Triethylamine-catalyzed efficient synthesis of oxathiolanes containing a highly polarized carbon-carbon double bond from reaction of malononitrile, carbon disulfide (CS2), and oxiranes

Article abstract of DOI:10.1002/hlca.201000231

An efficient synthesis of functionalized 2-(1,3-oxathiolan-2-ylidene) malononitriles containing a push-pull C=C bond via a simple reaction between malononitrile, CS₂, and oxiranes in the presence of Et₃N is described (Scheme 1). Copy

Full text of DOI:10.1002/hlca.201000231

Helvetica Chimica Acta – Vol. 94 (2011)
639
Triethylamine-Catalyzed Efficient Synthesis of Oxathiolanes Containing a
Highly Polarized Carbon-Carbon Double Bond from Reaction of
Malononitrile, Carbon Disulfide (CS ), and Oxiranes
2
by Issa Yavari*, Majid Ghazanfarpour-Darjani, Yazdan Solgi, and Salomeh Ahmadian
Department of Chemistry, Tarbiat Modares University, P.O. Box, 14115-175 Tehran, Iran
(
phone: þ 98-21-82883465; fax: þ 98-21-82883455; e-mail: yavarisa@modares.ac.ir)
An efficient synthesis of functionalized 2-(1,3-oxathiolan-2-ylidene)malononitriles containing a
push-pull C¼C bond via a simple reaction between malononitrile, CS , and oxiranes in the presence of
2
Et N is described (Scheme 1).
3
Introduction. – The concept of polarized (or push-pull) olefinic systems has played
an important role in organic chemistry for four decades. Substitution of one C-atom of
the C¼C bond with electron-donating groups and of the other with electron-
withdrawing groups diminishes the C¼C bond order by charge separation [1 – 4]. The
13
polarized structure of the C¼C bond is discernible by C-NMR spectroscopy due to the
extreme deshielded position of the alkene C-atom on the donor side and the
contrastingly shielded position of the C-atom on the acceptor side of the push-pull
alkene.
As part of our current studies on the development of new routes in heterocycle
synthesis [5 – 8], we report the synthesis of functionalized 2-(1,3-oxathiolan-2-
ylidene)malononitriles 2 from malononitrile, CS , and oxiranes in the presence of
2
Et N in high yields (Scheme 1). Structure 2 possesses a highly polarized push-pull C¼C
3
bond.
Scheme 1
ꢀ
2011 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 94 (2011)
Results and Discussion. – We began our study by looking at the reaction of
malononitrile with CS and oxiranes 1 in different solvent systems in the presence of
2
Et N, and the results are shown in the Table. The desired product 2a could be obtained
3
in 37 – 90% yield in MeCN, CH Cl , toluene, and THF as solvent (Table), but toluene
2
2
afforded the highest yield (Table, Entries 1 and 5). Other bases such as DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene), pyridine, and K CO gave lower yields of 2a (Table,
2
3
Entries 6 – 8). Increasing the amount of the base reduced the reaction time to 4 h with a
slight increase of the yield (Table, Entry 5).
Table. Optimization of the Reaction Conditions for the Synthesis of Compound 2a at Room Temperature
Entry
Base
Sovent
Time [h]
Yield [%]
1
2
3
4
5
6
7
8
Et N (0.5 equiv.)
toluene
CH Cl
MeCN
THF
toluene
toluene
toluene
toluene
5
6
6
6
4
6
6
6
87
61
48
66
90
40
51
37
3
Et N (0.5 equiv.)
3
2
2
Et N (0.5 equiv.)
3
Et N (0.5 equiv.)
3
Et N (1.0 equiv.)
3
DBU (0.5 equiv.)
pyridine (0.5 equiv.)
K CO (0.5 equiv.)
2
3
Under the optimized conditions, a wide range of oxiranes were successfully coupled
to afford the corresponding oxathiolane derivatives 2 (Scheme 1). The structures of the
1
latter were confirmed by spectroscopic analysis. For example, the H-NMR spectrum of
2
a showed a characteristic (AB)X spin system for the CH CH H-atoms and a d for the
2
13
Me group. The C-NMR spectrum of 2a exhibited 7 signals in agreement with the
proposed structure. The polarized nature of the C¼C bond of 2a was discernible from
13
its C-NMR shifts. The deshielded position of the alkene C-atom on the donor side was
d(C) 188.3, which is more than 100 ppm at lower field compared to the shielded
1
position of the C-atom on the acceptor side of this push-pull alkene. The H- and
13
C-NMR spectra of compounds 2b – 2h were similar to those of 2a, except for the
signals of the substituent R at C(5) of the oxathiolane moiety, which showed
characteristic signals in the appropriate regions of the spectra.
Electronic and steric variation of the oxiranes 1 showed no appreciable change in
the efficiency of the reaction (Scheme 1). The reaction conditions were compatible with
the presence of groups such as chloromethyl, phenoxy, and allyloxy groups, and of an
a,b-unsaturated ester moiety at the oxirane ring. The reaction was completely
regioselective so that only one regioisomer was obtained.
Although the mechanistic details of the formation of compounds 2 are not known, a
plausible rationalization is proposed in Scheme 2. It is conceivable that the reaction
starts with the formation of intermediate 3, followed by addition of 1 to generate 4.
Cyclization of this intermediate leads to 5, which is converted to 2 by elimination of
H S.
2
When cyclohexene oxide (¼ 7-oxabicyclo[4.1.0]heptane; 6) was used as the oxirane
component in these reactions, the fused bicyclic oxathiolane derivative 7 was obtained
in 82% yield (Scheme 3). The structure of compound 7 was again confirmed by its IR
and NMR data.

Helvetica Chimica Acta – Vol. 94 (2011)
641
Scheme 2
Scheme 3
In conclusion, we have described the use of malononitrile as a potential anionic
nucleophile in a reaction involving CS and oxiranes to produce functionalized 2-(1,3-
2
oxathiolan-2-ylidene)malononitriles. Simple mixing of the starting materials and the
potential diversity of this type of reaction are the advantages of this procedure.
Experimental Part
General. Oxiranes 1, malononitrile, CS , and solvents were obtained from Merck and used without
2
further purification. M.p.: Electrothermal-9100 apparatus. IR Spectra: Shimadzu-IR-460 spectrometer;
ꢀ
1
1
13
KBr; ˜n in cm . H- and C-NMR Spectra: Bruker-DRX-500-Avance instrument; in CDCl at 500.1 and
3
1
25.7 MHz, resp.; d in ppm rel. to Me Si as internal standard, J in Hz. MS: Finnigan-MAT-8430 mass
4
spectrometer; at 70 eV; in m/z (rel. %). Elemental analyses (C, H, N): Heraeus-CHN-O-Rapid analyzer.
Compounds 2: General Procedure. To a stirred mixture of malononitrile (0.07 g, 1.0 mmol), oxirane 1
(
1.0 mmol), and CS (0.23 g, 3 mmol) in toluene (3 ml) was slowly added Et N (0.10 g, 1.0 mmol) at r.t.
2
3
After completion of the reaction (4 – 6 h), as indicated by TLC (hexane/AcOEt 5 :1), the solvent was
evaporated, and the light brown residue was separated by CC (silica gel (230 – 400 mesh; Merck), hexane/
AcOEt mixture): pure 2.
2
-(5-Methyl-1,3-oxathiolan-2-ylidene)propanedinitrile (2a): Yield 0.15 g (90%). Pale yellow oil. IR:
1
3
2
3
2
910, 2242, 2239, 1555, 1175. H-NMR: 1.56 (d, J ¼ 6.3, Me); 3.30 (dd, J ¼ 11.1, J ¼ 7.6, CH); 3.65 (dd,
2
3
13
J ¼ 11.1, J ¼ 6.9, CH); 5.21 – 5.25 (m, CH). C-NMR: 18.8 (Me); 38.6 (CH ); 66.1 (CH); 88.7 (C); 111.0
2
þ
(
CN); 113.0 (CN); 188.3 (C). EI-MS: 166 (15, M ), 151 (78), 123 (100), 102 (64), 64 (48). Anal. calc. for
C H N OS (166.20): C 50.59, H 3.64; found: C 50.7, H 3.7.
7
6
2
2
-[5-(Chloromethyl)-1,3-oxathiolan-2-ylidene]propanedinitrile (2b): Yield 0.17 g (87%). Pale yellow
1
2
3
2
3
oil. IR: 2930, 2221, 2218, 1565, 1185. H-NMR: 2.61 (d, J ¼ 12.2, J ¼ 7.8, CH); 2.75 (dd, J ¼ 12.2, J ¼ 5.8,
13
CH); 3.65 – 3.88 (m, CH ); 5.28 – 5.38 (m, CH). C-NMR: 36.7 (CH ); 43.5 (CH ); 69.6 (CH); 88.1 (C);
2
2
2
þ
1
11.4 (CN); 113.8 (CN); 188.5 (C). EI-MS: 199 (8, M ), 151 (80), 123 (100), 102 (62), 64 (55), 36 (56).
Anal. calc. for C H ClN OS (199.98): C 41.90, H 2.51; found: C 42.0, H 2.6.
7
5
2
2
-(5-Ethyl-1,3-oxathiolan-2-ylidene)propanedinitrile (2c): Yield 0.16 g (90%). Pale yellow oil. IR:
1
3
2
3
2
7
(
960, 2251, 2247, 1585, 1179. H-NMR: 1.12 (t, J ¼ 7.4, Me); 1.88 – 2.08 (m, CH ); 3.42 (dd, J ¼ 11.9, J ¼
2
2
3
13
.5, CH); 3.65 (dd, J ¼ 11.9, J ¼ 5.5, CH); 5.05 – 5.09 (m, CH). C-NMR: 9.6 (Me); 26.3 (CH ); 36.8
2
þ
CH ); 57.7 (CH); 93.7 (C); 111.0 (CN); 113.0 (CN); 188.4 (C). EI-MS: 180 (10, M ), 151 (79), 123
2
(
100), 102 (65), 64 (53), 29 (33). Anal. calc. for C H N OS (180.04): C 53.31, H 4.47; found: C 53.4, H 4.5.
8
8
2
2
-(5-Phenyl-1,3-oxathiolan-2-ylidene)propanedinitrile (2d): Yield 0.20 g (88%). Colorless crystals.
1
2
3
M.p. 102 – 1048. IR: 2965, 2260, 2257, 1560, 1165. H-NMR: 4.90 (dd, J ¼ 12.0, J ¼ 5.6, CH); 5.10 (dd,

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Helvetica Chimica Acta – Vol. 94 (2011)
2
3
3
3
3
J ¼ 12.0, J ¼ 7.8, CH); 5.77 (dd, J ¼ 7.8, J ¼ 5.6, CH); 7.37 – 7.44 (m, 3 CH); 7.50 (d, J ¼ 7.2, 2 CH).
13
C-NMR: 54.1 (CH ); 83.2 (CH); 92.6 (C); 110.7 (CN); 112.7 (CN); 127.3 (2 CH); 129.3 (2 CH); 130.4
CH); 133.7 (C); 188.6 (C). EI-MS: 228 (10, M ), 151 (76), 123 (85), 91 (55), 77 (100). Anal. calc. for
2
þ
(
C H N OS (228.04): C 63.14, H 3.53; found: C 63.2, H 3.6.
12
8
2
2
-[5-(Phenoxymethyl)-1,3-oxathiolan-2-ylidene]propanedinitrile (2e): Yield 0.22 g (85%). Pale
1
2
3
yellow crystals. M.p. 92 – 948. IR: 2924, 2250, 2246, 1540, 1180. H-NMR: 3.74 (dd, J ¼ 12.3, J ¼ 6.5,
2
3
3
CH); 3.81 (dd, J ¼ 12.3, J ¼ 5.5, CH); 4.32 – 4.40 (m, CH ); 5.42 – 5.44 (m, CH); 6.93 (d, J ¼ 7.5, 2 CH);
2
3
3
13
7
(
.02 (t, J ¼ 7.5, CH); 7.33 (t, J ¼ 7.5, 2 CH). C-NMR: 34.5 (CH ); 65.9 (CH); 70.2 (CH); 88.7 (C); 110.7
2
þ
CN); 112.8 (CN); 114.7 (2 CH); 121.9 (CH); 129.7 (2 CH); 157.8 (C); 188.1 (C). EI-MS: 258 (10, M ),
1
65 (42), 151 (78), 123 (64), 93 (100), 65 (76). Anal. calc. for C H N O S (258.05): C 60.45, H 3.90;
13 10 2 2
found: C 60.6, H 4.0.
2
-{5-[(Prop-2-en-1-yloxy)methyl]-1,3-oxathiolan-2-ylidene}propanedinitrile (2f): Yield 0.20 g
1
2
3
(
3
92%). Pale yellow oil. IR: 2915, 2235, 2229, 1535, 1165. H-NMR: 3.46 (dd, J ¼ 9.8, J ¼ 5.8, CH);
2
3
3
2
3
.79 – 3.81 (m, CH); 3.94 (dd, J ¼ 12.1, J ¼ 4.7, CH); 4.04 (d, J ¼ 5.6, 2 CH); 4.07 (dd, J ¼ 12.1, J ¼ 5.7,
13
CH); 5.12 – 5.17 (m, CH); 5.20 – 5.30 (m, 2 CH); 5.83 – 5.91 (m, CH). C-NMR: 34.9 (CH ); 46.8 (CH);
2
6
9.2 (CH ); 72.1 (CH ); 90.1(C); 110.9 (CN); 113.1 (CN); 118.4 (CH ); 134.3 (CH); 188.9 (C). EI-MS:
2 2 2
þ
2
22 (15, M ), 158 (68), 151 (85), 123 (100), 98 (46), 71 (73), 64 (33). Anal. calc. for C H N O S (22.05):
10 10 2 2
C 54.04, H 4.53; found: C 54.2, H 4.4.
2
-{5-[(1-Methylethoxy)methyl]-1,3-oxathiolan-2-ylidene}propanedinitrile (2g): Yield 0.21 g (95%).
1
3
Colorless crystals. M.p. 81 – 838. IR: 2910, 2220, 2216, 1542, 1190. H-NMR: 1.12 (d, J ¼ 6.1, 2 Me); 3.53 –
2
3
2
3
3
(
9
.62 (m, CH ); 3.73 (m, CH); 3.89 (dd, J ¼ 12.0, J ¼ 5.9, CH); 4.01 (dd, J ¼ 12.0, J ¼ 6.7, CH); 5.40
2
3
13
sept., J ¼ 6.1, CH). C-NMR: 21.8 (Me); 21.9 (Me); 32.6 (CH ); 66.6 (CH ); 70.3 (CH); 73.1 (CH);
2
2
þ
0.4 (C); 111.5 (CN); 113.2 (CN); 189.1 (C). EI-MS: 224 (5, M ), 209 (73), 151 (84), 123 (100), 100 (52),
7
3 (36). Anal. calc. for C H N O S (224.06): C 53.55, H 5.39; found: C 53.85, H 5.26.
10
12
2
2
[
2-(Dicyanomethylene)-1,3-oxathiolan-5-yl]methyl 2-Methylprop-2-enoate (2h): Yield 0.20 g (86%).
1
2
3
Pale yellow oil. IR: 2985, 2270, 2264, 1703, 1580, 1183. H-NMR: 2.01 (s, Me); 3.66 (dd, J ¼ 14.0, J ¼ 7.0,
2
3
2
3
CH ); 4.08 (m, CH); 4.15 (dd, J ¼ 12.0, J ¼ 4.9, CH); 4.49 (dd, J ¼ 12.0, J ¼ 5.7, CH); 7.13 – 7.15 (m,
2
13
CH); 7.23 – 7.25 (m, CH). C-NMR: 31.2 (Me); 45.1 (CH ); 63.3 (CH ); 69.3 (CH); 90.4 (C); 111.5 (CN);
2
2
þ
1
1
13.2 (CN); 124.1 (C); 136.0 (CH ); 171.2 (COO); 188.4 (C). EI-MS: 236 (5, M ), 151 (84), 123 (100),
12 (52), 85 (90), 55 (61). Anal. calc. for C H N O S (236.03): C 52.79, H 4.03; found: C 53.1, H 4.0.
2
11
10
2
3
rel-2-[(3aR,7aS)-Hexahydro-1,3-benzooxathiol-2-ylidene]propanedinitrile (7): Yield 0.17 g (82%).
1
Colorless crystals. M.p. 2608 (dec.). IR: 2912, 2222, 2217, 1555, 1179. H-NMR: 1.43 – 1.48 (m, CH );
2
1
.68 – 1.75 (m, CH ); 1.93 – 1.97 (m, CH ); 2.17 – 2.22 (m, CH ); 3.32 – 3.35 (m, CH); 3.47 – 3.56 (m, CH).
2
2
2
13
C-NMR: 18.8 (CH ); 23.2 (CH ); 25.8 (CH ); 28.2 (CH ); 47.8 (CH); 74.0 (CH); 95 (C); 113.3 (CN);
2
2
2
2
þ
1
15.1 (CN); 188.6 (C). EI-MS: 206 (35, M ), 149 (78), 123 (100), 82 (64), 64 (48), 56 (45). Anal. calc. for
C H N OS (206.05): C 58.23, H 4.89; found: C 58.1, H 4.9.
10
10
2
REFERENCES
[
[
[
[
[
[
[
[
1] J. Sandstrom, I. Wenoerbeck, Acta Chem. Scand. 1970, 24, 1191.
2] J. Sandstrom, Top. Stereochem. 1983, 14, 83.
3] H. O. Kalinowski, H. Kessler, Top. Stereochem. 1973, 7, 303.
4] I. Yavari, A. Zonouzi, R. Hekmat-Shoar, Tetrahedron Lett. 1998, 39, 3841.
5] I. Yavari, G. Khalili, A. Mirzaei, Helv. Chim. Acta 2010, 93, 277.
6] I. Yavari, A. Mirzaei, G. Khalili, Helv. Chim. Acta 2010, 93, 654.
7] I. Yavari, M. Ghazanfarpour-Darjani, Z. Hossaini, M. Sabbaghan, N. Hosseini, Synlett 2008, 889.
8] I. Yavari, M. Sabbaghan, Z. Hossaini, M. Ghazanfarpour-Darjani, Helv. Chim. Acta 2008, 91, 1144.
Received June 12, 2010