Visible-Light-Mediated Eosin Y Photoredox-Catalyzed Vicinal Thioamination of Alkynes: Radical Cascade Annulation Strategy for 2-Substituted-3-sulfenylindoles

Article abstract of DOI:10.1002/ejoc.201800287

An organic dye photoredox-catalyzed regiospecific radical cascade annulation strategy of 2-alkynyl-azidoarenes to generate 3-sulfenylindoles via vicinal thioamination of alkynes at room temperature, mediated by visible light, was developed. The method req

Full text of DOI:10.1002/ejoc.201800287

A Journal of
Accepted Article
Title: Visible Light Mediated Eosin Y Photo-redox Catalyzed Vicinal
Thioamination of Alkynes: Radical Cascade Annulation Strategy
for 2-Substituted-3-sulfenylindoles
Authors: Umesh A. Kshirsagar, Shrikant D. Tambe, and Rajendra S.
Rohokale
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201800287
Link to VoR: http://dx.doi.org/10.1002/ejoc.201800287
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10.1002/ejoc.201800287
European Journal of Organic Chemistry
COMMUNICATION
Visible Light Mediated Eosin Y Photo-redox Catalyzed Vicinal
Thioamination of Alkynes: Radical Cascade Annulation Strategy
for 2-Substituted-3-sulfenylindoles
Shrikant D. Tambe[a] Rajendra S. Rohokale[a,b] and Umesh A. Kshirsagar*[a]
Dedication ((optional))
Abstract: Organic dye photo-redox catalyzed regio-specific radical
cascade annulation strategy of 2-alkynyl-azidoarenes to generate
important scaffold; 3-sulfenylindoles via vicinal thioamination of
alkynes at room temperature, mediated by visible light was
developed. The method requires mild condition such as visible light
as a traceless green energy source, room temperature, eosin Y
Figure 1. Some biologically active 3-sulfenylindoles.
organic dye as a photo-redox catalyst, ambient air as oxidant and
easily available starting materials thus provide green, efficient, metal
and strong oxidant-free synthesis of 3-sulfenylindoles with broad
polymerization inhibitor 3- sulfenylindoal (II), selective CRTh2
antagonist (IV) (Figure 1). Consequently, considerable synthetic
efforts have been reported for the synthesis of this scaffold. Due
to the electron- rich nature of indole ring at third position,
majority approaches are focused on direct C3−H sulfenylation of
indole ring catalyzed by metal such as ruthenium, iron, copper,
magnesium, vanadium, cerium with suitable sulfur source and
under transition metal free conditions such as iodine with
activated sulfur reagents (Scheme 1, a).6 Another strategy for
these compounds is electrophilic annulations of 2-alkynyl-aniline
derivatives (Scheme 1, b).7 Such as Larock et al. reported a
substrate scope through vicinal thioamination of alkynes.
Introduction
Over the past decade, visible light mediated photo-redox
catalysis for single electron transfer (SET) has been emerged as
an alternative, green, economical, practical and versatile tool for
important organic transformations such as oxidation/reduction,
C-C bond formation and importantly carbon-heteroatom bond
formation.1 Visible light photoredox catalysis becomes great
alternative not only for classical synthetic methods but also for
photochemical and electro-chemical reaction since these
methods suffer from cost-effectiveness and some limitations
such as by-products formation, a requirement of a specially
designed set-up. Hence photoredox catalysis has become the
most attractive and powerful approach in contemporary organic
synthesis. In this context, metal-based photo-redox catalyst such
as Ir, Ru and organic dyes photo-redox catalysts such as eosin-
Y, rose-bengal, rhodamine have been applied.2,3 Recently,
organic dyes have received increased attention due to cost
effectiveness and non-toxicity in comparison to metal based
photo-catalysts.
Substituted indoles are important and versatile motif due to
its increased importance in medicinal and pharmaceutical
chemistry as well as its dominance in several natural products.4
Of particularly, 2-Substituted-3-sulfenylindoles have attracted
significant attention due to their potent biological activities and
their therapeutic interest such as in the treatment of cancer, HIV,
heart disease, obesity, bacterial infection, and allergies.5 For
example, 5-lipoxygenase inhibitor and anticancer agent MK-886
(I), human breast cancer cell growth inhibitor and tubulin
[a]
[b]
Department of Chemistry, Savitribai Phule Pune University
(Formerly: University of Pune), Pune 411007, India.
E-mail: uakshirsagar@gmail.com,
uakshirsagar@chem.unipune.ac.in
CSIR-National Chemical Laboratory, Division of Organic Chemistry,
Dr. Homi Bhabha Road, Pune - 411008, India.
Scheme 1. Synthesis of 2-substituted-3-sulfenylindoles.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejoc.201800287
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COMMUNICATION
novel approach to the synthesis of 3-sulfenylindoles from N,N-
dialkyl-2-alkynyl-anilines via TBAI mediated electrophilic
cyclization with arylsulfenyl chloride.7a,b Li et al developed
palladium and iron/I2 catalyzed electrophilic annulation of 2-
alkynyl-anilines and N,N-dialkyl-2-alkynyl-anilines respectively
with disulfide for the synthesis of 3-sulfenylindoles.7c,d Zhou et al
developed copper catalyzed strategy from 2-alkynyl-anilines.7e
Tao et al.7f and Kuhkarn et al.7g disclosed iodine promoted
electrophilic cyclization of 2-alkynyl-aniline and N,N-dialkyl-2-
alkynyl-anilines respectively to construct 3-sulfenylindoles.
Recently, Jiang and co-workers developed palladium catalyzed
Table 1. Optimization Studies of the reactiona,b
.
entry
photo-catalyst
solvents
yield (%)b
1
Eosin Y
DCM
42
2
Eosin Y
THF
61
arylthiolation
of
2-alkynyl-anilines
in
presence
of
CuI/Phenathroline with arylboronic acid and S8 (Scheme 1, c).8
Fan and co-workers reported PhI(OAc)2 mediated one pot two-
step approach involving an oxidative nucleophilic cyclization of
2-alkynyl-aniline with thiophenols (Scheme 1, d).9 In the report
by Montevecchi and co-workers on the study of vinyl radical
cyclization onto the azido group, preparation of one compound
(3a) was found which was prepared by refluxing corresponding
azido compound in benzene in the presence of AIBN.10 In spite
of these, development of alternative, practical and
3
Eosin Y
CH3CN
CH3OH
DMF
75
4
Eosin Y
20
5
Eosin Y
trace
trace
68
6
Eosin Y
DMSO
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
7
Na2-Eosin Y
Rose Bengal
Acr-Mes+
Ru(bpy)3Cl2
Ir(ppy)3
8
46
9
49
10
11
12c
13d
14e
15f
27
environmentally
friendly
approach
for
2-substituted-3-
55
sulfenylindoles is still desirable. In continuation of our efforts to
develop simple, cheap, sustainable and green methods for the
construction of bioactive compounds,11 herein we would like to
report mild and convenient, visible light mediated, organic dye
photoredox catalyzed vicinal thioamination of alkyne and
cascade annulation strategy for 2-substituted-3-sulfenylindoles
from 2-alkynyl-azidoarenes.
Eosin Y
32
Eosin Y
37
Eosin Y
10
Eosin Y
56
aReaction conditions: 1a (0.114 mmol), 2a (0.171 mmol), photo-catalyst (5
mol %), solvent (1.5 mL), ambient air, blue LED, rt, 12h. bIsolated yield. c1.0
equiv. of 2a was used. d2.0 equiv. of 2a was used. eunder N2. funder oxygen
atmosphere.
Results and Discussion
Optimization of the reaction conditions was commenced with the
reaction between 1-azido-2-(phenylethynyl)benzene 1a (1.0
equiv.) and thiophenol 2a (1.5 equiv.) which was performed at
room temperature in the presence of 5 mol% eosin Y as
photocatalysts in an ambient air atmosphere. When
dichloromethane (DCM) was used as a solvent (entry 1, Table 1)
after 12h irradiation at room temperature, formation of 3a was
observed in 42% yield. With this encouragement, the reaction
was studied by varying the solvents systems (entries 1-7). When
THF was used as a solvent, it afforded 3a in 61% yield (entry 2).
Formation of 3a was observed in 75% yield when the reaction
was performed in acetonitrile (entry 3). When methanol was
used as a solvent, yield was dropped to 20% (entry 4). Product
formation was not observed in the solvent DMF and DMSO
(entry 5 and 6). Various photo-redox catalysts were screened
(entries 7-11). Na2-Eosin Y afforded slightly lower yield (68%,
entry 7) whereas rose-bengal gave 46% yield of 3a (entry 8).
Similarly, no improvement in the yield of 3a was observed when
other photo-catalysts were used such as Acr-Mes+ (49%, entry
9), Ru(bpy)3Cl2 (27%, entry 10) and Ir(ppy)3 (55%, entry 11).
Effect of equivalents of thiophenol on reaction yield was studied
and observed that when 1.0 equivalent of thiophenol (entery 12)
was used, 3a was isolated in 32% along with unreacted starting
material 1a. Use of 2.0 equivalent of thiophenol (entry 13) gave
37% of 3a along with some unidentified side products. When a
reaction was carried out under nitrogen atmosphere only 10%
yield of 3a was isolated with recovered starting material 1a
(entry 14). When reaction was performed under oxygen
atmosphere, no further improvment in the yield was observed
(56%, entry 15). With these optimized reaction conditions in
hand, the substrate scope of 2-alkynyl-azidoarenes and
thiophenols were examined (Scheme 2/3). Several 2-alkynyl-
azidoarenes were prepared using the literature procedure12 and
reacted with benzene thiol (2a). The reaction was effectively
amenable to a wide range of substrate scope of 2-phenylethynyl
aryl azides (1a-e) such as methyl, chloro, bromo and
trifluoromethyl to provide the desired 3-sulfenylindoles 3a-e in
70-80% yields. The scope of azido benzenes with aryl alkynyl
was further investigated. A range of arylethynyl i.e., p-Me, p-Et,
p-nBu, p-Br, p-OEt proceeded fine in the reaction to provide the
corresponding 3-sulfenylindoles products 3f-j in very good yields
(77-86%). Azidobenzenes of alkynyl with ethynylcyclopropane
(1k) was reacted with benzene thiol under the optimized
condition, provided corresponding product 3k in 62% yield. Next,
the scope of aryl thiols was explored. A variety of thiophenols
were applied under the optimized reaction condition with 1-
azido-2-(phenylethynyl)benzene 1a (Scheme 3). Aryl thiols such
as p-Me, p-tBu, p-Cl, p-Br, m-OMe proceeded smoothly to
deliver the products 3l-p in 73-76% yields. Interestingly, the
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10.1002/ejoc.201800287
European Journal of Organic Chemistry
COMMUNICATION
and 3s) in 71 and 68% yields. When aliphatic thiols such as
butane-1-thiol and 2-mercaptoethan-1-ol were treated with 1-
azido-2-(phenylethynyl)benzene, the corresponding products 3t
and 3u were formed in good yields ( 58 and 72%, respectively).
Some control experiments were carried out to have
mechanistic insight in the reaction. When the reaction was
performed under the standard condition in the presence of
classical radical inhibitor TEMPO, the formation of product was
not observed and starting material 1a was recovered which
suggest radical pathway involved in the reaction (Scheme 4, eq.
a). In absence of visible light (eq. b), no product formation was
observed whereas in absence of photo-redox catalysts (eq. c)
only 5% of product was obtained, which suggests the necessity
of photoredox catalyst and visible light for the reaction to occur.
Under the nitrogen atmosphere reaction afforded only 10% of 3a
with recovered 1a (table 1, entry 14) which suggest the
necessity of oxygen for the reaction. When the reaction was
performed with diphenyldisulfide instead of thiophenol, the
formation of 3a was not observed (eq. d).
Scheme 2. Scope of 2-Alkynyl Arylazides. Reaction conditions: 1 (0.114
mmol), 2 (0.171 mmol), eosin Y (5 mol %), CH3CN (1.5 mL), ambient air, blue
LED, rt, 12h.
benzothiazole-2-thiols also worked well and afforded the
targeted products 3q in 70% yield. In view of chemo-selective
functionalization in either ring, 3-sulfenylindoles with chloro and
bromo groups on two different aromatic rings were prepared (3r
Scheme 4 Control experiment
From above control experiments and the literature13 following
plausible radical cascade reaction pathway has been suggested
(Scheme 5). Visible light mediated photo-excitation of Eosin Y
(EY) produces Eosin Y (EY*). One electron oxidation of
thiophenol by this excited state EY* affords radical species (A)
with reduction of EY* to EY•- which could re-oxidized to its
Scheme 5 A plausible mechanism pathway
Scheme 3. Scope of thiols. Reaction conditions: 1 (0.114 mmol), 2 (0.171
mmol), eosin Y (5 mol %), CH3CN (1.5 mL), ambient air, blue LED, rt, 12h.
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10.1002/ejoc.201800287
European Journal of Organic Chemistry
COMMUNICATION
ground state by air oxygen to EY and O2•−. Deprotonation of
radical A gives radical B. Regioselective addition of radical B on
the triple bond of 1a gives radical intermediate C. Intramolecular
radical cyclization and release of N2 from intermediate C delivers
N-centered radical intermediate D. Hydrogen radical transfer
from hydrogen source present in the reaction mixture provides
3a.
(c) D. J. Wilger, N. J. Gesmundo and D. A. Nicewicz, Chem. Sci., 2013,
4, 3160; (d) D. P. Hari, P. Schroll and B. Koenig, J. Am. Chem. Soc.,
2012, 134, 2958. (e) M. Neumann, S. Fuldner, B. Konig and K. Zeitler,
Angew. Chem., Int. Ed., 2011, 50, 951; (f) Y. Pan, S. Wang, C. W. Kee,
E. Dubuisson, Y. Yang, K. P. Loh and C.-H. Tan, Green Chem., 2011,
13, 3341; (g) Y. Pan, C. W. Kee, L. Chen and C.-H. Tan, Green Chem.,
2011, 13, 2682.
[4]
(a) J. A. Joule, Indole and its Derivatives in Science of Synthesis:
Howben-Weyl Methods of Molecular Transformations; Thomas, E. J.,
Ed.; George Thieme: Stuttgart, 2001; Vol. 10, Chapter 10.13. (b) A.
Brancale, R. Silvestri, Med. Res. Rev. 2007, 27, 209. (c) G. C. Rieck, A.
N. Fiander, Mol. Nutr. Food Res. 2008, 52, 105. (a) J.-R. Weng, C.-H.
Tsai, S. K. Kulp, C.-S. Chen, Cancer Lett. 2008, 262, 153. (d) M.
Bandini, A. Eichholzer, Angew. Chem., Int. Ed. 2009, 48, 9608. (e) A. J.
Kochanowska-Karamyan, M. T. Hamann, Chem. Rev. 2010, 110, 4489.
(f) A. H. Sandtorv, Adv. Synth. Catal. 2015, 357, 2403.
Conclusions
In summary, an efficient and mild photo-redox catalyzed, visible
light induced radical cascade annulation strategy via vicinal
thioamination of alkyne for the synthesis of 3-sulfenylindoles
using organic dye as photo-redox catalyst and air as mild and
greenest oxidant has been developed. Reaction does not
require any sacrificial acceptor or donor and proceed at room
temperature.
[5]
(a) C. D. Funk, Nat. Rev. Drug Discovery 2005, 4, 664. (b) R. Ragno, A.
Coluccia, G. La Regina, G. De Martino, F. Piscitelli, A. Lavecchia, E.
Novellino, A. Bergamini, C. Ciaprini, A. Sinistro, G. Maga, E. Crespan,
M. Artico, R. Silvestri, J. Med. Chem. 2006, 49, 3172. (c) G. La Regina,
M. C. Edler, A. Brancale, S. Kandil, A. Coluccia, F. Piscitelli, E. Hamel,
G. De Martino, R. Matesanz, J. F. Díaz, A. I. Scovassi, E. Prosperi, A.
Lavecchia, E. Novellino, M. Artico, R. Silvestri, J. Med. Chem. 2007, 50,
2865. (d) R. E. Armer, G. M. Wynne, PCT Int. Appl. WO 2008012511,
2008. (e) G. D. Heffernan, R. D. Coghlan, E. S. Manas, R. E. McDevitt,
Y. Li, P. E. Mahaney, A. J. Robichaud, C. Huselton, P. Alfinito, J. A.
Bray, S. A. Cosmi, G. H. Johnston, T. Kenney, E. Koury, R. C.
Winneker, D. C. Deecher, E. J. Trybulski, Bioorg. Med. Chem. 2009, 17,
7802. (f) G. De Martino, M. C. Edler, G. La Regina, A. Coluccia, M. C.
Barbera, D. Barrow, R. I. Nicholson, G. Chiosis, A. Brancale, E. Hamel,
M. Artico, R. Silvestri, J. Med. Chem. 2006, 49, 947. (g) G. De Martino,
G. La Regina, A. Coluccia, M. C. Edler, M. C. Barbera, A. Brancale, E.
Wilcox, E. Hamel, M. Artico, R. Silvestri, J. Med. Chem. 2004, 47, 6120.
(h) V. S. N. Ramakrishna, V. S. Shirsath, R. S. Kambhampati, S.
Vishwakarma, N. V. Kandikere, S. Kota, V. Jasti, PCT Int. Appl. WO
2007020653, 2007. (i) F. Cianchi, C. Cortesini, L. Magnelli, E. Fanti, L.
Papucci, N. Schiavone, L. Messerini, A. Vannacci, S. Capaccioli, F.
Perna, M. Lulli, V. Fabbroni, G. Perigli, P. Bechi, E. Masini, Mol. Cancer
Ther. 2006, 5, 2716. (j) T. Luker, R. Bonnert, S. Brough, A. R. Cook, M.
R. Dickinson, I. Dougall, C. Logan, R. T. Mohammed, S. Paine, H. J.
Sanganee, C. Sargent, J. A. Schmidt, S. Teague, S. Thom, Bioorg.
Med. Chem. Lett. 2011, 21, 6288.
Acknowledgements
We thank Savitribai Phule Pune University for providing the
infrastructure. R. S. R. thankful for SERB, New Delhi for National
postdoctoral Fellowship (SERB-NPDF) and U.A.K. thanks for
DST-INDIA, New Delhi for the INSPIRE Faculty Award.
Keywords: Photoredox catalysis • Organic dye • 3-
sulfenylinodles • visible light • cascade annulation
[1]
For selected recent reviews on visible light mediated photoredox
catalysis, see: (a) N. A. Romero and D. A. Nicewicz, Chem. Rev., 2016,
116, 10075; (b) M. H. Shaw, J. Twilton and D. W. C. MacMillan, J. Org.
Chem., 2016, 81, 6898; (c) D. Ravelli, S. Protti and M. Fagnoni, Chem.
Rev., 2016, 116, 9850; (d) J. J. Douglas, M. J. Sevrin and C. R. J.
Stephenson, Org. Process Res. Dev., 2016, 20, 1134; (e) K. Teegardin,
J. I. Day, J. Chan and J. Weaver, Org. Process Res. Dev., 2016, 20,
1156; (f) J. C. Tellis, C. B. Kelly, D. N. Primer, M. Jouffroy, N. R. Patel
and G. A. Molander, Acc. Chem. Res., 2016, 49, 1429; (g) D. M.
Schultz and T. P. Yoon, Science, 2014, 343, 985; (h) D. Staveness, I.
Bosque and C. R. J. Stephenson, Acc. Chem. Res., 2016, 49, 2295; (i)
C. K. Prier, D. A. Rankic and D. W. C. MacMillan, Chem. Rev., 2013,
113, 5322; (j) D. P. Hari and B. Koenig, Angew. Chem., Int. Ed., 2013,
52, 4734; (k) S. Fukuzumi and K. Ohkubo, Org. Biomol. Chem., 2014,
12, 6059; (l) D. P. Hari and B. Koenig, Chem. Commun., 2014, 50,
6688 and references cited therein a-l.
[6]
(a) Y. Maeda, M. Koyabu, T. Nishimura, S. Uemura, J. Org. Chem.
2004, 69, 7688. (b) M. Tudge, M. Tamiya, C. Savarin, G. R. Humphrey,
Org. Lett. 2006, 8, 565. (.c) J. S. Yadav, B. V. S. Reddy, Y. J. Reddy, K.
Praneeth, Synthesis 2009, 1520. (b) X.-L. Fang, R.-Y. Tang, P. Zhong,
J.-H. Li, Synthesis 2009, 4183. (12) C. C. Silveira, S. R. Mendes, L.
Wolf, G. M. Martins, Tetrahedron Lett. 2010, 51, 2014. (13) (a) Z. Li, J.
Hong, X. Zhou, Tetrahedron 2011, 67, 3690. (b) Z. Li, L. Hong, R. Liu, J.
Shen, X. Zhou, Tetrahedron Lett. 2011, 52, 1343. (c) S. Ranjit, R. Lee,
D. Heryadi, C. Shen, E. Wu, P. Zhang, K.-W. Huang, X. Liu, J. Org.
Chem. 2011, 76, 8999. (14) M. Chen, Z.-T. Huang, Q.-Y. Zheng, Chem.
Commun. 2012, 48, 11686. (a) M. Tudge, M. Tamiya, C. Savarin, G. R.
Humphrey, Org. Lett. 2006, 8, 565. (e) P. Sang, Z. Chen, J. Zou, Y.
Zhang, Green Chem. 2013, 15, 2096. (g) Y. Liu, Y. Zhang, C. Hu, J.-P.
Wan, C. Wen, RSC Adv. 2014, 4, 35528. (h) J. B. Azeredo, M. Godoi,
G. M. Martins, C. C. Silveira, A. L. Braga, J. Org. Chem. 2014, 79, 4125.
(b) W. Ge, Y. Wei, Green Chem. 2012, 14, 2066. (d) F.-L. Yang, S.-K.
Tian, Angew. Chem., Int. Ed. 2013, 52, 4929. (e) H. Qi, T. Zhang, K.
Wan, M. Luo, J. Org. Chem. 2016, 81, 4262.
[2]
For selected recent examples using metal-based photoredox catalysts,
see: (a) L. Ruiz Espelt, I. S. McPherson, E. M. Wiensch and T. P. Yoon,
J. Am. Chem. Soc., 2015, 137, 2452; (b) S. Ventre, F. R. Petronijevic
and D. W. C. MacMillan, J. Am. Chem. Soc., 2015, 137, 5654; (c) A.
Noble, S. J. McCarver and D. W. C. MacMillan, J. Am. Chem. Soc.,
2015, 137, 624; (d) Y. Zhang, R. Qian, X. Zheng, Y. Zeng, J. Sun, Y.
Chen, A. Ding and H. Gao, Chem. Commun., 2015, 51, 54; (e) R. Lin,
H. Sun, C. Yang, W. Shen and W. Xia, Chem. Commun., 2015, 51,
399; (f) J. Zoller, D. C. Fabry, M. A. Ronge and M. Rueping, Angew.
Chem., Int. Ed., 2014, 53, 13264; (g) D. P. Hari, T. Hering and B. Konig,
Angew. Chem. Int. Ed., 2014, 53, 725.
[7]
(a) Y. Chen, C.-H. Cho, R. C. Larock, Org. Lett. 2009, 11, 173. (b) Y.
Chen, C.-H. Cho, F. Shi, R. C. Larock, J. Org. Chem. 2009, 74, 6802.
(c) Y.-J. Guo, R.-Y. Tang, J.-H. Li, P. Zhong, X.-G. Zhang, Adv. Synth.
Catal. 2009, 351, 2615. (d) H.-A. Du, R.-Y. Tang, C.-L. Deng, Y. Liu, J.-
H. Li, X.-G. Zhang, Adv. Synth. Catal. 2011, 353, 2739. (e) Z. Li, L.
Hong, J. Liu, J. Shen, X. Zhou, Tetrahedron Lett., 2011, 52, 1343. (f) L.
[3]
For selected recent examples using organic photoredox catalysts, see:
(a) W-L. Guo, L.-Q. Wang, Y.-N. Wang, J.-R. Chen and W.-J. Xiao,
Angew. Chem., Int. Ed., 2015, 54, 2265; (b) T. Xiao, L. Li, G. Lin, Q.
Wang, P. Zhang, Z. Mao and L. Zhou, Green Chem., 2014, 16, 2418;
This article is protected by copyright. All rights reserved.

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M. Tao, W. Q. Liu, Y. Zhou, A. T. Li, J. Chem. Res. 2012, 36, 644. (g) J.
Meesin, M. Pohmakotr, V. Reutrakul, D. Soorukram, P. Leowanawat, C.
Kuhakarn, Org. Biomol. Chem., 2017, 15, 3662.
[8]
[9]
J. Li, C. Li, S. Yang, Y. An, W. Wu, H. Jiang, J. Org. Chem. 2016, 81,
2875.
D. Han, Z. Li, R. Fan, Org. Lett. 2014, 16, 6508.
[10] P. C. Montevecchi, M. L. Navacchia, P. Spagnolo, Eur. J. Org. Chem.
1998, 1219.
[11] (a) R. S. Rohokale, S. D. Tambe, U. A. Kshirsagar, Org. Biomol. Chem.,
2018, 16, 536. (b) M. H. Shinde, U. A. Kshirsagar, Green Chem., 2016,
1455. (c) M. H. Shinde, U. A. Kshirsagar, Org. Biomol. Chem., 2016, 14,
858. (d) M. H. Shinde, U. A. Kshirsagar, RSC Advances 2016, 6, 52884.
[12] (a) Q. Liu, P. Chen, G. Liu, ACS Catal. 2013, 3, 178. (b) Z. Zhang, F.
Xiao, B. Huang, J. Hu, B. Fu, Z. Zhang, Org. Lett., 2016, 18, 908.
[13] (a) R. Rahaman, S. Das, P. Barman, Green Chem., 2018, 20, 141. (b)
H. Cui, W. Wei, D. Yang, Y. Zhang, H. Zhao, L. Wang H. Wang, Green
Chem., 2017, 19, 3520. (c) S. S. Zalesskiy, N. S. Shlapakov, V. P.
Ananikov, Chem. Sci., 2016, 7, 6740. (d) T. Keshari, V. K. Yadav, V. P.
Srivastava, L. D. S. Yadav, Green Chem., 2014, 16, 3986.
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COMMUNICATION
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COMMUNICATION
Key Topic* Photo-redox catalysis
Shrikant D. Tambe, Rajendra S.
Rohokale and Umesh A. Kshirsagar*
Page No. – Page No.
Visible Light Mediated Eosin Y Photo-
An efficient, mild and metal free, radical cascade annulation strategy for 2-
substituted-3-sulfenylindoles from 2-alkynyl-azidoarenes via vicinal thioamination of
alkyne catalyzed by eosin Y photoredox catalyst mediated by visible light in the
presence of air as mild oxidant.
redox
Catalyzed
Vicinal
Thioamination of Alkynes: Radical
Cascade Annulation Strategy for 2-
Substituted-3-sulfenylindoles
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