Ipso-hydroxylation of arylboronic acids and boronate esters by using sodium chlorite as an oxidant in water

Article abstract of DOI:10.1002/ejoc.201301228

A facile and efficient procedure for the ipso-hydroxylation of arylboronic acids to phenols in water was developed. A series of electron-rich and electron-deficient arylboronic acids were smoothly ipso-hydroxylated with this protocol to afford products in excellent yields. Moreover, the protocol is amenable to boronate esters. In most cases, the phenolic products were obtained in pure form without any chromatographic purification. An efficient procedure for the ipso-hydroxylation of arylboronic acids to phenols in water is reported. A wide range of electronically varied boronic acids are smoothly ipso-hydroxylated with this protocol, which is amenable to boronate esters. The reaction strategy is facile and clean, and the products are obtained in pure form and do not require chromatographic purification. Copyright

Full text of DOI:10.1002/ejoc.201301228

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201301228
ipso-Hydroxylation of Arylboronic Acids and Boronate Esters by Using
Sodium Chlorite as an Oxidant in Water
[a]
[a]
[a]
[a]
Pranjal Gogoi,* Pranjal Bezboruah, Junali Gogoi, and Romesh C. Boruah*
Keywords: Synthetic methods / Water chemistry / Hydroxylation / Oxidation / Phenols
A facile and efficient procedure for the ipso-hydroxylation of
arylboronic acids to phenols in water was developed. A series
of electron-rich and electron-deficient arylboronic acids were
smoothly ipso-hydroxylated with this protocol to afford prod-
ucts in excellent yields. Moreover, the protocol is amenable
to boronate esters. In most cases, the phenolic products were
obtained in pure form without any chromatographic purifica-
tion.
Introduction
readily available, nontoxic, shelf stable, and often react un-
der mild conditions with good functional group tolerance.
Moreover, they can be prepared by C–H bond functionali-
zation, which is complementary to the chemistry of aryl
halides. The oxidation of arylboronic acids and its deriva-
tives to phenols was first reported by Ainley and Chal-
The hydroxylation of aromatic compounds remains a
challenge in organic chemistry, even though phenols are
very useful intermediates for many pharmaceutical mole-
cules, natural products and polymers.[ Naturally, phenols
are produced by plants and microorganisms in response to
ecological and physiological pressures such as pathogens,
insect attack, UV radiation, and wounding.[ In industry,
phenols are synthesized as raw materials and as additives
for industrial wood processing and the chemical indus-
[6]
1]
[7a]
lenger
with alkaline hydrogen peroxide and was later
[7b]
[7c]
modified by Kuivila and Olah. Although this transfor-
mation is simple and green, electron-deficient arylboronic
acids give low yields and alkaline hydrogen peroxide can
lead to undesirable side reactions. To improve this transfor-
2]
[
1a]
tries.
In medicinal chemistry, they are known to exhibit
[7d]
[7e]
mation, I ,
acidic Al O ,
and Amberlite IR-120 res-
2
2
3
many pharmacological actions including antitumor, antivi-
ral, antibacterial, cardioprotective, pro-oxidant, and anti-
mutagenicity activities.[ The synthesis of phenols therefore
continues to attract the attention of organic chemists, and
various methods for their preparation have been developed.
Most commonly, phenols are produced by pyrolysis of the
sodium salt of benzene sulfonic acid, the Dow process,
[7f]
in have been used as catalysts with H O and complexes
2
2
of poly(N-vinylpyrrolidone)/hydrogen peroxide and poly(4-
3]
[7g]
vinylpyridine)/hydrogen peroxide.
Other catalysts/rea-
gents used for the transformation of arylboronic acids into
[7h]
phenols include CuSO /phenanthroline,
NH OH/
4
2
[7i]
[7j]
NaOH,
potassium peroxymonosulfate,
photoredox
[7k]
[7l]
catalysis with the use of visible light, and N-oxides, but
[
4]
hydrolysis of diazonium salts, or by the Hock process.
[7m,7n]
the search for better methods still continues.
the reported methods are not free from drawbacks such as
Most of
However, these methods invariably suffer from disadvan-
tages such as harsh reaction conditions and the production
of byproducts. In contrast, aryl iodides, bromides, and
chlorides can be converted into phenols by palladium- and
copper-catalyzed processes,[ which involve the use of rare
and expensive metal catalysts and sophisticated supporting
ligands and additionally require high reaction temperatures
and long reaction times. Over the last decade, arylboron
reagents have been recognized as valuable alternatives to
aryl groups for the synthesis of phenols, because they are
[7h]
the use of transition metals with ligands,
harsh reaction
chlorinated organic
and expensive reagents.
[7j]
[7i]
conditions,
long reaction times,
[7l]
[7k]
solvents as reaction media,
5]
Consequently, there is a genuine need for the development
of new methodologies for ipso-hydroxylation of arylboronic
acids and its derivatives.
Sodium chlorite (NaClO ), an easily available and inex-
2
pensive oxidizing agent, has been extensively used for
[8]
bleaching and stripping of textiles, pulp, and paper. In
addition, its applications have received growing interest of
a] Medicinal Chemistry Division, CSIR – North East Institute of the organic chemistry community in recent years. In organic
[
Science and Technology,
synthesis, sodium chlorite is frequently used for the Pinnick
Jorhat, Assam, India
[
9]
E-mail: gogoipranj@yahoo.co.uk
rc_boruah@yahoo.co.in
http://www.rrljorhat.res.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301228
oxidation of aldehydes, oxidation of allylamines to epoxy-
[8a]
amides,
ides,
oxidation of alkyl furans to γ-hydroxybutenol-
[
10a]
[10b]
epoxidation of olefins,
oxidation of sulfides to
[
10c]
chlorination of activated arenes[10d] and
sulfoxides,
Eur. J. Org. Chem. 2013, 7291–7294
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7291

P. Gogoi, P. Bezboruah, J. Gogoi, R. C. Boruah
SHORT COMMUNICATION
ketones,[10e] oxidation of saturated hydrocarbons,[10f] oxi- Both electron-rich and electron-poor arylboronic acids af-
dation of primary alcohols to the corresponding carboxylic forded the corresponding phenols in excellent yields. How-
acids in the presence of 2,2,6,6-tetramethylpiperidinyloxy ever, arylboronic acids bearing electron-poor groups re-
[
10g]
(
TEMPO),
mium as a catalyst.
knowledge, the use of sodium chlorite for the conversion of showed a great tolerance to a range of functional groups
and the dihydroxylation of olefins with os- quired longer reaction times than arylboronic acids bearing
[10]
Nevertheless, to the best of our electron-rich groups. The reaction conditions notably
arylboronic acid into phenol has not yet been reported.
including alkoxy, acetyl, halo, nitrile, and nitro moieties.
Sterically hindered arylboronic acids 1h, 1n, 1t, and 1u gave
the desired products in 83–92% yield. Naphthalene-1-
boronic acid (1v) and naphthalene-2-boronic acid (1w) were
smoothly oxidized to their corresponding ipso-hydroxylated
products. Importantly, oxidation-prone substituents such as
nitrile (as in 1d) and vinyl (as in 1s) groups were well toler-
Results and Discussion
In the context of our ongoing interest in the chemistry
of organoboron compounds,[11] we report here a novel and
simple procedure for the direct conversion of boronic acids
[
10b]
ated and oxidized products were not formed.
Remarka-
into phenols by using NaClO as the oxidizing agent in
2
bly, the aldehyde group (as in 1c and 1j) remained intact
water at room temperature. To understand the versatility
and applicability of our protocol, a wide array of substi-
tuted arylboronic acids were smoothly converted into their
corresponding phenols (Table 1).
under the reaction conditions, and Pinnick oxidized prod-
[
9]
ucts were not formed.
Having established the ipso-hydroxylation reaction for a
wide range of aromatic and acyclic boronic acid derivatives
(i.e., 1a–x), we examined the scope of the ipso-hydroxyl-
ation of other boronic acid surrogates (Table 2).
Table 1. ipso-Hydroxylation of arylboronic acids.[a]
Table 2. ipso-Hydroxylation of other boronic acid surrogates.[a]
[
a] The reaction was carried out with 1 (1 mmol), water (5 mL),
and NaClO (1.2 mmol) at room temperature in water.
2
Under the standard reaction conditions, phenylboronic
esters 2a–d afforded phenols 3a, 3b, 4a, 4b in excellent
yields. Boronate derivative 2c was efficiently converted into
the corresponding ipso-hydroxylated product without af-
fecting the benzylic nitrile group. Steroidal boronate estrone
[
a] The reaction was carried out with 1 (1 mmol), water (5 mL),
and NaClO (1.2 mmol) at room temperature.
2
The reaction of arylboronic acids 1 with sodium chlorite derivative 2d afforded estrone 4b in excellent yield. Requi-
took place under very mild conditions at room temperature; site starting boronic ester 2d was easily prepared from the
expected products 3 and 4 were afforded in excellent yields. corresponding triflate through a palladium-catalyzed cross-
7292
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7291–7294

ipso-Hydroxylation of Arylboronic Acids and Boronate Esters
coupling reaction with pinacolborane.[12] Additionally, the Experimental Section
ipso-hydroxylation of phenylboronic acid was performed on
General Experimental Procedure for the ipso-Hydroxylation of Aryl-
a gram scale (1.5 g), and the desired phenol was obtained
in excellent yield (91%).
A proposed reaction mechanism is depicted in Figure 1.
To investigate the role of sodium chlorite as the source of
boronic Acid to Phenol: A test tube was charged with phenylboronic
acid 1 (1 mmol). Water (5 mL) was then added. Subsequently, so-
dium chlorite (1.2 mmol) was added into the reaction mixture. The
mixture was stirred at room temperature for about 20 min until
phenolic oxygen, we carried out the oxidation of 1a inde- TLC showed that the starting material had been consumed. The
pendently under anaerobic conditions. To our surprise, ipso- reaction mixture was extracted with EtOAc (3ϫ 10 mL). The com-
hydroxylation reactions under these conditions also af- bined organic fraction was dried and concentrated. Phenol 3 was
obtained without any chromatographic purification.
forded desired phenol 3a in 92% yield. It was assumed that
aerial oxygen had no role to play in the oxidation reaction, Supporting Information (see footnote on the first page of this arti-
1
as the anaerobic conditions showed no difference in the cle): Experimental details, spectroscopic data, copies of the
H
1
3
NMR and C NMR spectra of all final products
yield and time of the reaction. It is proposed that NaClO2
is the sole oxidant for the conversion of phenylboronic acid
into phenol during the oxidation reaction. Nucleophilic at-
Acknowledgments
tack of NaClO on the boronic acid generates intermediate
2
[
I] (Figure 1, path A). Subsequent migration of the aryl The authors acknowledge the Council of Scientific and Industrial
group from boron to oxygen generates boronate ester [III]. Research (CSIR), New Delhi for their financial support. P. B. and
–
The OCl species generated from intermediate [I] reacts J. G. thank the University Grants Commission (UGC), New Delhi
and CSIR for Research Fellowships. The authors are grateful to
the Director, CSIR, NEIST, Jorhat, for his keen interests.
with another molecule of phenylboronic acid (Figure 1,
path B) to generate intermediate [II], which leads to [III]
with loss of a molecule of NaCl. In the presence of water,
[
1] a) Z. Rappoport, The Chemistry of Phenols, Willey-VCH,
Weinheim, Germany, 2003; b) J. H. P. Tyman, Synthetic and
Natural Phenols, Elsevier, New York, 1996; c) S. Quideau, D.
Deffieux, C. Douat-Casassus, L. Pouysegu, Angew. Chem.
2011, 123, 610–646; Angew. Chem. Int. Ed. 2011, 50, 586–621;
d) T. George, R. Mabon, G. Sweeney, J. B. Sweeney, A. Tavas-
soli, J. Chem. Soc. Perkin Trans. 1 2000, 2529–2574.
boronate ester intermediate [III] is hydrolyzed to phenol 3a.
To support our mechanism, we independently attempted
the hydroxylation of phenylboronic acid with NaOCl (4%
solution), and the desired hydroxylated product phenol was
obtained in good yield (65%).[
13]
[
[
2] J. Klepacka, E. Gujska, J. Michalak, Plant Foods Hum. Nutr.
2011, 66, 64–69.
3] a) S. Nandi, M. Vracko, M. C. Bagchi, Chem. Biol. Drug Des.
2
007, 70, 424–436; b) K.-H. Lee, Plant Phenolic Compounds as
Cytotoxic Antitumor Agents, in: ACS Symposium Series 507:
Phenolic Compounds in Food and Their Effects on Health II
(
Eds.: M.-T. Huang, C.-T. Ho, C. Y. Lee), American Chemical
Society, Washington, DC, 1992, p. 367–379; c) M. Greenberg,
M. Dodds, M. Tian, J. Agric. Food Chem. 2008, 56, 11151–
1
1156; d) G. W. Burton, T. Doba, E. J. Gabe, L. Hughes, F. L.
Lee, L. Prasadand, K. U. Ingold, J. Am. Chem. Soc. 1985, 107,
053–7065.
7
[
[
4] a) Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH,
Weinheim, Germany, 2002; b) P. Hanson, J. R. Jones, A. B.
Taylor, P. H. Walton, A. W. Timms, J. Chem. Soc. Perkin Trans.
Figure 1. Proposed reaction mechanism and intermediates.
2
2002, 1135–1150; c) C. Hoarau, T. R. R. Pettus, Synlett 2003,
127–137.
5] a) K. W. Anderson, T. Ikawa, R. E. Tundel, S. L. Buchwald, J.
Am. Chem. Soc. 2006, 128, 10694–10695; b) M. C. Willis, An-
gew. Chem. 2007, 119, 3470–3472; Angew. Chem. Int. Ed. 2007,
Conclusions
46, 3402–3404; c) B. J. Gallon, R. W. Kojima, R. B. Kaner, P. L.
Diaconescu, Angew. Chem. 2007, 119, 7389–7392; Angew.
Chem. Int. Ed. 2007, 46, 7251–7254; d) K. Yang, Z. Li, Z.
Wang, Z. Yao, S. Jiang, Org. Lett. 2011, 13, 4340–4343; e) A.
Tlili, N. Xia, F. Monnier, M. Taillefer, Angew. Chem. 2009, 121,
8881–8884; Angew. Chem. Int. Ed. 2009, 48, 8725–8728; f) D.
Zhao, N. Wu, S. Zhang, P. Xi, X. Su, J. Lan, J. You, Angew.
Chem. 2009, 121, 8885–8888; Angew. Chem. Int. Ed. 2009, 48,
In conclusion, we developed a simple catalyst-free pro-
cedure for the ipso-hydroxylation of arylboronic acids and
their derivatives to phenols by using sodium chlorite as the
oxidant. Our method has the advantage of broad functional
group compatibility for both electron-rich and electron-
poor substituents. In addition, our procedure is amenable
to boronate esters. The reaction strategy is facile and clean,
8729–8732; g) L. Jing, J. Wei, L. Zhou, Z. Huang, Z. Li, X.
Zhou, Chem. Commun. 2010, 46, 4767–4769.
as the phenolic products were obtained in pure form and [6] a) R. E. Maleczka, F. Shi, D. Holmes, M. R. Smith III, J. Am.
did not require chromatographic purification. Our pro-
cedure is operationally simple, practical, inexpensive, and
scalable, and it allows ipso-hydroxylation of arylboronic ac-
ids to substituted phenols with excellent scope under mild
conditions.
Chem. Soc. 2003, 125, 7792–7793; b) J. M. Murphy, C. C.
Tzschucke, J. F. Hartwig, Org. Lett. 2007, 9, 757–760; c) C. C.
Tzschucke, J. M. Murphy, J. F. Hartwig, Org. Lett. 2007, 9,
7
61–764; d) H. Chen, J. F. Hartwig, Angew. Chem. 1999, 111,
597–3599; Angew. Chem. Int. Ed. 1999, 38, 3391–3393; e)
3
H. Y. Chen, S. Schlecht, T. C. Semple, J. F. Hartwig, Science
Eur. J. Org. Chem. 2013, 7291–7294
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7293

P. Gogoi, P. Bezboruah, J. Gogoi, R. C. Boruah
SHORT COMMUNICATION
2
000, 287, 1995–1997; f) T. Ishiyama, J. Takagi, K. Ishida, N.
Miyaura, N. R. Anastasi, J. F. Hartwig, J. Am. Chem. Soc.
002, 124, 390–391.
ed. (Ed.: J. A. Kent), Van Nostrand Reinhold Company, New
York, 1983, p. 212–235.
[9] a) B. O. Lindgren, T. Nilsson, Acta Chem. Scand. 1973, 27,
888–890; b) G. A. Kraus, M. J. Taschner, J. Org. Chem. 1980,
2
[
7] a) A. D. Ainley, F. Challenger, J. Chem. Soc. 1930, 2171–2180;
b) H. G. Kuivila, J. Am. Chem. Soc. 1954, 76, 870–874; c) J.
Simon, S. Salzbrunn, G. K. Surya Prakash, N. A. Petasis, G. A.
Olah, J. Org. Chem. 2001, 66, 633–634; d) A. Gogoi, U. Bora,
Synlett 2012, 1079–1081; e) A. Gogoi, U. Bora, Tetrahedron
Lett. 2013, 54, 1821–1823; f) N. Mulakayala, Ismail, K. Mo-
han Kumar, R. K. Rapolu, B. Kandagatla, P. Rao, S. Oruganti,
M. Pal, Tetrahedron Lett. 2012, 53, 6004–6007; g) G. K. Su-
rya Prakash, S. Chacko, C. Panja, T. E. Thomas, L. Urung, G.
Rasul, T. Mathew, G. A. Olah, Adv. Synth. Catal. 2009, 351,
4
1
2
5, 1175–1176; c) E. Dalcanale, F. Montanari, J. Org. Chem.
986, 51, 567–569; d) A. Raach, O. Reiser, J. Prakt. Chem.
000, 342, 605–608.
[
10] a) D. L. J. Clive, L. Ou, J. Org. Chem. 2005, 70, 3318–3320; b)
X.-L. Geng, Z. Wang, X.-Q. Li, C. Zhang, J. Org. Chem. 2005,
7
0, 9610–9613; c) M. Hirano, S. Yakabe, J. H. Clark, T. Morim-
oto, J. Chem. Soc. Perkin Trans. 1 1996, 2693–2698; d) M. Hir-
ano, S. Yakabe, H. Monobe, J. H. Clark, T. Morimoto, J.
Chem. Soc. Perkin Trans. 1 1997, 3081–3084; e) S. Yakabe, M.
Hirano, T. Morimoto, Synth. Commun. 1998, 28, 131–138; f)
J. P. Collman, H. Tanaka, R. T. Hembre, J. I. Brauman, J. Am.
Chem. Soc. 1990, 112, 3689–3690; g) M. Zhao, J. Li, E. Mano,
Z. Song, D. M. Tschaen, E. J. J. Grabowski, P. J. Reider, J. Org.
Chem. 1999, 64, 2564–2566; h) M. H. Junttila, O. E. O. Hormi,
J. Org. Chem. 2004, 69, 4816–4820.
1
567–1574; h) J. Xu, X. Wang, C. Shao, D. Su, G. Cheng, Y.
Hu, Org. Lett. 2010, 12, 1964–1967; i) E. Kianmehr, M. Yah-
yaee, K. Tabatabai, Tetrahedron Lett. 2007, 48, 2713–2715; j)
K. S. Webb, D. Levy, Tetrahedron Lett. 1995, 36, 5117–5118; k)
Y.-Q. Zou, J.-R. Chen, X.-P. Liu, L.-Q. Lu, R. L. Davis, K. A.
Jørgensen, W.-J. Xiao, Angew. Chem. 2012, 124, 808–812; An-
gew. Chem. Int. Ed. 2012, 51, 784–788; l) C. Zhu, R. Wang,
J. R. Falck, Org. Lett. 2012, 14, 3494–3497; m) H. Jiang, L.
Lykke, S. U. Pedersen, W.-J. Xiao, K. A. Jørgensen, Chem.
Commun. 2012, 48, 7203–7205; n) H.-L. Qi, D.-S. Chen, J.-S.
Ye, J.-M. Huang, J. Org. Chem. 2013, 78, 7482–7487.
[
11] P. Gogoi, P. Bezboruah, R. C. Boruah, Eur. J. Org. Chem. 2013,
5032–5035.
[
12] J. M. Govan, A. L. McIver, C. Riggsbee, A. Deiters, Angew.
Chem. 2012, 124, 9200–9204; Angew. Chem. Int. Ed. 2012, 51,
9066–9070.
[
13] Q. Xu, K.-A. Lee, S. Lee, K. M. Lee, W.-J. Lee, J. Yoon, J. Am.
[
8] a) L. Fuentes, U. Osorio, L. Quintero, H. Höpfl, N. Vázquez-
Cabrera, F. Sartillo-Piscil, J. Org. Chem. 2012, 77, 5515–5524;
b) J. J. Leddy, Riegel’s Handbook of Industrial Chemistry, 8th
Chem. Soc. 2013, 135, 9944–9949.
Received: August 15, 2013
Published Online: October 9, 2013
7294
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7291–7294