Heterogeneous Esterification from Î±-Hydroxy Ketone and Alcohols

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Heterogeneous Esterification from #-Hydroxyl Ketone and Alcohols through A Tandem Oxidation Process over A Hydrotalcite-Supported Bimetallic Catalyst Xu Meng, Xiuru Bi, Gexin Chen, Baohua Chen, and Peiqing Zhao Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.8b00265 • Publication Date (Web): 08 Oct 2018 Downloaded from http://pubs.acs.org on October 8, 2018

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Organic Process Research & Development

Heterogeneous Esterification from αHydroxyl Ketone and Alcohols through A Tandem Oxidation Process over A Hydrotalcite-Supported Bimetallic Catalyst

Xu Meng,a,* Xiuru Bi,

a

Gexin Chen,a Baohua Chen,b Peiqing

Zhaoa,*

a

State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou

Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou 730000, China. Fax: + 96 931 8277008;

Tel:

+

86

931

4968688;

E-mail:

[email protected],

[email protected]

ACS Paragon Plus Environment

1

Organic Process Research & Development 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

b

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State Key Laboratory of Applied Organic Chemistry, Lanzhou University,

Lanzhou 730000, China

Table of Contents graphic:


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ABSTRACT: Heterogeneous aerobic oxidative esterification between α-hydroxy ketone

and

alcohols

was

achieved

catalyzed

by

a

hydrotalcite-supported

bimetallic catalyst (CuMn/HT) using O2 as green oxidant. Recyclable CuMn/HT

exhibits highly catalytic activity due to increased content of oxygen vacancies and newly generated CuMn2O4 crystal phase. This clean esterification proceeds

through a tandem oxidation process in the absence of any additives and ligands, which leads to α-ketoesters in good to excellent yields. Moreover, the catalytic system tolerates complicated bio-active molecules as raw materials and could be performed in multigram-scale.


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KEYWORDS: oxidative esterification, α-ketoesters, hydrotalcite, heterogeneous synthesis, supported catalyst


4

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INTRODUCTION α-Ketoesters, as key structural motifs, have been found in various biologically active compounds, pharmaceuticals, anticancer agents.1-3 Moreover, α-ketoesters are important precursors in organic synthesis, such as in asymmetric reduction, aminohydrocylation and aldol reaction.4-7 Therefore, efficient synthesis of αketoesters in a straight forward way is of great importance. Traditional synthetic methods involve esterification of α-ketoacyl derivatives, direct oxidation of αhydroxy esters and Pd-catalyzed carbonylation using CO.8-12 In recent years, acetophenone was directly used as substrate to react with alchohols for the synthesis of α-ketoesters in the presence of copper salts or I2.13-16 Additionally, Jiao and coworkers reported a method for α-ketoesters synthesis using αcarbonyl aldehydes and alcohols as raw catalyzed by copper with pyridine as additive.17-19 Novel synthetic approaches involving copper-catalyzed C-C or C-N oxidative cleavage were also emerged.20,21 However, stoichiometric amounts of iodide reagents, additives, ligands and peroxide (like TBHP) were inevitably employed in the previous methods. From the viewpoint of a green and environmental

perspective,

the

development

of

atom-economic

oxidative

esterification for synthesis of α-ketoesters based on a recyclable heterogeneous catalyst using oxygen as green oxidant is highly desirable and challenging. Heterogeneous catalysis based on solid catalysts is a significant process in organic transformation since the ease in catalyst handling and recyclability of catalysts.22-26 The preparation of solid catalysts, such as frequently used supported catalysts, generally employs wet-impregnation and co-precipitation. These methods all need suitable solvents in the procedures, while process employing mechanochemistry for preparation of solid catalysts provides merits including

simplicity,

swiftness

and

solventless

conditions.27,28

Particularly,

mechanochemical energy generated from ball-milling (BM) is able to provide new chemical composition or chemical reactivity on as-synthesized catalysts.29-32 More importantly, various of defects in the as-synthesized catalyst would be


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generated by the centrifugal force and friction during milling, which further significantly promotes its catalytic performance. In continuation of our research on clean organic transformation under heterogeneous catalytic systems,33-35 herein, we report a heterogeneous aerobic oxidative esterification between α-hydroxy ketone and various alcohols under neat conditions. As far as we known, this is the first example that direct using α-hydroxy ketone as the starting material to synthesize α-ketoesters via a tandem

oxidation

process.

The

reaction

is

catalyzed

by

hydrophobic

hydrotalcite-supported bimetallic catalyst (CuMn/HT) and uses O2 as green oxidant. The catalytic systems can tolerate a variety of alcohols and bio-active hydroxyl molecules without the help of additives and ligands. The highly active catalyst can be recovered and reused for 4 times without any loss of catalytic activity. O

O CuMn/HT, O2

OH

OR

neat conditions tandem oxidation O

oxidation

O R

O

oxidation

OH

H2O

hemiacetal

H2O

Scheme 1. CuMn/HT-catalyzed aerobic oxidative esterification.

RESULTS AND DISCUSSION At the beginning, a series of HT-supported catalysts were obtained by grinding in an agate mortar for 10 mins followed by ball-milling for 2 h and calcination.36-40 Nano-MgO (particle size is 20 nm) and Mg-Al oxide obtained via calcination of HT in air were also used as supports in bimetallic catalysts. And, regular wet-impregnation in EtOH solution (designated as CuMn/HT-WI)


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and grinding by hand in an agate mortar (designated as CuMn/HT-G) were employed to prepare bimetallic supported catalysts. As-synthesized

catalysts

were

examined

in

the

oxidative

esterification

between α-hydroxy ketone 1a and ethanol using O2 as oxidant under neat conditions (Table 1). Mechanically, 1a firstly is oxidized to the corresponding αcarbonyl aldehyde which reacts with alcohol to give the intermediate hemiacetal. Then, the oxidative dehydrogenation occurs on hemiacetal to give the final product α-ketoester. In this way, a capable catalyst must have excellent redox ability for this tandem oxidation process. The control experiments prove that the oxidative esterification did not proceed without any catalysts or in the presence of hydrophobic HT (Table 1, entries 1 and 2). Then, the reactions using signal component catalysts show that Cu/HT was catalytically active and manganese did not play a role as the catalytic metal in this system (Table 1, entries 3 and 4). However, bimetallic supported catalyst CuMn/HT was found to be efficient for the reaction and full conversion of 1a was observed under neat conditions, which indicates that cooperative synergistic effect was created between copper and manganese (Table 1, entry 5). The addition of Co or Fe to Cu/HT did not show the cooperative effect (Table S1, see SI). The similar influence that the introduction of manganese enhances the catalytic activity of copper was reported by Xu`s group and our group also reported that manganese oxide would transfer electrons from copper to oxidant in an oxidation improving the catalytic performance.41-45 Next, air and H2O2 were tried to replace O2 as

oxidants, which shows that air led to inferior result and hydrogen peroxide failed the reaction (Table 1, entry 5). Subsequently, the loadings of supported metals were investigated and the results show that the loading of copper was critical for the reaction and 8 wt% of Cu together with 2 wt% of Mn was the optimal option (Table 1, entries 6-9). On the other hand, other supports were employed to replace HT in bimetallic supported catalysts. It is found that nanoMgO and Mg-Al oxide did not give satisfactory results as HT did, which probably means that layered crystal structure and hydrophobic properties of HT are important for the activity of the catalyst (Table 1, entries 10 and 11). After


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that, various solvents were used in the catalytic system (0.4 mmol of EtOH was used in these cases) and the results show that the neat conditions were the best choice (Table 1, entries 12-15). Furthermore, Cu-Mn oxide was synthesized via co-precipitation using ammonia and it did not show any catalytic activity.46 And, the physical mixture of Cu-Mn oxide and HT as the catalyst failed the reaction as well (Table 1, entry 17). In addition, desired product 3a was isolated in moderate yields of 70% and 55% over CuMn/HT-WI and CuMn/HT-G respectively, which indicates that the catalyst preparation method seems affect the catalytic performance remarkably (Table 1, entries 5, 18 and 19). It is concluded that the best reaction conditions for esterification involve

using

CuMn/HT

as

catalyst

under

neat

conditions

(For

more

optimization, Table S1, see SI,). It is worth mentioning that the full conversion of 1a under neat conditions makes purification of 3a very easy and further column chromatography is unnecessary after removal of catalyst and excessive EtOH via filtration and distillation respectively. Table 1. Optimization of esterification of 1a.a O

O OH

catalyst, EtOH

OEt

solvent, 12 h, 70 oC, O2 3a

1a oxidation

H 2O

Entry

Catalyst

O

O

oxidation

O Et OH

H 2O

hemiacetal

Metal

weight Solvent

(wt%)b on HT Cu

Mn

Isolated yield (%)

1

-

-

-

EtOH

N.R.

2

HT

-

-

EtOH

N.R.


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3

Cu/HT

8

-

EtOH

47

4

Mn/HT

-

2

EtOH

Trace

5

CuMn/HT

8

2

EtOH

95 (57c, 0d)

6

CuMn/HT

2

8

EtOH

45

7

CuMn/HT

8

1

EtOH

58

8

CuMn/HT

4

2

EtOH

66

9

CuMn/HT

2

2

EtOH

20

10

CuMn/MgO

8

2

EtOH

35

11

CuMn/Mg-Al oxide

8

2

EtOH

28

12

CuMn/HT

8

2

DMC

25

13

CuMn/HT

8

2

DMF

0

14

CuMn/HT

8

2

PhMe

0

15

CuMn/HT

8

2

dioxane

0

16e

Cu-Mn oxide

-

-

EtOH

0

17f

Cu-Mn oxide + HT

-

-

EtOH

0

18

CuMn/HT-WI

8

2

EtOH

70

19

CuMn/HT-G

8

2

EtOH

55

a Reaction conditions: 1a (0.2 mmol), catalyst (20 mg), solvent (1 mL), O2 balloon, 70 oC, 12 h.

b Theoretical loading. c Under air. d 1.0 eq of H2O2 was used as oxidant.


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e 5 mg of Cu-Mn oxide was used. f The physical mixture of 5 mg of Cu-Mn oxide and 20 mg of HT was used.

After

the

optimized

catalyst

was

confirmed,

we

tried

to

analyze

its

physicochemical properties. First of all, the actual metal loadings were defined by ICP-AES as 7.1 wt% for Cu and 1.9 wt% for Mn in CuMn/HT catalyst. Next, the textural properties of support HT and the catalyst were analyzed and the information is summarized in Table 2. It is found that ball-milling did not change the textural properties of original HT obviously, while calcination made the surface area of HT enhance remarkably because HT turns into Mg-Al mixed oxide partially or fully under calcination via release of CO2 and H2O.47

Meanwhile, calcined HT had larger pore volume and much smaller pore size. CuMn/HT also showed enhanced surface area compared with original HT and the pore volume further enhanced significantly, although pore size was similar as original HT. As we known, great BET surface area and relatively large pore volume generally are necessary for superior catalytic performance. Table 2. Textural properties of materials. Catalyst

BET

surface Total

pore Average

area (m2/g)

volume (cm3/g)

size (nm)

HT

6.8

0.03

22.2

HT-BMa

7.0

0.05

32.8

HT-Calcinationb

74.5

0.09

5.3

CuMn/HT

45.5

0.17

19.4

pore

a HT after ball-milling. b HT after ball-milling followed by calcination at 350 oC for 2h in air.


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Next, the crystal structures of catalysts were analyzed by X-ray diffraction (XRD) (Figure 1). We can see that HT transferred into MgO (JCPDS No. 30794) and Al2O3 (JCPDS No. 77-2135) to some extent and a few of hydrotalcite phases (JCPDS No. 22-700) were remained because the calcination is not higher than 350 oC. And, strong diffraction peaks of CuO (JCPDS No. 45-937) and relatively weak diffraction peaks of MnOx (JCPDS No. 31-825) were detected. Interestingly, the diffraction peaks at around 2θ of 18.4o, 34.7o and 62.2o were observed, which proves that crystal phase of CuMn2O4 (JCPDS No.

71-1142) was formed by ball-milling process.48 The new induced chemical composition probably plays a role as catalytic active sites in the oxidation. Form the XRD patterns of CuMn/MgO, CuMn/Mg-Al oxide, CuMn/HT-WI and CuMn/HT-G, CuMn2O4 phase was no longer observed (Figure S1 and Figure S2).

Figure 1. XRD patterns of support HT and Cu-Mn/HT catalysts.

For an oxidative esterification over a solid catalyst, the most important factor that might affect the redox ability is the surface oxygen species because metal supported catalyst generally proceed the redox reaction via Mars-vanKrevelen mechanism.49 O1s spectrum mainly deconvoluted into two components: surface adsorbed oxygen species that contain surface adsorbed water and


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unsaturated oxygen species, and less mobile saturated lattice oxygen species.50 Surface adsorbed oxygen species are more active and mobile than lattice ones, thereby influencing the aerobic oxidation. As shown in Figure 2 and Table 3, CuMn/HT

had

more

content

of

adsorbed

oxygen

species

(85.1%)

than

CuMn/HT-WI (72.2%) and CuMn/HT-G (73.4%). In another word, Cu-Mn/HT is able to offer much more abundant surface oxygen vacancies.51-53 Abundant oxygen vacancies on catalyst surface induced by mechanochemical energy in ball-milling process might be responsible for the excellent catalytic performance of CuMn/HT.

Figure 2. XPS spectra of O 1s for HT-supported bimetallic catalyst prepared by different approaches. Table 3. XPS results of O 1s for CuMn/HT catalysts Catalyst Binding energy of Oxygen species (%) oxygen species in O 1s (eV) Adsorbed O Lattice O Adsorbed Lattice O O CuMn/HT 531.6 529.7 85.1 14.9 CuMn/HT-WI 531.3 529.6 72.2 27.8 CuMn/HT-G 531.4 529.6 73.4 26.6


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Finally, morphologies of the support HT and CuMn/HT were observed by scanning/transmission electron microscope (SEM and TEM). From Figure 3 and Figure S3, uniform and identical layered morphology was observed in HT and ball-milled HT, which means ball-milling did not change the HT morphology and particle size. Nevertheless, calcination of HT made obvious pores (like cracks between layers) appear in HT, which leads to enhanced surface area. In SEM images of Cu-Mn/HT, uniform and well-dispersed metal oxides were observed on support with layered morphology. These results are in agreement with the BET data and XRD information (Table 2).

Figure 3. SEM images of original HT (A), HT after ball-milling (B), calcined HT after ball-milling (C) and CuMn/HT (D).

In order to determine whether the observed catalysis was from the solid catalyst or the leached metal species in reaction solution, leaching experiment was carried out. The oxidative esterification of α-hydroxy ketone 1a and ethanol was performed under standard neat conditions with CuMn/HT. After the reaction performed for 6 h, it was stopped and the catalyst was isolated by filtration from the reaction mixture. At the time, the yield of the reaction was determined in 50% by NMR. The filtrate was kept running for further 6 h without adding fresh catalyst, and it is found that the yield of 3a did not increase. Meanwhile, the filtrate was examined by ICP-AES, which indicates that metal species in solution were barely detected (Cu and Mn were both below 0.01%). The used


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Page 14 of 26

catalyst was also analyzed by ICP-AES, which shows that the metal loadings were remained as 7.1 wt% for Cu and 1.9 wt% for Mn. These results indicate that the observed catalysis was derived from the supported catalyst rather than leached metal species in solution. Subsequently, the recyclability of CuMn/HT was investigated in gram-scale due to the need of enough amounts of retrieved catalyst

for

the

further

recycles

(Table

4).

CuMn/HT-catalyzed

oxidative

esterification proceeded smoothly in gram-scale and 95% isolated yield of 3a was offer. The catalyst was readily isolated from the reaction mixture by filtration and recovered by treatment in solution of Na2CO3. The XRD patterns

exhibit that recovered catalyst remained the crystal structure successfully (Figure 1). The experiments prove that retrieved catalyst could be recycled for 4 times without any loss of catalytic activity even in gram-scale synthesis (Table 4).

Table 4. The test of recyclability of Cu-Mn/HT in gram-scale.a O

O OH

CuMn/HT, EtOH

OEt O

12 h, 70 oC, O2 1a

Run

3a

1

Isolated

yield 95

2

3

4

5

94

96

96

94

(%) a Reaction conditions: 1a (10 mmol, 1.36 g), CuMn/HT (1 g), EtOH (50 mL), 70 oC, 12 h, O2 balloon.

Finally,

we

paid

our

attention

towards

the

scope

of

the

oxidative

esterification between α-hydroxy ketone and alcohols over Cu-Mn/HT (Table 5). General speaking, simple aliphatic alcohols, such as methanol, n-butyl alcohol,


14

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cyclopentanol and cyclohexylethanol, proceeded in the oxidative esterification smoothly under the neat conditions, which gives the corresponding α-ketoesters 3b-3f in good to excellent yields. When benzyl alcohols and cinnamic alcohol were used as raw, the reaction hardly proceeded under neat conditions. Delightedly, toluene was found to be a suited reaction medium for the oxidative esterification and moderate to good yields of corresponding α-ketoesters 3g-3k were obtained under standard conditions. In order to further examine the tolerance and practicability of the catalytic system, more complicated and useful molecules with bio-activity were tried to synthesize (Scheme 2). The oxidative esterification

of

testosterone

and

cholesterol

with

α-hydroxy

ketone

1a

proceeded successfully and efficiently and corresponding esterified bio-active products 3l and 3m were isolated in moderate yields. These clean organic transformations demonstrate the practicability and sustainability of CuMn/HTbased catalytic system. Moreover, the oxidative esterification could run in multigram scale smoothly. When 0.05 mol of α-hydroxy ketone 1a was catalyzed by 5 g of CuMn/HT in EtOH, full conversion and nearly quantitive yield of pure 3a without purification by silica gel chromatography were obtained after 24 h (Scheme 3). The high tolerance and being scalable up to multi-gram of this catalytic system make it practical and potential for industrial application.

Table 5. Scope of oxidative esterification of α-hydroxy ketone.a O

O OH +

R-OH

OR

CuMn/HT (20 mg) O

solvent-free or in Toluene 12 h, 70 oC, O2

O

3b-3k

O OMe

OBu

O

O

3b, 85%

3c, 95%


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Page 16 of 26

O

O

O

O O

O 3d, 90%

3e, 91%

O

O Ph

O

O

O

O

3g, 75%b

3f, 89%

O

O

O

O

O

O 3h,

80%b

3i, 78%b

O

NO2

O

O

O

Me

O

O

3j, 81%b

3k, 70%b

a Reaction conditions: 1a (0.2 mmol), alcohol (1 mL), CuMn/HT (20 mg), 70 oC,

12 h, O2 balloon, isolated yields.

b Toluene (1 mL) was used as solvent and alcohol (0.4 mmol) was used as substrates.

O OH

H3C

O OH

H

H3C

+

H

H3C CuMn/HT

H

O

Toluene, 70 C, 12 h, O2

O

H

H3C

o

H

Ph O

H

O 3l, 49%


16

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CH3

H3C

O

H

H3C

OH +

H

O

Me Me

H

H3C

Toluene, 70 oC Ph 12 h, O2

HO

CH3

H3C

Me CuMn/HT

H

H

Me H H

H O

O

3m, 50%

Scheme 2. Oxidative esterification of testosterone and cholesterol.

O

O

CuMn/HT (5g) EtOH (300 mL)

OH

OEt O

24 h, 70 oC, O2 1a, 50 mmol, 6.8 g

3a, 95%, 8.45 g

Scheme 3. CuMn/HT-catalyzed oxidative esterification in multi-gram scale.

CONCLUSION In conclusion, heterogeneous oxidative esterification between α-hydroxy ketone and alcohols via a tandem oxidation process using oxygen as green oxidant

was developed. The catalytic system based on the recyclable catalyst CuMn/HT with rich oxygen vacancies and CuMn2O4 active composition is highly tolerant

and scalable up to gram level. More importantly, the use of ball-milling method under solvent-free conditions provides an environmentally-friendly pathway for preparation of solid catalysts.

EXPERIMENTAL SECTION Preparation of CuMn/HT

Copper(II)

nitrate

trihydrate

(ranging

from

0.74 g

to

2.99

g),

Manganese(II) nitrate tetrahydrate (ranging from 0.56 g to 4.52 g)


17


Page 18 of 26

and HT (10 g) were mixed in an agate mortar. Then, the mixture was transferred into a 100 mL agate grinding jar with 5-15 mm diameter agate grinding balls. A planetary ball mill was employed to mill the raw for 2 h and rotation speed was set as 500 rpm. Next, the milled materials was collected and dried under air at 80 oC for 5 h followed by calcination under air at 350 oC for 2 h. Other HTsupported bimetallic catalysts that were listed in Table S1 were prepared by the same way. General esterification of α-hydroxy ketone 1a with alcohols under neat conditions (3a-3f) A Schlenk tube was charged with 20 mg of CuMn/HT and 0.2 mmol of α-hydroxy ketone 1a. Then, the tube was sealed with a rubber septum and degassed and recharged with O2 (5 times). Next, 1 mL of alcohol was injected into the reaction tube under O2. The reaction mixture was stirred at 70

oC

for 12 h. When the

reaction was finished, the catalyst was removed by filtration. The filtrate was removed by distillation under reduced pressure to afford the desired product. General esterification of α-hydroxy ketone 1a with alcohols in toluene (3g-3m) A Schlenk tube was charged with 20 mg of CuMn/HT and 0.2 mmol of α-hydroxy ketone 1a. Then, the tube was sealed with a rubber septum and degassed and recharged with O2 (5 times). Alcohol (0.4 mmol) and toluene (1 mL) were injected into the reaction mixture under O2 respectively. The reaction mixture was


18

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stirred at 70

oC

for 12 h. When the reaction was finished, the

catalyst was removed by filtration. The filtrate was removed by distillation under reduced pressure to offer the crude product which was

further

purified

by

silica

gel

chromatography

to

yield

corresponding pure product. Recovery of retrieved catalyst After each reaction, CuMn/HT was separated by filtration followed by washing and drying. Then, it was stirred in 0.5 M Na2CO3 solution under reflux conditions for 24 h. After that, the recovered catalyst was filtrated from the Na2CO3 solution and dried at 80 oC for 5 h. Finally, it was collected for the next run after calcination under air at 350 oC for 2 h. The reconstruction of HT occurs via a simple dissolution-reprecipitation process.47

AUTHOR INFORMATION Corresponding Author [email protected] [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources


19


Page 20 of 26

The Natural Science Foundation of China (No. 21403256, 21573261) and Youth Innovation

Promotion

Association

of

Chinses

Academy

of

Sciences

(No.

2018456). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We gratefully acknowledge the Natural Science Foundation of China (No. 21403256, 21573261) and Youth Innovation Promotion Association of the Chinses Academy of Sciences (No. 2018456). SUPPORTING INFORMATION Experimental information, characterization of catalyst, optimization and copies of 1H

and

13C

NMR for all products.

REFERENES (1) Han, W.; Hu, Z.; Jiang, X.; Decicco, C. P. α-Ketoamides, α-ketoesters and α-diketones as HCV NS3 protease inhibitors. Bioorg. Med. Chem. Lett.

2000, 10, 711-713.

(2) Aoki, Y.; Tanimoto, S.; Takahashi, D.; Toshima, K. Photodegradation and inhibition

of

drug-resistant

influenza

virus

neuraminidase

using

anthraquinone–sialic acid hybrids. Chem. Commun. 2013, 49, 1169-1171

(3) Nie, Y.; Xiao, R.; Xu, Y.; Montelione, G. T. Novel anti-prelog stereospecific carbonyl reductases from Candida parapsilosis for asymmetric reduction of prochiral ketones. Org. Biomol. Chem. 2011, 9, 4070-4078.

(4) Suzuki, S.; Kitamura, Y.; Lectard, S.; Hamashima, Y.; Sodeoka, M. Catalytic asymmetric mono-fluorination of α-keto esters: synthesis of optically active

β-fluoro-α-hydroxy and β-fluoro-α-amino acid derivatives. Angew. Chem. Int.

Ed. 2012, 51, 4581-4585.


20

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Zhu, X.; Lin, A.; Fang, L.; Li, W.; Zhu, C.; Cheng, Y. In situ formed bifunctional primary amine–imine catalyst for asymmetric aldol reactions of α-keto esters. Chem. Eur. J. 2011, 17, 8281–8284.

(6) Aizpurua, J. M.; Palomo, C.; Fratila, R. M.; Ferrn, P.; Benito, A.; GmezBengoa, E. Miranda, J. I. Santos, J. I. Mechanistic insights on the magnesium(II)

ion-activated

reduction

of

Methyl

Benzoylformate

with

chelated NADH peptide β-lactam models. J. Org. Chem. 2009, 74, 66916702.

(7) Xiao, X.; Xie, Y.; Su, C.; Liu, M.; Shi, Y. Organocatalytic asymmetric biomimetic transamination: from α-keto esters to optically active α-amino acid derivatives. J. Am. Chem. Soc. 2011, 133, 12914-12917.

(8) Bacchi, A.; Costa, M.; Della, C. N.; Gabriele, B.; Salerno, G.; Cassoni, S. Heterocyclic

derivative

syntheses

by

palladium-catalyzed

oxidative

cyclization-alkoxycarbonylation of substituted γ-oxoalkynes. J. Org. Chem.

2005, 70, 4971-4979.

(9) Sakakura, T.; Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M. Synthesis of alpha.-keto esters via palladium-catalyzed double carbonylation. (10)

J. Org. Chem. 1987, 52, 5733-5740.

Johnston, E. V.; Karlsson, E. A.; Tran, L.-H.; Aakermark, B.; Bäckvall, J.E. Efficient aerobic ruthenium-catalyzed oxidation of secondary alcohols by the use of a hybrid electron transfer catalyst. Eur. J. Org. Chem.

2010, 1971-1976. (11)

Su, Y.; Zhang, L.; Jiao, N. Utilization of natural sunlight and air in the

(12)

Hayashi, M.; Nakamura, S. Catalytic enantioselective protonation of α-

aerobic oxidation of benzyl halides. Org. Lett. 2011, 13, 2168-2171.

oxygenated ester enolates prepared through phospha-brook rearrangement.

(13)

(14)

Angew. Chem., Int. Ed. 2011, 50, 2249-2252.

Xu, X.; Ding, W.; Lin, Y.; Song, Q. Cu-catalyzed aerobic Oxidative

esterification of acetophenones with alcohols to α-ketoesters. Org. Lett.

2015, 17, 516-519;

Guo, S.; Dai, Z.; Yang, Z.; Zhu, N.; Wan, L.; Li, X.; Liu, C.; Fang, Z.;


21


Page 22 of 26

Guo, K. Metal-free oxidative esterification of acetophenones with alcohols:

a facile one-pot approach to α-ketoesters. RSC Adv. 2016, 6, 98422-

98426. (15)

Guo, S.; Dai, Z.; Hua, J.; Yang, Z.; Fang, Z.; Guo, K. Microfluidic synthesis of α-ketoesters via oxidative coupling of acetophenones with

(16)

alcohols under metal-free conditions. React. Chem. Eng. 2017, 2, 650-655.

Huang, X.; Li, X.; Zou, M.; Pan, J.; Jiao, N. TEMP and copper cocatalyzed

oxygenation

of

ketones

with

molecular

oxygen:

chemoselective synthesis of α-ketoesters. Org. Chem. Front. 2015, 2,

354-359. (17)

Zhang, C.; Jiao, N. A Cu-catalyzed practical approach to α-ketoesters under air: an efficient aerobic oxidative dehydrogenative coupling of

(18)

alcohols and α-carbonyl aldehydes. Org. Chem. Front. 2014, 1, 109-112.

Vadagaonkar, K. S.; Kalmode, H. P.; Shinde, S. L.; Chaskar, A. C. An efficient and metal-free synthesis of α-ketoesters via oxidative cross

(19)

coupling of arylglyoxals with alcohols. ChemistrySelect 2017, 2, 900 –903.

Battula, S.; Battini, N.; Singh, D.; Ahmed, Q. N. 2-Oxo promoted hydrophosphonylation & aerobic intramolecular nucleophilic displacement

(20)

reaction. Org. Biomol. Chem. 2015, 13, 8637-8641.

Zhang, C.; Feng, P.; Jiao, N. Cu-catalyzed esterification reaction via aerobic oxygenation and C–C bond cleavage: an approach to α-ketoesters.

(21)

J. Am. Chem. Soc. 2013, 135, 15257-15262.

Kumar, Y.; Jaiswal, Y.; Kumar, A. Copper(II)-Catalyzed Benzylic C(sp3)–H Aerobic

(22)

Oxidation

of

(Hetero)Aryl

Acetimidates:

Synthesis

ketoesters. J. Org. Chem. 2016, 81, 12247-12257.

of

Aryl-α-

Lu, T.; Du, Z.; Liu, J.; Chen, C.; Xu, J. Dehydrogenation of primary

aliphatic alcohols to aldehydes over Cu-Ni bimetallic catalysts. Chin. J.

Catal. 2014, 35, 1911-1916. (23)

Jia, X.; Ma, J.; Wang, M.; Li, X.; Xu, J. Alkali α-MnO2/NaxMnO2 collaboratively

catalyzed

ammoxidation–Pinner

tandem

aldehydes. Catal. Sci. Technol. 2016, 6, 7429-7436.


reaction

of

22

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Natte, K.; Neumman, H.; Wu, X.-F. Pd/C as an efficient heterogeneous catalyst

(25)

for

carbonylative

four-component

synthesis

quinazolinones. Catal. Sci. Technol. 2015, 5, 4474-4480.

of

4(3H)-

Li, X.; Ma, J.; Jia, X.; Xia, F.; Huang, Y.; Xu, Y.; Xu, J. Al-doping promoted

aerobic

amidation

of

5-hydroxymethylfurfural

to

2,5-

furandicarboxamide over cryptomelan. ACS Sustainable Chem. Eng. 2018, (26)

6, 8048−8054.

Li, X.; Jia, X.; Ma, J.; Xu, Y.; Huang, Y.; Xu, J. Catalytic amidation of 5hydroxymethylfurfural to 2,5-furandicarboxamide over alkali manganese

(27)

oxides. Chin. J. Chem. 2017, 35, 984-990.

Kamali, N.; Gniado, K.; McArdle, P.; Erxleben, A. Application of ball milling for highly selective mechanochemical polymorph transformations.

(28) (29)

(30)

Org. Process Res. Dev. 2018, 22, 796-802. Muñoz-Batista, M.

J.;

Rodriguez-Padron, D.;

Puente-Santiago, A.;

Luque, R. R. ACS Sustainable Chem. Eng. 2018, 6, 9530-9544.

Eckert, R.; Felderhoff, M.; Schgth, F. Preferential Carbon Monoxide

Oxidation over Copper‐Based Catalysts under In Situ Ball Milling. Angew.

Chem. Int. Ed. 2017, 56, 2445-2448.

Mahmoud, A. E. D.; Stolle, A.; Stelter, M. Sustainable synthesis of high-

surface-area graphite oxide via dry ball milling. ACS Sustainable Chem.

Eng. 2018, 6, 6358-6369.

(31) Yang, Y.; Zhang, S.; Wang, S.; Zhang, K.; Wang, H.; Huang, J.; Deng, S.; Wang, B.; Wang, Y.; Yu, G. Ball Milling Synthesized MnOx as Highly Active

Catalyst

for

Gaseous

POPs

Removal:

Significance

of

Mechanochemically Induced Oxygen Vacancies. Environ. Sci. Technol.

2015, 49, 4473-4480.

(32) Lin, X.;

Liang, Y.;

Lu, Z.;

Lou, H.;

Zhang, X.;

Liu, S.;

Zheng, B.;

Liu, R.; Fu, R.; Wu, D. Mechanochemistry: a green, activation-free and top-down strategy to high-surface-area carbon materials. ACS Sustainable

Chem. Eng. 2017, 5, 8535-8540.

(33) Meng, X.; Wang, Y.; Chen, B.; Chen, G.; Jing, Z.; Zhao, P. OMS2/H2O2/Dimethyl Carbonate: An Environmentally-Friendly Heterogeneous


23


Page 24 of 26

Catalytic System for the Oxidative Synthesis of Benzoxazoles at Room Temperature. Org. Process Res. Dev. 2017, 21, 2018−2024.

(34) Wang,

Y.;

Meng,

X.;

Chen,

G.;

Zhao,

P.

Direct

synthesis

of

quinazolinones by heterogeneous Cu(OH)x/OMS-2 catalyst under oxygen.

Catal. Commun. 2018, 104, 106-111.

(35) Meng, X.; Wang, Y.; Wang, Y.; Chen, B.; Jing, Z.; Chen, G.; Zhao, P. OMS-2-Supported Cu Hydroxide-Catalyzed Benzoxazoles Synthesis from Catechols

and

Amines

via

Domino

Oxidation

Temperature. J. Org. Chem. 2017, 82, 6922-6931.

(36) Kaneda,

K.;

Ebitani,

K.;

Mizugaki,

T.;

Mori,

Process K.

Design

at of

Room high-

performance heterogeneous metal catlaysts for gren and sustainable chemistry. Bull. Chem. Soc. Jpn. 2006, 79, 981-1016.

(37) Xu,

Z.;

Yu,

X.;

Sang,

X.;

Wang,

D.

BINAP-copper supported by

hydrotalcite as an efficient catalyst for the borrowing hydrogen reaction and dehydrogenation cyclization under water or solvent-free conditions.

Green Chem. 2018, 20, 2571-2577.

(38) Jayesh, T. B.; Itika, K.; Ramesh Babu, G. V.; Rao, K. S. R.; Keri, R. S.; Jadhav, A. H.; Nagaraja, B. M. Vapour phase selective hydrogenation of benzaldehyde to benzyl alcohol using Cu supported Mg-Al hydrotalicite catalyst. Catal. Commun. 2018, 106, 73-77.

(39) Lari, G. M.; Pastore, G.; Mondelli, C.; Pérez-Ramírez, J. Towards sustainable manufacture of epichlorohydrin from glycerol using hydrotalcitederived basic oxides. Green Chem. 2018, 20, 148-159.

(40) Du, Y.; Wang, Q.; Liang, X.; Yang, P.; He, Y.; Feng, J.; Li, D. The role of various oxygen species in Mn-based layered double hydroxide

catalysts in selective alcohol oxidation. Catal. Sci. Technol. 2017, 7,

4361-4365.

(41) Wang, F.; Yang, G.; Zhang, W.; Wu, W.; Xu, J. Copper and manganese: two concordant partners in the catalytic oxidation of p-cresol to phydroxybenzaldehyde. Chem. Commun. 2003, 1172-1173.

(42) Wang, F.; Yang, G.; Zhang, W.; Wu, W.; Xu, J. Oxidation of p-cresol to p-hydroxybenzaldehyde

with

molecular

oxygen


in

the

presence

of

24

Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CuMn‐oxide heterogeneous catalyst. Adv. Synth. Catal. 2004, 346, 633-

638.

(43) Meng, X.; Yu, C.; Chen, G.; Zhao, P. Heterogeneous biomimetic aerobic

synthesis

catalyzed

tandem

of

3-iodoimidazo[1,2-a]pyridines cyclization/iodination

via

and

CuOx/OMS-2-

their

functionalization. Catal. Sci. Technol. 2015, 5, 372-379.

late-stage

(44) Meng, X. Zhang, J. Chen, B. Jing, Z. Zhao, P. Copper supported on H+-modified manganese oxide octahedral molecular sieves (Cu/H-OMS2)

as

a

heterogeneous

biomimetic

catalyst

for

the

synthesis

imidazo[1,2-a]-N-heterocycles. Catal. Sci. Technol. 2016, 6, 890-896.

of

(45) Meng, X.; Bi, X.; Wang, Y.; Chen, G.; Chen, B.; Jing, Z.; Zhao, P. Heterogeneous selective synthesis of 1,2-dihydro-1,3,5-triazines from alcohols and amidines via Cu/OMS-2-catalyzed multistep oxidation.

Catal. Commun. 2017, 89, 34-39.

(46) Bharate, J. B.; Guru, S. K.; Jain, S.; Meena, K. S.; Singh, P. P.; Bhushan, S.; Singh, B.; Bharate, S. B.; Vishwakarma, R. A. Cu–Mn spinel

oxide

catalyzed

synthesis

of

imidazo[1,2-a]pyridines

through

domino three-component coupling and 5-exo-dig cyclization in water.

RSC Adv. 2013, 3, 20869-20876.

(47) Rajamathi, M.; Nataraja, G. D.; Ananthamurthy, S.; Kamath, P. V. Reversible thermal behavior of the layered double hydroxide of Mg with Al: mechanistic studies. J. Mater. Chem. 2000, 10, 2754-2757.

(48) Einage, H.; Kiya, A.; Yoshioka, S.; Teraoka, Y. Catalytic properties of copper–manganese

mixed

oxides

prepared

by

coprecipitation

using

tetramethylammonium hydroxide. Catal. Sci. Technol. 2014, 4, 37133722.

(49) Ross,

J.

R.

H.

Heterogeneous

Catalysis:

Fundamentals

and

Applications, Elsevier, 2012. (50) Bi, X. Meng, X. Chen, G. Chen, B. Zhao, P. Manganese oxide catalyzed synthesis of anti-HIV N-substituted benzimidazoles via a onepot multistep process. Catal. Commun. 2018, 116, 27-31.


25


Page 26 of 26

(51) Jia, J.; Yang, W.; Zhang, P.; Zhang, J. Facile synthesis of Fe-modified manganese oxide with high content of oxygen vacancies for efficient airborne ozone destruction. Appl. Catal. A, Gen. 2017, 546, 79-86.

(52) Sun, M.; Li, W.; Zhang, B.; Cheng, G.; Lan, B.; Ye, F.; Zheng, Y.; Cheng, X.; Yu, L. Enhanced catalytic performance by oxygen vacancy

and active interface originated from facile reduction of OMS-2. Chem.

Eng. J. 2018, 331, 626-635.

(53) Hou, J.; Luo, J.; Hu, Z.; Li, Y.; Mao, M.; Song, S.; Liao, Q.; Li, Q. Tremendous effect of oxygen vacancy defects on the oxidation of

arsenite to arsenate on cryptomelane-type manganese oxide. Chem.

Eng. J. 2016, 306, 597-606.


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Heterogeneous Esterification from Î±-Hydroxy Ketone and Alcohols

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