H2O2 in WERSA: An efficient green protocol for ipso-hydroxylation of aryl/heteroarylboronic acid

Article abstract of DOI:10.1039/c5ra21354a

A mild, green, economic and efficient protocol has been developed for ipso-hydroxylation of aryl/heteroarylboronic acids to phenols using 30% aqueous H₂O₂ as an oxidant and WERSA (water extract of rice straw ashes) as a neat reaction medium. All reactions were carried out without using metal, ligand, activator or hazardous organic solvent with excellent yield within a very short reaction time at room temperature. Therefore, this appears to be the cleanest and greenest alternative protocol for ipso-hydroxylation of aryl/heteroarylboronic acids.

Full text of DOI:10.1039/c5ra21354a

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DOI: 10.1039/C5RA21354A
Journal Name
ARTICLE
H O in WERSA: An efficient Green Protocol for Ipso-hydroxylation
2
2
of Aryl/Heteroarylboronic Acid
Eramoni Saikia, Sankar Jyoti Bora and Bolin Chetia*
fReceived 00th January 20xx,
Accepted 00th January 20xx
A mild, green, economic and efficient protocol has been developed for ipso-hydroxylation of aryl/heteroarylboronic acids
DOI: 10.1039/x0xx00000x
2 2
to phenols using 30% aqueous H O as oxidant and WERSA (Water Extract of Rice Straw Ashes) as neat reaction media. All
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reactions were carried out without using metal, ligand, activator and hazardous organic solvent with excellent yield within
a very short reaction time at room temperature. Therefore, this appears to be the cleanest and greenest alternative
protocol for ipso-hydroxylation of aryl/heteroarylboronic acids.
for ipso-hydroxylation of arylboronic acids to phenols using WERSA
Introduction
(Water Extract of Rice Straw Ashes) a highly abundant, cheap
2 2
natural feedstock as neat reaction media and 30% aqueous H O as
Phenols are ubiquitous in nature as they are the key structural
1
2
3
oxidant. To the best of our knowledge this is the first report on ipso-
hydroxylation of arylboronic acids to phenols using WERSA and we
therefore believe that this is an outstanding alternative protocol for
synthesis of phenols from arylboronic acids, as reaction condition is
mild, straightforward and without use of metal, ligand, bases and
constituent of various pharmaceuticals, agrochemicals, polymers
4
and naturally occurring compounds mainly as polyphenols (natural
antioxidants). Traditional methods for the preparation of phenols
involved nucleophilic substitution of activated aryl halides, Cu-
5
catalysed conversion of diazoarenes and Pd-catalysed conversion
6
solvents. Additional beauty of the protocol is the use of H
2
O
2
0
as
of aryl halides to phenols. But these existing routes require harsh
2
oxygen source rather than other oxygen sources like NaClO
2
,
N-
reaction conditions due to inactive nature of starting materials.
However, as a result of continuous effort of many research groups,
arylboronic acids have replaced the traditional inactive synthetic
precursor for phenols. Ipso-hydroxylation, the generalized method
2
1
22
Oxide, HOF as H
2 2
O is richer source of oxygen and forms water
as byproduct.
for the conversion of arylboronic acids to phenols is gaining Experimental
enormous importance due to higher availability, stability and
greater functional group diversity of arylboronic acids. As a result
At the beginning we tried our first reaction with phenylboronic acid
1 mmol) using 30% aqueous H (0.10 mL) as oxidant in WERSA (2
mL) (Scheme 1) which was prepared using the established
various protocols for ipso-hydroxylation of arylboronic acids were
(
2 2
O
7
put forwarded using different catalysts such as biosilica-H
2
O
2
, I
2
4
-
-
8
9
10
11
12
2
3
H
2
O
2
,
Al
2
O
3
-H
2
O
2
,
PEG-H
2
O
2
14
,
2
NH OH, KOH-TBHP, CuSO
procedure to check the feasibility of the reaction. We monitored
the reaction by TLC in every min and to our delight phenylboronic
acid fully converted to the desired product phenol within 10
minutes at room temperature. After that we moved on for
1
3
15
Phenantholine,
3 4 2 2
H BO -H O , Amberlite IR- 120 resin, supported
1
6
17
silver nano particle, organic hypervalent iodine (III) etc.
Even with all the existing protocols, majority of which found to be
effective for conversion of arylboronic acids to phenols via. Ipso-
hydroxylation, there is a serious need for “Green” protocols with
greater environmental and economical viability due to some
unavoidable drawbacks of the reported protocols such as use of
transition metal as catalyst, ligands, bases and harmful organic
solvents. Recently Saikia et.al., following the Green Chemistry tools
have explored natural feedstock as green alternatives for carrying
optimization of oxidant H
phenylboronic acid as model substrate. As a result of optimization
as depicted in Table 1 we found that 0.20 mL of 30% aqueous H O
2
2 2
O needed for full conversion taking
2
oxidant were sufficient to complete the reaction within 5 minutes.
Along with mild reaction condition, excellent yield, lesser toxicity,
operational plainness, cost effectiveness makes this hydroxylation
protocol one of the cleanest and greenest alternative protocol ever.
1
8
out two popular organic reactions Suzuki-Miyaura cross coupling
1
9
and Dakin reaction . Inspired by their work and following the
motion of “greening-up” here we wish to report a superb protocol
HO
OH
B
OH
WERSA, H O
2
2
rt
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India.
†
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Scheme 1: Ipso-hydroxylation of phenylboronic acid to phenol
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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DOI: 10.1039/C5RA21354A
ARTICLE
Journal Name
HO
OH
Table 1: Effects of the amount of 30% H
2
O
2
and time in the ipso-
7
8
9
OH
6
8
95
94
B
hydroxylation of phenylboronic acid in WERSA at room
a
temperature
b
NO2
OH
Entry
30% H
2
O
2
(mL)
Time (min/h)
24 h
Yield (%)
trace
92
NO2
OH
c
1
0.10
0.10
0.15
0.20
HO
HO
B
2
3
4
10 min
7 min
95
5 min
98
a
OH
Reaction conditions: phenylboronic acid (1 mmol), 30% H
2
O
2
in
8
97
92
B
OH
OH
WERSA (2 mL) at room temperature.
b
Isolated yields.
Reaction carried out without WERSA.
c
NO
OH
2
NO
2
1
0
10
HO
B
With the optimized condition, we then carried out numbers of
reactions with different electron-rich and electron-poor arylboronic
acid to study the substrate scope using this newly designed
protocol. According to our expectation, reactions proceeded very
smoothly converting various electron-donating and electron-
withdrawing groups bearing arylboronic acids to phenols with very
good to excellent yield within very short reaction time (Table 2).
Results showed that substrate containing electron withdrawing
groups were more efficient than electrons donating ones.
Moreover, we readily carried out the reaction with some
heteroarylboronic acids (Table 2). Till now, there is no earlier report
on ipso-hydroxylation using such a mild, green and economic
reaction condition. Therefore, this seems to be an evergreen
1
1
1
2
15
15
90
91
OH
B
OH
OH
S
S
OH
OH
B
O
O
OH
a
Reaction conditions: aryl/heteroarylboronic acid (1 mmol), 30%
H O (0.2 mL for each substrate) in WERSA (2 mL) at room
2
2
temperature.
b
Isolated yields.
Results and discussion
Nucleophilic activation of H
oxidant; as a result numbers of bases have already been used to
activate H by abstracting a proton so far. Here in this protocol
we used only WERSA with H as a neat reaction media for ipso-
2 2 2 2
O is a general fact to use H O as
protocol with
a wide range of substrate scope for ipso-
hydroxylation of arylboronic acids to phenols.
2
O
2
2 2
O
Table 2: Conversion of aryl/heteroarylboronic acid to phenols in
a
hydroxylation of arylboronic acids to phenols. Perhaps the exact
role of WERSA for the reaction is not clearly understood yet.
H O -WERSA system at room temperature
2
2
2
4
b
However, literature reveals that rice straw ashes contains oxides
of SiO (74.31%), Al (1.40%), Fe (0.73%), TiO (0.02%), CaO
(1.61%), MgO (1.89%), K O (11.30%), Na O (1.85%), P (2.65%) as
Entry
Starting
Products
Time
(min)
5
Yield
(%)
98
2
2
O
3
2
O
3
2
materials
HO
OH
2
2
2 5
O
1
2
B
OH
primary ingredients. Thus water extract of rice straw ashes may
contain KOH, NaOH which may be responsible for making WERSA
basic enough for nucleophilic activation of H
proton. Therefore we proposed a plausible mechanism for ipso-
hydroxylation of arylboronic acid to phenol using H in WERSA
Figure 1).
2 2
O by abstracting its
10
7
92
95
2
O
2
(
3
4
5
6
10
15
10
94
90
92
HO
HO
OH
OH
B
OH
Cl
B
Cl
OH
2
| J. Name., 2012, 00, 1-3
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3
(a) S. Quideau, D. Deffieux, C. Douat-Casassus, L. Pouysegu,
Figure 1: A plausible mechanism for ipso-hydroxylation of
Angew. Chem. Int. Ed. 2011, 50, 586-621; (b) Y. Ji, P. Li, X. Zhang, L.
Wang, Org. Biomol. Chem. 2013, 11, 4095-4101.
arylboronic acids to phenols
4
R. W. Owen, A. Giacosa, R. Haubner, B. Spiegel-hader, H. Bartsch,
Eur. J. Cancer. 2000, 36, 1235-1247.
Recyclability of WERSA is another attractive feature of this protocol.
th
5 P. Hanson, J. R. Jones, A. B. Taylor, P. H. Walton, A. W. J. Timms,
Chem. Soc.; Perkins Trans2002, 2, 1135–1150.
We reused WERSA upto 5 cycle without significant lose of
efficiency (Table 3). Taking phenylboronic acid as model substrate
we carried out the WERSA recyclability test. After completion of
the reactions, products were extracted with diethylether and
WERSA separated from product was washed with more
diethylether and reused. Thus we can consider WERSA as a reusable
homogeneous catalyst.
6
G. A. Sergeev, T. Schultz, C. Torbog, A. Spenenberge, H. Neumann,
Angew. Chem., Int. Ed. 2009, 48, 7595–7599.
7
2
8
9
Mahanta, A.; Adhikari, P.; Bora, U.; Thakur, A. J. Tetrahedron Lett.
015, 56, 1780-1783.
A. Gogoi, U. Bora, Synlett 2012, 1079-1081.
A. Gogoi, U. Bora, Tetrahedron Lett. 2013, 54, 1821-1823.
a
10 M. Gohain, M. D. Plessis, J. H. Tonder, B. C. B. Bezuidenhoudt,
Tetrahedron Lett. 2014, 55, 2082-2084.
Table 3: Recyclability of the catalytic system
b
Entry
1
Run
Time (min)
5
Yield (%)
98
st
11 E. Kinmehr, M. Yahyaee, K. Tabatabai, Tetrahedron Lett. 2007,
48, 2713-2715.
1
nd
2
3
4
5
2
5
5
98
96
94
90
rd
12 S. Guo, L. Lu, H. Cai, Synlett. 2014, 24, A-C
3
th
1
3 J. Xu, X. Wang, C. Shao, D. Su, G. Cheng, Y. Hu, Org. Lett. 2010,
2, 1964-1967.
4
7
th
1
5
10
a
14 K. Gogoi, A. Dewan, A. Gogoi, G. Borah, U. Bora, Heteroatom
Chem. 2014, 25, 127-130.
Reaction conditions: phenylboronic acid (1 mmol), 30% H O (0.2
2
2
mL) in WERSA (2 mL) at room temperature.
b
15 N. Mulakayala, Ismail, K.M. Kumar, R.K. Rapolu, B. Kandagatla, P.
Rao, S. Oruganti, M. Pal, Tetrahedron Lett. 2012, 53, 6004-6007.
Isolated yields.
1
6 T. Begum, A. Gogoi, P.K. Gogoi, U. Bora, Tetrahedron Lett. 2015,
6, 95-97.
5
Conclusions
17 N. Chatterjee, A. Goswami, Tetrahedron Lett. 2015, 56, 1524-
1
1
2
1
4
2
2
2
2
2
527.
In conclusion, we have developed a green, mild, efficient and
8 P. R. Boruah, A. A. Ali, B. Saikia, D. Sarma, Green Chemistry,
015, 17, 1442-1445.
aerobic protocol for ipso-hydroxylation of arylboronic acids to
2 2
phenols using H O as oxidant in WERSA at room temperature. With
9 B. Saikia, P. Borah, N. C. Barua, Green Chem. 2015, 17, 4533-
536.
these mild reaction conditions, our method is very compatible with
various electron-donating and electron-withdrawing groups at
ortho, meta and para positions on the aromatic ring. In addition, all
reactions occur in shortest reaction time without using any
activating agent, metal, ligand and organic solvent. From the
environmental and economical point of view, we believe that this is
the most greener and efficient protocol for ipso-hydroxylation of
0 P. Gogoi, P. Bezboruah, J. Gogoi, R. C. Boruah, Eur. J. Org. Chem.
013, 7291-7294.
1 C. Zhu, R. Wang, J. R. Falck, Org. Lett. 2012, 14, 3494-3497.
2 J. Gatenyo, I. Vints, S. Rozen, Chem. Commun. 2013, 7379-7381.
3 P. R. Boruah, A. A. Ali, M. Chetia, B. Saikia, D. Sarma, Chem.
Commun. 2015, 51, 11489-11492.
arylboronic acids to phenols. All these advantages make H
2 2
O -
2
1
4 B. M. Jenkins, R. R. Bakker, J. B. Wei, Biomass Bioenergy, 1996, 4,
WERSA very adaptable and competitive catalyst system,
a
77-200.
consequently can be used as clean and safer alternative for various
other reactions in laboratory as well as in industry in near future.
Acknowledgements
BC gratefully acknowledges UGC, New Delhi, for financial assistance
(Grant No. 42357/2013). ES is thankful to the Department of
Science and Technology (Government of India) for INSPIRE-
Fellowship and SAIF, NEHU-Shillong for spectral data.
Notes and references
1
Z. Rappoport, The Chemistry of Phenols; Weinheim, Germany:
Wiley-VCH, 2003.
2
J. H. P. Tyman, Synthetic and Natural Phenols; Elsevier: New York,
996.
1
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