Nano ZnO promoted synthesis of 1,3-oxazoline-2-thione derivatives

Article abstract of DOI:10.3184/174751914X13968048433084

The synthesis of 2-thioxo-1,3-oxazoles in the presence of zinc oxide nanoparticles (ZnO NPs, ca 21 nm) and under solvent-free conditions has been achieved through reaction of ammonium thiocyanate, acid chlorides, phenacyl bromide or its derivatives, and a catalytic amount of N-methylimidazole. The catalyst was recycled and reused six times with minor decrease in its catalytic activity. High yields, simple experimental procedure and short reaction times are advantages of this reaction.

Full text of DOI:10.3184/174751914X13968048433084

JOURNAL OF CHEMICAL RESEARCH 2014
VOL. 38 MAY, 295–296
RESEARCH PAPER 295
Nano ZnO promoted synthesis of 1,3-oxazoline-2-thione derivatives
B. Narjes Haerizade and Mohammad Z. Kassaee*
Department of Chemistry, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran
The synthesis of 2‑thioxo‑1,3‑oxazoles in the presence of zinc oxide nanoparticles (ZnO NPs, ca 21 nm) and under solvent‑free
conditions has been achieved through reaction of ammonium thiocyanate, acid chlorides, phenacyl bromide or its derivatives,
and a catalytic amount of N‑methylimidazole. The catalyst was recycled and reused six times with minor decrease in its
catalytic activity. High yields, simple experimental procedure and short reaction times are advantages of this reaction.
Keywords: zinc oxide nanoparticles, 2‑thioxo‑1,3‑oxazole, solvent‑free conditions, N‑methylimidazole
The value of nanosized materials has been described in several
scientific and technological areas, including the catalytic
activity of the metal oxide nanoparticles (NPs).1,2 The high
surface to volume ratio of metal oxide NPs is mainly responsible
for their improved catalytic properties.3 The catalytic influence
of nanocrystalline zinc oxide is utilised in gas sensors and
photo‑catalysts. Currently, the application of this nanocatalyst
in organic and inorganic reactions has emerged as a rapidly
growing field.4–7 A number of methods have been developed
to synthesise 1,3‑oxazolidine‑2‑thiones.8‑18 In this work, we
combine 1–3 in the presence of N‑methylimidazole and ZnO
NPs to obtain the desired product 4 (Scheme 1).
1,3‑oxazoline‑2‑thione ring system of 4a showed signals in
agreement with the proposed structure. A tentative mechanism
for this transformation has been proposed (Scheme 2). The
reaction may start with the formation of benzoyl isothiocyanate
5, followed by the addition of N‑methylimidazole and
formation of 1:1 adduct 6, which is subsequently attacked
by phenacyl bromide to produce 7. The latter undergoes the
elimination of HBr followed by a cyclisation reaction, and loss
of N‑methylimidazole to generate 4.
In conclusion, the reaction of phenacyl bromide or its
derivatives with acid chlorides and ammonium thiocyanate in
the presence of N‑methylimidazole (20 mol%) and ZnO NPs
(10 mol%) leads to functionalised 2‑thioxo‑2,3‑dihydro‑1,3‑
oxazoles in good yields. The solvent‑free conditions and the
simplicity of the procedure makes it an interesting alternative to
the more complex multistep approaches. The present procedure
has the advantage that not only is the reaction performed under
neutral conditions, but also the reactants can be mixed without
any prior activation or modification.
Result and discussion
Reaction of phenacyl bromide (3) or its derivatives with acid
chlorides (2) and ammonium thiocyanate (1) in the presence of
N‑methylimidazole (20 mol%) and ZnO NPs (10 mol%) lead to
functionalised 2‑thioxo‑2,3‑dihydro‑1,3‑oxazoles in good yield
(Scheme 1).
This reaction does not occur without the ZnO NPs.
Instead, a two‑component reaction occurs between N‑methyl
imidazole and phenacyl bromide 3. However, under similar
conditions but without ZnO NPs, this reaction also occurs
with ethyl bromopyruvate.18 The structures for 4a–e were
Experimental
All chemicals used in this work are purchased from Fluka (Buchs,
Switzerland) and used without further purification. Melting points
are measured on an Electrothermal 9100 apparatus. IR spectra are
measured on a Shimadzu IR‑460 spectrometer. 1H, and 13C NMR
spectra are obtained using a Bruker DRX‑400 Avance spectrometer at
400.1 and 125.8 MHz, respectively. Mass spectra were recorded on a
Finnigan‑MAT 8430 spectrometer operating at an ionisation potential
1
assigned from their IR, H NMR and 13C NMR spectra. The
1H NMR spectrum of 4a exhibits characteristic signals for
methine protons (δ=7.27 ppm). The 13C NMR spectra of the
N
S
O
N
O
Ar '
N
O
Me
NH4SCN
+
Br
Ar
+
Ar
Cl
O
Solvent-Free, ZnO NPs, r. t.
Ar '
3
4
1
2
Ar'
Yied % of 4
Ar
2, 3, 4
4-O2NC6H4
4-BrC6H4
95
75
a
b
c
4-BrC6H4
4-O2NC6H4
4-O2NC6H4
4-MeOC6H4
4-BrC6H4
4-MeOC6H4
4-BrC6H4
70
85
83
d
e
4-OMeC6H4
Scheme 1 Reaction of ammonium thiocyanate, acid chloride and phenacyl bromide or its derivatives in the
presence of ZnO NPs (10 mol%).
* Correspondent. E‑mail: kassaeem@modares.ac.ir
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296 JOURNAL OF CHEMICAL RESEARCH 2014
N
O
NMe
O
S
+
3
+
+
1
2
N
C
S
Ar
Ar
N
N
NMe
NMe
ZnO (NPs)
5
6
O
S
O
S
S
O
N
N
Ar
N
N
N
N
NMe
_
NMe
NMe
Ar
N
_
O
HBr
O
4
O
Ar'
Ar'
Br
Ar'
9
8
7
Scheme 2 Proposed mechanism for the formation of 4.
of 70 eV. 1H and 13C NMR spectra were obtained for solutions in CDCl3
using TMS as the internal standard.
(2 CH); 128.6 (C), 129.3 (2 CH); 143.4 (C); 151.8 (2 C); 160.1 (C=O);
164.6 (C=S). Anal. calcd for C17H12BrNO3S (390.25): C, 52.32; H, 3.10;
N, 3.59; found: C, 52.40; H, 3.22; N, 3.67%.
Synthesis of compounds 4; general procedure
(4‑Bromophenyl)[5‑(4‑methoxyphenyl)‑2‑thioxo‑1,3‑oxazol‑3(2H)‑
yl]methanone (4e): Pale yellow powder; yield 83%; m.p. 163–165 °C. IR
(KBr): 1734, 1672, 1514, 1449 and 1263 cm–1. 1H NMR: δ 3.88 (3 H, s,
MeO), 5.21 (1 H, s, CH), 6.81–7.69 (8 H, m,8 CH) ppm. 13C NMR: δ
53.2 (MeO), 114.0 (3 CH); 121.3 (2 CH); 124.6 (C), 126.9 (2 CH); 129.3
(2 CH), 130.9 (C), 142.7 (C); 145.4 (C), 149.2 (C); 160.7 (C=O); 165.9
(C=S). Anal. calcd for C17H12BrNO3S (390.25): C, 52.32; H, 3.10; N,
3.59; found: C, 52.40; H, 3.20; N, 3.68%.
We first prepared ZnO NPs through a solid-state reaction method
reported by Zhu and co‑workers.19,20 The ZnO NPs was used as a
catalyst in the synthesis of functionalised 1,3‑oxazoline‑2‑thiones
derivatives. A magnetically stirred mixture of 1 (0.15 g, 2 mmol)
and acid chloride 2 (2 mmol) was warmed at about 70 °C in a water
bath for 20 min. Phenacyl bromide 3 or its derivatives (2 mmol) is
added gently and the mixture is allowed to cool to room temperature.
N‑methylimidazole (0.032 g, 20 mol%) and ZnO NPs (10 mol%) were
added. The reaction mixture was stirred for 12 h and extracted by Et2O
(2×5 mL) to afford the pure title compounds.
Received 9 November 2013; accepted 13 March 2014
Paper 1302278 doi: 10.3184/174751914X13968048433084
Published online: 6 May 2014
(4‑Bromophenyl)[5‑(4‑nitrophenyl)‑2‑thioxo‑1,3‑oxazol‑3(2H)‑
yl]methanone (4a): Pale yellow powder; 0.59 g; yield 95%; m.p.
132–134 °C. IR (KBr) (νmax/cm–1): 1728, 1576, 1453, 1369 and
1293 cm–1. 1H NMR: δ 7.27 (1 H, s, CH); 7.20–7.66 (6 H, m, 6 CH); 7.87
(2 H, d, 3J=7.4 Hz, 2CH) ppm. 13C NMR: δ 95.4 (CH), 124.5 (C), 127.7
(2 CH); 127.9 (2 CH); 128.5 (2 CH); 130.5 (2 CH); 135.1 (C); 147.6 (C);
151.0 (2C); 161.9 (C=O); 163.8 (C=S) ppm. MS, m/z (%): 405 (M+, 15),
181 (100), 150 (87), 127 (64), 77 (95). Anal. calcd for C16H9BrN2O4S
(405.22): C, 47.43; H, 2.24; N, 6.91; found: C, 47.52; H, 2.32; N, 6.98%.
(4‑Nitrophenyl)[5‑(4‑bromophenyl)‑2‑thioxo‑1,3‑oxazol‑3(2H)‑
yl]methanone (4b): Yellow crystals; yield 75%; m.p. 131–133 °C. IR
(KBr): 1723, 1631, 1552, 1440 and 1373 cm–1. 1H NMR: δ 7.02 (1 H, s,
CH); 7.45–8.58 (8 H, m, 8 CH) ppm. 13C NMR: δ 119.8 (CH), 124.9 (C),
127.7 (2 CH); 127.9 (2 CH); 128.4 (2 CH); 130.8 (2 CH); 143.4 (C); 149.4
(C); 151.8 (2C); 160.1 (C=O); 164.6 (C=S) ppm. MS, m/z (%): 405 (M+,
10), 181 (88), 150 (86), 127 (58), 77 (100). Anal. calcd for C16H9BrN2O4S
(405.22): C, 47.43; H, 2.24; N, 6.91; found: C, 47.54; H, 2.35; N, 7.00%.
(4‑Nitrophenyl)[5‑(4‑methoxyphenyl)‑2‑thioxo‑1,3‑oxazol‑3(2H)‑
yl]methanone (4c): Yellow crystals; yield 70%; m.p. 157–159 °C. IR
(KBr): 1730, 1591, 1548, 1513 and 1432 cm–1. 1H NMR: δ 4.09 (3 H, s,
MeO), 6.62 (1 H, s, CH), 7.48–8.06 (8 H, m,8 CH) ppm. 13C NMR: δ
53.6 (MeO), 110.0 (CH); 115.5 (2 CH); 127.9 (C); 128.1 (2 CH), 129.5
(2 CH); 130.8 (C), 134.6 (2 CH); 145.6 (C); 154.9 (2 C); 159.5 (C=O);
167.8 (C=S). MS, m/z (%): 356 (M+, 10), 249 (78), 151 (100), 107 (88),
31 (100). Anal. calcd for C17H12BrN2O5S (356.35): C, 57.30; H, 3.39; N,
7.86; found: C, 57.43; H, 3.45; N, 7.96%.
References
1
2
3
4
A. Yamaguchiling, F. Uejo, T. Yoda, Y. Tanamura, T. Yamashita and N.
Teramae, Nat. Mater., 2004, 3, 337.
P. Claus, A.C. Mohr and H. Hofmeister, J. Am. Chem. Soc., 2000, 122,
11430.
M. Kidwai, V. Bansal, N.K. Mirsha, A. Kumar and S. Mozumdar, Synlett,
2007, 1581.
K.M. Parida, S.S. Dash and D.P.J. Das, Colloid Interface Sci., 2006, 298,
787.
5
6
A. Roucoux, J. Schulz and H. Patin, Chem. Rev., 2002, 102, 3757.
D. Hernandez‑Santos, M.B. Gonzalez‑Garcia and A.C. Garcia,
Electroanalysis, 2002, 14, 1225.
7
8
9
J.A. Widegren and R.G. Finke, J. Mol. Cata, A: Chem., 2003, 191, 187.
J.F. Willems and A.B. Vandenberghe, Soc. Chim. Belg., 1961, 70, 745.
G. Lacasse and J.M. Muchowki, Can, J. Chem., 1972, 50, 3082.
10 C.K. Bradscher and W.J. Jones, J. Org. Chem., 1967, 32, 2079.
11 C. Guimon, G. Pfister‑Guillouzo, M. Arbelot and M. Chanon, Tetrahedron,
1974, 30, 3831.
12 G.S. Kapsomenos and P.D.D. Akrivos, Can. J. Chem., 1988, 66, 2835.
13 C.M. Shafer and T.F. Molinski, J. Org. Chem., 1998, 63, 551.
14 C. Gonzalez‑Romero and R. Martinez‑Palou, H.A. Jimenez‑Vazquez, A.
Fuentes, F. Jimenez and J. Tamariz, Heterocycles, 2007, 71, 305.
15 V. Bobosik, A. Piklerova and A. Maretvon, Coll. Czech. Chem. Commun.,
1983, 48, 3421.
16 A. Tatibouët, S. Lawrence, P. Rollin and G.D. Holman, Synlett, 2004, 1945.
17 N. Leconte, S. Silva, A. Tatibouët, A.P. Rauter and P. Rollin, Synlett, 2006,
301.
18 I. Yavari, Z.S. Hossaini, S. Souri and M. Sabbaghan, Synlett, 2008, 9, 1287.
19 Y. Zhu and Y. Zhou, Appl Phys A, 2008, 92, 275.
20 M.Z. Kassaee, H. Masrouri and F. Movahedi, Monatsh Chem., 2010, 141,
317.
(4‑Methoxyphenyl)[5‑(4‑bromophenyl)‑2‑thioxo‑1,3‑oxazol‑3(2H)‑
yl]methanone (4d): Yellow powder; yield 85%; m.p. 162–164 °C. IR
(KBr): 1723, 1548, 1500, 1460 and 1372 cm–1. 1H NMR: δ 4.07 (3 H, s,
MeO), 7.03 (1 H, s, CH), 7.29–8.52 (8 H, m,8 CH) ppm. 13C NMR: δ
53.3 (MeO), 111.6 (CH); 118.3 (2 CH); 123.0 (C); 124.6 (2 CH), 127.7
JCR1302278_FINAL.indd 296
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