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Chemistry Letters Vol.36, No.7 (2007)
New Preparative Method of Aryl Tosylates by Using Organobismuth Reagents
Naoto Sakurai1 and Teruaki Mukaiyamaꢀ1;2
1Center for Basic Research, The Kitasato Institute, 6-15-5 (TCI) Toshima, Kita-ku, Tokyo 114-0003
2Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641
(Received May 14, 2007; CL-070518; E-mail: mukaiyam@abeam.ocn.ne.jp)
A new method for the preparation of aryl tosylates by
Table 1. Reaction of 1a with various oxidants and sulfonic
acids
using pentavalent bismuth is described. Treatment of 10-aryl-
phenothiabismine 5,5-dioxides, m-chloroperoxybenzoic acid
(MCPBA) and p-toluenesulfonic acid monohydrate in dichloro-
methane affords aryl tosylates in good to high yields.
O
O
S
Oxidant (1.1 equiv.)
RSO3H
PhOSO2R
−78 to 0 °C, 10 min,
then reflux, 4 h, CH2Cl2
Bi
1a
Ph
Aryl tosylates are common reagents in organic synthesis not
only as protected substrates of phenolic hydroxy group1 but also
as starting materials of various reactions. They recently become
more attractive in transition-metal-catalyzed cross-coupling
reactions because of their increased stability compared with aryl
triflate, and it was reported that aryl tosylates were applicable for
palladium- and nickel-catalyzed Suzuki–Miyaura2 and Kumada
coupling reaction,3 and palladium-catalyzed alkoxycarbonyla-
tion.4
The most general procedure for the preparation of aryl
tosylates is to react phenols with toluene-4-sulfonyl chloride
(TsCl) in the presence of organic bases such as pyridine or Et3N.
Recently, solvent-free tosylation of phenols by using polyoxo-
metalates as catalyst5 or microwave activation6 was reported,
whereas general procedures without using phenols are not
known yet.
Entry
RSO3H/equiv.
Oxidant
Yield/%
1
2
3
4
5a
6
7
8
9
t-BuOOH
(PhCOO)2
CH3COOOH
MCPBA
MCPBA
MCPBA
MCPBA
MCPBA
MCPBA
b
NDb
ND
49
.
TsOH H2O/2.2
.
TsOH H2O/2.2
.
TsOH H2O/2.2
.
TsOH H2O/2.2
87
.
TsOH H2O/2.2
48
.
TsOH H2O/1.1
63
.
TsOH H2O/2.8
91
MsOH/2.8
TfOH/2.2
80
29
aReaction was carried out at rt for 30 h. Not Detected.
tosylate was not obtained (Entries 1 and 2). Instead, the desired
phenyl tosylate was respectively obtained in 49 and 87%
yields when an oxidant such as peracetic acid or MCPBA was
used (Entries 3 and 4). The reaction was sluggish when carried
out at room temperature (Entry 5). The yield of PhOTs decreased
to 63% yield when the amount of TsOH H2O was reduced to 1.1
equiv. (Entry 6). In the view of reproducibility, it was found that
.
the amount of TsOH H2O was needed more than 2 equiv., and
the best result was obtained by using 2.8 equiv. of TsOH H2O
(Entry 7). Next, other sulfonic acids were examined, and it
was observed that methanesulfonic acid (MsOH) gave the
desired phenyl mesylate in 80% yield (Entry 8). On the other
hand, trifluoromethanesulfonic acid (TfOH) gave the desired
phenyl triflate in only 29% yield because 1a was decomposed
by TfOH (Entry 9).
In the next place, reactivity of other bismuth reagents was
examined (see Table 2). This reaction proceeded only when 1a
was used. It is, therefore, assumed that triphenylbismuthane
(3), phenylbiphenyl-2,20-ylenebismuthane10 (4) and 10-phenyl-
Organobismuth reagents are well studied as mild oxidants
and arylation reagents.7 It is also reported from our laboratory
that pentavalent organobismuths are effective for N-arylation
of pyridin-2(1H)-ones, O-phenylation of tertiary alcohols and
oxidative coupling reaction of carbonyl compounds.8 These re-
actions are attributed to the unique character of valency change
from BiV to BiIII. Thus, two ligands on the pentavalent bismuth
are coupled accompanied with reductive elimination to generate
trivalent bismuth simultaneously. Ligand coupling reactions of
pentavalent bismuth dihalides or diacetates are reported,7a,7d,7e
while those of pentavalent bismuth ditosylates were not known.
Then, we would like to report a synthesis of aryl tosylates by
using a novel ligand coupling reaction of pentavalent bismuth
ditosylates generated in situ. First, heterocyclic bismuth 1a
was selected as a model substrate of aryl donor in consideration
of that reactivity and selectivity reported by Suzuki’s group.9
They reported that heterocyclic pentavalent bismuth dichloride
.
.
ꢀ
such as 10-dichloro-10-(40-methylphenyl)phenothia-10 5-bis-
Table 2. Effect of organobismuth reagents
mine 5,5-dioxide prepared from 1b was quite unstable to form
4-chlorotoluene quantitatively by reductive elimination and that
only 4-methylphenyl group participated in the reductive elimina-
tion while heterocyclic bismuth part remained unchanged.
In the first place, the effects of oxidants and sulfonic acids
were examined. The results of the reaction carried out by using
10-phenylphenothiabismine 5,5-dioxide9 (1a), 1.1 equiv. of
oxidants in the presence of some sulfonic acids in CH2Cl2 are
summarized in Table 1. When tert-butyl hydroperoxide and
benzoyl peroxide were used as an oxidant, the expected phenyl
MCPBA (1.1 equiv.)
BiIII
Entry
BiIII
•
PhOTs
TsOH H2O
−78 to 0 °C, 10 min,
(2.2 equiv.)
2a
then reflux, 4 h, CH2Cl2
1
2
3
O
4
Ph3Bi
1a
Bi
Ph
1
Bi
3
4
5
Ph
trace
87
Yield/%
ND
Copyright Ó 2007 The Chemical Society of Japan