Selective synthesis of pyrimidines from cinnamyl alcohols and amidines using the heterogeneous OMS-2 catalyst

Article abstract of DOI:10.1016/j.catcom.2019.105846

Herein, an efficient aerobic oxidative synthesis of pyrimidines was carried out using cinnamyl alcohols and amidines catalyzed by manganese oxide octahedral molecular sieve (OMS-2). The heterogeneous catalytic method features base-/additive-free conditions, wide substrate scope, use of O₂ as a green oxidant, and simple operation. Moreover, the OMS-2 catalyst prepared by the conventional reflux method demonstrates catalytic selectivity, activity, and excellent recyclability.

Full text of DOI:10.1016/j.catcom.2019.105846

Catalysis Communications xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Selective synthesis of pyrimidines from cinnamyl alcohols and amidines
using the heterogeneous OMS-2 catalyst
a,⁎
b
Jian Shen , Xu Meng
a
School of Materials and Chemical Engineering, Ningbo University of Technology, Ningbo 315016, China
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of
b
Sciences, Lanzhou 730000, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Herein, an efficient aerobic oxidative synthesis of pyrimidines was carried out using cinnamyl alcohols and
Manganese oxide
Heterogeneous catalyst
Pyrimidine
Selective oxidation
N-heterocycles
amidines catalyzed by manganese oxide octahedral molecular sieve (OMS-2). The heterogeneous catalytic
method features base-/additive-free conditions, wide substrate scope, use of O as a green oxidant, and simple
2
operation. Moreover, the OMS-2 catalyst prepared by the conventional reflux method demonstrates catalytic
selectivity, activity, and excellent recyclability.
1. Introduction
has been used as agents for catalysis, battery materials, ion exchange,
and adsorption materials [19–24]. In addition, OMS-2 has a mixed-
valence of Mn (majority of Mn4+; minority of Mn
3+
and Mn ) and
2+
Pyrimidines and their derivatives are valuable and important N-
heterocyclic compounds because they are widely applied in agro-
chemicals, organic synthesis, natural products, functional materials,
molecular devices, and coordination chemistry as electron-rich ligands
shows an average oxidation state of 3.8 for manganese, which enables it
to be an excellent heterogeneous redox catalyst in the synthesis of fine
chemicals, removal of VOCs, degradation of pollutants in wastewater,
electrocatalysis, and water oxidation [21–28]. In terms of OMS-2 pre-
paration, in addition to the conventional reflux and hydrothermal
methods, solvent-free, microwave, and sonochemical methods were
developed [16,35]. Because of the different physicochemical properties
of OMS-2 obtained by various methods, it shows selective catalytic
activity toward certain oxidation reactions [18,21]. In recent years, our
group has devoted to the preparation methods of manganese dioxide-
based materials and their catalytic application in the clean synthesis of
N-containing heterocycles [29–32]. In 2017, we reported copper oxide-
modified OMS-2-catalyzed 1,2-dihydro-1,3,5-triazine synthesis using
alcohols and N-aryl amidines, and modification of OMS-2 with urea as
an additive during the preparation was found to be efficient for the
synthesis of quinazolines from the same substrates in the next year
(Scheme 1, a and b) [29,30]. Interestingly, when benzimidamides were
used as substrates and allowed to react with alcohols, 1,3,5-triazines
[
1–4]. Additionally, because of their biological and pharmacological
activities, they frequently occur in pharmaceutical molecules including
antitumor, antibacterial, and antifungal agents as well as antic-
onvulsants [5–7]. Therefore, the synthesis of functional pyrimidines has
attracted increasing attention in recent years. Thus far, pyrimidines can
be synthesized by reactions between amidines and 1,3-dicarbonyl
compounds, triazines, alkynones, or ketones [8–11]. Multicomponent
synthesis of pyrimidines from amidines and different alcohols using
copper salts, Ir, or Mn PNP pincer complexes was also achieved
[
12–14]. Moreover, metal-free synthesis of pyrimidines between cin-
namaldehydes and amidines was developed, although stoichiometric
amounts of inorganic base were used [15]. Nevertheless, with regard to
clean synthesis and green chemistry, the development of atom-eco-
nomic synthesis of pyrimidines under base−/additive-free conditions
using recyclable catalysts continues to be highly desired.
As a metal oxide, manganese oxide octahedral molecular sieve
2 2
were obtained using OMS-2 synthesized with the use of H O -trapped
(
OMS-2) has recently drawn broad attention and been extensively
reagent (designed as OMS-2-SH) during the preparation and OMS-2
prepared by the conventional reflux method (designed as K-OMS-2) did
not show catalytic activity (Scheme 1, c) [31]. In the case of cinnamyl
alcohol, (E)-2,4-diphenyl-6-styryl-1,3,5-triazine was isolated using
OMS-2-SH as mentioned in our previous report. Unexpectedly, when K-
studied. OMS-2, which is composed of the edge- and corner-sharing
MnO units, has a 2 × 2 tunnel architecture with K ions inside the
6
tunnel to balance the valence and maintain the structure [16–18]. Be-
cause of its redox, adsorption, and semiconductive properties, OMS-2
+
⁎
Corresponding author.
E-mail address: shenjian@nbut.edu.cn (J. Shen).
https://doi.org/10.1016/j.catcom.2019.105846
Received 10 September 2019; Received in revised form 8 October 2019; Accepted 9 October 2019
1566-7367/ © 2019 Published by Elsevier B.V.
Please cite this article as: Jian Shen and Xu Meng, Catalysis Communications, https://doi.org/10.1016/j.catcom.2019.105846

J. Shen and X. Meng
Catalysis Communications xxx (xxxx) xxxx
2. Experimental
2.1. Catalyst preparation
K-OMS-2 was synthesized by the conventional reflux method [17].
First, KMnO (5.89 g, 37 mmol) was dissolved in deionized water to
prepare the KMnO solution, and MnSO was dissolved in deionized
water to prepare the MnSO solution. Concentrated HNO (3 ml) was
added dropwise to the MnSO (8.8 g, 52 mmol) solution, followed by
dropwise addition of the KMnO solution at room temperature. Then,
4
4
4
4
3
4
4
the mixture was stirred for 24 h at reflux temperature. The solid ma-
terial was collected by filtration and washed with water. Finally, the
solid material was dried at 120 °C for 12 h in air. OMS-2-SH, amorphous
manganese oxide (AMO), and H-OMS-2 were synthesized following the
corresponding procedures reported in the literature [31,33,34].
2.2. General procedure for K-OMS-2-catalyzed pyrimidine synthesis
All catalytic reactions were performed with oxygen balloons.
Cinnamyl alcohol (0.6 mmol), amidine (0.4 mmol), and K-OMS-2
13 mol%, 40 mg) were placed in a Schlenk flask with an O balloon.
(
2
Scheme 1. Synthesis of N-containing heterocycles from alcohols and amidines
Air was removed, and PhMe (2 ml) was added into the tube using a
syringe. If cinnamyl alcohol was used in the liquid form, then it was
added after toluene using a syringe. Then, the reaction mixture was
catalyzed by OMS-2-based materials.
OMS-2 was employed as the catalyst in the reaction of cinnamyl alcohol
with amidine, a pyrimidine compound was detected as the sole product.
The K-OMS-2 catalyst showed excellent catalytic activity and selectivity
in the oxidative cyclization reaction of cinnamyl alcohol with benzi-
midamide (Scheme 1, d).
2
stirred at 110 °C for 18 h under O atmosphere. After the reaction, the
reaction mixture was cooled and separated by filtration. The filtrate
was concentrated using a rotary evaporator, and the crude product was
purified by silica gel chromatography to obtain the pure product.
In this study, we describe that the conventional K-OMS-2 material
was found to be an efficient heterogeneous catalyst for the synthesis of
pyrimidines under base- and additive-free conditions. In the reaction of
cinnamyl alcohols with amidines, K-OMS-2 showed highly catalytic
activity, selectivity, and recyclability when O was used as the oxidant.
2
A number of substrates could be tolerated in the catalytic system.
2
.3. Recycling reaction of catalyst for synthesis of 3a
Amidine 2a (20 mmol, 2.4 g) and K-OMS-2 (13 mol%, 2 g) were
2
placed in a Schlenk flask with an O balloon. Air was removed, and
PhMe (120 ml) was added into the flask using a syringe. Cinnamyl al-
cohol 1a (30 mmol, 4.02 g), was added after toluene using a syringe.
Then, the reaction mixture was stirred at 110 °C for 24 h under O
2
Table 1
Reaction optimization .
a
Entry
Catalyst
Solvent
Oxidant
Yield (%)b
1
2
3
K-OMS-2
OMS-2-SH
–
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
DMC
O
O
O
O
O
O
O
2
2
2
2
2
2
2
88
0
0
0
0
75
78
61
49
0
0
5
8
0
56
72
c
4
5
KMnO
4
d
MnSO
AMO
4
6
7
8
9
H-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
K-OMS-2
air
H
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
1
1
1
1
1
1
1
0
1
2
3
4
5
6
2-Me-THF
EtOH
H
2
O
DMSO
PhMe
PhMe
e
f
a
2
Reaction conditions: 1a (0.6 mmol), 2a (0.4 mmol), catalyst (13 mol%, 40 mg), PhMe (2 ml), O balloon, 110 °C, 18 h.
NMR yields using CH Br as the internal standard.
2 2
b
c
d
e
f
0
0
.04 mmol of KMnO
4
was used.
was used.
.04 mmol of MnSO
4
10 mg of K-OMS-2 was used.
At 100 °C.
2

J. Shen and X. Meng
Catalysis Communications xxx (xxxx) xxxx
Table 2
Scope of reaction.a
Compound
Ar=
R1=
R2=
R3=
Yield (%)b
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
4-Me-Ph
4-OMe-Ph
H
H
H
H
H
H
H
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Br
H
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
3-OMe-Ph
4-Cl-Ph
4-Pyridyl
94
92
92
93
88
87
85
82
92
90
89
91
88
89
76
72
85
4-CF
3
-Ph
4-F-Ph
4-Cl-Ph
3-Cl-Ph
2-Furyl
Ph
4-OMe-Ph
4-Cl-Ph
2-Cl-Ph
4-Me-Ph
4-OMe-Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-F-Ph
4-OMe-Ph
Me
Me
Me
Me
Me
Me
H
Cyclopropyl
71
76
85
N.R.
N.R.
N.R.
Me
Ph
Ph
(Me)
Ph
u
Me
Me
H
2
-N
4
2
-NO -Ph
a
Reaction conditions: 1 (0.6 mmol), 2 (0.4 mmol), K-OMS-2 (13 mol%, 40 mg), PhMe (2 ml), O
Isolated yields.
2
balloon, 110 °C, 18 h.
b
Fig. 1. TEM images of (a) fresh K-OMS-2 and (b) retrieved K-OMS-2.
atmosphere. After the reaction, the reaction mixture was cooled and
separated by filtration. The used catalyst was collected by filtration and
washed with water, ethyl acetate, and pure ethanol. Then, it was dried
in an air-drying oven at 120 °C for subsequent use. The filtrate was
concentrated using a rotary evaporator, and the crude product was
purified by silica gel chromatography to obtain the pure product.
reaction of 1a with 2a [31]. As expected, OMS-2-SH did not show
catalytic selectivity for the synthesis of pyrimidine, and a 90% yield of
(E)-2,4-diphenyl-6-styryl-1,3,5-triazine was detected (Table 1, entry 2).
One tends to believe that the smaller particle size, weaker crystalline,
and higher content of Mn(IV) make K-OMS-2 to show exclusive cata-
lytic selectivity when compared with OMS-2-SH (For characterization
information of K-OMS-2, see SI). Next, the blank experiment indicated
that the reaction did not occur without any catalysts (Table 1, entry 3).
3. Results and discussion
Precursors of OMS-2, such as KMnO
pyrimidine synthesis, although cinnamyl aldehyde was detected using
KMnO (Table 1, entries 4 and 5). To further better the reaction, AMO
4 4
and MnSO , could not proceed the
The reaction between cinnamyl alcohol 1a and amidine 2a in to-
4
luene under oxygen was chosen as the model reaction to optimize the
conditions (Table 1). When conventional K-OMS-2 was employed as the
catalyst, the reaction between 1a and 2a proceeded smoothly and an
and acid-modified OMS-2 (H-OMS-2) were tested, and moderate yields
of pyrimidine were observed (Table 1, entries 6 and 7). Next, other
green oxidants such as air and hydrogen peroxide provided a lower
yield of 3a than that of oxygen (Table 1, entries 8 and 9). To make the
reaction more environment friendly, a series of biomass-derived sol-
vents were examined in the reaction. However, no satisfactory results
8
8% yield of pyrimidine 3a was observed without any by-products such
as (E)-2,4-diphenyl-6-styryl-1,3,5-triazine (Table 1, entry 1). In our
previous research, OMS-2-SH synthesized using an H -trapped re-
agent provided (E)-2,4-diphenyl-6-styryl-1,3,5-triazine from the
2 2
O
3

J. Shen and X. Meng
Catalysis Communications xxx (xxxx) xxxx
2
2
-ol and NO
a at all.
2
-substututed cinnamyl alcohol did not react with amidine
Lastly, the leaching experiment was carefully carried out using
cinnamyl alcohol 1a and amidine 2a as the model substrates. The re-
action was stopped after stirring for 1 h, and a 45% yield of 3a was
1
observed by H NMR. Then, K-OMS-2 was separated by filtration, and
the filtrate without the catalyst was kept stirring for another 10 h. The
yield of 3a did not increase further. The filtrate was also analyzed by
ICP-MS, which shows that Mn and K were both below 10 μg/L. These
results indicate that the metal species of K-OMS-2 did not leach into the
reaction solution and the observed catalysis truly derived from the solid
catalyst. K-OMS-2 was easily retrieved by filtration, then washed using
ethanol and water, and dried at 120 °C for the next use. From the
analysis of TEM and XRD, the retrieved catalyst very well maintained
its morphology and the crystal phase of cryptomelane (JCPDS 29–1020)
(
Figs. 1 and 2). Importantly, K-OMS-2 also maintained its catalytic
activity even in a gram-scale reaction (0.02 mol of amidine), and it
could be reused for at least 5 times without obvious loss of activity
(
Fig. 3).
On the basis of our experimental results and previous reports
11,31], it is believed that the synthesis of pyrimidine would begin from
[
Fig. 2. XRD patterns of fresh K-OMS-2 and retrieved K-OMS-2.
the K-OMS-2-catalyzed aerobic oxidation of cinnamyl alcohol to cin-
namyl aldehyde. Furthermore, benzimidamide reacts with the C]C
double bond of cinnamyl aldehyde to generate an imine intermediate
through intermolecular Michael addition promoted by K-OMS-2
[
34,35]. Then the intramolecular condensation occurs, followed by the
oxidative aromatization catalyzed by K-OMS-2 to form the final desired
pyrimidine product.
4. Conclusion
In summary, we developed a heterogeneous synthesis of multi-
substituted pyrimidines between cinnamyl alcohols and amidines
through an aerobic oxidation reaction under base- and additive-free
conditions. The catalyst K-OMS-2 obtained by the reflux method
showed good catalytic selectivity and activity, which makes pyr-
imidines as the sole products without any triazines. The present cata-
lytic system is simple to operate, can tolerate various substrates, and
Fig. 3. Recycling experiment.
2
enables O to be an efficient green oxidant. Gram-scale synthesis of
were obtained (Table 1, entries 10–13). Moreover, the polar solvent
dimethyl sulfoxide (DMSO) could also not proceed the reaction
pyrimidines could also be achieved with a good yield using K-OMS-2.
Moreover, K-OMS-2 has great structural stability and recyclability. The
other application of OMS-2-based catalysts in the clean synthesis of
functional molecules is ongoing in our laboratory.
(
Table 1, entry 14). Finally, experiments were attempted with lower
amounts of the catalyst and reaction temperature, and a low yield of
pyrimidine was obtained (Table 1, entries 15 and 16). Consequently,
the optimized reaction conditions included use of K-OMS-2 as the cat-
alyst in toluene at 110 °C for approximately 18 h.
Acknowledgments
With the optimized conditions in hand, the substrate scope of the
reaction was investigated with a broad range of cinnamyl alcohols and
various amidines (Table 2). First, substituted cinnamyl alcohols were
tested with benzimidamide 2a. All the oxidative cyclization reactions
proceeded very well, and good-to-excellent yields of the corresponding
pyrimidines were isolated, although 3-(furan-2-yl)prop-2-en-1-ol pro-
duced a slightly low yield of 3 h (Table 2, 3b-3 h). Subsequently, (E)-
We gratefully acknowledge the National Natural Science
Foundation of China (Grant No. 21606136 and 21403256) and the
Youth Innovation Promotion Association CAS (Grant No. 2018456).
Declaration of Interest Statement
The authors declare no competing financial interest.
Appendix A. Supplementary data
1,3-diphenylprop-2-en-1-ol and its derivatives that are the oxidative
precursors of chalcones were employed as substrates to assess the tol-
erance of the catalytic system. The electronic effect of substrates did not
influence the reaction, and 82–91% yields of the multi-substituted
pyrimidines 3i-3n were collected (Table 2, 3i-3n). Then, (E)-4-phe-
nylbut-3-en-2-ol was used to examine the scope of amidines under the
present catalytic conditions. A wide range of amidines including aro-
matic, heteroatom-containing, and aliphatic ones could be tolerated in
the reaction, and good results were obtained (Table 2, 3i-3n). More-
over, 2-methyl-substituted (E)-3-phenylprop-2-en-1-ol successfully
participated in the reaction (Table 2, 3u). However, 1,1-dimethylgua-
nidine could not proceed with the reaction and only the oxidative
product of cinnamyl alcohol was observed. 3-Bromo-4-phenylbut-3-en-
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.catcom.2019.105846.
References
[
1] J.-L. Liang, J.E. Cochran, W.A. Dorsch, I. Davies, M.P. Clark, Development of a
scalable synthesis of an azaindolyl-pyrimidine inhibitor of influenza virus replica-
tion, Org. Process. Res. Dev. 20 (2016) 965.
[
[
[
2] I.M. Lagoja, Pyrimidine as constituent of natural biologically active compounds,
Chem. Biodivers. 2 (1) (2005).
3] K. Singh, T. Kaur, Pyrimidine-based antimalarials: design strategies and anti-
plasmodial effects, MedChemComm 7 (2016) 749.
4] J. An, S.J. Geib, N.L. Rosi, High and selective CO2 uptake in a cobalt adeninate
4

J. Shen and X. Meng
Catalysis Communications xxx (xxxx) xxxx
metal-organic framework exhibiting pyrimidine- and amino-decorated pores, J. Am.
(spinel) manganese oxides, J. Mater. Chem. 4 (2016) 8812.
Chem. Soc. 132 (2010) 38.
[22] M. Wang, Y. Wei, Q. Zou, W. Zhang, A. Xu, X. Li, Tuning manganese (III) species in
manganese oxide octahedral molecular sieve by interaction with carbon nanofibers
for enhanced pollutant degradation in the presence of peroxymonosulfate, J.
Colloid Interface Sci. 536 (2019) 271.
[
5] A.A. Parent, J.R. Gunther, J.A. Katzenellenbogen, Blocking estrogen signaling after
the hormone: pyrimidine-core inhibitors of estrogen receptor-coactivator binding,
J. Med. Chem. 51 (2008) 6512.
[
6] S. Manzetti, J. Zhang, D. vander Spoel, Thiamin function, metabolism, uptake, and
[23] X. Li, J. Ma, X. Jia, F. Xia, Y. Huang, Y. Xu, J. Xu, Al-doping promoted aerobic
amidation of 5-hydroxymethylfurfural to 2,5-furandicarboxamide over cryptome-
lane, ACS Sustain. Chem. Eng. 6 (2018) 8048.
[24] K. Yamaguchi, Y. Wang, N. Mizuno, A widely applicable regioselective aerobic a-
cyanation of tertiary amines heterogeneously catalyzed by manganese oxides,
ChemCatChem 5 (2013) 2835.
[25] X. Meng, Y. Wang, Y. Wang, B. Chen, Z. Jing, G. Chen, P. Zhao, OMS-2-supported
Cu hydroxide-catalyzed benzoxazoles synthesis from catechols and amines via
domino oxidation process at room temperature, J. Org. Chem. 82 (2017) 6922.
[26] G. Elmaci, O. Icten, A.N. Ay, B. Zümreoglu-karan, Boron isotopic fractionation in
aqueous boric acid solutions over synthetic minerals: effect of layer and surface
charge on fractionation factor, Appl. Clay Sci. 107 (2015) 117.
[27] G. Elmaci, A.S. Ertürk, M. Sevim, Ö. Metin, MnO2 nanowires anchored on meso-
porous graphitic carbon nitride (MnO2@mpg-C3N4) as a highly efficient electro-
catalyst for the oxygen evolution reaction, Int. J. Hydrog. Energy 44 (2019) 17995.
[28] G. Elmaci, S. Cerci, D. Sunar-Cerci, The evaluation of the long-term stability of α-
MnO2 based OER electrocatalyst in neutral medium by using data processing ap-
proach, J. Mol. Struct. 1195 (2019) 632.
transport, Biochemistry 54 (2014) 821.
[
7] S. Lee, D. Lim, E. Lee, Discovery of carbohybrid-based 2-aminopyrimi-dine analo-
gues as a new class of rapid-acting antimalarial agents using imagebased cytological
profiling assay, J. Med. Chem. 57 (2014) 7425.
[
8] K.S. Vadagaonkar, H.P. Kalmode, S. Prakash, Greener [3+3] tandem annulatio-
noxidation approach towards the synthesis of substituted pyrimidines, New J.
Chem. 39 (2015) 3639.
[9] E.D. Anderson, D.L. Boger, Scope of the inverse electron demand diels-alder reac-
tions of 1,2,3-triazine, Org. Lett. 13 (2011) 2492.
[
10] M. Lin, Q.Z. Chen, Y. Zhu, Copper(II)-catalyzed synthesis of pyrimidines from
propargylic alcohols and amidine: a propargylation-cyclization-oxidation tandem
reaction, Synlett 8 (2011) 1179.
11] J.-L. Zhan, M.-W. Wu, F. Chen, B. Han, Cu-catalyzed [3 + 3] annulation for the
synthesis of pyrimidines via β-C(sp3)–H functionalization of saturated ketones, J.
Org. Chem. 81 (2016) 11994.
12] T. Shi, F. Qin, Q. Lin, W. Zhang, Copper-catalyzed three-component synthesis of
pyrimidines from amidines and alcohols, Org. Biomol. Chem. 16 (2018) 9487.
13] N. Deibl, K. Ament, R. Kempe, A sustainable mlticomponent pyrimidine synthesis, J.
Am. Chem. Soc. 137 (2015) 12804.
14] M. Mastalir, M. Glatz, E. Pittenauer, G. Allmaier, K. Kirchner, Sustainable synthesis
of quinolines and pyrimidines catalyzed by manganese PNP pincer complexes, J.
Am. Chem. Soc. 138 (2016) 15543.
[
[
[
[
[29] X. Meng, X. Bi, Y. Wang, G. Chen, B. Chen, Z. Jing, P. Zhao, Heterogeneous selective
synthesis of 1,2-dihydro-1,3,5-rriazines from alcohols and amidines via Cu/OMS-2-
catalyzed multistep oxidation, Catal. Commun. 89 (2017) 34.
[30] B. Li, C. Li, L. Tian, J. Zhou, J. Huang, X. Meng, Heterogeneous oxidative synthesis
of quinazolines over OMS-2 under ligand-free conditions, New J. Chem. 42 (2018)
15985.
[
15] W. Guo, Base mediated direct C–H amination for pyrimidines synthesis from ami-
dines and cinnamaldehydes using oxygen as green oxidants, Chinese Chem. Lett. 27
[31] J. Shen, X. Meng, Base-free synthesis of 1,3,5-triazines via aerobic oxidation of
alcohols and benzamidine over a recyclable OMS-2 catalyst, Catal. Commun. 127
(2019) 58.
[32] X. Meng, X. Bi, C. Yu, G. Chen, B. Chen, Z. Jing, P. Zhao, Ball-milling synthesized
hydrotalcite supported cu–Mn mixed oxide under solvent-free conditions: an active
catalyst for aerobic oxidative synthesis of 2-acylbenzothiazoles and quinoxalines,
Green Chem. 20 (2018) 4638.
(2016) 47.
[
16] S.L. Suib, Porous manganese oxide octahedral molecular sieves and octahedral
layered materials, Acc. Chem. Res. 41 (2008) 479.
17] X. Meng, Y. Wang, B. Chen, G. Chen, Z. Jing, P. Zhao, OMS-2/H2O2/dimethyl
carbonate: an environmentally-friendly heterogeneous catalytic system for oxida-
tive synthesis of benzoxazoles at room temperature, Org. Process. Res. Dev. 21
[
(
2017) 2018.
[33] Y. Wang, K. Yamaguchi, N. Mizuno, Manganese oxide promoted liquid-phase
aerobic oxidative amidation of methylarenes to monoamides using ammonia sur-
rogates, Angew. Chem. Int. Ed. 51 (2012) 7250.
[34] X. Meng, J. Zhang, B. Chen, Z. Jing, P. Zhao, Copper supported on H+-modified
manganese oxide octahedral molecular sieves (Cu/H-OMS-2) as a heterogeneous
biomimetic catalyst for the synthesis of imidazo[1,2-a]-N-heterocycles, Catal. Sci.
Technol. 6 (2016) 890.
[
[
[
[
18] X. Liu, Y. Huang, X. Meng, J. Li, D. Wang, Y. Chen, D. Tang, B. Chen, Recent de-
velopments in the synthesis of nitrogen-containing heterocycles through C–H/N–H
bond functionalizations and oxidative cyclization, Synlett 20 (2019) 1026.
19] X. Meng, J. Zhang, B. Chen, G. Chen, P. Zhao, Heterogeneous synthesis of 1,4-
enediones and 1,4-diketones with manganese oxide molecular sieves OMS-2 as a
recyclable catalyst, Catal. Commun. 69 (2015) 239.
20] M. Wang, J. Ma, M. Yu, Z. Zhang, F. Wang, Oxidative coupling of anilines to azo-
benzenes using heterogeneous manganese oxide catalysts, Catal. Sci. Technol 6
[35] B. Sarmah, R. Srivastava, P. Manjunathan, G.V. Shanbhag, Green and sustainable
tandem catalytic approach for fine-chemicals synthesis using octahedral MnO
2
(2016) 1940.
molecular sieve: catalytic activity versus method of catalyst synthesis, ACS Sustain.
Chem. Eng. 2 (2015) 2933.
21] G. Elmaci, C.E. Frey, P. Kurz, B. Zümreoglu-karan, Water oxidation catalysis by
using nanomanganese ferrite supported 1D-(tunnelled), 2D-(layered) and 3D-
5