Sustainable access to sulfonic acids from halides and thiourea dioxide with air

Article abstract of DOI:10.1039/d0gc03135f

A sustainable and mild one-step strategy is explored for the synthesis of aryl and alkyl sulfonic acids using a facile combination of halides and sulfur dioxide surrogates under air. The cheap industrial material thiourea dioxide was employed as an eco-friendly and easy-handling sulfur dioxide surrogate, while air was used as a green oxidant. Both aryl and alkyl sulfonic acids were obtained under transition metal-catalyzed or transition metal-free conditions. Mechanistic studies demonstrated that sulfinate was involved as an intermediate in this transformation. Notably, this protocol has been applied to the late-stage sulfonation of the drugs naproxen, isoxepac and ibuprofen.

Full text of DOI:10.1039/d0gc03135f

View Article Online
View Journal
Green
Chemistry
Cutting-edge research for a greener sustainable future
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Zhang, M.
Wang and X. Jiang, Green Chem., 2020, DOI: 10.1039/D0GC03135F.
Volume 20
This is an Accepted Manuscript, which has been through the
Number
May 2018
Pages 1919-2160
9
7
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
rsc.li/greenchem
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1463-9262
PAPER
Paul T. Anastas et al.
The Green ChemisTREE: 20 years after taking root with the 12
principles
rsc.li/greenchem

Please do not adjust margins
Page 1 of 5
Green Chemistry
View Article Online
DOI: 10.1039/D0GC03135F
COMMUNICATION
Sustainable Access to Sulfonic Acids from Halides and Thiourea
Dioxide with Air
Hui Zhang,a Ming Wang *a and Xuefeng Jiang *a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
(A) Pharmaceuticals and bioactive natural products
A sustainable and mild one-step strategy is explored for the
synthesis of aryl and alkyl sulfonic acids with facile combination of
halides and sulfur dioxide surrogates under air conditions. The
cheap industrial material thiourea dioxide was employed as an
eco-friendly and easy-handling sulfur dioxide surrogate,
meanwhile air was used as a green oxidant. Both aryl and alkyl
sulfonic acids were obtained under transition metal-catalyzed or
Me
Me
Me
O
Na+
O
O
O
S
O
Me
S
Na
O
Me
Me
O
O
Na
S
Me
HO
Me
Me
O
O
Me
O
Me
Me
Sodium Azulene Sulfonate
Sodium Paeonol Sulfonate
Sodium Dibunate
antiulcer drug
analgesic drug
antitussive drug
transition
metal-free
conditions.
Mechanistic
studies
O
O
O
OH
Me
Me
O
O
demonstrated that sulfinate was involved as intermediates in this
transformation. Notably, this protocol has been applied to the
late-stage sulfonation of drugs naproxen, isoxepac and ibuprofen.
S
N
H
N
S
S
O
N
Me
OH
N
Br
N
N
H
N
Na+
O
O
HN
O
O
S
O
N
O
HO
Sulbenicillin
antimicrobial agents
O
H
O
Sulfonic acid is an indispensable motif in pharmaceuticals1,
natural products2 and fine chemicals.3 For example, diverse
sulfonic acids served in antipyretic analgesics, antiulcer drug,
antimicrobial agents, hemostatic and antiatherosclerotic
Metamizole Sodium Tablets
Callyspongisine B
antipyretic analgesics
natural product
(B) Previous method
H
H2O2, Br2
RSH or RS-SR
con. H2SO4
R'
drugs.4-8
Sulfonic
acid-containing
natural
product
R = aryl
R = alkyl
Callyspongisine B was isolated from an Australian marine
sponge, Callyspongia sp.2a Furthermore, sulfonic acid is an
important starting material for the preparation of sulfonyl
chloride in organic synthesis.9 Generally, alkylsulfonic acids are
prepared by the oxidation of thiols with bromine in the
presence of hydrogen peroxide combined with acetic acid.10
Sulfonation of aromatic compounds is a frequently used
synthetic method for the synthesis aryl sulfonic acids, in which
concentrated sulfuric acid is employed and the regio-
byproducts are inevitable.11 In 2001, Ishii developed a novel
approach for alkyl sulfonic acids by SO2/O2 under the
assistance of VO(acac)2.12 Recently, Cornella et al explored the
transformation of primary sulphonamides to aryl sulfonic acids
via a sulfonyl chloride intermediate.13 Although these elegant
works have been achieved, it is still desiderating to develop
green and mild methods for the construction of sulfonic acid.
O
S
O
R
OH
VO(acac)2
OH
O O
+
H
SO2/O2
+
R
S
R = aryl
R = alkyl
Ar
NH2
BF4
O
(1 atm)
(C) Our stragegy
mask group
Pd catalyst
Aryl SO3H
R = aryl
HN
O
air
R
X
+
S
transition-metal-free
H2N
OH
Alkyl SO3H
R = alkyl
readily available material
O
O
air (O2)
O
S
S
R
O
Eox = 0.6 V vs SCE
Scheme 1. The significance and synthesis of sulfonic acid.
To the best of our knowledge, there is still no general method
for both aryl and alkyl sulfonic acid construction with sensitive
functional group under mild conditions. In the past years, the
strategy of parallel-oxidative-state introduction of hypervalent
sulfur has been well developed.14 Thiourea dioxide, which is a
bleaching and decolorizing agent used in printing and
papermaking industry, enable to generate sulfur dioxide anion
serving as a sulfur dioxide source under base conditions.15,16c
a. Shanghai Key Laboratory of Green Chemistry and Chemical Process,
School of Chemistry and Molecular Engineering, East China Normal University, 3663
North Zhongshan Road, Shanghai 200062, P. R. China.
b State Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin
300071, P. R. China
E-mail: xfjiang@chem.ecnu.edu.cn; wangming@chem.ecnu.edu.cn
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 5
COMMUNICATION
Journal Name
Table 1 Conditions optimizationa
the yield of the desired sulfonic acid 2a had no apparent
View Article Online
O
O
decline (Table 1, entry 8). However, noDsOuIl:f1o0n.1i0c3a9/cDid0GpCr0o3d1u35cFt
was detected in the absence of PdCl2(dppf) catalyst even with
the addition of TBAB (Table 1, entry 9). The desired sulfonic
acid product can be obtained in an excellent yield even in the
absence of phase transfer catalyst TBAB (Table 1, entry 10). It
was found that the addition of water can not affect the
transformation in non-drying reaction system (Table 1, entry
11). The efficiency of the transformation was not further
improved in the pure oxygen atmosphere (Table 1, entry 12).
With the optimal conditions in hand, the reaction scope was
explored for this sulfonation reaction, which afforded a
functionalized sulfonic acid library (Scheme 2). A broad range
of aryl iodides with electron-neutral, -rich (2a-2d) groups were
well tolerated in this transformation and provided the desired
products with high efficiency. Gram-scale operation of 4-
iodotoluene could afford the desired product 2a in a moderate
yield by recrystallization. It should be noted that thiomethyl
was compatible in the current reaction, which was not found
the corresponding oxidized sulfone (2d). Subsequently, various
aryl iodides with electron-deficient (2e-2i) groups, including
fluoro (2f) were well tolerated in this sulfonation reaction.
Notably, the substrates containing sensitive but transformable
functional groups, such as bromine (2h) and carboxyl (2i),
generated the corresponding products in good yields.
Substituents, including ester and cyano groups at the meta and
even ortho positions of the aromatic ring of the aryl iodides
were compatible. Aryl iodides with fused ring systems were
converted to the desired sulfonic acids in good yields (2m-2p).
The structure of 2m was further confirmed via X-ray diffraction
analysis.17 This reaction was quite efficient for
heteroaryliodide, namely, thiophene-derived substrate (2q).
Compounds 2r and 2s were afforded in excellent yields when
piperonyl and polysubstituted substrates were employed in
the current transformation. Besides aryl iodide substrates, the
bromostyrene was proven to be applicable in this
transformation as well, affording the alkenyl sulfonic acid
product 2t in a moderate yield. The sulfonation of
functionalized molecules worked smoothly under the standard
conditions, and the desired product 2v and 2w were obtained
in excellent yields. Furthermore, this sulfonation reaction can
be successfully applied to nonsteroidal anti-inflammatory drug
naproxen-derived aryl iodide (2x).
Catalyst (x mol %)
Cs2CO3 (2 equiv)
I
S
OH
+
SO source
"
2
"
DMSO, 100 oC, air
Me
Me
1a
2a
Yield[a]
Entry
Catalyat (x mol % )
PTC
"SO2" source
TBAB
TBAB
TBAB
"SO2"[b]
"SO2"[b]
"SO2"[b]
NR
NR
1
2
Fe(acac)3 (10 mol %)
CuCl2 (10 mol %)
3
4
NR
NiCl·DME (10 mol %)
(
PdCl2 dppf) (10 mol %)
NR
TBAB
TBAB
Na2S2O5
Na2S2O4
(
PdCl2 dppf) (10 mol %)
5
6
7
8
9
46%
(
PdCl2 dppf) (10 mol %)
TBAB
CH4N2O2S
CH4N2O2S
CH4N2O2S
CH4N2O2S
CH4N2O2S
CH4N2O2S
CH4N2O2S
>95%
67-88%[c]
>95%
(
PdCl2 dppf) (10 mol %)
TBAB
(
PdCl2 dppf) (2.5 mol %)
TBAB
-
TBAB
NR
PdCl2(dppf) (2.5 mol %)
PdCl2(dppf) (2.5 mol %)
87%
10
11
12
-
-
-
85%[d]
86%[e]
PdCl2(dppf) (2.5 mol %)
[a] Standard conditions: 1a (0.1 mmol), sulflur source (0.3 mmol), base (0.2
mmol), PTC (0.15 mmol), DMSO (1 mL), 14 h, yield is determined by LC-MS using
4-chlorobenzenesulfonic acid as an internal standard. [b] “SO2” = CH4N2O2S,
Na2S2O5 and Na2S2O4. [c] DIPEA, DBU, NaHCO3 or K3PO4 takes place of Cs2CO3. [d]
H2O (10 equiv) was added. [e] Under O2 atmosphere. PTC = phase transfer
catalyst.
We envisioned that the nucleophilic property of sulfur dioxide
radical anion accords with the general construction of both
aryl and alkyl sulfinates respectively, followed by a compatible
oxidation with matched oxidation potential (E = 0.6 V vs SCE)
(Scheme 1C). Based on the transformation from inorganic
sulfur to organic sulfides in our group,16 herein, we employed
the abundant industrial material thiourea dioxide as the
hypervalent sulfur source to achieve the synthesis of organic
sulfonic acids under air condition.
We commenced the sulfonation reaction with 4-
methyliodobenzene 1a and sulfur dioxide source in the
existence of base under air condition. To increase the solubility
of sulfur dioxide salts, a stoichiometric amount of phase
transfer catalyst tetrabuylammonium bromide (TBAB) was
added. Different iron, copper and nickel catalysts were tested
employing different sulfur dioxide sources. However, the
desired sulfonic acid 2a was not detected (Table 1, entries 1-3).
When sodium metabisulfite was used as the sulfur dioxide
source, the desired product was not available under the
assistant of PdCl2(dppf) catalyst either (Table 1, entry 4).
Delightfully, sulfonic acid 2a was obtained in 46% yield when
sodium dithionite was employed as sulfur dioxide source
(Table 1, entry 5). Further evaluation of hypervanlent sulfur
salts revealed that thiourea dioxide furnished the best yield of
95% (Table 1, entry 6). Various bases were further investigated
for their assisted ability of releasing sulfur dioxide anion from
thiourea dioxide, in which caesium carbonate was found to be
the best results (Table 1, entry 7). When the equivalent of
PdCl2(dppf) catalyst was decreased from 10 mol% to 2.5 mol%,
Encouraged by the above results, this protocol was further
applied in the preparation of alkyl sulfonic acids (Scheme 2).
Excitingly, the sulfonation reaction of alkyl bromide substrates
can be achieved under a transition-metal-free condition to
provide the corresponding alkyl sulfonic acid products
efficiently. KI was added to activate alkyl bromide via a
bromine-iodide exchange process. Diverse chain length alkyl
bromides were well tolerated in the sulfonation reaction under
standard conditions, delivering the desired alkyl sulfonic acid
products 3a-3b. Anti-inflammatory drug isoxepac and ibuprofen-
derived alkyl bromides were successfully compatible (3c-3d).
Gram-scale operation of ibuprofen-derived alkyl bromide could
afford the desired product 3d in a moderate yield.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 3 of 5
Green Chemistry
COMMUNICATION
Journal Name
View Article Online
DOI: 10.1039/D0GC03135F
O
OH
NH
O O
S
S
standard conditions
+
R
X
R
OH
H2N
1
O O
O O
S
O O
S
O O
S
O O
S
O O
S
S
OH
OH
OH
OH
OH
OH
EtO2C
R
MeS
F
Cl
Br
2d
2e
2f
2g
2h
75%
53%
60%
41%
74%
2a
R = Me 78%
gram-scale
2b
2c
recrystallization
: 61%, 1.05 g (
R = OMe, 71%
R = H, 86%
O O
)
O O
S
O O
S
O O
S
O O
S
OH
S
OH
OH
OH
OH
CO2Me
HOOC
iPr
66%
CN
2l
2m
X-ray (
)
2i
2j
2k
2m
81%
67%
62 %
83%
CCDC: 2017488
O O
S
OH
S
Me
O
O
O O
S
O
S
O
O
OH
O
O
O
OH
OH
S
OH
OH
Me
S
S
O O
2q
2r
82%
77%
2n
2o
2p
2s
65%
72%
71%
64%
Cl
S
O O
O O
S
O
S
O O
Me
O
OH
OH
O
O
S
S
OH
O
Me
N
N
O
H
H
Me
(from naproxen)
OH
Me
O
(from alkenyl bromide)
2t
2u
83%
2v
2w
56%
57%
52%
O
O
Me
O O
S
S
O
OH
OH
OH
Me
OH
S
S
O O
O O
Me
O
(from Ibuprofen)
gram-scale
: 52%, 1.25 g)
(from isoxepac)
3c
3d
3a
3b
61% (
57%
43%
53%
Scheme 2. General synthesis of sulfonic acidsa a R = aryl iodides: 1 (0.5 mmol), CH4N2O2S (1.5 mmol), PdCl2(dppf) (0.0125 mmol), Cs2CO3 (1.0 mmol); R =
alkyl bromides: 1 (0.5 mmol), CH4N2O2S (1.5 mmol), Cs2CO3 (1.0 mmol), KI (1.0 mmol). DMSO (5 mL), 100 oC, under air, 14 h, isolated yields.
In order to investigate the source of oxygen in sulfonic acid, 18O-
labeling experiment was conducted. When the reaction was
conducted under 18O atmosphere, the single 18O-labeling
(Scheme 5-4). Control experiments with active oxygen species
inhibitors, such as singlet oxygen (1O2) inhibitors (NaN3 and
Co(acac)3), and hydroxyl radical (•OH) inhibitors, indicated that
neither singlet oxygen (1O2) nor hydroxyl radicals (•OH) were
crucial species (Scheme 5-5). UV-Vis absorption of I3-
demonstrated that hydrogen peroxide was not generated in
the system (Scheme 5-6). Thus, a postulated reaction pathway
is displayed in Scheme 5-7. Initially, the sulfur dioxide anion 6
was formed from thiourea dioxide in the presence of caesium
carbonate and water (non-drying reaction system). An oxygen
exchange happened between 6 and water, which was proved
in the control experiments. Oxidation addition of Pd0 catalyst
with aryl iodide generated palladium species 7. The ligand
exchange between intermediates 7 and 6 afforded
sulfonic acid product was afforded, which indicated that
sulfinate was oxidized to sulfonic acid by oxygen (Scheme 5-1).
Interestingly, the entire 18O-labeling sulfinic acid product was
also furnished when H218O was added and the reaction was
conducted under O2 atmosphere (Scheme 5-2). However, no
18O-labeling sulfonic acid product was obtained when sodium
benzenesulfinate was conducted under the conditions of H218O
and air (Scheme 5-3). These results indicated that water was
involved in the exchange with thiourea dioxide to release sulfur
dioxide source. Ring-opened product 5 was obtained in 10%
yield, which provided strong evidences for an alkyl radical
intermediate being involved in the alkyl sulfonic acid formation
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 5
COMMUNICATION
Journal Name
O
O
O
O
halogen radical was generated first. Sulfur dioxide anion 6
DOI: 10.1039/D0GC03135F
underwent a single electron oxidation by halogen radical to
(1)
Me
I
PdCl2dppf
Cs2CO3, DMSO
O
OH
NH
View Article Online
S
S
S
18OH
+
OH
+
100 oC, 18O2
14 h
Me
H2N
Me
form sulfur dioxide radical anion 10. Meanwhile, alkyl radical
was trapped with sulfur dioxide radical anion providing
sulfinate intermediate 11. Then, sulfinate intermediate 11 was
oxidized to radical intermediate 12,18 which is equilibrium with
intermediate 13. Intermediate 13 was trapped by oxygen to
generate bis(sulfonyl) peroxide intermediate 14,19 which was
reduced by sulfinate to furnished intermediate 15. Finally, the
desired product was formed by acidification.
28%
51%
(2)
Ar
PdCl2dppf
Cs2CO3, DMSO
100 oC, N2
18O
S
O
OH
O
S
O
S
S
+
+
I
+
Ar
Ar
18OH
18OH
Ar
OH
H2N
NH
H218O (10 equiv)
m/z=158
m/z=160
m/z=156
19%
2 h
Ar = 4-Me-C6H4
40%
30%
O
O
O
S
(3)
H218O(10 equiv)
S
OH
ONa
DMSO, air, 100 o
14 h
C
Me
Me
2a
75%
Conclusions
O
OH
NH
(4)
(5)
Br
OH
O
KI, Cs2CO3
S
S
+
DMSO, air, 100 o
14 h
C
O
O
In summary, a protocol to access both aryl and alkyl sulfonic
acids was established via the coupling of halides and thiourea
dioxide under air conditions. The abundant industrial material
thiourea dioxide was used as the hypervalent sulfur source,
and air was employed as the green and mild oxidant. Aryl
sulfonic acids were furnished in low catalyst loading conditions,
and alkyl sulfonic acids could be achieved in a transition-metal-
free condition. Furthermore, the late-stage direct sulfonation
of pharmaceuticals naproxen, isoxepac and ibuprofen were
achieved efficiently through the current transformation.
Mechanistic studies further demonstrated that two kinds of
sulfur dioxide intermediates were involved in the current
reaction to achieve the construction of aryl and alkyl sulfonic
acids respectively. Further hypervalent sulfur molecules
syntheses and corresponding drug discovery are in progress in
our laboratory.
H2N
4
5 10%
O
S
O
Additives (x equiv)
DMSO, 100 °C, air
S
OH
ONa
Me
Me
Entry
Additives (x equiv)
Yields
Funcations
1
2
3
4
-
-
84%
71%
89%
72%
1O2 inhibitor
1O2 inhibitor
NaN3 (1 equiv)
Co(acac)2 (0.06 equiv)
tBuOH (1 equiv)
HO inhibitor
O
O
O
(6)
DMSO, 100 °C
air, 14 h
S
S
OH
ONa
Me
in-situ generated H2O2: 2.77 x 10-4 mmol
Me
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors are grateful for financial support provided by the
National Key Research and Development Program of China
(2017YFD0200500), NSFC (21971065, 21722202, 21672069
and 21871089 for M.W.), STCSM (20XD1421500, 20JC1416800,
18JC1415600), Innovative Research Team of High-Level Local
Universities in Shanghai (SSMU-ZLCX20180501), and Professor
of Special Appointment (Eastern Scholar) at Shanghai
Institutions of Higher Learning.
R
(9)
(R = alkyl)
(7) proposed mechanism
(1)
X
R
+
X
X
H2O
O
H2O
O
HO
O
HO
HO
O
O
S
6
S
6
S
6
S
H2O
base
10
urea
R
(9)
HN
O
R
O
S
O
O
LnPd
S
S
13
X
R
R
O
H2N
X
OH
7
12
O2
R
X
O
O
Pd(0)
1
O2
S
O
R
O
R
O
S
O
(R = aryl)
O
R
14
S
LnPd
8
O
R
O
11
S
11
Notes and references
13
O
O
O
S
O
O
‡ Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the
matter under discussion, limited experimental and spectral data,
and crystallographic data.
R
OH
S
acid
2
R
O
15
Scheme 5. Mechanistic study.
1
(a) “Sulfur Chemistry”: X. Jiang, Topics in Current Chemistry,
Springer, Berlin, 2018. (b) E. A. Ilardi, E. Vitaku and J. T.
Njardarson, J. Med. Chem., 2014, 57, 2832; (b) M. Feng, B.
Tang, S. Liang and X. Jiang, Curr. Top. Med. Chem., 2016, 16,
intermediate 8, which underwent a reductive elimination
formed sulfinate intermediate 11. On the other hand, when
alkyl bromides were used as the substrates, alkyl radical
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
Green Chemistry
Please do not adjust margins
Journal Name
COMMUNICATION
1200; (d) K. A. Scott and J. T. Njardarson, Top. Med. Chem.,
2018, 376, 5.
(a) F. Plisson, P. Prasad, X. Xiao, A. M. Piggott, X. Huang, Z.
Khalil and R. J. Capon, Org. Biomol. Chem., 2014, 12, 1579; (b)
N. Wang, P. Saidhareddy and X. Jiang, Nat. Prod. Rep., 2020,
37, 246.
View Article Online
DOI: 10.1039/D0GC03135F
2
3
4
(a) R. D. Howells and J. D. McCown, Chem. Rev., 1977, 77, 69.
(b) G. A. El-Hiti, Sulfur Reports, 2001, 22, 217.
D. C. F. Garbutt, K. G. R. Pachler and J. R. Parrish, J. Chem.
Soc. 1965, 2324.
5
6
Z. Sun, C. Lin and J. Zheng, CN104140704, 2014.
H. Sakai and M. Misawa, Basic Clin. Pharmacol. Toxicol., 2005,
96, 54.
7
8
9
A. Eldor, E. Zylber-Katz and M. Levy, Eur. J. Clin. Pharmacol.,
1984, 26, 171.
S. Ripa, F. Mignini, I. Patrizi, L. Ferrante, M. Prenna and E.
Falcioni, Chemioterapia, 1987, 6, 277.
(a) I. R. Greig, A. I. Idris, S. H. Ralston and R. J. van’t Hof, J.
Med. Chem., 2006, 49, 7487; (b) M. Nakamura, M. Ueda, S.
Watanabe, S. Kumamoto and K. Yamana, Tetrahedron Lett.,
2007, 48, 6159; (c) G. Szabó, J. Fischer, Á. Kis-Varga and K.
Gyires, J. Med. Chem., 2008, 51, 142.
10 (a) H. A. Young, J. Am. Chem. Soc., 1937, 59, 811; (b) F. P.
Ballistreri, G. A. Tomaselli and R. M. Toscano, Tetrahedron
Lett., 2008, 49, 3291.
11 J. Aziz, S. Messaoudi, M. Alami and A. Hamze, Org. Biomol.
Chem., 2014, 12, 9743.
12 Y. Ishii, K. Matsunaka and S. Sakaguchi J. Am. Chem. Soc.,
2000, 122, 7390.
13 A. Gómez-Palomino and J. Cornella, Angew. Chem., Int. Ed.,
2019, 58, 18235.
14 Representative reviews, see: (a) J. Aziz, S. Messaoudi, M.
Alami and A. Hamze, Org. Biomol. Chem., 2014, 12, 9743; (b)
E. J. Emmett and M. C. Willis, Asian J. Org. Chem., 2015, 4,
602; (c) G. Qiu, K. Zhou, L. Gao and J. Wu, Org. Chem. Front.,
2018, 5, 691; (d) K. Hofman, N.-W. Liu and G. Manolikakes,
Chem. -Eur. J., 2018, 24, 11852; (e) M. Wang and X. Jiang,
Chin. Sci. Bull., 2018, 63, 2707; (f) G. Qiu, K. Zhou and J. Wu,
Chem. Commun., 2018, 54, 12561; (g) S. Ye, G. Qiu and J. Wu,
Chem. Commun., 2019, 55, 1013; (h) S. Ye, M. Yang, J. Wu,
Chem. Commun., 2020, 56, 4145.
15 S. Ye, Y. Li, J. Wu and Z. Li, Chem. Commun., 2019, 55, 2489.
16 (a) Y. Meng, M. Wang and X. Jiang, Angew. Chem., Int. Ed.,
2020, 59, 1346; (b) Y. Li, S. Chen, M. Wang and X. Jiang,
Angew. Chem., Int. Ed., 2020, 59, 8907; (c) S. Chen, Y. Li, M.
Wang and X. Jiang, Green Chem., 2020, 22, 322; (d) Y. Li, S. A.
Rizvi, D. Hu, D. Sun, A. Gao, Y. Zhou, J. Li and X. Jiang, Angew.
Chem., Int. Ed., 2019, 58, 13499; (e) M. Wang, Z. Dai and X.
Jiang, Nat. Commun., 2019, 10, 2661; (f) M. Wang, J. Zhao
and X. Jiang, ChemSusChem, 2019, 12, 3064; (g) X. Xiao, J.
Xue and X. Jiang, Nat. Commun., 2018, 9, 2191; (h) M. Wang,
Q. Fan and X. Jiang, Green Chem., 2018, 20, 5469; (i) M.
Wang, Q. Fan and X. Jiang, Org. Lett., 2018, 20, 216; (j) Y. Li,
M. Wang and X. Jiang, ACS Catal., 2017, 7, 7587; (k) M. Wang,
S. Chen and X. Jiang, Org. Lett., 2017, 19, 4916; (l) X. Xiao, M.
Feng and X. Jiang, Angew. Chem., Int. Ed., 2016, 55, 14121.
17 CCDC 2017488 (2m) can be obtained free of charge from The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
18 (a) Q. Lu, J. Zhang, F. Wei, Y. Qi, H. Wang, Z. Liu and A. Lei,
Angew. Chem., Int. Ed., 2013, 52, 7156; (b) Q. Lu, J. Zhang, G.
Zhao, Y. Qi, H. Wang and A. Lei, J. Am. Chem. Soc., 2013,
135, 11481; (c) L. Gao, Z. Liu, X. Ma and Z. Li, Org. Lett., 2020,
22, 5246.
19 (a) E. Hatzigrigoriou, A. Varvoglis and M. Bakola-
Christianopoulou, J. Org. Chem., 1990, 55, 315; (b) J. Börgel,
L. Tanwar, F. Berger and T. Ritter, J. Am. Chem. Soc., 2018,
140, 16026.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins