[3+1+1] type cyclization of ClCF2COONa for the assembly of imidazoles and tetrazolesvia in situgenerated isocyanides

Article abstract of DOI:10.1039/d0cc01919d

A facile synthesis of imidazoles and tetrazolesvia[3+1+1] type cyclization of ClCF₂COONa is developed. A diverse array of imidazoles and tetrazoles were obtained in decent yieldsviaisocyanide intermediates. Notably, this is the first example of the cycloaddition ofin situgenerated isocyanides.

Full text of DOI:10.1039/d0cc01919d

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DOI: 10.1039/D0CC01919D
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[3+1+1] Type Cyclization of ClCF2COONa for the Assembly of
Imidazoles and Tetrazoles via In-Situ Generated Isocyanides
Ya Wanga, Yao Zhouc and Qiuling Song*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A facile synthesis of imidazoles and tetrazoles via [3+1+1] type
cyclization of ClCF2COONa is developed. A diverse array of
imidazoles and tetrazoles were obtained in decent yields via
isocyanide intermediates. Notably, this is the first example for
cycloaddition of in-situ generated isocyanides.
a) Our envisage:
1,3-dipole
[3+1+1]
C
N
C
N
N
C
+
valuable N-heterocycles
naked C1
b) Previous work:
Owing to the flexible and diverse reactivities, isocyanides have
demonstrably proven to be multitask reagents and have been
comprehensively applied in organic, medicinal, and combinatorial
chemistry.1-4 One of the promising reactions of isocyanides is the
Nu-H
Nu-CF2H
known
difluorocarbene
O
R-NH2
R
NH
N
known
carbonyl
Cl
O
N
F
cycloaddition, which has been extensively applied to assemble a
COONa
F
Nu1
Nu1
N
NH
4
diverse array of nitrogen heterocycles.2,
However, the
known
and
C1 synthon
R
N
R
preconstruction of isocyanides from amines is prerequisite to use
isocyanides as starting materials in previous cycloadditions.5 In
addition, most of these reactions merely involve the
functionalization of the terminal carbon atom of isocyanide,2-4
leaving the nitrogen atom intact. Meanwhile, the isocyanides which
have low molecular weight usually have extreme strong odor, which
makes the synthesis, purification and application of isocyanides
unpleasant and reluctant.6 Therefore, the development of an
expedient route to accomplish the cycloaddition via transformation
of in-situ generated isocyanides and exploration of both the
nitrogen and carbon atoms of isocynides as reactive sites is highly
desirable.7 Based on our previous studies, we envision that amines
and naked C1 source generated from XCF2COR in basic conditions
will lead to isocyanides in situ, which further is consumed for
R-NH2
R
N
unknown
isocyanides
c) This work:
N
N
CN
COOEt
COOEt
N
R
Cl
[3+1+1]
R
R
NH2
R
N
+
F
COONa
F
N
N
N
TMSN3
isocynides generated in situ and consumed in situ
both C and N atoms in isocynides involved in the cyclization,
leading to valuable N-heterocycles
Scheme 1. The reactions of ClCF2COONa.
In organic synthesis, the most important applications of sodium
chlorodifluoroacetate (ClCF2COONa) are the utilization as
outstanding difluorocarbene equivalent via C-Cl and C-C bond
cleavage.9 In sharp contrast to difluoromethylation reactions, the
literature on the quadruple cleavage of ClCF2COONa is relatively
sparse. At this point, our group reported a novel N-formylation of
primary amines using ClCF2COONa as a new promising formylation
reagent.10 Recently, both our group and Liu’s group11 independently
8
cycloaddition with 1,3-dipole4,
with both N and C atoms
incorporated into the final product (Scheme 1a). To our knowledge,
the cycloaddition from in-situ generated isocyanides has never
been documented up to date.
aInstitute of Next Generation Matter Transformation, College of Materials Science
& Engineering at Huaqiao University, 668 Jimei Blvd, Xiamen, Fujian, 361021, P. R.
China
developed
a transition metal-free and external oxidant-free
synthesis of 1,3,5-triazines and quinazolinones by employing
ClCF2COONa as the C1 synthon. Despite these undisputed advance
of ClCF2COONa, the [3+1+1] cyclization of ClCF2COONa with amines
via transformation of in-situ generated isocyanides has yet to be
supplemented. As our ongoing interest in transformation of
halogenated difluoro compounds,12 herein, we demonstrate a
simple and effective method to streamline synthesis of imidazoles
bFujian University Key Laboratory of Molecule Synthesis and Function Discovery,
College of Chemistry, Fuzhou University, Fuzhou, Fujian, China, 350108
cCollege of Chemistry and Chemical Engineering, Hubei Normal University,
Huangshi 435002, Hubei, P. R China.
Email: qsong@hqu.edu.cn; fax:86-592-6162990;
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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and tetrazoles via [3+1+1] cyclization of ClCF2COONa, which modest yields. The submitting of disubstitutedVieawnAilritnicele Onalninde
DOI: 10.1039/D0CC01919D
represents the first example for cycloaddition of in-situ generated benzylamine to this reaction was also successful, in which the
isocyanides.
expected 4u and 4v were achieved in 81% and 41% yields,
To explore the feasibility of our proposal, we selected aniline respectively. To our delight, 2-naphthylamine and heterocyclic
(1a), ClCF2COONa and ethyl isocyanoacetate (3a) as the model amines demonstrated decent reactivity in this cyclization reaction
substrates for our investigations. To our delight, when the reaction as well, finishing the targeted products 4w-4aa in moderate to good
was carried out in the presence of CuCl2 and 1,10-Phen by using yields. Of note, the indole was well-tolerated under the identified
Na2CO3 as base, the expected ethyl 1-phenyl-1H-imidazole-4- conditions without difluoromethylation of the free N-H of indole.
carboxylate (4a) was indeed achieved in 52% yield (Table 1, entry Compared to ethyl isocyanoacetate, methyl isocyanoacetate was
1). Inspired by this result and in light of our previous researches, a also good cyclization partner, giving rise to the production of 4ab in
bunch of difluorides were also inspected (Table 1, entries 2-5). 70% yield.
Among the difluoro reagents tested, ClCF2COONa still demonstrated
Scheme 2. Scope for the Synthesis of Imidazole Derivatives
the optimum efficiency. Subsequently, a range of bases were
screened to examine the effect of different bases on this reaction,
which turned out that Cs2CO3 was proven to be the best choice to
deliver the desired product 4a in 75% yield (Table 1, entries 6-11).
In order to enhance the yield of 4a, we also inspected a number of
solvents (Table 1, entries 12-15). However, no superior results were
gained and it’s was found that CH3CN was still the optimized
reaction medium. Gratifyingly, when we increased the amount of
ClCF2COONa to 3 equivalents, the targeted 1-phenyl-1H-imidazole-
4-carboxylate (4a) could be isolated in 81% yield (Table 1, entry 16).
Control experiments indicated that Cu salt, ligand and base were all
indispensable for this transformation (Table 1, entries 17-19).
N
Cl
COOEt
NH2
N
CuCl2, 1,10-Phen
+
+
CN
Het
COOR1
F
Het
COONa
Cs2CO3, CH3CN
100 oC, N2
F
1
2
3
4
N
N
N
COOEt
COOEt
N
COOEt
N
N
N
R
NC
a
4n,
N
60%
4m
, 67%
4a
R = H, , 81%
N
4b
R = F, , 72%
N
COOEt
4c
R = Cl, , 62%
COOEt
N
4d
R = Br, , 55%
a
a
4e
R = Me, , 95%
O2
N
4f
O
R = Pr, , 65%
b
4p
, 52%
4o
, 61%
R = iPr, , 60%
4g
R = tBu, , 80%
N
N
4h
a
COOEt
4i
R = Ph, , 78%
COOEt
N
N
4j
R = OEt, , 75%
NC
4k
R = SMe, , 70%
EtOOC
a
4l
R = OPh, , 80%
4q
N
, 48%
4r
, 55%
N
N
COOEt
Table 1. Screening of Optimized Reaction Conditions
N
COOEt
F
N
X
CuCl2, 1,10-Phen
CF3
COOEt
Ph NH2
N
+
+
R
CN
COOEt
F
Ph
4s
, 50%
4t
, 52%
Base, Slovent
X-ray of 4e
F
1a
2
3a
4a
Yieldb
N
N
N
Entrya
2
Base
Solvent
COOEt
COOEt
N
1
2
ClCF2COONa
BrCF2COOEt
BrCF2COOH
ClCF2H
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
K2CO3
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
52
40
4v, 41%
X-ray of 4u
4u
, 81%
20
3
4
N
N
N
trace
24
COOEt
N
COOEt
N
5
6
BrCF2PO(OEt)2
ClCF2COONa
ClCF2COONa
ClCF2COONa
ClCF2COONa
COOEt
COOEt
N
53
N
H
7
Cs2CO3
K3PO4
75
a
4y
, 61%
4w
, 67%
4x
, 65%
20
8
N
N
N
N
9
Na3PO4
trace
COOEt
N
COOMe
N
10
11
N
S
ClCF2COONa
ClCF2COONa
ClCF2COONa
ClCF2COONa
ClCF2COONa
KOH
CH3CN
CH3CN
trace
55
N
NaHCO3
Cs2CO3
Cs2CO3
Cs2CO3
1,4-dioxane
EA
trace
20
12
13
4ab
, 70%
Reaction condition: (0.2 mmol), (0.6 mmol), (0.3 mmol), CuCl2 (15 mol %), 1,10-phen
a 3
4z, 40%
4aa
, 81%
1
2
3
(20 mol%), Cs2CO3 (0.6 mmol), CH3CN (2 mL), N2, 100 oC, 16 h.
(0.6 mmol). b110 oC.
14
THF
trace
15
16c
17d
18e
19f
ClCF2COONa
ClCF2COONa
ClCF2COONa
ClCF2COONa
ClCF2COONa
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
-
DCE
15
CH3CN
CH3CN
CH3CN
CH3CN
81
N.R.
trace
N.R.
Inspired by the success for the assembly of imidazole derivatives
via this novel [3+1+1] cyclization of ClCF2COONa, we were
inquisitive that whether TMSN3 could be used as effective partner
for this [3+1+1] cyclization of ClCF2COONa. If so, the tetrazole
derivatives will be constructed in one pot. To verify our hypothesis,
the reaction of p-methylaniline, TMSN3 and ClCF2COONa was
carried out. Pleasurably, the product 1-(p-tolyl)-1H-tetrazole 6a was
obtained in 31% yield. The structure of 6a was definitely confirmed
by X-ray single crystal diffraction.13 After investigating a range of
reaction parameters, the desired 1-(p-tolyl)-1H-tetrazole 6a was
readily gained in 78% yield under transitionmetal free conditions by
using NaHCO3 as base.
Having optimized the reaction conditions for the synthesis of
tetrazoles, the generality of this base-promoted [3+1+1] cyclization
reaction to forge tetrazole derivatives was then evaluated, which
was summarized in Scheme 3. Electron-donating substituted
anilines were found to be good candidates in this transformation,
enabling the production of the 6a-6i in 65%-81% yields. Compared
a
1a
2
3a
(0.3 mmol), base
All reactions were carried out with
(0.2 mmol), (0.4 mmol),
(0.6 mmol) CuCl2 (15 mol%) and 1,10-Phen (20 mol%) in slovent (2 mL) under N2
atmosphere at 100 oC for 16 h. b Isolated yield.
1,10-Phen. e Without 1,10-phen. f Without base.
(0.6 mmol). d Without CuCl2 and
c 2
Under the optimized reaction conditions, a broad range of the
imidazole derivatives via the [3+1+1] cyclization of ClCF2COONa
were formed in excellent yields. As showcased in Scheme 2, halo-
substituted anilines (1b-1d) were well amenable to this cyclization
reaction, enabling the formation of 4b-4d in 55%-72% yields.
Moreover, a variety of anilines bearing electron-donating and
electron-withdrawing groups were proven to be good candidates in
this transformation, affording the desired imidazole products (4e-
4r) in 48%-95% yields. The structure of 4e was definitely confirmed
by X-ray single crystal diffraction.13 In addition to para-substituted
anilines, ortho- and meta-substituted anilines could work smoothly
in this reaction as well, providing corresponding imidazoles 4s-4t in
2 | J. Name., 2012, 00, 1-3
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N
NH2
CuCl2, 1,10-Phen
Cs2CO3, CH3CN
100 oC, N2, 16 h
to electron-donating substituted anilines, electron-withdrawing
substituted anilines showed relatively poor reactivity in this
reaction. For instance, ethyl 4-aminobenzoate just provided the
corresponding tetrazole 6j in 36% yield. Halo-substituted anilines
were well compatible in this reaction, delivering the targeted
tetrazoles 6k-6m in 47%-73% yields. Disubstituted aniline could
undergo this base-promoted [3+1+1] cyclization reaction as well, in
which the desired tetrazoles 6n was gained in 61% yield. To our
delight, heterocyclic anilines and could also be engaged in the
synthesis of tetrazoles via this cyclization reaction, leading to the
formation of the expected tetrazoles 6o-6p in 60% yields. It’s
noteworthy that the current protocol can be extended to aliphatic
amines and the functionalized tetrazoles 6r and 6s could be
obtained in 65% and 62% yields, respectively.
COOEt
View Article Online
N
(a)
+
+
ClCF2COONa CN
COOEt
DOI: 10.1039/D0CC01919D
Ph
Ph
4i
, 60%
1i
, 2 mmol
N
N
N
N
NH2
(b)
(c)
NaHCO3 (1.5 equiv)
+
ClCF2COONa
N
TMS
3
+
N
CH3CN (20 mL)
100 oC, N2, 16 h
N
6p
, 65%
1p
, 2 mmol
N
N
N
N
NH2
NaHCO3 (1.5 equiv)
+
ClCF2COONa
N
TMS
3
+
CH3CN (20 mL)
100 oC, N2, 16 h
1m
, 2 mmol
6m
, 60 %
N
N
N
H
H
NC
N
N
K2CO3 (2 equiv)
Ag2O (20 mol%)
COOMe
(d)
(e)
COOMe
+
THF (2 mL), 100 o
C
N
N
6p
7,
42%
Ph
N
KOAc (2 equiv)
N
N
Ph
NH2
N
Cu(OAc)2 (2 equiv)
+
Ph
Ph
[Cp*PhCl2
]2 (2.5 mol%)
N
DMA (2 mL)
8,
50%
6m
Scheme 3. Transition-Metal Free Synthesis of Tetrazoles
Scheme 4. Scale-ups and Synthetic Transformations
N
N
Cl
NH2
N
NaHCO3 (3 equiv)
CH3CN (2 mL)
100 oC, N2
N
+
+
TMS
N
Het
indicating a radical-type process might not be involved in this
[3+1+1] cyclization reaction. Subsequently, a range of control
experiments were carried out to gain insight into the possible
intermediates in this reaction.
3
F
COONa
Het
F
2
6
1
5
N
N
N
N
N
N
N
N
N
N
N
N
iPr
tBu
N
6a
X-ray of
COOEt
N
NH2
6a
6c
, 71 %
, 78 %
6b
, 65 %
standard conditions
(a)
(b)
(c)
(d)
+
+
ClCF2COONa CN
COOEt
N
N
N
N
TEMPO (3 eq)
N
N
N
N
Ph
N
N
N
N
N
N
Ph
N
N
3
2
BHT (3 eq)
or
TEMPO, 4i
BHT 4i
,
,
76%
1i
1q
9
, 78%
N
N
N
N
S
Ph
O
Pr
NH2
6g
standard conditions
6e
6f
, 70%
, 66 %
, 81 %
6d
, 65 %
+
+
ClCF2COONa
TMSN3
N
N
N
N
TEMPO (3 eq)
N
N
N
N
N
N
N
N
N
N
2
5
BHT (3 eq)
or
TEMPO, 6q
BHT 6q
,
32%
N
N
,
, 56%
N
N
Ph
EtOOC
O
Br
NC
COOEt
CuCl2, 1,10-Phen
N
6h
6i
6j
6k
, 47 %
, 76%
,
, 36 %
65%
+
CN
COOEt
Cs2CO3, CH3CN
100 oC, N2, 16 h
N
Ph
N
N
Ph
with Cu/L , 98%
3
N
N
N
N
N
N
N
N
N
, 4i
N
N
4i
N
without Cu/L, , 20%
N
O
N
N
N
H
N
O
NC
N
F
Cl
Cs2CO3, CH3CN
100 oC, N2, 16 h
TMSN3
+
6l,
6n
6o
, 60%
73 %
, 61 %
6m
, 62 %
5
N
6q
10
, 50%
N
N
N
N
N
N
COOEt
N
N
N
N
N
N
N
N
benzimidazole
standard conditions
N
N
(e) 1i
+
ClCF2COONa
CN
+
COOEt
+
N
N
N
3
Ph
2
CF2
H
N
4i,
11,
trace
95%
p
6q,
6r
6s
, 62%
56%
, 65 %
6
, 60%
N
N
N
N
N
N
benzimidazole
standard conditions
+
(f) 1q + ClCF2COONa
TMSN3
1
2
3
Reaction condition: (0.2 mmol), (0.6 mmol), (0.6 mmol), NaHCO3 (0.6 mmol),
CH3CN (2 mL), N2, 100 oC, 16 h.
+
2
5
CF2
H
6q,
11,
5%
90%
Scheme 5. Control Experiments
We also studied the scalability of this [3+1+1] cyclization reaction
to access tetrazoles. When current protocol was scaled up ten times,
the desired imidazoles and tetrazoles 4i, 6p and 6m could be readily
obtained in 60%, 65% and 60% yields without loss of efficiency,
respectively (Scheme 4a, 4b and 4c). Further transformations of the
tetrazoles were executed. The highly functionalized (E)-N-cyano
enamine 7 could be obtained in moderate yield via Ag-catalyzed
1,2-addition reaction of tetrazole 6p with alkyl propiolates (Scheme
4d).14 2-Aminoquinolines are significant pharmacophores and have
been embed in a range of pharmaceutical molecules. The synthetic
utility of this approach was also showcased by the assembly of 6,7-
When [1,1'-biphenyl]-4-amine 1i, 2-naphthylamine 1q or
ClCF2COONa was exposed to isocyanoacetate 3a or TMSN3 5, no
intermediates were detected by GC-MS or 19F-NMR (see the
Supporting Information). However, the treatment of amines 1i or
1q and ClCF2COONa under basic conditions enabled the formation
of isocyanides 9 and 10 (see the Supporting Information). And
whenpure isocyanides 9 or 10 was submitted to the standard
conditions, the desired 4i and 6q was isolated in 98% and 50% yield
(Scheme 5c and 5d), which manifested that isocyanide might be the
key intermediate for this [3+1+1] cyclization reaction. Based on our
previous quadruple cleavage of halogenated difluoro compounds,
difluorocarbenes (:CF2) was generated in-situ. To verify the
production of difluorocarbene in this reaction, the difluorocarbene
trapping experiment was conducted. When benzimidazole was
added as difluorocarbene trapper, the 1-(difluoromethyl)-1H-
benzo[d]imidazole (11) was indeed obtained in 95% yield (Scheme
5e and 5f).
dimethyl-3,4-diphenylquinolin-2-amine
8
via
Rh-catalyzed
denitrogenative double C-H bond activation (Scheme 4e).15
We then turned our attention to shed light on mechanism of this
[3+1+1] cyclization reaction. Radical trapping experiments were
investigated firstly. When 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) and 2,6-di-tert-butyl-4-methylphenol (BHT) were served as
radical scavengers under the standard conditions, this [3+1+1]
cyclization reaction has no significant influence (Scheme 5a and 5b),
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L. Shao, J.-Y. Liao, Y. A. Ho and Y. Zhao, Angew. Chem. Int. Ed.,
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Chem. Int. Ed., 2019, 58, 1494.
Based on the above experimental results and previous literatures,
a possible reaction mechanism for the cyclization reaction of
ClCF2COONa is depicted in Scheme 6. Firstly, difluorocarbene is
formed via dechlorination and decarboxylation of ClCF2COONa. The
in-situ generated difluorocarbene is immediately captured by the
primary amine to afford an active difluoromethylamine A, with the
assistance of base, which rapidly undergoes the C-F cleavage and
the evulsion of protons to deliver the isocyanide B. Simultaneously,
isocyanoacetate 3 reacts with Cu(II) species and Under this basic
conditions to gives the formation of intermediate C, which further
goes through the cycloaddition of isocyanide B to render the Cu(II)
complex D. Finally, protonation of Cu(II) complex D furnishes the
desired product 4 and regenerates Cu(II) species for the next
catalytic cycle (Scheme 6 I). In Scheme 6 II, isocyanide B was
trapped HN3 formed in situ by TMSN3 5 reacts with water in the
solvent to comes up with the intermediate E, which subsequently
underwent cyclization to affords target product 6.
3
4
H2
1
N
R
5
6
M. Kim, W. B. Euler and W. Rosen, J. Org. Chem., 1997, 62,
3766;
R
N
F
F
F
A
a) R. W. Stephany, M. J. A. de Bie and W. Drenth, Org. Magn.
Reson., 1974, 6, 45; b) V. P. McCaffrey and M. D. E. Forbes, J.
Phys. Chem. A., 2005, 109, 4891; c) B. Kim, J. M. Beebe, Y.
Jun, X.-Y. Zhu and C. D. Frisbie, J. Am. Chem. Soc., 2006, 128,
4970; d) T. Iseki, K. Kawabata, H. Kawashima and H. Goto,
Polymer., 2014, 55, 66; e) L. Zhu, J. Zhang, H. Yang and C. Cui,
J. Am. Chem. Soc., 2019, 141, 19600.
a) Z. Hu, H. Yuan, Y. Men, Q. Liu, J. Zhang and X. Xu, Angew.
Chem. Int. Ed., 2016, 55, 7077; b) Y. Gao, Z. Hu. J. Dong, J. Liu
and X. Xu, Org. Lett., 2017, 19, 5292; c) H.-W. Liang, Z. Yang,
K. Jiang, Y. Ye and Y. Wei, Angew. Chem. Int. Ed., 2018, 57,
5720; d) D. Chen, Y. Shan, J. Li, J. You, X. Sun, X. Sun and G.
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H
Base
Base
Cl
F
R
N
GWE
COONa
F
N
B
2
HN3
E
CuII/L, Base
H2
O
CuII
C
Ⅰ
Ⅱ
7
TMSN3
GWE
NC
R
CuII
R
3
5
N
N
N
N
6
N
N
N
N
N
N
4
N
N
R
D
EWG
EWG
F
R
Scheme 6. Proposed Reaction Mechanism for the Synthesis of
Imidazole Derivatives
8
9
For recent cycloaddition of TMSN3, see; a) J. Xu and Q. Song,
Org. Chem. Front., 2017, 4, 938; b) X. Yu, J. Xu, Y. Zhou and Q.
Song, Org. Chem. Front., 2018, 5, 2463; c) Q. Xiong and S.
Dong, Y. Chen, X. Liu, X. Feng, Nature. Commun., 2019, 10,
2116.
a) V. P. Mehta and M. F. Greaney, Org. Lett., 2013, 15, 5036;
b) P. Zhang, W. Chen, M. Liu and H. Wu, Org. Lett., 2019, 21,
9326.
In conclusion, we have disclosed a novel [3+1+1] cyclization of
ClCF2COONa for the assembly of imidazoles and tetrazoles under
mild conditions. The desired products were achieved in decent
yields with a wide substrate scope of amines by using ClCF2COONa
as promising C1 synthon. In analogy of the reaction, the current
protocol proceeded via transformation of in-situ generated
isocyanides, which represents the first example for cycloaddition of
isocyanide in-situ. Further applications of this unique in-situ
generated isocyanides are underway in our laboratory.
This research was financially supported by the National Natural
Science Foundation (21772046) and the Natural Science Foundation
of Fujian Province (2016J01064) are gratefully acknowledged. We
also thank the Instrumental Analysis Center of Huaqiao University
for analysis support. Y. W. thanks the Subsidized Project for
Cultivating Postgraduates’ Innovative Ability in Scientifific Research
of Huaqiao University.
10 X. Ma, Y. Zhou and Q. Song, Org. Lett., 2018, 20, 4777.
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Chem., 2019, 17, 8071.
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Chem., 2019, 8, 694; b) X. Ma, J. Su, X. Zhang and Q. Song,
iScience., 2019, 19, 1; c) S. Deng, H. Chen, X. Ma, Y. Zhou, K.
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13 CCDC-1917599 (4e), CCDC-1917630 (4u) and CCDC-1937993
(6a) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
Notes and references
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4 | J. Name., 2012, 00, 1-3
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