1
140
Chemistry Letters Vol.35, No.10 (2006)
Copper(II)-catalyzed O-Phenylation of Alcohols with Organobismuth(V) Reagents:
A Convenient Method for the Synthesis of Simple tert-Alkyl Phenyl Ethers
ꢀ1;2
1
1
Teruaki Mukaiyama, Naoto Sakurai, and Kazuhiro Ikegai
Center for Basic Research, The Kitasato Institute, 6-15-5 (TCI) Toshima, Kita-ku, Tokyo 114-0003
1
2
Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641
Received July 6, 2006; CL-060768; E-mail: mukaiyam@abeam.ocn.ne.jp)
(
Table 1. Effect of organobismuth reagents
A convenient method for copper(II)-catalyzed O-phenyla-
tion of simple alcohols with organobismuth(V) compounds un-
der mild conditions is described. Treatment of tetraphenylbis-
muth fluoride (Ph4BiF) with various simple alcohols in the pres-
1.6 equiv. Bi reagent
cat. Cu(OAc)2
OH
2 equiv. Cy NMe
OPh
2
II
1a
CH Cl , rt, 3 h
2a
ence of a catalytic amount of Cu acetate affords the correspond-
2
2
ing phenyl ethers in good yields and the present reaction is
successfully applied to the prepararion of various tert-alkyl
phenyl ethers.
a
Entry
Bi reagent
Cu(OAc)2/mol %
Yield/%
b
1
2
3
4
5
Ph3Bi(OAc)2
15
15
15
15
15
15
5
ND
þ
ꢁ
[Ph4Bi ][BF4 ]
ND
ND
ND
6
54
3
þ ꢁ
[Ph4Bi ][OTf ]
þ
ꢁ
[Ph4Bi ][OTs ]
Ph4BiOCOCF3
Ph BiF
To date, a C(aryl)–O bond formation was generally carried
out by using transition metal-catalyzed (Cu or Pd) coupling reac-
1
6
7
tions between aryl halides and alcohols developed by Buchwald
2
4
4
Ph BiF
b
and Hartwig. The copper-catalyzed reaction (classical Ullmann
type) needed harsh reaction conditions and no reaction was dem-
onstrated concerning tertiary alcohols under above-mentioned
conditions. The Pd-catalyzed reaction was applied to tertiary al-
cohols, however, it needed to use a strongly basic nucleophile
a
Isolated yields. Not Detected.
3
þ
ꢁ
13
[Ph4Bi ][OTs ] were employed, the expected phenyl ether
was not formed (Entries 1–4). Instead, the desired phenyl ether
was obtained in 6 and 54% yields, respectively, when the
reaction was carried out in the presence of Ph4BiOCOCF313 or
Ph4BiF (Entries 5 and 6) though the reaction was sluggish by us-
ing 5 mol % of Cu(OAc)2 (Entry 7). It was assumed that reactiv-
ity of organobismuth(V) reagents correlate with the cationic
4
such as alkoxide. Recently, Batey reported that an alternative
C(aryl)–O bond formation by using cross-coupling reaction of
potassium organotrifluoroborate salts and alcohols proceeded
under mild conditions which is a modified protocol of Chan–
Evans’s method, whereas etherification of tertiary alcohols did
not proceed at all.5
˚
character of Bi atom (Bi–F bond of Ph4BiF was 2.218 A and
þ ꢁ þ ꢁ
˚
Bi –O bond of [Ph4Bi ][OTs ] was 2.77 A).
9,13
Arylations of simple alcohols by using organobismuth re-
6
agents were studied intensively by Barton, Finet, and Dodonov.
However, fewer examples were reported in the case of tertiary
alcohols and the yields were moderate. Recently, it was reported
In the next place, the effects of copper salts and of solvents
were examined. O-Phenylation of 1a was examined by the com-
bined use of Ph4BiF (1.6 equiv.), copper salts (15 mol %) and
Cy2NMe (2 equiv.) in various solvents at room temperature,
and the results are summarized in Table 2. It was shown that
II
from our laboratory that Cu -catalyzed O-phenylation of
functionalized tertiary alcohols proceed smoothly by using
7
triphenyl or tetraphenyl bismuth(V) complexes (Ph3Bi(OAc)2,
[
þ ꢁ
8
9
10
Table 2. Effect of solvents and copper salts
Ph4Bi ][BF4 ], or Ph4BiF ) as phenyl donor. In the above
examples, the participation of a neighboring functional group
such as carbonyl group was needed to complete the full conver-
1.6 equiv. Ph BiF
4
1
2
5 mol % Copper salt
equiv. Cy NMe
6
a,11
2
sion to afford the corresponding ethers.
Thus, effective
1a
2a
C(aryl)–O bond formation of simple tertiary alcohols such as
t-butanol under mild conditions has not yet been developed.
Now, we would like to describe a convenient and successful
method for the phenylation of simple alcohols with Ph4BiF
in the presence of Cu(OAc)2. Further, we discussed remarkable
reactivity differences of organobismuth(V) reagents and effects
of copper salts.
Solvent, rt, 3 h
a
Entry
Copper salt
Solvent
Yield/%
1
2
3
4
5
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
MEK
THF
CH3CN
DMF
toluene
toluene
toluene
toluene
toluene
toluene
59
49
43
22
84
In the first place, the effects of Bi reagents were examined
by taking 2-methyl-4-phenylbutan-2-ol (1a) as a simple sub-
b
6
quant.
trace
63
V
7
8
9
CuOAc
strate. The results of the reaction of various Bi reagents with
1a in the coexistence of a catalytic amount of Cu(OAc)2 and 2
.
Cu(OCOCF3)2 xH2O
Cu(OTf)2
c
ND
ND
equiv. of a base, N,N-dicyclohexylmethylamine (Cy2NMe),
are summarized in Table 1. When triphenylbismuth complex
such as Ph3Bi(OAc)2 and cationic tetraphenylbismuthonium
1
0
CuF2
aIsolated yields. b2 equiv. of Ph BiF and 20 mol % of
4
þ
ꢁ
þ
ꢁ
12
c
complexes such as [Ph4Bi ][BF4 ], [Ph4Bi ][OTf ], or
Cu(OAc) were used. Not Detected.
2
Copyright Ó 2006 The Chemical Society of Japan