Fluoroalcohols: Versatile solvents in hypervalent iodine chemistry and syntheses of diaryliodonium(III) salts

Article abstract of DOI:10.1016/j.tet.2010.04.116

We first introduced 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and 2,2,2-trifluoroethanol (TFE) as unique solvents for reactions involving hypervalent iodine-mediated phenolic oxidations in the 1980s, in which the fluoroalcohols have been successfully utili

Full text of DOI:10.1016/j.tet.2010.04.116

Tetrahedron 66 (2010) 5775e5785
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Fluoroalcohols: versatile solvents in hypervalent iodine chemistry and syntheses
of diaryliodonium(III) salts
*
Toshifumi Dohi, Nobutaka Yamaoka, Yasuyuki Kita
College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We first introduced 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and 2,2,2-trifluoroethanol (TFE) as unique
solvents for reactions involving hypervalent iodine-mediated phenolic oxidations in the 1980s, in which
the fluoroalcohols have been successfully utilized as stabilizing solvents of the reactive cationic
intermediates, generated in situ by the action of phenyliodine(III) diacetate (PIDA) and phenyliodine bis
(trifluoroacetate) (PIFA). This pioneering study produced a breakthrough in hypervalent iodine chem-
istry, and many synthetic applications that enable a variety of transformations have appeared utilizing
this unique medium. For example, the single-electron-transfer (SET) oxidation ability of PIFA toward
phenyl ethers has been discovered for the first time in HFIP and TFE, taking advantage of the unique acid-
like behaviors to stabilize the aromatic cation radicals. More recently, the catalytic strategy of hyper-
valent iodine reagents has found extensive applications with the aid of the fluoroalcohols to produce
highly reactive catalytic species under mild conditions. The fluoroalcohols are now widely used as
versatile solvents not only in hypervalent iodine chemistry, but also in other organic syntheses. This
manuscript for the Special Issue deals with the background of the hypervalent iodine chemistry and
a new topic concerning the utility of fluoroalcohols for the synthesis of diaryliodonium(III) salts.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 25 March 2010
Received in revised form 26 April 2010
Accepted 26 April 2010
Available online 23 May 2010
Keywords:
Fluoroalcohol
Hypervalent iodine
Diaryliodonium salt
Oxidation
1. Introduction
is active and the number of available solvents is increasing. In
particular, the use of fluorous liquids,3 ionic liquids,4 and super-
Most chemical transformations known to date in organic syn-
thesis were carried out in the solution phase using solvents. The
solvents employed would work to break the self-association
between the molecules and dissolve the reactants and reagents,
allowing the opportunity for all components to react on a molecular
level in one flask. In exothermic processes, the heat transport
ability of the medium is particularly important, and reactions
would often result in proceeding disorderly, and sometimes even
explosively, in the absence of solvents. Many other properties of
solvents have been summarized as macroscopic physical parame-
ters and constants, such as the boiling point, density, dipole
moment, hydrogen-bond donor and acceptor capability, etc., by
which the solvent effect on organic reactions would be now
quantitatively estimated.1 ‘A reaction cannot be separated from the
medium in which it is performed’,2 and no one can neglect this
long-live theme when performing the reactions.
critical fluids5 as solvents is actively being promoted with the
growing impetus of greener synthetic processes.
The fluoroalcohols, i.e., 1,1,1,3,3,3-hexafluoroisopropanol (HFIP)
and 2,2,2-trifluoroethanol (TFE), appear as a group of solvents with
unique properties (Fig. 1). These are significantly different from
classic alcohols, and the presence of the fluoroalkyl groups provides
many specific properties that no other solvents show. The highly
polar [ET(30)¼69.3 for HFIP, 59.8 for TFE],6a but low nucleophilic
[N¼ꢀ4.23 (HFIP), ꢀ2.78 (TFE)]7 fluoroalcohols are unique solvents
that exhibits a high ionizing power [Y¼3.8 (HFIP), 1.8 (TFE)]7 with
a pKa higher [9.3 (HFIP), 12.4 (TFE)]6b than that of acetic acid
[pKa¼5.2]. In addition, HFIP, and TFE have quite excellent hydrogen-
bond donor abilities [
a
¼1.96 (HFIP), 1.51 (TFE)].6c Due to these
For this objective, the selection of an appropriate solvent is
indispensable for enhancing the efficiency of most chemical pro-
cesses. Even recently, progress regarding a new solvent foundation
* Corresponding author. Tel./fax: þ81 77 561 5829; e-mail address: kita@ph.rit-
sumei.ac.jp (Y. Kita).
Figure 1. Fluorinated alcohols as solvents in organic synthesis.
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.04.116

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T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
unique properties, the fluoroalcohols sometimes dramatically di-
rect the course of reactions as the solvent. That is, the synthetic
potential of fluoroalcohols as an attractive and unique alternative to
ordinary commercially available solvents has been growing in in-
terest in modern organic synthesis.8
a new mechanism should apparently be involved. A few years later,
we determined the generation of aromatic cation radicals 4 pro-
duced by the SET oxidation through the charge-transfer (CT)-
complex of phenyl ethers 3 and PIFA (Scheme 2), based on detailed
UV and ESR spectroscopic measurements.11b This is the first strong
evidence that clarified the SET oxidation ability of hypervalent io-
dine reagents toward aromatic rings, the success of which has
found further applications for the synthesis as the method of CeH
functionalization to directly introduce a wide range of nucleophiles
Although the solvents show the characteristic properties, the
reports that applied the unique solvents were relatively sporadic in
organic synthesis until recently. In the 1980s, the authors
introduced for the first time these alcohols as polar, but less
nucleophilic solvents, in hypervalent iodine chemistry to perform
the oxidation of phenols for the purpose of synthesizing
spirodienones,9 and applied the reaction to the synthesis of natural
products having the spirodienone moiety.10 Thereafter, the ability
to stabilize aromatic cation radicals was first established for HFIP
and TFE during our continuing study of the single-electron-transfer
(SET) oxidations of aromatic compounds using hypervalent iodine
reagents.11 These two cases are good examples that the fluoro-
alcohols directed the reactive intermediates and the course of the
reactions as solvents.
For the oxidation of phenols 1 using hypervalent iodine
reagents, i.e., PIDA and PIFA, the reactions are typically explained by
the two-electron-transfer processes that involve the initial ligand
exchange at the iodine centers (Scheme 1).12 Thus, the iodine(III)
centers of PIDA and PIFA would react with phenolic oxygens to give
the phenoxyiodine(III) intermediates 2. The excellent leaving
ability of the high-valent iodine atoms may smoothly generate the
phenoxenium ions in the solvents, HFIP and TFE,13 which were
trapped by various concomitant types of nucleophiles,9 thus
(AcO, ArS, SCN, CN, b
-dicarbonyl compounds, etc.)11beg into aro-
matic compounds and for the oxidative biaryl couplings.18 Appli-
cations of HFIP as a solvent for the spectroscopic studies of cation
radicals have now become the reasonable choice.8b
The pioneering works including ours have triggered a recent
rapid promotion of their use as solvent in hypervalent iodine
chemistry as well as in the vast field of organic synthesis, and
the utility seems to go beyond the initial perspective as new
unique outcomes are revealed.
Recently, during our study of hypervalent iodine chemistry, we
found a remarkable rate enhancement caused by the addition of
fluoroalcohols for the condensation of aromatic compounds and
hypervalent iodine reagents.19 This finding has given rise to the
opportunity for realizing a highly efficient dehydrative approach
for diaryliodonium(III) salts. Notably, the fluoroalcohols were in-
dispensable for the success of each reaction, while other typical
solvents were unsatisfactory in terms of the reaction rate and yield
of the products, which seems to support involvement of the
Wheland type of cationic
s
-complexes suggested in the related
Ph
I
OH
O
OCOR''
O
OCOR''
in HFIP
or
Ph
I
R
R
R
ligand exchange
TFE
OCOR''
R'
R'
R'
Nu
R'' = CH3 (PIDA)
R'' = CF3 (PIFA)
Nu
Nu
HO2CR''
PhI
R''CO2
-
2
1
Scheme 1. Hypervalent iodine(III)-mediated oxidations of phenols in HFIP and TFE.
Scheme 2. Aromatic cation radical generation in HFIP and TFE in the hypervalent iodine-induced SET processes.
completing the oxidations. Based on the combination of the
versatility of the reactions with the excellent features of the
reagents as safe and low-toxic alternatives to heavy metal
oxidizers, such as lead, mercury, cadmium, and thallium-based
agents,14 the oxidation of phenols basis of the umpolung of aro-
matic rings using hypervalent iodine reagents is recognized, for
natural product synthesis, as the most practical and important
biomimetic dearomatization process.15e17
studies of diaryliodonium(III) synthesis.20 In the following sections,
we discuss the versatility of our new dehydrative approach to
diaryliodonium(III) salts in fluoroalcohol solvents (Scheme 3). The
method is very clean, only producing water as the sole coproduct.
On the other hand, the hypervalent iodine(III) reagents also act
as excellent SET oxidizing agents in the fluoroalcohol solvents. In
1991, we reported the aromatic azidation of phenyl ethers by the
treatment of PIFA in HFIP in the presence of TMSN3.11a Interestingly,
the novel aromatic azidation only proceeded in the fluoroalcohol
solvents. For the novel aromatic substitution process, therefore,
Scheme 3. Direct dehydrative approach to diaryliodonium(III) salts in fluoroalcohol
solvents, TFE and HFIP.

T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
5777
2. Results and discussion
alleviate the limitation of the direct methodology, stepwise
approaches using organometallic compounds, i.e., lithio-, silyl-,
stannyl-, and boryl-functionalized aromatic compounds, should be
prepared and used for this purpose.20 The situation prompted us to
examine the versatility and scope of our method utilizing fluo-
roalcohol medium in diaryliodonium salt syntheses.
2.1. Remarkable influence of the solvents in direct
dehydrative approach for diaryliodonium(III) salts
The dehydrative condensation of hypervalent iodine(III) re-
agents and aromatic compounds is considered to be a simple and
clean approach to diaryliodonium(III) salts.21 Typically, such direct
methods were achieved using the activated iodine(III) compounds
with strong acids21a,b or Koser’s reagent [PhI(OH)OTs]21c for limited
types of products and counterions in moderate yields and/or with
poor regioselectivities. In these studies, the effect of the solvent has
never been evaluated.
To elucidate the solvent effect on the dehydrative iodonium(III)
salts formations, we screened a number of solvents for the reaction
of mesitylene 5a and Koser’s reagent (Table 1). As reported by Koser
and Margida,21c neat conditions (entry 1) as well as the use of
dichloromethane (entry 2), acetonitrile (entry 3), and methanol
(entry 4) as solvents did not produce the desired iodonium(III) salt
6a in the case of the alkylbenzene 5a. In contrast, a remarkable
effect of the solvent was clearly observed in fluoroalcohols. Sur-
prisingly, the dehydrative condensation smoothly proceeded at
room temperature to give the salt 6a in nearly quantitative yields
(entries 5 and 6). The reactions in TFE and HFIP were completed in
a few hours with no excess reagent, and the product was obtained
as the pure form after precipitation by adding Et2O. Thus, the only
coproduct from the reactions is water after the dehydration. Ap-
parently, the fluoroalcohols played a critical role in the enhanced
reactivity of Koser’s reagent.
To determine the influence of the substituent on the benzene
ring, we first examined the reactions of benzene derivatives 5bei.
Table 2 represents the results and Hammet
s constants of sub-
stituents. In this screening, the yield of the iodonium salts obtained
from the reactions seems to show a good correlation with the sP
constants to support the intermediacy of the cationic species to-
ward the diaryliodonium salts.20 Thus, methoxybenzene 5b having
a negative sP value (sP¼ꢀ0.12) smoothly reacted, and the presence
of the methoxy group controlled the regioselectivity to give a para-
Table 2
Substitution effect of the benzene ringa
Entry
R
sP
Product
Yieldb (%)
1c
2
3
4
5
6
7
8
OMe (5b)
H (5c)
Cl (5d)
ꢀ0.12
0
6b-OTs
6c-OTs
6d-OTs
6e-OTs
6f-OTs
6g-OTs
6h-OTs
6i-OTs
89
89
0.24
0.26
0.31
0.47
0.53
0.81
57d
51d
n.d.e
n.d.e
n.r.
n.r.
Br (5e)
OAc (5f)
COMe (5g)
CF3 (5h)
NO2 (5i)
Table 1
a
Solvent effect in the reaction of 5a and Koser’s reagenta
Reactions were examined using equimolar amount of 5bei and Koser’s reagent
for 24 h at room temperature.
b
Isolated yield of pure product after precipitation.
TFE was used as solvent.
Products were obtained as a mixture of two regioisomers.
Yield was not determined due to contamination of p-TsOH to the product.
c
d
e
substituted iodonium salt 6b-OTs (entry 1). In contrast, the sub-
stituents having positive sP values, such as halogens, diminished
both the regioselectivity and the yield compared to benzene 5c
itself (entries 2e4). As the results, the products 6d-OTs and 6e-OTs
were obtained in lower yields as a mixture of regioisomers. As the
electron-withdrawing character of the substituent increases, the
reactions would hardly occur. The reactions of the electron-de-
ficient aryl moieties were quite slow, which also made isolation of
the products troublesome because of the contamination of p-TsOH
and other impurities (entries 5 and 6). Trifluoromethylbenzene 5h
and nitrobenzene 5i did not react at all under these conditions
(entries 7 and 8). Instead, the reagent-derived iodonium salt A,
which is considered to be a condensation product of the in situ
formed iodobenzene and Koser’s reagent, was detected (Fig. 2).
Entry
Solvent
dc
Yieldb (%)
1
2
3
4
5
6
n.r.d
15e
n.r.d
n.d.f
97
CH2Cl2
CH3CN
MeOH
TFE
HFIP
94
a
All reactions were performed using an equimolar amount of 5a and Koser’s
reagent, [PhI(OH)OTs], for 24 h.
b
Isolated yield after precipitation.
Mesitylene 5a was used as solvent.
No reaction was observed with the recovery of PhI(OH)OTs.
Product was obtained as a mixture including large amount of inseparable
c
d
e
impurities.
f
n.d.¼not determined.
2.2. Direct synthesis of diaryliodonium(III) salts from
aromatic compounds and hypervalent iodine reagents: Scope
and limitations
Figure 2. Potential byproduct A from Koser’s reagent.
The diaryliodonium(III) salts, ArIþAr0Xꢀ (where, Ar and Ar0¼aryl,
X¼counterion), represent one of the most useful and important
classes of hypervalent iodine compounds, which show a wide range
of applicability, such as arylating agents and benzyne precursors in
organic synthesis, active bactericides, a photoacid generator (PAG)
for cationic polymerization processes, etc.22 These beneficial
chemical and physical properties highly depend on both the
structure of the iodonium(III) part and anionic counterion, Xꢀ, and
hence the development of general methods for diaryliodonium
salts with a large structural diversity is strongly desired.23 To
For the alkylbenzenes, phenyl ethers, and other electron-rich
aromatic and heteroaromatic compounds, the new protocol pro-
vided a facile access to a wide range of diaryliodonium salts 6-OTs
(Table 3, see the Experimental section). Under the optimized con-
ditions, the reaction of 5j afforded 6j-OTs in quantitative yield as
a single isomer (entry 1). The result clearly suggests that the re-
action might be dependent on the steric environments of the re-
active sites, although the sterically congested product 6k-OTs could
be obtained in an acceptable yield (entry 2). The para-disubstituted

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T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
Table 3
Selected examples of substratesa
Entry
Substrate (5)
Product (6-OTs)
Yieldb (%)
Entry
10
Substrate (5)
Product (6-OTs)
Yieldb (%)
1
99
97
2
3
4
5
62
88
81
72
11
12
13
14c
88
99
72
99
5t
6
93
96
15c
5u
99
86
7
8
16
94
96
17
18
93
62
9
a
Reactions were performed using equimolar amount of aromatic compounds 5 and Koser’s reagent (1 equiv) in TFE at room temperature unless otherwise noted.
Isolated yield after purification.
Koser’s reagent (2 equiv) was used.
b
c
benzene 5l reacted at the ortho position producing the iodonium
the thiophenes, 5w and 5x (entries 16 and 17), while the
a-di-
salt 6l-OTs (entry 3). Similar results were obtained in other elec-
tron-rich aromatic compounds with or without some functional
groups (entries 4e13). In substrates 5t and 5u, perfect control of
the products, 6t-OTs versus 6t0-OTs or 6u-OTs versus 6u0-OTs, was
attained by the amounts of the added reagent (entries 11, 12, 14,
substituted thiophene 5y produced the -thienyl salt 6y-OTs in
b
good yield (entry 18). All of the products 6 were precipitated as
solids after replacement of TFE with Et2O, and did not contain other
iodine(III) impurities and regioisomeric products.
For the 3-substituted thiophenes 5z-af, the condensation should
preferentially occur at the a-positions of the sulfur atom, among
and 15).24 The
a
-thienyliodonium salts were obtained from

T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
5779
which the 2-positions were more reactive (Table 4). Even 5ad-af
containing an aryl, alkoxy, and halogen at the 3-position were
converted to the products in good yields with complete regiose-
lectivity (entries 5e7). It should be noted that a serious background
side reaction of uncontrollable polymerization25 caused by the
highly electron-rich alkoxy thiophene moiety in 5ae was excluded
under the stated conditions. A remarkable solvent effect was clearly
observed in each case, and the reactions finished within a shorter
reaction time (by 3 h) when compared to other solvents, such as
CH2Cl2.21c The iodonium salts having thienyl moieties have found
new applications as organic non-linear optic materials,26a active
bacteriocides,26b,c precursors of fluorinated aromatic com-
pounds,26d etc.
Table 4
Reactivity of 3-substitituted thiophenes 5z-af
Scheme 5. Reactions of organoborane compounds 5aj and 5ak.
As described above, a new condensation method utilizing flu-
oroalcohols is quite simple and versatile. The high efficiency of the
method made polymer functionalization possible by the in-
corporation of the iodonium(III) group. The synthesis of the iodo-
nium(III)-supported poly(styrene)s was reported more than forty
years ago to control the physical and chemical properties of the
polymers,29 but multistep transformations (typically, iodination,
oxidation followed by conversion to the iodonium(III) forms)
starting from poly(styrene)s should be employed for this purpose,
resulting in the unsatisfactory loading of the function sites
(w1.5 mmol loading of I(III) sites per gram). It became clear in our
study that our straightforward procedure was applicable for the
low-reactive polymers (Scheme 6). The use of a mixed solvent
system, TFE, and CH2Cl2, was plausible for solving the solubility
issue of the initial polymer, and accordingly, after stirring the dis-
solved solution of the linear poly(styrene) 5al (100 mg, Mw:
1.09ꢁ106) and PhI(OH)OMs (317 mg, 1.0 mmol)30 at ambient tem-
perature, the iodine(III)-containing polymer 6al-OMs (369 mg, ca.
85% incorporation of the iodine(III) reagent) was obtained by pre-
cipitation of the crude mixture in Et2O. Elemental analysis of the
polymer 6al-OMs revealed that it contains ca. 2.3 mmol/g of the
functionalized iodine(III) sites. The high loading of the iodonium
(III) site in 6al-OMs allowed the umpolung of the polarity, leading
to the high solubility of the polymer in MeOH that is compatible
with the monomeric diphenyl iodonium mesylate,31 thus we called
this comcept, ‘polymer reforming’.
Entry
R
Product
Yielda (%)
1
2
3
4
5
6
7
Me (5z)
6z-OTs
98
84
74
93
88
89
95
Hex (5aa)
c-Hex (5ab)
i-Bu (5ac)
Ph (5ad)
OMe (5ae)
Br (5af)
6aa-OTs
6ab-OTs
6ac-OTs
6ad-OTs
6ae-OTs
6af-OTs
a
Isolated yield of pure product after precipitation.
Our method is particularly valuable when performing the re-
actions of substrates with acid-sensitive functional groups. The
reactions of protected alcohols and the epoxide 5ag-ai in Scheme 4
are good examples in which the advantage was highlighted. In this
t
examination, deprotection of the Bu and MOM groups as well as
the ring-opening of the epoxide were not observed. In addition, the
reactions of 5aj and 5ak proceeded with retention of the metalloid
element and furnished the organoborane moieties in iodonium(III)
salts that are potentially suitable for further applications (Scheme
5).27 To our knowledge, report on the iodonium salts containing
such the acid-labile moieties and metalloid elements are quite
limited28 this should account for the significant synthetic merit of
our method utilizing the fluoroalcohols for expanding the struc-
tural diversity of the diaryliodonium(III) salts.
Scheme 6. Application of the method for a poly(styrene) reforming.
A large number of Koser’s-type iodine(III) derivatives are now
readily available,32 and the variation of the reagents in the reaction
could also expand the structural diversity of the obtained products.
Selected examples utilizing these types of iodine compounds are
shown in Table 5. Iodonium salts 6ae12a having different kind of
aryl rings were obtained from a single substrate 5a and Koser’s type
of iodine derivatives. Regarding the reagents, ArI(OH)X, both the
electron-rich and deficient aryl moieties were applicable (entries
4e9). One of the significant advantages of using fluoroalcohol
Scheme 4. Substrates having acid-labile functional groups.

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T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
Table 5
Reactions using Koser’s reagent derivativesa
Yieldb (%)
Figure 3. Limitation of substrate types.
Entry
ArI(OH)X
Product
1
2
3
4
5
6
7
8
PhI(OH)OTs
PhI(OH)OMs
PhI(OH)OCs
C6F5I(OH)OTs
(p-CF3)C6H4I(OH)OTs
(p-NO2)C6H4I(OH)OTs
(p-MeO)C6H4I(OH)OTs
(Mesityl)I(OH)OTs
6a-OTs
6a-OMs
6a-OCs
7a-OTs
8a-OTs
9a-OTs
10a-OTs
11a-OTs
97
87
98
81
92
86
62
62
such as naphthalene, could be used in the oxidations, rather than
the iodonium salt formation, resulting in the formation of un-
identified oxidized products.
After discovering that the fluoroalcohols work as excellent
promoters for the direct dehydrative condensation, they became
a promising solvent in exploiting the diaryliodonium(III) salts
synthesis. For example, the solvent was partially utilized for the
new straightforward synthesis of diaryl iodonium(III) salts from
iodoarenes with stoichiometric oxidants in recent studies.23d,e
9c
12a-OTs
93
OMs¼methanesulfonyloxy. OCs¼(þ)-10-camphorsulfonyloxy.
a
2.3. Mechanistic remarks
Reactions were performed using equimolar amount of 5a and ArI(OH)X.
Isolated yield of pure product after precipitation.
ArI(OH)OTs (0.5 equiv) was used.
b
c
In previous reports on the dehydrative condensation of aromatic
compounds and hypervalent iodine(III) reagents, the Wheland s-
solvents in the reactions is that various types of reagents can be
used in these ways.
complexes were typically considered to be the key in-
termediate.20,21 The clear dependence between the product yield
and aryl-ring substituent shown in Table 2 is also consistent with
The chemical and physical properties of the diaryliodonium(III)
salts also highly depend on the nature of the anionic counterpart.
Modification of the counterions was easily attainable using iodo-
sobenzene, [PhIO]n, instead of Koser’s reagent, and Brønsted acids
(Scheme 7). A variety of counterions, Xꢀ, were thus conveniently
introduced into the products 6a by this strategy. This can avoid the
circuitous anion metatheses work-ups.20,21,23
the reaction mechanism involving the s-complexes, the formation
of which should be further accelerated by using the cation-stabl-
izing solvents, TFE, and HFIP, in our case. Thus, one plausible ex-
planation of the reaction mechanism leading to the diaryliodonium
(III) salts should be the formation of the s-complexes by electro-
philic attack of the iodine(III) centers on aromatic rings, followed by
the elimination of water (Scheme 9).
Scheme 7. Incorporation of other counterions, Xꢀ
.
Unfortunately, an attempt to prepare iodonium salts from 1H-
pyrrole was unsuccessful. However suitably N-substituted pyrroles
5am and 5an formed the corresponding iodonium salts 6am-OAc
or 6an-OAc in nearly quantitative yields with PIDA (Scheme 8).
Scheme 9. Reaction mechanism involving the s-complexes.
Nevertheless, based on the principle for the cation radical gen-
eration from the electron-rich aromatic compounds, i.e., alkylar-
enes, phenyl ethers, and thiophenes, by the iodine(III)-induced SET
oxidation in the fluoroalcohols8a as well as the recent participation
of Koser’s reagent in that chemistry,34 the involvement of the ar-
omatic cation radicals shown in Scheme 2 as an alternative possible
reaction intermediate is not perfectly excluded. Indeed, the spec-
troscopic study of the intermediate for the reaction of 3-methyl-
thiophene 5z and Koser’s reagent (Eq. 1) in the fluoroalcohol
solvent suggested the generation of the aromatic cation radicals of
5z. Based on the UVevis measurement, the spectrum of the re-
action mixture showed a good agreement with the known ab-
sorption band between the wavelengths of 500 and 600 nm for the
cation radical species of 5z (Fig. 4).35,36 This is the first establish-
ment of the SET oxidation ability of Koser’s reagent by successful
spectroscopic detection of the aromatic cation radicals. We thus
strongly propose the aromatic cation radicals as potential
Scheme 8. Preparation of pyrrole iodonium(III) salts.
The presence of an electron-withdrawing group apparently in-
terferes with the dehydrative condensation as shown in Table 2
(vide ante). Other limitations of our method are also present. The
synthesis of highly congested iodonium salts was difficult, and tert-
alkyl groups at the ortho position to the reactive site retarded the
condensation as shown by the 1,3-di(tert-butyl)benzene (Fig. 3).
Similarly, the trimethysilyl group did not positively affect the yield
of 6ao-OTs, a benzyne precursor.33 The polycyclic aromatic rings,

T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
5781
characteristics as highly polar, but low nucleophilic solvents, to
stabilize the cationic intermediates involved during the reactions.
In the reactions, a remarkable rate-acceleration effect of the fluo-
roalcohol solvents was clearly observed, and thus the diary-
liodonium(III) salts were directly obtained using a variety of
electron-rich aromatic compounds including the non-activated
benzene and thiophene using only 1 equiv of hypervalent iodine
(III) reagents with or without Brønsted acids in shorter reaction
times and higher yields when compared with other classical sol-
vents. The present dehydrative approach is, therefore, very clean
because it produces only water as a coproduct, and versatile be-
cause it is capable of affording a variety of the diaryliodonium(III)
salts. In addition, the use of fluoroalcohols in the direct dehydrative
approach for diaryliodonium(III) salts can avoid the preparation of
metalated substrates, and reduce byproducts and metal waste. As
a result, a direct greener method for the synthesis of diary-
liodonium(III) salts has been established by using the fluoroalcohol
solvents without the production of any harmful byproducts.
The diaryliodonium(III) salts prepared by our methods and
others are not only useful compounds as the classical arylating
agents, but also have found some new attractive applications.22a In
this study, we have recently developed a metal-free cross-coupling
reaction of electron-rich aromatic compounds to give biaryls, uti-
lizing the diaryliodonium salts(III) as the selective heteroaryl
transfer agents.38 With further innovation to synthesize these
classes of compounds, the design of iodonium salts as stoichio-
metric reagents and catalysts will be extensively studied for the
purpose of realizing more environmentally friendly reactions as
well as asymmetric transformations.39 Hence, the application of
a variety of salts would become one of the exciting areas in
hypervalent iodine chemistry and organic synthesis in the forth-
coming decade, which has a significant potential to partially re-
place conventional methods using transition metals in view of
green sustainable chemistry.
Figure 4. UVevis spectrum of the reaction of 3-methylthiophene 5z and Koser’s
reagent in TFE.
intermediates leading to the diaryliodonium(III) salts, especially in
the electron-rich phenyl ethers and thiophenes.
A unique selectivity was observed for the organo-silicon com-
pounds 5ap and 5aq in our method (Scheme 10). The ipso-sub-
stitution products at the silicon-bound carbon atoms as a result of
the silicon-iodine(III) exchange via the Wheland type of
s-com-
plex20d,37 were not obtained at all, but the dehydrative condensa-
tion products 6ap-OTs and 6aq-OTs, in which the carbonesilicon
bonds are maintained, were instead produced. This clarifies the
difference in our strategy to other reported methods.
In this paper, we described the versatility of fluoroalcohol sol-
vents for the synthesis of diaryliodonium(III) salts along with
a brief introduction of their historical background and importance
in hypervalent iodine chemistry. It has also found significant ac-
tivity in the new area of hypervalent iodine chemistry as organo-
catalysts,14m and the scope of the catalytic strategy is expanding
with the aid of the fluoroalcohols.40,41 The promising ability to
produce highly reactive hypervalent iodine species under mild
conditions should not only contribute to the development of new
catalytic transformations, but also improve the known methods by
replacing the originally developed catalytic systems.
Typically, the solvent exists as a major component in most ho-
mogeneous systems, but it is often regarded to take a secondary role
for the reactions on the basis of only few physical factors, such as
solubility and polarity, etc., once a new solvent is accepted as a com-
mon tool in organic synthesis. The fluoroalcohols are beyond the
success up to ordinary solvents in hypervalent iodine chemistry. The
uses of these solvents are sometimes indispensable for initiating
chemical transformations, which is the major reason for the so-called
‘magic solvent’ by many researchersengaged in the field ofchemistry.
Despite their unique characteristics, it seems that they no longer
belong to an unusual choice of solvent in modern organic synthesis.
Based on the unique characteristics thus far revealed, further syn-
thetic applications highlighting the fluoroalcohols as unique solvents
and additives should be encouraged in future studies.
Scheme 10. Unique reactivities in organosilanes 5ap and 5aq *6aq-OTs obtained in-
cluded small amount of its regioisomer.
From these observations, it is very difficult to define the real
reaction intermediates involved during the reactions in each case.
In any way, the fluoroalcohols can work for the generation and
stabilization of both the s
-complexes and aromatic cation radicals,8
which seems to be a key to the effective reaction progress.
3. Conclusion
4. Experimental
4.1. General
The present study revealed that the fluoroalcohols, i.e., TFE and
HFIP, can positively affect the initiation of the dehydrative con-
densation of hypervalent iodine reagents toward aromatic and
heteroaromatic compounds by taking advantage of their unique
Melting points (mp) are uncorrected. The 1H NMR (and 13C
NMR) spectra were recorded by a JEOL JMN-300 spectrometer

5782
T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
operating at 300 MHz (75.3 MHz for 13C NMR) in CDCl3 at 25 ꢂC
with tetramethylsilane as the internal standard. The data are
reported as follows: chemical shift in parts per million (d), in-
136.9, 139.1, 139.6, 158.6 ppm. HRMS (FAB) calcd for C13H11BrIO
[MꢀOTs]þ 388.9038, found 388.9038.
tegration, multiplicity (s¼singlet, d¼doublet, t¼triplet, q¼quartet,
br s¼broad singlet, m¼multiplet), and coupling constant (Hz). The
infrared spectra (IR) were obtained using a Hitachi 270-50 spec-
trometer. The high resolution mass spectra were performed by the
Elemental Analysis Section of Osaka University. PhI(OH)OTs (HTIB,
Koser’s reagent) is a commercially available compound and was
used as received. Solvents were obtained from commercial sup-
pliers and were used without further purification.
4.2.5. (4-Benzyloxylphenyl)(phenyl)iodonium tosylate (6r-OTs). A
colorless solid, mp 183e185 ꢂC. IR (KBr) cmꢀ1: 3071, 3046, 2934,
1578,1567,1482,1454,1442,1402,1381,1291,1235,1193,1131,1043,
1013,1003, 858, 832, 314, 756, 736, 696. 1H NMR (400 MHz, CD3OD)
d
2.34 (s, 3H), 5.13 (s, 2H), 7.11 (d, 2H, J¼8.0 Hz), 7.20(d, 2H,
J¼8.0 Hz), 7.33e7.41 (m, 5H), 7.50 (t, 2H, J¼8.0 Hz), 7.67 (t, 3H,
J¼8.0 Hz), 8.05e8.11 (m, 4H) ppm. 13C NMR (75.5 MHz, CD3OD)
d
21.3, 71.5, 104.7, 116.5, 119.7, 127.0, 128.7, 129.3, 129.6, 129.8, 133.0,
133.5, 136.0, 137.5, 138.5, 141.6, 143.6, 163.5 ppm. HRMS (FAB) calcd
for C19H16IO [MꢀOTs]þ 387.0246, found 387.0257.
4.2. General procedure for direct dehydrative approach to
diaryliodonium(III) salts in fluoroalcohol solvents
4.2.6. (2,4-Dimethoxylphenyl)(phenyl)iodonium tosylate (6t-OTs). A
colorless solid, mp 203e206 ꢂC. IR (KBr) cmꢀ1: 3009, 2942, 1578,
1468,1439, 1410,1308, 1285,1254,1211, 1190,1165, 1132,1045, 1015,
To
a stirred solution of arene 5 (1.0 mmol) in 2,2,2-tri-
fluoroethanol (5 mL), HTIB (392 mg, 1.0 mmol) was added in one
portion at room temperature under air, and it was stirred for
1e24 h. MeOH was then added to the reaction mixture when the
solvents were removed under vacuum. The resulting oily crude
product 6-OTs was precipitated by addition of Et2O with stirring.
The precipitate was filtered and dried in vacuo to give pure 6 as
a powder.
833, 816, 746, 694. 1H NMR (300 MHz, CDCl3)
d 2.31 (s, 3H), 3.81 (s,
3Hꢁ2), 6.48 (d, 2H, J¼2.7 Hz), 7.05 (d, 2H, J¼7.8 Hz), 7.30 (t, 2H,
J¼7.8 Hz), 7.46 (t, 1H, J¼7.8 Hz), 7.58 (d, 2H, J¼7.8 Hz), 7.84e7.90 (m,
3H) ppm. 13C NMR (75.5 MHz, CDCl3)
d 21.2, 55.8, 56.7, 93.4, 99.7,
108.5, 115.0, 126.0, 128.4, 131.3, 131.4, 134.3, 138.5, 139.4, 142.4,
158.6, 165.1 ppm. HRMS (FAB) calcd for C14H14IO2 [MꢀOTs]þ
341.0039, found 341.0060.
4.2.1. (4-Bromophenyl)(phenyl)iodonium tosylate (6e-OTs, including
a small amount of regioisomer). A slightly yellow solid. IR (KBr)
cmꢀ1: 3066, 3045, 2990, 1635, 1564, 1469, 1440, 1394, 1377, 1195,
1132, 1107, 1063, 1043, 1014, 988, 818, 738, 696. 1H NMR (400 MHz,
4.2.7. Bis(iodonium) tosylate (6t0-OTs). A slightly brown solid, mp
49e50 ꢂC. IR (KBr) cmꢀ1: 3051, 2988, 2943, 2922, 1568, 1470, 1440,
1370, 1283, 1215, 1190, 1132, 1107, 1045, 1013, 991, 816, 739, 696. 1H
NMR (300 MHz, CD3OD) d 2.36 (s, 6H), 4.05 (s, 6H), 6.93 (s, 1H), 7.19
CD3OD)
d
2.35 (s, 3H), 7.00 (d, 2H, J¼9.3 Hz), 7.21 (d, 2H, J¼8.0 Hz),
(d, 4H, J¼7.8 Hz), 7.46 (t, 4H, J¼7.8 Hz), 7.61e7.68 (m, 6H), 8.08 (d,
7.52 (t, 2H, J¼8.0 Hz), 7.67 (d, 4H, J¼8.0 Hz), 7.86 (d, 1H, J¼4.8 Hz),
4H, J¼7.8 Hz), 9.12 (s, 1H) ppm. 13C NMR (75.5 MHz, CD3OD)
d 21.4,
8.05 (d, 2H, J¼8.0 Hz), 8.17 (d, 2H, J¼8.0 Hz) ppm. 13C NMR
58.5, 97.3, 98.6, 116.2, 126.8, 129.7, 132.9, 133.4, 136.3, 141.5, 143.3,
146.0, 164.1 ppm. HRMS (FAB) calcd for C27H25I2O5S [MꢀOTs]þ
714.9507, found 714.9525.
(100.53 MHz, CD3OD)
d 21.3, 126.9, 129.8, 133.1, 133.2, 133.8, 133.9,
136.2, 136.4, 136.5, 138.1, 141.7, 142.3 ppm.
4.2.2. (4-Benzylphenyl)(phenyl)iodonium tosylate (6n-OTs). A col-
orless solid, mp 147e148 ꢂC. IR (KBr) cmꢀ1: 3027, 2920, 1715, 1658,
1600, 1577, 1495, 1470, 1452, 1439, 1400, 1312, 1190, 1132, 1045,
1014, 1001, 991, 923, 816, 786, 740, 696. 1H NMR (400 MHz,
4.2.8. [{4-(2-tert-Buthoxy)ethoxy}phenyl](phenyl)iodonium tosylate
(6ag-OTs). A colorless solid, mp 164e168 ꢂC. IR (KBr) cmꢀ1: 3047,
2973, 2937, 2872, 1580, 1486, 1471, 1452, 1441, 1403, 1363, 1297,
1254, 1193, 1131, 1095, 1043, 1013, 990, 969, 915, 816, 709, 693. 1H
CD3OD)
d
2.34 (s, 3H), 4.00 (s, 2H), 7.15e7.19 (m, 5H), 7.24(d, 1H,
NMR (400 MHz, CDCl3) d 1.91 (s, 9H), 2.30 (s, 3H), 3.67 (t, 2H,
J¼8.0 Hz), 7.34 (d, 2H, J¼8.0 Hz), 7.49 (t, 2H, J¼8.0 Hz), 7.63e7.69
J¼5.2 Hz), 4.04 (t, 2H, J¼5.2 Hz), 6.87 (d, 2H, J¼8.0 Hz), 7.05 (d, 2H,
J¼8.0 Hz), 7.31 (t, 2H, J¼8.0 Hz), 7.45 (t, 1H, J¼8.0 Hz), 7.57 (d, 2H,
J¼8.0 Hz), 7.81 (d, 2H, J¼8.0 Hz), 7.87 (d, 2H, J¼8.0 Hz) ppm. 13C
(m, 4H), 8.04 (d, 2H, J¼8.0 Hz), 8.12 (d, 2H, J¼8.0 Hz) ppm. 13C
NMR (100.5 MHz, CD OD)
d 21.3, 42.3, 113.0, 116.1, 127.0, 127.6,
129.7, 129.8, 130.0, 133.1, 133.6(ꢁ2), 136.3, 136.4, 136.6, 141.1, 141.7,
148.5 ppm. HRMS (FAB) calcd for C19H16IO [MꢀOTs]þ 371.0297,
found 371.0299.
NMR (100.53 MHz, CD3OD) d 21.3, 27.7, 61.3, 61.5, 69.8, 116.5, 119.4
(ꢁ2), 126.9, 129.8, 133.0, 133.4, 136.0, 138.5, 141.6, 143.6, 163.8 ppm.
4.2.9. [{4-(2-Methoxymethoxy)ethoxy}phenyl](phenyl)iodonium to-
4.2.3. [4-(3-Cianopropyl)phenyl](phenyl)iodonium tosylate (6o-
OTs). A colorless solid, mp 131e133 ꢂC. IR (KBr) cmꢀ1: 3048, 3028,
2936, 2866, 2243, 1566, 1483, 1470, 1441, 1424, 1402, 1323, 1190,
1132, 1107, 1045, 1015, 991, 816, 789, 745, 694, 682. 1H NMR
sylate (6ah-OTs). A colorless solid, mp 156e158 ꢂC. IR (KBr) cmꢀ1
:
2939, 1580, 1485, 1442, 1403, 1297, 1254, 1173, 1155, 1118, 1044, 991,
913, 827, 742, 683. 1H NMR (400 MHz, CDCl3)
d
2.32 (s, 3H), 3.34 (s,
3H), 3.89 (t, 2H, J¼4.4 Hz), 4.14 (t, 2H, J¼4.4 Hz), 4.69 (s, 2H), 6.90 (d,
2H, J¼8.8 Hz), 7.07 (d, 2H, J¼7.6 Hz), 7.36 (t, 2H, J¼7.6 Hz), 7.51 (t,
1H, J¼7.6 Hz), 7.59 (d, 2H, J¼7.6 Hz), 7.85e7.90 (m, 4H) ppm. 13C
(300 MHz, CDCl3)
d
1.91 (quin, 2H, J¼7.8 Hz), 2.30 (t, 2H, J¼7.8 Hz),
2.31 (s, 3H), 2.74 (t, 2H, J¼7.8 Hz), 7.01 (d, 2H, J¼7.8 Hz), 7.15 (d, 2H,
J¼7.8 Hz), 7.32 (t, 2H, J¼7.8 Hz), 7.45e7.52 (m, 3H), 7.89 (d, 2H,
J¼7.8 Hz), 7.95 (d, 2H, J¼7.8 Hz) ppm. 13C NMR (75.5 MHz, CD3OD)
NMR (100.53 MHz, CDCl3)
d 21.2, 65.5, 67.8, 77.2, 96.6, 118.1, 118.2,
126.0, 128.6, 131.7, 131.8, 134.3, 134.4, 137.3, 137.4, 139.5, 161.8 ppm.
HRMS (FAB) calcd for C16H18IO3 [MꢀOTs]þ 385.0301, found
385.0279.
d
16.3, 21.2, 26.3, 33.9, 112.7, 115.3, 119.1, 125.8, 128.4, 131.4, 131.5,
134.4, 135.1, 135.6, 139.4, 142.3, 144.0 ppm.
4.2.4. (3-Bromo-4-methoxyphenyl)(phenyl)iodonium tosylate (6p-
OTs). A colorless solid, mp 158e159 ꢂC. IR (KBr) cmꢀ1: 3050, 3015,
2936, 1566, 1476, 1439, 1379, 1292, 1271, 1255, 1207, 1192, 1155,
1132, 1045, 1015, 991, 816, 758, 692. 1H NMR (300 MHz, CDCl3)
4.2.10. (4-Oxiranylmethoxyphenyl)(phenyl)iodonium tosylate (6ai-
OTs). A colorless solid, mp 143e146 ꢂC. IR (KBr) cmꢀ1: 3028, 1572,
1485, 1440, 1251, 1188, 1132, 1045, 1014, 987, 815, 767, 696. 1H NMR
(300 MHz, CDCl3)
d
2.30 (s, 3H), 2.73 (dd, 1H, J¼4.5, 2.7 Hz), 2.91 (t,
d
2.30 (s, 3H), 3.84 (s, 3H), 6.80 (d, 1H, J¼7.8 Hz), 7.00 (d, 2H,
1H, J¼4.5 Hz), 3.32 (m, 1H), 3.86 (dd, 1H, J¼10.8, 6.0 Hz), 4.26 (dd,
1H, J¼10.8, 2.7 Hz), 6.87 (d, 2H, J¼7.5 Hz), 7.03 (d, 2H, J¼8.1 Hz),
7.33 (t, 2H, J¼7.5 Hz), 7.46e7.52 (m, 3H), 7.85e7.92 (m, 4H) ppm. 13C
J¼7.8 Hz), 7.30 (t, 2H, J¼7.8 Hz), 7.40e7.47 (m, 3H), 8.11e8.15 (m,
3H), 8.37 (d, 1H, J¼2.1 Hz) ppm. 13C NMR (75.5 MHz, CDCl3)
d 21.3,
56.4, 104.3, 113.8, 114.3, 116.2, 125.9, 128.5, 130.7, 131.4, 131.5, 134.9,
NMR (100.53 MHz, CDCl3) d 21.1, 44.3, 49.7, 69.0, 104.2, 115.6, 117.9,

T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
5783
125.7, 128.4, 131.3, 131.4, 134.6, 137.4, 139.3, 142.4, 161.0 ppm. HRMS
118.1, 122.5, 124.7 (q, J¼271 Hz), 126.9, 129.7 (q, J¼3.8 Hz), 129.8,
131.4, 134.6 (q, J¼33.6 Hz), 135.9, 141.6, 143.5, 143.6, 146.1 ppm.
HRMS (FAB) calcd for C16H15F3I [MꢀOTs]þ 391.0171, found 391.0157.
(FAB) calcd for C15H14IO2 [MꢀOTs]þ 353.0039, found 353.0035.
4.2.11. (3-Boronpinacolate-4-methoxyphenyl)(phenyl)iodonium to-
sylate (6aj-OTs). A colorless solid, mp 171e172 ꢂC. IR (KBr) cmꢀ1
:
4.4.2. (4-Nitrophenyl)(2,4,6-trimethylphenyl)iodonium tosylate (9a-
OTs). A colorless solid, mp 163e165 ꢂC. IR (KBr) cmꢀ1: 2969, 1601,
1568,1530,1468, 1350,1343,1312,1300,1192, 1132, 1043, 1005, 849,
3048, 2978, 2938, 2845, 1584, 1555, 1481, 1460, 1441, 1398, 1339,
1317, 1256, 1190, 1144, 1134, 1065, 1045, 1015, 963, 860, 816, 752,
696. 1H NMR (300 MHz, CDCl3)
d
1.33 (s, 12H), 2.31 (s, 3H), 3.83 (s,
816, 752, 734, 696. 1H NMR (300 MHz, CD3OD)
d 2.34 (s, 3H), 2.35 (s,
3H), 6.84 (d, 1H, J¼7.8 Hz), 7.05 (d, 2H, J¼7.8 Hz), 7.33 (t, 2H,
3H), 2.63 (s, 6H), 6.39 (d, 2H, J¼7.8 Hz), 7.24 (s, 2H), 7.62 (d, 2H,
J¼7.8 Hz), 7.48 (t, 1H, J¼7.8 Hz), 7.56 (d, 2H, J¼7.8 Hz), 7.91 (d, 2H,
J¼7.8 Hz), 8.09 (d, 2H, J¼7.8 Hz), 8.24 (d, 2H, J¼7.8 Hz). 13C NMR
J¼7.8 Hz), 8.11 (m, 2H) ppm. 13C NMR (75.5 MHz, CDCl3)
d
21.2, 24.7,
(75.5 MHz, CD3OD) d 21.1, 21.3, 27.1, 120.0, 122.6, 126.9, 127.5, 129.8,
56.0, 84.1, 103.2, 113.9, 115.6, 125.9, 128.4, 131.2, 131.4, 134.2, 134.8,
139.2, 140.7, 142.5, 143.8, 166.6 ppm.
131.5, 136.3, 141.7, 143.5, 143.7, 146.3, 151.3 ppm. HRMS (FAB) calcd
for C15H15INO2 [MꢀOTs]þ 368.0148, found 368.0137.
4.2.12. (4-Boronpinacolate-2-thienyl)(phenyl)iodonium
tosylate
4.4.3. (4-Methoxyphenyl)(2,4,6-trimethylphenyl)iodonium tosylate
(10a-OTs). A colorless solid, mp 159e160 ꢂC. IR (KBr) cmꢀ1: 3460,
3428, 3059, 3020, 2947, 2920, 2866, 2835, 1581, 1570, 1485, 1458,
1398, 1300, 1251, 1190, 1130, 1044, 1014, 993, 851, 820, 750, 694. 1H
(6ak-OTs). A colorless solid, mp 165e168 ꢂC. IR (KBr) cmꢀ1: 3054,
2979, 1563, 1511, 1469, 1314, 1269, 1192, 1135, 1088, 1048, 1014, 990,
966, 951, 854, 815, 737, 697, 684.1H NMR (400 MHz, CD3OD)
d 1.32 (s,
12H), 2.36 (s, 3H), 7.21 (d, 2H, J¼8.0 Hz), 7.52 (d, 2H, J¼8.0 Hz), 7.68 (t,
NMR (300 MHz, CD3OD) d 2.31 (s, 3H), 2.33 (s, 3H), 2.63 (s, 6H), 3.79
3H, J¼8.0 Hz), 8.15 (t, 3H, J¼8.0 Hz), 8.25 (d, 1H, J¼1.2 Hz) ppm. 13C
(s, 3H), 7.00 (d, 2H, J¼7.8 Hz), 7.15 (s, 2H), 7.17 (d, 2H, J¼7.8 Hz), 7.64
NMR (100.53 MHz, CD3OD) d 21.3, 25.1, 85.8,118.8,127.0,129.8,133.1,
(d, 2H, J¼7.8 Hz), 7.83 (d, 2H, J¼7.8 Hz). 13C NMR (100.53 MHz,
133.2, 133.7, 135.7, 135.8, 141.6, 143.6, 146.5, 148.2 ppm. HRMS (FAB)
CD3OD) d 21.0, 21.1, 27.0, 56.3, 102.7, 118.8, 122.9, 126.9, 129.8, 131.1,
calcd for C16H19BIO2S [MꢀOTs]þ 413.0238, found 413.0240.
137.5, 141.6, 143.2, 143.5, 145.3, 164.0 ppm.
4.3. General procedure for dehydrative condensation of
mesitylene 5a and iodosobenzene in the presence of Bronsted
acids (Scheme 7)
4.4.4. Bis(iodonium) tosylate (12a-OTs). A colorless solid, mp
201e202 ꢂC. IR (KBr) cmꢀ1: 3051, 2988, 2943, 2922, 1568, 1470,
1440, 1370, 1283, 1215, 1190, 1132, 1107, 1045, 1013, 991, 816, 739,
€
696. 1H NMR (400 MHz, CD3OD)
d
2.35 (s, 6Hꢁ2), 2.58 (s, 12H), 7.21
To a stirred solution of mesitylene 5a (105 mg, 1.0 mmol) in
2,2,2-trifluoroethanol (5 mL), iodosobenzene (220 mg, 1.0 mmol)
(s, 4Hꢁ2), 7.63 (s, 4H), 7.92 (s, 4H) ppm. 13C NMR (100.53 MHz,
CD3OD)
d 21.1, 21.3, 27.1, 66.9, 117.8, 122.5, 126.9, 129.8, 131.5, 137.9,
and perchloric acid aqueous solution (60%, 334
mL) were added at
141.7, 143.7, 146.3 ppm.
0 ꢂC under air, and it was stirred for 2 h at room temperature. After
the reaction was completed, CH2Cl2 was added to the mixture. The
organic layer was separated and aqueous phase was extracted with
CH2Cl2. The combined extract was dried over anhydrous Na2SO4
and evaporated. The resulting oily crude product 6aeClO4 was
precipitated by adding Et2O with stirring. The precipitate was fil-
tered off and dried in vacuo to give 6aeClO4 (298 mg, 73%) as
a colorless powder.
4.4.5. Iodonium polymer (6al-OMs).19. White powder. IR (KBr):
3020, 1471, 1438, 1330, 1265, 1217, 1056, 1014, 941, 899, 779, 752,
700 cmꢀ1. Elemental Anal. Found: S, 7.32; I, 29.07 (theoretical
loading of I: 291 mg I/g 6al-OMs¼2.28 mmol I/g 6al-OMs).
4.4.6. (1-Phenylpyrrol-2-yl)(phenyl)iodonium acetate (6am-OAc). A
colorless solid, mp 155e156 ꢂC. IR (KBr) cmꢀ1: 2926, 1714, 1516,
1402,1381,1282,1253,1180,1099, 839, 736, 615. 1H NMR (400 MHz,
4.3.1. Phenyl(2,4,6-trimethylphenyl)iodonium perchlorate (6aeClO4)19.
CDCl3)
7.31e7.36 (m, 2H), 7.39e7.43 (m, 2H), 7.55e7.60 (m, 6H) ppm. 13C
NMR (100.53 MHz, CDCl3) 24.2, 94.5, 114.0, 119.5, 126.6, 128.0,
d
1.87 (s, 3H), 6.54e6.57 (m, 1H), 7.25 (dd, 2H, J¼6.6, 1.8 Hz),
A colorless solid, mp 79 ꢂC. IR (KBr) cmꢀ1: 3057, 2983, 1564, 1469,
1379,1300,1267,1110, 989, 746, 680, 624. 1H NMR (300 MHz)
d
2.34 (s,
d
3H), 2.65 (s, 6H), 7.23 (s, 2H), 7.50 (t, 2H, J¼7.8 Hz), 7.63 (t, 1H,
130.6, 130.9, 131.2, 113.2, 133.0, 134.8, 140.2, 180.1 ppm.
J¼7.8 Hz), 7.90 (d, 2H, J¼7.8 Hz) ppm. 13C NMR (75.5 MHz)
d 21.0, 27.1,
114.0, 122.2, 131.3, 133.2, 133.3, 135.3, 143.5, 145.8 ppm.
4.4.7. [1-(4-Methoxyphenyl)pyrrol-2-yl](phenyl)iodonium tosylate
(6an-OAc). A colorless solid, mp 150e151 ꢂC. IR (KBr) cmꢀ1: 3055,
1716, 1556, 1537, 1496, 1402, 1384, 1321, 1282, 1261, 1213, 1180, 1139,
4.4. General procedure for dehydrative condensation using
Koser’s reagent derivatives and PIDA (Table 5, Schemes 6 and 8)
1099, 841, 763, 734, 650, 605. 1H NMR (400 MHz, CDCl3)
d 1.85 (s,
3H), 3.88 (s, 3H), 6.51 (t,1H, J¼3.4 Hz), 7.05 (d, 2H, J¼7.2 Hz), 7.13 (d,
To a stirred solution of arene 5 (1.0 mmol) in 2,2,2-trifluoro-
ethanol (5 mL), Koser’s reagent derivatives (100 mol % I(III)) or PIDA
(322 mg, 1.0 mmol) was added in one portion at room temperature
under air, and it was stirred for 3e24 h. MeOH was then added to
the reaction mixture when the solvents were removed under vac-
uum. The resulting oily crude product was precipitated by addition
of Et2O with stirring. The precipitate was filtered and dried in vacuo
to give pure product as a powder.
2H, J¼7.2 Hz), 7.25 (t, 1H, J¼2.1 Hz), 7.29 (m, 1H), 7.42 (t, 2H,
J¼7.8 Hz), 7.60 (m, 3H) ppm. 13C NMR (100.53 MHz, CDCl3)
d 24.2,
56.2, 94.3, 113.8, 115.8, 119.1, 126.2, 129.4, 131.7, 132.8, 132.9, 133.2,
134.8, 162.0, 180.2 ppm.
4.5. Reactions of organo-silicon compounds with Koser’s
reagent (Fig. 3 and Scheme 10)
The corresponding diaryliodonium(III) salts were obtained
according to the procedure described in Experimental section, 4.2.
4.4.1. (4-Trifluoromethylphenyl)(2,4,6-trimethylphenyl)iodonium to-
sylate (8a-OTs). A colorless solid, mp 165e166 ꢂC. IR (KBr) cmꢀ1
:
3034, 2969, 2920, 1593, 1449, 1393, 1323, 1300, 1188, 1132, 1103,
4.5.1. Phenyl(2-trimethylsilyl-4,6-dimethoxyphenyl)iodonium toꢀsy1-
1067, 1045, 1015, 1003, 991, 853, 827, 816, 772, 754, 696. 1H NMR
late (6ao-OTs). A colorless solid, mp 158e159 ꢂC. IR (KBr) cm
:
(300 MHz, CD3OD)
d
2.34 (s, 3Hꢁ2), 2.63 (s, 6H), 7.18 (d, 2H,
3053, 3009, 2949, 2897, 2843,1566,1387,1310,1271,1252,1217,1190,
J¼7.8 Hz), 7.22 (s, 2H), 7.62 (d, 2H, J¼7.8 Hz), 7.76 (d, 2H, J¼7.8 Hz),
1161, 1132, 1065, 1044, 1013, 991, 864, 841, 816, 758, 696. 1H NMR
8.06 (d, 2H, J¼7.8 Hz).13C NMR (100.53 MHz, CD3OD)
d
21.1, 21.3, 27.1,
(400 MHz, CDCl3) d 0.00 (s, 9H),1.95 (s, 3H), 3.45 (s, 3H), 3.52 (s, 3H),

5784
T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
S.; Sakurai, H.; Oka, S. J. Am. Chem. Soc. 1994, 116, 3684; (c) Kita, Y.; Takada, T.;
Mihara, S.; Tohma, H. Synlett 1995, 211; (d) Kita, Y.; Takada, T.; Mihara, S.;
Whelan, B. A.; Tohma, H. J. Org. Chem. 1995, 60, 7144; (e) Kita, Y.; Egi, M.;
Okajima, A.; Ohtsubo, M.; Takada, T.; Tohma, H. Chem. Commun. 1996, 1491; (f)
Arisawa, M.; Ramesh, N. G.; Nakajima, M.; Tohma, H.; Kita, Y. J. Org. Chem. 2001,
66, 59 See also Ref. 8a..
6.24 (s,1H), 6.38 (s,1H), 6.73 (d, 2H, J¼8.0 Hz), 6.96 (t, 2H, J¼8.0 Hz),
7.08 (t, 1H, J¼8.0 Hz), 7.34 (d, 4H, J¼8.0 Hz) ppm. 13C NMR
(100.53 MHz, CDCl3)
d 0.0, 21.2, 55.7, 57.0, 99.2, 99.4, 115.1, 116.0,
125.9, 128.4, 131.0, 131.6, 131.9, 139.3, 142.8, 150.6, 159.2, 164.7 ppm.
12. (a) Moriarty, R. M.; Prakash, O. Acc. Chem. Res. 1986, 19, 244; (b) Ligand Coupling
Reaction with Heteroatomic Compounds; Finet, P., Ed.Tetrahedron Organic
Chemistry Series; Pergamon: Oxford, 1998; Vol. 18; (c) Ozanne-Beaudenon, A.;
Quideau, S. Angew. Chem., Int. Ed. 2005, 44, 7065 and references cited therein.
13. Recently, these fluoroalcohols have been shown to be useful for the stabiliza-
tion of the phenoxenium ions, see the discussion in: Dohi, T.; Maruyama, A.;
Takenage, N.; Senami, K.; Minamitsuji, Y.; Fujioka, H.; Caemmerer, S. B.; Kita, Y.
Angew. Chem., Int. Ed. 2008, 47, 3787 and references therein.
14. For recent reviews and publications, see: (a) Varvoglis, A. Tetrahedron 1997, 53,
1179; (b) Varvoglis, A. Hyperv alent Iodine in Organic Synthesis; Academic: San
Diego, 1997; (c) Kitamura, T.; Fujiwara, Y. Org. Prep. Proced. Int. 1997, 29, 409; (d)
Kirschning, A. Eur. J. Org. Chem. 1998, 11, 2267; (e) Zhdankin, V. V.; Stang, P. J.
Chem. Rev. 2002, 102, 2523; (f) Wirth, T.; Ochiai, M.; Zhdankin, V. V.; Koser, G. F.;
Tohma, H.; Kita, Y. Hypervalent Iodine Chemistry-Modern Developments in Or-
ganic Synthesis. Top. Curr. Chem.; Springer: Berlin, 2003; (g) Tohma, H.; Kita, Y.
Adv. Synth. Catal. 2004, 346, 111; (h) Moriarty, R. M. J. Org. Chem. 2005, 70, 2893;
(i) Wirth, T. Angew. Chem., Int. Ed. 2005, 44, 3656; (j) Zhdankin, V. V.; Stang, P. J.
Chem. Rev. 2008, 108, 5299; (k) Moriarty, R. M.; Prakash, O. Hypervalent Iodine in
Organic Chemistry: Chemical Transformations; john Wiley & Sons Ltd: New York,
NY, 2007; (l) Zhdankin, V. V. ARKIVOC 2009, 1; (m) Dohi, T.; Kita, Y. Chem.
Commun. 2009, 2073.
4.6. Measurement of UVevis absorption spectrum (Fig. 4)36
To
a
stirred solution of 3-methylthiophene (1.0 mg,
1.0ꢁ10ꢀ2 mmol) in CF3CH2OH (5 mL) was added HTIB (3.9 mg,
1.0ꢁ10ꢀ2 mmol) in one portion at room temperature under air. The
UVevis absorption spectrum of the reaction mixture was measured
on SHIMADZU 2200 UVevis spectrometer.
Acknowledgements
This work was partially supported by Grant-in-Aid for Scientific
Research (A) from the Japan Society for the Promotion of Science
(JSPS), Young Scientists (B) from the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), and Ritsumeikan Global
Innovation Research Organization (R-GIRO) project. T.D. also ac-
knowledges support from the Industrial Technology Research Grant
Program from the New Energy and Industrial Technology De-
velopment Organization (NEDO) of Japan.
15. For reviews, see: (a) Tohma, H.; Kita, Y. Top. Curr. Chem. 2003, 224, 209; (b)
Ciufolini, M. A.; Braun, N. A.; Canesi, S.; Ousmer, M.; Chang, J.; Chai, D. Synthesis
2007, 3759; (c) Quideau, S.; Pouységu, L.; Deffieux, D. Synlett 2008, 467; (d)
Nicolaou, K. C.; Chen, J. S.; Edmonds, D. J.; Estrada, A. A. Angew. Chem., Int. Ed.
2009, 48, 660; (e) Pouységu, L.; Deffieux, D.; Quideau, S. Tetrahedron 2010, 66,
2235.
References and notes
16. Selected examples for recent directions in natural product syntheses: (a) Liang,
H.; Ciufolini, M. A. Org. Lett. 2010, 12, 1760 and references cited therein; (b)
Mendelsohn, B. A.; Ciufolini, M. A. Org. Lett. 2009, 11, 4736; (c) Mendelsohn, B.
A.; Lee, S.; Kim, S.; Teyssier, F.; Aulakh, V. S.; Ciufolini, M. A. Org. Lett. 2009, 11,
1539; (d) Guerard, K. C.; Sabot, C.; Racicot, L.; Canesi, S. J. Org. Chem. 2009, 74,
2039; (e) Sabot, C.; Guerard, K. C.; Canesi, S. Chem. Commun. 2009, 2941.
17. For aromatic ring umpolung concept, see Ref. 15e and follows: (a) Sabot, C.;
Berard, D.; Canesi, S. Org. Lett. 2008, 10, 4629; (b) Guerard, K. C.; Chapelle, C.;
Giroux, M.-A.; Sabot, C.; Beaulieu, M.-A.; Achache, N.; Canesi, S. Org. Lett. 2009,
11, 4756.
18. (a) Kita, Y.; Egi, M.; Ohtsubo, M.; Saiki, T.; Takada, T.; Tohma, H. Chem. Commun.
1996, 2225; (b) Kita, Y.; Gyoten, M.; Ohtsubo, M.; Tohma, H.; Takada, T. Chem.
Commun. 1996, 1481; (c) Takada, T.; Arisawa, M.; Gyoten, M.; Hamada, R.;
Tohma, H.; Kita, Y. J. Org. Chem. 1998, 63, 7698; (d) Arisawa, M.; Utsumi, S.;
Nakajima, M.; Ramesh, N. G.; Tohma, H.; Kita, Y. Chem. Commun. 1999, 469; (e)
Tohma, H.; Morioka, H.; Takizawa, S.; Arisawa, M.; Kita, Y. Tetrahedron 2001, 57,
345; (f) Tohma, H.; Iwata, M.; Maegawa, T.; Kita, Y. Tetrahedron Lett. 2002, 8,
5377; (g) Tohma, H.; Iwata, M.; Maegawa, T.; Kiyono, Y.; Maruyama, A.; Kita, Y.
Org. Biomol. Chem. 2003, 1, 1647; (h) Dohi, T.; Morimoto, K.; Kiyono, Y.; Mar-
uyama, A.; Tohma, H.; Kita, Y. Chem. Commun. 2005, 2930; (i) Dohi, T.; Mor-
imoto, K.; Maruyama, A.; Kita, Y. Org. Lett. 2006, 8, 2007; (j) Dohi, T.; Morimoto,
K.; Ito, M.; Kita, Y. Synthesis 2007, 2913; (k) Dohi, T.; Ito, M.; Morimoto, K.;
Iwata, M.; Kita, Y. Angew. Chem., Int. Ed. 2008, 47, 1301; (l) Dohi, T.; Ito, M.;
Yamaoka, N.; Morimoto, K.; Fujioka, H.; Kita, Y. Tetrahedron 2009, 65, 10797.
19. Preliminary communication: Dohi, T.; Ito, M.; Morimoto, K.; Minamitsuji, Y.;
Takenaga, N.; Kita, Y. Chem. Commun. 2007, 4152.
1. For selected reviews, see: (a) Reichardt, C. Org. Process Res. Dev. 2007, 11, 105; (b)
Katritzky, A. R.; Fara, D. C.; Yang, H.; Taemm, K.; Tamm, T.; Karelson, M. Chem.
Rev. 2004, 104, 175; (c) Reichardt, C. Chem. Rev. 1994, 94, 2319; (d) Hansch, C.;
Leo, A.; Taft, R. W. Chem. Rev. 1991, 97, 165; (e) Reichardt, C. Pure Appl. Chem.
1982, 54, 1867; (f) Katritzky, A. R.; Fowler, F. W.; Rutherford, J. D. J. Chem. Soc. B
1971, 460; (g) Reichardt, C.; Dimroth, K. Fortschr. Chem. Forsch. 1968, 11, 1.
2. (a) Menshutkin, N. Z. Physiol. Chem. 1900, 34, 157; (b) Abboud, J.-L. M.; Notario,
R.; Bertrán, J.; Solá, M. Prog. Phys. Org. Chem. 1993, 19, 1.
3. For recent review, see: (a) Zhang, W. Chem. Rev. 2009, 109, 749; (b) Zhang, W.;
Curran, D. P. Tetrahedron 2006, 62, 11837; (c) Curran, D. P. Aldrichimica Acta
2006, 39, 3; (d) Zhang, W. Chem. Rev. 2004, 104, 2531; (e) Zhang, W. Tetrahedron
2003, 59, 4475; (f) Dobbs, A. P.; Kimberley, M. R. J. Fluorine Chem. 2002, 118, 3;
(g) Gladysz, J. A.; Curran, D. P. Tetrahedron 2002, 58, 3823; (h) Curran, D. P. Pure
Appl. Chem. 2000, 72, 1649.
4. (a) Hapiot, P.; Lagrost, C. Chem. Rev. 2008, 108, 2238; (b) Kobrak, M. N. Adv.
Chem. Phys. 2008, 139, 85; (c) Van Rantwijk, F.; Sheldon, R. A. Chem. Rev. 2007,
107, 2757; (d) Malhotra, S. V.; Kumar, V.; Parmar, V. S. Curr. Org. Synth. 2007, 4,
370; (e) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772.
5. (a) Ciriminna, R.; Carraro, M. L.; Campestrini, S.; Pagliaro, M. Adv. Synth. Catal.
2008, 350, 221; (b) Rayner, C. M. Org. Process Res. Dev. 2007, 11, 121; (c) Beck-
man, E. J. J. Supercrit. Fluids 2004, 28, 121; (d) Jessop, P. G. J. Supercrit. Fluids
2006, 38, 211; (e) Raveendran, P.; Ikushima, Y.; Wallen, S. L. Acc. Chem. Res.
2005, 38, 478; (f) Prajapati, D.; Gohain, M. Tetrahedron 2004, 60, 815; (g)
Leitner, W. Acc. Chem. Res. 2002, 35, 746; (h) Oakes, R. S.; Clifford, A. A.; Rayner,
C. M. J. Chem. Soc., Perkin Trans. 1 2001, 917.
20. (a) Beringer, F. M.; Dehn, J. W., Jr.; Winicov, M. J. Am. Chem. Soc. 1960, 82, 2948;
(b) Koser, G. F.; Wettach, R. H.; Smith, C. S. J. Org. Chem. 1980, 45, 1543; (c)
Carman, C. S.; Koser, G. F. J. Org. Chem. 1983, 48, 2534; (d) Pike, V. W.; Butt, F.;
Shah, A.; Widdowson, D. A. J. Chem. Soc., Perkin Trans. 1 1999, 245; (e) Carroll,
M. A.; Pike, V. W.; Widdowson, D. A. Tetrahedron Lett. 2000, 41, 5393.
21. (a) Beringer, F. M.; Drexler, M.; Gindler, E. M.; Lumpkin, C. C. J. Am. Chem. Soc.
1953, 75, 2705; (b) Kitamura, T.; Matsuyuki, J.; Nagata, K.; Furuki, R.; Taniguchi,
H. Synthesis 1992, 945; (c) Margida, A. J.; Koser, G. F. J. Org. Chem. 1984, 49, 3643.
22. Reviews: (a) Merritt, E. A.; Olofsson, B. Angew. Chem., Int. Ed. 2009, 48, 9052; (b)
Deprez, N. R.; Sanford, M. S. Inorg. Chem. 2007, 46, 1924; (c) Stang, P. J. J. Org.
Chem. 2003, 68, 2997; (d) Múller, U. Trends Photochem. Photobiol. 1999, 5, 117;
(e) Frechet, J. M. C. Pure Appl. Chem. 1992, 64, 1239; (f) Koser, G. F. In The
Chemistry of Functional Groups, Supplement D; Patai, S., Rappoport, Z., Eds.;
Wiley: New York, NY, 1983, Chapter 25.
23. For the recent improved preparative methods, see: (a) Hossain, M. D.; Kita-
mura, T. Tetrahedron 2006, 62, 6955; (b) Bielawski, M.; Aili, D.; Olofsson, B. J.
Org. Chem. 2008, 73, 4602 and references cited therein; (c) Kraszkiewicz, L.;
Skulski, L. Synthesis 2008, 2373; (d) Zhu, M.; Jalalian, N.; Olofsson, B. Synlett
2008, 592; (e) Merritt, E. A.; Malmgren, J.; Klinke, F. J.; Olofsson, B. Synlett 2009,
2277.
6. (a) Reichardt, C. Angew. Chem., Int. Ed. Engl. 1979, 18, 98; (b) Eberson, L.;
Hartshorn, M. P.; Persson, O. J. Chem. Soc., Perkin Trans. 2 1995, 1735; (c) Kamlet,
M. J.; Abboud, J. L. M.; Abraham, M. H.; Taft, R. W. J. Org. Chem. 1983, 48, 2877.
7. (a) Schadt, F. L.; Bentley, T. W.; Schleyer, P. V. R. J. Am. Chem. Soc.1976, 98, 7667; (b)
Allard, B.; Casadevall, A.; Casadevall, E.; Largeau, C. Nouv. J. Chim. 1979, 3, 335; (c)
Allard, B.; Casadevall, A.; Casadevall, E.; Largeau, C. Nouv. J. Chim. 1980, 3, 539.
8. (a) Kita, Y.; Takada, T.; Tohma, H. Pure Appl. Chem. 1996, 68, 627; (b) Eberson, L.;
Hartshorn, M. P.; Persson, O.; Radner, F. Chem. Commun. 1996, 2105; (c) Bégué,
J. P.; Bonnet-Delpon, D.; Crousse, B. Synlett 2004, 18; (d) Shuklov, I. A.; Du-
brovina, N. V.; Boerner, A. Synthesis 2007, 2925.
9. (a) Tamura, Y.; Yakura, T.; Haruta, J.; Kita, Y. J. Org. Chem.1987, 52, 3927; (b) Kita, Y.;
Yakura, T.; Tohma, H.; Kikuchi, K.; Tamura, Y. Tetrahedron Lett. 1989, 30, 1119; (c)
Kita, Y.; Tohma, H.; Kikuchi, K.; Inagaki, M.; Yakura, T. J. Org. Chem. 1991, 56, 435.
10. (a) Kita, Y.; Tohma, H.; Inagaki, M.; Hatanaka, K.; Kikuchi, K.; Yakura, T. Tetra-
hedron Lett. 1991, 32, 2035; (b) Kita, Y.; Tohma, H.; Inagaki, M.; Hatanaka, K.;
Yakura, T. J. Am. Chem. Soc. 1992, 114, 2175; (c) Kita, Y.; Takada, T.; Ibaraki, M.;
Gyoten, M.; Mihara, S.; Fujita, S.; Tohma, H. J. Org. Chem. 1996, 61, 223; (d) Kita,
Y.; Takada, T.; Gyoten, M.; Tohma, H.; Zenk, M. H.; Eichhorn, J. J. Org. Chem. 1996,
61, 5857; (e) Kita, Y.; Watanabe, H.; Egi, M.; Saiki, T.; Fukuoka, Y.; Tohma, H. J.
Chem. Soc., Perkin Trans. 1 1998, 635; (f) Kita, Y.; Arisawa, M.; Gyoten, M.; Na-
kajima, M.; Hamada, R.; Tohma, H.; Takada, T. J. Org. Chem. 1998, 63, 6625; (g)
Kita, Y.; Egi, M.; Tohma, H. Chem. Commun. 1999, 143; (h) Tohma, H.; Harayama,
Y.; Hashizume, M.; Iwata, M.; Egi, M.; Kita, Y. Angew. Chem., Int. Ed. 2002, 41,
348; (i) Tohma, H.; Harayama, Y.; Hashizume, M.; Iwata, M.; Kiyono, Y.; Egi, M.;
Kita, Y. J. Am. Chem. Soc. 2003, 125, 11235.
24. Substrates 5t and 5u could react with Koser’s reagent or other iodine(III) re-
agents in CH2Cl2 under the conditions described in Ref. 21, but afforded
a mixture of 6t-OTs and 6t0-OTs or 6u-OTs and 6u0-OTs in low product yields
and chemoselectivities.
25. Dian, G.; Barbey, G. Synth. Met. 1986, 13, 281.
26. (a) Bykowski, D.; McDonald, R.; Hinkle, R. J.; Tykwinski, R. R. J. Org. Chem. 2002,
11. (a) Kita, Y.; Tohma, H.; Inagaki, M.; Hatanaka, K.; Yakura, T. Tetrahedron Lett.
1991, 32, 4321; (b) Kita, Y.; Tohma, H.; Hatanaka, K.; Takada, T.; Fujita, S.; Mitoh,
67, 2798; (b) Gallop, P. M.; Paz, M. A.; Flückiger, R.; Stang, P. J.; Zhdankin, V. V.;

T. Dohi et al. / Tetrahedron 66 (2010) 5775e5785
5785
Tykwinski, R. J. Am. Chem. Soc. 1993, 115, 11702; (c) Martin-Santamaría, S.;
Carroll, M. A.; Carroll, C. M.; Carter, C. D.; Pike, V. W.; Rzepa, H. S.; Widdowson,
D. A. Chem. Commun. 2000, 649; (d) Ross, T. L.; Ermert, J.; Hocke, C.; Coenen, H.
H. J. Am. Chem. Soc. 2007, 129, 8018.
34. (a) Koser, G. F.; Telu, S.; Laali, K. K. Tetrahedron Lett. 2006, 47, 7011; (b) Telu, S.;
Durmus, S.; Koser, G. F. Tetrahedron Lett. 2007, 48, 1863.
35. (a) Hoier, S. N.; Park, S.-M. J. Electrochem. Soc. 1993, 140, 2454; (b) Lee, H.-J.;
Park, S.-M. J. Phys. Chem. B 2004, 108, 16365.
27. In contrast, the corresponding boronic acid did not produce the condensation
product 6 and caused the boroneiodine(III) exchange. See, Ref. 20e.
28. (a) Crivello, J. V.; Narayan, R. Chem. Mater. 1992, 4, 692; (b) Shah, A.; Pike, V. W.;
Widdowson, D. A. J. Chem. Soc., Perkin Trans. 1 1998, 2043.
29. (a) Yamada, Y.; Okawara, M. Macromol. Chem. 1972, 152, 153; (b) Crivello, J. V.;
Lee, J. L. Polym. Bull. 1986, 16, 243; (c) Huang, X.; Zhu, Q.; Xu, Y. Synth. Commun.
2001, 31, 2823.
36. Ito, M.; Ogawa, C.; Yamaoka, N.; Fujioka, H.; Dohi, T.; Kita, Y. Molecules 2010, 15,
1918.
37. Ye, X.-S.; Li, W.-K.; Wong, H. N. C. J. Am. Chem. Soc. 1996, 118, 2511.
38. (a) Kita, Y.; Morimoto, K.; Ito, M.; Ogawa, C.; Goto, A.; Dohi, T. J. Am. Chem. Soc.
2009, 131, 1668; (b) Dohi, T.; Ito, M.; Yamaoka, N.; Morimoto, K.; Fujioka, H.;
Kita, Y. Angew. Chem., Int. Ed. 2010, 49, 3334.
39. (a) Ochiai, M.; Kitagawa, Y.; Takayama, N.; Takaoka, Y.; Shiro, M. J. Am. Chem.
Soc. 1999, 121, 9233; (b) Aggarwal, V. K.; Olofsson, B. Angew. Chem., Int. Ed. 2005,
44, 5516.
40. (a) Dohi, T.; Maruyama, A.; Minamitsuji, Y.; Takenaga, N.; Kita, Y. Chem. Com-
mun. 2007, 1224; (b) Dohi, T.; Minamitsuji, Y.; Maruyama, A.; Hirose, S.; Kita, Y.
Org. Lett. 2008, 10, 3559; (c) Minamitsuji, Y.; Kato, D.; Fujioka, H.; Dohi, T.; Kita,
Y. Aust. J. Chem. 2009, 62, 648; (d) Dohi, T. Chem. Pharm. Bull. 2010, 58, 135.
41. Other reports have appeared after we first introduced the fluoroalcohols for the
catalytic utilization of hypervalent iodine reagents. See: Moroda, A.; Togo, H.
Synthesis 2008, 1257; (b) Yakura, T.; Yamauchi, Y.; Tian, Y.; Omoto, M. Chem.
Pharm. Bull. 2008, 56, 1632; (c) Miyamoto, K.; Sei, Y.; Yamaguchi, K.; Ochiai, M. J.
Am. Chem. Soc. 2009, 131, 1382; (d) Yakura, T.; Tian, Y.; Yamauchi, Y.; Omoto, M.;
Konishi, T. Chem. Pharm. Bull. 2009, 57, 252; (e) Ishiwata, Y.; Togo, H. Tetrahedron
Lett. 2009, 50, 5354.
30. PhI(OH)OMs was used instead of Koser’s reagent to avoid the contamination of
the formed polymer with a small amount of p-TsOH.
31. In our measurement, the solubility of the polymer 6al-OMs in MeOH at 25 ꢂC
was at least more than 30 mg/mL.
32. (a) Koser, G. F. Aldrichimica Acta 2001, 34, 89 For preparative methods, see: (b)
Koser, G. F.; Wettach, R. H. J. Org. Chem. 1980, 45, 1542; (c) Yusubov, M. S.;
Wirth, T. Org. Lett. 2005, 7, 519; (d) Yamamoto, Y.; Togo, H. Synlett 2005, 2486.
33. (a) Kitamura, T.; Yamane, M. J. Chem. Soc., Chem. Commun. 1995, 983; (b)
Okuma, K.; Yamamoto, T.; Shirokawa, T.; Kitamura, T.; Fujiwara, Y. Tetrahedron
Lett. 1996, 37, 8883; (c) Kitamura, T.; Yamane, M.; Inoue, K.; Todaka, M.; Fu-
katsu, N.; Meng, Z.; Fujiwara, Y. J. Am. Chem. Soc. 1999, 121, 11674; (d) Kitamura,
T.; Meng, Z.; Fujiwara, Y. Tetrahedron Lett. 2000, 41, 6611; (e) Kitamura, T.;
Todaka, M.; Fujiwara, Y. Org. Synth. 2002, 78, 104.