Pd/C-catalyzed one-pot Suzuki-Miyaura cross-coupling/hydrogenation of pyridine derivatives

Article abstract of DOI:10.1002/jhet.4341

Using bromopyridines and methoxyphenyl boronic acid as starting materials, consecutive Suzuki-Miyaura cross-coupling and hydrogenation reactions were undertaken using a heterogeneous Pd/C catalyst in one-pot manner under mild conditions (balloon-pressure at room temperature for hydrogenation) with excellent yield. To counter Pd leaching as well as catalyst poisoning, addition of an appropriate amount of H₂O was crucial to achieving successful AcOH-promoted hydrogenation, which ensured a selective reduction of the pyridine rings to the corresponding piperidines.

Full text of DOI:10.1002/jhet.4341

Received: 14 May 2021
DOI: 10.1002/jhet.4341
Revised: 9 June 2021
Accepted: 5 July 2021
C O M M U N I C A T I O N S
Pd/C-catalyzed one-pot Suzuki-Miyaura cross-coupling/
hydrogenation of pyridine derivatives
Dinda B. Pitna | Nao Tanaka | Toyonobu Usuki
Department of Materials and Life
Abstract
Sciences, Faculty of Science and
Technology, Sophia University, Tokyo,
Japan
Using bromopyridines and methoxyphenyl boronic acid as starting materials,
consecutive Suzuki-Miyaura cross-coupling and hydrogenation reactions were
undertaken using a heterogeneous Pd/C catalyst in one-pot manner under
mild conditions (balloon-pressure at room temperature for hydrogenation)
with excellent yield. To counter Pd leaching as well as catalyst poisoning, addi-
tion of an appropriate amount of H2O was crucial to achieving successful
AcOH-promoted hydrogenation, which ensured a selective reduction of the
pyridine rings to the corresponding piperidines.
Correspondence
Toyonobu Usuki, Department of Materials
and Life Sciences, Faculty of Science and
Technology, Sophia University, 7-1
Kioicho, Chiyoda-ku, Tokyo 102-8554,
Japan.
Email: t-usuki@sophia.ac.jp
Funding information
JSPS KAKENHI, Grant/Award Number:
20K05734
1 | INTRODUCTION
synthesis strategy [6]. Recently, our laboratory developed
an unprecedented Pd/C-mediated hydrogenation of
Palladium on activated carbon (Pd/C) is a powerful het-
erogeneous catalyst that has been used for various
heterogeneous coupling reactions even in the absence of
ligands, such as in the Heck [1], Sonogashira [2], and
Suzuki-Miyaura reactions [3]. Not only is the Pd/C cata-
lyst used for coupling reactions, but the reactivity of the
catalyst has also been examined extensively for a variety
of hydrogenative reductions of alkyne, benzylic carbonyl,
olefin, and hydroxyl groups [4]. The attractiveness of the
Pd/C catalyst relates to it being readily available and
being re-usable, which contributes to an overall cost
effectiveness as well as providing green chemistry solu-
tions for the chemical industry.
Despite the above benefits, Pd/C-catalyzed coupling
reactions have limitations including the use of
heteroarenes as substrates. Sajiki and co-workers
reported the great work: a ligandless-heteroaryl-aryl
Suzuki-Miyaura cross-coupling reaction using Pd/C with
excellent yields and high Pd reusability [5]. The limita-
tions of Pd/C also extend to hydrogenative reactions of
heterocyclic compounds. Numerous studies have
reported synthetic methods for substituted piperidine
products; however, most of the reports adopt a multi-step
42 heteroarenes/arenes-related substrates to furnish the
corresponding piperidines/cyclohexane compounds
under mild conditions (balloon pressure and room tem-
perature), along with application to the synthesis of
donepezil, a drug used for treatment of dementia in
Alzheimer's disease [7].
When a heterogeneous catalyst is used in a one-pot
manner, the approach represents a powerful means to per-
form environmentally friendly reactions. Although several
examples of such one-pot reactions with simple benzene
groups have been reported [8], there have been no such
reports on preparative methods for heterocyclic-containing
compounds. Herein, we report a Pd/C-mediated one-pot
sequential Suzuki-Miyaura coupling/hydrogenation reac-
tion to produce aryl-piperidine compounds.
2 | MATERIALS AND METHODS
2.1 | General procedures
All coupling reactions were conducted under ambient air
with magnetic stirring unless otherwise indicated. In
J Heterocyclic Chem. 2021;1–6.
wileyonlinelibrary.com/journal/jhet
© 2021 Wiley Periodicals LLC.
1

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PITNA ET AL.
regards to reactions conducted at room temperature, the
established range includes temperatures between 24 and
28 ꢀC. All reagents were obtained from commercial sup-
pliers and used without further purification unless other-
wise stated. 10 wt% palladium on carbon (Pd/C) was
purchased from Sigma Aldrich (St. Louis, MO, USA).
Hydrogen gas (>99.999%) was purchased from Fujii
Bussan (Tokyo, Japan). Analytical thin-layer chromatogra-
phy (TLC) was performed on Silica gel 60 F254 plates pro-
duced by Merck. Column chromatography was performed
with acidic Silica gel 60 (spherical, 40–50 μm) or neutral
Silica gel 60 N (spherical, 40–50 μm) produced by Kanto
Chemicals (Tokyo, Japan). Removal of a small amount of
solvent was performed by Smart Evaporator CEV1-SQ-P2,
CEV1-SK-P2, and CEV1A-GR-P2 (Kanagawa, Japan).
1H and 13C nuclear magnetic resonance (NMR) spec-
tra were recorded on Bruker Avance III HD 400 spectrom-
eter (400 MHz) or JEOL JNM-ECA 500 spectrometer
(500 MHz). 1H NMR data are reported as follows: chemi-
cal shift (δ, ppm), integration, multiplicity (s, singlet; d,
doublet; t, triplet; td, triplet doublet; q, quartet; m, multi-
plet), coupling constants (J) in Hz, assignments. 13C
NMR data are reported in terms of chemical shift (δ,
ppm). Gas chromatography electron impact quadrupole
mass spectrometry (GC-EI-Q-MS) spectra were recorded
on a Shimadzu GCMS QP5050A instrument. Electron
spray ionization time-of-flight mass spectrometry (ESI-
TOF-MS) spectra were recorded on a JEOL JMS-T100LC
instrument. Mass spectra are reported in mass-to-charge
ratio (m/z).
2.3 | General procedure for one-pot
Suzuki-Miyaura cross-coupling and
hydrogenation reaction
To a 10-ml flask equipped with a magnetic stir bar was
added 3-bromopyridine (0.25 mmol, 1.0 equiv),
4-methoxyphenyl boronic acid (57 mg, 0.375 mmol, 1.5
equiv), Na3PO4ꢁ12H2O (332 mg, 0.875 mmol, 3.5 equiv),
10 wt% Pd/C (9.3 mg, 0.00875 mmol, 3.5 mol%), and
iPrOH (1 ml). The reaction mixture was stirred vigorously
at 80 ꢀC. No nitrogen exchange was conducted however
to prevent solvent evaporation a balloon filled with nitro-
gen gas was used. After stirring for 6 h at 80 ꢀC, 10 wt%
Pd/C (44 mg, 0.0413 mmol, 16.5 mol%), AcOH (124 μl,
1.75 mmol, 8.7 equiv), and H2O (1 ml) were added to the
flask and hydrogen-filled balloon was attached. After
the mixture was stirred vigorously at room temperature
for 48 h, the reaction mixture was diluted with MeOH
and filtered through a Cellite pad. The filtrate was added
1 N HCl (2.75 ml, 1.1 equiv) and then repeated MeOH
evaporation to afford crude product. Without purifica-
1
tion, the yield was calculated based on H NMR yield.
When the conversion was not 100%, the yield was calcu-
lated based on the ratio of the starting material and the
product in 1H NMR analysis.
2.4 | 2-(4-Methoxyphenyl)-pyridine (3a)
The spectroscopic data was compared with previously
published data [1].
2.2 | General procedure for Suzuki-
Miyaura cross-coupling reaction
2.5 | 2-(4-Methoxyphenyl)-piperidine
hydrochloride (4aꢁHCl)
To a 10-ml flask equipped with a magnetic stir bar was
added halogenated pyridine (0.25 mmol, 1.0 equiv),
4-methoxyphenyl boronic acid (57 mg, 0.375 mmol, 1.5
equiv), Na3PO4ꢁ12H2O (332 mg, 0.875 mmol, 3.5 equiv),
10% Pd/C (9.3 mg, 0.00875 mmol, 3.5 mol%), and H2O/
iPrOH (0.5 ml each). No nitrogen exchange was con-
ducted however to prevent solvent evaporation a balloon
filled with nitrogen gas was used and the reaction mix-
ture was stirred vigorously at 80 ꢀC. After stirring for 3 h
at 80 ꢀC, the reaction mixture was allowed to cool down
to room temperature before quenching with water. The
reaction mixture was separated by filtration through Cel-
ite pad eluting with ether. The aqueous layer was then
extracted with ether (3 ꢂ 2 ml). The combined organic
layers were washed with brine, dried over Na2SO4, and
concentrated in vacuo. Purification by flash column chro-
matography afforded the coupling product.
1H NMR (500 MHz, CD3OD) δ 7.39–7.37 (2H, d,
J = 7.4 Hz), 6.96–6.96 (2H, d, J = 8.8 Hz), 4.11 (1H, m),
3.77 (3H, s,), 3.39–3.37 (1H, d, J = 13.1 Hz), 3.14–3.09
(2H, m), 1.98 (2H, m), 1.79–1.65 (3H, m); ESI-HRMS
(m/z) calcd for C12H18NO [M + H]+ 192.1388, found
192.1369.
2.6 | 3-(4-Methoxyphenyl)-piperidine
hydrochloride (4bꢁHCl)
1H NMR (500 MHz, CD3OD) δ 7.49–7.47 (2H, d,
J = 9.2 Hz), 6.97–6.95 (2H, d, J = 8.6 Hz), 3.85 (3H, s,
Me), 1.57 (5H, m), 1.27 (3H, m), 0.90–0.88 (1H, m); ESI-
MS (m/z) calcd for C12H18NO [M + H]+ 192.14, found
192.14.

PITNA ET AL.
3
2.7 | 4-(4-Methoxyphenyl)-piperidine
hydrochloride (4cꢁHCl)
1H NMR (500 MHz, CD3OD) δ 7.19–7.17 (2H, d,
J = 8.6 Hz), 6.88–6.87 (2H, d, J = 8.8 Hz), 3.77 (3H, s,
Me), 3.48–3.46 (2H, d, J = 12.5 Hz), 3.12–3.07 (2H, td,
J = 2.5, 13.2 Hz), 2.85–2.80 (1H, m), 2.03–2.00 (2H, m),
1.90–1.80 (2H, m); ESI-MS (m/z) calcd for C12H18NO [M
+ H]+ 192.14, found 192.14.
coupling reaction product 3a, hydrogenation was carried
out according to a previously reported protocol (10 mol%
Pd/C, H2-balloon pressure) [7]. It was found that the
hydrogenation of a biaryl compound required a longer
reaction time of 48 h (compared to just pyridine hydroge-
nation, which only required 15 h) to afford 4a. Given
confirmation of the reduction of the pyridine ring with a
directly attached aryl group to the aryl piperidine com-
pound, the sequential one-pot Suzuki-Miyaura coupling/
hydrogenation reaction was attempted.
In a follow-up study, we examined the suitability of
the solvent for the hydrogenation of 2-(4-methoxyphenyl)-
pyridine (3a) to 2-(4-methoxyphenyl)-piperidine (4a) using
20 mol% Pd/C at room temperature under a balloon-
pressure H2 atmosphere in the same pot as the first step
(Table 1). For the standard conditions, compound 3a was
afforded using the Suzuki-Miyaura cross-coupling reaction
from the previously mentioned procedure but with a slight
modification, whereby the reaction flask was not purged
with N2 gas. After the coupling reaction was complete
(monitored by TLC), the product was subjected to hydro-
genation by attaching the H2 balloon without further puri-
fication. The conditions were varied with regards to the
loading amount of the Pd/C catalyst (x mol%), additional
solvent (y ml), and additives (z equiv) before attaching the
H2 balloon. After vigorous stirring for 48 h, the reaction
was quenched with HCl (1 N, 1.1 equiv) and the yield was
calculated by 1H NMR.
2.8 | 2-(4-Methoxyphenyl)-
3-methylpiperidine hydrochloride (4dꢁHCl)
1H NMR (500 MHz, CD3OD) δ 7.23 (2H, d, J = 8.8 Hz),
7.02 (2H, d, J = 9.0 Hz), 4.47 (1H, s), 3.81 (3H, s), 3.46
(1H, d, J = 13.4 Hz), 3.16 (1H, s), 2.30 (1H, m), 2.08–1.63
(4H, m), 0.90 (3H, d, J = 7.4 Hz); 13C NMR (125 MHz,
CD3OD) δ 16.1.1, 129.5, 128.7, 63.7, 55.9, 46.8, 34.2, 30.5,
30.2, 18.3, 12.1; ESI-HRMS (m/z) calcd for C13H19NO [M
+ H]+ 206.1545, found 206.1543.
3 | RESULTS AND DISCUSSION
The study commenced with examining the feasibility of
performing a hydrogenation reaction of a heterocylic-aryl
compound over Pd/C in a stepwise manner (Scheme 1).
Pd/C (x mol%)
H2 (balloon)
(HO)2B
Na3PO4·12H2O (1 equiv)
additive (z equiv)
N
H
solvent (y mL)
rt, 48 h
N
Br
iPrOH/H2O (1/1; 1 mL)
80 °C, 2 h
OMe
2 (1.5 equiv)
OMe
1a
4a
First, 2-bromopyridine (1a) and 4-methoxyphenyl
boronic acid (2) were selected as model substrates and
subjected to Suzuki-Miyaura cross-coupling according to
Sajiki's protocol (3.5 mol% Pd/C, Na3PO4ꢁ12H2O, 3 h,
80 ꢀC, 50% iPrOH, N2 atmosphere) [5]. Then with the
First, 0.5 ml of additional H2O and 2 equivalents of
AcOH were added during hydrogenation and product 4a
was obtained in 56% yield (entry 1, Table 1). Two equiva-
lents of acid were used assuming that the first equivalent
would neutralize the base from the coupling reaction
N
Br
Pd/C (3.5 mol%)
Pd/C (10 mol%)
H2 (balloon)
1a
Na3PO4·12H2O
(3.5 equiv)
N
H
N
AcOH
iPrOH/H2O (1/1)
OMe
OMe
rt, 48 h, quant
(HO)2B
80 °C, 3 h, quant
SCHEME 1 Feasibility test of
hydrogenation of 3a using the
above protocol (stepwise, not
one-pot)
4a
3a
OMe
2 (1.5 equiv)

4
PITNA ET AL.
TABLE 1 Investigation of catalyst
amount, solvent, and additive in one-
pot sequential Suzuki-Miyaura coupling
and hydrogenation reaction
Entry
Pd/C (x mol%)
Solvent (y ml)
H2O (0.5)
H2O (0.25)
H2O (1)
Additive (z equiv)
AcOH (2)
AcOH (2)
AcOH (2)
AcOH (4)
AcOH (2)
TBAF (1)
KF (2)
Yield of 4a/%
1
10
10
10
10
10
10
10
10
10
10
20
20
56
33
50
22
11
54
-
2
3
4
H2O (1)
5
H2O (2)
6
H2O (0.5)
H2O (0.5)
-
7
8
HCl (1.1)
-
52
41
42
93
Quant
9
iPrOH (0.5)
H2O (0.5)
H2O (0.5)
H2O (0.5)
10
11
12
-
TBAF (1)
AcOH (2)
Pd/C (10 mol%)
Meanwhile, although KF successfully facilitated the de-
aromatization of the pyridine ring of 1b (Equation 1), it
did not promote the hydrogenation reaction of the biaryl
compound 3a.
H2 (balloon)
Br
TBAF or KF (1 equiv)
(eq 1)
N
H
AcOH
N
rt, 15 h, quant
HCl was used instead of AcOH and afforded similar
reactivity to that in entry 1 (entry 8). The combination of
additional H2O and Clꢃ may have promoted the hydroge-
nation. The addition of only iPrOH (entry 9) or H2O
(entry 10) did not provide as high a yield as entry 1, indi-
cating the important role of AcOH. When the Pd/C load-
ing was increased to 20 mol%, the overall yield was
improved to 93% (entry 11), which was almost twice that
of entry 6 (54%). The reaction conducted under similar
conditions to that of entry 1, but with a higher loading
amount of catalyst, furnished a quantitative yield (entry
12). Based on these investigations, the optimum condi-
tions for the subsequent hydrogenation reaction were as
follows: 20 mol% Pd/C, H2O (0.5 ml), and AcOH
(2 equiv). Given that TBAF is relatively expensive, AcOH
was used as the additive in subsequent experiments with
different substrates.
The conditions of the Suzuki-Miyaura cross-coupling
reaction were changed depending on the substrates
(Scheme 3). For 2-bromopyridine 1a, 1 equivalent of base
was sufficient, and the solvent was a mixture of iPrOH
and H2O, whereas the other isomers 1b and 1c required
use of a minimum of 3.5 equivalents in an absolute
iPrOH solvent system. In the case of 1c, another equiva-
lent of base was employed to neutralize the HCl of the
starting material. For these three substrates, Pd/C was
added gradually because the addition of 20 mol% of Pd/C
at the beginning of the reaction hindered the coupling.
The reaction of 1d required large amounts of Pd/C,
20 mol% and 80 mol%, at the coupling step and the
piperidine
1b
Pd/C (10 mol%)[7]
H2 (balloon)
Br
(eq 2)
AcOH
N
N
rt, 15 h, quant
pyridine
1b
SCHEME 2 Hydrogenation of 1b using TBAF or KF as an
additive (Equation 1); hydrodehalogenation of 1b [7] (Equation 2)
whereas the other equivalent would protonate the sub-
strate and thereby promote the hydrogenation reaction.
From the results of the investigation of concentration as
shown in entries 1–5, the concentration needed to be
kept between 0.125 and 0.25 μM. TBAF and KF were
tested as additives (entries 6 and 7) because these
reagents were able to catalyze hydrogenation of
3-bromopyridine (1b) to afford a quantitative yield of
piperidine in a preliminary experiment (Equation 1,
Scheme 2). The pyridine ring of 1b is not reducible in
AcOH solvent due to catalyst poisoning by the bromide
ion according to a previous report (Equation 2) [8,9].
Despite TBAF being a mild base, its performance gave
the desired product with a similar yield to that in entry
1, implying acidic conditions are not strictly necessary to
catalyze the hydrogenation reaction but rather the pres-
ence of a counter ion to interact with the bromide ion
generated from the coupling reaction is required.

PITNA ET AL.
5
1) Pd/C (3.5 mol%)
The reaction rate of the hydrogenation step is highly
dependent on the electronic states of the pyridine rings
as well as the positions and the steric hindrances of the
substituents according to previous reports [7,10].
Although the aryl group attached directly to the pyridine
core could be sterically bulky, the loading of 20 mol% of
Pd/C was sufficient to furnish the piperidine rings within
the target compounds 4a-c. The chemo-selectivity of the
hydrogenation in this work was not consistent with the
previous report [7] where a pyridine-type moiety could
be completely reduced while a benzene-type arene could
persist under the reaction conditions. This selectivity can
be accounted for by the frontier molecular orbital proper-
ties of the protonated aryl-pyridines. Most importantly,
the mechanism of the hydrogenation is completely differ-
ent than that of the cross-coupling reaction, that is, the
substrates can be hydrogenated on the Pd surface
whereas the homogeneous catalytic cycle is triggered by
leaching of Pd due to the oxidative addition of heteroaryl
halides [11]. As such, a careful selection of H2O as the
solvent was crucial to the efficiency of the hydrogenation
step [7,12] when considering the necessity to promote
reabsorption of Pd back onto the support and to restrict
the catalyst poisoning activity of the released bromide ion
on the metal surface [13].
OMe
Na3PO4·12H2O (3.5 equiv)
iPrOH (1 mL), 80 °C, 6 h
Br
2) Pd/C (16.5 mol%)
H2 (balloon)
N
N
H
4b (96%)
1b
AcOH (7 equiv), H2O (1 mL)
rt, 48 h
1) Pd/C (3.5 mol%)
Na3PO4·12H2O (4.5 equiv)
iPrOH (1 mL), 80 °C, 3 h
OMe
Br
2) Pd/C (16.5 mol%)
HN
N
·HCl
H2 (balloon)
AcOH (7 equiv), H2O (1 mL)
rt, 48 h
4c (98%)
1c
1) Pd/C (20 mol%)
Na3PO4·12H2O (1 equiv)
iPrOH/H2O (0.5 mL/0.5 mL)
80 °C, 3 h
N
H
2) Pd/C (80 mol%)
H2 (balloon)
N
Br
OMe
4d (64%)
1d
AcOH (2 equiv), H2O (0.5 mL)
rt, 48 h
SCHEME 3 Scope of one-pot Suzuki-Miyaura cross-coupling/
hydrogenation reaction for various substrates. The heteroarene
compound (1 equiv) was stirred with 2 (1.5 equiv) under ambient
air in the presence of Pd/C (3.5 mol%) and Na3PO4ꢁ12H2O at 80 ꢀC.
after the coupling reaction was complete, additional Pd/C and H2O
were added and stirred under a H2 atmosphere. The yield was
determined by 1H NMR analysis
4 | CONCLUSION
In conclusion, optimization of a one-pot method for a
sequential Suzuki-Miyaura coupling and mild hydroge-
nation of heteroarenes-aryl compound using catalytic
Pd/C under H2-balloon pressure at room temperature
was achieved. The Suzuki-Miyaura cross-coupling reac-
tion can proceed under ambient air conditions and
hydrogenation of the pyridine requires only AcOH/H2O
to afford aryl piperidine under H2 balloon-pressure at
room temperature. The proposed reaction scheme would
be applicable to other one-pot cross-coupling and hydro-
genation reactions for synthesis of more complex
molecules.
hydrogenation stage, respectively, due to steric hindrance
effects. The reaction of 3-amino-2-bromopyridine was
conducted under the same condition as 1b. However, the
trace amount of product was obtained (data not shown).
Moreover, the quantity of AcOH and H2O added for
hydrogenation varied depending on the amount of base
and H2O used for the coupling reaction, respectively.
From the investigation of the substrates, it was necessary
to add not only 2x equivalents of AcOH for each
x equivalent of base (Equation 3) but also a certain
amount of H2O to ensure that the starting material con-
centration (0.25 M) with respect to H2O (Equation 4) was
optimal for achieving a successful hydrogenation. These
observations showed the importance of using H2O as a
major component of the solvent system during hydroge-
nation in the presence of the halogen ion.
ACKNOWLEDGMENT
This work was supported in part by JSPS KAKENHI
grant number 20K05734.
CONFLICT OF INTEREST
For each x equiv of base ¼ 2x equiv of AcOH
ð3Þ
ð4Þ
The authors declare no conflicts of interest.
DATA AVAILABILITY STATEMENT
No data available for the study.
Concentration of substrate in total amount of H2O
¼ 0:25 M

6
PITNA ET AL.
[7] N. Tanaka, T. Usuki, Eur. J. Org. Chem. 2020, 2020, 5514.
ORCID
[8] L. Pedersen, M. F. Mady, M. O. Sydnes, Tetrahedron Lett.
2013, 54, 4772.
Toyonobu Usuki https://orcid.org/0000-0002-0212-5371
[9] a) K. Mackenzie, H. Frenzel, F. D. Kopinke, Appl. Catal. B
REFERENCES
ꢀ
2006, 63, 161. b) M. A. Aramendía, V. Borau, I. M. García, C.
[1] a) A. Eisenstadt, Chem. Ind. 1998, 75, 415. b) V. M. Wall, A.
Eisenstadt, D. J. Ager, S. A. Laneman, Platinum Met. Rev.
1999, 43, 138. c) T. Sakamoto, H. Arakida, K. Edo, H.
Yamanaka, Heterocycles 1981, 16, 965. d) A. Modak, J.
Mondal, V. K. Aswal, A. Bhaumik, J. Mat. Chem. 2010, 37,
8099.
Jiménez, A. Marinas, J. M. Marinas, F. J. Urban, Appl. Catal. B
2003, 43, 71. c) F. J. Urbano, J. M. Marinas, J. Mol. Catal. A
Chem. 2001, 173, 329.
[10] T. Usuki, A. Komatsu, Tetrahedron Lett. 2017, 58, 2856.
[11] I. W. Davies, L. Matty, D. L. Hughes, P. J. Reider, J. Am. Chem.
Soc. 2001, 123, 10139.
[2] a) S. Mori, T. Yanase, S. Aoyagi, Y. Monguchi, T. Maegawa, H.
Sajiki, Chem. Eur. J. 2008, 14, 6994. b) B. M. Choudary, S.
Madhi, M. L. Kantam, B. Sreedhar, Y. Iwasawa, J. Am. Chem.
Soc. 2004, 126, 2292.
[12] M. Soto, R. G. Soengas, H. Rodríguez-Solla, Adv. Synth. Catal.
2020, 362, 5422.
[13] J. Zhao, Y. Yuan, X. Meng, L. Duan, R. Zhou, Materials 2019,
12, 46.
[3] a) G. Marck, A. Villiger, R. Buchecker, Tetrahedron Lett. 1994,
35, 3277. b) C. R. LeBlond, A. T. Andrews, Y. K. Sun, J. R.
Sowa, Org. Lett. 2001, 3, 1555. c) K. Sarkar, M. Nandi, M.
Islam, M. Mubarak, A. Bhaumik, Appl. Catal. A: Gen. 2009,
352, 81.
[4] a) H. Sajiki, K. Hattori, K. J. Hirota, Chem. Soc. Perkin Trans.
1998, 1, 4043. b) K. Hattori, H. Sajiki, K. Hirota, Tetrahedron
2001, 57, 4817. c) A. Mori, Y. Miyakawa, E. Ohashi, T. Hago,
T. Maegawa, H. Sajiki, Org. Lett. 2006, 8, 3279.
[5] Y. Kitamura, S. Sako, A. Tsutsui, Y. Monguchi, T. Maegawa,
Y. Kitade, H. Sajiki, Adv. Synth. Catal. 2010, 352, 718.
[6] C. L. J. Wang, M. A. Wuonola, Org. Prep. Proced. Int. 1992,
24, 583.
SUPPORTING INFORMATION
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in the Supporting Information section at the end of this
article.
How to cite this article: D. B. Pitna, N. Tanaka,
T. Usuki, J. Heterocycl. Chem. 2021, 1. https://doi.
org/10.1002/jhet.4341