Reaction of arenes with iodine in the presence of potassium peroxodisulfate in trifluoroacetic acid. Direct and simple synthesis of diaryliodonium triflates

Article abstract of DOI:10.1021/jo061889q

Diaryliodonium triflates have been directly prepared by reaction of arenes with elemental iodine in good yields by using K₂S₂O ₈ and TFA, followed by treatment with NaOTf. This procedure avoids the use of high temperature

Full text of DOI:10.1021/jo061889q

Reaction of Arenes with Iodine in the Presence of
Potassium Peroxodisulfate in Trifluoroacetic
Acid. Direct and Simple Synthesis of
Diaryliodonium Triflates
convenient synthesis of diaryliodonium triflates via the reac-
tion of (diacetoxyiodo)benzene and triflic acid with aromatic
substrates; (c) A direct synthesis of diaryliodonium triflates
8
by the reaction of iodosyl triflate with the trimethylsilyl
9
derivatives of aromatic compounds; (d) Synthesis of unsym-
metrical diaryliodonium triflates by the treatment of â-(trifyl-
†
‡
Md. Delwar Hossain, Yasuyuki Ikegami, and
10
oxy)vinyl iodonium triflates with aryl lithium reagents; (e) A
generalized synthesis of unsymmetrical functionalized diaryl-
iodonium triflates through the direct reaction of (diacetoxyiodo)-
arenes with arenes in a triflic acid or trifluoroacetic acid
,
†
Tsugio Kitamura*
Department of Chemistry and Applied Chemistry, Faculty of
Science and Engineering, and Institute of Ocean Energy, Saga
UniVersity, Honjo-machi, Saga 840-8502, Japan
1
1
medium; (f) Diaryliodonium triflates were prepared by the
reaction of xenon difluoride, triflic acid, iodoarenes, and
kitamura@cc.saga-u.ac.jp
1
2
aromatic compounds.
ReceiVed September 12, 2006
However, the above methods mostly involve iodoarenes,
iodosylarenes, and (diacetoxyiodo)arenes. Considering the useful
properties of salts and other derivatives of triflic acid,13 the
development of a simple and efficient procedure for the
preparation of diaryliodonium triflates is a desirable goal. The
most ideal procedure for diphenyliodonium triflate should
involve a straightforward synthesis from benzene and iodine.
This procedure gives a direct and efficient method that does
Diaryliodonium triflates have been directly prepared by
reaction of arenes with elemental iodine in good yields by
using K S O and TFA, followed by treatment with NaOTf.
2 2 8
This procedure avoids the use of high temperature and severe
reaction conditions.
(
1) Reviews on organohypervalent iodine compounds and their applica-
tions in organic synthesis: (a) Varvoglis, A. Chem. Soc. ReV. 1981, 10,
77-407. (b) Varvoglis, A. The Organic Chemistry of Polycoordinated
3
Iodine; VCH: Weinheim, Germany, 1992. (c) Stang, P. J.; Zhdankin, V.
V. Chem. ReV. 1996, 96, 1123-1178. (d) Varvoglis, A. HyperValent Iodine
in Organic Synthesis; Academic: San Diego, CA, 1997. (e) Kitamura, T.;
Fujiwara, Y. Org. Prep. Proced. Int. 1997, 29, 409-458. (f) Varvoglis, A.
Tetrahedron 1997, 53, 1179-1255. (g) Muraki, T.; Togo, H.; Yokoyama,
M. ReV. Heteroat. Chem. 1997, 17, 213-243. (h) Kirschning, A. Eur. J.
Org. Chem. 1998, 11, 2267-2274. (i) Zhdankin, V. V.; Stang, P. J.
Tetrahedron 1998, 54, 10927-10966. (j) Varvoglis, A.; Spyroudis, S. Synlett
Hypervalent iodine reagents have attracted increasing interest
as useful oxidants in organic synthesis due to their low toxicity,
ready availability, easy handling, high efficiency, stability to
air and moisture, and as an environment-friendly alternative to
heavy metal reagents such as lead(IV), thallium(III), and
mercury(II). Recently, extensive studies on hypervalent iodine
compounds such as (diacetoxyiodo)arenes, [bis(trifluoroacetoxy)-
iodo]arenes, [hydroxy(tosyloxy)iodo]arenes, and diaryliodonium
salts have been carried out, and their application for organic
1
1
998, 221-232. (k) Kita, Y.; Egi, M.; Takada, T.; Tohma, H. Synthesis
999, 885-897. (l) Wirth, T.; Hirt, V. H. Synthesis 1999, 1271-1287. (m)
Chemistry of HyperValent Compounds; Akiba, K., Ed.; VCH: New York,
1999; pp 359-387. (n) Grushin, V. V. Chem. Soc. ReV. 2000, 29, 315-
324. (o) Zhdankin, V. V.; Stang, P. J. Chem. ReV. 2002, 102, 2523-2584.
(
p) Tohma, H.; Kita, Y. AdV. Synth. Catal. 2004, 346, 111-124. (q)
HyperValent Iodine Chemistry; Wirth, T., Ed.; Springer: Berlin, 2003. (r)
Togo, H.; Sakuratani, K. Synlett 2002, 1966-1975. (s) Wirth, T. Angew.
Chem., Int. Ed. 2001, 40, 2812-2814. (t) Chaudhari, S. S. Synlett 2000,
278. (u) Ochiai, M. ReV. Heteroat. Chem. 1989, 2, 92-111. (v) Moriarty,
R. M.; Vaid, R. K.; Koser, G. F. Synlett 1990, 7, 365-383. (w) Moriarty,
R. M.; Vaid, R. K. Synthesis 1990, 431-447. (x) Stang, P. J. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 274-285. (y) Prakash, O.; Sainai, N.; Sharma, P.
K. Synlett 1994, 221-227. (z) Umemoto, T. Chem. ReV. 1996, 96, 1757-
1777. (aa) Kita, Y.; Takada, T.; Tohma, H. Pure Appl. Chem. 1996, 68,
1
synthesis has been reviewed. Especially, symmetric and un-
symmetric diaryliodonium salts represent an important class of
aromatic iodine(III) derivatives. They are used in organic syn-
thesis mostly as arylating reagents for a variety of organic and
2
inorganic nucleophiles and have been applied to the photo-
6
(
27-630. (bb) Zhdankin, V. V. ReV. Heteroat. Chem. 1997, 17, 133-151.
3
chemical polymerization process as a photoacid generator and
cc) Togo, H.; Katohgi, M. Synlett 2001, 565-581. (dd) Stang, P. J. J.
4
to chemical amplification in imaging systems. In addition, some
Org. Chem. 2003, 68, 2997-3008. (ee) Tohma, H.; Kita, Y. AdV. Synth.
5
Catal. 2004, 346, 111-124.
of the diaryliodonium salts have also shown biological activity.
(2) (a) Chen, D.-J.; Chen, Z.-C. Synlett 2000, 1175-1177. (b) Wang,
Diaryliodonium salts are generally solid compounds, mostly
stable toward heat, oxygen, and humidity; they are mildly light-
sensitive and should be stored in the dark, without refrigeration.
Many methods have been described for the preparation of
L.; Chen, Z.-C. Synth. Commun. 2000, 30, 3607-3612. (c) Radhakrishnan,
U.; Stang, P. J. Org. Lett. 2001, 3, 859-860. (d) Crivello, J. V.; Bulut, U.
J. Polym. Sci., Part A: Polym. Chem. 2005, 88, 290-296. (e) Zhang, B.-
X.; Nuka, T.; Fujiwara, Y.; Yamaji, T.; Hou, Z.; Kitamura, T. Heterocycles
2
004, 64, 199-206. (f) Zhou, T.; Chen, Z.-C. Synth. Commun. 2002, 32,
6
symmetric and unsymmetric diaryliodonium salts, but very few
887-891. (g) Wang, L.; Chen, Z.-C. J. Chem. Res., Synop. 2000, 372-
373. (h) Zhou, T.; Chen, Z.-C. Synth. Commun. 2002, 32, 903-907. (i)
Makioka, Y.; Fujiwara, Y.; Kitamura, T. J. Organomet. Chem. 2002, 611,
of these involve the synthesis of diaryliodonium triflate salts
3
that can be used as a strong acid generator. The methods used
5
2
09-513. (j) Wang, F.-Y.; Chen, Z.-C.; Zheng, Q.-G. J. Chem. Res., Synop.
so far are generally as follows: (a) One-pot preparation of
diaryliodonium triflates through the in situ preparation of a
reactive hypervalent iodine(III) reagent from iodosylbenzene and
003, 810-811. (k) Davydov, D. V.; Beletskaya, I. P.; Leninsky, G.
Tetrahedron Lett. 2002, 43, 6217-6219. (l) Kang, S.-K.; Yamaguchi, T.;
Ho, P.-S.; Kim, W.-Y.; Ryu, H.-C. J. Chem. Soc., Perkin Trans. 1 1998,
8
41-842. (m) Hou, R.-S.; Wang, H.-M.; Lin, Y.-C.; Chen, L.-C. J. Chin.
7
triflic acid and its reaction with aromatic substrates; (b) A
Chem. Soc. 2005, 52, 1029-1032. (n) Zhou, T.; Chen, Z.-C. Heteroat.
Chem. 2002, 13, 617-619. (o) Wang, L.; Chen, Z.-C.; Zheng, Q.-G. Chin.
J. Chem. 2002, 20, 1457-1459. (p) Zhou, T.; Chen, Z.-C. J. Chem. Res.,
Synop. 2001, 235-237.
†
Faculty of Science and Engineering, Saga University.
Institute of Ocean Energy, Saga University.
‡
1
0.1021/jo061889q CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/30/2006
J. Org. Chem. 2006, 71, 9903-9905
9903

SCHEME 1
of our systematic studies on effective and easy preparation of
hypervalent iodine compounds, we examined a simpler and more
convenient method for preparing ArI(OCOCF3)2. This simple
and convenient system consisted of arenes and molecular iodine.
We expected that diaryliodonium salts would be formed when
iodoarenes were produced in situ in the reaction of arenes with
iodine. Thus, we conducted the reaction of arenes with molecular
iodine in the presence of K2S2O8 in TFA, followed by treatment
with NaOTf. Herein, we wish to report a direct, easy method
for the preparation of diphenyliodonium triflate from benzene.
Also, we describe an application to tert-butylbenzene, toluene,
and less reactive halobenzenes.
TABLE 1. Optimization for Preparation of Diphenyliodonium
a
Triflate
benzene
I2
K2S2O8 TFA ClCH2CH2Cl time yield
entry (mmol) (mmol) (mmol) (mL)
(mL)
(h)
(%)
1
2
3
4
5
6
7
4
10
10
10
20
0.5
0.5
0.5
0.5
0.5
0.5
5
4
4
5
6
5
9
9
9
9
9
5
5
5
5
5
48
72
72
72
72
72
72
48
58
66
64
45
71
69
A simple, easy, and efficient method for the direct preparation
10
100
5
50
10
100
5
50
+
-
of diphenyliodonium triflate, Ph2I OTf , from benzene and
iodine was examined. At first, the reaction of benzene with
elemental iodine was conducted in TFA in the presence of
commercial K2S2O8 as the oxidant at 40 °C, where diphenyl-
a
The reaction of benzene with iodine was carried out in TFA and 1,2-
dichloroethane in the presence of K2S2O8 at 40 °C. Then, the reaction
mixture was treated with NaOTf solution at room temperature for 12 h.
+
-
iodonium trifluoroacetate [Ph2I (OCOCF3) ] was formed.
K2S2O8 is used as a strong oxidizing agent in many applications.
It has the particular advantages of being almost nonhygroscopic,
having particularly good storage stability and being easy and
safe to handle. 1,2-Dichloroethane was added for dissolving
not contain the step via iodobenzene or the related synthesis.
However, to the best of our knowledge, there are no methods
for preparing diphenyliodonium triflate directly from benzene
and iodine.
Recently, we have reported easy preparation of [bis(trifluo-
roacetoxy)iodo]arenes, ArI(OCOCF3)2, from respective iodo-
arenes in trifluoroacetic acid (TFA), using commercial potassium
peroxodisulfate, K2S2O8, as the oxidant.14 ArI(OCOCF3)2 is a
relatively reactive reagent and can undergo arylation reaction
to give diaryliodoniun salts. We also found that diaryliodonium
salts were formed by the reaction of iodoarenes with aromatic
substrates in the presence of K2S2O8 in TFA.15 During the course
+
-
iodine completely. Next, Ph2I (OCOCF3) was treated with
aqueous sodium triflate (NaOTf) solution at room temperature
to provide the corresponding diphenyliodonium triflate. The
outline is shown in Scheme 1.
Table 1 summarizes the results obtained by optimization of
the preparation of diphenyliodonium triflate. The reaction of
benzene (4 mmol) with iodine (0.5 mmol) was carried out in
the presence of K2S2O8 (4 mmol) in TFA and 1,2-dichloroethane
at room temperature for 48 h. After treatment with aqueous
NaOTf, diphenyliodonium triflate was obtained in 48% yield
(entry 1). Use of 10 mmol of benzene gave diphenyliodonium
triflate in 58% yield (entry 2). Use of 5 mmol of K2S2O8 led to
better yield, 66%, but further improvement was observed in the
case of 6 mmol of K2S2O8 (entries 3 and 4). Increase of benzene
from 10 to 20 mmol decreased the yield, 45% (entry 5). The
best result, 71% yield, was obtained by using benzene (10
mmol), iodine (0.5 mmol), K2S2O8 (5 mmol), TFA (10 mL),
and 1,2-dichloroethane (5 mL) (entry 6). The direct conversion
of benzene to diphenyliodonium triflate can be easily scaled
up and has the advantages of K2S2O8 outlined above, together
with the complete absence of effluent or byproduct problems.
When the reaction of benzene (100 mmol) with iodine (5 mmol)
was conducted in the presence of K2S2O8 (50 mmol) in TFA
(100 mL) and 1,2-dichloroethane (50 mL) under the same
conditions, diphenyliodonium triflate was obtained in 69% yield
(
3) (a) Crivello, J. V. AdV. Polym. Sci. 1984, 62, 1-48. (b) Pappas, S.
P. Prog. Org. Coat. 1985, 13, 35-64. (c) Yagci, Y.; Schnabel, W.
Makromol. Chem. Macromol. Symp. 1988, 13/14, 161-174. (d) Wilson,
C. G.; Bowden, M. J. CHEMTECH 1989, 19, 182-189.
(
(
4) Ito, H.; Ueda, M. J. Photopolym. Sci. Technol. 1989, 2, 1-10.
5) Koser, G. F. In The Chemistry of Functional Groups, Supplement
D; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1983; Chapter 25.
6) (a) Zefirov, N. S.; Kasumov, T. M.; Koz’min, A. S.; Sorokin, V. D.;
(
Stang, P. J.; Zhadankin, V. V. Synthesis 1993, 1209-1210. (b) Beringer,
F. M.; Dresler, M.; Gindler, E. M.; Lumpkin, C. C. J. Am. Chem. Soc.
1
953, 75, 2705-2708. (c) Beringer, F. M.; Falk, R. A.; Karniol, M.; Lillien,
I.; Masullo, G.; Mausner, M.; Sommer, E. J. Am. Chem. Soc. 1959, 81,
342-351. (d) Beringer, F. M.; Chang, L. L. J. Org. Chem. 1972, 37, 1516-
1519. (e) Tyrra, W.; Butter, H.; Naumann, D. J. Fluorine Chem. 1993, 60,
79-83. (f) Beringer, F. M.; Dehn, J. W.; Winicov, M. J. Am. Chem. Soc.
1960, 82, 2948-2952. (g) Schmeisser, M.; Dahmen, K.; Sartori, P. Chem.
Ber. 1970, 103, 307-311. (h) Stang, P. J.; Tykwinski, R.; Zhdankin, V. V.
J. Heterocycl. Chem. 1992, 29, 815-818. (i) Beringer, F. M.; Lillien, I. J.
Am. Chem. Soc. 1960, 82, 725-731. (j) Kasumov, T. M.; Brel, V. K.;
Kozmin, A. S.; Zefirov, N. S. Synthesis 1995, 775-776.
(entry 7). No large decrease of the yield was observed even in
(7) Kitamura, T.; Matsuyuki, J.; Nagata, K.; Furuki, R.; Taniguchi, H.
the case of the 10-fold scale experiment.
Synthesis 1992, 945-946.
(
(
8) Kitamura, T.; Matsuyuki, J.; Taniguchi, H. Synthesis 1994, 147-148.
As described above, the reaction of benzene with iodine in
the presence of K2S2O8 initially affords diphenyliodonium
trifluoroacetate, which is subject to exchange acetate with triflate
to give diphenyliodonium triflate. To confirm the formation of
diphenyliodonium trifluoroacetate, we examined the isolation
of diphenyliodonium trifluoroacetate. We worked up the reaction
mixture without the treatment with aqueous NaOTf solution.
After completion of the reaction according to entry 6 in Table
9) Stang, P. J.; Zhdankin, V. V.; Tykwinski, R.; Zefirov, N. S.
Tetrahedron Lett. 1991, 32, 7497-7498.
10) Kitamura, T.; Kotani, M.; Fujiwara, Y. Tetrahedron Lett. 1996, 37,
721-3722.
11) Shah, A.; Pike, V. W.; Widdowson, D. A. J. Chem. Soc., Perkin
Trans. 1 1997, 2463-2465.
12) Kasumov, T. M.; Brel, V. K.; Kozmin, A. S.; Zefirov, N. S.;
Potekhin, K. A.; Stang, P. J. New J. Chem. 1997, 21, 1347-1351.
13) For reviews, see: (a) Huang, W.-Y.; Chen, Q.-Y. In The Chemistry
(
3
(
(
(
of Sulfonic Acids, Esters and Their DeriVatiVes; Patai, S., Rappoport, Z.,
Eds.; Wiley-Interscience: Chichester, UK, 1991; Chapter 21. (b) Stang, P.
J.; White, M. R. Aldrichimica Acta 1983, 16, 15-22. (c) Howells, R. D.;
McCown, J. D. Chem. ReV. 1977, 77, 69-92. (d) Stang, P. J.; Hanack, M.;
Subramanian, L. R. Synthesis 1982, 85-126.
1, the reaction mixture was quenched with water and the product
was extracted with CH2Cl2. Evaporation of the solvent gave
diphenyliodonium trifluoroacetate in 81% yield, as shown in
(
44.
14) Hossain, M. D.; Kitamura, T. Bull. Chem. Soc. Jpn. 2006, 79, 142-
1
(15) Hossain, M. D.; Kitamura, T. Tetrahedron 2006, 62, 6955-6960.
9
904 J. Org. Chem., Vol. 71, No. 26, 2006

SCHEME 2
SCHEME 3
Selectfluor-promoted preparation of difluoroiodoarenes or (di-
1
6
acetoxyiodo)arenes has been reported, there are no reports on
the synthesis of [bis(trifluoroacetoxy)iodo]arenes. According to
1
6,17
the literature,
the Selectfluor-promoted reaction seems to
be applicable only for electron-rich aromatics. The mechanism
on the formation of [bis(trifluoroacetoxy)iodo]arenes is not clear,
but it is considered that the mechanism involves the oxidation
of iodoarenes by K2S2O8 because iodoarenes are efficiently
oxidized by K2S2O8 in TFA to give [bis(trifluoroacetoxy)iodo]-
14
arenes. Once [bis(trifluoroacetoxy)iodo]arenes are formed, they
immediately react with arenes to yield diaryliodonium trifluo-
1
5
roacetates. Finally, exchange of anions in the diaryliodonium
salts is well recognized and occurs easily.The present method
described above covers relatively electron-rich to weakly
deactivated aromatic substrates. This method involves funda-
mental starting materials (simple arenes and elemental iodine,
and commercial K2S2O8). The simple and convenient procedure
for diaryliodonium triflates has a significant advantage over the
previous reported ones.
TABLE 2. Preparation of Diaryliodonium Triflates from Arenesa
entry
arene
product
yield (%)
+
-
-
1
2
3
4
5
6
chlorobenzene
bromobenzene
fluorobenzene
iodobenzene
tert-butylbenzene
toluene
(4-ClC6H4)2I TfO
57
54
60
69
55
11
+
(4-BrC6H4)2I TfO
+
-
(4-FC6H4)2I TfO
+
-
(4-IC6H4)(Ph)I TfO
+
-
(4-tert-BuC6H4)2I TfO
+
-
(4-MeC6H4)2I TfO
In conclusion, we have demonstrated a novel, simple, and
direct method for the preparation of diaryliodonium triflates.
The new method gives diaryliodonium triflates in good yields
by the reaction of arenes with elemental iodine, K2S2O8, TFA,
and 1,2-dichloroethane at 40 °C, followed by treatment with
NaOTf. Since the present procedure can be scaled up easily, it
is expected that this procedure will be used widely for many
purposes.
a
The reaction of an arene (10 mmol) was carried out in TFA (10 mL),
,2-dichloroethane (5 mL), and iodine (0.5 mmol) in the presence of K2S2O8
1
(
5 mmol) at 40 °C for 72 h. Then, the reaction mixture was treated with
NaOTf solution (10 mL) at room temperature for 12 h.
SCHEME 4
Experimental Section
Optimized Procedure for Preparing Diaryliodonium Triflates
from Arenes. A solution of the appropriate arene (10 mmol) in a
mixture of molecular iodine (0.5 mmol), TFA (10 mL), and 1,2-
dichloroethane (5 mL) was heated with stirring to 40 °C. After
Scheme 2. This result indicates that diphenyliodonium trifluo-
roacetate is formed at the first step, and then it is converted to
diphenyliodonium triflate by anion exchange.
2 2 8
dissolving iodine, K S O (5 mmol) was added. The reaction
The presence of K2S2O8 was indispensable for this reaction
because without its addition the oxidation reactions did not
proceed and the starting materials were recovered unchanged.
In order to explore the scope of this reaction, we applied it to
other aromatic substrates. The outline is shown in Scheme 3.
The results are given in Table 2. Interestingly, arenes bearing
weakly deactivated groups such as chloro, bromo, and fluoro
groups gave diaryliodonium triflates in good yields. However,
a similar reaction of iodobenzene did not give bis(4-iodophenyl)-
iodonium triflate but afforded (4-iodophenyl)(phenyl)iodonium
triflate in 69% yield. In the reaction of iodobenzene, it is con-
sidered that the iodo group of iodobenzene is oxidized to form
mixture was stirred at that temperature for 72 h. After completion
of the reaction, water (20 mL) was added. The resulting precipitates
were collected by filtration under reduced pressure, washed with
CH
by extraction of the filtrate with CH
drying (anhydrous Na SO ), filtration, and removal of the solvent
by evaporation. The crude product was treated with aqueous NaOTf
ca. 1 M, 10 mL) solution at room temperature for 12 h. The
precipitates were collected by filtration under reduced pressure,
washed with H O (10 mL), and dried in vacuo. Another crop was
obtained by extraction of the filtrate with dichloromethane (3 ×
0 mL), followed by drying (anhydrous Na SO ), filtration, and
2
Cl
2
(10 mL), and discarded. The crude product was obtained
2
Cl
2
(3 × 10 mL), followed by
2
4
(
2
1
2
4
removal of the solvent by evaporation. The combined crude product
was recrystallized from CH Cl /hexane.
[bis(trifluoroacetoxy)iodo]benzene, which reacts with iodoben-
2
2
zene to yield the (4-iodophenyl)(phenyl)iodonium salt. tert-
Butylbenzene also gave bis(4-tert-butylphenyl)iodonium triflate
in good yield, but toluene afforded bis(4-methylphenyl)iodonium
triflate only in 11% yield. This method was not applicable for
electron-rich arenes such as anisole, mesitylene, and p-xylene.
For example, in the case of anisole, the reaction mixture was
quickly oxidized to indicate black color, but no diaryliodonium
salts were obtained. This method was not effective for arenes
with strong electron-withdrawing groups such as trifluoromethyl
and nitro groups due to their decreased reactivity.
Large-scale synthesis was conducted for diphenyliodonium
triflate in a similar manner. A solution of benzene (7.9 g, 100 mmol)
in a mixture of TFA (100 mL), 1,2-dichloroethane (50 mL), and I
1.28 g, 5 mmol) was heated with stirring to 40 °C. After dissolving
iodine, K (50 mmol) was added, and the stirring was continued
2
(
2 2 8
S O
for 72 h, followed by treatment with NaOTf (ca. 1 M, 100 mL).
Workup of the reaction mixture gave pure product (2.97 g, 69%).
Supporting Information Available: Characterization data for
iodonium salts obtained. This material is available free of charge
via the Internet at http://pubs.acs.org.
From the above results, it is considered that the reaction
proceeds with three major fundamental steps: bis(trifluoro-
acetoxy)iodination, arylation, and anion exchange. The key step
is the first bis(trifluoroacetoxy)iodination. The in situ formation
of [bis(trifluoroacetoxy)iodo]arenes is a novel direct reaction
from arenes and iodine promoted by K2S2O8. Although a similar
JO061889Q
(16) Ye, C.; Twamley, B.; Shreeve, J. M. Org. Lett. 2005, 7, 3961-3964.
(
17) (a) Zupan, M.; Iskra, J.; Stavber, S. Tetrahedron Lett. 1997, 38,
6
4
305-6306. (b) Stavber, S.; Jereb, M.; Zupan, M. Chem. Commun. 2002,
88-489. (c) Pavlinac, J.; Zupan, M.; Stavber, S. J. Org. Chem. 2006, 71,
1027-1032.
J. Org. Chem, Vol. 71, No. 26, 2006 9905