March 1998
SYNLETT
287
In conclusion, the iodinane 1A is a very useful and reactive reagent for
the iodination of aromatic rings as compared with previous iodinanes
1
B ~ 1E. The advantages of this reagent are: 1) low toxicity, 2) simple
experimental operation, and 3) high yields of halogenation products.
References and Notes
Monosubstituted benzenes, such as anisole and tert-butylbenzene, were
converted to the corresponding iodinated compounds in good yields (80
and 79 %), and ortho and/or para orientation of iodine indicates that this
reaction proceeds via a cationic iodonium species. Phenyl acetate (2i)
was iodinated only in 39 % yield under the same conditions. The
amount of solvent was then decreased from 5 ml to 1.5 ml to form
iodinated product 3i in 75 % yield together with 4-iodophenol in 12 %
yield. In entry 5, 4-iodotoluene was formed in 37 % yield instead of 4-
chloroiodobenzene. We then used chlorobenzene as a solvent and 4-
chloroiodobenzene was obtained in 40 % yield. 4-Bromoanisole and p-
xylene gave the iodinated compounds in high yields. These results
suggest that the iodination of chlorobenzene represents the limit of the
scope of the reaction method in view of electron density on the aromatic
ring. Here, we attempted the decomposition of iodinane 1A in the
presence of iodine under the dark conditions, and consequently 4-
iodotoluene was obtained in 57 % yield (Scheme 1). Thus, it is seen
that, when the reactivity of the aromatic substrate to iodinane 1A is
insufficient, 4-iodotoluene may be formed.
(1) Krasutsky, A. P.; Kuehl, C. J.; Zhdankin, V. V. Synlett 1995,
1081; Zhdankin, V. V.; Krasutsky, A. P.; Kuehl, C. J.; Simonsen,
A. J.; Woodward, J. K.; Mismash, B.; Bolz, J. T. J. Am. Chem.
Soc. 1996, 118, 5192; Zhdankin, V. V.; Kuehl, C. J.; Krasutsky,
A. P.; Bolz, J. T.; Mismash, B.; Woodward, J. K.; Simonsen, A. J.
Tetrahedron Lett. 1995, 36, 7975; Zhdankin, V. V.; McSherry,
M.; Mismash, B.; Bolz, J. T.; Woodward, J. K.; Arbit, R. M.;
Erickson, S. Tetrahedron Lett. 1997, 38, 21.
(2) Ochiai, M.; Ito, T.; Takahashi, H.; Nakanishi, A.; Toyonari, M.;
Sueda, T.; Goto, S.; Shiro, M. J. Am. Chem. Soc. 1996, 118, 7716;
Ochiai, M.; Nakanishi, A.; Yamada, A. Tetrahedron Lett. 1997,
38, 3927.
(
3) Zhdankin, V. V.; Kuehl, C. J.; Bolz, J. T.; Formaneck, M. S.;
Simonsen, A. J. Tetrahedron Lett. 1994, 35, 7323; Zhdankin, V.
V.; Kuehl, C. J.; Krasutsky, A. P.; Bolz, J. T.; Simonsen, A. J. J.
Org. Chem. 1996, 61, 6547.
(
4) Recent review: Moriarty, R. M.; Vaid, R. K. Synthesis 1990, 431;
Moriarty, R. M.; Vaid, R. K. Koser, G. F. Synlett 1990, 365;
Stang, P. J. Angew. Chem., Int. Ed. Engl. 1992, 31, 274; Prakash,
O.; Saini, N.; Sharma, P. K. Heterocycles 1994, 38, 409; Synlett
1
994, 221; Kitamuta, T. Yuki Gosei Kagaku Kyoukaishi 1995, 53,
6
9; Stang, P. J.; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123; Kita,
Y.; Takada, T.; Tohma, H. Pure Appl. Chem. 1996, 68, 627;
Zefirov, N. S. Pure Appl. Chem. 1996, 68, 881; Togo, H.;
Hoshina, Y.; Nogami, G.; Yokoyama, M. Yuki Gosei Kagaku
Kyoukaishi 1997, 55, 14; Varvoglis, A. Tetrahedron, 1997, 53,
The reaction in Scheme 1 is recognized as a desulfonyloxylation
reaction via tosyl hypoiodite, like decarboxylation of acyl hypoiodite.
Here, there are two plausible reaction mechanisms: one is that, after
homolytic cleavage of the O-I bond of tosyl hypoiodite derived from
iodinane 1A and iodine, a tolyl radical is generated from the tosyloxy
radical via a desulfonyloxylation pathway, and reacted with iodine to
form 4-iodotoluene; the other is that a cationic iodonium species by the
reaction of iodinane 1A with iodine is substituted at the ipso-sulfur
position of tosylate. Clarification of the reaction mechanism is now
under study. Finally, aromatic heterocycles were iodinated (Scheme 2).
1
179.
(5) Merkushev, E. B. Russ. Chem. Rev. 1984, 53, 343; Synthesis
1988, 923; Larock, R. C. Comprehensive Organic
Transformations; VCH Publishers, Inc.: New York, 1989; p 315;
Kajigaeshi, S.; Kakinami, T.; Yamasaki, H.; Fujisaki, S.; Kondo,
M.; Okamoto, T. Chem. Lett. 1987, 2109; Kaligashi, S.;
Kakinami, T.; Moriwaki, M.; Watanabe, M.; Fujisaki, S.;
Okamoto, T. Chem. Lett. 1988, 795; Orito, K.; Hatakeyama, T.;
Takeo, M.; Suginome, H. Synthesis 1995, 1273; Orito, K.;
Hatakeyama, T.; Takeo, M.; Siginome, H.; Tokuda, M. Synthesis,
2
,3-Benzothiophene was mainly converted to 3-iodobenzothiophene
m-i in 68 % yield and 2,3-diiodo compound 3m-ii was also obtained
in 12 % yield. N-Benzenesulfonyl indole 2n gave the 3-iodo compound
n in moderate yield, together with a dimerized product of indole at the
-position in 24 % yield.
1997, 23; Majetich, G.; Hicks, R.; Reister, S. J. Org. Chem. 1997,
62, 4321; Noda, Y.; Kashima, M. Tetrahedron Lett. 1997, 38,
6225; Sugiyama, T. Bull. Chem. Soc. Jpn. 1981, 54, 2847; Zupan,
3
3
3
M.; Iskra, J.; Stavber, S. Tetrahedron Lett. 1997, 38, 6305;