One-pot syntheses of diaryliodonium salts from aryl iodides using peracetic acid as green oxidant

Article abstract of DOI:10.1071/CH11057

The rate-accelerating effects of fluoroalcohol solvents for generating trivalent hypervalent iodine species and the conversion into diaryliodonium(iii) salts have been used for the first time to realize a facile and clean one-pot synthesis of diaryliodoni

Full text of DOI:10.1071/CH11057

RESEARCH FRONT
Communication
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2011, 64, 529–535
One-Pot Syntheses of Diaryliodonium Salts from Aryl
Iodides Using Peracetic Acid as Green Oxidant
A
A
A
Toshifumi Dohi, Nobutaka Yamaoka, Itsuki Itani,
A B
,
and Yasuyuki Kita
A
College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi,
Kusatsu, Shiga, 525-8577, Japan.
B
Corresponding author. Email: kita@ph.ritsumei.ac.jp
The rate-accelerating effects of fluoroalcohol solvents for generating trivalent hypervalent iodine species and the
conversion into diaryliodonium(III) salts have been used for the first time to realize a facile and clean one-pot synthesis
of diaryliodonium(III) salts 3 from aryl iodides 1 and suitable arene partners 2 with peracetic acid (PAA). The use of PAA
as a green and practical oxidant is significantly effective in fluoroalcohol solvents. The scope and limitations of the
methodology are elucidated by investigation of a wide variety of representative substrates.
Manuscript received: 1 February 2011.
Manuscript accepted: 21 February 2011.
Introduction
stannyl-, and boryl-arenes, have been used to circumvent the
limitation of the original methodology.[6] More recently, synthetic
interest has focussed on a more straightforward route, that is, the
couplings starting from aryl iodides 1 and suitable arene partners 2
under oxidative conditions (Scheme 1),[7–11] otherwise, the former
two routes require several further synthetic steps to the salts 3.[5,6]
Chromium oxide,[7] sodium perborate,[8] potassium peroxodisul-
fate,[9] m-chloroperbenzoic acid,[10] and urea-hydrogen peroxide/
triflic anhydride,[11] have been employed as the concomitant
oxidants in Scheme 1. Indeed, the stoichiometric use of these
oxidants has realized facile and high-yielding syntheses of diaryl-
iodonium(III) salts from the corresponding aryl iodides 1 and
aromatic partners 2 with an acceptable substrate scope,* however,
the nature of the employed oxidants always caused the production
of large amounts of inorganic and organic byproducts and/or toxic
waste after the preparations despite being removable by aqueous
workup. Thus, thesynthetichurdleatthepresenttimeisconsidered
to be a replacement of the oxidants to other more favourable
alternatives for decreasing the undesirable waste materials.
Based on this situation, we examined the use of peracetic acid
(PAA) as an environmentally friendly and practical oxidant for
the straightforward syntheses of diaryl iodonium salts 3 from
aryl iodides 1 and the corresponding arene partners 2. The
important key for the successful transformation is that fluoro-
alcohols consistently act as extreme promoters during the
The diaryl-l3-iodanes constitute one of the unique classes of
hypervalent iodine compounds as reprþesented by the classically
known diaryliodonium(III) salts, ArI Ar0Xꢀ (where, Ar and
Ar0 ¼ aryls, and X ¼ anionic counterion).[1] A broad range of
specific applications, such as arylating agents and benzyne
precursors in organic synthesis,[1a,b] active bactericides,[1c]
a
practical photoacid generator (PAG) for initiating cationic
polymerization processes,[1d,e] etc., have been found. In com-
bination with the expedient leaving ability of the aryl iodonio
group,[1,2] the unusual physical properties and chemical beha-
viours compared with other onium salts has pioneered innova-
tive research to allow novel metal-free carbon–carbon bond
constructions[3] as well as other metal-involved transforma-
tions[4] in recent times. In such applications in organic synthesis
and other fields of chemistry, the diaryliodonium(III) salts serve
as useful and environmentally friendly chemical tools meeting
the recent demands in green chemistry because of their salient
features of typical hypervalent iodine compounds,[2] such as
low toxicity, high stability, ready availability, easy handling,
and unique reactivities similar to that of heavy metals.
Many synthetic routes are now available to obtain structural
diversity in the available series of diaryliodonium(III) salts. The
synthesiswasoriginallycarriedoutbythecondensationofisolated
trivalent iodine compounds and a suitable aromatic partner with a
Bro¨nsted acid.[5] However, such direct methods could only be
achieved in a limited number of substrates and counterions using
iodine(III) compounds activated with strong acids[5a,b] or reactive
[hydroxy(tosyloxy)iodo]benzene (HTIB)[5c] in moderate yields
with poor regioselectivities. Therefore, stepwise methods using
avarietyoforganometallicaromaticcompounds,i.e.,lithio-,silyl-,
ϩ
[O]
HX
RЈ
RЈ
R
R
I
I
ϩ
XϪ
1
2
3-X
Scheme 1.
*New straightforward protocols enabling the synthesis of diaryliodonium(III) salts from aromatic compounds in the presence of elemental iodine or inorganic
periodate have been developed, however, their synthetic scope is strictly limited to obtaining symmetrical salts having the same aryl groups. See ref. [12].
Ó CSIRO 2011
10.1071/CH11057
0004-9425/11/050529

RESEARCH FRONT
530
T. Dohi et al.
Step 2
RЈ
Step 1
9% PAA
OAc
I
OAc
ϩ
2
RЈ
R
R
R
I
I
XϪ
Fluoroalcohol
HX
1
Fluoroalcohol
1؅
3-X
X ϭ OTs, etc.
Scheme 2. PAA ¼ peracetic acid, Ts ¼ p-toluenesulfonyl.
reaction. We now report the primary results obtained for the one-
pot syntheses of diaryliodonium salts 3 using PAA as the green
oxidant.
Table 1. Solvent screening in the diaryliodonium salt formation
3aa-OTsA
(i) 9% PAA
ϩ
I
ϪOTs
35°C, 1 h
I
Results and Discussion
(ii) HOTs
mesitylene
PAA is an extremely green oxidant and has frequently been
used as a practical and environmentally friendly oxidant.[13] Its
priority of use has been favoured in recent years in not only the
laboratory, but also in industrial-scale processes because PAA
only releases non-toxic co-products after its consumption, that
is, easily removable acetic acid and water, making isolation
of the products easy when using this organic oxidant. It is
commercially available as dilute acetic acid solutions, or alter-
natively, can be prepared from hydrogen peroxide and acetic
anhydride before use.[14] Also, a 0.2–0.3% aqueous solution
of PAA is widely used as a disinfectant in medical situations
because of its well confirmed safety toward humans.
1a
3aa-OTs
2a
r.t.
Entry
Solvent
Time [h]
Yield of 3aa [%]B
C
1
2
3
4
5
6
7
8
HFIP/CH2Cl2
HFIP
3
3
83
89
TFE
3
89
D
TFE/CH2Cl2
MeOH
3
89
n.d.E
24
24
24
3
CH2Cl2
CH3CN
AcOH
57
42
77
Recently, we found a remarkable rate-accelerating effect
of fluoroalcohol solvents, i.e., hexafluoroisopropanol (HFIP)
and trifluoroethanol (TFE), for the dehydrative condensation of
HTIB with various electron-sufficient aromatic rings to form the
corresponding type 3 diaryliodonium(III) salts.[15,16] Thereafter,
the fluoroalcohols were successfully introduced as effective
solvents for enhancing the low activity of PAA to generate
aryliodine(III) species and to construct hypervalent iodine(III)-
involved catalytic cycles.[17] Based on this knowledge, we now
considered the effects of fluoroalcohols as the key to establish-
ing a one-pot approach to diaryliodonium(III) salts 3 from the
aryl iodide 1 and aromatic partners 2 with PAA that is shown in
Scheme 2. The net conversion mainly consisted of two steps,
i.e., the generation of aryliodine(III) diacetates 10 with PAA
(step 1) followed by the condensation of 10 with aromatic rings
of 2 in the presence of the appropriate anions, Xꢀ (step 2),
both of which would be accelerated by the use of the unique
fluoroalcohol solvents.[18]
Based on this idea, we attempted the conversion of iodo-
benzene 1a into mesityl(phenyl)iodonium tosylate 3aa-OTs by
selecting the mixed solvent system of HFIP/CH2Cl2 (1/1, v/v)[17]
as the first choice. With a commercially available ,9% (v/v)
PAA solution in acetic acid (obtained from Sigma–Aldrich,
,5 equiv. was used), the reaction was performed around
the temperature of 358C for 1 h to suitably generate the
aryliodine(III) diacetate 10 in situ. To the reaction mixture,
p-toluenesulfonic acid (TsOH, 2 equiv.) and a slight excess
amount of mesitylene 2a (1.5 equiv.) were added and mixed at
room temperature for 3 h, from which the desired iodonium(III)
salt 3aa-OTs could be obtained in 83% yield with high purity by
precipitation in ether (Table 1, entry 1). Motivated by this
encouraging result, we then screened minor modifications of
the solvent systems using HFIP and TFE, all giving similar
product yields of 3aa-OTs as suggested by entries 2–4. Thus,
the concentration of fluoroalcohols was less influential, and the
reactions could be performed without any conversion losses of
AReactions were examined using 1a (1 equiv.), 2a (1.5 equiv.), 9% PAA
solution (,5 equiv. of PAA), and p-toluenesulfonic acid monohydrate
(HOTs, 2 equiv.) under 0.2 M concentration of 1a.
BIsolated yield based on 1a used.
C1/1 v/v of the solvents.
D10/1 v/v of TFE/CH2Cl2.
ENot determined because of a very low-yield of formation of 3aa (o5%).
1a and 2a using various ratios of the fluoroalcohols and
dichloromethane (up to 1/1 v/v).
However, other conventional alcohols and polar or non-polar
solvents, such as methanol, acetonitrile, and dichloromethane,
generally gave inferior results as we expected (entries 5–7). The
slightly higher formations of 3aa-OTs in the case of acetonitrile
(42%) and dichloromethane (57%) after prolonged reaction
times are rationalized by the positive effect of the concomitant
acetic acid in the PAA solution on the one-pot synthesis,
although less effective than the fluoroalcohols, as implied in the
better product yield when using the acetic acid solvent (entry 8).
Our fast and greener synthetic method of producing diaryl
iodonium(III) salts 3 with PAA has become the most successful
of the fluoroalcohol systems based on these studies.
We next verified the versatility of the method in several kinds
of aryl iodides 1 using the optimized conditions (Table 2).
Among the examined fluoroalcohol systems, we selected for
this examination TFE/CH2Cl2 (10/1 v/v) to eliminate the solu-
bility factor of the aryl iodides 1a–f in the solvent. A series
of aryl iodides 1a–f are soluble enough in the solvent mixture,
and the corresponding iodonium(III) salts 3 having different
aryl rings could be obtained from the iodoarenes 1 except for
4-iodoanisole 1c (entries a–f). Thus, the problem seems to be the
unavailability of the aryl iodide 1c having a strong resonance-
donating group (entry c, see the discussion in Fig. 1). The use
of HFIP was particularly beneficial in the case of the aryl iodide
having a very strong electron-withdrawing group, such as a nitro
group, because of the difficult smooth generation of the iodine(III)

RESEARCH FRONT
One-Pot Syntheses of Diaryliodonium Salts
531
Table 2. Variation of starting iodoarenes 1 for the PAA methodA
Entry
Iodoarene (1)
Iodonium salt (3-X)
Yield of 3-X [%]B
R2
R2
R1
R1
I
Iϩ
ϪOTs
R2
R2
a
b
c
d
e
f
R1 ¼ R2 ¼ H (1a)
R1 ¼ R2 ¼ H (3aa-OTs)
89
94
R1 ¼ R2 ¼ Me (1b)
R1 ¼ R2 ¼ Me (3ba-OTs)
R1 ¼ OMe, R2 ¼ H (3ca-OTs)
R1 ¼ Cl, R2 ¼ H (3da-OTs)
R1 ¼ CF3, R2 ¼ H (3ea-OTs)
R1 ¼ NO2, R2 ¼ H (3fa-OTs)
R1 ¼ OMe, R2 ¼ H (1c)
R1 ¼ Cl, R2 ¼ H (1d)
R1 ¼ CF3, R2 ¼ H (1e)
R1 ¼ NO2, R2 ¼ H (1f)
Trace
89
82
18 (73)C
AReactions were performed with the optimized experimental procedure and reaction time (3 h) described in Table 1, entry 4 unless otherwise noted. Reagents
and conditions: iodoarene (1a–f; 1 equiv.), mesitylene (2a; 1.5 equiv.), 9% PAA (,5 equiv.), HX (X ¼ OTs; 2 equiv.) in TFE/CH2Cl2 (10/1 v/v).
BIsolated yield of the product 3 based on iodoarene (1a–f) used.
CHFIP was used as solvent.
Aryl iodides (1)
MeO
I
I
Cl
O
I
F3C
I
O2N
I
Poor
Excellent
Moderate
Aryl partners (2)
OMe
N
Cl
CO2Me
Poor
CF3
Excellent
Fig. 1. Summary of applicability of aromatic substrates.
species 10 for such an aryl iodide 1f (entry f). As a large number
of aryl iodides 1 are now commercially available, the variation of
the aryl iodides 1 in the reaction can further expand the structural
diversity of the obtained salts 3.
formations of mono-iodonium(III) salts 3ag-OTs and 3ah-OTs
occurred on the one aryl ring without any production of the bis-
iodonium salt (entries j and k). A series of counterions, ꢀOTf
(Tf ¼ trifluoromethanesulfonyl), ꢀOMs (Ms ¼ methanesulfonyl),
and ꢀOCs (Cs ¼ (þ)-10-camphorsulfonyl), were conveniently
introduced into the product 3aa using this methodology by
changing the added sulfonic acids (entries a–d). Throughout the
operations, no tedious workup and special equipment was neces-
sary as the reactions only produced easily removable acetic acid
and water as the main coproducts, which proved to be a distinct
advantage of the PAA method.
Based on these investigations, the scope and limitation of our
methodology are summarized in Fig. 1. For a wide range of aryl
iodides 1 not having an oxidizable functionality, the one-pot
preparation was effective, and even more versatile when com-
pared with the reported methods except for 1c.[5–16] The failure
of the iodoanisole 1c in Table 2 is rationalized by the expected in
situ instability of the active iodonium(III) species. In the reaction
profile depicted as Scheme 3, the conversions should take into
account the formation of [hydroxyl(tosyloxy)iodo]arenes 100
(X ¼ OTs) before starting the condensation with 2, as the
first generated aryliodine(III) diacetate 10 can react very slowly
with the aromatic coupling partners 2.y In general, the arylio-
donium(III) species are very unstable in the presence of strong
Regarding the aromatic coupling partners 2, the new protocol
provided the permissible options for the alkylbenzenes, phenyl-
ethers, and suitably protected aniline derivatives. To elucidate the
selectivity and scope of the functional groups, we tested several
types of aromatic compounds 2 for the reactions of iodobenzene
1a, and selected examples are shown in Table 3. Among the
ring positions in the multi-substituted alkylbenzene 2b, the
less hindered site exclusively reacted to give a salt 3ab-OTs
as the single isomer (entry e). The reactions were usually
para-selective to the donating substituents, but the 1,4-disubsti-
tuted benzene could give an iodonium salt 3ac-OTs during the
reaction at the ortho-position of 2c, although HFIP was required
for the transformation (entry f). As shown in entry g, a signifi-
cantly electron-rich arene 2d was compatible and rather
an excellent aromatic partner 2 in contrast to the result of the
electron-rich aryl iodide 1c in Table 2. In turn, moderate electron-
withdrawing functional groups, such as a halogen (entry h) and
ester (entry i), on the anisoleringdidnotaffect thereaction results.
These substrate results are similar to those of the other straight-
forward systems.[7–11] For the diaryl ethers 2g and 2h, selective
y[Hydroxy(sulfonyloxy)iodo] arenes 100 can be generated rapidly from aryliodine(III) diacetates 10 and sulfonic acids in the presence of stoichiometric amounts
of water. For preparative methods, see ref. [19].

RESEARCH FRONT
532
T. Dohi et al.
Table 3. Syntheses of diaryliodonium salts 3-X (X 5 OTs, OTf, OMs,
OCs)A from iodobenzene 1a and various electron-rich arenes 2a i using
acids once an electron-donating group is attached to the aryl
ring.z[20] Thus, the collapse of the intermediate 100, [hydroxyl
(tosyloxy)iodo]anisole (R ¼ 4-OMe, X ¼ OTs), did not give the
desired iodonium(III) salt 3ca-OTs.
]
the PAA methodB
Entry
Arene (2)
Iodonium salt (3-X)
Yield of 3-X [%]C
Electron-rich aromatic compounds 2 are the common excel-
lent partners for the aryl iodides 1. In contrast, the presence of
an electron-withdrawing group in the aromatic compounds 2
apparently retards the condensation with the [hydroxyl(tosyl-
oxy)iodo]arenes 10, as seen in the other procedures.[5–16] Unfor-
tunately, our effort to extend the one-pot strategy with PAA to
the heteroaryl-involving iodonium(III) salt synthesis almost
failed, resulting in the complex formation of unidentified
oxidized products of heteroaromatic compounds. The limited
successful cases include the aryl iodides 1 and electron-rich
thiophenes, such as the combination of iodobenzene 1a and
compound 2j or 2k (Scheme 4). For the five-membered hetero-
aromatics, the reactions usually occurred at the a-position of the
thiophene rings of 2j and 2k, in which the 2-position was more
reactive than the other 5-position. It should be noted that the
iodonium salts having these thienyl moieties are known to have
special applications as the precursors of fluorinated aromatic
compounds, organic non-linear optic materials, active bacter-
iocides, etc.[21]
Iϩ
XϪ
a
b
c
d
2a
2a
2a
2a
3aa-OTs (X ¼ OTs)
3aa-OTf (X ¼ OTf)
3aa-OMs (X ¼ OMs)
3aa-OCs (X ¼ OCs)
89
87
89
90
Iϩ
XϪ
tBu
tBu
e
2b
2c
3ab-OTs (X ¼ OTs)
91
ϩ
f
I
Xϩ
3ac-OTs (X ¼ OTs)
37 (82)D
MeO
MeO
MeO
Iϩ
g
OMe
OMe
Conclusion
XϪ
A practical and clean oxidant, PAA, has been used for the first
time for the synthesis of diaryliodonium(III) salts 3 from aryl
iodides 1. The transformation proceeded in exceptionally high
yields with short reaction times for various types of substrate
combinations, that is, various aryl iodide 1 except for those
having an electron-rich aromatic moiety, and electron-rich
aromatic partners 2, under mild conditions when using PAA in
the fluoroalcohol solvents, HFIP and TFE. This study shows the
importance of the fluoroalcohol solvents in the generation of
hypervalent iodine(III) species, whose functions should make all
the conversion steps to the salts 3 smooth and effective. The use
of PAA results in the formation of only non-toxic acetic acid
and water, and its applicability usually improves the cost and
impact on the environment by reducing the undesirable waste.
We believe that the present system, consistent with the recent
direction of green chemistry, would become valuable for the
production of industrial chemicals involving diaryliodonium(III)
salts.
MeO
2d
3ad-OTs (X ¼ OTs)
85
84
Br
Br
+
h
OMe
I
OMe
XϪ
2e
3ae-OTs (X ¼ OTs)
CO2Me
CO2Me
OMe
Iϩ
i
OMe
XϪ
2f
3af-OTs (X ¼ OTs)
84
91
98
Iϩ
OBn
OBn
j
XϪ
2g
3ag-OTs (X ¼ OTs)
Iϩ
OPh
OPh
k
XϪ
2h
3ah-OTs (X ¼ OTs)
Experimental
O
O
Iϩ
l
Melting points (mp) were measured using a Bu¨chi B-545
apparatus. Infrared (IR) spectra were recorded on a Hitachi
270-50 spectrometer; absorptions are reported in reciprocal
centimetres. 1H and 13C NMR spectra were recorded on JEOL
JMN-300 or 400 spectrometers operating at 300 or 400 MHz in
CD3OD at 258C with tetramethylsilane as the internal standard.
Data are reported as follows: chemical shift in ppm (d), multi-
plicity (s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet, br ¼
broad singlet, m ¼ multiplet), coupling constant [Hz], and
integration. TLC was carried out on Merck Silica gel 60 (230–
400 mesh) using hexane/AcOEt as eluent; the spots were
detected by UV irradiation (254, 365 nm). The 9% v/v PAA
N
N
XϪ
2i
3ai-OTs (X ¼ OTs)
85
ATf ¼ trifluoromethanesulfonyl; Ms ¼ methanesulfonyl; Cs ¼ (þ)-10-
camphorsulfonyl.
BReactions were performed with the optimized experimental procedure
and reaction time (3 h) described in Table 1, entry 4 unless otherwise
noted. Reagents and conditions: iodobenzene (1a; 1 equiv.), arene (2a–i;
1.5 equiv.), 9% PAA (,5 equiv.), HX (X ¼ OTs, OTf, OMs, OCs; 2 equiv.)
in TFE/CH2Cl2 (10/1 v/v).
CIsolated yield of the product 3 based on iodobenzene (1a) used.
DHFIP was used as solvent.
zInteresting reactivities have been found by us for aryliodonium(III) species having electron-rich aryl moieties. See ref. [3].

RESEARCH FRONT
One-Pot Syntheses of Diaryliodonium Salts
533
Step 1
9% PAA
OAc
I
OAc
R
R
I
Fluoroalcohol
1
1Ј
RЈ
OH
I
X
Step 2
HX
Iϩ
2
RЈ
R
R
XϪ
Fluoroalcohol
1Љ
3-X
X ϭ OTs, etc.
Scheme 3.
3aa/OTf:[15a] a colourless solid; mp 1488C. nmax (KBr)/cmꢀ1
RЈ
(i) 9% PAA
35°C, 1h
ϩ
I
3053, 2983, 1622, 1566, 1469, 1379, 1259, 1163, 1029, 989,
746, 638. dH (CD3OD, 300 MHz) 2.35 (s, 3H), 2.65 (s, 6H), 7.23
(s, 2H), 7.50 (t, J 7.5, 2H), 7.63 (t, J 7.5, 1H), 7.90 (d, J 7.5, 2H).
dC (CD3OD, 75 MHz) 21.0, 27.0, 114.0, 119.7, 122.2, 131.3,
133.2, 133.3, 135.2, 143.5, 145.8.
I
ϪOTs
S
(ii) HOTs
RЈ
1a
3aj-OTs: RЈ ϭ Me; 91%
3ak-OTs: RЈ ϭ Br; 88%
S
3aa/OMs:[15a] a colourless solid; mp 135–1368C. nmax
(KBr)/cmꢀ1 3018, 2950, 1566, 1438, 1218, 1058, 995, 750.
dH (CD3OD, 300 MHz) 2.34 (s, 3H), 2.53 (s, 3H), 2.65 (s, 6H),
7.08 (s, 2H), 7.38 (t, J 7.5, 2H), 7.49 (t, J 7.5, 1H), 7.75 (d, J 7.8,
2H). dC (CD3OD, 75 MHz) 21.0, 26.9, 39.0, 113.3, 121.7, 129.8,
131.0, 131.6, 132.9, 142.1, 143.5.
3aa/OCs:[15a] a colourless solid; mp 173–1748C. nmax
(KBr)/cmꢀ1 2955, 1741, 1566, 1454, 1415, 1265, 1190, 1045,
995, 750. dH (CD3OD, 300 MHz) 0.81 (s, 3H), 1.09 (s, 3H),
1.32–1.39 (m, 1H), 1.50–1.58 (m, 1H), 1.85 (d, J 18.3, 1H),
1.98–2.02 (m, 2H), 2.28–2.35 (m, 4H), 2.57–2.72 (m, 8H), 3.26
(d, J 15.0, 1H), 7.23 (s, 2H), 7.50 (t, J 7.8, 2H), 7.64 (t, J 7.5, 1H),
7.91 (d, J 7.8, 2H). dC (CD3OD, 75 MHz) 20.1, 20.5, 21.0, 25.7,
27.1, 27.8, 43.6, 44.0, 48.1, 59.5, 114.2, 122.4, 131.3, 133.2,
133.2, 135.3, 143.5, 145.7, 218.1.
3ab/OTs:[15a] a colourless solid; mp 1578C. nmax (KBr)/cmꢀ1
3018, 2968, 1568, 1472, 1219, 1132, 1045, 928, 772, 665, 627.
dH (CD3OD, 300 MHz) 1.30 (s, 9H), 2.34 (s, 3H), 2.68 (s, 6H),
7.18 (d, J 8.4, 2H), 7.42–7.50 (m, 4H), 7.57–7.66 (m, 3H), 7.90
(d, J 8.4, 2H). dC (CD3OD, 75 MHz) 21.3, 27.3, 31.3, 35.8,
114.1, 122.5, 126.9, 127.9, 129.8, 133.2, 133.3, 135.3, 141.5,
143.2, 143.6, 158.3.
3ac/OTs:[16] a colourless solid; mp 1438C. nmax (KBr)/cmꢀ1
3027, 2973, 2919, 1787, 1601, 1578, 1563, 1491, 1633, 1471,
1440, 1377, 1321, 1274, 1193, 1129, 1039, 1012, 991, 8897,
845, 812, 738, 688, 650. dH (CD3OD, 400 MHz) 2.35 (s, 3H),
2.36 (s, 3H), 2.58 (s, 3H), 7.21 (d, J 8.0, 2H), 7.42 (s, 2H), 7.50
(t, J 8.0, 2H), 7.65–7.68 (m, 3H), 8.07 (d, J 8.0, 2H), 8.13 (s, 1H).
dC (CD3OD, 100.75 MHz) 20.5, 21.3, 25.1, 115.1, 120.7, 126.9,
129.8, 1332.5, 133.2, 133.4, 135.3, 136.1, 138.6, 139.2, 141.4,
141.6, 143.6.
2j, k
TFE/CH2Cl2, r.t.
Scheme 4.
solution was purchased from Sigma–Aldrich, Japan. All aryl
iodides and other chemicals were commercially available, and
were used as received without further purification.
General Experimental Procedure for the Syntheses
of Diaryliodonium Salts 1 from Aryl Iodides 2
(Tables 1–3, Scheme 4)
To a stirred solution of iodobenzene (204 mg, 1.0 mmol) in 5 mL
of 2,2,2-trifluoroethanol (TFE) and dichloromethane (10:1) was
added the commercially available PAA solution (9% v/v in
acetic acid, 2.2 mL, ,5 mmol of PAA). The reaction mixture
was then stirred for 1 h while the reaction temperature was
maintained around 358C. After cooling to room temperature,
mesitylene (180 mg, 1.5 mmol) and TsOHꢁH2O (380 mg,
2.0 mmol) were added to the mixture, and then stirred for 3 h
at room temperature. After the disappearance of mesitylene
(checked by TLC), CH2Cl2 was added to the mixture and the
organic layer was washed with water, and then dried over
anhydrous Na2SO4. After filtration, evaporation of the solvents
under vacuum afforded an oily crude product 3aa-OTs, which
was further purified by the addition of Et2O with stirring. The
precipitate was collected and dried under vacuum to give the
pure 3aa-OTs (438.5 mg, 0.89 mmol) in 89% yield. The sol-
vents could be reused repeatedly after distillation.
Iodonium salts 3aa-X (X ¼ OTf, OMs, OCs) having other
counterions could be prepared by replacement of p-toluene-
sulfonic acid monohydrate (p-TsOHꢁH2O) with the appropriate
sulfonic acids (HX).
3ad/OTs:[16] a slightly yellow solid; mp 178–1808C. nmax
(KBr)/cmꢀ1 2942, 2840, 2595, 2067, 1587, 1469, 1413, 1342,
1229, 1125, 1065, 1045, 1014, 992, 947, 913, 815, 740, 695, 642.
dH (CD3OD, 400 MHz) 2.34 (s, 3H), 3.88 (s, 3H), 3.96 (s, 6H),
6.40 (s 2H), 7.20 (d, J 8.0, 2H), 7.44 (t, J 8.0, 2H), 7.60 (t, J 8.0,
1H), 7.68 (d, J 8.0, 2H), 7.93 (d, J 8.0, 2H). dC (CD3OD,
75 MHz) 21.3, 56.7, 57.7, 86.2, 92.8, 115.9, 126.9, 129.8,
132.7, 133.0, 135.8, 141.6, 143.6, 161.4, 168.7.
3ae/OTs:[16] a colourless solid; mp 158–1598C. nmax (KBr)/
cmꢀ1 3050, 3015, 2936, 1566, 1476, 1439, 1379, 1292, 1271,
1255, 1207, 1192, 1155, 1132, 1045, 1015, 991, 816, 758, 692.
dH (CD3OD, 300 MHz) 2.30 (s, 3H), 3.84 (s, 3H), 6.80 (d, J 7.8,
Compound Data for Table 3
3aa/OTs:[15a] a colourless solid; mp 153–1578C. nmax (KBr)/cmꢀ1
3045, 2951, 1566, 1469, 1438, 1230, 1192, 1132, 1045, 989, 737,
696. dH (CD3OD, 300 MHz) 2.32 (s, 3H), 2.33 (s, 3H), 2.62
(s, 6H), 7.16–7.18 (m, 4H), 7.45 (d, J 7.5, 1H), 7.48 (d, J 7.5, 1H),
7.58–7.65 (m, 3H), 7.87 (d, J 7.8, 2H). dC (CD3OD, 75 MHz) 21.0,
21.3, 27.0, 114.1, 122.4, 126.9, 129.8, 131.2, 133.1, 133.2, 135.2,
141.5, 143.4, 143.6, 145.6.

RESEARCH FRONT
534
T. Dohi et al.
1H), 7.00 (d, J 7.8, 2H), 7.30 (t, J 7.8, 2H), 7.40–7.47 (m, 3H),
8.11–8.15 (m, 3H), 8.37 (d, J 2.1, 1H). dC (CDCl3, 75 MHz)
21.3, 56.4, 104.3, 113.8, 114.3, 116.2, 125.9, 128.5, 130.7,
131.4, 131.5, 134.9, 136.9, 139.1, 139.6, 158.6.
(q, J 3.8), 129.8, 131.4, 134.6 (q, J 33.6), 135.9, 141.6, 143.5,
143.6, 146.1.
3fa/OTs:[16] a colourless solid; mp 163–1658C. nmax
(KBr)/cmꢀ1 2969, 1601, 1568, 1530, 1468, 1350, 1343, 1312,
1300, 1192, 1132, 1043, 1005, 849, 816, 752, 734, 696.
dH (CD3OD, 300 MHz) 2.34 (s, 3H), 2.35 (s, 3H), 2.63
(s, 6H), 6.39 (d, J 7.8, 2H), 7.24 (s, 2H), 7.62 (d, J 7.8, 2H),
8.09 (d, J 7.8, 2H), 8.24 (d, J 7.8, 2H). dC (CD3OD, 75 MHz)
21.1, 21.3, 27.1, 120.0, 122.6, 126.9, 127.5, 129.8, 131.5, 136.3,
141.7, 143.5, 143.7, 146.3, 151.3.
3af/OTs:[15a] a colourless solid; mp 1708C. nmax (KBr)/cmꢀ1
3018, 1585, 1487, 1434, 1265, 1218, 771, 667. dH (CD3OD,
300 MHz) 2.34 (s, 3H), 3.86 (s, 3H), 3.90 (s, 3H), 7.21 (t, J 8.7,
3H), 7.50 (t, J 7.8, 2H), 7.67 (d, J 7.8, 3H), 8.15 (d, J 7.8, 2H),
8.28 (d, J 9.0, 1H), 8.49 (d, J 1.8, 1H). dC (CD3OD, 75 MHz)
21.3, 53.1, 57.1, 104.1, 116.7, 117.1, 124.5, 126.9, 129.8, 133.1,
133.6, 136.2, 139.5, 141.6, 142.0, 143.6, 163.2, 166.0.
3ag/OTs:[16] a colourless solid; mp 183–1858C. nmax
(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. dH (CD3OD, 300 MHz) 2.34 (s, 3H),
5.13 (s, 2H), 7.11 (d, J 8.0, 2H), 7.20 (d, J 8.0, 2H), 7.33–7.41
(m, 5H), 7.50 (t, J 8.0, 2H), 7.67 (t, J 8.0, 3H), 8.05–8.11
(m, 4H). dC (CD3OD, 75 MHz) 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.
3ah/OTs:[15a] a colourless solid; mp 138–1398C. nmax
(KBr)/cmꢀ1 3020, 1568, 1479, 1440, 1217, 1132, 1043, 815,
752, 692. dH (CD3OD, 300 MHz) 2.30 (s, 3H), 6.94–7.02
(m, 4H), 7.16–7.24 (m, 3H), 7.37–7.49 (m, 4H), 7.59–7.70
(m, 3H), 8.08–8.15 (m, 4H). dC (CD3OD, 75 MHz) 21.3,
106.9, 116.5, 121.3, 121.5, 126.3, 126.9, 129.8, 131.4, 133.0,
133.4, 136.2, 138.8, 141.6, 143.6, 156.1, 162.8.
Compound Data for Scheme 4
3aj/OTs:[15b] an off-white solid; mp 1658C. nmax (KBr)/cmꢀ1
3051, 1575, 1469, 1440, 1377, 1191, 1132, 1045, 1014, 991,
815, 746, 680. dH (CD3OD, 300 MHz) 2.33 (s, 3H), 2.49 (s, 3H),
7.03 (d, J 5.1, 1H), 7.19 (d, J 7.2, 2H), 7.46–7.49 (m, 2H), 7.59–
7.67 (m, 3H), 7.83 (d, J 5.1, 1H), 8.05 (d, J 7.8, 2H). dC (CD3OD,
75 MHz) 17.5, 21.3, 98.4, 118.4, 126.9, 129.8, 131.0, 133.0,
133.1, 133.4, 135.4, 137.7, 141.6, 150.0.
3ak/OTs:[15b] a colourless solid; mp 498C. nmax (KBr)/cmꢀ1
3045, 1562, 1469, 1438, 1373, 1330, 1191, 1130, 1043, 1014, 860,
815, 740, 692. dH (CD3OD, 300 MHz) 2.35 (s, 3H), 7.19–7.24
(m, 3H), 7.53 (t, J 7.8, 2H), 7.67 (d, J 7.8, 3H), 7.98 (d, J 5.7, 1H),
8.16 (d, J7.8, 2H). dC (CD3OD, 75 MHz) 21.3, 119.2, 125.6, 126.9,
129.8, 132.1, 133.2, 133.9, 135.9, 139.8, 141.4, 141.7, 143.5.
Acknowledgements
3ai/OTs:[15a] a colourless solid; mp 798C. nmax (KBr)/cmꢀ1
3051, 2981, 1693, 1579, 1487, 1384, 1303, 1191, 1130, 1043,
817, 746, 694. dH (CD3OD, 300 MHz) 2.13 (m, 2H), 2.34
(s, 3H), 2.58 (t, J 8.1, 2H), 3.86 (t, J 6.9, 2H), 7.20 (d, J 7.8,
2H), 7.49 (t, J 7.8, 2H), 7.63–7.69 (m, 3H), 7.80 (d, J 8.7, 2H),
8.13 (d, J 8.7, 4H). dC (CD3OD, 75 MHz) 18.6, 21.3, 35.6, 108.9,
116.5, 123.7, 126.9, 129.8, 133.1, 133.5, 136.2, 137.3, 141.6,
143.6, 144.5, 177.5.
This work was partially supported by a 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 acknowledges support from the
Industrial Technology Research Grant Program from the New Energy and
Industrial Technology Development Organization (NEDO) of Japan.
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Compound Data for Table 2
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(KBr)/cmꢀ1 3034, 2969, 2920, 1593, 1449, 1393, 1323, 1300,
1188, 1132, 1103, 1067, 1045, 1015, 1003, 991, 853, 827, 816,
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