Single-electron-transfer (SET)-induced oxidative biaryl coupling by polyalkoxybenzene-derived diaryliodonium(III) salts

Article abstract of DOI:10.1002/chem.201301148

Metal-free oxidative C-C coupling by using polyalkoxybenzene-derived diaryliodonium(III) salts as both the oxidant and aryl source has been developed. These salts can induce single-electron-transfer (SET) oxidation to yield electron-rich arenes and subsequently transfer the polyalkoxyphenyl group into in situ generated aromatic radical cations to produce biaryl products. The reaction is promoted by a Lewis acid that activates the iodonium salts. It has been revealed that the reactivity of the salts under acidic conditions is quite different to their known behavior under basic conditions. The reactivity preference of a series of iodonium salts in the SET oxidation and their ligand transfer abilities have been systematically investigated and the results are summarized in this report. Copyright

Full text of DOI:10.1002/chem.201301148

FULL PAPER
DOI: 10.1002/chem.201301148
Single-Electron-Transfer (SET)-Induced Oxidative Biaryl Coupling by
Polyalkoxybenzene-Derived DiaryliodoniumACHTNUTRGNE(UNG III) Salts
Nobutaka Yamaoka, Kohei Sumida, Itsuki Itani, Hiroko Kubo, Yusuke Ohnishi,
Sho Sekiguchi, Toshifumi Dohi, and Yasuyuki Kita*[a]
À
Abstract: Metal-free oxidative C C
coupling by using polyalkoxybenzene-
omatic radical cations to produce
biaryl products. The reaction is pro-
moted by a Lewis acid that activates
the iodonium salts. It has been re-
vealed that the reactivity of the salts
under acidic conditions is quite differ-
ent to their known behavior under
basic conditions. The reactivity prefer-
ence of a series of iodonium salts in
the SET oxidation and their ligand
transfer abilities have been systemati-
cally investigated and the results are
summarized in this report.
derived diaryliodoniumACHTNUTRGNE(NUG III) salts as
both the oxidant and aryl source has
been developed. These salts can induce
single-electron-transfer (SET) oxida-
tion to yield electron-rich arenes and
subsequently transfer the polyalkoxy-
phenyl group into in situ generated ar-
Keywords: biaryls · cross coupling ·
hypervalent compound · iodine ·
radical ions · umpolung
Introduction
alyzed coupling reactions[4] have been developed by using
iodonium salts in chemical reactions. These reactions rarely
proceed except under basic conditions by activation with a
transition-metal catalyst and/or at high temperature.[5]
Hence the reactivities of diaryliodonium salts as arylating
agents under acidic conditions have rarely been reported to
date.
DiaryliodoniumACHTUNGTRENNUNG(III) salts (Figure 1), in which the iodine
atom adopts a T-shaped form with two bound aryl moieties
and a ligand (X), have been used in organic synthesis as ver-
Our research group has recently become interested in the
chemical behavior of diaryliodonium salts under acidic con-
ditions. During our investigations we have discovered that
unprecedented metal-free oxidative coupling reactions occur
under acidic conditions with in situ formed diaryliodonium
salts of heteroaromatic compounds as the key intermedi-
Figure 1. Structural description of diaryliodoniumACTHNUTRGENUG(N III) salts.
AHCTUNGTRENNUNG
ates.[6a] Later, regioselective dimerization reactions to pro-
satile arylating agents and benzyne precursors as well as for
other applications, such as active bactericides and photoacid
generators (PAG) for cationic polymerization processes.[1]
These compounds are generally air- and moisture-stable,
and in recent years some research groups have successfully
developed convenient synthetic routes to diaryliodonium
salts from nonfunctionalized arenes and hypervalent iodine
reagents or iodoarenes in combination with appropriate
oxidants.[2]
By taking advantage of the excellent leaving ability as
more stable monovalent iodoarene moieties, nucleophilic
substitution reactions with organometallic reagents or eno-
lates under basic conditions[3] as well as transition-metal-cat-
duce head-to-tail bithiophenes were also accomplished by
this strategy.[6b–d] In these studies we unexpectedly discov-
ered the single-electron-transfer (SET) oxidizing ability of
hetACTHNUGRTENUNGeroaryliodonium bromides through the activation of tri-
methylsilyl triflate (TMSOTf) during cross-coupling reac-
tions with electron-rich arenes and heteroaromatic com-
pounds under metal-free conditions (Scheme 1).[7]
Regarding the SET oxidizing ability of a hypervalent
iodine reagent, our research group first discovered in the
early 1990s that various nucleophiles can be introduced into
[a] N. Yamaoka, K. Sumida, I. Itani, H. Kubo, Y. Ohnishi, S. Sekiguchi,
Dr. T. Dohi, Prof. Dr. Y. Kita
College of Pharmaceutical Sciences, Ritsumeikan University
1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577 (Japan)
Fax : (+81)77-561-5829
E-mail: kita@ph.ritsumei.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301148.
Scheme 1. ipso-Substitution of thienyliodonium bromides under acidic
conditions. HFIP=1,1,1,3,3,3-hexafluoroisopropanol.
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

phenyl ethers by the SET oxidation of the aromatic rings in-
duced by phenyliodine
(III) bis(trifluoroacetate) (PIFA).[8a,b]
functionalization of aromatic rings have been reported,[11]
but this led to the production of a large amount of waste
material (Scheme 3, stepwise route B). On the other hand,
we have recently developed a direct dehydrative approach
AHCTUNGTRENNUNG
By using this unique umpolung aromatic ring strategy, a
series of metal-free couplings of nucleophiles[8] as well as
biaryl couplings[9] were achieved with various electron-rich
aromatic compounds in specific solvents and/or in combina-
tion with Lewis acids. Encouraged by these results, SET oxi-
dation reactions with other hypervalent iodine reagents, for
example, [hydroxyACHTUNGTRENNUNG(tosyloxy)iodo]benzene (HTIB, Koserꢁs
reagent), were also recently proposed.[10] On the other hand,
the SET oxidizing ability of diaryliodonium salts has never
been investigated. Our newly discovered coupling of hetero-
aryl-containing diaryliodonium salts is the first and only ex-
ample revealing the unprecedented SET oxidation ability of
the salts.[7]
Nonetheless, it is still unclear whether diaryliodonium
salts containing non-heteroaryl groups can induce the SET
oxidation of aromatic compounds. Therefore we were inter-
ested in investigating the SET oxidizing ability of an exten-
sive series of diaryliodonium salts in the metal-free coupling
of aromatic compounds. To this objective, we now report
our study on the SET oxidation reactions with diaryliodoni-
um salts derived from polyalkoxybenzenes instead of het-
Scheme 3. General approaches for to the preparation of alkoxybenzene-
derived diaryliodonium salts 1.
towards various diaryliodonium salts with polyalkoxyben-
zenes as the starting substrates in fluoroalcohols as sol-
vent,[12] and in a greener strategy, the corresponding iodoni-
um salts 1 were readily prepared without the prefunctionali-
zation of arenes (Scheme 3, direct route A). The use of fluo-
roalcohols can enhance the oxidation of iodine to its triva-
lent form,[13] and thus the preparation of iodonium salts
from aryl iodides by not using a hypervalent iodine com-
pound was also possible.[12e] The counter ions, X, can be
easily exchanged by treating with the required acids or inor-
ganic salts after the preparations.[11f]
ACHTUNGTRENNUNGeroaryls as the aryl ligand on the iodine atom (Scheme 2).
With these diaryliodonium salts 1 in hand, relying on our
previous reaction system,[7] we first examined the iodonium
bromide 1a-Br (X=Br), derived from 1,3,5-trimethoxyben-
zene in the presence of TMSOTf (2 equiv), in the coupling
reaction with 1,4-dimethoxynaphthalene (2a, 1.5 equiv) in
hexafluoroisopropanol (HFIP) as solvent at room tempera-
ture [Eq. (1)].
Scheme 2. New coupling reaction based on the SET mechanism initiated
by polyalkoxybenzene-derived diaryliodonium salts 1.
The reactivities of these salts in the SET oxidation reactions
with Lewis acids and the subsequent ligand transfer into the
generated aromatic radical cations to produce oxidatively
coupled substrates have been investigated in detail.
However, the reaction barely proceeded under these con-
ditions (14% formation of the product 3aa), and the salts
1a-X with other counter ions, for example, Cl, BF4, and
OTf, also gave poor results, producing only the coupling
product 3aa in low yields with HFIP as solvent (up to
45%). Therefore we needed to optimize the reaction condi-
tions for the salt 1a (Table 1). Although HFIP was not a
suitable solvent for the reaction of the alkoxybenzene-de-
rived iodonium salt 1a-X, the less polar fluoroalcohol, 2,2,2-
trifluroethanol (TFE), led to slight improvements in the
yields of 3aa for all the salts 1a-X with different counter
ions (Table 1, entries 1–4). These two fluoroalcohols, HFIP
Results and Discussion
Biaryl coupling reactions of aromatic compounds by using
polyalkoxybenzene-derived diaryliodoniumACTHUNRTGNEUNG(III) salts by the
SET oxidation pathway: In our previous work, the presence
of electron-rich heteroaryl groups in the thienyliodonium-
ACHTUNGTRENNUNG(III) bromides was crucial for initiating the coupling reac-
tions, electron-deficient salts showing no reaction.[7] We thus
speculated on the reactivity of diaryliodonium salts 1 de-
rived from electron-rich alkoxybenzenes. Conventional syn-
thetic approaches to these iodonium salts 1 by the metal
&
2
&
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Oxidative Biaryl Coupling
FULL PAPER
Table 1. Screening of solvents and counterions in the coupling reaction
in Equation (1).[a]
Table 2. Relationship between the reactivity and oxidation potential of
the aromatic compounds 2.[a]
Entry
Counter ion (X)
Solvent
Temperature
Yield [%][b]
1
2
3
4
5
6
7
8
Br
Cl
BF4
OTf
Br
Cl
BF4
OTf
TFE
TFE
TFE
RT
RT
RT
RT
08C–RT
08C–RT
08C–RT
08C–RT
30
67
43
69
39
77
74
85
TFE[c]
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Entry
1
Ar-H (2)
Eox [V]
(vs. SCE)[b]
Product 3
Coupling
G
yield [%][c]
[a] Reagents and conditions: diaryliodonium salt 1a-X (1 equiv), 1,4-di-
methoxynaphthalene (2a, 1.5 equiv), TMSOTf (2 equiv), solvent (0.1m
for the salt 1a-X), 12 h, 08C–RT. [b] Isolated yield after purification.
[c] TFE=2,2,2-trifluoroethanol (CF3CH2OH).
2a
1.10
3aa
74
2
3
2b
2c
1.09
1.59
3ab
3ac
65
31
and TFE, are highly polar solvents exhibiting the empirical
polarity parameters ET(30)=69.3 and 59.5, respectively.[14]
Because the neutral l3 form of the iodonium salts 1 exists in
equilibrium with an ionized species in solution, as shown in
Figure 1, depending on the solvent,[15] it appears in polar
media that the salts 1 are in general fully dissociated or at
least present in the ionized form, which seems to render the
salts 1a-X less reactive during the reaction as a result of sol-
vation. Accordingly, the use of nonpolar dichloromethane as
solvent was examined. The reaction was conducted between
08C and ambient temperature and, fortunately, the reaction
proceeded more readily to give the coupling product 3aa in
higher yields (entries 5–8) than was achieved in the fluoro
alcohols. The iodonium salts with the counter ions Cl, BF4,
and OTf gave acceptable yields of the product 3aa, whereas
1a-Br with a bromo group was less effective due to the in-
stability of this salt relative to the others.
Further optimization of the Lewis acid promoter by using
the iodonium triflate 1a-OTf in dichloromethane revealed
that other silicon- and boron-based Lewis acids, that is, tri-
methylsilyl chloride (TMSCl) and boron trifluoride
(BF3·Et2O), and even Brønsted acids, for example, trifluoro-
acetic acid, were all effective for this reaction (78–83%).
Based on the optimized conditions for the salt 1a-BF4, we
then sought to investigate the scope and limitation of the
coupling partners 2. According to our hypothesis, the diaryl-
4
5
2d
2e
1.64
1.83
3ad
3ae
45[d]
trace
[a] Reagents and conditions: salt 1a-BF4 (1 equiv), arene 2 (1.5 equiv),
TMSOTf (2 equiv), CH2Cl2 (0.1m relative to the salt), 12 h, 08C–RT.
[b] For Ar-H 2, see ref. [16] for the reported values. [c] Isolated yield.
[d] Formation of a very small amount of regioisomer was observed.
1.83 V),[16c] did not react at all and was recovered unreacted.
These results indicate that the salts 1a react with arenes 2
with a range of oxidation potentials below 1.65 V.
We then examined the reactivity of derivatives of the di-
AHCTUNGTREGaNNUN ryliodonium salt 1a. As shown in Scheme 4, the salts 1a-
OTf and 1b-OTf derived from 1,3,5-trimethoxybenzene
gave the coupling product 3aa in excellent yields regardless
of the presence of the 4-CF3 aryl group in 1b-OTf. Interest-
ingly, in the latter case, only the electron-rich 1,3,5-trime-
ACHTUNGTRENNUNGiodonium salts 1 would induce a one-electron oxidation of
the electron-rich arene 2a to generate the corresponding ar-
omatic radical cation species, and thus we explored the rela-
tionship between the oxidation potential of the aromatic
compounds 2 and the yields of the coupling products 3
(Table 2). Electron-rich arenes 2 with low oxidation poten-
tials (ca. 1.10 V (vs SCE)), 1,4-dimethoxynaphthalene (2a)
and anthracene (2b),[16a] readily reacted to give 3aa and 3ab
in yields of 74 and 65%, respectively. On the other hand,
compounds 2 with much higher oxidation potentials were
less effective coupling partners, and lower yields were ob-
served in their reactions, especially for substrates 2c–e,
which have oxidation potentials greater than 1.5 V. Al-
though the salt 1a-BF4 was still reactive towards the aromat-
ic compounds 2c and 2d (Eox =1.59–1.64 V),[16b] phenan-
threne (2e), which is more difficult to oxidize (Eox =
Scheme 4. Reactivity of diaryliodonium salt derivatives 1a–f. Reagents
and conditions: iodonium salt 1-OTf (1 equiv), 1,4-dimethoxynaphthalene
(2a, 1.5 equiv), TMSOTf (2 equiv). CH2Cl2 at 08C–RT for 12 h (see
Table 1).
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

Y. Kita et al.
thoxybenzene moiety coupled with the partner 2a, whereas
the other electron-poor aromatic ring with a trifluoromethyl
group, which preferentially reacts with nucleophiles under
basic conditions,[17] did not participate in the coupling reac-
tion under our acidic conditions. When one of the methoxy
substituents was replaced by a methyl group, salt 1c, the
coupling yield decreased to 57%. When one of the methoxy
substituents was replaced by a hydrogen, salt 1d, the yield
was even lower, and the presence of a methoxy group on
the other aromatic ring, iodonium salt 1e, did not signifi-
cantly affect the reactivity. In brief, the substituent on the
other aromatic ring (R’) was not influential in the coupling
selectivities of the polyalkoxybenzenes. Importantly, the
well-known “ortho effect” rule for anticipating the reactivity
of diaryliodonium salts under basic conditions[18] was totally
invalid for these coupling reactions under acidic conditions.
Thus, the exclusive reaction of the dimethoxyphenyl group
of the iodonium salt 1 f to produce 3da was observed and
not the reaction of the bulkier 4,6-diisopropylaryl group as
predicted by the “ortho effect”. These results clearly show
that the presence of the electron-rich aryl moieties in the io-
donium salts 1 is crucial for inducing the coupling reactions.
Encouraged by these outcomes, we surveyed the coupling
reactions of a range of diaryliodonium triflates 1-OTf and
electron-rich naphthalenes 2 bearing functional groups. Rep-
resentative results are presented in Scheme 5. The diarylio-
Scheme 6. Selectivity of the reaction of 1a with unsymmetrical naphtha-
lenes 2. Reagents and conditions: iodonium salt 1a-X (1 equiv), electron-
rich naphthalene 2 (1.5 equiv) under the optimized condition. [a] The
structure and ratio of the regioisomers 3 and 3’ were determined by
1H NMR and NOE measurements (see the Supporting Information).
[b] The desilylated product was obtained.
thalene 2g. The methyl group in naphthalene 2h acts as a
stronger directing group for the coupling reaction than the
methoxy group, with the product 3’ah with the biaryl link-
age at the position ortho to the methyl group solely ob-
tained. Interestingly, the naphthalene 2i bearing the reso-
nance-donating bromo group directed the selectivity to-
wards the 3-position of the 1,4-disubstituted naphthalene.
Following a similar trend, the product 3’aj was exclusively
obtained in the case of the silyl-protected substrate 2j, al-
though the product was desilylated. On the other hand, the
naphthalenes 2k and 2l, bearing electron-withdrawing OTf
and OAc protecting groups, directed the reactivities of the
naphthalenes towards the 2-position, which is in clear con-
trast to the two previous results. The polyalkoxybiaryls ob-
tained, and their oxidized quinones, belong to a class of
highly valued synthetic intermediates frequently found as
core structures in many natural products.[19] Thus, we dem-
onstrated the elaboration of the biaryl 3aa towards the ben-
zo[b]naphthofuran 4 (Scheme 7, for experimental details see
the Supporting Information).
Scheme 5. Reactivity of diaryliodonium salt derivatives. Reagents and
conditions: iodonium salt 1-X (1 equiv), electron-rich naphthalene
2
(1.5 equiv) under the optimized conditions. [a] The formation of very
small amount of a regioisomer was detected.
donium salt 1g bearing other alkoxy moieties, for example,
an ethoxy group, also showed good reactivity. The function-
alized salt 1h led to ipso substitution at the carbon bound to
the iodine to selectively provide the product 3ha in which
the naphthalene 1a is linked to the ortho position of the cy-
anoalkoxy functionality. Meanwhile, the naphthalene 2 f
bearing the bulkier isobutyl substituent, was also reactive in
the coupling reaction with salt 1a, the corresponding prod-
uct 3af being obtained in high yield.
Scheme 7. Synthesis of benzo[b]naphthofuran 4 from biaryl 3aa.
SET oxidation of the diaryliodoniumACTHNUTRGNE(NUG III) salts 1: With
Next we examined the reactions with unsymmetrical
naphthalenes 2g–l to investigate the regioselectivity of the
reaction (Scheme 6). The regioselectivity was not biased by
the introduction of a bulky alkoxy moiety (R4), the products
3ag and 3’ag being quantitatively obtained from the naph-
regard to the reaction mechanism, in accord with the results
in Table 2 for the SET-sensitive and -inactive substrates 2a–
e, we hypothesize that the SET oxidation process is induced
by the polyalkoxybenzene-derived diaryliodonium
ACHTUNGTRENUN(NG III) salts
1 (Scheme 8). The salts 1 are themselves inactive towards
&
4
&
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Oxidative Biaryl Coupling
FULL PAPER
and high nucleophilicity[22] of the arene 2m. Because the for-
mation of the radical cation of the arene 2m leads to the
rapid dimerization and production of the homocoupling
product under SET oxidation conditions, we studied the ho-
mocoupling reaction of a series of diaryliodonium salts 1.
Similarly to the salt 1a, the reactive and productive iodoni-
um salts 1c and 1d in our coupling reaction (see Scheme 4)
initiated the cation-radical-mediated homocoupling of the
arene 2m (yields of 59 and 61%, respectively). In accord
with our expectations, the nonproductive salt 1i having only
one methoxy group in our coupling reaction gave only trace
amounts of the homocoupling products homo-2m in the re-
action with the arene 2m due to the poor SET activity to-
wards the generation of the radical cation.
Scheme 8. Mechanistic hypothesis for the SET oxidation leading to the
coupling of diaryliodonium salts 1a-X and aromatic compound 2a.
From these results we can conclude that the diaryliodoni-
um salts 1 based on polyalkoxybenzenes have excellent SET
oxidation activities in coupling reactions in comparison with
other diaryliodonium salts (Figure 2).
the aromatic compounds 2, and therefore the Lewis acid
plays an indispensable role in their activation. It seems that
the coordination of the Lewis acid to the ligand X of the
salts 1 increases the electrophilicity of the iodine atom,
which can then form a charge-transfer (CT) complex with
the arene 2. SET oxidation of the electron-rich arene 2
occurs within the complex to generate the radical-ion pair
involving the aromatic radical cation of 2, to which the elec-
tron-rich alkoxyphenyl ring can transfer preferentially over
the phenyl group.[20] As experimental support for this radical
pathway, we tested the reaction of the salts 1a-X with arene
2a in the presence of 1 equiv of a radical scavenger, the gal-
vinoxyl free radical,[21] which resulted in no formation of the
coupling product 3aa.
Figure 2. SET oxidation activity of diaryliodonium salts 1.
Ligand transfer preference in the diaryliodoniumACTHNUTRGENUG(N III) salts
Further investigation based on this hypothesis provided
strong evidence for the SET coupling mechanism. During
the coupling of the salt 1a-OTf with 1,2,4-trimethoxyben-
zene (2m, Scheme 9), the radical homocoupling product
1: In our previous studies, the intermediate aromatic radical
cations formed by treatment with PIFA reacted with exter-
nal aromatic nucleophiles to give various biaryls.[9e–m] Thus,
the reaction with the diaryliodoniumACTHNUTRGNEUNG(III) salts 1 would pro-
ceed not only in the suggested “pseudo-intramolecular” cou-
pling manner through the collapse of the radical-ion pair
(see the mechanism in Scheme 8), but might also cause a
similar intermolecular coupling if a second aromatic nucleo-
phile is present.[23] To gain insight into the ligand-transfer
properties of the arene ligands in the iodonium salts 1, we
further explored the coupling reactions with 1,4-dimethoxy-
naphthalene (2a) and the salts 1 in the presence of a second
nucleophile 5 (Scheme 10). First, the 1,3,5-trimethoxyben-
zene-derived iodonium salt 1a-OTf gave the coupling prod-
uct 3aa as the sole product even in the presence of the addi-
tional aromatic molecule 5, which implies a fast “pseudo-in-
tramolecular” coupling involving the rapid transfer of the
aryl ligand transfer from the salt 1a-OTf. However, the io-
donium salts 1c and 1d bearing dimethoxybenzene moieties
competitively form the intermolecular coupling product 6
with 1,4-dimethoxynaphthalene (2a) and the second arene
5, probably because of the poorer nucleophilicity of the aryl
ligands. The contamination with the latter biaryl 6 during
the coupling reactions can be explained by considering the
same intermediate as in the reactions leading to the cou-
pling products 3, which suggests inferior ligand-transfer abil-
ity of the radical-ion pair formed from the salts 1c-OTf and
1d-OTf with naphthalene 2a (Scheme 10).
Scheme 9. Homocoupling study based on the SET oxidation of the arene
2m. Reagents and conditions: iodonium salts 1-OTf (1 equiv), 1,2,4-tri-
methoxybenzene (2m, 2 equiv), TMSOTf (2 equiv), CH2Cl2 (0.1m of 1-
OTf), 08C–RT. [a] Formation of ca. 10% of the corresponding cross-cou-
pling product 3 was observed (see Scheme 4). [b] 1a-BF4 was used in-
stead of 1a-OTf.
homo-2m was obtained with only a small amount of the
coupling product of 1a-OTf and arene 2m, which has been
attributed to the low oxidation potential (Eox =1.12 V)[16d]
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

Y. Kita et al.
Conclusion
We have succeeded in the oxidative coupling of electron-
rich arenes with the polyalkoxybenzene groups of the
diaryliodoniumACHTUNTRGNEUNG(III) salts 1 in an extended study of heteroar-
omatic iodonium salts.[7] This reaction proceeds without any
metal catalyst and thus occurs by a unique mechanism in-
volving single-electron-transfer (SET) oxidation by the di-
AHCTUNGTREGaNNUN ryliodonium salts 1 followed by electron-rich aryl transfer.
Importantly, the presence of the alkoxy groups on the aro-
matic ring of the salts 1 facilitates the SET oxidation process
and aryl transfer. Note that this is the first observation of
SET oxidation with diaryliodonium salts, providing a new
aspect to the oxidative cross-coupling of polyalkoxyben-
zene-derived compounds. The diaryliodonium salts, which
are usually inert towards many aromatic compounds, are ef-
ficiently activated by a Lewis acid thereby enabling the cou-
pling reactions to proceed. In addition, we have revealed
that the reactivity of the salts 1 under acidic conditions is
quite different to their behavior under known basic condi-
tions. Considering the recent advances in the easy and direct
preparation of diaryliodonium salts, including those bearing
heteroaromatic ligands,[12] this coupling strategy may con-
tribute to the development of this field as a novel alterna-
tive to known coupling technologies and, based on this
Scheme 10. Coupling reaction in the presence of a second aromatic nucle-
ophile 5. Reagents and conditions: iodonium salts 1-OTf (1 equiv), 2a
(1.5 equiv), and 1-cyanomethoxy-3,5-dimethoxybenzene
5 (1 equiv),
TMSOTf (2 equiv), CH2Cl2, 08C–RT for 12 h.
Based on this observation, we can summarize the ligand-
transfer preference of the diaryliodonium salts 1 as shown in
Figure 3. The reactivities of the aryl ligands seem to be in
À
knowledge, some diverse new C C coupling products will
possibly appear in future studies by exploiting the unique
characteristics of the iodonium salts.
Experimental Section
General: Melting points were measured with a Stuart melting point appa-
ratus SMP3 AC input 100 V. 1H (and 13C NMR) spectra were recorded
with a JEOL JMN-400 spectrometer operating at 400 or 300 MHz (100
or 75 MHz) in CDCl3 at 258C with tetramethylsilane as an internal stand-
ard. The data are reported as follows: chemical shift in ppm (d), multi-
plicity (s=singlet, d=doublet, t=triplet, m=multiplet), integration, and
coupling constant (Hz). The IR spectra were obtained by using an Hita-
chi 270-50 spectrometer. High-resolution mass spectra (HRMS) were re-
corded with a JEOL LMS-D 300 spectrometer at the Elemental Analysis
Section of Osaka University and Osaka University of Pharmaceutical
Sciences.
Figure 3. Ligand transfer ability of diaryliodonium salts 1.
good agreement with the electronic nature and nucleophilic-
ity of the aryl rings. Electron-rich aromatic rings in the salts
À
1 are advantageous for developing the C C coupling step
via the radical-ion pair. Thus, the ligands in the salts 1 show
the same trend in ligand-transfer ability as the SET oxida-
tion activities. Achieving both factors by the introduction of
electron-rich aryl moieties is thus highly important for the
success of the coupling reactions.
Diaryliodonium
ACHTUNGTRENNUNG
ybenzenes by treatment with [hydroxyAHCUTNGTRENNUNG
1 equiv) according to our previously reported procedure by using 2,2,2-
trifluoroethanol as solvent.[12] The counter ions, X, of the salts 1 were ex-
changed by treatment with a methanolic aqueous solution of the corre-
sponding metal salts, namely potassium bromide, sodium chloride,
sodium tetrafluoroborate, and sodium triflate.[11f] All other chemicals
were obtained from commercial suppliers and used as received. Column
chromatography for the isolation of the products was carried out on
Merck silica gel 60 (230–400 mesh) eluting with hexane and ethyl acetate.
Analytical TLC was performed on Merck silica gel, grade 60 F254. The
spots and bands were detected by irradiation with UV light (254,
365 nm) and/or by staining with 5% phosphomolybdic acid followed by
heating.
The coupling reactions described in this report show hith-
erto unknown and unusual chemical behavior of the alkoxy-
benzene-derived diaryliodonium salts 1 under acidic condi-
tions that lead to SET oxidation reactions and exclusive
electron-rich aryl transfer. We have established that elec-
tron-rich diaryliodonium salts 1, especially those having
more than two alkoxy groups on the aromatic ring, show
excellent performance in SET oxidation reactions and aryl
transfer to the generated aromatic radical cations of ar-
enes 2.
General procedure for the oxidative coupling reaction by utilizing
diaryliodonium
Schemes 4 and 6): Trimethylsilyl triflate (TMSOTf, 0.18 mL, 1.0 mmol)
was added to a stirred solution of the diaryliodonium salt 1 (0.50 mmol)
and electron-rich arene 2 (0.75 mmol) in dichloromethane (5 mL) under
ACHTUNGTRNE(UGN III) salts 1 with electron-rich arenes 2 (Table 2 and
AHCTUNGTRENNUNG
&
6
&
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Oxidative Biaryl Coupling
FULL PAPER
nitrogen atmosphere at 08C. The reaction mixture was then stirred over-
night as the solution was allowed to warm to ambient temperature. After
completion of the reaction (TLC), aqueous saturated sodium hydrogen
carbonate was added to the reaction mixture, and the aqueous phase was
extracted with dichloromethane three times. The combined extracts were
dried over anhydrous sodium sulfate and then evaporated to dryness.
The crude residue was purified by column chromatography on silica gel
to give the pure coupled biaryls 3.
[2] For recent advances, see: a) M. D. Hossain, T. Kitamura, Tetrahe-
dron 2006, 62, 6955–6960; b) M. D. Hossain, Y. Ikegami, T. Kita-
mura, J. Org. Chem. 2006, 71, 9903–9905; c) L. Kraszkiewicz, L.
Skulski, Synthesis 2008, 2373–2380; d) M. Bielawski, M. Zhu, B.
Olofsson, Adv. Synth. Catal. 2007, 349, 2610–2618; e) M. Bielawski,
D. Aili, B. Olofsson, J. Org. Chem. 2008, 73, 4602–4607; f) N. Jalali-
an, B. Olofsson, Tetrahedron 2010, 66, 5793–5800; g) E. A. Merritt,
V. M. T. Carneiro, L. F. Silva, Jr., B. Olofsson, J. Org. Chem. 2010,
75, 7416–7419; see, also reference [12].
[3] For early reports, see: a) F. M. Beringer, A. Brierley, M. Drexler,
E. M. Gindler, C. C. Lumpkin, J. Am. Chem. Soc. 1953, 75, 2708–
2712; b) A. Dibbo, L. Stephenson, T. Walker, W. K. Warburton, J.
Chem. Soc. 1961, 2645–2651; c) J. R. Crowder, E. E. Glover, M. F.
Grundon, H. X. Kaempfen, J. Chem. Soc. 1963, 4578–4585; d) J. J.
Lubinkowski, J. W. Knapczyk, J. L. Calderon, L. R. Petit, W. E.
McEwen, J. Org. Chem. 1975, 40, 3010–3015; Recent reports: e) P.-
O. Norrby, T. B. Petersen, M. Bielawski, B. Olofsson, Chem. Eur. J.
2010, 16, 8251–8254; f) F. Guo, L. Wang, P. Wang, J. Yu, J. Han,
Asian J. Org. Chem. 2012, 1, 218–221; g) J. Wen, R.-Y. Zhang, S.-Y.
Chen, J. Zhang, X.-Q. Yu, J. Org. Chem. 2012, 77, 766–771; h) J. Li,
L. Liu, RSC Adv. 2012, 2, 10485–10487; i) N. Jalalian, T. B. Petersen,
B. Olofsson, Chem. Eur. J. 2012, 18, 14140–14149, and references
cited therein.
[4] a) F. Bellina, R. Rossi, Tetrahedron 2009, 65, 10269–10310, and ref-
erences therein; for recent reports, see: b) W. Li, J. Zhang, Chem.
Commun. 2010, 46, 8839–8841; c) A. M. Wagner, M. S. Sanford,
Org. Lett. 2011, 13, 288–291; d) R. J. Phipps, L. McMurray, S. Ritter,
H. A. Duong, M. J. Gaunt, J. Am. Chem. Soc. 2012, 134, 10773–
10776; e) D. Lubriks, I. Sokolovs, E. Suna, J. Am. Chem. Soc. 2012,
134, 15436–15442; f) N. Gigant, L. Chausset-Boissarie, M.-C. Bel-
homme, T. Poisson, X. Pannecoucke, I. Gillaizeau, Org. Lett. 2013,
15, 278–281; g) S. Rousseaux, E. Vrancken, J.-M. Campagne,
Angew. Chem. 2012, 124, 11092–11094; Angew. Chem. Int. Ed. 2012,
51, 10934–10935 and references therein; early reports h) Y. Tamura,
M. W. Chun, K. Inoue, J. Minamikawa, Synthesis 1978, 822; i) S. K.
Kang, H. W. Lee, S. B. Jang, P. S. Ho, J. Org. Chem. 1996, 61, 4720–
4724.
[5] a) S. Castro, J. J. Fernandez, R. Vicente, F. J. Fananas, F. Rodriguez,
Chem. Commun. 2012, 48, 9089–9091; b) L. Ackermann, M. Del-
l’Acqua, S. Fenner, R. Vicente, R. Sandmann, Org. Lett. 2011, 13,
2358–2360; c) J. Yan, M. Zhu, Z. Zhou, Eur. J. Org. Chem. 2006,
2060–2062; d) J. Yan, W. Hu, G. Rao, Synthesis 2006, 943–945.
[6] a) Y. Kita, K. Morimoto, M. Ito, C. Ogawa, A. Goto, T. Dohi, J.
Am. Chem. Soc. 2009, 131, 1668–1669; b) K. Morimoto, N. Yamao-
ka, C. Ogawa, T. Nakae, H. Fujioka, T. Dohi, Y. Kita, Org. Lett.
2010, 12, 3804–3807; c) K. Morimoto, T. Nakae, N. Yamaoka, T.
Dohi, Y. Kita, Eur. J. Org. Chem. 2011, 6326–6334; d) T. Dohi, N.
Yamaoka, S. Nakamura, K. Sumida, K. Morimoto, Y. Kita, Chem.
Eur. J. 2013, 19, 2067–2075.
1,4-Dimethoxy-2-(2,4,6-trimethoxyphenyl)naphthalene (3aa). A colorless
1
solid; m.p. 143–1458C; H NMR (400 MHz, CDCl3): d=3.62 (s, 3H), 3.74
(s, 3H), 3.90 (s, 6H), 3.96 (s, 3H), 6.30 (s, 2H), 6.61 (s, 1H), 7.45–7.54
(m, 2H), 8.14 (dd, J=7.6, 0.7 Hz, 1H), 8.26 ppm (dd, J=7.6, 0.7 Hz,
1H); 13C NMR (75 MHz, CDCl3): d=55.3, 55.5, 55.9, 61.2, 90.8, 108.0,
109.5, 122.1, 122.2, 122.6, 125.0, 126.0, 126.1, 128.7, 147.9, 150.9, 158.7,
160.9 ppm; IR (KBr): n˜ =2937, 2837, 1606, 1504, 1454, 1415, 1365, 1334,
1222, 1203, 1157, 1126, 1101, 1070, 1037, 999, 970, 948, 844, 812, 771,
567 cmÀ1; elemental analysis calcd (%) for C21H22O5: C 71.17, H 6.26;
found: C 71.04, H, 6.26.
Competitive coupling reactions of 1,4-dimethoxynaphthalene 2a versus 1-
cyanomethoxy-3,5-dimethoxybenzene 5 (Scheme 10): TMSOTf (0.18 mL,
1.00 mmol) was added to a stirred solution containing diaryliodonium
salts 1-OTf (0.50 mmol), 1,4-dimethoxynaphthalene (2a; 0.75 mmol), and
1-cyanomethoxy-3,5-dimethoxybenzene (5, 0.50 mmol) in dichlorome-
thane (5 mL) under nitrogen atmosphere at 08C. The reaction mixture
was then stirred at 08C to ambient temperature for 12 h. After comple-
tion of the reaction (TLC), aqueous saturated sodium hydrogen carbo-
nate was added to the mixture and the aqueous phase was extracted with
dichloromethane. The combined extract was dried over anhydrous
sodium sulfate and then evaporated to dryness. The crude residue was
purified by column chromatography on silica gel to separate the pure
cross-coupling biaryls 3aa, 3cc,or 3da and 6.
2-(1-Cyanomethoxy-3,5-dimethoxyphenyl)-1,4-dimethoxynaphthalene (6).
A colorless amorphous solid; 1H NMR (400 MHz, CDCl3): d=3.57 (s,
3H), 3.74 (s, 3H), 3.89 (s, 3H), 3.94 (s, 3H), 4.56–4.67 (m, 2H), 6.38–6.40
(m, 2H), 6.56 (s, 1H), 7.47–7.52 (m, 2H), 8.10 (dd, J=8.0, 1.0 Hz, 1H),
8.25 ppm (dd, J=8.0, 1.0 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=54.7,
55.5, 55.6, 56.0, 61.4, 93.4, 93.8, 107.4, 111.2, 115.4, 121.5, 122.2, 122.3,
125.4, 126.2, 126.3, 128.6, 147.8, 151.2, 155.6, 159.1, 161.0 ppm; IR (KBr):
n˜ =3071, 3004, 2938, 2842, 2251, 1611, 1582, 1505, 1459, 1419, 1390, 1368,
1327, 1269, 1224, 1200, 1160, 1124, 1071, 1047, 998, 971, 948, 912, 814,
771, 738, 670, 651 cmÀ1; HRMS (EI) calcd for C20H21NO5 [M]+: 379.1420;
found: 379.1414.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (A)
and Encouragement of Young Scientists (A) from the JSPS, a Grant-in-
Aid for Scientific Research on Innovative Areas “Advanced Molecular
Transformations by Organocatalysts” from MEXT, and the Ritsumeikan
Global Innovation Research Organization (R-GIRO) Project. T.D. is
grateful for financial support from the Asahi Glass Foundation and the
Industrial Technology Research Grant Program of NEDO of Japan. N.Y.
thanks the JSPS for Young Scientists for a research fellowship.
[7] T. Dohi, M. Ito, N. Yamaoka, K. Morimoto, H. Fujioka, Y. Kita,
Angew. Chem. 2010, 122, 3406–3409; Angew. Chem. Int. Ed. 2010,
49, 3334–3337.
[8] a) Y. Kita, H. Tohma, M. Inagaki, K. Hatanaka, T. Yakura, Tetrahe-
dron Lett. 1991, 32, 4321–4324; b) Y. Kita, H. Tohma, K. Hatanaka,
T. Takada, S. Fujita, S. Mitoh, H. Sakurai, S. Oka, J. Am. Chem. Soc.
1994, 116, 3684–3691; Account: c) Y. Kita, T. Takada, H. Tohma,
Pure Appl. Chem. 1996, 68, 627–630; d) Y. Kita, T. Takada, S.
Mihara, B. A. Whelan, H. Tohma, J. Org. Chem. 1995, 60, 7144–
7148; e) Y. Kita, M. Egi, A. Okajima, M. Ohtsubo, T. Takada, H.
Tohma, Chem. Commun. 1996, 1491–1492; f) Y. Kita, M. Egi, M.
Ohtsubo, T. Saiki, T. Takada, H. Tohma, Chem. Commun. 1996,
2225–2226; g) Y. Kita, H. Watanabe, M. Egi, T. Saiki, Y. Fukuoka,
H. Tohma, J. Chem. Soc. Perkin Trans. 1 1998, 635–636; h) Y. Kita,
M. Egi, H. Tohma, Chem. Commun. 1999, 143–144; i) M. Arisawa,
N. G. Ramesh, M. Nakajima, H. Tohma, Y. Kita, J. Org. Chem.
2001, 66, 59–65; j) H. Hamamoto, K. Hata, H. Nambu, Y. Shiozaki,
H. Tohma, Y. Kita, Tetrahedron Lett. 2004, 45, 2293–2295; k) H.
Hamamoto, Y. Shiozaki, H. Nambu, K. Hata, H. Tohma, Y. Kita,
Chem. Eur. J. 2004, 10, 4977–4982; l) K. Hata, H. Hamamoto, Y.
[1] For reviews, see: a) E. A. Merritt, B. Olofsson, Angew. Chem. 2009,
121, 9214–9234; Angew. Chem. Int. Ed. 2009, 48, 9052–9070;
b) M. S. Yusubov, A. V. Maskaev, V. V. Zhdankin, ARKIVOC (Gain-
esville, FL, U.S.) 2011, 1, 370–409; c) P. J. Stang, J. Org. Chem. 2003,
68, 2997–3008; d) V. V. Zhdankin, P. J. Stang, Chem. Rev. 2008, 108,
5299–5358; e) G. F. Koser in The Chemistry of Functional Groups,
Supplement D (Eds.: S. Patai, Z. Rappoport), Wiley, New York,
1983, Chapter 25; f) J. M. C. Frechet, Pure Appl. Chem. 1992, 64,
1239–1248; g) N. R. Deprez, M. S. Sanford, Inorg. Chem. 2007, 46,
1924–1935; h) U. Mffller, Trends Photochem. Photobiol. 1999, 5,
117–138.
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

Y. Kita et al.
Shiozaki, Y. Kita, Chem. Commun. 2005, 2465–2467; m) T. Dohi, K.
Morimoto, Y. Kiyono, H. Tohma, Y. Kita, Org. Lett. 2005, 7, 537–
540; n) T. Dohi, K. Morimoto, N. Takenaga, A. Goto, A. Maruyama,
Y. Kiyono, H. Tohma, Y. Kita, J. Org. Chem. 2007, 72, 109–116;
o) K. Hata, H. Hamamoto, Y. Shiozaki, S. B. Cämmerer, Y. Kita,
Tetrahedron 2007, 63, 4052–4060; p) T. Dohi, M. Ito, N. Yamaoka,
K. Morimoto, H. Fujioka, Y. Kita, Tetrahedron 2009, 65, 10797–
10815.
[15] a) F. M. Beringer, M. Mausner, J. Am. Chem. Soc. 1958, 80, 4535–
4536; b) Y. Yamada, K. Kashima, M. Okawara, Polym. Lett. Ed.
1976, 14, 65–71; c) N. P. Hacker, D. V. Leff, J. L. Dektar, J. Org.
ˇˇ
Chem. 1991, 56, 2280–2282; d) Y.-S. Lee, M. Hodoscek, J.-H. Chun,
V. W. Pike, Chem. Eur. J. 2010, 16, 10418–10423; e) V. V. Grushin,
Acc. Chem. Res. 1992, 25, 529–536; it has been reported that nucle-
ophilic substitution was more difficult in highly polar solvents, see:
f) T. Sato, K. Shimizu, H. Moriya, J. Chem. Soc. Perkin Trans. 1
1974, 1537–1539.
[9] For the Lewis acid activation of phenyliodineACTHNUTRGNEUG(N III) bis(trifluoroace-
[16] a) A. Zweig, A. H. Maurer, B. G. Roberts, J. Org. Chem. 1967, 32,
1322–1329; b) P. H. Milne, D. D. M. Wayner, Can. J. Chem. 1992,
70, 121–127; c) V. D. Parker, J. Am. Chem. Soc. 1976, 98, 98–103;
d) S. Farid, J. P. Dinnocenzo, P. B. Merkel, R. H. Young, D. Shukla,
G. Guirado, J. Am. Chem. Soc. 2011, 133, 11580–11587.
[17] a) Y. Yamada, M. Okawara, Bull. Chem. Soc. Jpn. 1972, 45, 2515–
2519; b) C.-H. Oh, J.-S. Kim, H.-H. Jung, J. Org. Chem. 1999, 64,
1338–1343; c) T. B. Petersen, R. Khan, B. Olofsson, Org. Lett. 2011,
13, 3462–3465, and references therein; d) D. B. Haydock, T. P. C.
Mulholland, B. Telford, J. M. Thorp, J. S. Wain, Eur. J. Med. Chem.
1984, 19, 205–214; e) T. L. Ross, J. Ermert, C. Hocke, H. H.
Coenen, J. Am. Chem. Soc. 2007, 129, 8018–8025.
[18] a) Y. Yamada, M. Okawara, Bull. Chem. Soc. Jpn. 1972, 45, 1860–
1863; b) K. M. Lancer, G. H. Wiegand, J. Org. Chem. 1976, 41,
3360–3364; c) V. V. Grushin, I. I. Demkina, T. P. Tolstaya, J. Chem.
Soc. Perkin Trans. 2 1992, 505–511; d) S. Martín-Santamaría, M. A.
Carroll, C. M. Carroll, C. D. Carter, V. W. Pike, H. S. Rzepa, D. A.
Widdowson, Chem. Commun. 2000, 649–650; e) M. A. Carroll,
R. A. Wood, Tetrahedron 2007, 63, 11349–11354, and references
therein.
[19] a) C. Hertweck, Angew. Chem. 2009, 121, 4782–4811; Angew. Chem.
Int. Ed. 2009, 48, 4688–4716; b) G. Bringmann, C. Gunther, M.
Ochse, O. Schupp, S. Tasler, Prog. Chem. Org. Nat. Prod. 2001, 82,
1–293; c) C. A. James, V. Snieckus, J. Org. Chem. 2009, 74, 4080–
4093; d) A. Martínez, J. C. Barcia, A. M. EstØvez, F. Fernµndez, L.
Gonzµlez, J. C. EstØvez, R. J. EstØvez, Tetrahedron Lett. 2007, 48,
2147–2149; e) K. Yoshida, Y. Ooyama, H. Miyazaki, S. Watanabe, J.
Chem. Soc. Perkin Trans. 2 2002, 700–707; f) A. Arienti, F. Bigi, R.
Maggi, P. Moggi, M. Rastelli, G. Sarttori, A. Trer›, J. Chem. Soc.
Perkin Trans. 1 1997, 1391–1393; g) H. E. Hçgberg, J. Chem. Soc.
Perkin Trans. 1 1979, 2517–2520.
tate) (PIFA) and its derivatives during the SET-induced oxidative
biaryl coupling reactions, see: a) Y. Kita, M. Gyoten, M. Ohtsubo,
H. Tohma, T. Takada, Chem. Commun. 1996, 1481–1482; b) T.
Takada, M. Arisawa, M. Gyoten, R. Hamada, H. Tohma, Y. Kita, J.
Org. Chem. 1998, 63, 7698–7706; c) H. Hamamoto, G. Anilkumar,
H. Tohma, Y. Kita, Chem. Commun. 2002, 450–451; d) H. Hamamo-
to, G. Anilkumar, H. Tohma, Y. Kita, Chem. Eur. J. 2002, 8, 5377–
5383; e) M. Arisawa, S. Utsumi, M. Nakajima, N. G. Ramesh, H.
Tohma, Y. Kita, Chem. Commun. 1999, 469–470; f) H. Tohma, H.
Morioka, S. Takizawa, M. Arisawa, Y. Kita, Tetrahedron 2001, 57,
345–352; g) T. Dohi, M. Ito, I. Itani, N. Yamaoka, K. Morimoto, H.
Fujioka, Y. Kita, Org. Lett. 2011, 13, 6208–6211; h) H. Tohma, M.
Iwata, T. Maegawa, Y. Kita, Tetrahedron Lett. 2002, 43, 9241–9244;
i) T. Dohi, M. Ito, K. Morimoto, M. Iwata, Y. Kita, Angew. Chem.
2008, 120, 1321–1324; Angew. Chem. Int. Ed. 2008, 47, 1301–1304;
For heteroaromatic compounds: j) H. Tohma, M. Iwata, T. Maega-
wa, Y. Kiyono, A. Maruyama, Y. Kita, Org. Biomol. Chem. 2003, 1,
1647–1649; k) T. Dohi, K. Morimoto, Y. Kiyono, A. Maruyama, H.
Tohma, Y. Kita, Chem. Commun. 2005, 2930–2932; l) T. Dohi, K.
Morimoto, A. Maruyama, Y. Kita, Org. Lett. 2006, 8, 2007–2010;
m) T. Dohi, K. Morimoto, M. Ito, Y. Kita, Synthesis 2007, 2913–
2919.
[10] a) G. F. Koser, S. Telu, K. K. Laali, Tetrahedron Lett. 2006, 47, 7011–
7015; b) S. Telu, S. Durmus, G. F. Koser, Tetrahedron Lett. 2007, 48,
1863–1866.
[11] a) F. M. Beringer, J. W. Dehn Jr, M. Winicov, J. Am. Chem. Soc.
1960, 82, 2948–2952; b) G. F. Koser, R. H. Wettach, C. S. Smith, J.
Org. Chem. 1980, 45, 1543–1544; c) A. J. Margida, G. F. Koser, J.
Org. Chem. 1984, 49, 4703–4706; d) M. Ochiai, M. Toyonari, T.
Sueda, Y. Kitagawa, Tetrahedron Lett. 1996, 37, 8421–8424; e) V. W.
Pike, F. Butt, A. Shah, D. A. Widdowson, J. Chem. Soc. Perkin
Trans. 1 1999, 245–248; f) M. A. Carroll, V. W. Pike, D. A. Wid-
dowson, Tetrahedron Lett. 2000, 41, 5393–5396.
[20] Carbon group transfers from the iodineACTHNUTRGNE(NUG III) atom to aromatic radi-
cal cations have rarely been proposed, see references [8m,n] and
[10b].
[12] a) T. Dohi, M. Ito, K. Morimoto, Y. Minamitsuji, N. Takenaga, Y.
Kita, Chem. Commun. 2007, 4152–4154; b) M. Ito, C. Ogawa, N.
Yamaoka, H. Fujioka, T. Dohi, Y. Kita, Molecules 2010, 15, 1918–
1931; c) T. Dohi, N. Yamaoka, Y. Kita, Tetrahedron 2010, 66, 5775–
5785; d) M. Ito, I. Itani, Y. Toyoda, K. Morimoto, T. Dohi, Y. Kita,
Angew. Chem. 2012, 124, 12723–12726; Angew. Chem. Int. Ed. 2012,
51, 12555–12558; e) T. Dohi, N. Yamaoka, I. Itani, Y. Kita, Aust. J.
Chem. 2011, 64, 529–535.
[21] a) P. D. Bartlett, S. T. Purrington, J. Am. Chem. Soc. 1966, 88, 3303–
3309; b) J. F. Areizaga, G. M. Guzman, Makromol. Chem. Macro-
mol. Symp. 1988, 20/21, 77–82; see also reference [9].
[22] a) H. Mayr, T. Bug, M. F. Gotta, N. Hering, B. Irrgang, B. Janker, B.
Kempf, R. Loos, A. R. Ofial, G. Remennikov, H. Schimmel, J. Am.
Chem. Soc. 2001, 123, 9500–9512; b) H. Mayr, B. Kempf, A. R.
Ofial, Acc. Chem. Res. 2003, 36, 66–77; c) J. Ammer, C. Nolte, H.
Mayr, J. Am. Chem. Soc. 2012, 134, 13902–13911.
[13] a) T. Dohi, A. Maruyama, Y. Minamitsuji, N. Takenaga, Y. Kita,
Chem. Commun. 2007, 1224–1226; b) Y. Minamitsuji, D. Kato, H.
Fujioka, T. Dohi, Y. Kita, Aust. J. Chem. 2009, 62, 648–652; c) T.
Dohi, Y. Kita, Chem. Commun. 2009, 2073–2085.
[14] a) C. Reichardt, Angew. Chem. 1979, 91, 119–131; Angew. Chem.
Int. Ed. Engl. 1979, 18, 98–110; b) C. Reichardt, T. Welton, Solvents
and Solvent Effects in Organic Chemistry, Wiley-VCH, Weinheim,
2010; c) A. R. Katritzky, D. C. Fara, H. Yang, K. Tämm, Chem. Rev.
2004, 104, 175–198; d) C. Reichardt, Org. Process Res. Dev. 2007,
11, 105–113.
[23] For a discussion of radical reactions in coordination spheres, see:
a) M. Kameyama, N. Kamigata, M. Kobayashi, J. Org. Chem. 1987,
52, 3312–3316 and references therein; b) J. D. Morrison, Assymmet-
ric Synthesis Academic, New York, 1985, Vol.5; c) P. R. Schreiner,
A. A. Fokin, Chem. Rec. 2004, 3, 247–257; d) S. Hashizume, K.
Oisaki, M. Kanai, Chem. Rec. 2011, 11, 236–241.
Received: March 26, 2013
Revised: July 7, 2013
Published online: && &&, 0000
&
8
&
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Oxidative Biaryl Coupling
FULL PAPER
Biaryl Coupling
N. Yamaoka, K. Sumida, I. Itani,
H. Kubo, Y. Ohnishi, S. Sekiguchi,
T. Dohi, Y. Kita* ............. &&&& — &&&&
Single-Electron-Transfer (SET)-
Induced Oxidative Biaryl Coupling by
Polyalkoxybenzene-Derived
Coupling in the pair: Metal-free oxida-
(SET) oxidation towards electron-rich
aromatic compounds and subsequently
transfer the polyalkoxyphenyl group
into in situ generated aromatic radical
cations to produce biaryl products (see
scheme).
À
tive C C coupling to yield electron-
rich biaryls have been achieved by
using polyalkoxybenzene-derived
DiaryliodoniumACTHNUGTRNEUNG(III) Salts
diaryliodoniumACHTUNGTRENNUNG(III) salts as both the
oxidant and aryl source. These salts
can induce single-electron-transfer
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!