1055/s-2006-942352; Art ID: T13905SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
0
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T. Kurz et al.
PAPER
tions. However, when compound 4a was heated to reflux The structures of compounds 4 and 5 were elucidated by
with either triethylamine–dichloromethane or with sodi- IR, 1H, 13C NMR spectroscopy and elemental analysis.
um methoxide (0.2 equiv) in methanol the starting materi-
al was recovered unchanged.
In conclusion, we have established a novel one-pot reac-
tion for the synthesis of N-substituted 4-iminooxazolidin-
Interestingly, the reaction of 4a with equimolar amounts 2-ones by reacting cyanohydrins 1 stepwise with 1,1¢-car-
of sodium methoxide in refluxing methanol furnished the bonyldiimidazole and primary amines. Furthermore, we
rearranged 4-(3-fluorophenylimino)-5-(1-naphthyl)ox- describe the microwave-assisted, base-catalysed rear-
azolidin-2-one (5a) in 52% yield after three hours. Dis- rangement of N-substituted 4-iminooxazolidin-2-ones 4
crimination between the structures of compounds 4a and into the target compounds 5.
5a was accomplished by IR, 1H and 13C NMR spectrosco-
py. While the IR spectrum of 4a showed two characteris-
Melting points were determined on a Mettler FP 62 apparatus and
are uncorrected. Elemental analyses were carried out with a Herae-
tic absorption bands at 1789 (C=O) cm–1 and 1676 (C=N)
cm–1, the spectrum of 5a showed two bathochromic-shift-
us CHN-O-Rapid instrument. IR spectra were recorded on a Shi-
ed absorption bands at 1747 (C=O) cm–1 and 1630 (C=N)
cm–1.
1
madzu FT-IR 8300 spectrometer. H NMR (400 MHz) and 13C
NMR (100 MHz) spectra were recorded on a Bruker AMX 400
spectrometer using tetramethylsilane as an internal standard and
DMSO-d6 as solvent. Microwave chemistry was carried out using a
CEM Corporation Focused Microwave System, Model Discover.
Next we turned our attention to the microwave-assisted
synthesis of compounds 5. Indeed, treatment of com-
pounds 4a–e with equimolar amounts of sodium methox-
ide in methanol led to 4-aryl(arylalkyl)iminooxazolidin-
2-ones 5a–e in only 5–20.5 minutes (Scheme 2, Table 2,
parameters a). However, the microwave-assisted rear-
rangement of 4-fluorobenzyl and 2-chlorobenzyl substi-
tuted 4-iminooxazolidin-2-ones 4f,g into 5f,g required
somewhat harsher reaction conditions (parameters b). A
simple standard work-up procedure followed by recrystal-
lisation from an appropriate solvent afforded the target
compounds 5a–g in 51–72% yield.8
Preparation of 4a–g; General Procedure
A solution of cyanohydrin 1 (5 mmol) in anhyd CH2Cl2 (5 mL) was
added dropwise over a period of 10 min to a suspension of 1,1¢-car-
bonyldiimidazole (851 mg, 5.25 mmol) in anhyd CH2Cl2 (5 mL) un-
der ice cooling. After stirring at r.t. for 10 min a solution of the
appropriate amine (5 mmol) in anhyd CH2Cl2 (5 mL) was added and
the reaction mixture was stirred at r.t. for 1 h. Et3N (3 mL) was add-
ed and the reaction mixture was stirred for 6–12 h until two sharp
bands in the IR spectra appeared at 1760–1791 cm–1 and 1670–1685
cm–1. The solvent was removed under reduced pressure and the res-
idue was dissolved in EtOAc (25 mL). The organic layer was
washed with H2O (3 × 10 mL), dried over MgSO4 and evaporated.
Removal of the solvent afforded 4a–g as solid compounds. Analyt-
ically pure products were obtained after recrystallisation from
EtOAc–hexane (4b,c,e–g) or THF (4a,d).
O
O
O
O
N
H
O
N
O
N
R2
NH
NaOMe
MeOH
R1
R1
R1
4a–g
N
HN
R2
R2
3-(3-Fluorophenyl)-4-imino-5-(1-naphthyl)oxazolidin-2-one
(4a)
5a–g
Yield: 1.04 g (65%); colourless solid; mp 125 °C (THF).
IR (KBr): 1789, 1676 cm–1.
Scheme 2 Synthesis of 4-arylimino- and 4-arylalkyliminooxazolidin-
2-ones 5.
1H NMR (DMSO-d6): d = 6.95 (s, 1 H), 7.20 (t, J = 7.1 Hz, 1 H),
7.30–7.40 (m, 2 H), 7.45–7.70 (m, 5 H), 7.95 (t, J = 8.9 Hz, 2 H),
8.10 (d, J = 7.9 Hz, 1 H), 8.72 (s, 1 H).
Table 2 Synthesis of 4-Arylimino- and 4-Arylalkyliminooxazoli-
din-2-ones 5
13C NMR (DMSO-d6): d = 79.9, 113.4, 113.8, 116.5, 116.6, 122.0,
123.2, 124.8, 125.6, 127.4, 128.0, 129.5, 131.0, 131.1, 131.6, 142.4,
150.8, 160.5.
5
a
b
c
d
e
f
R1
R2
Yield (%) Hold time (min)a
1-Naphthyl
Cyclopropyl
1-Naphthyl
2-Naphthyl
CH3
3-FPh
64
60
63
69
72
61
51
4.5b
8.5b
5.5b
5.5b
Anal Calcd for C19H13N2O2: C, 71.24; H, 4.09; N, 8.75. Found: C,
71.10; H, 4.20; N, 8.80.
4-CNPh
4-CNPh
4-FPh
3-(4-Cyanophenyl)-5-cyclopropyl-4-iminooxazolidin-2-one (4b)
Yield: 0.86 g (72%); colourless solid; mp 118 °C (EtOAc–hexane).
IR (KBr): 1780, 1685 cm–1.
1H NMR (DMSO-d6): d = 0.45–0.82 (m, 4 H), 1.36–1.46 (m, 1 H),
4.64 (d, J = 8.4 Hz, 1 H), 7.75 (d, J = 8.7 Hz, 2 H), 7.98 (d, J = 8.7
Hz, 2 H), 8.72 (s, 1 H).
13C NMR (DMSO-d6): d = 1.6, 11.2, 79.8, 108.3, 116.7, 125.8,
131.1, 135.4, 152.3, 160.4.
4-CH3Bn
4-FBn
2-ClBn
20b
10c
3.5b
CH3
g
Ph
a Hold time + ramp time = 0.5 min.
b See ‘Parameters a’ in the experimental part for more detailed condi-
Anal. Calcd for C13H11N3O2: C, 64.72; H, 4.60; N, 17.42. Found: C,
64.55; H, 4.70; N, 17.60.
tions.
c See ‘Parameters b’ in the experimental part for more detailed condi-
tions.
3-(4-Cyanophenyl)-4-imino-5-(1-naphthyl)oxazolidin-2-one
(4c)
Yield: 1.14 g (70%); colourless solid; mp 150 °C (EtOAc–hexane).
Synthesis 2006, No. 11, 1803–1806 © Thieme Stuttgart · New York

PAPER
Microwave-Assisted Synthesis of 4-Substituted Iminooxazolidin-2-ones
1805
IR (KBr): 1790, 1675 cm–1.
or b (Table 2). The reaction mixture was allowed to cool to r.t. and
transferred to a round-bottomed flask. The solvent was evaporated,
H2O (0.5 mL) was added and the mixture was extracted with
CH2Cl2 (3 × 10 mL). The combined extracts were dried over MgSO4
and the solution was concentrated. Addition of MeOH (0.5 mL) and
Et2O (3–5 mL) provided 5a–g as solid compounds.
1H NMR (DMSO-d6): d = 6.85 (s, 1 H), 7.40 (d, J = 8.7 Hz, 1 H),
7.60 (t, J = 7.4 Hz, 1 H), 7.65 (t, J = 7.1 Hz, 1 H), 7.71 (t, J = 7.4
Hz, 1 H), 7.90 (d, J = 8.7 Hz, 2 H), 8.00 (d, J = 8.4 Hz, 2 H), 8.10
(t, J = 8.7 Hz, 2 H), 8.24 (d, J = 8.4 Hz, 1 H), 8.70 (s, 1 H).
13C NMR (DMSO-d6): d = 79.3, 113.8, 115.1, 119.8, 123.5, 125.8,
127.3, 128.6, 128.8, 129.2, 129.8, 130.5, 131.2, 133.5, 152.8, 161.7.
Parameters a for compounds 5a–e: Discover mode; power: 200 W;
ramp time: 30 s; hold time: as indicated in Table 2; temperature:
100 °C; pressure: 12 bar; PowerMax-cooling.
Anal. Calcd for C20H13N3O2: C, 73.39; H, 4.00; N, 12.84. Found: C,
73.20; H, 4.15; N, 12.70.
Parameters b for compound 5f,g: Discover mode, power: 250 W;
ramp time: 30 s; hold time: as indicated in Table 2; temperature:
150 °C; pressure: 15 bar, PowerMax-cooling.
3-(4-Fluorophenyl)-4-imino-5-(2-naphthyl)oxazolidin-2-one
(4d)
Yield: 1.09 g (68%); colourless solid; mp 169 °C (THF).
IR (KBr): 1773, 1670 cm–1.
4-(3-Fluorophenylimino)-5-(1-naphthyl)oxazolidin-2-one (5a)
Yield: 0.10 g (64%); colourless solid; mp 180 °C (Et2O–MeOH).
1H NMR (DMSO-d6): d = 6.85 (s, 1 H), 7.01 (d, J = 7.4 Hz, 2 H),
7.42 (d, J = 7.1 Hz, 1 H), 7.60–7.72 (m, 5 H), 8.10 (t, J = 7.4 Hz, 2
H), 8.25 (d, J = 8.4 Hz, 1 H), 8.70 (s, 1 H).
13C NMR (DMSO-d6): d = 79.2, 113.9, 122.0, 123.3, 125.8, 126.2,
128.0, 128.9, 130.3, 131.6, 133.5, 155.6, 162.8.
IR (KBr): 1747, 1630 cm–1.
1H NMR (DMSO-d6): d = 7.01 (s, 1 H), 7.16 (t, J = 7.1 Hz, 1 H),
7.31–7.38 (m, 2 H), 7.46–7.68 (m, 5 H), 7.96 (t, J = 8.9 Hz, 2 H),
8.10 (d, J = 7.9 Hz, 1 H), 11.30 (s, 1 H).
13C NMR (DMSO-d6): d = 78.6, 113.4, 113.7, 116.4, 116.6, 121.4,
123.5, 124.7, 125.6, 127.1, 127.9, 129.5, 130.98, 131.1, 131.5,
142.0, 152.0, 164.0.
Anal. Calcd for C19H13FN2O2: C, 71.24; H, 4.09; N, 8.75. Found: C,
71.07; H, 4.20; N, 8.60.
Anal. Calcd for C19H13FN2O2: C, 71.24; H, 4.09; N, 8.75. Found: C,
71.06; H, 4.15; N, 8.76.
4-Imino-5-methyl-3-(4-methylbenzyl)oxazolidin-2-one (4e)
Yield: 0.82 g (75%); colourless solid; mp 75 °C (EtOAc–hexane).
IR (KBr): 1760, 1672 cm–1.
4-(4-Cyanophenylimino)-5-cyclopropyloxazolidin-2-one (5b)
1H NMR (DMSO-d6): d = 1.40 (d, J = 7.1 Hz, 3 H), 2.30 (s, 3 H),
4.50 (s, 2 H), 5.05 (q, J = 7.1 Hz, 1 H), 7.20 (d, J = 7.6 Hz, 2 H),
7.24 (d, J = 7.6 Hz, 2 H), 8.70 (s, 1 H).
13C NMR (DMSO-d6): d = 18.2, 20.5, 46.0, 75.9, 127.4, 128.9,
134.3, 136.5, 153.6, 163.0.
Yield: 0.07 g (60%); colourless solid; mp 205 °C (Et2O–MeOH).
IR (KBr): 1750, 1629 cm–1.
1H NMR (DMSO-d6): d = 0.23–0.30 (m, 1 H), 0.45–0.61 (m, 1 H),
0.63 (d, J = 5.9 Hz, 2 H), 1.37 (d, J = 5.3 Hz, 1 H), 5.04 (d, J = 5.3
Hz, 1 H), 7.87 (d, J = 8.7 Hz, 2 H), 7.92 (d, J = 8.7 Hz, 2 H), 11.18
(s, 1 H).
Anal. Calcd for C12H14N2O2: C, 66.04; H, 6.47; N, 12.84. Found: C,
65.85; H, 6.60; N, 12.62.
13C NMR (DMSO-d6): d = 1.9, 12.2, 79.3, 106.0, 118.8, 120.9,
133.3, 135.2, 150.1, 163.1.
3-(4-Fluorobenzyl)-4-imino-5-methyloxazolidin-2-one (4f)
Yield: 0.81 g (73%); colourless solid; mp 104 °C (EtOAc–hexane).
IR (KBr): 1761, 1670 cm–1.
Anal. Calcd for C13H11N3O2: C, 64.72; H, 4.60; N, 17.42. Found: C,
64.60; H, 4.73; N, 17.30.
1H NMR (DMSO-d6): d = 1.35 (d, J = 7.1 Hz, 3 H), 4.55 (s, 2 H),
5.10 (q, J = 7.1 Hz, 1 H), 7.20 (d, J = 8.9 Hz, 2 H), 7.35 (d, J = 8.9
Hz, 2 H), 8.60 (s, 1 H).
13C NMR (DMSO-d6): d = 18.4, 41.9, 75.3, 115.2, 129.3, 129.7,
132.5, 155.7, 163.5.
4-(4-Cyanophenylimino)-5-(1-naphthyl)oxazolidin-2-one (5c)
Yield: 0.10 g (63%); colourless solid; mp 238 °C (Et2O–MeOH).
IR (KBr): 1750, 1612 cm–1.
1H NMR (DMSO-d6): d = 7.10 (s, 1 H), 7.39 (d, J = 8.65 Hz, 1 H),
7.57 (t, J = 7.4 Hz, 1 H), 7.65 (t, J = 7.1 Hz, 1 H), 7.71 (t, J = 7.4
Hz, 1 H), 7.91 (d, J = 8.7 Hz, 2 H), 8.02 (d, J = 8.4 Hz, 2 H), 8.08
(t, J = 8.7 Hz, 2 H), 8.24 (d, J = 8.4 Hz, 1 H), 11.34 (s, 1 H).
Anal. Calcd for C11H11FN2O2: C, 59.46; H, 4.99; N, 12.61. Found:
C, 59.30; H, 5.20; N, 12.55.
13C NMR (DMSO-d6): d = 78.1, 106.6, 118.7, 120.6, 122.9, 125.7,
126.4, 126.5, 127.2, 128.8, 130.5, 131.5, 133.4, 133.5, 142.0, 152.1,
168.4.
3-(2-Chlorobenzyl)-4-imino-5-phenyloxazolidin-2-one (4g)
Yield: 0.75 g (50%); colourless solid; mp 85 °C (EtOAc–hexane).
IR (KBr): 1791, 1674 cm–1.
1H NMR (DMSO-d6): d = 4.51 (s, 2 H), 5.60 (s, 1 H), 6.90–7.30 (m,
5 H), 7.51–7.70 (m, 4 H), 9.05 (s, 1 H).
13C NMR (DMSO-d6): d = 41.3, 75.2, 125.5, 127.7, 128.5, 128.9,
129.3, 129.6, 131.8, 133.1, 139.2, 155.5, 162.9.
Anal. Calcd for C20H13N3O2: C, 73.39; H, 4.00; N, 12.84. Found: C,
73.12; H, 4.21; N, 12.76.
4-(4-Fluorophenylimino)-5-(2-naphthyl)oxazolidin-2-one (5d)
Yield: 0.11 g (69%); colourless solid; mp 193 °C (Et2O–MeOH).
IR (KBr): 1734, 1633 cm–1.
1H NMR (DMSO-d6): d = 6.92 (s, 1 H), 7.00 (d, J = 7.4 Hz, 2 H),
7.38 (d, J = 7.1 Hz, 1 H), 7.58–7.70 (m, 5 H), 8.05 (t, J = 7.4 Hz, 2
H), 8.23 (d, J = 8.4 Hz, 1 H), 10.85 (s, 1 H).
13C NMR (DMSO-d6): d = 77.6, 114.0, 121.9, 123.1, 125.7, 126.3,
127.0, 128.7, 130.1, 131.5, 133.4, 156.2, 168.3.
Anal. Calcd for C16H13ClN2O2: C, 63.90; H, 4.36; N, 9.31. Found:
C, 63.75; H, 4.60; N, 9.21.
Microwave-Assisted Synthesis of 5a–g; General Procedure
Compound 4a–g (0.5 mmol) and an equimolar amount of NaOMe
were weighed in a 10 mL glass pressure microwave tube equipped
with a magnetic stirrer bar. MeOH (5 mL) was added, the tube was
closed with a silicon septum and the reaction mixture was subjected
to microwave irradiation for the indicated time using parameters a
Anal. Calcd for C19H13FN2O2: C, 71.24; H, 4.09; N, 8.75. Found: C,
70.99; H, 4.24; N, 8.62.
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1806
T. Kurz et al.
PAPER
5-Methyl-4-(4-methylbenzylimino)oxazolidin-2-one (5e)
Yield: 0.08 g (72%); colourless solid; mp 116 °C (Et2O–MeOH).
1H NMR (DMSO-d6): d = 4.58 (s, 2 H), 6.09 (s, 1 H), 7.25–7.35 (m,
5 H), 7.42–7.49 (m, 4 H), 9.25 (s, 1 H).
IR (KBr): 1740, 1630 cm–1.
13C NMR (DMSO-d6): d = 44.5, 79.6, 127.6, 127.9, 129.3, 129.6,
129.7, 132.7, 134.6, 135.2, 152.1, 161.0.
1H NMR (DMSO-d6): d = 1.41 (d, J = 7.12 Hz, 3 H), 2.29 (s, 3 H),
4.48 (s, 2 H), 5.01 (q, J = 7.1 Hz, 1 H), 7.17 (d, J = 7.6 Hz, 2 H),
7.21 (d, J = 7.6 Hz, 2 H), 9.17 (s, 1 H).
Anal. Calcd for C16H13ClN2O2: C, 63.90; H, 4.36; N, 9.31. Found:
C, 63.77; H, 4.58; N, 9.19.
13C NMR (DMSO-d6): d = 18.0, 20.6, 45.7, 73.8, 127.4, 128.9,
134.3, 136.5, 156.1, 166.7.
References
Anal. Calcd for C12H14N2O2: C, 66.04; H, 6.47; N, 12.84. Found: C,
65.90; H, 6.63; N, 12.60.
(1) (a) Kappe, C. O. Angew. Chem. Int. Ed. 2004, 43, 6250.
(b) Wathey, B.; Tiemey, J.; Lidstrom, P.; Westman, J. Drug
Discovery Today 2002, 7, 373.
(2) (a) Fujinami, A.; Ozaki, T.; Yamamoto, S. Agric. Biol.
Chem. 1971, 35, 1707. (b) Fujinami, A.; Ozaki, T.;
Yamamoto, S.; Akiba, K.; Ooba, S.; Tanaka, K.; Kameda,
N.; Nodera, K.; Ohishi, T. Ger. Offen. 2002410, 1970;
Chem. Abstr. 1970, 73, 87912c.
(3) Kauffman, W. J. J. Org. Chem. 1970, 35, 4244.
(4) Wu, T.-T.; Huang, J.; Arrigton, N. D.; Dill, G. M. J. Agric.
Food Chem. 1987, 35, 817.
(5) L’abbé, G.; Verbruggen, A.; Toppet, S. Bull. Soc. Chim.
Belg. 1981, 90, 99.
4-(4-Fluorobenzylimino)-5-methyloxazolidin-2-one (5f)
Yield: 0.07 g (61%); colourless solid; mp 149 °C (Et2O–MeOH).
IR (KBr): 1742, 1633 cm–1.
1H NMR (DMSO-d6): d = 1.41 (d, J = 7.1 Hz, 3 H), 4.51 (s, 2 H),
5.04 (q, J = 7.1 Hz, 1 H), 7.20 (d, J = 8.9 Hz, 2 H), 7.36 (d, J = 8.9
Hz, 2 H), 9.26 (s, 1 H).
13C NMR (DMSO-d6): d = 17.9, 45.1, 73.8, 115.1, 129.6, 133.5,
152.4, 160.2, 162.6.
Anal. Calcd for C11H11FN2O2: C, 59.46; H, 4.99; N, 12.61. Found:
C, 59.35; H, 5.20; N, 12.53.
(6) Kurz, T.; Widyan, K. Org. Lett. 2004, 6, 4403.
(7) Widyan, K.; Kurz, T. Synthesis 2005, 1340.
(8) Compounds 5 might also appear in a tautomeric form with
endocyclic double bond (Scheme 2).
4-(2-Chlorobenzylimino)-5-phenyloxazolidin-2-one (5g)
Yield: 0.08 g (51%); colourless solid; mp 128 °C (Et2O–MeOH).
IR (KBr): 1757, 1616 cm–1.
Synthesis 2006, No. 11, 1803–1806 © Thieme Stuttgart · New York