1
124
Z.-G. Le, J.-P. Xu, H.-Y. Rao, M. Ying
Vol 43
Table 1
Direct Synthesis of 2-Alkylaminobenzothiazoles from phenyl isothiocyanate and amine with [Bmim]Br
3
4
in [Bmim]BF [a]
Entry
RR’NH
MeNH
PrNH
i-PrNH
HOCH CH
MeOCO(CH
Yield(%)
Mp(°C)
141-142
79-80
93-94
105-106
111
Lit.mp(°C)
140-141[10]
79-80[10]
1
2
3
4
5
6
7
2
60
2
80 (78) [b]
2
78
81
60
93-94.5[14]
2
2
NH
NH
2
104-105.5[10]
110-111[10]
98-100[15]
2
)
3
2
pyrrolidine
Piperidine
78 (77) [b]
75
99-100
93
92.5-93.5[10]
6
[a] Isolated yield based on phenyl isothiocyanate; [b] In ionic liquid [Bmim][PF ].
method [15] reports 2-pyrrolidinobenzotriazole was only
ꢀꢁꢂꢁꢃꢄꢄ), the Science and Technology Foundation of the
Education Department of JiangXi Province and the President
Foundation of East China Institute of Technology.
7
7
%, however, using the present method, the yield was
8%.
In conclusion, we have demonstrated the synthesis of 2-
aminobenzothiazoles from phenyl isothiocyanate and
amines using a new reagent of 1-butyl-3-methylimida-
REFERENCES AND NOTES
[
[
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3
3
-methylimidazolium tetraflouoroborate ([Bmim]BF ).
4
4
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This method will be highly useful because of its ease,
simplicity, high yields, short reaction time and
environmentally benign nature.
[
[
[
EXPERIMENTAL
[
Melting points were determined on a digital melting point
apparatus and were not corrected. Infrared spectra were recorded
on a VECTOR22 (Bruker). Nuclear magnetic resonance spectra
were recorded on AVANCE DMX 400 (Bruker) spectrometer.
[
[
8] J. M. Sprague, A. H. Land, In Heterocyclic Compounds;
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19 (2002); [f] D. Zhao, M. Wu, Y. Kou, et al., Catal Today, 74, 157
2002).
[12a] Ionic liquids in Synthesis, P. Wassercheid, T. Welton, Eds:
The ionic liquids [Bmim]Br was synthesized by reaction of an
3
equimolar amount of [Bmim]Br and Br2 for 3 h at room
temperature. The ionic liquids [Bmim]BF and [Bmim]PF were
4
6
(
synthesized according to reported procedures [16]. The other
materials were commercially available and were used without
further purification.
[
General Procedure for Synthesis of 2-Aminobenzothiazoles.
Amine (1.2 mmol) and phenyl isothiocyanate (1 mmol) were
4
(
added to [Bmim]BF (1 mL). The resultant mixture was stirred
4
for 5 min at room temperature, treated with [Bmim]Br3 and
VCH Wiley: Weinheim, Germany, 2002; [b] H. Ohara, H. Kiyokane,
stirred 10 h. The crude product was extracted with Et O, and
and T. Itoh, Tetrahedron Lett., 43, 3041 (2002).
2
purified or directly purified by recrystallization with ethanol or
separated by preparative thin-layer chromatography on silica gel
using a mixture of chloroform and petroleum ether as developer
to give the corresponding pure product.
[13a] Z. G. Le, Z. C. Chen, Y. Hu, Q.G. Zheng, Synthesis, 208
(
(
2004); [b]) Z. G. Le, Z. C. Chen, Y. Hu, Q.G. Zheng, Synthesis, 995
2004); [c] Z. G. Le, Z. C. Chen, Y. Hu, Q.G. Zheng, Heterocycles, 63,
1
077 (2004).
[
[
14] Y. Iwakura, K. Kurita, Bull. Chem. Soc. Jp., 43, 2535 (1970).
15] A. I. Khalaf, R. G. Alvarez, C. J. Suckling, R. D. Waigh,
Acnowlegement.
Tetrahedron, 56, 8567 (2000).
This work was financially supported by the Science
Foundation of JiangXi and ZheJiang Province (0520001,
[16] G. S. Owens, M. M. Abu-Omer, J. Mol. Cata. A: Chem., 187,
211 (2002).