Catalysis by Amberlite IR-120 resin: A rapid and green method for the synthesis of phenols from arylboronic acids under metal, ligand, and base-free conditions

Article abstract of DOI:10.1016/j.tetlet.2012.08.087

A clean process has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to the corresponding phenols using commercially available and recyclable Amberlite IR-120 resin and aqueous hydrogen peroxide as an oxidizing agent. The ion-exchange sulfonic acid resin catalyst could be readily recycled by filtration and directly reused at least four times without any significant loss of activity.

Full text of DOI:10.1016/j.tetlet.2012.08.087

Tetrahedron Letters 53 (2012) 6004–6007
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Catalysis by Amberlite IR-120 resin: a rapid and green method
for the synthesis of phenols from arylboronic acids under metal, ligand,
and base-free conditions
⇑
Naveen Mulakayala , Ismail, Kottur Mohan Kumar, Rajesh Kumar Rapolu, Bhaskar Kandagatla,
Pallavi Rao, Srinivas Oruganti, Manojit Pal
Cosmic Discoveries, Institute of Life Sciences, University of Hyderabad Campus, Gachibowli, Hyderabad 500046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A clean process has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to the
corresponding phenols using commercially available and recyclable Amberlite IR-120 resin and aqueous
hydrogen peroxide as an oxidizing agent. The ion-exchange sulfonic acid resin catalyst could be readily
recycled by filtration and directly reused at least four times without any significant loss of activity.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 22 June 2012
Revised 21 August 2012
Accepted 23 August 2012
Available online 31 August 2012
Keywords:
Arylboronic acid
Phenol
Amberlite IR-120 resin
Catalysis
Green synthesis
Phenols and their derivatives have been found to be integral part
of numerous natural products. They are important precursors for
the synthesis of pharmaceuticals, polymers, and naturally occurring
compounds.1 The synthesis of phenols therefore continues to attract
the attention of organic chemists and various methods have been
reported for their synthesis. Among the several approaches re-
ported, nucleophilic aromatic substitution of aryl halides, copper-
catalyzed transformation of diazoarenes and benzyne protocols
are dominant.2 However, these methods invariably suffer from dis-
advantages such as harsh reaction conditions or diazotization of the
amino groups to diazoarenes, which is not compatible with many
other functional groups. Conversion of aryl bromides and chlorides
into phenols in the presence of palladium-based catalysts and phos-
phine ligands is another approach.3Aryl iodides are also converted
into the corresponding phenols in the presence of a copper catalyst
using non-phosphine ligands4 at elevated temperature. Over the
last decade, arylboronic acids have become valuable synthetic pre-
cursors in a range of organic transformations.5 While phenols have
been reported as by-products in several metal catalyzed reactions of
arylboronic acids,6 only a few reports however are available on the
direct conversion of arylboronic acids into phenols. The safe nature
of aryl boronic acids, which are generally stable to heat, air, and
moisture, and their wide range of availability, make them an attrac-
tive and valuable precursor to phenols. Thus, phenols are prepared
from arylboronic acid in the presence of a wide variety of catalysts
or reagents including I2–H2O2,7 CuSO4–phenanthroline,8 H2O2–poly
(N-vinylpyrrolidone),9 NH2OH,10 potassium peroxymonosulfate,11
12
aqueous H2O2 etc. However, requirement of longer reaction
times,7,10,12 and the use of ligand/base,8 and chlorinated solvents9
highlight the need for a new, rapid, and eco-friendly catalytic
method.
Aqueous hydrogen peroxide is considered as an environmen-
tally acceptable oxidant that shows a high efficiency per weight
of oxidant.13 Use of acidic resin, either stoichiometric or in catalytic
systems has gained importance in organic synthesis due to several
advantages such as, operational simplicity, reusability, low cost,
and ease of isolation after completion of the reaction. For example,
Amberlite-IR 120 resin has emerged as an efficient heterogeneous
catalyst for chemical transformations.14 Due to our continuous
interest in the use of a recyclable solid catalyst, we now wish to re-
port the use of Amberlite IR-120 resin15 as an extremely powerful
promoter for oxidative ipso-hydroxylation of aryl and heteroaryl
boronic acids at room temperature under ligand-, metal-, and
base-free conditions. We have observed that arylboronic acids (1)
react with aqueous H2O2 in the presence of Amberlite IR-120 resin
to give the corresponding phenols (2) in good to excellent yields
(Scheme 1).
⇑
Corresponding author. Tel.: +91 40 665 71626; fax: +91 40 665 71158.
E-mail
addresses:
Naveenm@ilsresearch.org,
naveen071280@gmail.com
(N. Mulakayala).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.087

N. Mulakayala et al. / Tetrahedron Letters 53 (2012) 6004–6007
6005
HO
OH
R
To understand the versatility of the current methodology, a
wide array of diverse arylboronic acids were treated with Amber-
lite IR-120/H2O2 as catalyst under the condition of entry 10 of
Table 1.16 The results are presented in Table 2. In general, arylbo-
ronic acids with either electron-withdrawing or electron-donating
substituents such as Cl, F, I, OMe, COOH, CHO, and NH2 (Table 2,
entries 2–12) underwent the ipso-hydroxylation reaction in good
yields (86–98%). It was observed that a variety of substituents on
the aromatic ring were well tolerated. The reaction was also com-
patible with naphthylboronic acids (Table 2, entries 13 and 14) as
well as heteroarylboronic acid (Table 2, entry 15).
The reaction mechanism was proposed in Scheme 2. Hydrogen
peroxide reacts with phenylboronic acid to form adduct A. Re-
moval of H+ followed by H2O and subsequent phenyl migration
to oxygen generate adduct B. Finally, hydrolysis of adduct B leads
to the formation of phenol.
Recyclability of the Amberlite IR-120 catalyst was examined.
For this reason, the catalyst used was recovered from the reaction
of phenyl boronic acid (1a) to phenol (2a) via filtration, dried, and
reused for the same reaction. This procedure was repeated for four
times and results are summarized in Table 3. It is evident from
Table 3 that the catalyst can be recycled successfully for several
times without significant loss of its catalytic activities.
In summary, we have developed a clean process for the synthe-
sis of phenols starting from arylboronic acids with aqueous
hydrogen peroxide using a commercially available, strongly acidic
cross-linked Amberlite IR-120 as a recyclable catalyst. The features
of this process include (a) an almost waste-free procedure, except
for the regeneration of the resin catalyst at its first use; (b) the
acidic ion-exchange-resin catalyst could be readily separated from
the products by simple filtration and directly reused at least four
times without any reactivation, while showing no significant loss
of activity; (c) the technique is effective with a wide range of
substituted aryl and heteroaryl boronic acids giving phenols as
products in good to excellent yields.
OH
B
H2O2
Amberlite IR-120
rt, 5-15 min
> 90%
R
2
1
Scheme 1. Amberlite IR-120 mediated preparation of phenols (2) from arylboronic
acids (1).
To examine the role of H2O2 (30% aq) in the present reaction,
phenylboronic acid (1a; 1 mmol) was chosen as a model substrate
to perform the reactions under open vessel conditions at room tem-
perature. The results are summarized in Table 1. When a mixture of
1a (1 mmol) and aqueous hydrogen peroxide (2 mL) was stirred at
room temperature in the absence of any organic solvent for
60 min, only a trace amount of phenol (2a) was obtained (Table 1,
entry 1). The use of an organic solvent, for example, acetonitrile
did not improve the product yield (Table 1, entry 2). Surprisingly,
the yield of 2a increased dramatically to 88%when the same reaction
was performed in the presence of Amberlite IR-120 resin for 30 min
(Table 1, entry 3). The use of other solvents, for example, MeOH, THF,
and DCM were examined and found to be effective (Table 1, entries
4–6). Notably, the reaction was found to be not sensitive to the pres-
ence of large volume of water as the use of 1:1 aqueous acetonitrile,
aqueous THF, and aqueous MeOH was successful (Table 1, entries
7–9). Nevertheless, the best results were achieved when the reaction
was performed in the absence of any solvent (Table 1, entry 10).
The increase in quantity of resin did not improve the product
yield whereas a decrease in quantity lowered the yield (Table 1,
entries 11–12). The reaction was found to be abnormally slow in
the absence of resin indicating its key role in accelerating the reac-
tion (Table 1, entry 13). When the reaction was carried out using
oxone or t-BuOOH as an oxidant moderate yields were observed.
(Table 1, entries 14 and 15). Based on the observation of entries
1, 10, and 13 it was evident that a combination of Amberlite
IR-120 resin and H2O2 was necessary for the quick and effective
conversion of phenylboronic acid to phenol.
Table 1
Optimization of reaction conditions for Amberlite IR-120 mediated ipso-hydroxylation of 1aa
HO
OH
OH
B
Amberlite IR-120
No solvent, rt,
H2O2
+
5-20 min, 86-98 %
2a
1a
Entry
Catalyst (amount)
Oxidant
Solventa
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
—
—
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
Oxone
t-BuOOH
—
60
60
30
30
30
60
30
30
30
5
5
5
40 h
60
60
05
08
88
83
81
74
82
86
MeCN
MeCN
MeOH
THF
DCM
MeCN–H2O (1:1)
THF–H2O (1:1)
MeOH–H2O (1:1)
—
—
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (20 mg)
Amberlite IR-120 (15 mg)
Amberlite IR-120 (30 mg)
Amberlite IR-120 (10 mg)
–
9
84
95
93
10
11
12
13
14
15
—
—
MeCN
—
88c
82c
Traced
45e
Amberlite IR-120 (15 mg)
Amberlite IR-120 (15 mg)
a
b
c
Reagents and conditions: phenylboronic acid (1 mmol), H2O2 (30% aq, 2 mL), Amberlite IR-120 (15 mg), solvent (2 mL), ca 30 °C.
Isolated yields.
The reaction did not reach to completion.
Reagents and conditions: phenylboronic acid (1 mmol), Oxone (1 mmol), MeCN (2 mL), Amberlite IR-120 (15 mg), ca 30 °C.
Reagents and conditions: phenylboronic acid (1 mmol), t-BuOOH (70% aq, 2 mL),, Amberlite IR-120 (15 mg), ca 30 °C.
d
e

6006
N. Mulakayala et al. / Tetrahedron Letters 53 (2012) 6004–6007
Table 2
Table 2 (continued)
Amberlite IR-120 mediated synthesis of phenols (2)a
Entry
Boronic acid (1)
Product (2)
Time (min)
18
Yield (%)
90
Entry
Boronic acid (1)
Product (2)
Time (min)
Yield (%)
98
HO
OH
OH
B
HO
OH
OH
NH2
B
NH2
12
1
2
2l
1l
2a
1a
OH
OH
HO
OH
OH
B
B
OH
13
10
86
2m
2
3
4
5
5
5
92
90
91
1m
Cl
Cl
OH
2b
HO
OH
OH
1b
B
HO
HO
OH
F
B
14
15
10
10
88
86
F
2n
1n
2c
1c
OH
OH
S
B
OH
OH
S
B
2o
OH
1o
a
Reagents and conditions: phenylboronic acid (1 mmol), H2O2 (30% aq, 2 mL),
Amberlite IR-120 (15 mg), ca 30 °C.
F
F
2d
1d
HO
OH
OH
B
5
6
7
5
5
5
92
89
90
H
OH
F
O
OH
HO
OH
HO
F
2e
B
B
O
O
1e
OH
H
H
B
O
HO
HO
OH
OH
I
OH
B
-H
I
OH
1
A
2f
1f
H
OH
OH
B
OH
OH2
HO
B
OB(OH)2
O
OH
I
-H2O
I
2g
1g
HO
HO
OH
OH
2
B
B
8
9
10
12
94
96
H2
H2
H
H
C C C C
O
*
*
O
2h
1h
=
SO3H
H2
OH
OH
HO3S
B
C C
H
*
*
Scheme 2. Amberlite IR-120 mediated preparation of phenols (2) from arylboronic
acids (1).
O
2i
O
1i
HO
HO
OH
OH
Table 3
B
Recycle of the Amberlite IR-120 catalyst
10
11
20
12
92
86
H2O2
2a
COOH
1a
COOH
Amberlite IR-120
rt, 5 min
2j
1j
OH
OH
B
Cycle
Amberlite
IR-120 (mg)
Yield (%)
1
2
3
4
15
15
14
13
98
96
93
92
CHO
CHO
2k
1k

N. Mulakayala et al. / Tetrahedron Letters 53 (2012) 6004–6007
6007
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Acknowledgment
6. (a) Sakurai, H.; Tsunoyama, H.; Tsunoyama, H.; Tsukuda, T. J. Organomet. Chem.
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Tetrahedron Lett. 2003, 44, 1691; (c) Jung, Y. C.; Mishra, R. K.; Yoon, C. H.; Jung,
K. W. Org. Lett. 2003, 5, 2231.
We thank the management of Institute of Life Sciences,
Hyderabad for support and encouragement.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.08.
087.
12. Simon, J.; Salzbrunn, S.; Surya Prakash, G. K.; Petasis, N. A.; Olah, G. A. J. Org.
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(c) Park, T.-J.; Weiwer, M.; Yuan, X.; Baytas, S. N.; Munoz, E. M.; Murugesan, S.;
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Arab. J. Chem. In press 2012. http://dx.doi.org/10.1016/j.arabjc.2011.08.002.
15. Sulfonic acid resin (Amberlite-IR 120) was purchased from Sigma-Aldrich and
regenerated as follows: 100 g of the resin was stirred with 10% sulfuric acid
(500 mL) for 30 min, filtered, and washed with deionized water until the
washings were free of acid. The resin was then washed with THF, acetone, or
absolute alcohol (3 Â 30 mL), dried in an oven at 75–80 °C for 12 h, and kept
over P2O5 in a vacuum desiccator for a week. The sulfonic acid loading will be
4.4 meq/g.
16. General procedure for the preparation of compound 3: A mixture of arylboronic
acid (1.0 mmol), 30% H2O2 (2 mL), and Amberlite IR-120 resin (15 mg) was
stirred at room temperature for the time indicated in Table 2. After completion
of the reaction (indicated by TLC) the solid was separated by filtration,
extracted with EtOAc (10 mL), washed with 10% NaHCO3 (2 Â 5 mL), and the
organic layer was evaporated to give the desired product without further
purification.
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