A palladium-catalyzed regiocontrollable hydroarylation reaction of allenamides with B2pin2/H2O

Article abstract of DOI:10.1039/c9cc00797k

A novel palladium-catalyzed regiocontrollable hydroarylation reaction of allenamides with B₂pin₂/H₂O has been disclosed. H₂O as an ideal hydrogen source was activated by B₂pin₂ to furnish allylamines or enamines with a broad functional group tolerance. The regioselectivity for both of the two products was up to 99:1 for most of the examples, which was achieved by adjusting the addition order of the catalyst and iodobenzene derivatives. The tentative investigation of the mechanism proved the reaction to be a non-radical process and the deuterium-labeled experiments indicated that the hydrogen was from H₂O.

Full text of DOI:10.1039/c9cc00797k

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DOI: 10.1039/C9CC00797K
Authors
Jie Cui,a Long Meng,a Xiaochen Chi,a Qing Liu,a Pingping Zhao,b Dao-peng Zhang,a Lei Chen,a Xinjin
Li,a Yunhui Donga and Hui Liua,*
Affiliations
a School of Chemistry & Chemical Engineering, Shandong University of Technology, 266 West
Xincun Road, Zibo 255049, P. R. China
b College of chemical and environmental engineering, Shandong university of science and
technology, 579 Qianwangang Road, Huangdao District, Qingdao, 266590, P.R.China
Acknowledgements
We thank the Shandong Provincial Natural Science Foundation (ZR2018MB008, ZR2018MB012), the
National Natural Science Foundation of China (21671121), the Shandong Provincial Key Research
and Development program of China (2017GGX20131).

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DOI: 10.1039/C9CC00797K
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Palladium-Catalyzed Regiocontrollable Hydroarylation Reaction of
Allenamides with B2pin2/H2O
Received 00th January 20xx,
Accepted 00th January 20xx
Jie Cui,a Long Meng,a Xiaochen Chi,a Qing Liu,a Pingping Zhao,b Dao-peng Zhang,a Lei Chen,a Xinjin
Li,a Yunhui Donga and Hui Liua,*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A
novel palladium-catalyzed regiocontrollable hydroarylation delocalization of the lone-pair electrons on nitrogen, the sp
reaction of allenamides with B2pin2/H2O has been disclosed. H2O carbon atom of allenamide has a partial negative charge.
as an ideal hydrogen source was activated by B2pin2 to furnish Therefore, allenamide exhibits improved stability and has
allylamines or enamines with a broad functional groups tolerance. become to be a powerful and versatile building blocks in
The regioselectivity for both of the two products was up to 99:1 organic synthesis, especially for substituted allylamine and
for most of examples, which was achieved by adjusting the enamine.6 In 2013, Sato’ and Saito’ group developed a Ni(0)-
addition order of catalyst and iodobenzene derivatives. The catalyzed carboxylation of allenamides with carbon dioxide
tentative investigation to the mechanism proved the reaction to proceeded via a nickelalactone intermediate to give β-amino
be a non-radical process and deuterium-labeled experiments acid derivatives (Scheme 1d).7 It was proved that the
indicated the hydrogen was from H2O.
substituents on the allene part strongly affected the
regioselectivity at the oxidative addition step. In 2017, Bandini
group developed a Ni-catalyzed stereoselective β-arylation of
allenamides by exploiting the nucleophilic character of allyl-Ni
Transition-metal-catalyzed hydrocarbonation of C-C multiple
bonds have been developed into a powerful tool for the
formation of carbon-carbon bonds over the past few decades.1
Among them, hydrocarbonation of allenes is an effective
method to synthesize valuable multisubstituted-alkenes. In
2014, Montgomery and co-workers demonstrated a one-pot
hydroarylation reaction of allene (Scheme 1a).2 It combined
the regioselective hydrosilylation strategy with Pd(0)-catalyzed
cross-coupling reaction of iodides to deliver various di-
substituted alkenes. In 2017, Tsuji and Fujihara group
described a Cu-catalyzed hydroallylation of allenes employing
hydrosilane and allyl chlorides to afford (E)-1,5-dienes
selectively (Scheme 1b).3 In the same year, Lalic and co-
workers reported Cu-catalyzed hydroalkylation of allenes using
alkyl triflates as electrophiles and silane as a hydride source
(Scheme 1c).4
species (Scheme 1e).8 This is
a one-pot tricomponent
procedure involving the final allylation of aldehydes to
produce substituted enamines. It is well known that carbon-
carbon double bond is one of the most versatile building
blocks in synthetic chemistry, which is easy to be
functionalized. Our group has been working on developing
new methodologies to synthesize substituted alkenes or
heterocycles bearing alkenes,9 especially from allenamide
derivates.9e-g Herein we reported
a palladium-catalyzed
regiocontrollable hydroarylation of allenamides in the
presence of B2pin2/H2O to afford allylamines or enamines
selectively. The regioselectivity of this strategy was achieved
successfully by adjusting the addition order of catalyst and
iodobenzene derivatives. It was worth noting that this
transformation utilized H2O as hydrogen source which was
activated by B2pin2 under simple and mild conditions.
Moreover, Song group has also proved that B2pin2 could be
used as the H2O activator to assist the transfer of H atom.10
Furthermore, since D2O is the most readily available deuterium
source, another obvious advantage in the method with water
as hydrogen donor over other hydrogen sources is easily to
access D-labeled compounds, which are very important
molecules in life science and pharmaceuticals.
Since the palladium-catalyzed hydroarylation and
hydrovinylation of carbon-carbon multiple bonds was
disclosed by the Cacchi group,5 hydrocarbonation of
allenamides has also been well-exploited. Due to
a. School of Chemistry & Chemical Engineering, Shandong University of Technology,
266 West Xincun Road, Zibo 255049, P. R. China
b. College of chemical and environmental engineering, Shandong university of
science and technology, 579 Qianwangang Road, Huangdao District, Qingdao,
266590, P.R.China
E-mail: huiliu1030@sdut.edu.cn
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Scheme 1. Development of Hydrocarbonation of Allenamides.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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(a) Regioselective allene hydroarylation via one-pot
rather positive effect in the transformation, providing 84%
View Article Online
ArI
TBAF
Ar
SiR3
Pd(0)
R1
yield. Moreover, the desired product 3aDaOwI:a10s.1n0o3t9/oCb9tCaCin00e7d97inK
the absence of Pd(PPh3)4, indicating that the catalyst was
essential for this transformation (entry 13). On the basis of
these results, the optimal condition A was determined to be
Pd(PPh3)4 (10 mol %), Cs2CO3 (2.0 equiv) in THF at 60 °C (entry
10). Under all these conditions, only a trace amont of the
R1
+
R1

R3SiH

Pd(0)
L HX
(b) Copper-catalyzed hydroallylation of allenes
R2
R2
cat. Cu
R1
R1

+
Cl
R3
R3
H
Si
(c) Hydroalkylation of allenes
H
R2
R1
SIPrCuF
R
R1
+
R2 OTf

(Me2HSi)2
O
1
R
isomer product 4aa were detected by HNMR with excellent
(d) Hydrocarbonation of allenamide with carbon dioxide
regioselectivity (entries 1–12). Moreover, the desired product
4aa was obtained in 58% isolated yield under the condition B
(entry 14). Then we evaluated a series of catalysts for this
reaction, but did not show an obvious influence on the
reaction (entries 15–17). Other common base such as K2CO3,
K3PO4 were not viable, only a trace amont of the desired
product 4aa were detected by 1HNMR (entries 18 and 19).
Finally, Pd(PPh3)4 (10 mol %) and Cs2CO3 (2.0 equiv) in THF at
60 °C were chosen as the optimized condition B. For more
reaction conditions A and B, see supporting information.
O
O
Ni(cod)2
CO2
EWG
EWG
EWG

N
R2
N
OMe
N
OMe
or
R1
R1
R1
CH2N2
R2
R2
(e) Site-selective -arylation of allenamides
R
EWG
+
Ni
N
E
cat. Ni
E
R
N
EWG
ArB(OH)2
N

Ar
EWG
Ar
R
E: H+, RCHO
This work: Regioselective hydroarylation of allenamides
cat. Pd(0)
H2
Ar
O
(one step)
R
H
N

Ar-I
Ts
+
(BPin)2
H
R
N
Ar-I
step 2
cat. Pd(0)
Ar
Ts
(two step)
H2O
R
step 1
N
Ts
Table 2. Scope of Regiocontrollable Hydroarylation of Allenamidesa,b
R2
R2
R2
H
Table 1. Optimization of the Reaction Conditionsa,b
I
Pd(PPh3)4 (10 mol%)
Cs2CO3 (2.0 equiv)
Ar
or

R1
or
R1
+
+ (BPin)2
MeO
N
+
MeO
+
R1
THF, 60 oC, N2, 12 h
H2O (2.0 equiv)
H
N
Ts
R1
N
Ts
I
Ts
H
Ar
N
H
Br
+
Pd
Ts
1
3
4
2
OMe
2a
Me
Ph
Ph
MeO
H
N
N
Condition A
Ts
Ts
4aa
3aa (major)

ligand/base
I
+
(BPin)2
MeO
H
N
Ts
MeO
H
N
solvent, H2O,
t, N2, 12 h
H
N
N
H
Ts
Ts
3aa, 84% (82:18)
Ts
3ab, 61% (96:4)
Bromobenzene: 52% (96:4)
OMe
3ac, 63% (98:2)
Pd
+
2a
1a
Ph
N
Ph
H
3aa
Condition B
N
Ts
4aa (major)
HO
Ts
Me
yieldc of
3aa
(%) yieldc of
4aa
(%)
t (oC)
ligand
solvent
entry
catalyst
base
H
N
Ts
H
N
Pd(OAc)2
Pd2(dba)3
PdCl2(dppf)
dppf
dppf
Cs2CO3
Cs2CO3
Cs2CO3
toluene
toluene
60
60
trace
trace
H
N
1
2
57
Ts
3af, 71% (97:3)
Ts
3ad, 71% (>99:1)
40
3ae, 56% (98:2)
3
4
5
-
-
-
-
-
-
-
-
-
-
-
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
60
60
60
60
60
60
60
60
60
60
60
trace
trace
trace
trace
trace
trace
trace
trace
trace
trace
-
O
59
66
61
13
Pd(PPh3
)
Cs2CO3
Cs2CO3
4
BzO
EtO
PdCl2(PPh3
)
2
F
6
Pd(PPh3
Pd(PPh3
Pd(PPh3
)
)
)
K2CO3
KOtBu
4
H
N
7
trace
36
trace
H
N
Ts
4
4
H
N
Ts
3ag, 68% (99:1)
Ts
3ah, 64% (>99:1)
8
K3PO4
3ai, 54% (>99:1)
Cy2NMe
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
9
Pd(PPh3)
4
4
4
4
Cl
F
10
11
12
13
Pd(PPh3)
84
1,4-dioxane
MeCN
Pd(PPh3
Pd(PPh3
-
)
57
59
NR
-
Cl
)
H
N
Ts
THF
H
N
H
N
Ts
3aj, 61% (98:2)
Ts
3ak, 51% (>99:1)
14
Pd(PPh3
)
-
Cs2CO3
THF
60
58
4
3al, 64% (>99:1)
PdCl2(dppf)
-
-
-
-
-
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
THF
THF
THF
THF
THF
60
60
60
60
60
15
16
-
-
42
44
27
PdCl2(PPh3
)
2
Cl
MeO
Cl
Pd(dba)2
17
18
19
-
-
Pd(PPh3
Pd(PPh3
)
)
trace
4
Cl
K3PO4
-
4
trace
H
N
H
N
H
N
Ts
Ts
3am, 36% (>99:1)
Ts
3an, 46% (77:23)
3ao, 42% (97:3)
aReaction conditions A (one step): 1a (0.2 mmol), 2a (0.4 mmol), (BPin)2 (0.4 mmol),
[Pd] (0.02 mmol), base (0.4 mmol), solvent (2.0 mL), H2O (0.4 mmol), N2, 12 h.
bReaction conditions B (two step): 1a (0.2 mmol), (BPin)2 (0.4 mmol), [Pd] (0.02 mmol),
base (0.4 mmol), solvent (2.0 mL), H2O (0.4 mmol), N2, 12 h; 2a (0.4 mmol). cIsolated
yields.
MeO
MeO
MeO
Me
H
N
H
N
Ts
H
N
Ts
3da, 63% (>99:1)
Ts
3ba, 72% (86:14)
Me
3ca,67% (>99:1)
MeO
MeO
MeO
MeO
MeO
Me
OEt
Me
H
N
H
N
H
N
Me
Ts
3ga, 63% (>99:1)
Ts
3ea, 57% (>99:1)
Ts
3fa, 65% (>99:1)
OEt
We initiated our studies by testing the reaction of
allenamide 1a with 1-iodo-4-methoxybenzene 2a in the
presence of (BPin)2 (Table 1). At the outset, the desired
product 3aa could be afforded in 57% isolated yield in the
presence of 10 mol % of Pd(OAc)2 and 15 mol % of dppf with
B2pin2 (2.0 equiv), H2O (2.0 equiv) and Cs2CO3 (2.0 equiv) at
60 °C in toluene under condition A (Table 1, entry 1). The
combination of Pd2(dba)3/dppf as the catalyst did not improve
the transformation (entry 2). Then PdCl2(dppf), Pd(PPh3)4 and
PdCl2(PPh3)2 were examined (entries 3–5). The use of
Pd(PPh3)4 greatly increased the yield to 66%. Inorganic and
organic bases did not give better results on the reaction
(entries 6–9). The screening of base revealed that Cs2CO3 was
still the best choice. Furthermore, we examined the effect of
the solvent (entries 10–12). To our delight, THF exhibited a
MeO
H
N
H
N
H
N
Ms
3ia, 43% (>99:1)
Ns
3ja, 32% (>99:1)
Ms
3ha, 47% (>99:1)
aReaction conditions A (one step): 1 (0.2 mmol), 2 (0.4 mmol), (BPin)2 (0.4 mmol),
Pd(PPh3)4 (0.02 mmol), Cs2CO3 (0.4 mmol), THF (2.0 mL), H2O (0.4 mmol), N2, 12 h. bThe
ratio of 3:4 in parentheses was determined by 1HNMR spectroscopy.
With the optimized conditions in hand, we subsequently
explored to the substrate scope of this reaction, and the
results were given in Table 2. Firstly, different iodobenzenes
were investigated. The aryl of iodides bearing an electron-
donating group at the para position, such as methoxy, methyl
and tertiary butyl, performed very well under the standard
conditions and delivered the desired products in moderate to
2 | J. Name., 2012, 00, 1-3
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good yields (3aa−3ad). Among them, bromobenzene could yield with 84% deuterium incorporation (entry 1,VSiecwhAertmicleeO2nlain)e.
DOI: 10.1039/C9CC00797K
also give the desired product 3ab in moderate yield. Compared Nevertheless, when the reaction was conducted in THF-D8 and
to the para-substituted iodobenzenes, meta-substituted H2O, only product 3aa without deuterium labeling was
iodobenzene 2e produced 3ae in a slightly lower yield, obtained (entry 2, Scheme 2a). Subsequently, the
indicating that the substituent position on the aromatic ring transformation was carried out by employing a mixture of THF
influenced the reaction strongly. Substrates 2f and 2g and D2O under condition B (entry 1, Scheme 2b). The
performed smoothly, giving 71% and 68% yields respectively deuterated product 4aa-II was isolated with 71% deuterium.
(3af and 3ag). Subsequently, iodobenzenes with various Additionly, only product 4aa without deuterium labeling was
electron-withdrawing groups were also examined. Substrates also isolated in THF-D8 and H2O under condition B (entry 2,
including ethyl ester, fluoro or chloro at the meta or para Scheme 2b). Apparently, the observation of these results
position worked well to afford the desired products in supports that the hydrogen atom is derived from water but
moderate yields (3ah−3al). Additionally, iodobenzene bearing not the solvent. Next, this reaction was conducted in the
two chloro group was also compatible as well under the presence of the radical scavenger TEMPO and in this case the
standard condition, albeit with lower yield (3am).
transformation could still go smoothly under condition A and
The scope of this reaction was further expanded to vinyl condition B (Scheme 2c and Scheme 2d). This result revealed
halides. The reaction of E-(2-bromovinyl)benzene derivatives that this transformation might not undergo a radical process.
2n and 2o with 1a could also investigated, leading to the Furthermore, we added allenamide 1a in the 12 hours prior to
desired product 3an and 3ao in relative lower yields. the addition of the Ar-I and another second allenamide 1a in
Furthermore, we also evaluated the substitution of R1 on the reaction system, and a mixture of products were obtained
allenamides. To our satisfaction, the results showed that both (Scheme 2e). This indicated that allenamide 1a has become a
phenmethyl, alkenes, nPr, iPr and diethoxyethyl could hydroboration intermediate (the 1HNMR spectrum see
successfully give the corresponding products in decent yield supporting information).
(3ba-3ga). To further investigate the substrate scope of this
strategy, we tested Ms and Ns protected allenamides, and the
Scheme 2. Preliminary mechanism exploration.
I
(a)
Pd(PPh3)4 (10 mol%)
MeO
desired product were obtained smoothly (3ha-3ja).
Cs2CO3 (2.0 equiv)

+
+
(BPin)2
Solvent, 60 oC, N2, 12 h
N
Ts
N
OMe
(D)H
3aa-I
Ts
Table 3. Scope of Regiocontrollable Hydroarylation of Allenamidesa,b
1a
2a
I
Entry
deuterated ratio (%)
solvent/additive
R2
R2
H
THF/D2O (20:1)
THF-D8/H2
1
2
84
0
(1.2 equiv)
Pd(PPh3)4 (10 mol%)
Cs2CO3 (2.0 equiv)

O
2
(BPin)
+
R2
R1
+
2
R1
R1
N
N
THF, 60 oC, N2, 12 h
H2O (2.0 equiv)
I
MeO
(b)
Ts
N
H
3
H(D)
Pd(PPh3)4 (10 mol%)
Ts
Ts
1
4

Cs2CO3 (2.0 equiv)
2a
OMe
(BPin)2
+
Me
H
tBu
MeO
Solvent, 60 oC, N2, 12 h
H
N
H
H
Ts
N
4aa-II Ts
1a
N
N
Entry
solvent/additive
deuterated ratio (%)
Ts
N
N
Ts
Ts
Ts
4ab, 65% (>99:1)
Bromobenzene: 51% (>99:1)
4ad, 54% (>99:1)
4ac, 55% (>99:1)
71
0
THF/D2
O
4aa, 58% (87:13)
1
2
O
THF-D8/H2
O
Cl
Cl
F
H
H
H
EtO
H
(c)
I
Pd(PPh3)4 (10 mol%)
Cs2CO3 (2.0 equiv)
MeO
Me

+
+
(BPin)2
N
N
N
THF, 60 oC, N2, 12 h
H2O (2.0 equiv)
N
Ts
Ts
N
Ts
Ts
Ts
4am, 51% (>99:1)
H
N
OMe
4aj, 48% (>99:1)
4ah, 52% (>99:1)
4ae, 49% (>99:1)
Ts
3aa
TEMPO (3.0 equiv)
1a
2a
Yield = 76%
I
Pd(PPh3)4 (10 mol%)
MeO
C3H7
(d)
MeO
OEt
MeO
MeO
MeO
Me
H
H
H
H
H

Cs2CO3 (2.0 equiv)
2a
OMe
(BPin)2
+
N
THF, 60 oC, N2, 12 h
H2O (2.0 equiv)
TEMPO (3.0 equiv)
Yield = 52%
N
N
Ts
N
N
N
Ts
4aa
Ts
Ms
Ts
1a
OEt
Ts
4ha, 22% (95:5)
4ba, 55% (96:4)
4ea
4ga
, 57% (>99:1)
, 50% (>99:1)
(e)
MeO
MeO
H

Pd(PPh3)4/Cs2CO3
aReaction conditions B (two step): 1 (0.2 mmol), (BPin)2 (0.4 mmol), Pd(PPh3)4 (0.02
mmol), Cs2CO3 (0.4 mmol), THF (2.0 mL), H2O (0.4 mmol), N2, 12 h; 2 (0.4 mmol). bThe
ratio of 4:3 in parentheses was determined by 1HNMR spectroscopy.
2a
1a
+
(BPin)2
+
THF, H2O, 60 o
N2, 12 h
C
N
Ts
H
N
N
Ts
1a
4aa Ts
3aa
On the basis of all the experiments results as well as
precedent reports, we proposed a tentative mechanism which
is shown in Scheme 3. For catalytic cycle under condition A,
oxidative addition of Pd(PPh3)4 to 2b would afford palladium
complex 5. Subsequently, transmetalation between palladium
complex 5 and B2pin2 offered PdII intermediate 6 in situ.
Subsequently, the intermediate 6 would readily coordinate
with H2O, which might facilitate the H atom transfer from H2O
to palladium, affording [Pd−H] species 7 and releasing
HOBpin.10b Then the insertion of allenamide 1a to [Pd−H]
species would form π-allylpalladium intermediate 8, which
gave the corresponding product 3ab via reductive elimination
and regenerated Pd(0) catalyst. For catalytic cycle under
condition B, oxidative addition of B2pin2 to palladium
Subsequently, we adjusted the addition order of
iodobenzene derivatives and catalyst to produce a wide range
of substituted enamines
4
(Table 3). Although the
iodobenzenes bearing methoxy, alkyl, esters and halides were
all performed well to deliver the corresponding products
showing good functional group compatibility, the yields were
relatively low. Additionally, methanesulfonyl-protected
allenamides reacted with 1-iodo-4-methoxybenzene to
generate the corresponding product 4ha.
In order to understand the origin of hydrogen in this
transformation, deuterium-labeled experiments were carried
out with 1a (Scheme 2). Initially, we performed this
transformation in the mixture of THF/D2O (20:1) under
condition A. The deuterated product 3aa-I was isolated in 72%
This journal is © The Royal Society of Chemistry 20xx
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ChemComm
COMMUNICATION
Journal Name
1
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generated a boryl palladium species 9. Then the insertion of
allenamide 1a to B-Pd bond formed PdII intermediate 10,
which then worked with H2O to afford hydroboration
intermediate 11 and released HOBpin. Next, reductive
elimination of intermediate 11 afforded intermediate 12 and
regenerated Pd(0) catalyst. Subsequently, oxidative addition of
Pd(0) to 2b would afford palladium complex 5. The
intermediate 12 underwent Suzuki-Miyaura coupling upon
addition of 5 to form Pd(II)-H intermediate 13. In the end,
reductive elimination of Pd(II)-H intermediate 13 gave the
desired product 4ab with concurrent regeneration of Pd(0)
catalyst.
Scheme 3. Possible mechanism.

N
B2pin2
Ts
1a
pinB
PdII
I
I
Pd
pinB Pd Bpin
pinB
2b
9
5
H2O
Ph
N
Ts
I
Bpin
10
B2pin2
HOBpin
pinB
Pd Bpin
6
PdH
Pd(0)
Condition B
Condition A
Ph
H
H2
O
Ph
N
Ts
N
11
H
H
Ts
Ph
HOBpin
Pd
Bpin
3ab
H
B
pin
H
I
Pd
Ph
Ph
Ph
N
Pd(0)
N
2
3
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For a review on early work, see S. Cacchi, Pure Appl. Chem.,
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Ts
Ph
PdII
Ph
H
12 Ts
N
Ts
4ab
13
7
PdII
I
N
I
8
Ts

N
5
2b
4
5
6
Ts 1a
In conclusion, we have developed a palladium-catalyzed
regioselective hydroarylation reaction of allenamides with
B2pin2 and water as hydrogen donor. The regioselectivity was
achieved successfully by adjusting the addition order of
catalyst and iodobenzene derivatives. With the optimized
conditions, this reaction performed very well with a broad
functional groups tolerance in moderate to excellent yields,
affording allylamines or enamines efficiently. The origin of
hydrogen was proved to be from H2O via deuterium-labeled
experiments. TEMPO testing experiments proved the reaction
to be a non-radical process. The reaction mechanisms for the
two products were also proposed basing on the control
experiments and previous work. Further studies on the
detailed mechanism and its applications are currently
underway.
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
We thank the Shandong Provincial Natural Science Founda-
tion (ZR2018MB008, ZR2018MB012), the National Natural
Science Foundation of China (21671121), the Shandong
Provincal Key Research and Development program of China
(2017GGX20131).
Notes and references
4 | J. Name., 2012, 00, 1-3
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