Synthesis of (4Z)-4-(arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-thiones by the reaction of ethyl (2Z)-3-aryl-2-isothiocyanatoprop-2-enoates with organolithium compounds

Article abstract of DOI:10.1002/hlca.201200479

A convenient one-pot method for the preparation of (4Z)-4-(arylmethylidene) -5-ethoxy-1,3-oxazolidine-2-thiones 2 and 3 from ethyl (2Z)-3-aryl-2- isothiocyanatoprop-2-enoates 1, which can be easily prepared from ethyl 2-azidoacetate and aromatic aldehydes, has been developed. Thus, these α-isothiocyanato α,β-unsaturated esters were treated with organolithium compounds, including lithium enolates of acetates, to provide 5-substituted (4Z)-4-(arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-thiones, 2, and 2-[(4Z)-(4-arylmethylidene)-5-ethoxy-2-thioxo-1,3-oxazolidin-5-yl]acetates, 3. Copyright

Full text of DOI:10.1002/hlca.201200479

Helvetica Chimica Acta – Vol. 96 (2013)
431
Synthesis of (4Z)-4-(Arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-thiones by
the Reaction of Ethyl (2Z)-3-Aryl-2-isothiocyanatoprop-2-enoates with
Organolithium Compounds
by Kazuhiro Kobayashi*, Kosuke Ezaki, and Hiroo Hashimoto
Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of
Engineering, Tottori University, 4-101 Koyama-minami, Tottori 680-8552, Japan
(phone/fax: þ 81-857-315263; e-mail: kkoba@chem.tottori-u.ac.jp)
A convenient one-pot method for the preparation of (4Z)-4-(arylmethylidene)-5-ethoxy-1,3-
oxazolidine-2-thiones 2 and 3 from ethyl (2Z)-3-aryl-2-isothiocyanatoprop-2-enoates 1, which can be
easily prepared from ethyl 2-azidoacetate and aromatic aldehydes, has been developed. Thus, these a-
isothiocyanato a,b-unsaturated esters were treated with organolithium compounds, including lithium
enolates of acetates, to provide 5-substituted (4Z)-4-(arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-
thiones, 2, and 2-[(4Z)-(4-arylmethylidene)-5-ethoxy-2-thioxo-1,3-oxazolidin-5-yl]acetates, 3.
Introduction. – 1,3-Oxazolidine-2-thiones are important heterocycles, because some
compounds with this heterocyclic unit have been reported to exhibit biological
activities [1]. The most common method for the preparation of 1,3-oxazolidine-2-
thiones is based on the reaction of 2-aminoethanols with CSCl2 or CS2 [2]1). On the
other hand, we recently demonstrated that 4-substituted 4-alkoxy-1,4-dihydrobenzox-
azine-2-thiones could be obtained by the reaction of 2-isothiocyanatobenzoates with
organolithium compounds, including lithium enolates of esters and tertiary acetamides
[3]. This success encouraged us to investigate the possibility of the formation of 4-
(arylmethylidene)-1,3-oxazolidine-2-thiones by the reaction of 3-aryl-2-isothiocyana-
toprop-2-enoates with organolithium compounds. In this article, we wish to describe the
results of our study, which provide a convenient method for the preparation of 5-
alkyl(or aryl)-(4Z)-4-(arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-thiones 2 and ethyl
2-[(4Z)-4-(arylimethylidene)-5-ethoxy-2-thioxo-1,3-oxazolidin-5-yl]acetates 3 by the
reaction of ethyl (2Z)-3-aryl-2-isothiocyanatoprop-2-enoates 1 with alkyl(or aryl)lithi-
um and lithium enolates of acetates, respectively. To date, there have been no reports
on the synthesis of these types of 1,3-oxazolidine-2-thiones.
Results and Discussion. – The one-pot synthesis of (4Z)-5-alkyl(or aryl)-4-
(arylmethylidene)-5-ethoxy-1,3-oxazolidine-2-thiones 2 from ethyl (2Z)-3-aryl-2-iso-
thiocyanatoprop-2-enoates 1 was accomplished as outlined in Scheme 1. The starting
materials 1 were easily prepared by the successive treatment of ethyl (2Z)-3-aryl-2-
azidoprop-2-enoates, derived from ethyl 2-azidoacetate and aromatic aldehydes [4],
1
)
A method via the reaction of NH4SCN, acid chloride, and bromopyruvate or 2-chloroacetoacetate
has been published [2d].
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 96 (2013)
Scheme 1
with Ph3P and CS2 under conditions reported by Sun and co-workers [5]. We started
this study by reacting (2Z)-2-isothiocyanato-1-phenylprop-2-enoates (1a) with BuLi in
THF at ꢀ 788. After aqueous workup, followed by purification using column
chromatography, the desired product, (4Z)-5-butyl-5-ethoxy-4-(phenylmethylidene)-
1,3-oxazolidine-2-thione (2a), was obtained as a single stereoisomer in 77% yield. The
structure of 2a was determined on the basis of its spectroscopic data. Mass
spectrometry and elemental analysis established the molecular formula of the product
as C16H21NO2S. The IR spectrum showed absorption bands at 3216, 1685, and 1190 cmꢀ1
due to NꢀH, C¼C, and C¼S groups, respectively. The 13C-NMR spectrum exhibited 14
signals including a signal at 185.81 ppm assignable to the thiocarbamate C-atom. The
1H-NMR data are in good agreement with the structure of 2a (see Exper. Part). We
determined the configuration of the C¼C bond as (Z), because isomerization, during
the reaction sequence, or the workup and purification process appears to be
impropable. When the other four starting materials, 1b – 1e, were treated with five
organolithium compounds including BuLi, the corresponding desired products 2b – 2h
were obtained in comparable yields, as compiled in Table 1. The highly selective attack
of an organolithium compound on the ester C¼O group of 1 in a 1,2-addition fashion,
followed by the quick cyclization of the resulting lithium 1-aryl-3-ethoxy-2-isothiocya-
natoalk-1-en-3-yl oxide intermediates A by the attack of alkenyl oxide on the
isothiocyanate C-atom (before elimination of ethoxide), is assumed to take place to
give the expected products 2.
Table 1. Preparation of (4Z)-4-Arylidene-1,3-oxazolidine-2-thiones 2
Entry
1
Ar
R
2
Yielda) [%]
1
2
3
4
5
6
7
8
1a
1b
1b
1b
1c
1d
1e
1e
Ph
Bu
Ph
tBu
2a
2b
2c
2d
2e
2f
2g
2h
77
72
71
67
63
64
68
79
4-MeꢀC6H4
4-MeꢀC6H4
4-MeꢀC6H4
4-ClꢀC6H4
4-MeOꢀC6H4
Thiophen-2-yl
Thiophen-2-yl
Thiophen-2-yl
Me
Me
Bu
Ph
a) Yields of isolated products.
With the above-mentioned results in hand, the preparation of 2-[(4Z)-4-
(arylmethylidene)-5-ethoxy-2-thioxooxazolidin-5-yl]acetates 3 by the reaction of 1
with lithium enolates of acetates was then addressed, as depicted in Scheme 2. A similar

Helvetica Chimica Acta – Vol. 96 (2013)
433
Scheme 2
additionꢀcyclization sequence, as described above for the preparation of 2, also
proceeded cleanly to afford, after the subsequent aqueous workup, the desired products
3 in fair yields, as collected in Table 2. Unfortunately, it should be noted that attempts to
obtain 2-[(4Z)-4-(arylmethylidene)-2-thioxo-1,3-oxazolidin-5-yl]-N,N-dimethylacet-
amides using N,N-dimethylacetamide in place of acetates were unsuccessful. The
reactions resulted in the formation of rather complicated mixtures of products, from
which only a very low yield of the desired product contaminated with structurally
undefined products was obtained in each case (results not shown in Table 2).
Table 2. Preparation of 2-[(4Z)-4-Arylidene-2-thioxo-1,3-oxazolidin-5-yl]acetates 3
Entry
1
Ar
R
3
Yielda)[%]
1
2
3
4
5
1a
1c
1d
1d
1e
Ph
tBu
tBu
tBu
Et
3a
3b
3c
3d
3e
77
62
69
61
68
4-ClꢀC6H4
4-MeOꢀC6H4
4-MeOꢀC6H4
Thiophen-2-yl
tBu
a) Yields of isolated products.
In conclusion, the aforementioned results demonstrate that the reaction of (2Z)-3-
aryl-2-isothiocyanatoprop-2-enoates with organolithium compounds, including lithium
enolates of acetates, provides a facile method for the preparation of a new type of 1,3-
oxazolidine-2-thiones, i.e., 5-substituted (4Z)-4-(arylmethylidene)-1,3-oxazolidine-2-
thiones. As the starting materials are readily available, and the manipulations are very
simple, the present method may be valuable in organic synthesis.
Experimental Part
General. All of the org. solvents used in this study were dried on appropriate drying agents and
distilled prior to use. TLC: Merck silica gel 60 PF254. Column chromatography (CC): Wako Gel C-
200E. M.p.: Laboratory Devices MEL-TEMP II apparatus; uncorrected. IR Spectra: PerkinꢀElmer
Spectrum65 FT-IR spectrophotometer; ˜n in cmꢀ1 1H-NMR Spectra: JEOL ECP500 FT NMR
.
spectrometer, at 500 MHz or JEOL LA400 FT NMR spectrometer at 400 MHz; in CDCl3; d in ppm
rel. to Me4Si as internal standard, J in Hz. 13C-NMR Spectra: Bruker Biospin AVANCE II 600 at
150 MHz, JEOL ECP500 FT NMR spectrometer at 125 MHz, or JEOL LA400 FT NMR spectrometer at
100 MHz; in CDCl3; d in ppm rel. to Me4Si as internal standard. EI-MS (70 eV): JEOL JMS AX505 HA
spectrometer; in m/z (rel. %). HR-MS (DARTꢂ, pos.): Thermo Scientific Exactive spectrometer; in m/z.

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Ethyl (2Z)-2-isothiocyanato-3-phenylprop-2-enoate (1a) was prepared from ethyl (2Z)-2-azido-3-
phenylprop-2-enoate as described in [5]. BuLi was supplied by Asia Lithium Corporation. All other
chemicals used in this study were commercially available.
(2Z)-3-Aryl-2-isothiocyanatoprop-2-enoates 1b – 1e were prepared from the respective azides under
the conditions used for the preparation of 1a.
Ethyl (2Z)-2-Isothiocyanato-3-(4-methylphenyl)prop-2-enoate (1b). Yield: 49%. White solid. M.p.
53 – 548 (hexane). IR (KBr): 2030, 1724, 1260. 1H-NMR (400 MHz): 1.41 (t, J ¼ 6.8, 3 H); 2.40 (s, 3 H);
4.38 (q, J ¼ 6.8, 2 H); 7.24 (s, 1 H); 7.26 (d, J ¼ 7.3, 2 H); 7.72 (d, J ¼ 7.3, 2 H). Anal. calc. for C13H13NO2S
(247.31): C 63.13, H 5.30, N 5.66; found: C 62.91, H 57.38, N 5.61.
Ethyl (2Z)-3-(4-Chlorophenyl)-2-isothiocyanatoprop-2-enoate (1c). Yield: 64%. White solid. M.p.
107 – 1098 (hexane/Et2O). IR (KBr): 2047, 1718, 1626, 1260. 1H-NMR (500 MHz): 1.41 (t, J ¼ 6.9, 3 H);
4.38 (t, J ¼ 6.9, 2 H); 7.21 (s, 1 H); 7.40 (d, J ¼ 8.4, 2 H); 7.76 (d, J ¼ 8.4, 2 H). Anal. calc. for
C12H10ClNO2S (267.73): C 53.83, H 3.76, N 5.23; found: C 53.65, H 4.04, N 5.22.
Ethyl (2Z)-2-Isothiocyanato-3-(4-methoxyphenyl)prop-2-enoate (1d). Yield: 56%. Pale-yellow oil.
Rf (THF/hexane 1:20) 0.25. IR (neat): 2062, 1716, 1617, 1269. 1H-NMR (500 MHz): 1.40 (t, J ¼ 7.4, 3 H);
3.86 (s, 3 H); 4.37 (q, J ¼ 7.4, 2 H); 6.95 (d, J ¼ 8.6, 2 H); 7.23 (s, 1 H); 7.80 (d, J ¼ 8.6, 2 H). Anal. calc. for
C13H13NO3S (263.31): C 59.30, H 4.98, N 5.32; found: C 59.23, H 4.94, N 5.54.
Ethyl (2Z)-2-Isothiocyanato-3-(thiophen-2-yl)prop-2-enoate (1e). Yield: 78%. Pale-yellow solid.
1
M.p. 150 – 1528 (hexane/Et2O). IR (KBr): 2057, 1721, 1615, 1254. H-NMR (500 MHz): 1.40 (t, J ¼ 6.9,
3 H); 4.37 (q, J ¼ 6.9, 2 H); 7.12 (dd, J ¼ 4.6, 3.8, 1 H); 7.43 (d, J ¼ 3.8, 1 H); 7.51 (s, 1 H); 7.57 (d, J ¼ 4.6,
1 H). Anal. calc. for C10H9NO2S2 (239.31): C 50.19, H 3.79, N 5.85; found: C 50.02, H 3.93, N 5.55.
(4Z)-5-Butyl-5-ethoxy-4-(phenylmethylidene)-1,3-oxazolidine-2-thione (2a). Representative Proce-
dure. To a stirred soln. of 1a (0.12 g, 0.51 mmol) in THF (4 ml) at ꢀ 788 was added BuLi (1.6m in hexane,
0.51 mmol) dropwise. After 15 min, sat. aq. NH4Cl (10 ml) was added, and the mixture was warmed to r.t.
and extracted with AcOEt (3 ꢁ 10 ml). The combined extracts were washed with brine (10 ml), dried
(Na2SO4), and concentrated by evaporation. The residue was purified by PLC (SiO2; AcOEt/hexane
1:10) to give 2a (0.12 g, 77%). Pale-yellow oil. Rf (AcOEt/hexane 1:10) 0.42. IR (neat): 3216, 1685, 1465,
1190. 1H-NMR (500 MHz): 0.92 (t, J ¼ 7.4, 3 H); 1.24 (t, J ¼ 6.9, 3 H); 1.34 – 1.51 (m, 4 H); 1.90 – 1.96 (m,
1 H); 2.10 – 2.16 (m, 1 H); 3.51 – 3.63 (m, 2 H); 5.66 (s, 1 H); 7.26 (d, J ¼ 7.4, 2 H); 7.30 (t, J ¼ 7.3, 1 H);
7.41 (t, J ¼ 7.4, 2 H); 8.72 (br. s, 1 H). 13C-NMR (125 MHz): 13.84; 14.89; 22.40; 24.54; 39.23; 59.81;
102.93; 116.22; 127.43; 127.79; 129.33; 134.00; 134.11; 185.81. HR-MS: 292.1354 ([M þ H]þ,
C16H22NO2Sþ; calc. 292.1371). Anal. calc. for C16H21NO2S (291.41): C 65.96, H 7.26, N 4.81; found: C
65.82, H 7.30, N 4.71.
(4Z)-5-Ethoxy-5-phenyl-4-[(4-methylphenyl)methylidene]-1,3-oxazolidine-2-thione (2b). White sol-
id. M.p. 147 – 1488 (hexane/Et2O). IR (KBr): 3120, 1685, 1463, 1174. 1H-NMR (400 MHz): 1.35 (t, J ¼ 7.3,
3 H); 2.35 (s, 3 H); 3.68 – 3.83 (m, 2 H); 5.59 (s, 1 H); 7.11 (d, J ¼ 8.3, 2 H); 7.19 (d, J ¼ 8.3, 2 H); 7.41 – 7.44
(m, 3 H); 7.56 – 7.58 (m, 2 H); 8.79 (br. s, 1 H). 13C-NMR (150 MHz): 14.98; 21.22; 60.54; 105.52; 114.14;
125.74; 127.35; 128.60; 129.71; 129.93; 130.91; 134.12; 137.60; 137.95; 185.30. HR-MS: 326.1227 ([M þ
H]þ, C19H20NO2Sþ; calc. 326.1215). Anal. calc. for C19H19NO2S (325.42): C 70.12, H 5.88, N 4.30;
found: C 70.03, H 5.65, N 4.15.
(4Z)-5-(1,1-Dimethylethyl)-5-ethoxy-4-[(4-methylphenyl)methylidene]-1,3-oxazolidine-2-thione
(2c). White solid. M.p. 148 – 1508 (hexane/CH2Cl2). IR (KBr): 3230, 1680, 1454, 1176. 1H-NMR
(500 MHz): 1.10 (s, 9 H); 1.24 (t, J ¼ 6.9, 3 H); 2.37 (s, 3 H); 3.48 – 3.61 (m, 2 H); 5.68 (s, 1 H); 7.14 (d, J ¼
8.0, 2 H); 7.22 (d, J ¼ 8.0, 2 H); 8.67 (br. s, 1 H). 13C-NMR (150 MHz): 14.82; 21.22; 23.65; 40.28; 60.33;
104.95; 120.17; 127.37; 129.98; 131.09; 131.75; 137.79; 185.94. HR-MS: 306.1509 ([M þ H]þ, C17H24NO2Sþ;
calc. 306.1528). Anal. calc. for C17H23NO2S (305.44): C 66.85, H 7.59, N 4.59; found: C 66.80, H 7.78, N
4.58.
(4Z)-5-Ethoxy-4-[(4-methylphenyl)methylidene]-5-(thiophen-2-yl)-1,3-oxazolidine-2-thione (2d).
Pale-yellow, viscous oil. Rf (AcOEt/hexane 1:10) 0.33. IR (neat): 3239, 1684, 1461, 1166. 1H-NMR
(500 MHz): 1.34 (t, J ¼ 6.9, 3 H); 2.37 (s, 3 H); 3.69 – 3.81 (m, 2 H); 5.78 (s, 1 H); 7.02 (dd, J ¼ 5.4, 3.8,
1 H); 7.16 (d, J ¼ 7.6, 2 H); 7.21 – 7.22 (m, 3 H); 7.41 (d, J ¼ 5.4, 1 H); 8.83 (br. s, 1 H). 13C-NMR
(125 MHz): 14.55; 20.86; 60.53; 105.64; 111.91; 126.52; 126.58; 127.10; 127.35; 129.61; 130.37; 132.89;

Helvetica Chimica Acta – Vol. 96 (2013)
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137.76; 140.31; 184.24. HR-MS: 332.0765 ([M þ H]þ, C17H18NO2S2þ ; calc. 332.0779). Anal. calc. for
C17H17NO2S2 (331.45): C 61.60, H 5.17, N 4.23; found: C 61.54, H 5.46, N 4.19.
(4Z)-4-[(4-Chlorophenyl)methylidene]-5-ethoxy-5-methyl-1,3-oxazolidine-2-thione (2e). Pale-yel-
low solid. M.p. 109 – 1118 (hexane). IR (KBr): 3225, 1687, 1461, 1189. 1H-NMR (500 MHz): 1.25 (t,
J ¼ 6.9, 3 H); 1.81 (s, 3 H); 3.54 – 3.58 (m, 2 H); 5.62 (s, 1 H); 7.19 (d, J ¼ 8.4, 2 H); 7.38 (d, J ¼ 8.4, 2 H);
8.70 (br. s, 1 H). 13C-NMR (125 MHz): 14.87; 26.13; 60.04; 101.66; 113.83; 128.73; 129.48; 132.29; 133.53;
135.43; 185.51. HR-MS: 284.0508 ([M þ H]þ, C13H15ClNO2Sþ; calc. 284.0512). Anal. calc. for
C13H14ClNO2S (283.77): C 55.02, H 4.97, N 4.94; found: C 54.91, H 5.04, N 4.83.
(4Z)-5-Ethoxy-4-[(4-methoxyphenyl)methylidene]-5-methyl-1,3-oxazolidine-2-thione (2f). Pale-yel-
low solid. M.p. 99 – 1018 (hexane/CH2Cl2). IR (KBr): 3239, 1686, 1463, 1178. 1H-NMR (500 MHz): 1.24
(t, J ¼ 7.4, 3 H); 1.80 (s, 3 H); 3.52 – 3.59 (m, 2 H); 3.84 (s, 3 H); 5.63 (s, 1 H); 6.93 (d, J ¼ 8.6, 2 H); 7.19 (d,
J ¼ 8.6, 2 H); 8.74 (br. s, 1 H). 13C-NMR (125 MHz): 14.87; 26.21; 55.35; 59.88; 102.85; 113.80; 114.71;
126.26; 128.75; 133.31; 159.10; 185.44. HR-MS: 280.1008 ([M þ H]þ, C14H18NO3Sþ; calc. 280.1007). Anal.
calc. for C14H17NO3S (279.35): C 60.19, H 6.13, N 5.01; found: C 59.98, H 6.14, N 4.98.
(4Z)-5-Butyl-5-ethoxy-4-[(thiophen-2-yl)methylidene]-1,3-oxazolidine-2-thione (2g). Pale-yellow,
viscous oil. Rf (AcOEt/hexane 1:10) 0.33. IR (neat): 3239, 1679, 1452, 1189. 1H-NMR (500 MHz):
0.90 (t, J ¼ 7.6, 3 H); 1.22 (t, J ¼ 6.9, 3 H); 1.32 – 1.47 (m, 4 H); 1.87 – 1.93 (m, 1 H); 2.08 – 2.14 (m, 1 H);
3.50 – 3.56 (m, 2 H); 5.81 (s, 1 H); 7.02 (d, J ¼ 3.1, 1 H); 7.08 (dd, J ¼ 5.3, 3.1, 1 H); 7.34 (d, J ¼ 5.3, 1 H);
8.81 (br. s, 1 H). 13C-NMR (125 MHz): 13.78; 14.82; 22.35; 24.46; 39.14; 59.84; 96.21; 116.18; 125.15;
126.57; 127.93; 132.47; 136.60; 185.36. HR-MS: 298.0932 ([M þ H]þ, C14H20NO2S2þ ; calc. 298.0935). Anal.
calc. for C14H19NO2S2 (297.44): C 56.53, H 6.44, N 4.71; found: C 56.46, H 6.53, N 4.61.
(4Z)-5-Ethoxy-5-phenyl-4-[(thiophen-2-yl)methylidene]-1,3-oxazolidine-2-thiones (2h). Pale-yellow,
viscous oil. Rf (AcOEt/hexane 1:5) 0.41. IR (neat): 3248, 1678, 1449, 1175. 1H-NMR (500 MHz): 1.34 (t,
J ¼ 7.6, 3 H); 3.67 – 3.78 (m, 2 H); 5.76 (s, 1 H); 6.96 (d, J ¼ 3.8, 1 H); 7.04 (dd, J ¼ 5.3, 3.8, 1 H); 7.32 (d,
J ¼ 5.3, 1 H); 7.41 – 7.42 (m, 3 H); 7.56 (dd, J ¼ 7.6, 1.5, 2 H); 8.87 (br. s, 1 H). 13C-NMR (125 MHz): 14.93;
60.62; 98.63; 114.10; 125.33; 125.68; 126.91; 127.93; 128.65; 129.80; 133.27; 136.62; 137.37; 184.93. HR-
MS: 318.0630 ([M þ H]þ, C15H16NO2S2þ ; calc. 318.0622). Anal. calc. for C16H15NO2S2 (317.43): C 60.54, H
4.76, N 4.41; found: C 60.37, H 4.85, N 4.17.
1,1-Dimethylethyl 2-[(4Z)-5-Ethoxy-4-(phenylmethylidene)-2-thioxo-1,3-oxazolidin-5-yl]acetate
(3a). Representative Procedure. To a stirred soln. of LDA (LiNiPr2; 0.51 mmol), generated by the
standard method from BuLi and iPr2NH, in THF (2 ml) at ꢀ 788, was added AcOtBu (60 mg, 0.51 mmol)
dropwise. After 15 min, a soln. of 1a (0.12 g, 0.51 mmol) in THF (2 ml) was added, and stirring was
continued for 10 min before sat. aq. NH4Cl (10 ml) was added. The mixture was warmed to r.t. and
extracted with AcOEt (3 ꢁ 10 ml). The combined extracts were washed with brine (10 ml), dried
(Na2SO4), and concentrated by evaporation. The residue was purified by PLC (SiO2; AcOEt/hexane
1:5) to give 3a (0.13 g, 77%). White solid. M.p. 90 – 928 (hexane). IR (KBr): 3230, 1732, 1691, 1470, 1149.
1H-NMR (500 MHz): 1.24 (t, J ¼ 6.9, 3 H); 1.42 (s, 9 H); 2.99 (d, J ¼ 16.0, 1 H); 3.21 (d, J ¼ 16.0, 1 H);
3.52 – 3.63 (m, 2 H); 5.72 (s, 1 H); 7.26 (d, J ¼ 8.0, 2 H); 7.30 (t, J ¼ 7.4, 1 H); 7.41 (dd, J ¼ 8.0, 7.4, 2 H);
8.78 (br. s, 1 H). 13C-NMR (150 MHz): 14.81; 27.95; 45.03; 59.42; 82.11; 103.20; 111.59; 127.39; 127.86;
129.33; 133.87; 133.92; 166.22; 185.69. LR-MS: 349 (46, Mþ), 293 (68), 247 (100). Anal. calc. for
C18H23NO4S (349.44): C 61.87, H 6.63, N 4.01; found: C 61.80, H 6.69, N 3.97.
1,1-Dimethylethyl 2-{(4Z)-4-[(4-Chlorophenyl)methylidene]-5-ethoxy-2-thioxo-1,3-oxazolidin-5-
yl}acetate (3b). White solid. M.p. 128 – 1308 (hexane/AcOEt). IR (KBr): 3200, 1733, 1692, 1465, 1142.
1H-NMR (500 MHz): 1.24 (t, J ¼ 6.9, 3 H); 1.41 (s, 9 H); 2.98 (d, J ¼ 16.8, 1 H); 3.20 (d, J ¼ 16.8, 1 H);
3.52 – 3.59 (m, 2 H); 5.65 (s, 1 H); 7.18 (d, J ¼ 8.4, 2 H); 7.38 (d, J ¼ 8.4, 2 H); 8.88 (br. s, 1 H). 13C-NMR
(125 MHz): 14.80; 27.95; 44.97; 59.48; 82.17; 101.88; 111.62; 128.67; 129.52; 132.33; 133.59; 134.40; 166.20;
185.70. HR-MS: 384.1029 ([M þ H]þ, C18H23ClNO4Sþ; calc. 384.1036). Anal. calc. for C18H22ClNO4S
(383.89): C 56.32, H 5.78, N 3.65; found: C 56.17, H 6.01, N 3.64.
1,1-Dimethylethyl 2-{5-Ethoxy-(4Z)-4-[(4-methoxyphenyl)methylidene]-2-thioxo-1,3-oxazolidin-5-
yl}acetate (3c). Pale-yellow solid. M.p. 121 – 1238 (hexane/Et2O). IR (neat): 3283, 1733, 1608, 1466,
1
1179. H-NMR (500 MHz): 1.23 (t, J ¼ 7.4, 3 H); 1.41 (s, 9 H); 2.97 (d, J ¼ 16.6, 1 H); 3.19 (d, J ¼ 16.6,
1 H); 3.51 – 3.60 (m, 2 H); 3.85 (s, 3 H); 5.66 (s, 1 H); 6.93 (d, J ¼ 8.6, 2 H); 7.19 (d, J ¼ 8.6, 2 H); 8.75 (br.
s, 1 H). 13C-NMR (100 MHz): 14.80; 27.95; 45.10; 55.37; 59.34; 82.02; 103.17; 111.59; 114.74; 126.28;

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128.72; 132.25; 159.15; 166.27; 185.64. HR-MS: 380.1531 ([M þ H]þ, C19H26NO5Sþ; calc. 380.1532). Anal.
calc. for C19H25NO5S (379.47): C 60.14, H 6.64, N 3.69; found: C 60.12, H 6.72, N 3.43.
Ethyl 2-{5-Ethoxy-(4Z)-4-[(4-methoxyphenyl)methylidene]-2-thioxo-1,3-oxazolidin-5-yl}acetate
(3d). Pale-yellow, viscous oil. Rf (AcOEt/hexane 1:5) 0.23. IR (neat): 3271, 1740, 1687, 1607, 1468,
1176. 1H-NMR (500 MHz): 1.22, 1.23 (2t, J ¼ 6.9 each, total 6 H); 3.05 (d, J ¼ 16.8, 1 H); 3.25 (d, J ¼ 16.8,
1 H); 3.53 – 3.61 (m, 2 H); 3.83 (s, 3 H); 4.10 – 4.17 (m, 2 H); 5.66 (s, 1 H); 6.93 (d, J ¼ 8.4, 2 H); 7.20 (d,
J ¼ 8.4, 2 H); 8.7 (br., 1 H). 13C-NMR (125 MHz): 14.03; 14.75; 43.71; 55.38; 59.34; 61.07; 103.25; 111.28;
114.67; 126.17; 128.81; 132.05; 159.13; 167.23; 185.68. HR-MS: 352.1225 ([M þ H]þ, C17H22NO5Sþ; calc.
352.1219). Anal. calc. for C17H21NO5S (351.42): C 58.10, H 6.02, N 3.99; found: C 58.01, H 6.06, N 3.92.
1,1-Dimethylethyl 2-{(4Z)-5-Butyl-5-ethoxy-4-[(thiophen-2-yl)methylidene]-2-thioxo-1,3-oxazolin-5-
yl}acetate (3e). Pale-yellow solid. M.p. 90 – 928 (hexane/Et2O). IR (KBr): 3261, 1733, 1683, 1461, 1151.
1H-NMR (500 MHz): 1.22 (t, J ¼ 7.4, 3 H); 1.40 (s, 9 H); 2.97 (d, J ¼ 16.6, 1 H); 3.20 (d, J ¼ 16.6, 1 H);
3.51 – 3.56 (m, 2 H); 5.89 (s, 1 H); 7.02 (d, J ¼ 4.0, 1 H); 7.08 (dd, J ¼ 5.1, 4.0, 1 H); 7.35 (d, J ¼ 5.1, 1 H);
8.80 (br. s, 1 H). 13C-NMR (125 MHz): 14.75; 27.90; 45.08; 59.51; 82.22; 96.57; 111.63; 125.24; 126.74;
127.97; 132.18; 136.45; 166.06; 185.19. HR-MS: 350.0971 ([M þ H]þ, C16H22NO4S2þ ; calc. 356.0990). Anal.
calc. for C16H21NO4S2 (355.47): C 54.06, H 5.95, N 3.94; found: C 54.15, H 6.16, N 3.75.
Mrs. Miyuki Tanmatsu of our university is acknowledged for recording mass spectra and performing
combustion analyses.
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Received August 16, 2012