Visible-light-enabled regioselective aerobic oxidative C(sp2)-H thiocyanation of aromatic compounds by Eosin-Y photocatalyst

Article abstract of DOI:10.1016/j.tetlet.2020.152628

Herein, visible-light-enabled regioselective aerobic oxidative C(sp²)-H thiocyanation of aromatic compounds has been developed by employing eosin-Y as effective photocatalyst and oxygen as the green terminal oxidant. This process featured green, efficient and operationally simple. Furthermore, the practicality and utility of this protocol was demonstrated by the gram scale synthesis. Mechanistic studies suggested that this reaction was realized via a photoredox radical pathway.

Full text of DOI:10.1016/j.tetlet.2020.152628

Journal Pre-proofs
2
Visible-Light-Enabled Regioselective Aerobic Oxidative C(sp )-H Thiocya‐
nation of Aromatic Compounds by Eosin-Y Photocatalyst
Bing Yi, Xiaoyong Wen, Ziqi Yi, Yanjun Xie, Qiang Wang, Jian-Ping Tan
PII:
S0040-4039(20)31133-3
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.152628
TETL 152628
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
3 September 2020
29 October 2020
2 November 2020
Please cite this article as: Yi, B., Wen, X., Yi, Z., Xie, Y., Wang, Q., Tan, J-P., Visible-Light-Enabled
2
Regioselective Aerobic Oxidative C(sp )-H Thiocyanation of Aromatic Compounds by Eosin-Y Photocatalyst,
Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.152628
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Visible-Light-Enabled Regioselective
Aerobic Oxidative C(sp )-H Thiocyanation of
Leave this area blank for abstract info.
2
Aromatic Compounds by Eosin-Y
Photocatalyst
a,
b
c
a,
a
a,
Bing Yi *, Xiaoyong Wen , Ziqi Yi , Yanjun Xie *, Qiang Wang , Jian-Ping Tan *
Br
Br
HO
Br
O
O
Br
COOH
Eosin Y)
O2 , CH3CN, rt
FG
Ar
FG
Ar
H
(
+
4
NH SCN
SCN
FG: NH2, NHR, NR2, OH



Esoin Y as photocatalyst
Oxygen as green oxidant
para-Regioselective
* Broad substrate scopes
* Gram scale synthesis
* Green, efficient and simple

1
Tetrahedron Letters
journal homepage: www.elsevier.com
2
Visible-Light-Enabled Regioselective Aerobic Oxidative C(sp )-H Thiocyanation of
Aromatic Compounds by Eosin-Y Photocatalyst
a,
b
c
a,
a
a,
Bing Yi *, Xiaoyong Wen , Ziqi Yi , Yanjun Xie *, Qiang Wang , Jian-Ping Tan *
a
Hunan Province Key Laboratory of Environmental Catalysis and Waste Recycling, College of Materials and Chemical Engineering, Hunan Institute of
Engineering, Xiangtan, 411104, P. R. China.
b
College of Chemistry, Xiangtan University, Xiangtan, 411105, P. R. China.
CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing, P. R. China
c
ARTICLE INFO
ABSTRACT
2
Article history:
Received
Received in revised form
Accepted
Herein, visible-light-enabled regioselective aerobic oxidative C(sp )-H thiocyanation of
aromatic compounds has been developed by employing eosin-Y as effective photocatalyst and
oxygen as the green terminal oxidant. This process featured green, efficient and operationally
simple. Furthermore, the practicality and utility of this protocol was demonstrated by the gram
scale synthesis. Mechanistic studies suggested that this reaction was realized via a photoredox
radical pathway.
Available online
Keywords:
2
009 Elsevier Ltd. All rights reserved.
Visible-Light photocatalysis
2
C(sp )-H thiocyanation reaction
Eosin-Y
Regioselective
Aromatic sulfur compounds
Visible-light photoredox catalysis, featured renewable,
environment friendly, readily available and abundant has been
experiencing a renaissance in the past decades.1 Since the
number of efforts have thus been directed toward the
development of new process to access these scaffold. As a
consequence, many kinds of methods involved the use of
9
2
pioneering and landmark works by the groups of Bach and
4
ammonium thiocyanate salts (NH SCN) in the presence of strong
3
10
11
12
MacMillan, the synthetic chemistry field has witnessed the rapid
oxidants, strong acids, transition metal, corrosive halogen
1
3
14
development and breathtaking achievement of organic synthesis
through visible-light-promoted photochemical reactions.
Consequently, various organic transformations by employing
structurally diverse metal-based complexes as photoredox
reagents and others have been disclosed. However, despite of
their efficiencies, when in term of green chemistry and
sustainable development requirement in mind, these mentioned
approaches often suffered from many drawbacks obviously.
Thus, it is highly desirable to explore alternatively practical,
green and environmentally friendly protocol toward aromatic
organosulfur
4
catalysts have been well established. However, in term of more
stringent requirements for green chemistry manner and industrial
applications, these metal-involved photocatalytic transformations
still suffer from expensive and potentially toxic challenges.
Accordingly, the metal-free involved organic dyes such as eosin-
Y and rose bengal has attracted much attention for their
utilization as organic photoredox catalyst via absorbing visible
light to generate photoexcited species which usually possess a
long life time and prominent redox properties that may engage in
a single-electron transfer (SET) process with substrates. 5
*
stoichiometric oxidants
* strong acids
*
*
transition metals
halogen reagents
Previous work:
Het
H
* Ag/TiO2 nanotube, etc.
Het
/Ar
SCN
/
Ar
+
NH SCN
4
Br Br
HO
O
O
Br
Br
On the other hand, aromatic organosulfur compounds,6
especially thiocyanate-containing scaffolds are widely existed in
many drugs and biological molecules with a plethora of
promising biological activities, such as antiviral and
This work:
FG
COOH
(
Visible light )
(EosinY)
Ar
H
+
Ar
NH SCN
4
FG
SCN
O2
FG: NR2, OH
7
antimicrobial activities. The direct C-H thiocyanation reaction is
Scheme 1. Thiocyanation strategies for (hetero)aromatic compounds.
one of the most effective and straightforward synthetic technique
to construct C-S bond. Meanwhile, the thiocyanate functional
group could be easily converted into various sulfur-containing
derivatives, which usually serve as the synthetic precursors of
organosulfur molecules.8 Due to these significant synthetic
values and practical applications, Not surprisingly, a large
skeletons. To the best of our knowledge, only sporadic examples
for thiocyanation of indoles, N-aryltetrahydroisoquinoline and
other heterocycles by using visible-light photocatalytic system
1
5
16
1
7

2
Tetrahedron
[
a]
have been reported in recent years. In sharp contrast, the
visible-light-enabled direct thiocyanation of functionalized arenes
was virtually very rare. Very recently, the Ag/TiO nanotubes
Table 2. Scope of substrates
R2
R2
R3
R3
N
N
2
R1
Eosin Y (5 mol%)
R1
NH4
SCN
+
were synthesized painstakingly and utilized as photocatalyst to
fulfil the thiocyanation of N-bearing (hetero) aromatic
compounds was developed by the group of Hosseini-Sarvari.18
As part of our group research interest in the field of visible-light-
mediated photoredox organic chemical transformation.19 We
envisioned that employment of a simple and green organic dye as
photocatalyst under the oxygen atmosphere to challenge this
thiocyanation reaction. Herein, we describe the regioselective
CH CN, Green LEDs, O
3
2
NCS
1a
2
3a
H
N
H
H
H
N
N
N
Bn
Me
iPr
Et
NCS
NCS
NCS
NCS
3
a, 85% yield
3b, 81% yield
3
c, 80% yield
3d, 83% yield
Cl
H
Me
H
H
N
H
N
2
N
Cl
N
aerobic oxidative C(sp )-H thiocyanation of aromatic compounds
Ph
Me
Me
Bn
by employing commercially available and low-cost eosin-Y as
effective photocatalyst and oxygen as the green terminal oxidant.
NCS
3e, 90% yield
NCS
NCS
NCS
3
f, 84% yield
[c]
3g, 77% yield
3h, 78% yield
Table 1. Optimization of reaction conditions[a]
H
H
N
H
H
F
N
Cl
Br
N
MeO
N
Bn
Bn
Bn
Bn
H
N
H
N
NCS
NCS
NCS
NCS
[c]3l, 72% yield
Bn
Catalyst (5 mol%)
Bn
[c]3i
[c]3j, 76% yield
[c]3k, 72% yield
,
73% yield
NH2
NH4SCN
+
Solvent, Light source, O2
NCS
Me
Br
1
a
2
3a
NH2
NH2
Me
NCS
3p,73% yield
NH2
Entry
Catalyst
Solvent
Light source
Green LEDs
Yield [b]
NCS
NCS
NCS
[c]3m, 81% yield
3n, 92% yield
3
o, 93% yield
1
2
3
4
5
6
8
9
Eosin Y
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
68
65
trace
trace
6
iPr
NH2
N
OH
OH
Ru(bpy)
3
(PF
(PF
(PF
6
)
2
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
CFL
iPr
NCS
NCS
3r, 89% yield
NCS
[c]3s, 53% yield
Fe(bpy)
Co(bpy)
TiO
3
6
)
2
[c]3q, 95% yield
n, d SCN
3
6 2
)
[
a] Reaction conditions: 1a (0.2 mmol), 2 (0.6 mmol) and Eosin Y (5 mol%)
2
in CH CN (2 mL) and O atmosphere under 30 W green LEDs irradiation at
3
2
room temperature for 24 h. [b] Isolated yield. [c] 36 h.
Rose Bengal
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
Eosin Y
-
49
54
58
20
58
71
85
37
35
63
78
82
81
0
evaluated the catalytic reactivities of different photocatalysts.
Fisrtly, metal-based complexes such as Ru(bpy)
Fe(bpy) (PF and Co(bpy) (PF were used as photocatalyst in
the reaction (entries 2-4), Unexpectedly, only Ru(bpy) (PF as
catalyst was effective to the thiocyanation process, affording the
desired product with moderate yield (entry 2). Titanium dioxide
3 6 2
(PF ) ,
Blue LEDs
Red LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
Green LEDs
-
3
6
)
2
3
6 2
)
1
1
1
1
1
1
0
1
2
3
4
5
3
6 2
)
CH
3
OH
(
2
TiO ) usually serve as a practical and impactful heterogeneous
THF
photocatalyst was also tested in this reaction but giving the target
product with only 6% yield (entry 5). Actually, the organic dye
rose bengal was also found to be effective to promote this
thiocyanation reaction for affording the desired product with 49%
yield (entry 6). Next, we investigated the effects of different light
sources on the reaction, including 30 W compact fluorescent
lamps (CFL), 30 W blue LEDs and 30 W red LEDs, and the
results demonstrated that green LEDs was the most favorable
light source for this thiocyanation process (entries 8-10). Solvent
usually have a large effect in the visible-light-photoredox
promoted reactions. Thus, several common solvents such as
CH
3
CN
DMSO
2 2
CH Cl
1
1
1
6[c]
7[d]
8[e]
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
CN
CN
CN
CN
CN
CN
1
9[f]
CH
CH
3
OH, THF, CH
3 2 2
CN, DMSO, and CH Cl were examined, and
2
2
0[g]
3
CN was turned out to be the best, which can provide the
1[h]
desired product with 85% isolated yield (entry 13). Furthermore,
the amount of NH SCN was also screened, and 3.0 equiv.
NH SCN was proved to appropriate choice, while reducing or
improving the equivalent of NH SCN did not bring better results
Green LEDs
0
4
[
a] Reaction conditions: 1a (0.2 mmol), 2 (0.6 mmol) and catalyst (5 mol%)
in Solvent (2 mL) and O atmosphere under 30 W green LEDs irradiation at
room temperature for 24 h. [b] Isolated yield. [c] 1.0 equiv. NH SCN was
used. [d] 2.0 equiv. NH SCN was used. [e] 4.0 equiv. NH SCN was used. [f]
Air instead of O , [g] In the dark. [h] Without photocatalyst.
4
2
4
4
(entries 16-18). Therefore, the optimized reaction conditions
were obtained using 5 mol % of eosin Y as photocatalyst and 3.0
4
4
2
equiv. NH
ambient O
could not occur without photocatalyst or light irradiation (entries
0-21), which clearly revealed that they were indispensable
4
SCN in CH
3
CN under 30 W green LEDs irradiation in
2
at room temperature for 24 h. Of note, the reaction
We began our studies by using eosin-Y as photocatalyst to
investigate this C(sp )-H thiocyanation reaction of N-
2
2
benzylaniline 1a with NH
4
SCN under the 30 W green LEDs and
conditions for this photocatalytic transfromation.
O
2
atmosphere in DMF at room temperature for 24 h (Table 1).
To our delight, the regiospecificity thiocyanation product 3a at
the para-position of N-benzylaniline was obtained in 68%
isolated yield (entry 1). Encouraged by this initial result, we next
With the optimized reaction conditions in hand, the substrate
scopes for the thiocyanation reaction of aromatic amines with
NH SCN was explored. As shown in the Table 2, various
4

3
aromatic amines including primary amine, secondary amine and
tertiary amine regardless of the positions and electronic
properties of the substituents on the phenyl ring and nitrogen
atom moiety could be well employed, the regiospecificity
thiocyanation product at the para-position of aromatic amines
were obtained with moderate to good yields. Specifically,
different substituents including Bn, Me, Et, Pr and Ph groups on
the nitrogen atom moiety could were well tolerated the reaction
conditions, and the corresponding products were obtained in 80-
the reaction under the standard conditions, the reaction did not
proceed and the similar result was obtained when the reaction
was carried out in the dark (Scheme 3, c, d). According to the
aforementioned results, it can be strongly deduced that the
reactions proceed through visible-light-induced aerobic radical
mechanism. Moreover, when the para-position of N-arylamine
was occupied by methoxy group, no ortho-thiocyanated product
was formed, and the starting material was recovered completely,
demonstrating high para-selectivity in this C-H thiocyanation
reaction (Scheme 3, e). Of note, Similar phenomenon of
i
9
0% yields (3a-e). When the substituent group Cl at the ortho-
position of N-methylaniline could give the product (3f) with 84%
yield, which is better than that at meta-position of N-
methylaniline (3g). Substrates bearing both electron-donating and
electron-withdrawing group at either ortho- or meta-position of
the N-benzylaniline were also tolerated and afforded the
corresponding products with moderate to good yields (3h-l).
Moreover, kinds of primary aromatic amines bearing various
substituent groups at diffierent position on the phenyl ring moiety
were also compatible with template reaction conditions,
producing the expected products in 73-93% yields. (3m-p).
Notably, when the aniline bearing two isopropyl groups at the
ortho position was also well tolerated to afford the product (3q)
in 95% yield. It is worth mentioning that the tertiary amine was
still proved as a good substrate in our catalytic system and the
target product was obtained in 89% yield, which is far superior to
regioselectivity at the para-position has been also appeared in
10b,18
earlier reports
. In addition, luminescence quenching
experiments (Scheme 4) and cyclic voltammetry test to
investigate the reaction mechanism were also conducted (see SI
for more details). Based on the results of fluorescence quenching
experiments, the more notable decrease of fluorescence intensity
of Eosin Y was recorded with increasing the concentration of
4 4
NH SCN, which might suggest that NH SCN is more easily to
undergo single-electron transfer process with the excited state
photocatalyst (EY*) under the standard reaction conditions. On
the other hand, the obvious oxidation peaks of N-benzylaniline
and NH
4
SCN were observed +0.95 V, +0.75V (vs Ag/AgCl)
SCN would be more
respectively, which might suggest that NH
4
easily than N-benzylaniline to be oxidated under the standard
reaction conditions in our catalytic system. (Figure S4).
the result of Ag/TiO
2
nanotubes photocatalyst in previous
[18]
report . In addition, When phenol was used as the substrate, this
2
C(sp )-H regiospecificity thiocyanation reaction also occured and
H
N
H
N
afforded the expected product (3s) with 53% yield in 36 h.
However, when 1-naphthol was used as the substrate,
Surprisingly, the target thiocyanation product was not obtained.
Bn
Bn
Standard Conditions
Bn
(a)
NH4SCN
NH4SCN
+
+
TEMPO (2.0 equiv.)
NCS
NCS
3
a, 10% GC yield
To demonstrate the utility and practicality of this visible-
H
N
H
N
2
light-enabled regioselective oxidative C(sp )-H thiocyanation
Standard Conditions
Bn
(b)
reaction, the large-scale reaction between N-benzylaniline 1a (6.0
mmol, 1.098 g) and NH SCN was performed under the optimal
4
BHT (2.0 equiv.)
3a, 13% GC yield
reaction conditions with prolonging the reaction time to 48 h, and
the corresponding product 3a was obtained in 81% yield (1.45 g).
Analogously, when the primary amine 1m (8.0 mmol，0.744 g)
was used as substrate, the corresponding product 3m was
obtained in 80% yield (0.96 g).
H
N
H
N
Bn
Bn
Bn
Standard Conditions
Bn
Bn
Bn
(c)
(d)
(e)
NH4
SCN
+
+
+
N2 instead of O2
NCS
NCS
MeO
NR
NR
H
N
H
N
Standard Conditions
NH4SCN
H
N
H
N
without light
(in dark)
Bn
Eosin Y (5 mol%)
Bn
NH4
SCN
SCN
+
CH3CN, Green LEDs,
O2, 48 h
(1)
(2)
H
N
NCS
H
N
1
a
3a
(
(
6 mmol, 1.098 g)
(81%, 1.45 g)
Standard Conditions
NH4
SCN
MeO
SCN
H
H
N
N
H
not detected by GC-MS
Eosin Y (5 mol%)
H
+
NH4
CH3CN, Green LEDs,
O2, 48 h
NCS
Scheme 3. Control experiments
On the basis of our observations of the control experiments
1
m
3m
8 mmol, 0.744 g)
(80%, 0.96 g)
Scheme 2. Gram-scale synthesis
17a
and previous literatures,
a plausible mechanism has been
proposed in Scheme 4. Initially, Eosin-Y (EY) is being
photoexcited in the presence of green LEDs light irradiation to
converted into an excited state EY*, and then SCN anion is being
Subsequently, In order to further understand the reaction
mechanism, a series of control experiments were performed.20 As
shown in Scheme 3, Firstly, the radical traping experiments were
carried out. When the common radical quenchers 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO) and 2,6-di-tertbutyl-4-
methylphenol (BHT) was added to the reaction under the
standard conditions, the target product 3a was only obtained with
-
oxidized to SCN• radical through single-electron transfer.
Subsequently, the SCN• radical attacked the substrate 1 to
generate another radical intermediate A, which was oxidized
quickly to form the cationic intermediate B. Then the cationic
intermediate B via deprotonation process to turn into the target
product 3. In addition, oxygen may plays a crucial role to
complete the photoredox cycle through oxidation of the EY•-
radical anion back to the ground state EY, Which enter into the
next catalytic cycle (Scheme 5).
1
0% and 13% GC yield, respectively (Scheme 3, a, b ). These
results revealed that the reaction may underwent free radical
pathway. Besides, When nitrogen instead of oxygen was used in

4
Tetrahedron
4
4
3
3
2
2
1
1
0
.5
.0
.5
.0
.5
.0
.5
.0
.5
NH SCN
D. W. C. J. Org. Chem. 2016, 81, 6898. (e) Zhou, Q.-Q.; Zou, Y.-
Q.; Lu, L.-Q.; Xiao, W.-J. Angew. Chem., Int. Ed. 2019, 58, 1586.
(f) Yu, X.-Y.; Zhao, Q.-Q.; Chen, J.; Xiao, W.-J.; Chen, J.-R. Acc.
Chem. Res. 2020, 53, 1066. (g) Yu, X.-Y.; Chen, J.-R.; Xiao, W.-J.
Chem. Rev. 2020, DOI:10.1021/acs.chemrev.0c00030. (h) Xuan,
J.; Xiao, W.-J. Angew. Chem. Int. Ed. 2012, 51, 6828. (i) Festa, A.
A.; Voskressensky, L.G.; Van der Eycken, E. V. Chem. Soc. Rev.
4
N-Benzylaniline
2
y = 2395.1316 x+ 1, R = 0.9994
2
y = 358.7564 x+1, R = 0.9936
2
019, 48, 4401.
2
.
.
Bauer, A.; Westkämper, F.; Grimme, S.; Bach, T. Nature. 2005,
436, 40.
Nicewicz, D. A.; MacMillan, D. W. C. Science. 2008, 322, 77.
(a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
3
4.
2
013, 113, 5322. (b) Glaser, F.; Wenger, O. S. Coordin. Chem.
Rev. 2020, 405, 213129. (c) Nicholls, T. P.; Bissember, A. C.
Tetrahedron Lett. 2019, 60, 150883.
(a) Yan, D.-M.; Chen, J.-R.; Xiao, W.-J. Angew. Chem., Int. Ed.
5
6
.
.
0
.000
0.002
0.004
0.006
0.008
0.010
2
019, 58, 378. (b) Ravelli, D.; Fagnoni, M. ChemCatChem 2012,
Concentration [M]
4
, 169.
Scheme 4. Luminescence quenching experiments
(a) Erian, A. W.; Sherif, S. M. Tetrahedron. Lett. 1999, 55, 7957.
b) Zhao, P.; Yin, H.; Gao, H.; Xi, C. J. Org. Chem. 2013, 78,
001. (c) Artico, M.; Silvestri, R.; Pagnozzi, E.; Bruno, B.;
(
5
Novellino, E.; Greco, G.; Massa, S.; Ettorre, A.; Giulia, A. J. Med.
Chem. 2000, 43, 1886. (d) Arjmandi-Tash, H.; Belyaeva, L. A.;
Schneide, G. F. Chem. Soc. Rev. 2016, 45, 476. (e). Qiao, Z.; Liu,
H.; Xiao, X.; Fu, Y.; Wei, J.; Li, Y.; Jiang, X. Org. Lett. 2013, 15,
R1
hv
NCS
N
R2
3
2
594. (f) Dutta, S.; Abe, H.; Aoyagi, S.; Kibayashi, C.; Gates, K.
EY
-H+
S. J. Am. Chem. Soc. 2005, 127, 15004. (g) Pham, A. T.; Ichiba, T.;
Yoshida, W. Y.; Scheuer, P. J.; Uchida, T.; Tanaka, J.-I.; Higa, T.
Tetrahedron Lett. 1991, 32, 4843.
(a) Yasman, R.; Edrada, A.; Wray, V.; Proksch, P. J. Nat. Prod.
2003, 66, 1512; (b) Elhalem, E.; Bailey, B. N.; Docampo, R.;
Ujvary, I.; Szajnman, S. H.; Rodriguez, J. B. J. Med. Chem. 2002,
EY*
R1
-
SCN
SCN
O2
NCS
+
N
R2
7.
8.
B
EY
O2
[
O]
4
5, 3984.
R1
N
R1
(a) Demko, Z. P.; Sharpless, K. B. Org. Lett. 2001, 3, 4091. (b)
Wang, F.; Chen, C.; Deng, G.; Xi, C. J. Org. Chem. 2012, 77,
NCS
N
R2
R2
4
148. (c) Lei, W.-L.; Wang, I.; Feng, K.-W.; Wu, L.-Z.; Liu, Q.
1
A
ACS Catal. 2017, 7, 7941. (d) Grant, M.; Snyder, H. J. Am. Chem.
Soc. 1960, 82, 2742.
Scheme 5. Proposed reaction mechanism
In summary, we have developed regiospecificity oxidative
9
1
.
(a) Zhu, D.; Chang, D.; Shi, L. Chem. Commun. 2015, 51, 7180.
(
(
b) Grant, M. S.; Snyder, H. R. J. Am. Chem. Soc. 1960, 82, 2742.
c) Toste, F. D.; Stefano, V.; Still, De I. W. Synth. Commun. 1995,
2
25, 1277. (d) Bhalerao, D. S.; Akamanchi, K. G. Synlett 2007,
007, 2952.
C(sp )-H thiocyanation of aromatic compounds by employing
eosin-Y as photocatalyst and oxygen as the green oxidant. A
variety of aromatic amines including primary amine, secondary
amine and tertiary amine could proceed well to afford the
corresponding products with moderate to good yields. This
method featured green, efficient and environmentally friendly
Moreover, the practicality and utility of this protocol was also
demonstrated by the gram-scale synthesis and Mechanistic
studies suggested that this reaction was realized via a photoredox
radical pathway.
2
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Acknowledgments
This work was supported by the National Science Foundation of
China (No. 21772035), and the Provincial Natural Science
Foundation of Hunan (No. 2019JJ50104). J.-P Tan also
acknowledge the comprehensive training platform of the
Specialized Laboratory in the College of Chemistry at Sichuan
University for some valuable tests.
5
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Notes
The authors declare no competing financial interest.
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45, 24.
2
0. See SI for more details.
Supplementary Material
Supplementary data associated with this article can be found
in the online version, at xxx.
Br
Br
HO
Br
O
O
Br
COOH
FG
Ar
FG
Ar
H
(
Eosin Y)
+
NH SCN
4
O , CH CN, rt
2
3
SCN
FG: NH , NHR, NR , OH
2
2



Esoin Y as photocatalyst
Oxygen as green oxidant
para-Regioselective
* Broad substrate scopes
* Gram scale synthesis
* Green, efficient and simple
Highlights
1
.Visible-light-enabled regioselective
2
C(sp )-H thiocyanation
. Eosin-Y as photocatalyst and oxygen as
the green oxidant.
2
3
4
. Green, efficient and operationally simple
. Broad substrate scopes and gram scale
synthesis