Cu3(BTC)2 as heterogeneous catalyst for the room temperature oxidative hydroxylation of arylboronic acids

Article abstract of DOI:10.1016/j.tet.2016.03.098

A well known copper based-metal organic framework (MOF), namely Cu₃(BTC)₂, is a suitable heterogeneous catalyst to promote the oxidative room-temperature hydroxylation of arylboronic acids to the corresponding phenols by H₂O₂. Using 0.5 equiv of H₂O₂, Cu₃(BTC)₂ exhibits 80% conversion in 60 min that is higher than 70% conversion achieved with Fe(BTC) under the same conditions and reaction time. Cu₃(BTC)₂ is reusable with no significant drop in the activity. Furthermore, powder XRD of the reused Cu₃(BTC)₂ shows no changes in crystallinity compared to the fresh Cu₃(BTC)₂, indicating catalyst stability is maintained under reaction conditions. The scope of Cu₃(BTC)₂ as heterogeneous catalyst for the oxidative hydroxylation was studied for various phenylboronic acids.

Full text of DOI:10.1016/j.tet.2016.03.098

Accepted Manuscript
Cu (BTC) as heterogeneous catalyst for the room temperature oxidative
3
2
hydroxylation of arylboronic acids
Amarajothi Dhakshinamoorthy, Abdullah M. Asiri, Hermenegildo Garcia
PII:
S0040-4020(16)30241-1
10.1016/j.tet.2016.03.098
TET 27638
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 1 March 2016
Revised Date: 21 March 2016
Accepted Date: 31 March 2016
Please cite this article as: Dhakshinamoorthy A, Asiri AM, Garcia H, Cu (BTC) as heterogeneous
3
2
catalyst for the room temperature oxidative hydroxylation of arylboronic acids, Tetrahedron (2016), doi:
10.1016/j.tet.2016.03.098.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
TOC Graphic
B(OH)2
OH
H2O2
This work describes the use of Cu3(BTC)2 as heterogeneous catalyst to promote
the oxidative hydroxylation of arylboronic acids to the corresponding phenols by H2O2
at room temperature. Cu3(BTC)2 can be reused with no significant drop in the activity.

ACCEPTED MANUSCRIPT
Cu3(BTC)2 as heterogeneous catalyst for the room temperature oxidative hydroxylation
of arylboronic acids
Amarajothi Dhakshinamoorthy,a* Abdullah M. Asirib and Hermenegildo Garciab,c*
aSchool of Chemistry, Madurai Kamaraj University, Tamil Nadu, India 625 021.
E-mail:admguru@gmail.com
bCentre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah,
Saudi Arabia.
cInstituto Universitario de Tecnología Química CSIV-UPV, Universidad Politecnica de
Valencia, Av. De los Naranjos s/n, 46022, Valencia, Spain. E-mail: hgarcia@qim.upv.es
Abstract
A well known copper based-metal organic framework (MOF), namely Cu3(BTC)2, is
a suitable heterogeneous catalyst to promote the oxidative room-temperature hydroxylation of
arylboronic acids to the corresponding phenols by H2O2. Using 0.5 eq. of H2O2, Cu3(BTC)2
exhibits 80% conversion in 60 min that is higher than 70% conversion achieved with
Fe(BTC) under the same conditions and reaction time. Cu3(BTC)2 is reusable with no
significant drop in the activity. Furthermore, powder XRD of the reused Cu3(BTC)2 shows no
changes in crystallinity compared to the fresh Cu3(BTC)2, indicating catalyst stability is
maintained under reaction conditions. The scope of Cu3(BTC)2 as heterogeneous catalyst for
the oxidative hydroxylation was studied for various phenylboronic acids.
Keywords: Metal-organic frameworks; Cu3(BTC)2; phenylboronic acid; oxidation; hydrogen
peroxide.
1

ACCEPTED MANUSCRIPT
1. Introduction
Phenols and their derivatives exhibit many important chemical and biological
activities and are present in numerous natural products.1 Further, they are potential precursors
for the synthesis of pharmaceuticals, polymers, and naturally occurring compounds.2
Therefore, novel synthetic procedures for the preparation of this type of compounds are of
continued interest. Among the numerous reactions reported, nucleophilic aromatic
substitution of aryl halides, copper-catalyzed transformation of diazoarenes and protocols
based on the intermediacy of benzyne are dominant.3-5 However, these methods suffer from
disadvantages such as harsh reaction conditions or lack of control of diazotation of the amino
groups to aryldiazonium ions. Conversion of aryl bromides and chlorides into phenols in the
presence of palladium-based catalysts and phosphine ligands is another approach.6,7 Aryl
iodides can also be converted into the corresponding phenols in the presence of a copper
catalyst using non-phosphine ligands at elevated temperature.8,9 More recently, the
photochemical conversion of arylboronic acids into the corresponding phenols has been
reported.10-12 Arylboronic acids have become valuable synthetic precursors in a wide range of
organic transformations.13 On the other hand, phenols have been reported as by-products in
several metal-catalyzed coupling reactions of arylboronic acids as substrates.14,15
Metal organic frameworks (MOFs) are crystalline porous materials constituted by
metallic nodes of a single metal ion or a cluster with a few metal ions that are coordinated by
Coulombic and metal-ligand coordination forces with rigid bi- or multipodal organic
linkers.16 MOFs have been prepared for virtually all transition metals and even alkali earth
and heavy metals have been used in the preparation of MOFs. Aromatic polycarboxylates and
nitrogenated heterocycles are the most common organic linkers.17
2

ACCEPTED MANUSCRIPT
One of the most promising applications of MOFs is as heterogeneous catalysts since
these materials encompass large surface area, high metal content and some of them are stable
under catalytic conditions.18,19 One of the MOFs that has been most widely studied as
heterogeneous catalysts is Cu3(BTC)2 (BTC: 1,3,5-benzenetricarboxylic acid). The structure
of Cu3(BTC)2 has a dimeric Cu unit that is coordinated with four BTC units defining
octahedra around each Cu2+ ion with a paddle wheel shape.20 One coordination position of
each copper is occupied by a solvent molecule such as DMF or water that upon removal
releases a free coordination position around each Cu2+ ion allowing the interaction of
catalytically active Cu2+ with substrates and reagents. While Cu3(BTC)2 has been used as
solid catalysts for a large variety of reactions including cyanosilylation of aldehydes,21
alcohol oxidation22 and benzylic hydrocarbon oxidation23 among others,24,25 one of its main
drawbacks is its relatively low stability that is not compatible with the use of some reagents
like thiols26 or amines.27
Aqueous H2O2 is considered an environmentally friendly oxidizing reagent from the
green chemistry point of view, since water is the resulting byproduct of the oxidation.28 There
are numerous reports in the literature showing the feasibility of the oxidative hydroxylation
of phenylboronic acid to the corresponding phenol in the presence of an oxidant and additives
and several of them have used H2O/H2O2 as oxidant.29,30 However, they employ an excess of
H2O2, homogenous catalysts or temperatures above the ambient. Other procedures involve
the use of light, such as the use of [Ru(bpy)3Cl2]·6H2O (bpy = bipyridine) in the presence of
Et3N and air under visible light irradiation12 or employing Zr-based MOF with
tetrakis(carboxyphenyl)-porphyrin groups as photocatalyst and Et3N as electron donor using
green LED light as irradiation source.10 Other catalysts and oxidants that have also been used
for the transformation of arylboronic acids into phenols include Pd-based complex/O2/Et3N,31
solid
poly(N-vinylpyrrolidone)/H2O2,32
poly(4-vinylpyridine)/H2O2,32
UiO-67-
3

ACCEPTED MANUSCRIPT
[Ru(bpy)3]0.1/i-Pr2NEt,11 lactic acid/H2O2,33 PhI/NaIO4,34 CuCl2/O2,35 Cu2O/NH4OH,36 CuII–
β-cyclodextrin complex,37 CuSO4/phenanthroline/KOH,38 Amberlite IR-120/H2O2,39
biosilica/H2O2,40 Ag nanoparticles supported on K10-montmorillonite/H2O2,41 and Cu
nanoparticles/ellagic acid composite among others.42 In the present manuscript, we report that
commercially available Cu3(BTC)2 is a convenient and efficient catalyst to convert
arylboronic acids to the corresponding phenols using H2O2 as oxidant.
The advantages of the present procedure compared to the earlier methods are the
heterogeneous nature of the catalyst, allowing easy recovery and recycling, mild reaction
conditions and short reaction times. This commercially available Cu MOF does not require
any post-synthetic modification. In addition, this catalytic system does not rely on noble or
critical metals and exhibits a high catalytic activity and broad substrate scope.
2. Results and Discussion
Phenylboronic acid was initially selected as model substrate to screen the conditions
for the room temperature oxidative hydroxylation to phenol using 30% aqueous H2O2 added
at the starting time. The catalytic activity of a series of different MOF catalysts was tested. In
the absence of H2O2 or in the presence of H2O2 in the absence of catalyst no conversion of
phenylboronic acid was observed at room temperature under the reaction conditions used.
Fe(BTC) and Cu3(BTC)2 exhibited 70 and 80% conversions of phenylboronic acid,
respectively at room temperature with 0.5 mmol of H2O2 (Table 1, entries 3 and 4).
Quantitative conversion of phenylboronic acid was achieved after 1 h at room temperature
using 1 mmol of H2O2 in the presence of Fe(BTC) or Cu3(BTC)2 (Table 1, entries 5 and 6).
Furthermore, Fe(BTC) and Cu3(BTC)2 did not show any conversion of phenylboronic acid
using air as oxidant at room temperature after 2 h (Table 1, entries 10 and 11). Most of the
reports in the literature have promoted the reaction with the presence of a base that was
4

ACCEPTED MANUSCRIPT
considered essential in this transformation. For example, Xu and coworkers have reported
copper-catalyzed oxidative hydroxylation of arylboronic acid38 in the presence of potassium
hydroxide as a base and 1,10-phenanthroline as ligand. Hence, a further development would
be to find a catalytic system which avoids the use of base or any additive as cocatalyst to
promote this transformation.
In the present work, it has been found that oxidative hydroxylation of phenylboronic
acid with H2O2 in the presence of triethylamine is catalyzed by Cu3(BTC)2 reaching complete
conversion of phenylboronic acid (Table 1, entry 8). Furthermore, the reaction also exhibited
quantitative conversion using Cu3(BTC)2 with 1 mmol of H2O2 in the presence of 4-NH2-
TEMPO (Table 1, entry 9), thus ruling out a reaction mechanism involving of carbon centred
radical reaction intermediates. In the literature there are several reports describing the use of
hydrogen peroxide in combination with different catalysts/promoters to promote the
conversion of phenylboronic acid to phenol (Table 1, entries 12-16) with high yield.
However, the major drawback in these systems is the excess use of hydrogen peroxide
required. Hence, progress in this reaction requires development of a catalytic process in
where a minimum amount of hydrogen peroxide is used as oxidant for this transformation.
Furthermore, the present data show that the conversion of phenylboronic acid to phenol
catalyzed by Cu3(BTC)2 takes place without the addition of base or additive, thus increasing
the environmental benignity and the economic competitiveness of the entire chemical
process.
Table 1. Oxidative hydroxylation of phenylboronic acid to phenol catalyzed by MOFs.a
S. No
Catalyst
Time (min) Oxidant
Oxidant
Conversion
5

ACCEPTED MANUSCRIPT
(mmol)
(%)b
-
1
Fe(BTC)
-
-
-
2
Cu3(BTC)2
Fe(BTC)
-
-
-
-
3
60
60
60
60
60
60
60
60
60
5
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
Open air
Open air
H2O2
H2O2
H2O2
H2O2
H2O2
0.5
0.5
1
70
4
Cu3(BTC)2
Fe(BTC)
80
5
>99
>99
>99c
98d
97e
-
6
Cu3(BTC)2
Cu3(BTC)2
Cu3(BTC)2
Cu3(BTC)2
Fe(BTC)
1
7
1
8
1
9
1
10
11
12
13
14
15
16
-
Cu3(BTC)2
Lactic acid33
Biosilica40
Ag0/K10 mont.41
-
2f
17.6f
4.4f
35.2f
2f
-
95g
93g
92g
88g
97g
5
15
35
120
43
H3BO3
44
NH4HCO3
aReaction conditions: Phenylboronic acid (1mmol), catalyst (50 mg), acetone (3 mL), room
b
c
temperature, 1 h; Determined by gas chromatography; Reaction was performed in CDCl3
1
d
e
and the conversion was determined by H-NMR; With 0.2 mL of triethylamine; With 120
f
mg of 4-NH2-TEMPO; mmol of H2O2 required to convert 1 mmol of phenylboronic acid;
gReported yield.
Although Cu3(BTC)2 and Fe(BTC) exhibited comparable activity for the
transformation of arylboronic acids to phenols under the present experimental conditions,
further studies were performed using Cu3(BTC)2 that exhibits somewhat higher catalytic
activity than Fe(BTC) (Table 1, entries 3 and 4). Thus, the study of the catalytic activity of
Cu3(BTC)2 as a heterogeneous catalyst for the oxidative hydroxylation of phenylboronic acid
to phenol was expanded to phenylboronic acids substituted with electron donating or
withdrawing groups under optimized reaction conditions. The results attained are given in
Table 2. 4-Chlorophenylboronic acid and 4-fluorophenylboronic acid resulted in quantitative
6

ACCEPTED MANUSCRIPT
conversion with very high selectivity towards the corresponding phenols in 1 h time (Table 2,
entries 1 and 2). 4-Formylphenylboronic acid and 4-carboxyphenylboronic acid gave 99 and
97% conversions in 45 and 60 min, respectively, without oxidation of the formyl group
(Table 2, entries 3 and 4). Interestingly, the oxidation conditions are also compatible with the
presence of C=C double bonds that are generally reactive under oxidation conditions at
temperatures higher than ambient and, in this way, 4-vinylphenylboronic acid exhibited 99%
conversion and complete selectivity to 4-hydroxystyrene in 45 min (Table 2, entry 5). This
selectivity derives from the room temperature and short reaction times required for the
Cu3(BTC)2 oxidation. Interestingly, 4-trifluoromethylphenylboronic acid also afforded the
respective phenol in quantitative conversion with 99% selectivity in spite of the strong
electron withdrawing effect of the –CF3 group (Table 2, entry 6). 4-Methylphenylboronic
acid and 4-methylthiophenylboronic acid showed 99 and 98% conversions in 60 min,
respectively, with very high selectivities under optimized reaction conditions (Table 2, entries
7 and 8). The reaction also proceeds for condensed polycyclic arenes and in this way, 2-
napthylboronic acid also gave 99% conversion with 99% selectivity of 2-naphthol in 60 min
(Table 2, entry 9). In contrast, 2-bromo-5-thiophenylboronic acid resulted in the formation of
2-bromothiophene with 95% conversion and 96% selectivity (Table 2, entry 10). Finally,
oxidation of 4-hydroxyphenylboronic acid pinacolyl ester resulted in the formation of a
mixture of hydroquinone and quinone after 9 h (Table 2, entry 11). The requirement of longer
reaction times in this case may be explained as due to the steric encumbrance of pinacolyl
ester respect to boronic acids and the fact that the reaction is taking place inside the pores of
Cu3(BTC)2.
Table 2. Scope of Cu3(BTC)2 as a heterogeneous catalyst for the oxidative hydroxylation of
various phenylboronic acids to the corresponding phenols.
7

ACCEPTED MANUSCRIPT
S. No Substrate
1
product
Time
(min)
Conversion Selectivity
(%)b
(%)b
60
60
45
60
45
60
60
60
60
99
98
2
3
4
5
6
7
8
9
98
99
97
99
99
99
98
99
99
97
96
99
99
98
98
99
10
11
120
540
95
99
96
99c
aReaction conditions: Phenylboronic acid (1 mmol), Cu3(BTC)2 (50 mg), acetone (3 mL),
H2O2 (1 mmol), room temperature; bDetermined by gas chromatography; cCorresponds to the
combined selectivity to hydroquinone and quinine.
8

ACCEPTED MANUSCRIPT
One of the main advantages of the heterogeneous catalysts is the possibility to recover
the solid from the reaction mixture, allowing its reuse in subsequent runs. In this context,
Cu3(BTC)2 was reused as catalyst. After completion of the reaction, the catalyst was filtered,
washed with acetone, dried in an oven, and reused for the next run. The catalytic activity of
Cu3(BTC)2 showed no significant change in its activity after two reuses. The Cu3(BTC)2
stability under the oxidation conditions was further confirmed by the absence of leached
copper in the reaction mixture as evidenced by ICP-OES elemental analysis of the liquid
phase after the reaction. Figure 1 shows the powder XRD of the fresh and two times used
Cu3(BTC)2. It was observed that the crystallinity of the reused solid coincides with that of the
fresh catalyst, thus confirming the stability of the catalyst under the present oxidation
conditions. Furthermore, Figure 2 shows EPR spectra of fresh and two times reused
Cu3(BTC)2. The oxidation state of Cu in the reused catalyst is still +2, although it seems that
the intensity of the peak is reduced. This may be due to the adsorption of some reactants or
products in the pore of Cu3(BTC)2 or to partial reduction of some Cu(II) ions to Cu(I) by
H2O2 as reducing agent in low extent without resulting in noticeable collapse of the
Cu3(BTC)2 structure.
9

ACCEPTED MANUSCRIPT
(b)
(a)
10
20
30
40
50
60
70
o
2 Theta ( )
Figure 1. Powder XRD of (a) fresh Cu3(BTC)2 and (b) two times reused Cu3(BTC)2.
2000
2500
3000
3500
4000
Magnetic Field Strength (G)
Figure 2. EPR spectra of fresh Cu3(BTC)2 (blue line) and two times reused Cu3(BTC)2 (red
line).
10

ACCEPTED MANUSCRIPT
3. Conclusions
In conclusion, the catalytic activity of Cu3(BTC)2 as heterogeneous catalyst for the
oxidative hydroxylation of phenylboronic acids to the corresponding phenols using H2O2 as
oxidant at room temperature is described. The main advantages of Cu3(BTC)2 as catalyst is
that no base or additives are required. Furthermore, the reaction is highly selective towards
the formation of phenol and products derived from other oxidation processes are not
observed, even when the compound contains substituents able to undergo oxidation. This
catalyst can be reused without significant drop in its activity. Although Fe(BTC) exhibits also
notable catalytic activity, its performance is somewhat lower than that of Cu3(BTC)2.
4. Experimental
4.1. Materials
Cu3(BTC)2 and Fe(BTC) are commercially available from Sigma Aldrich as Basolite
C 300 (31.5% of Cu) and F 300 (25.2% of Fe) MOFs, respectively. Phenylboronic acid and
its derivatives (95-99% purity) and 35% H2O2 were purchased from Sigma Aldrich and used
as received. Solvents used in the present study were purchased from Sigma Aldrich and are
AR grade.
4.2 Instrumentation
Powder XRD diffraction patterns were measured in the refraction mode in a Philips
X’Pert diffractometer using the CuKα radiation (λ = 1.54178 Å) as the incident beam,
PW3050/60 (2 theta) as Goniometer, PW 1774 spinner as sample stage, PW 3011 as detector,
incident mask fixed with 10 mm. PW3123/10 for Cu was used as a monochromator.
PW3373/00 Cu LFF was used as X-ray tube with power scanning of 45 kV and 40 mA
current. The sample powder was loaded into a holder and levelled with a glass slide before
11

ACCEPTED MANUSCRIPT
mounting it on the sample chamber. The specimens were scanned between 2o and 70o with
the scan rate of 0.02o/s. ESR spectra were recorded by using a Bruker EMX spectrometer,
with the typical settings (frequency 9.80 GHz, sweep width 30.6 G, time constant 80 ms,
modulation frequency 100 kHz, modulation width 0.2 G, microwave power 200 mW).
4.3 Reaction procedure
In a typical reaction, 50 mg of catalyst was added to 3 mL of acetone containg 1
mmol of phenylboronic acid. This reaction mixture was stirred at room temperature for the
required time as indicated in Tables 1 and 2. The reaction progress was monitored by gas
chromatography and after completion of the reaction, the mixture was washed twice with
acetone and filtered. Then, the solvent was removed and the product is analyzed by gas
chromatography for its purity and selectivity. Conversion and selectivity were determined by
Agilent gas chromatography using internal standard method. 1H-NMR spectra were recorded
with 400 MHz using tetramethylsilane as internal standard. The same procedure is followed
for the reusability experiments.
Acknowledgements
ADM thanks University Grants Commission (UGC), New Delhi for the award of
Assistant Professorship under its Faculty Recharge Programme. ADM also thanks
Department of Science and Technology, India, for the financial support through Fast Track
project (SB/FT/CS-166/2013) and the Generalidad Valenciana for financial aid supporting his
stay at Valencia through the Prometeo programme. Financial support by the Spanish Ministry
of Economy and Competitiveness (CTQ-2012-32315 and Severo Ochoa) and Generalidad
Valenciana (Prometeo 2012-014) is gratefully acknowledged. The research leading to these
results has received partial funding from the European Community’s Seventh Framework
Programme (FP7/2007–2013) under grant agreement no. 228862.
12

ACCEPTED MANUSCRIPT
References and notes
1.
2.
3.
4.
Tyman, J. H. P. Synthetic and Natural Phenols; Elsevier: New York 1996.
Rappoport, Z. The Chemistry of Phenols; Willey-VCH: Weinheim 2003.
Hoarau, C.; Pettus, T. R. R. Synlett. 2003, 127.
Hanson, P.; Jones, J. R.; Taylor, A. B.; Walton, P. H.; Timms, A. W. J.Chem. Soc., Perkin Trans.
2 2002, 1135.
5.
6.
7.
Thakur, K. G.; Sekar, G. Chem. Commun. 2011, 47, 6692.
Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. J. Am. Chem. Soc. 2006, 128, 10694.
Schulz, T.; Torborg, C.; Schaffner, B.; Huang, J.; Zapf, A.; Kadyrov, R.; Borner, A.; Beller, M.
Angew. Chem., Int. Ed. 2009, 48, 918.
8.
Zhao, D.; Wu, N.; Zhang, S.; Xi, P.; Su, X.; Lan, J.; You, J. Angew. Chem., Int. Ed. 2009, 48,
8729.
9.
10.
Tlili, A.; Xia, N.; Monnier, F.; Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 8725.
Toyao, T.; Ueno, N.; Miyahara, K.; Matsui, Y.; Kim, T.-H.; Horiuchi, Y.; Ikeda, H.; Matsuoka, M.
Chem. Commun. 2015, 10.1039/c5cc06163f.
11.
12.
Yu, X.; Cohen, S. M. Chem. Commun. 2015, 51, 9880-9883.
Zou, Y.-Q.; Chen, J. R.; Liu, X.-P.; Lu, L.-Q.; Davis, R. L.; Jørgensen, K. A.; Xiao, W.-J. Angew.
Chem. Int. Ed. 2012, 51, 784 -788.
13.
14.
Pelter, A.; Smith, K.; Brown, H. C. Borane Reagents; Academic Press: New York 1988.
Lam, P. Y. S.; Bonne, D.; Vincent, G.; Clark, C. G.; Combs, A. P. Tetrahedron Lett. 2003, 44,
1691.
15.
16.
Jung, Y. C.; Mishra, R. K.; Yoon, C. H.; Jung, K. W. Org. Lett. 2003, 5, 2231.
Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O’Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev.
2009, 38, 1257-1283.
17.
18.
19.
20.
Natarajan, S.; Mahata, P. Chem. Soc. Rev. 2009, 38, 2304-2318.
Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Catal. Sci. Technol. 2011, 1, 856-867.
Dhakshinamoorthy, A.; Asiri, A. M.; Garcia, H. Chem. Soc. Rev. 2015, 44, 1922-1947.
Chui, S. S. Y.; Lo, S. M.-F.; Charmant, J. P. H.; Guy Orpen, A.; Williams, I. D. Science 1999, 283,
1148-1150.
21.
22.
23.
24.
25.
26.
Schlichte, K.; Kratzke, T.; Kaskel, S. Micropor. Mesopor. Mater. 2004, 73, 81-88.
Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. ACS Catal. 2011, 1, 48-53.
Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. J. Catal. 2009, 267, 1-4.
Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Chem. Eur. J. 2010, 16, 8530 - 8536.
Dhakshinamoorthy, A.; Garcia, H. Chem. Soc. Rev. 2014, 43, 5750-5765.
Dhakshinamoorthy, A.; Alvaro, M.; Concepcion, P.; Garcia, H. Catal. Commun. 2011, 12,
1018-1021.
27.
28.
29.
Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Catal. Lett. 2015, 145, 1600-1605.
Piera, J.; Backvall, J.-E. Angew. Chem., Int. Ed. 2008, 47, 3506.
Simon, J.; Salzbrunn, S.; Surya Prakash, G. K.; Petasis, N. A.; Olah, G. A. J. Org. Chem. 2001,
66, 633-634.
30.
31.
Chatterjee, N.; Chowdhury, H.; Sneh, K.; Goswami, A. Tetrahedron Lett., 2015, 56, 172-174.
Chowdhury, A. D.; Mobin, S. M.; Mukherjee, S.; Bhaduri, S.; Lahiri, G. K. Eur. J. Inorg. Chem.
2011, 3232-3239.
32.
Surya Prakash, G. K.; Chacko, S.; Panja, C.; Thomas, T. E.; Gurung, L.; Rasul, G.; Mathew, T.;
Olah, G. A. Adv. Synth. Catal. 2009, 351, 1567 - 1574.
33.
34.
35.
36.
37.
Gupta, S.; Chaudhary, P.; Seva, L.; Sabiah, S.; Kandasamy, J. RSC Adv. 2015, 5, 89133-89138.
Chatterjee, N.; Goswami, A. Tetrahedron Lett. 2015, 56 1524-1527.
Inamoto, K.; Nozawa, K.; Yonemoto, M.; Kondo, Y. Chem. Commun. 2011, 47, 11775-11777.
Yang, H.; Li, Y.; Jiang, M.; Wang, J.; Fu, H. Chem. Eur. J. 2011, 17, 5652 - 5660.
Kaboudin, B.; Abedi, Y.; Yokomatsu, T. Eur. J. Org. Chem. 2011, 6656-6662.
13

ACCEPTED MANUSCRIPT
38.
39.
Xu, J.; Wang, X.; Shao, C.; Su, D.; Cheng, G.; Hu, Y. Org. Lett. 2010, 12, 1964-1967.
Mulakayala, N.; Ismail; Kumar, K. M.; Rapolu, R. K.; Kandagatla, B.; Rao, P.; Oruganti, S.; Pal,
M. Tetrahedron Lett. 2012, 53 6004-6007.
40.
41.
42.
Mahanta, A.; Adhikari, P.; Bora, U.; Thakur, A. J. Tetrahedron Lett. 2015, 56 1780-1783.
Begum, T.; Gogoi, A.; Gogoi, P. K.; Bora, U. Tetrahedron Lett. 2015, 56 95-97.
Affrose, A.; Azath, I. A.; Dhakshinamoorthy, A.; Pitchumani, K. J. Mol. Catal. A: Chem. 2014,
395 500-505.
43.
44.
Gogoi, K.; Dewan, A.; Gogoi, A.; Borah, G.; Bora, U. Heteroatom Chem. 2014, 25, 127-130.
Jiang, M.; Yang, H.-J.; Li, Y.; Jia, Z.-Y.; Fu, H. Chin. Chem. Lett. 2014, 25, 715-719.
14