H. Firouzabadi et al. / Tetrahedron Letters 45 (2004) 7451–7454
Table 2. ZrCl4/NaI used for selective iodination of different alcohols
7453
Entry
1a
Alcohols
Products
Time (min)
% Conversionc
85
20
OH
I
60
I
OH
97
7
OH
OH
I
I
2b
10
5
OH
I
I
100
15
3b
OH
100d
0
I
HO
I
4a
20
OH
HO
I
a Reactions were conducted at reflux.
b Reactions were conducted at room temperature.
c GC yield.
d 1H NMR yield.
to obtain the corresponding diiodide. However, we ob-
served that a mixture of mono and diiodo compounds
were produced after 5h in 70% and 30% yields,
respectively.
ZrCl4 (0.116g, 0.5mmol) in several portions (it is very
important to note that ZrCl4 with a faint pink hue
should not be used).
The mixture was stirred at rt and the progress of the
reaction was monitored by TLC or GC. After 10min,
the reaction mixture was diluted with ether (10mL)
and water (10mL). The organic layer was separated
and washed with an aqueous solution of Na2S2O3
(10%, 10mL), then H2O (10mL). The organic layer
was separated and dried over anhydrous Na2SO4. Evap-
oration of the solvent under reduced pressure at rt gave
benzyl iodide (0.103g, 95%) of a very high purity.
We have also examined the selectivity of ZrCl4/NaI in
several competing reactions between structurally differ-
ent alcohols. The results for selective iodination reac-
tions are given in Table 2.
It is important to note that the pinkish ZrCl4 should not
be used for these reactions. The reactions proceeded
sluggishly in the presence of the excess amounts of the
pinkish compound. We believe that the pinkish com-
pound is a mixture of ZrCl4, ZrOCl2 and ZrO2. In these
reactions, ZrCl4 is probably converted to ZrO2 accord-
ing to the following reaction scheme.
Acknowledgements
Support for this work by Iran TWAS Chapter at ISMO
and Shiraz University Research Council is highly
appreciated.
-Cl-
-HCl
R-I + ZrOCl2
R-O- ZrCl3
I-
R-O-H + ZrCl4
1)
2)
References and notes
-Cl-
-HCl
R-O- ZrOCl
I-
R-I + ZrO2
R-O-H + ZrOCl2
1. (a) Bohlmann, R. In Comprehensive Organic Synthesis;
Trost, B. M., Fleming, I, Eds.; Pergamon: Oxford, 1991;
Vol. 6, pp 203–223; (b) Hudlicky, M.; Hudlicky, T In The
Chemistry of Functional Groups, Supplement D; Patai, S.,
Rappoport, Z., Eds.; Wiley: New York, 1983; p 1021; (c)
Chambers, R. D.; James, S. R. In Comprehensive Organic
Chemistry; Barton, D., Ollis, W. D., Eds.; Pergamon:
Oxford, 1979; Vol. 1, pp 493–575; (d) Su, M.-D.; Chu
S.-Y. J. Am. Chem. Soc. 1999, 121, 1045–1058.
2. (a) Kita, Y.; Gotanda, K.; Sano, A.; Oka, M.; Murata, K.;
Suemura, M.; Matsugi, M. Tetrahedron Lett. 1997, 48,
8345–8348; (b) Kita, Y.; Sano, A.; Yamaguchi, T.; Oka,
M.; Gotanda, K.; Matsugi, M. Tetrahedron Lett. 1997, 38,
3549–3552; (c) Kita, Y.; Sano, A.; Yamaguchi, T.; Oka,
M.; Gotanda, K.; Matsugi, M. J. Org. Chem. 1999, 64,
675–678; (d) Kita, Y.; Nambu, H.; Ramesh, N. G.;
Anilkumar, G.; Matsugi, M. Org. Lett. 2001, 3, 1157–
1160; (e) Kita, Y.; Matsugi, M. In Radicals in Organic
In conclusion, in this study we have introduced a new
system for the iodination of structurally diverse alcoh-
ols. ZrCl4/NaI conducts the reactions with high yields
and selectivity. The low toxicity of ZrCl4, its ease of han-
dling and its commercial availability accompanied with
the simple work-up of the reaction mixture are the
strong practical points of the presented method.
Typical procedure
To a solution of benzyl alcohol (0.108g, 1mmol) and
NaI (0.225g, 1.5mmol) in dry CH3CN (2mL) was added