LETTER
Efficient Reductions of Nitroarenes with SnCl2
1837
specifically the reluctance of p-nitrophenol (entry 6) to
undergo reduction. The easy reduction of p-nitrophenol in
presence of KI (10 mol% of SnCl ·2H O) may be attribut-
(5) (a) George, J.; Chandrasekaran, S. Synth. Commun. 1983,
495. (b) Yuste, F.; Saldana, M.; Walls, F. Tetrahedron Lett.
1982, 147. (c) Babler, J. H.; Sarussi, S. J. Synth. Commun.
1981, 925. (d) Neilson, T.; Wood, H. G. S.; Wylie, A. G. J.
2
2
–
–
ed to the greater stability of SnCl I than SnCl Br in view
2
2
Chem. Soc. 1962, 371. (e) Nose, A.; Kudo, T. Chem. Pharm.
Bull. Jpn. 1981, 29, 1159. (f) Liou, K. F.; Cheng, C. H. J.
Org. Chem. 1982, 47, 3018. (g) Vass, A.; Dudar, J.; Varma,
R. S. Tetrahedron Lett. 2001, 42, 5347. (h) Meshram, H.
M.; Ganesh, Y. S. S.; Sekhar, K. C.; Yadav, J. S. Synlett
2000, 993. (i) Khan, F. A.; Dash, J.; Sudheer, Ch.; Gupta, R.
K. Tetrahedron Lett. 2003, 44, 7783. (j) Zheng, X. L.;
Zheng, Y. M. Chin. J. Chem. 2002, 20, 925.
of their relative rate of dissociation in comparison to that
of the phenolic proton. The fact that ortho substituted ni-
troarenes (entries 3 and 5) undergo faster reduction than
para isomers (entries 2 and 4) can be explained on the
8
basis of steric acceleration effect i.e. the steric crowding
of the ortho substituent forces C-N bond to get twisted in
order to put a break on resonance inhibition.
(6) Bellamy, F. D.; Ou, K. Tetrahedron Lett. 1984, 25, 839.
In conclusion, a mild, efficient, green and general proto-
col for reduction of nitroarenes with different substituents
has been developed employing traditional SnCl ·2H O in
(7) Advanced Inorganic Chemistry, A Comprehensive Text, 2nd
ed.; Cotton, F. A.; Wilkinson, G., Eds.; Interscience
Publishers: New York, 1966, 481.
2
2
(
(
8) Xing, W. K.; Ogata, Y. J. Org. Chem. 1982, 47, 3577.
9) (a) Welton, T. Chem. Rev. 1999, 99, 2071.
ionic liquid TBAB which functions as a source of unsol-
1
2
vated bromide ion as well. Improved yields, lower reac-
tion times, non-excess stoichiometry, recyclable solvent,
cheap reagents and a less demanding purification proce-
dure are the advantageous features of this method. Above
all, the chemical aspects regarding the presence of halide
ions in this reduction process have been accomplished.
(
b) Wasserscheid, P.; Keim, W. Angew. Chem. Int. Ed. 2000,
9, 3772. (c) DuPont, J.; De Souza, R. F.; Surez, P. A. Z.
Chem. Rev. 2002, 102, 3667.
(10) Chemistry of the Elements, In Germanium, Tin and Lead,
nd ed; Greenwood, N. N.; Earnshaw, A., Eds.; Butterworth
3
2
Heinemann: Great Britain, 1997, 380–381.
11) (a) Donaldson, J. D.; Silver, J.; Hadjiminolis, S.; Ross, S. D.
J. Chem. Soc., Dalton Trans. 1975, 1500. (b) Donaldson, J.
D.; Silver, J.; Hadjiminolis, S.; Ross, S. D. J. Chem. Soc.,
Dalton Trans. 1975, 1980.
(
Acknowledgment
The author is highly indebted to Mrs. K. De for inspiration and Uni-
versity of Kalyani for financial help as UGC minor research grant.
Thanks to DST for FIST programme.
(12) Representative Procedure for Reduction of Nitroarenes
with SnCl in Ionic Liquid: Nitroarene (2 mmol) was
2
mixed with TBAB (1 g) with stirring and to this mixture was
added SnCl ·2H O (1350 mg, 6 mmol, 3 equiv). The mixture
2
2
was stirred until a clear melt resulted. Then it was kept on
water bath at 90 °C for completion (TLC monitoring) and
References
extracted with Et O (3 × 5 mL). The combined organic layer
2
(
1) Sun, W.-C.; Gee, K. R.; Haughland, R. P. Bioorg. Med.
Chem. Lett. 1998, 8, 3107.
2) Amir, E.; Hass, E. Biochemistry 1998, 27, 8889.
3) Adronov, A.; Fréchet, J. M. J. Chem. Commun. 2000, 1707.
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Neuwahl, F. V. R.; Fleming, G. R. J. Am. Chem. Soc. 2000,
was washed with H O, brine and dried over anhyd Na SO .
2
2
4
Removal of solvent gave the crude product, which was
purified by column chromatography over silica gel to furnish
aminoarene exclusively.
(
(
(
122, 1175.
Synlett 2004, No. 10, 1835–1837 © Thieme Stuttgart · New York