Facile One-Pot Synthesis of Diaryliodonium Salts from Arenes and Aryl Iodides with Oxone

Article abstract of DOI:10.1002/open.201600129

A straightforward synthesis of diaryliodonium salts is achieved by using Oxone as the stoichiometric oxidant. Slow addition is the key to obtaining good yields and purities of the reaction products, which are highly useful reagents in many different areas of organic synthesis.

Full text of DOI:10.1002/open.201600129

DOI: 10.1002/open.201600129
Facile One-Pot Synthesis of Diaryliodonium Salts from
Arenes and Aryl Iodides with Oxone
Natalia Soldatova,[a] Pavel Postnikov,[a] Olga Kukurina,[a] Viktor V. Zhdankin,[a, b] Akira Yoshimura,[b]
Thomas Wirth,*[c] and Mekhman S. Yusubov*[a]
A straightforward synthesis of diaryliodonium salts is achieved
by using Oxone as the stoichiometric oxidant. Slow addition is
the key to obtaining good yields and purities of the reaction
products, which are highly useful reagents in many different
areas of organic synthesis.
from iodoarenes 1 and arenes 2 is very simple. Initially, iodoar-
ene 1 is reacted with Oxone in the presence of trifluoroacetic
acid to generate [bis(trifluoroacetoxy)iodo]arenes before arene
2 is added to the reaction mixture (method A). The workup
only consists of an extraction followed by recrystallization of
the reaction product. The diaryliodonium compounds are ob-
tained as the trifluoroacetate salts in very good yields
(Scheme 1, Table 1). The yields of the overall transformation
Diaryliodonium salts are well-investigated compounds in or-
ganic synthesis. They are typically prepared from the corre-
sponding iodoarenes by using oxidative reaction conditions,
but iodine(III) compounds have also been used for the genera-
tion of diaryliodonium salts and most of these reactions have
been summarized in Review articles.[1] These compounds have
found many applications in synthesis,[2] but also in polymeri-
zations as photoinitiators, and some of these compounds even
possess biologic activities. Many different strategies have been
reported for the synthesis of this compound class by various
research groups[3] and us.[4]
Scheme 1. Synthesis of diaryliodonium trifluoroacetates using Oxone as
a stoichiometric oxidant.
Herein, we describe the straightforward and facile synthesis
of symmetrically and unsymmetrically substituted diaryliodoni-
um salts from arenes and iodoarenes in the presence of tri-
fluoroacetic acid with Oxone as stoichiometric oxidant. Similar
procedures have been reported by using peroxodisulfates as
oxidants,[5] but Oxone is more economically viable. We have al-
ready investigated the use of Oxone in the presence of tri-
fluoroacetic acid and found it to be more convenient in the
synthesis of [bis(trifluoroacetoxy)iodo]arenes.[6] Oxone has also
been used by Yakura et al. for the oxidation of iodine(I).[7] The
experimental procedure used to obtain the reaction products
could be improved when arene 2 was added slowly over
a period of several hours (method B) to the preformed [bis(tri-
fluoroacetoxy)iodo]arenes. In other cases, the speed of arene
addition did not have an influence on the outcome of the syn-
thesis of diaryliodonium salts 3.
By exchanging trifluoroacetic acid with trifluoromethanesul-
fonic acid, the corresponding diaryliodonium triflates are ac-
cessible. However, slow addition of a mixture of iodoarene
1 and arene 2 to the Oxone with trifluoromethanesulfonic acid
is required for good yields in this process. Fast addition will
lead to dark-colored solutions and to the formation of decom-
position products. The reactions leading to symmetrical as well
as unsymmetrical diaryliodonium triflates are summarized in
Table 2. Recently, similar protocols have been reported for the
synthesis of unsymmetrical diaryliodonium tosylates, although
the synthesis consisted of two steps: firstly the oxidation to io-
dine(III) and secondly the generation of the diaryliodonium
species.[8]
[a] N. Soldatova, P. Postnikov, Dr. O. Kukurina, Prof. Dr. V. V. Zhdankin,
Prof. Dr. M. S. Yusubov
Tomsk Polytechnic University and Siberian State Medical University
634050 Tomsk (Russia)
E-mail: yusubov@mail.ru
Homepage: http://blogs.cardiff.ac.uk/wirth/
[b] Prof. Dr. V. V. Zhdankin, Dr. A. Yoshimura
Department of Chemistry and Biochemistry
University of Minnesota Duluth, Duluth, MN 55812 (USA)
The yields in this reaction are moderate to good and all
products have been purified by recrystallization from ethyl ace-
tate/ hexane (1:10). The reaction is limited to arenes with elec-
tron-donating substituents. Even in the case of benzene as an
unsubstituted arene, the yield of the aryliodonium salt is quite
low, as compound 4a was isolated in only 31% yield (Table 2,
entry 1). Entry 13 (Table 2) shows that also heteroaromatic io-
dides such as 3-iodopyridine can be employed in this reaction,
leading to the diaryliodonium compound 4m in good yield.
The reaction described here is operationally very simple,
uses readily available reagents and starting materials and pro-
[c] Prof. Dr. T. Wirth
School of Chemistry, Cardiff University
Park Place, Main Building, Cardiff CF10 3AT (UK)
E-mail: wirth@cf.ac.uk
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
open.201600129.
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Table 1. Synthesis of diaryliodonium trifluoroacetates.
Entry Iodoarene 1 Arene 2 Product 3
Table 2. Synthesis of diaryliodonium triflates.
Yield 3 [%]
(method)[a]
49 (A)[b]
64 (B)[b]
1
2
PhI
PhI
PhMe
Entry Iodoarene 1 Arene 2
Product 4
Yield 4 [%]
1
2
PhI
PhI
PhH
31
1,2-Me2C6H4
80 (A)
PhMe
68[a]
92 (A)
94 (B)
3
4
PhI
PhI
1,3,5-Me3C6H3
PhOMe
3
4
PhI
PhI
1,4-Me2C6H4
52
81 (B)
1,3,5-Me3C6H3
82
5
6
3-CF3C6H4I
3-CF3C6H4I
PhMe
87 (B)[b]
5
6
7
8
3-CF3C6H4I
3-CF3C6H4I
3-CF3C6H4I
3-CF3C6H4I
PhH
33
1,4-Me2C6H4
86 (B)
PhMe
51[a]
89 (A)
87 (B)
7
8
9
3-CF3C6H4I
3-CF3C6H4I
C6F5I
1,3,5-Me3C6H3
4-MeOC6H4Br
PhMe
1,4-Me2C6H4
1,3,5-Me3C6H3
51
94 (B)
84
9
4-ClC6H4I
4-ClC6H4I
4-BrC6H4I
4-BrC6H4I
PhMe
61[a]
53
62 (B)[b]
10
11
12
1,3,5-Me3C6H3
PhMe
10
C6F5I
1,4-Me2C6H4
59 (B)
60[a]
61
74 (A)
80 (B)
1,3,5-Me3C6H3
11
12
C6F5I
1,3,5-Me3C6H3
13
3-I-C5H4N
1,3,5-Me3C6H3
68
C6F5I
PhOMe
91 (B)
[a] Small amounts (2–5%) of ortho-isomer were observed.
[a] Method A: Addition of 2 directly after formation of [bis(trifluoroacetox-
y)iodo]arene. Method B: Addition of 2 over 6 h after formation of [bis(tri-
fluoroacetoxy)iodo]arene. [b] Small amounts (2–5%) of ortho-isomer were
observed.
vides pure reaction products in good yields. Synthetic applica-
tions of the diaryliodonium compounds are not provided here;
electronically[9] or sterically very different substituents can react
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selectively, whereas similar aryl moieties often lead to mixed
results in aryl-transfer reactions.[10] Recently, even catalytic ap-
proaches involving diaryliodonium compounds have been
published.[11]
Acknowledgements
This work was supported by the Russian Foundation for Basic Re-
search (RFBR-KO_a 16-53-10046) and the Royal Society
(IE160304). Support from the School of Chemistry, Cardiff Univer-
sity, is also gratefully acknowledged. We thank the EPSRC Nation-
al Mass Spectrometry Facility, Swansea, for mass spectrometric
data. We thank Prof. B. Olofsson, Stockholm, for valuable discus-
sions.
In summary, we report a practically very simple, high-yield-
ing process to make diaryliodonium triflates and trifluoroacte-
tates in good yields by using Oxone as a cheap stoichiometric
oxidant.
Experimental Section
Synthesis of Diaryliodonium Trifluoroacetates
Method A
Conflict of Interest
The authors declare no conflict of interest.
To a solution of iodoarene 1 (1.0 mmol) in a mixture of trifluoroace-
tic acid (1.5 mL) and chloroform (0.5 mL), Oxone (400 mg,
1.3 mmol) was added whilst stirring at room temperature. After
complete disappearance of the iodoarene (monitored by TLC),
arene 2 (1.7–3.5 mmol) was added and the solution was stirred for
approximately 20 h (see supporting information). A change to
a dark brown color was observed. After addition of CH2Cl2 (5 mL)
and H2O (5 mL), the organic layer was separated, washed with H2O
(5 mL), dried (Na2SO4), and the organic solvent removed under
vacuum. The crude products 3 were further purified by recrystalli-
zation from EtOAc/hexane (1:10).
Keywords: diaryliodonium
trifluoroacetates · iodine(III) compounds · oxidation · synthesis
triflates
·
diaryliodonium
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Synthesis of Diaryliodonium Trifluoroacetates
Method B
To a solution of iodoarene 1 (1.0 mmol) in a mixture of trifluoroace-
tic acid (1.5 mL) and chloroform (0.5 mL), Oxone (400 mg,
1.3 mmol) was added whilst stirring at room temperature. After
complete disappearance of the iodoarene (monitored by TLC),
arene 2 (1.05–1.50 mmol) in CHCl3 (2 mL) was added over 6 h by
using a syringe pump, and the solution was stirred for approxi-
mately 20 h (see the Supporting Information). A change to a light
brown color was observed. After addition of CH2Cl2 (5 mL) and H2O
(5 mL), the organic layer was separated, washed with H2O (5 mL),
dried (Na2SO4), and the organic solvent removed under vacuum.
The crude products 3 were further purified by recrystallization
from EtOAc/hexane (1:10).
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Synthesis of Diaryliodonium Triflates
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To a solution of trifluoromethanesulfonic acid (2.26 mmol, 339 mg,
200 mL) and Oxone (614 mg, 2 mmol) in CH2Cl2 (2 mL), a solution
of iodoarene 1 (1.0 mmol) and arene 2 (1.2 mmol) in acetonitrile
(2 mL) was added over 6 h by using a syringe pump. Then, Oxone
(307 mg, 1 mmol) was added to the reaction mixture. The reaction
mixture was stirred at room temperature overnight and a color
change from red–orange to pale yellow was observed. After addi-
tion of CH2Cl2 (5 mL) and H2O (5 mL), the organic layer was sepa-
rated, washed with H2O (5 mL), dried (Na2SO4), and the organic sol-
vent removed under vacuum. The crude products 4 were further
purified by recrystallization from EtOAc/hexane (1:10).
Received: October 22, 2016
Revised: November 21, 2016
Published online on && &&, 2016
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COMMUNICATIONS
N. Soldatova, P. Postnikov, O. Kukurina,
V. V. Zhdankin, A. Yoshimura, T. Wirth,*
M. S. Yusubov*
Pass the salt: Slow addition is the key
for a high-yielding synthesis of different
diaryliodonium salts from iodoarenes
and arenes using Oxone as the oxidant.
&& – &&
Facile One-Pot Synthesis of
Diaryliodonium Salts from Arenes and
Aryl Iodides with Oxone
&
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ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!