COMMUNICATION
DOI: 10.1002/chem.201102770
Copper(II)-Catalyzed Monoarylation of Vicinal Diols with Diaryliodonium
Salts
Masami Kuriyama,* Norihisa Hamaguchi, and Osamu Onomura*[a]
vate diols[13] and catalyze C O bond formation[14] in the cou-
pling of vicinal diols with diaryliodonium salts. A series of
diphenyliodonium salts was examined in the monophenyla-
tion of cis-1,2-cyclooctanediol (1a) catalyzed by copper(II)
triflate, which was conducted in the presence of potassium
phosphate tribasic in toluene at 1008C (Table 1). Iodonium
À
The selective transformation of diols is one of the signifi-
cant challenges in organic synthesis, especially when they
contain sterically and electronically similar hydroxyl
groups.[1,2] In particular, the selective monoarylation of vici-
nal diols is highly important, because some kinds of aryl
groups, such as 4-methoxyphenyl, 4-chlorophenyl, and 4-ni-
trophenyl groups, have been utilized for the protection of
hydroxyl groups[3] and b-aryloxy alcohols, which can be pre-
pared by monoarylation of vicinal diols, are known as useful
synthetic intermediates.[4] Over the past decade, catalytic
Table 1. Screening of diphenyliodonium salts.[a]
À
methods for the C O bond formation have been actively
pursued and even the catalytic arylation of primary and sec-
ondary alcohols was successfully achieved, overcoming prob-
lems such as b-hydrogen elimination and the use of a large
Entry
X
Yield [%][b]
Entry
X
Yield [%][b]
1
2
3
4
Cl
Br
I
13
21
11
20
5
6
7
8
ClO4
OTf
BF4
PF6
37
72
61
61
excess of alcohols.[5,6] In spite of these efforts, the mono
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
NO3
monophenylation of diols was reported as a non-catalytic
version with triphenylbismuth diacetate.[7] Then, copper(II)
was found to be an effective catalyst in this reaction,[8a]
which was applied for the development of enantioselective
monophenylations of diols.[8b–d] In terms of usefulness in or-
ganic synthesis, more efficient processes with a broad scope
of substrates are desirable.
[a] Reaction conditions: Diol 1a (1.0 mmol), diphenyliodonium salt
(1.5 mmol), Cu(OTf)2 (10 mol%), K3PO4 (2.0 mmol), toluene (2.0 mL),
1008C, 15 h. [b] Isolated yield.
AHCTUNGTRENNUNG
salts bearing stable polyatomic anions showed higher reac-
tivity than iodonium halides, which could be dependent on
their solubilities,[10e] and diphenyliodonium triflate was
found to be a superior reagent.
Recently, diaryliodonium salts have attracted attention as
selective, nontoxic, and easily available reagents.[9] While
the cross-coupling reaction of phenol derivatives with diACTHNUTRGNEUaGN ryl-
A
Therefore, optimization of the reaction conditions was
carried out with cis-1,2-cyclooctanediol (1a) and diphenyl-
AHCTUNGTREGiNNUN odonium triflate (2a) as model substrates (Table 2). The ex-
method towards diaryl ethers,[10,11] the synthesis of alkyl–aryl
ethers with diaryliodonium salts requires an excess of alkox-
ides.[12] We envisaged that diaryliodonium salts could ach-
ploration of bases revealed that sodium phosphate tribasic
was the reagent of choice (entries 1–7). Both mono- and di-
valent copper salts with stable anions served as good cata-
lysts and copper(II) triflate showed superior catalytic activi-
ty (entries 2 and 8–14). On the other hand, the reaction
without catalyst resulted in drastically reduced yield
(entry 15). The influence of solvents was examined and tolu-
ene proved to be most suitable, while more polar solvents
led to lower yields (entries 2, 16, and 17). Decreasing the
amount of toluene improved the reaction efficiency, giving
the desired compound 3aa in 93% yield without the diphe-
nylated product (entry 18).
In addition, this reaction system showed high chemoselec-
tivity, even in the phenylation reaction using a 1:1 mixture
of cis-1,2-cyclooctanediol (1a) and cyclooctanol, to give cis-
2-phenoxycyclooctanol (3aa) and phenoxycyclooctane in 92
and 5% yields, respectively (Scheme 1).
ieve high efficiency in the C O bond formation with diols
and the coupling of alcohols with this type of reagents has
not been widely explored.[9c,12] Herein, we would like to
report the copper(II)-catalyzed monoarylation of vicinal
diols with diaryliodonium triflates.
In the earliest stage of investigation, we selected copper
salts as catalysts, because of their potential abilitiy to acti-
[a] Dr. M. Kuriyama, N. Hamaguchi, Prof. Dr. O. Onomura
Graduate School of Biomedical Sciences
Nagasaki University, 1-14 Bunkyo-machi
Nagasaki 852-8521 (Japan)
Chem. Eur. J. 2012, 18, 1591 – 1594
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1591