Heterogeneous synthesis of 1,4-enediones and 1,4-diketones with manganese oxide molecular sieves OMS-2 as a recyclable catalyst

Article abstract of DOI:10.1016/j.catcom.2015.07.003

An efficient manganese oxide octahedral molecular sieves OMS-2-catalyzed chemoselective synthesis of 1,4-enediones and 1,4-diketones from 1,3-dicarbonyls and α-iodoacetophenones is described. The present catalytic system can be applied in one-pot, three-c

Full text of DOI:10.1016/j.catcom.2015.07.003

Heterogeneous synthesis of 1,4-enediones and 1,4-diketones with manganese
oxide molecular sieves OMS-2 as a recyclable catalyst
Xu Meng, Jinqi Zhang, Gexin Chen, Baohua Chen, Peiqing Zhao
PII:
DOI:
Reference:
S1566-7367(15)30013-3
doi: 10.1016/j.catcom.2015.07.003
CATCOM 4375
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
26 May 2015
1 July 2015
3 July 2015
Please cite this article as: Xu Meng, Jinqi Zhang, Gexin Chen, Baohua Chen, Peiqing
Zhao, Heterogeneous synthesis of 1,4-enediones and 1,4-diketones with manganese oxide
molecular sieves OMS-2 as a recyclable catalyst, Catalysis Communications (2015), doi:
10.1016/j.catcom.2015.07.003
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ACCEPTED MANUSCRIPT
Heterogeneous synthesis of 1,4-enediones and 1,4-diketones
with manganese oxide molecular sieves OMS-2 as a
recyclable catalyst
Xu Meng,a Jinqi Zhang,a Gexin Chen,a Baohua Chenb and Peiqing Zhao*a
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation,
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, P. R China. Fax:+96 931 8277008; Tel: +86 931
4968688; E-mail: zhaopq@licp.cas.cn
b
State Key Laboratory of Applied Organic Chemistry, Lanzhou
University, Lanzhou, 730000, P. R. China
Abstract: An efficient manganese oxide octahedral molecular sieves
OMS-2-catalyzed chemoselective synthesis of 1,4-enediones and
1,4-diketones from 1,3-dicarbonyls and α-iodoacetophenones is described.
The present catalytic system can be applied in one-pot, three-component
reactions of methyl ketones, 1,3-dicarbonyls and iodine. Moreover,
OMS-2 can be reused at least 5 times without loss of activity.
Keywords: heterogeneous catalysis, OMS-2, C-C bond formation,
1,4-enediones, 1,4-diketones
1. Introduction
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Heterogeneous catalysis plays an important role in a wide range of
applications, due to convenient catalyst handling, recyclability of catalyst
and easy separation of catalyst from reaction medium [1-4]. As a mixed
valent material, OMS-2 (cryptomelane-type manganese oxide-based
octahedral molecular sieves, KMn8O16) has captured broad attention and
also been applied to catalysis, ion-exchange, battery materials and
adsorption because it is crystalline and semi-conductive [5]. OMS-2 has a
2 × 2 edge- and corner-shared MnO6 octahedral chain, which is corner
connected to form a one-dimensional tunnel structure with a pore size of
4.6Å, and shows ~3.8 as the average oxidation state [6, 7]. Previously,
OMS-2 had been used as a heterogeneous catalyst in oxidation [8],
cyanation [9], dehydrogenation [10], epoxidation [11], ring opening [12],
as well as the synthesis of imines, amides, quinoxalines and
2-aminodiphenylamines [13-17].
1,4-Enediones are not only important structural motifs in natural
products and pharmaceutical compounds [18], but also versatile building
blocks for the synthesis of heterocycles [19]. Many synthetic routes have
been established, including oxidation of furans and enones [20],
rearrangement of 2-alkynyl alcohols [21], Stille coupling [22], Wittig
reaction [23], nucleophilic addition of dibenzoylacetylenes and oxidative
coupling [24]. Most recently, Wu`s group reported an oxidative synthesis
of 1,4-enediones from acetophenones and 1,3-dicarbonyls mediated by
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stoichiometric amounts of CuO and I2 [25]. However, these approaches
are not eco-friendly and generally suffer from limited substrate scope.
Therefore, there is an incentive to develop a convenient and
straightforward
approach
for
producing
1,4-enediones
by
environmentally friendly way with a recyclable catalyst. In continuation
of our research towards heterogeneous catalysis [26-28], we would like to
describe a heterogeneous OMS-2-catalyzed chemoselective synthesis of
1,4-enediones and 1,4-diketones from α-iodoacetophenones and
1,3-dicarbonyls. This synthetic method avoids using stoichiometric
amounts of metal reagents, which can be an alternative to previous
methods (Scheme 1).
Scheme 1. OMS-2-catalyzed synthesis of 1,4-enediones and
1,4-diketones.
2. Experimental
2.1. Catalyst preparation [26]
5.89 g of KMnO4 in 100 mL of water was added to a solution of 8.8 g
of MnSO4·H2O in 30 mL of water and 3 mL concentrated HNO3. The
o
solution was refluxed at 100 C for 24 h, and the product was filtered,
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washed, and dried at 120 oC for 8 h. Finally, the dry OMS-2 was calcined
in a muffle furnace at 350 oC for 2 h. Then, the black powder OMS-2 was
obtained. BET surface area: 158.4870 m2/g; Pore volume: 0.5249 cm3/g;
Pore size: 127.058 Å.
2.2. Characterization
The specific surface areas (SBET) of the catalysts were measured from
a multipoint Braunauer–Emmett–Teller (BET) analysis of the nitrogen
adsorption isotherms at 77K recorded on a Quantachrome Autosorb-1
apparatus. The transmission electron microscopy (TEM) images of the
catalysts were obtained on a JEM2010 microscope operated at 200 kV.
The sample was dispersed into ethanol with ultrasonic treatment for 1 h,
and drops of the suspension were placed on a copper grid for TEM
observations. The X-ray diffraction (XRD) patterns were collected on a
PANalytical X`Pert PRO MPD powder diffractometer using Cu Kα
radiation (λ = 0.1542 nm). The working voltage was 40 kV and the
current was 40 mA. The intensity data were collected at 25 ◦C in a 2θ
range from 10o to 90o, with a scanning speed of 0.7o s-1 and a step of
0.03o.
2.3. General procedure for the synthesis of 1.4-enedione
OMS-2 (12 mg, 0.015 mmol, 5 mol%), α-iodoacetophenone (0.3
mmol), 1,3-dicarbonyl compound (0.3 mmol), DCB (1 mL) were added
o
to a flask with a stirring bar. The mixture was stirred at 100 C for 12 h
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under air. After cooling to room temperature, the mixture was diluted
with ethyl acetate and filtered. The filtrate was removed under reduced
pressure to get the crude product, which was further purified by silica gel
chromatography to yield corresponding product.
2.4. General procedure for the synthesis of 1,4-diketones
OMS-2 (12 mg, 0.015 mmol, 5 mol%), α-iodoacetophenone (0.3
mmol), 1,3-dicarbonyl compound (0.3 mmol), EtOH (1 mL) were added
o
to a flask with a stirring bar. The mixture was stirred at 70 C for 12 h
under air. After cooling to room temperature, the mixture was diluted
with ethyl acetate and filtered. The filtrate was removed under reduced
pressure to get the crude product, which was further purified by silica gel
chromatography to yield corresponding product.
3. Results and discussion
In our initial study, the reaction between α-iodoacetophenone 1a and
1,3-dicarbonyl compound 2a was chosen as a model reaction (Table 1 and
S1). Firstly, the reaction did not proceed without a catalyst in DMSO
(Table 1, entry 1). Using OMS-2 as a catalyst in DCB also failed the
transformation (Table 1, entry 2). Interestingly, increasing reaction
temperature to 100 oC enabled the formation of 1,4-enedione 3a with E/Z
mixture in 92% yield (Table 1, entry 3). Next, more experiments
confirmed that increasing or decreasing OMS-2 loading did not enhance
reactivity and the reaction did not occur without OMS-2 even at a higher
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temperature (Table 1, entries 4-6). Using MnSO4 and KMnO4 that are
precursors of OMS-2 as catalysts gave inferior results (Table 1, entries 7
and 8). Moreover, MnO2 was tested and it did not trigger the reaction at
all (Table 1, entry 9). Surprisingly, the reaction offered 98% yield of
o
1,4-diketone 4a [29] instead of 3a in EtOH at 70 C via nucleophilic
substitution (Table 1, entry 10). Then, more experiments were conducted
in EtOH to better the yield of 4a and results showed that the reaction did
not work without OMS-2, and decreasing reaction temperature slowed
down the transformation (Table 1, entries 11-13). Finally, the formation
of 4a also worked efficiently under nitrogen (Table 1, entry 14).
Table 1 Optimization of the reaction conditions.a
Entry Catalyst
Solvent
Temp. (oC)
Yield (%)b
3a
0
4a
1
2
3
4
5
6
-
DMSO
DCB
70
0
0
0
0
0
0
OMS-2
OMS-2
70
trace
92
90
72
0
DCB
100
100
100
100
OMS-2 (10 mol%) DCB
OMS-2 (2 mol%) DCB
-
DCB
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7c
MnSO4
KMnO4
MnO2
OMS-2
-
DCB
DCB
DCB
EtOH
EtOH
EtOH
EtOH
EtOH
100
100
100
70
10
15
0
0
8c
0
9c
0
10
11
12
13
14d
0
98
0
70
0
OMS-2
OMS-2
OMS-2
r.t.
0
20
23
92
40
0
70
0
a
Reaction conditions: catalyst (for OMS-2,12 mg, 0.015 mmol, 5 mol%), 1a (0.3 mmol), 2a
(0.3 mmol), solvent (1 mL), temperature, air, 12 h.
b Isolated yields.
c 5 mol% of catalyst was used.
d Under N2 atmosphere.
In order to prove that the observed catalysis is derived from the solid
catalyst OMS-2 rather than the leached Mn species, the hot filtration
experiment was conducted (see ESI, Figure S1) and the results suggested
that the observed catalysis is heterogeneous. Then, the recyclability of
OMS-2 on the synthesis of 1,4-enedione 3a was investigated (Table 2).
After each run, OMS-2 was separated by filtration and washed with
o
deionized water and EtOH respectively, then dried at 110 C for 4 h. It
was found that OMS-2 can be reused at least 5 times without obvious loss
of activity.
Table 2 Reusability of OMS-2 on the synthesis of 3a.a
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Cycle
1
2
3
4
5
92
90
92
89
90
Isolated yield of 3a (%)
a
Reaction conditions: OMS-2 (12 mg, 0.015 mmol, 5 mol%), 1a (0.3 mmol), 2a (0.3 mmol),
DCB (1 mL), 100 oC, air, 12 h.
Then, transmission electron microscopy (TEM) and X-ray diffraction
(XRD) were employed to characterize the fresh and retrieved OMS-2
(Figure 1 and 2). Specifically, the TEM image of OMS-2 demonstrated
that the fresh catalyst was composed of short nanorods which were
structurally single crystalline (Figure 1, A). Additionally, the TEM image
showed retrieved OMS-2 which was used for 1 cycle maintained the
morphology and lattice structure (Figure 1, B). The XRD pattern of
OMS-2 showed peaks which can be indexed to the pure cryptomelane
phase consistent with JCPDS file No. 29-1020. Reused OMS-2 was also
characterized by XRD, which confirmed that the structure of it was not
altered even after the fifth cycle (Figure 2). TEM and XRD revealed that
OMS-2 has good structural stability.
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Figure 1. TEM images of fresh OMS-2 (A) and OMS-2 after 1 cycle (B).
Figure 2. XRD pattern of OMS-2 (a), OMS-2 after 1 cycle (b) and
OMS-2 after 5 cycles (c).
With the optimized reaction conditions in hand, we examined the scope
of the C-C bond formation between α-iodoacetophenones and
1,3-dicarbonyls using OMS-2 as the catalyst in DCB (Table 3).
Gratifyingly, the reactions were tolerant of various substrates and gave
moderate to good yields of corresponding 1,4-enediones with mixture of
major thermodynamically stable E-isomers and minor Z-isomers.
Electron-rich iodoacetophenones offered slightly higher yields of
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1,4-enediones than electron-poor ones did (Table 3, 3b-3i). Heterocyclic
α-iodoketone, 1-(furan-2-yl)-2-iodoethanone, also proceeded in a good
yield (Table 3, 3j). On the other hand, various 1,3-dicarbonyls
participated in the reactions and good yields were obtained (Table 3,
3k-3o).
Unfortunately,
aliphatic
α-iodoketones,
such
as
1-iodobutan-2-one and 1-iodopropan-2-one, did not participate in the
reactions and aliphatic acetylacetone was not a suitable substrate for this
catalytic system. And α-bromo acetophenone did not react under the
present reaction conditions.
Table 3 OMS-2-catalyzed synthesis of 1,4-enediones.a
Product
3b
Ar
R1
H
H
H
H
H
H
H
H
R2
Yield (%)b
p-MeO-C6H4
p-Me-C6H4
p-Cl-C6H4
p-Br-C6H4
p-F-C6H4
p-CF3-C6H4
p-NO2-C6H4
2-Naphthyl
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
90 (E:Z = 88:12)
91 (E:Z = 87:13)
87 (E:Z = 92:8)
85 (E:Z = 96:4)
80 (E:Z = 90:10)
82 (E:Z = 93:7)
72 (E:Z = 80:20)
88 (E:Z = 89:11)
3c
3d
3e
3f
3g
3h
3i
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Furan-2-yl
H
OEt
OEt
OEt
OMe
OMe
Ph
70 (E:Z > 99:1)
90 (E:Z = 89:11)
80 (E:Z = 82:18)
70 (E:Z = 97:3)
88 (E:Z = 93:7)
65
3j
Ph
Ph
Ph
Ph
Ph
p-F
3k
3l
p-OMe
p-Cl
p-OMe
H
3m
3n
3o
a Reaction conditions: OMS-2 (12 mg, 0.015 mmol, 5 mol%), 1 (0.3 mmol), 2 (0.3 mmol), DCB
(1 mL), 100 oC, air, 12 h.
b Isolated yields, E:Z ratio determined by 1H NMR.
Since the excellent chemoselectivity of this heterogeneous catalytic
system,
a
number of 1,4-diketones were synthesized via
OMS-2-catalyzed nucleophilic substitutions in EtOH (Table 4). In all
cases, the desired 1,4-diketones were obtained chemoselectively.
Ortho-substituted α-iodoacetophenones gave low yields of 1,4-diketones,
which indicates the reaction was affected by steric hindrance of the
substrates (Table 4, 4b-4m). 1,3-Dicarbonyls with substitutions
underwent reactions to furnish desired products in excellent yields (Table
4, 4n and 4o). When aliphatic acetylacetone was employed as a substrate,
the desired product 4p was isolated in a low yield of 8%. However, the
reactions of aliphatic α-iodoketones, such as 1-iodobutan-2-one and
1-iodopropan-2-one, did not occur under the present reaction conditions.
Table 4 OMS-2-catalyzed synthesis of 1,4-diketones.a
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Product
4b
4c
Ar
R1
Ph
Ph
Ph
Ph
Ph
Ph
R2
Yield (%)b
p-Cl-C6H4
m-Cl-C6H4
o-Cl-C6H4
p-Br-C6H4
p-F-C6H4
p-Me-C6H4
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
92
88
65
88
84
83
76
82
70
63
88
73
93
95
8
4d
4e
4f
4g
m-Me-C6H4 Ph
p-OMe-C6H4 Ph
m-OMe-C6H4 Ph
o-OMe-C6H4 Ph
4h
4i
4j
4k
4l
2-Naphthyl
Furan-2-yl
Ph
Ph
Ph
4m
4n
4o
p-OMe-C6H4 OEt
Ph
p-F-C6H4
OEt
p-Cl-C6H4
Me
Me
4p
a Reaction conditions: OMS-2 (12 mg, 0.015 mmol, 5 mol%), 1 (0.3 mmol), 2 (0.3 mmol), EtOH
(1 mL), 70 oC, air, 12 h.
b Isolated yields.
Because α-iodoacetophenones are easily formed from corresponding
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acetophenones with iodine [26, 30, 31], the one-pot, three-component
reactions of I2, acetophenones and 1,3-dicarbonyls catalyzed by OMS-2
to yield 1,4-enediones and 1,4-diketones were smoothly realized (see ESI,
Scheme S1).
Based on the previous reports [25, 30, 31] and control experiments we
performed (see ESI, Scheme S2), α-ketoaldehyde A (Scheme S2)
probably is an intermediate during the oxidative synthesis of 1,4-enedione.
In the presence of OMS-2, α-ketoaldehyde A that is formed from
α-iodoacetophenone under air reacts with 1,3-dicarbonyl via
Knoevenagel condensation to afford the desired 1,4-enedione after loss of
H2O [32]. In EtOH, 1,4-diketone is generated by OMS-2-assisted
nucleophilic substitution between electrophilic α-iodoacetophenone and
nucleophilic 1,3-dicarbonyl compound.
4. Conclusion
In summary, we have developed a heterogeneous OMS-2-catalyzed
oxidative C-C bond formation between α-iodoacetophenones and
1,3-dicarbonyls for the synthesis of 1,4-enediones. By changing the
reaction solvent, the catalytic system can afford high yields of
1,4-diketones. This simple catalytic system tolerates a variety of
substrates and can be performed in one-pot, three-component reaction of
acetophenones, 1,3-dicarbonyls and I2. Furthermore, OMS-2 can be
reused 5 times without loss of catalytic activity.
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Acknowledgements
We gratefully acknowledge the Natural Science Foundation of China
(No. 21403256, 21372102).
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
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Highlights
1. OMS-2 acts as an efficient heterogeneous catalyst for C-C
bond-forming.
2. The catalyst can be recycled for 5 times.
3. Chemoselectivity of reactions can be tuned by reaction solvents.
4. 1,4-enediones and 1,4-diketones can be prepared in one-pot manner.
17