Aerobic oxidation and oxidative esterification of alcohols through cooperative catalysis under metal-free conditions

Article abstract of DOI:10.1039/d1cc02937a

The ABNO@PMO-IL-Br material obtained by anchoring 9-azabicyclo[3.3.1]nonane-3-oneN-oxyl (keto-ABNO) within the mesopores of periodic mesoporous organosilica with bridged imidazolium groups is a robust bifunctional catalyst for the metal-free aerobic oxidation of numerous primary and secondary alcohols under oxygen balloon reaction conditions. The catalyst, furthermore, can be successfully employed in the first metal-free self-esterification of primary aliphatic alcohols affording valued esters.

Full text of DOI:10.1039/d1cc02937a

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Aerobic oxidation and oxidative esterification of
alcohols through cooperative catalysis under
metal-free conditions†
Cite this: DOI: 10.1039/d1cc02937a
Received 5th June 2021,
Accepted 9th August 2021
ab
Babak Karimi,
Mario Pagliaro
*
Mina Ghahremani,a Hojatollah Vali,c Rosaria Ciriminnad and
d
*
DOI: 10.1039/d1cc02937a
rsc.li/chemcomm
The ABNO@PMO-IL-Br material obtained by anchoring 9- oxidation of primary alcohols in the presence of unprotected
azabicyclo[3.3.1]nonane-3-one N-oxyl (keto-ABNO) within the secondary alcohol groups, but the applicability of TEMPO-
mesopores of periodic mesoporous organosilica with bridged imi- based catalysts in the oxidation of non-activated aliphatic,
dazolium groups is a robust bifunctional catalyst for the metal-free secondary and sterically hindered primary alcohols is often
aerobic oxidation of numerous primary and secondary alcohols limited by the same steric constraints.5 To expand the scope of
under oxygen balloon reaction conditions. The catalyst, further- nitroxyl radical mediated-oxidations, the use of less hindered
more, can be successfully employed in the first metal-free self- bicyclic nitroxyl radicals such as 2-azaadamantan-N-oxyl (AZADO)
esterification of primary aliphatic alcohols affording valued esters. and 9-azabicyclo[3.3.1]nonane-N-oxyl (ABNO) has become increas-
ingly common.6
Thanks to their high selectivity and pronounced versatility, stable
Obtained through a multi-step (i.e. up to four steps to
nitroxyl radicals of the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) synthesis 1-Me-AZADO) synthetic process,7 AZADO derivatives
family are now well established as environmentally benign catalysts are relatively difficult to access. Prepared through a three-step
for the selective oxidation of a wide variety of alcohols to carbonyl synthetic route, the radical ABNO is an economically viable
compounds (and to carboxylic acids when reaction is carried out in nitroxyl radical bearing hydrogen atoms on the a-carbons
water).1 Primary oxidants such as bleach (NaOCl), hypervalent (avoiding to violate Bredt’s rule) alternative to AZADO.8 Known
iodine reagents, and O2 in combination with NOx co-catalysts such since the mid-1960s,9 such less-hindered nitroxyl radicals med-
as tert-butylnitrite (TBN)2 and sodium nitrite3 are generally iate the oxidation of sterically hindered alcohols for which
employed to promote catalytic turnover. Since the first transition- TEMPO is not a suitable catalyst. Applications include the
metal-free TEMPO-catalyzed aerobic oxidation of alcohols using efficient oxidation of chiral alcohols using chirally modified
molecular oxygen as a terminal oxidant, the catalytic method has AZADOs,10 as well as 9-azanoradamantane N-oxyl (Nor-AZADO)
replaced most alcohol oxidation stoichiometric routes, especially exhibiting higher catalytic activity than AZADO, ABNO and
those based on highly toxic chromium(VI) reagents and other metal TEMPO.11 Furthermore, combined with HNO3, NaNO2 (or both)
oxidants that until a decade ago were still widely employed to as co-catalysts and O2 as primary oxidant, ABNO and
oxidise alcohols in the fine chemical and pharmaceutical 9-azabicyclo[3.3.1]nonane-3-one N-oxyl (keto-ABNO) effectively
industries.4
mediate the oxidation of secondary alcohols along with imines
Sterically hindered by the four methyl groups, the oxo- bearing diverse functional groups.12 Similarly, in combination
ammonium group of TEMPO ensures the chemoselective with a catalytic amount of Cu(I), keto-ABNO successfully cata-
lyzes the selective oxidation of secondary alcohols, including
unactivated aliphatic substrates.13 The first metal- and
halogen-free keto-ABNO catalyst for the aerobic oxidation of
a Faculty of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS),
Gava Zang, PO Box 45195-1159, Zanjan 45137-66731, Iran.
alcohols under mild reaction conditions was reported in
2014.14a Denoted as SABNO, the latter is an heterogeneous
catalytic system comprised of SBA-15 functionalized with keto-
ABNO showing superior catalytic activity over SBA-15-supported
TEMPO in the aerobic oxidation of a wide range of alcohols
bearing diverse functional groups under conditions similar to
E-mail: karimi@iasbs.ac.ir
b Research Center for Basic Sciences & Modern Technologies (RBST), Institute for
Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
c Department of Anatomy and Cell Biology and Facility for Electron Microscopy
Research McGill University, Montreal, Quebec, H3A 2A7, Canada
d Istituto per lo Studio dei Materiali Nanostrutturati, CNR via U. La Malfa 153,
Palermo 90146, Italy. E-mail: mario.pagliaro@cnr.it
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1cc02937a those used with homogenous catalysts.14b We now report a
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Fig. 1 Schematic representation of ABNO@PMO-IL; for details of the
preparation, see ESI.†
Fig. 2 (a) N2 adsorption–desorption isotherms of all materials including
PMO-IL and ABNO@PMO-IL-Cl and inset BJH pore size distribution.
Va refers to the volume of adsorbed nitrogen in the pores of the materials.
(b) Side view TEM images of ABNO@PMO-IL-Cl. (Scale bar: 100 nm).
newly supported ABNO heterogeneous catalyst using a periodic
mesoporous silica functionalized with an imidazolium frame-
work (PMO-IL) as support in the metal-free aerobic oxidation of
alcohols, in analogy to the catalyst system comprising a robust
PMO with bridged imidazolium network (PMO-IL) further
functionalized with TEMPO (Fig. 1).15
The new catalyst, ABNO@PMO-IL, displays enhanced cata-
lytic activity in comparison to the latter PMO-IL system as well
to IL-free analogues due to the imidazolium bromide units in
close proximity to the ABNO moieties. A robust PMO with
bridged imidazolium network (PMO-IL) was initially prepared
according to previously reported protocol, wherein 1,3-bis
(3-trimethoxysilylpropyl)imidazolium chloride and Si(OMe)4 Fig. 3 XPS survey spectrum of ABNO@PMO-IL, and (inset) XPS spectrum
of the N (1s) electrons of ABNO@PMO-IL.
are hydrolyzed and co-condensed in the presence of Pluronic
P123 as a template under acidic conditions.16 The ABNO radical
According to literature data,17 the peak at 401.17 is attributed to
was then anchored to the inner mesoporous network by mixing
ABNO-functionalized silane, obtained via reductive amination
of keto-ABNO with 3-(amino propyl) trimethoxysilane in the
group NO,18 part of the ABNO molecular moieties attached to
presence of NaBH3CN. The textural properties of the resulting
ABNO@PMO-IL-Cl catalyst and PMO-IL are shown in Table 1
and Fig. 2a (wherein for clarity isotherms are shifted along the
finding is further corroborated by the results of the thermo-
y-axis) illustrate.
The type IV N2 adsorption–desorption isotherms with sharp
hysteresis loop (Fig. 2a) are characteristic of highly ordered
two nitrogen atoms in the imidazolium ring, whereas the first
signal at 399.26 is attributed to the nitrogen of the nitroxide
the surface of PMO-IL through the C–N covalent bond. This
gravimetric analysis (TGA) pointing to a loading of ABNO and IL
groups at 0.26 and 0.97 mmol gÀ1, respectively (ESI,† Fig. S1).
Evidence of successful anchoring of ABNO on the inner surface
mesoporous materials with a regular array of 2D hexagonal
of PMO-IL was further obtained by Fourier-transform infrared
pore structure. The specific surface area, total pore volume and
spectroscopy (FT-IR). Besides the signals characteristic of alkylimi-
pore diameter of ABNO@PMO-IL-Cl lower than those of pris-
dazolium groups, the FTIR spectrum of ABNO@PMO-IL-Cl dis-
plays a new band at 1351 cmÀ1 related to the N–O free radicals
tine PMO-IL, indicate that the organic moieties are grafted in
the inner surface of the mesochannels. This outcome is further
(Fig. S2, ESI†) in good agreement with previous results concerning
PMO-IL functionalized with TEMPO.15
supported by TEM images of ABNO@PMO-IL, showing highly
ordered cylindrical pores of uniform size (Fig. 2b). The X-ray
photoelectron spectroscopy (XPS) survey of ABNO@PMO-IL-Cl
a model substrate under relatively mild conditions with TBN as
(Fig. 3) confirms the presence of C, Si, O, Cl and N as the only
elements comprising this material, with chlorine present in the
form of chloride ions balancing the positive charge of the IL
framework. A closer look at the photoemission spectrum of the
decided to replace the chloride counter ions with bromide ions
N (1s) line reveals (inset in Fig. 3) two main contributions at
Tested in the aerobic oxidation of benzyl alcohol (BnOH) as
nitrite source (1 mol% catalyst, 0.5 mL toluene, 10 mol% HCl,
8 mol% TBN) at 50 1C, the ABNO@PMO-IL-Cl showed more
activity than SABNO (Table 2, entries 1 and 2). Therefore, we
by stirring the ABNO@PMO-IL-Cl catalyst in a saturated
399.26 eV (with a full width at half maximum, FWHM, of 1.48
solution of NaBr for 24 h. To our delight, employed in the
eV) and 401.17 eV (FWHM = 2.02) binding energy, respectively.
aerobic oxidation of BnOH under the aforementioned condi-
tions, the new ABNO@PMO-IL-Br catalyst exhibited excellent
catalytic activity not only in comparison to ABNO@PMO-IL-Cl
but also to IL-free SABNO, PMO-IL functionalized with TEMPO,
and even to homogeneous keto-ABNO (Table 2). The use
PMO-IL as a catalyst (Table 2; entry 6) resulted only in 15%
yields of benzaldehyde even after 12 h, clearly showing the
Table 1 Textural properties of PMO-IL and ABNO@PMO-IL-Cl
Material
SBET (m2 gÀ1
)
rP (nm)
VP (cm3 gÀ1
)
PMO-IL
ABNO@PMO-IL
526.65
231.10
5.29
3.53
1.002
0.43
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Table 2 Screening of aerobic oxidation of benzyl alcohol using ABNO
Table 3 Aerobic oxidation of various alcohols using ABNO@PMO-IL-Br
functionalized PMO-IL and SBA-15 catalysts
catalyst under metal-free conditions
Entry
Material
t (min)
Conv. (%)
1
2
3
4
5
6
ABNO@PMO-IL-Cl
ABNO@SBA-15 (SABNO)
ABNO@PMO-IL-Br
TEMPO@PMO-IL-Br
Keto-ABNO
120
120
30
120
30
97a
90a
499a
98
Entry
R1
R2
t (h)
Yielda (%)
90b
15c
1
2
3
4
5
6
7
8
C6H5
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
0.5
0.5
0.5
0.66
0.66
1
1
1.25
1
1.5
2
1.5
2
5
1.5
2
1.5
1
1
12
1
4
3
4
7
7
499
499
499
499
499
499
97
97
498
95
87
94
86
67
PMO-IL
12 h
4-Me–C6H5
3-Me–C6H5
2-Me–C6H5
4-iPr-C6H5
4-Cl–C6H5
3-Cl–C6H5
2-Cl–C6H5
4-Br–C6H5
2-Br–C6H5
2,4-DiCl–C6H5
4-NO2–C6H5
3-NO2–C6H5
2-NO2–C6H5
4-MeO–C6H5
2-MeO–C6H5
4-MeS–C6H5
1-Naphtyl
C6H5
a
Conditions: catalyst (1 mol%) in the presence of O2 (oxygen balloon,
621–622 torr) HCl (10 mol%) as additive and t-BuONO (TBN, 8 mol%) in
toluene (0.5 mL) as a solvent in the presence of molecular oxygen.
b
c
Using homogeneous Keto-ABNO (1 mol%). Using PMO-IL at the
corresponding IL loading (10%) (40 mg) prolonged time to 12 h.
All yields obtained via GC analysis using a standard method.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
crucial importance of co-supported ABNO and imidazolium
bromide in obtaining high catalytic activity. We thus tested
the new catalyst and the catalytic protocol in the selective
oxidation of different alcohol substrates. Results in Table 3
show that good to excellent yields were obtained in relatively
short time with all substrates.
94
95
95
H
H
Me
Me
Et
Ph
Cyclopentyl
—
Me
Me
Me
—
—
—
—
H
498
98b
499b
97b
96b
95b
97b
92c
Even deactivated 2-nitrobenzyl alcohol was converted into
the corresponding 2-nitrobenzaldehyde (an important precur-
sor of indigo carmine) in 67% yield (entry 14 in Table 3). The
oxidation of sterically hindered a-tetralol smoothly proceeded,
affording in 4 h a 96% yield in 1-tetralone (entry 24). For
comparison, the state-of-the art oxidation at room temperature
of the same substrate affording 89% yield in 1-tetralone
mediated by (Ph4P)[RuO2Cl3] dissolved in dichloromethane
requires a three-fold excess of N-methylmorpholine-N-oxide
(NMO) a primary oxidant in the presence of 4 Å molecular
sieves.19 The lowest yield in selectively oxidised product was
recorded for cyclooctanol affording 63% yield in cyclooctanone
(entry 29). For comparison, the oxidative dehydrogenation
of cyclooctanol to cyclooctanone over Pd/MgO under O2 at
70–80 1C affords a 58% yield.20 Not involving catalytic metal
species, the ABNO@PMO-IL-Br catalyst is ideally suited for
4-Ph–C6H5
C6H5
C6H5
C6H5
a-Tetralol
CH3(CH2)4
CH3(CH2)5
Cyclohexyl
Cycloheptyl
Cyclooctyl
Norbornyl
2-Admantyl
C6H5
90c
8
9
10
10
8
95c
99c
63c
86c
499c
7d
12
a
Conditions. Catalyst (1 mol%) in the presence of O2 (oxygen balloon,
b
621–622 torr), 10 mol% HCl, 8 mol% TBN, 0.3 mL toluene. 5 mol%
c
HCl. 1.5–2 mol% catalyst, 16 mol% TBN, 5 mol% HCl, 0.3 mL toluene.
d
Catalyst-free conditions. All yields obtained via GC analysis using an
internal standard FID calibration method (Fig. S4–S33).
the conversion of sulfur-containing substrates such as has been widely investigated as an important and highly atom-
4-(methylthio)benzyl alcohol which is quickly converted into economic process. Although being a highly desirable process
4-(methylthio) benzaldehyde in 98% yield (entry 17). The alde- for the industrial production of esters, the environmental and
hyde is the valued raw material of nonsteroidal anti- economic concerns associated with the high temperature and
inflammatory drug ‘‘sulindac’’. For comparison the best cur- pressure involved in state-of-the-art catalytic processes using
rent catalyst using air as primary oxidant, MnCo2O4, catalyzes precious metal catalysts are important issues that remain to be
the selective oxidation of 4-(methylthio)benzyl alcohol to the addressed.28 We thus investigated the activity of ABNO@PMO-
4-(methylthio) benzaldehyde in 96.5% yield.21 Finally, it is IL-Br in the direct oxidative esterification of alcohols, carrying
remarkable how the new catalyst successfully mediates the out the aerobic oxidation of BnOH under the optimized condi-
oxidation of secondary alcohols (entries 19–23 and 25–27) tions of entry 1 in Table 3. Prolonging the reaction time to 24 h
affording excellent (495%) yields under the same conditions showed no self-esterification product. Similarly, increasing the
employed for converting primary and secondary alcohols to amount of catalyst to 2 mol% and using 16 mol% of TBN nitrite
aldehydes and to ketones, respectively. The latter alcohols are source and 5 mol% of HCl, did not lead to the formation of
generally considered to be unaffected under the conditions benzyl benzoate. However, using the new catalyst in the aerobic
employed for the conversion of primary and secondary alcohol oxidation of primary aliphatic alcohols efficiently affords self-
substrates.22 The suitability of the catalysis for acid-sensitive esterified products (Table 4). To the best of our knowledge, this
silyl ether and acetal groups remains to be investigated.
is the first report on the self-esterification of primary aliphatic
The direct oxidative esterification of alcohols to esters over alcohols using a nitroxyl radical catalyst system under metal-
metal catalysts such as Ru,23 Pd,24 Ir,25 Au,26 Co (and Co3O4)27 free conditions (for proposed mechanism of self-esterification
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Table 4 Self-esterification of primary aliphatic alcohols over ABNO@
PMO-IL-Br under metal-free conditions
Notes and references
1 R. A. Sheldon, Catal. Today, 2015, 247, 4.
2 (a) Y. Xie, W. M. Mo, D. Xu, Z. L. Shen, N. Sun, B. X. Hu and X. Q. Hu,
J. Org. Chem., 2007, 72, 4288; (b) X. He, Z. Shen, W. Mo, N. Sun,
B. Hu and X. Hu, Adv. Synth. Catal., 2009, 351, 89; (c) C. Qiu, L. Jin,
Z. Huang, Z. Tang, A. Lei, Z. Shen, N. Sun, W. Mo, B. Hu and X. Hu,
ChemCatChem, 2012, 4, 76.
3 (a) X. Wang, R. Liu, Y. Jin and X. Liang, Chem. – Eur. J., 2008,
14, 2679; (b) C.-X. Miao, L.-N. He, J. Wang and J. Wang, Adv. Synth.
Catal., 2009, 351, 2209; (c) C.-X. Miao, L.-N. He, J. Wang and F. Wu,
J. Org. Chem., 2010, 75, 257.
4 (a) R. H. Liu, X. M. Liang, C. Y. X. Dong and Q. Hu, J. Am. Chem. Soc.,
2004, 126, 4112; (b) R. Ciriminna and M. Pagliaro, Org. Process Res.
Dev., 2010, 14, 245.
5 H. A. Beejapur, Q. Zhang, K. Hu, L. Zhu, J. Wang and Z. Ye, ACS
Catal., 2019, 9(4), 2777.
Entry
R
t (h)
Conv.a (%)
1
2
3
4
5
6
7
8
PhCH2CH2
CH3(CH2)2
CH3(CH2)3
CH3(CH2)6
CH3(CH2)7
CH3(CH2)8
PhCH2CH2
PhCH2CH2
20
15
15
15
15
20
20
20
75
91
80
87
85
83
(95)b
94c
6 S. Wertz and A. Studer, Green Chem., 2013, 15, 3116.
7 (a) M. Shibuya, Y. Osada, Y. Sasano, M. Tomizawa and Y. Iwabuchi,
J. Am. Chem. Soc., 2011, 133, 6497; (b) M. Shibuya, Y. Sasano,
M. Tomizawa, T. Hamada, M. Kozawa, N. Nagahama and
Y. Iwabuchi, Synthesis, 2011, 3418–3425.
8 M. Shibuya, M. Tomizawa, Y. Sasano and Y. Iwabuchi, J. Org. Chem.,
2009, 74, 4619.
9 R. M. Dupeyre and A. Rassat, J. Am. Chem. Soc., 1966, 88, 3180.
10 M. Tomizawa, M. Shibuya and Y. Iwabuchi, Org. Lett., 2009,
11, 1829.
a
Conditions. 1.5–2 mol% of catalyst in the presence of molecular
oxygen, 5 mol% HCl as an additive and 16 mol% TBN in 0.3 mL
toluene as a solvent. All products were detected using NMR spectro-
b
scopy. The progress of the reactions was monitored by GC. Using
Keto-ABNO (2 mol%), yields in parenthesis refer to the corresponding
aldehyde. Using SABNO (2 mol%), yield refer to the corresponding
c
aldehyde.
11 (a) M. Hayashi, Y. Sasano, S. Nagasawa, M. Shibuya and Y. Iwabuchi,
Chem. Pharm. Bull., 2011, 59, 1570; (b) H. Inada, K. Furukawa,
M. Shibuya and Y. Yamamoto, Chem. Commun., 2019, 55, 15105.
12 (a) M. B. Lauber and S. S. Stahl, ACS Catal., 2013, 3, 2612;
(b) T. Sonobe, K. Oisaki and M. Kanai, Chem. Sci., 2012, 3, 3249.
13 L. Rogan, N. L. Hughes, Q. Cao, L. M. Dornan and M. J. Muldoon,
Catal. Sci. Technol., 2014, 4, 1720.
14 (a) B. Karimi, E. Farhangi, H. Vali and S. Vahdati, ChemSusChem,
2014, 7, 2735; (b) B. Karimi, A. Biglari, J. H. Clark and V. Budarin,
Angew. Chem., Int. Ed., 2007, 46, 7210.
see Scheme S1 in the ESI†). Attempts to synthesis self-esterification
products either using homogenous keto-ABNO or SABNO under
optimized conditions were unsuccessful (aldehydes are the sole
products). This result highlights the importance of near molecular
proximity of supported ABNO and imidazolium bromide in the
nanoscale cavities of ABNO@PMO-IL-Br that could synergistically
contribute to the unique selective oxidative self-esterification of
primary aliphatic alcohols.
15 B. Karimi, S. Vahdati and H. Vali, RSC Adv., 2016, 6, 63717.
16 B. Karimi, D. Elhamifar, J. H. Clark and A. J. Hunt, Chem. – Eur. J.,
2010, 16, 8047.
In summary, we have discovered that anchoring of ABNO
moieties within the nanochannels of a PMO functionalized with
17 (a) J. Tan, D. Fang, Y. Liu and L. Hu, New J. Chem., 2019, 43, 2583;
(b) H. P. Steinruck, Phys. Chem. Chem. Phys., 2012, 14, 5010.
18 (a) O. Swiech, R. Bilewicz and E. Megiel, RSC Adv., 2013, 3, 5979;
(b) A. C. Dengel, W. P. Griffith, A. M. El-Hendawy and J. M. Jolliffe,
Polyhedron, 1990, 9, 1751–1756.
19 U. R. Pillai and E. Sahle-Demessie, Green Chem., 2004, 6, 161.
20 D. Li, F. Ruan, Y. Jin, Q. Ke, Y. Cao, H. Wang, T. Wang, Y. Song and
P. Cui, Catal. Sci. Technol., 2019, 9, 418.
imidazolium bromide network affords
a catalyst showing
enhanced catalytic activity in the metal-free aerobic oxidation of
numerous primary benzylic and secondary alcohols. Activity is
much higher than that of IL-free SABNO and PMO-IL function-
alized with TEMPO excellent catalysts, and even slightly higher
than homogenous keto-ABNO. The same ABNO@PMO-IL-Br solid
catalyst allows to perform the one-pot oxidative esterification of
non-activated aliphatic alcohols under mild reaction conditions.
The catalyst could be recycled in three consecutive reactions run in
the oxidation of benzyl alcohol with only a slight decrease in
catalytic activity. Besides a few interesting metal-free protocols for
aerobic oxidation of alcohols,28 these results open the route to new
effective and versatile approach for carrying out alcohol selective
oxidations and selective oxidative self-esterification of primary
aliphatic alcohols under mild metal-free conditions (oxygen bal-
loon, 50 1C).
21 D. Chen, Y. Zhang, X. Pan, F. Wang and S. Huang, Adv. Synth. Catal.,
2018, 360, 3607.
22 (a) J. Zhang, G. Leitus, Y. Ben-David and D. Milstein, J. Am. Chem.
Soc., 2005, 127, 10840; (b) C. Gunanathan, L. J. W. Shimon and
D. Milstein, J. Am. Chem. Soc., 2009, 131, 3146; (c) M. Nielsen,
H. Junge, A. Kammer and M. Beller, Angew. Chem., Int. Ed., 2012,
51, 5711.
23 (a) S. Gowrisankar, H. Neumann and M. Beller, Angew. Chem., Int.
Ed., 2011, 50, 5139; (b) C. Liu, J. Wang, L. Meng, Y. Deng, Y. Li and
A. Lei, Angew. Chem., Int. Ed., 2011, 22, 5144.
24 N. Yamamoto, Y. Obora and Y. Ishii, J. Org. Chem., 2011, 76, 2937.
25 H. Miyamura, T. Yasukawa and S. Kobayashi, Green Chem., 2010,
12, 776.
26 (a) R. V. Jagadeesh, H. Junge, M.-M. Pohl, J. Radnik, A. Bru¨ckner and
M. Beller, J. Am. Chem. Soc., 2013, 135, 10776; (b) W. Zhong, H. Liu,
C. Bai, S. Liao and Y. Li, ACS Catal., 2015, 5, 1850.
27 J. Otera and J. Nishikido, Esterification: Methods, Reactions, and
Applications, John Wiley & Sons, New York, 2nd edn, 2010.
28 (a) Z. Wang, J. Shi, D. Wang, Y. Pu, J. X. Wang and J. F. Chen, React.
Chem. Eng., 2019, 4, 507–515; (b) A. Das and S. S. Stahl, Angew.
Chem., Int. Ed., 2017, 56, 8892–8897; (c) W. Schilling, D. Riemer,
Y. Zhang, N. Hatami and S. Das, ACS Catal., 2018, 8(6), 5425–5430;
(d) S. Abednatanzi, P. G. Derakhshandeh, K. Leus, H. Vrielinck,
F. Callens, J. Schmidt, A. Savateev and P. Van Der Voort, Sci. Adv.,
2020, 6, eaaz2310.
The authors acknowledge IASBS Research Councils, and
Iranian National Science Foundation (INSF) to grant the
research (No. 99022450), the Alexander von Humboldt Founda-
tion (B. K.), NanoQuebec and NSER Council of Canada (H. V.)
for support of this work.
Conflicts of interest
The authors have no conflicts of interest to declare.
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