Enantioselective copper-catalyzed remote c(sp3)-h alkynylation of linear primary sulfonamides

Article abstract of DOI:10.1021/acs.orglett.0c01325

The highly efficient copper-catalyzed enantioselective alkynylation of the remote C(sp³)-H bond on linear primary sulfonamides is presented here using a radical relay strategy. The chiral box-copper complex, which is used to recapture the in-situ-generated alkyl radical via a 1,5-HAT strategy, is the key to success, affording the chiral alkynes after a following reductive elimination. A general substrate scope, mild conditions, and excellent regio- and enantioselective control are demonstrated in this method.

Full text of DOI:10.1021/acs.orglett.0c01325

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Letter
Enantioselective Copper-Catalyzed Remote C(sp3)−H Alkynylation
of Linear Primary Sulfonamides
Cheng-Yu Wang,† Zi-Yang Qin,† Yu-Ling Huang, Yi-Ming Hou, Ruo-Xing Jin, Chao Li,
and Xi-Sheng Wang*
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ABSTRACT: The highly efficient copper-catalyzed enantioselective alkynylation of the remote C(sp3)−H bond on linear primary
sulfonamides is presented here using a radical relay strategy. The chiral box−copper complex, which is used to recapture the in-situ-
generated alkyl radical via a 1,5-HAT strategy, is the key to success, affording the chiral alkynes after a following reductive
elimination. A general substrate scope, mild conditions, and excellent regio- and enantioselective control are demonstrated in this
method.
enefitting from their electronic properties and various
methods for further transformations, alkynes have been
capture of the trifluoromethyl radical with styrenes was
B
involved (Scheme 1a).8 Very recently, the Liu group
found in multiple natural products, and they often serve as
special material synthons and are widely used as pivotal
intermediates for the total synthesis of complex biologically
active or functional molecules. Accordingly, chiral alkynes have
long attracted increasing attention as a vital building block in
therapeutics and biological molecules and a useful chiral
synthon in organic synthesis.1 Therefore, many efforts have
been dedicated to finding new methods for the concise and
efficient synthesis of various optically active alkynes over the
past several decades.2 Although the catalytic enantioselective
hydroalkynylation of alkene has been well established,3,4
methods for the direct enantioselective alkynylation of remote
C(sp3)−H bonds are still very rare and remain a major issue to
be solved. The first breakthrough was made by the Li group
with an enantioselective copper-catalyzed alkynylation, which
was limited only by its prerequisite that the later-functionalized
C(sp3)−H bonds must be positioned next to a nitrogen atom,
and the method achieved only moderate ee.5 Meanwhile, the
Shi group recently demonstrated an enantioselective alkynyla-
tion of methylene C(sp3)−H bonds under a Pd(II)-catalyzed
system.6 Despite such advances in this area, direct asymmetric
C(sp3)−H alkynylation is consistently a heated research area
that should be addressed.
Scheme 1. Radical-Involved Enantioselective Alkynylation
established a radical-involved asymmetric Sonogashira cross-
coupling reaction (Scheme 1b).9 However, although hydrogen-
atom abstraction via the radical pathway has long been
recognized as one of the most efficient methods to realize
various functionalization of C(sp3)−H bonds, the direct
enantioselective alkynylation of C(sp3)−H bonds through
selective hydrogen-atom abstraction is worth establishing.
Inspired by the well-established reaction pattern in 1,5-
Given the intrinsic high activity and instability of radicals,
the transition-metal-catalyzed asymmetric functionalization via
the radical pathway has already shown its significance while
being a huge challenge.7 It must be said that this radial-
involved enantioselective functionalization strategy has been
successfully utilized for asymmetric alkynylation very recently.
The Liu group described a copper-catalyzed enantioselective
alkynylation in which a benzylic radical generated by the
Received: April 16, 2020
https://dx.doi.org/10.1021/acs.orglett.0c01325
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
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Letter
hydrogen atom transfer (1,5-HAT),10−12 we reckoned that the
selective cleavage of the δ-C(sp3)−H bond on the aliphatic
chain leading to the generation of a remote carbon radical via
1,5-HAT could be recaptured by a chiral alkynyl copper
catalyst, which then furnished the desired optically pure
alkynes after the following enantioselective reductive elimi-
nation from the resulting chiral copper complex.
a
Table 1. Optimization of Conditions
Herein we present an enantioselective alkynylation of the
C(sp3)−H bond under copper catalysis using the 1,5-HAT
strategy with excellent enantioselectivity (up to 96% ee).
Besides high reactivity, a broad substrate scope, and mild
conditions, excellent regio- and enantioselective control have
been revealed in our newly established method. The radical
relay strategy presented here supplies an efficient solution to
the construction of chiral alkynes by the functionalization of
omnipresent inert C(sp3)−H bonds with high regio- and
enantioselective control.
b
c
entry
[Cu]
CuCN
solvent
L
yield (%)
ee (%)
d
1
2
3
4
5
6
7
8
PhCF3
DCM
DCE
L1
L1
L1
L1
L1
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L8
L9
L1
L1
L1
49 (20 )
46 (12 )
46 (11 )
41 (24 )
93
90
83
84
74
d
CuCN
CuCN
CuCN
CuCN
Cu(MeCN)4PF6
CuI
CuSCN
Cu(OAc)2
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
d
d
PhCl
d
MeCN
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
43 (22 )
trace
Considering that the Thorpe−Ingold effect could enable the
HAT process to minimize the entropy, the use of alkyl amides
with substituents on the alkyl chain normally serves as an
efficient strategy for remote C−H functionalization, whereas its
synthetic utility is evidently constrained due to the scope
limitation. Indeed, C(sp3)−H bonds on N-sulfonylated linear
primary amines are debatably the most difficult substrates in
the selective functionalization via 1,5-HAT.12d,13,14 To address
this challenge, we commenced our initial investigation with 1a
as the starting material, disilyl-substituted acetylene (2a) as the
alkynylating reagent, and a catalytic amount of CuCN (10 mol
%) in PhCF3 at 0 °C. To our great delight, the desired
alkynylation product 3a was obtained in 49% yield with 93% ee
when using chiral bis(oxazoline) ligand L1 (Table 1, entry 1).
Next, we carefully performed experiments to identify optimal
solvents and copper salts using L1 as the ligand (Table 1,
entries 2−9). Actually, the use of dichloromethane (DCM) as
the solvent or CuSCN as the copper source could afford 3a in
similar yields with slightly lower ee (Table 1, entries 2 and 8).
Guided by our previous research experience, determining the
best chiral ligand for each reaction is a very important factor in
the enantioselective reactions. Therefore, we tested a number
of chiral bis(oxazoline) ligands (Table 1, entries 10−17) and
found that compared with L1, all of the other ligands gave
lower yields and ee. To further improve the yield, we then
carefully analyzed this reaction system and found that a large
amount of the H-abstraction byproduct of nitrogen was hard to
suppress. It was conjectured that the rate of the enantiose-
lective alkynylation step, where the benzyl radicals were
trapped by the chiral copper complex to afford 3a, might be
slow and thus enabled the abstraction of the hydrogen atom of
the nitrogen-centered radical then stopped the following
remote functionalization. Therefore, we intended to slow
down the rate of the generation of the nitrogen-centered
radical and coordinated the trapping rate of the in-situ-
generated carbon radical by the copper complex and thus
improve the yields. Accordingly, the reduction of the reaction
temperature to −10 °C slightly improved the yield to 58%
(Table 1, entry 18). Considering that oxygen might be
detrimental to the yields and ee, the yield was remarkably
increased to 81% with slightly higher ee (94%) when degassed
PhCF3 was used as the solvent in a lower concentration (Table
1, entries 19 and 20).
d
68 (19 )
58 (23 )
41 (25 )
84
90
82
31
72
77
53
57
69
82
79
93
94
94
d
d
9
10
11
12
13
14
15
16
17
18
19
20
34
32
23
41
36
35
35
43
e
d
58 (24 )
72 (23 )
81 (19 )
e f
d
,
e fg
d
, ,
a
Reaction conditions: 1a (0.1 mmol, 1.0 equiv), 2a (2.0 equiv), [Cu]
(10 mol %), L (12 mol %), PhCF3 (2.0 mL), 0 °C, Ar. Isolated
yields. ee values were determined by HPLC analysis on a chiral
b
c
d
e
stationary phase. NMR yields for H-abstraction side products. −10
f
g
°C. Degassed PhCF3. PhCF3 (3.0 mL).
number of N-fluorosulfonamides installed with various types of
substituted benzenesulfonyl protecting groups (ArSO2) were
first examined. Various substrates with a para-substituted (R1)
functional group, such as Me (1b), MeO (1c), Cl (1d), and
CF3 (1e), were all greatly tolerated, and the desired alkynes 3
could be afforded in good to excellent yield along with
excellent ee. Furthermore, we studied the substituent effect
(R2) of the aromatic ring that was linked to the aliphatic chain.
To our satisfaction, both electron-donating groups, such as Me
(1f, 1n), nC5H11 (1g), and OMe (1g), and electron-
withdrawing groups like Cl (1j, 1o), Br (1k), and CF3 (1l,
1p), were also well tolerated under our copper-catalyzed
system, giving a good yield of desired products 3 with excellent
ee. Notably, Br (1k) as well as Cl (1j, 1o) on the aromatic ring
provided a solution for further derivatizations of these chiral
alkynes via different kinds of transition-metal-catalyzed cross-
coupling reactions. Moreover, ortho-F (1q) substrate gave a
moderate yield (30%) and satisfactory enantioselectivity (76%
ee). However, when bulkier substituents like −Me or −CF3
were introduced at ortho position, such transformations failed
to perform with good reactivity. Furthermore, a heteroaromatic
ring (1r) linked to the alkyl chain was also well tolerant, giving
the product of 2r with high ee in moderate yield. At last, to
inspect the structural variations in the alkynylating reagents 2,
some other alkynylating reagents loading with aryl and alkyl
groups at the terminal position (2b, 2c) were also studied and
After completing the optimization of reaction conditions, we
set out to test the functional group compatibility of this
catalytic asymmetric alkynylation. As shown in Scheme 2, a
B
https://dx.doi.org/10.1021/acs.orglett.0c01325
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pubs.acs.org/OrgLett
Letter
a b c
, ,
potential for the further construction of biologically active
chiral molecules using the Sonogashira cross-coupling strategy.
To gain some insight into the enantioselective alkynation
system, a series of mechanistic studies were also performed.
The 5-exo cyclization product 6 was afforded in 43% yield
when adding alkene 5 into the reaction; this experiment
confirmed that a nitrogen-centered radical was produced by
copper catalysis (Scheme 4a). Moreover, in the radical clock
Scheme 2. Substrate Scope
Scheme 4. Mechanistic Study
experiment, we obtained the ring-opening product 8 in 39%
yield with 7, and this suggested that, initiated by a N-radical, an
in-situ-generated carbon-centered radical via 1,5-HAT was
involved in this catalytic cycle (Scheme 4b).
On the basis of the above results and previous reports,10−12
a radical relay pathway under a Cu(I)/Cu(II)-catalyzed
catalytic cycle is proposed. (For more details, see the
Supporting Information.) Initiating from the L*Cu(I) catalyst,
a single electron transfer (SET) between the Cu(I) species and
N-fluorosulfonamide 1 affords a higher valency chiral copper
complex and a nitrogen-centered radical A. Futhermore, A
undergoes an intramolecular hydrogen atom transfer and
furnishes an in-situ-generated carbon radical B; meanwhile, the
L*Cu(II)F complex generates an L*Cu(II)-alkynyl species
with 2. The final enantioselective trapping of B with the
L*Cu(II)−alkynyl species, which is utterly crucial for
constructing the propargylic stereocenter, gives the chiral δ-
alkynylated sulfonamides 3 and regenerates the L*Cu(I)
catalyst to enter the next catalytic cycle.
In conclusion, we have established an enantioselective
alkynylation of remote C(sp3)−H bonds in linear primary
sulfonamides under copper catalysis. Excellent regio- and
enantioselective control, mild conditions, and a general
substrate scope are demonstrated in our system. This radical
relay strategy has offered an efficient solution to remote
enantioselective alkynylation producing δ-alkynated amines
and their pharmaceutical derivatives. Further investigations on
novel radial-involved enantioselective remote functionalization
via 1,5-HAT are still in progress in our laboratory.
a
Reaction conditions: 1 (0.2 mmol, 1.0 equiv), 2 (2.0 equiv), CuCN
b
(10 mol %), L1 (12 mol %), PhCF3 (6.0 mL), −10 °C, Ar. Isolated
yields. ee values were determined by HPLC analysis on a chiral
stationary phase. Reactions carried out on a 1 mmol scale.
c
d
exhibited good reactivity, furnishing the corresponding
products (3s, 3t, 3u, 3v) in excellent yield with excellent ee
(88−94%). A millimole-scale experiment was carried out as
well with no decrease in yield or enantioselectivity (84% yield,
94% ee).
Next, we performed the derivatization study and successfully
obtained the desired transformation product. Excitingly, the
treatment of 3a with ammonium fluoride successfully removed
the trimethylsilyl (TMS) group and generated the terminal
alkyne 4 in 82% yield without any decline of ee value (Scheme
3). This result showed that our method had the synthetic
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01325.
Experimental procedure and characterization of all new
compounds (PDF)
Scheme 3. Further Transformation
AUTHOR INFORMATION
Corresponding Author
■
Xi-Sheng Wang − Hefei National Laboratory for Physical
Sciences at the Microscale and Department of Chemistry, Center
for Excellence in Molecular Synthesis of CAS, University of
Science and Technology of China, Hefei, Anhui 230026, China;
C
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Organic Letters
orcid.org/0000-0003-2398-5669; Email: xswang77@
pubs.acs.org/OrgLett
Letter
Nervig, C. S.; DeLuca, R. J.; Sigman, M. S. Angew. Chem., Int. Ed.
2017, 56, 6651. (h) Koradin, C.; Polborn, K.; Knochel, P. Angew.
Chem., Int. Ed. 2002, 41, 2535.
ustc.edu.cn
(4) For selected examples of the asymmetric hydroalkynylation of
electron-deficient alkenes, see: (a) Zhi, Y.; Huang, J.; Liu, N.; Lu, T.;
Dou, X. Org. Lett. 2017, 19, 2378. (b) Dou, X.; Huang, Y.; Hayashi, T.
Angew. Chem., Int. Ed. 2016, 55, 1133. (c) Blay, G.; Cardona, L.;
Pedro, J. R.; Sanz-Marco, A. Chem. - Eur. J. 2012, 18, 12966.
(d) Yazaki, R.; Kumagai, N.; Shibasaki, M. J. Am. Chem. Soc. 2010,
132, 10275. (e) Fillion, E.; Zorzitto, A. K. J. Am. Chem. Soc. 2009,
131, 14608. (f) Nishimura, T.; Sawano, T.; Hayashi, T. Angew. Chem.,
Int. Ed. 2009, 48, 8057. (g) Nishimura, T.; Guo, X.-X.; Uchiyama, N.;
Katoh, T.; Hayashi, T. J. Am. Chem. Soc. 2008, 130, 1576.
(h) Knoepfel, T. F.; Zarotti, P.; Ichikawa, T.; Carreira, E. M. J. Am.
Chem. Soc. 2005, 127, 9682. (i) Kwak, Y. S.; Corey, E. Org. Lett. 2004,
6, 3385.
Authors
Cheng-Yu Wang − Hefei National Laboratory for Physical
Sciences at the Microscale and Department of Chemistry, Center
for Excellence in Molecular Synthesis of CAS, University of
Science and Technology of China, Hefei, Anhui 230026, China
Zi-Yang Qin − Hefei National Laboratory for Physical Sciences
at the Microscale and Department of Chemistry, Center for
Excellence in Molecular Synthesis of CAS, University of Science
and Technology of China, Hefei, Anhui 230026, China
Yu-Ling Huang − Hefei National Laboratory for Physical
Sciences at the Microscale and Department of Chemistry,
Center for Excellence in Molecular Synthesis of CAS, University
of Science and Technology of China, Hefei, Anhui 230026,
China
(5) Li, Z.; Li, C.-J. Org. Lett. 2004, 6, 4997.
(6) Han, Y.-Q.; Ding, Y.; Zhou, T.; Yan, S.-Y.; Song, H.; Shi, B.-F. J.
Am. Chem. Soc. 2019, 141, 4558.
Yi-Ming Hou − Hefei National Laboratory for Physical Sciences
at the Microscale and Department of Chemistry, Center for
Excellence in Molecular Synthesis of CAS, University of Science
and Technology of China, Hefei, Anhui 230026, China
Ruo-Xing Jin − Hefei National Laboratory for Physical Sciences
at the Microscale and Department of Chemistry, Center for
Excellence in Molecular Synthesis of CAS, University of Science
and Technology of China, Hefei, Anhui 230026, China
Chao Li − Hefei National Laboratory for Physical Sciences at the
Microscale and Department of Chemistry, Center for Excellence
in Molecular Synthesis of CAS, University of Science and
Technology of China, Hefei, Anhui 230026, China
(7) For selected reviews, see: (a) Wang, F.; Chen, P.; Liu, G. Acc.
Chem. Res. 2018, 51, 2036. (b) Wang, K.; Kong, W. Chin. J. Chem.
2018, 36, 247. (c) Lu, Q.; Glorius, F. Angew. Chem., Int. Ed. 2017, 56,
49. (d) Sibi, M. P.; Manyem, S.; Zimmerman, J. Chem. Rev. 2003, 103,
3263.
(8) Fu, L.; Zhou, S.; Wan, X.; Chen, P.; Liu, G. J. Am. Chem. Soc.
2018, 140, 10965.
(9) Dong, X.-Y.; Zhang, Y.-F.; Ma, C.-L.; Gu, Q.-S.; Wang, F.-L.; Li,
Z.-L.; Jiang, S.-P.; Liu, X.-Y. Nat. Chem. 2019, 11, 1158.
(10) For selected reviews of the 1,5-HAT strategy, see: (a) Chu, J.
C. K.; Rovis, T. Angew. Chem., Int. Ed. 2018, 57, 62. (b) Stateman, L.
M.; Nakafuku, K. M.; Nagib, D. A. Synthesis 2018, 50, 1569.
(c) Chiba, S.; Chen, H. Org. Biomol. Chem. 2014, 12, 4051.
̌
̌
́
(d) Cekovic, Z. Tetrahedron 2003, 59, 8073. (e) Robertson, J.; Pillai,
J.; Lush, R. K. Chem. Soc. Rev. 2001, 30, 94.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01325
(11) For the recent development of the 1,5-HAT strategy initiated
by the N-centered radical, see: (a) Bafaluy, D.; Mun
Funes-Ardoiz, I.; Herold, S.; de Aguirre, A. J.; Zhang, H.; Maseras, F.;
̃
oz-Molina, J. M.;
Author Contributions
†C.-Y.W. and Z.-Y.Q. contributed equally.
́
Belderrain, T. R.; Perez, P. J.; Muniz, K. Angew. Chem., Int. Ed. 2019,
̃
58, 8912. (b) Na, C. G.; Alexanian, E. J. Angew. Chem., Int. Ed. 2018,
57, 13106. (c) Xia, Y.; Wang, L.; Studer, A. Angew. Chem., Int. Ed.
2018, 57, 12940. (d) Chen, D.; Chu, J. C. K.; Rovis, T. J. Am. Chem.
Soc. 2017, 139, 14897. (e) Wang, R.; Jin, R.-X.; Qin, Z.-Y.; Bian, K.-J.;
Wang, X.-S. Chem. Commun. 2017, 53, 12229. (f) Wang, R.; Li, Y.;
Jin, R.-X.; Wang, X.-S. Chem. Sci. 2017, 8, 3838. (g) Chu, J. C. K.;
Rovis, T. Nature 2016, 539, 272. (h) Choi, G. J.; Zhu, Q.; Miller, D.
C.; Gu, C. J.; Knowles, R. R. Nature 2016, 539, 268. (i) Wappes, E.
A.; Fosu, S. C.; Chopko, T. C.; Nagib, D. A. Angew. Chem., Int. Ed.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Basic Research
Program of China (973 Program 2015CB856600) and the
National Science Foundation of China (21971228, 21772187,
21522208) for financial support.
2016, 55, 9974. (j) Martínez, C.; Mun
2015, 54, 8287.
̃
iz, K. Angew. Chem., Int. Ed.
(12) For recent examples of metal-catalyzed cross-coupling-involved
1,5-HAT process, see: (a) Wang, C.-Y.; Qin, Z.-Y.; Huang, Y.-L.; Jin,
R.-X.; Lan, Q.; Wang, X.-S. iScience 2019, 21, 490. (b) Zhang, Z.;
Stateman, L. M.; Nagib, D. A. Chem. Sci. 2019, 10, 1207. (c) Liu, Z.;
Xiao, H.; Zhang, B.; Shen, H.; Zhu, L.; Li, C. Angew. Chem., Int. Ed.
2019, 58, 2510. (d) Bao, X.; Wang, Q.; Zhu, J. Angew. Chem., Int. Ed.
2019, 58, 2139. (e) Li, Z.; Wang, Q.; Zhu, J. Angew. Chem., Int. Ed.
2018, 57, 13288. (f) Groendyke, B. J.; AbuSalim, D. I.; Cook, S. P. J.
Am. Chem. Soc. 2016, 138, 12771. (g) Cheng, Z.-M.; Chen, P.-H.; Liu,
G.-S. Huaxue Xuebao 2019, 77, 856.
REFERENCES
■
(1) (a) Modern Alkyne Chemistry; Trost, B. M., Li, C.-J., Eds.; Wiley-
VCH: New York, 2014. (b) von Franco
̧
is Diederich, H.; Stang, P. J.;
Tykwinski, R. R. Acetylene Chemistry: Chemistry, Biology, and Material
Science; Wiley-VCH: Weinheim, Germany, 2005. (c) Modern Acetylene
Chemistry; Stang, P. J., Diederich, F., Eds.; Wiley-VCH: Weinheim,
Germany, 1995.
(2) For a recent review on the catalytic enantioselective hydro-
alkynylation of alkenes, see: Wang, Z.-X.; Bai, X.-Y.; Li, B.-J. Synlett
2017, 28, 509.
(13) Mayer, J. M. Acc. Chem. Res. 2011, 44, 36.
(3) For the catalytic enantioselective hydroalkynylation of alkenes
using transition-metal catalysts, see: (a) Bai, X.-Y.; Zhang, W.-W.; Li,
Q.; Li, B.-J. J. Am. Chem. Soc. 2018, 140, 506. (b) Bai, X.-Y.; Wang, Z.-
X.; Li, B.-J. Angew. Chem., Int. Ed. 2016, 55, 9007. (c) Fan, B.; Xu, J.;
Yang, Q.; Li, S.; Chen, H.; Liu, S.; Yu, L.; Zhou, Y.; Wang, L. Org.
Lett. 2013, 15, 5956. (d) Sawano, T.; Ou, K. Y.; Nishimura, T.;
Hayashi, T. Chem. Commun. 2012, 48, 6106. (e) Fan, B.-M.; Yang, Q.-
J.; Hu, J.; Fan, C.-L.; Li, S.-F.; Yu, L.; Huang, C.; Tsang, W. W.;
Kwong, F. Y. Angew. Chem., Int. Ed. 2012, 51, 7821. (f) Shirakura, M.;
Suginome, M. Angew. Chem., Int. Ed. 2010, 49, 3827. (g) Chen, Z.-M.;
(14) During the preparation of this manuscript, an enantioselective
copper-catalyzed alkynylation of C−H bonds was published, but none
of the linear primary sulfonamides were compatible with that method.
For details, see: Zhang, Z.-H.; Dong, X.-Y.; Du, X.-Y.; Gu, Q.-S.; Li,
Z.-L.; Liu, X.-Y. Nat. Commun. 2019, 10, 5689.
D
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