Organophotoredox-Catalyzed Direct C-H Amination of 2 H-Indazoles with Amines

Article abstract of DOI:10.1021/acs.orglett.0c01973

A general and practical method for the direct C-H amination of 2H-indazoles with a series of amines including aliphatic primary amines, secondary amines, azoles, and sulfoximines via organophotoredox-catalyzed oxidative coupling has been disclosed at room temperature under ambient air conditions. Additionally, this protocol is used for free aminated 2H-indazole synthesis. A mechanistic study revealed that a single electron transfer (SET) pathway might be involved in this reaction.

Full text of DOI:10.1021/acs.orglett.0c01973

pubs.acs.org/OrgLett
Letter
Organophotoredox-Catalyzed Direct C−H Amination of
2H‑Indazoles with Amines
Sukanya Neogi, Asim Kumar Ghosh, Koushik Majhi, Sadhanendu Samanta, Golam Kibriya,
and Alakananda Hajra*
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ABSTRACT: A general and practical method for the direct C−H amination of 2H-indazoles with a series of amines including
aliphatic primary amines, secondary amines, azoles, and sulfoximines via organophotoredox-catalyzed oxidative coupling has been
disclosed at room temperature under ambient air conditions. Additionally, this protocol is used for free aminated 2H-indazole
synthesis. A mechanistic study revealed that a single electron transfer (SET) pathway might be involved in this reaction.
chemistry and material sciences.11 In particular, anti-inflam-
he development of a practical method to build up the C−
TN bond is highly demanding in organic synthesis due to matory, antitumor, antimicrobial, HIV-protease inhibition,
anticancer, antiplatelet, antidepressant drugs, etc. are shown
by indazole. Some marketed drugs like bendazac (nonsteroidal
anti-inflammatory drug), pazopanib or votrient (tyrosine
kinase inhibitor), MK-4827 (anticancer agent), etc. contain
an indazole skeleton.11,12 Importantly, indazole derivatives
have elite photophysical properties and are used as fluorescent
probes.13 On the other hand, aliphatic amines and azoles are
important structural features, present in natural products and
pharmaceuticals.14 Therefore, the development of a practical
methodology for the synthesis of amino-substituted 2H-
indazoles is highly desirable.
In recent times, visible-light-mediated photoredox-catalyzed
reactions offer an intriguing opportunity to explore modern
organic transformations.15 Organic redox-active molecules are
employed as superior alternatives to their metal counterparts
due to their nontoxicity, synthetic usefulness, and better
environmental perspective.16 However, to the best of our
knowledge, C−H amination reaction of 2H-indazoles is not yet
established in the current literature.17 With our continuous
efforts on photochemical C−H functionalization of hetero-
cycles,18 herein we wish to report a strategy of organo-
photoredox-catalyzed direct C−H amination of 2H-indazoles
the extensive manifestation of nitrogen-containing molecules in
natural products, pharmaceuticals, agrochemicals, and polymer
sciences.1 Transition-metal-catalyzed Buchwald−Hartwig, Ull-
mann−Goldberg, and Chan−Lam cross couplings are great
achievements in this field.2 In addition, the photochemical and
thermal decomposition of the N−X bond (X = N, O, S,
halogen) into a N-centered radical offers a concise route for
oxidative C−H amination of various arenes.3,4 Classical
methods on radical amination of arenes with N-chloroamines
under strong acidic conditions were reported by Minisci,5a
Chow,5b and Kompa.5c Harsh reaction conditions, limited
substrate scope, and tedious synthetic steps to preincorporate
the functional groups in the substrate sometimes diminish the
synthetic utility of these methodologies. As an alternative, C−
H/N−H oxidative cross-coupling reactions have recently
acquired much attention because of their straightforwardness
and high atom economy.6 Normally, transition-metal catalysts
along with terminal oxidants are used for such a C−N bond
formation.7 In some cases, a stoichiometric amount of
hypervalent iodine reagents is extensively utilized for amination
reactions.8 Recently, photocatalytic C−H amination has gained
considerable attention.9,10 For example, Nicewicz et al.
reported a breakthrough work for the direct C−H amination
of activated arenes with azoles and primary aliphatic amines.9
Received: June 12, 2020
Similarly, a dual catalytic system was also introduced by Lei10a
10b
̈
and Konig for the generation and utilization of various N-
centered radicals.
Indazoles as a privileged skeleton of nitrogen-containing
fused heterocycles are widely used in the field of medicinal
https://dx.doi.org/10.1021/acs.orglett.0c01973
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

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Letter
with primary and secondary amines, azoles, and sulfoximine
(Scheme 1).
depicted in Scheme 2. At first, the effect of different substituent
on the phenyl ring of 2H-indazole derivatives was examined. In
a b
,
Scheme 2. Scope of 2H-Indazoles
Scheme 1. C−H Amination Reactions of 2H-Indazoles
We commenced our study by taking 2-(p-tolyl)-2H-indazole
(1b) and morpholine (2a) as model substrates (Table 1).
a
Table 1. Optimization of the Reaction Conditions
entry
photocatalyst
solvent
yields (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
Acr+-MesClO4
TPPT
eosin Y
rhodamin 6G
rose bengal
Ru(bpy)3Cl2·6H2O
-
Acr+-MesClO4
Acr+-MesClO4
CH3CN
THF
toluene
DCM
1,2-DCE
1,4-dioxane
DMSO
DMF
65
48
55
68
86
trace
21
nr
nr
27
nr
nr
nr
a
Reaction conditions: 0.2 mmol of 1, 0.6 mmol of 2a in the presence
of 3 mol % of Acr+-MesClO4 in 2 mL of 1,2-DCE at room
b
c
temperature under blue LED. Isolated yields. 5 mmol scale.
d
Reaction time 10 h.
this case, a series of 3-amino 2H-indazole derivatives were
achieved in good to excellent yields (3aa−3na). 2H-Indazole
derivatives bearing −Me, −OMe, and halogen like −F and −Cl
substituents at the para position afforded the corresponding
products in moderate to good yields (3aa−3ea). Interestingly
−CO2Et-substituted indazole also reacted well with 2a to give
3fa in 80% yield. Gratifyingly, meta-substituted 2H-indazole
derivatives effectively provided the desired aminated products
in synthetically useful yields (3ga−3ia). Moreover, some
disubstituted indazoles were compatible under the present
reaction conditions (3ja−3na). The gram-scale synthesis was
also executed taking 2-(p-tolyl)-2H-indazole (1b) and
morpholine (2a). The yield of coupling product 3ba did not
decrease significantly, which suggests the scalability and
practicality of the present protocol.
H2O
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
nr
nr
nr
nr
b
c
a
Reaction conditions: 1b (0.2 mmol), 2a (0.6 mmol), photocatalyst
b
c
(3 mol %), solvent (2 mL), 34 W blue LED. In the dark. Under
argon atmosphere. nr = no reaction.
Initially, the reaction was carried out using 3 equiv of
morpholine and 3 mol % of Acr+-MesClO4 (9-mesityl-10-
methylacridinium ion) as photocatalyst in CH3CN under
ambient air and blue LED irradiation. Pleasingly, the desired
coupling product 3ba was obtained in 65% yield after 24 h
(Table 1, entry 1). Being motivated by this initial result,
various common solvents were screened including THF,
toluene, DCM, 1,2-DCE, 1,4-dioxane, DMSO, DMF, and
H2O (Table 1, entries 2−9). Among these, 1,2-DCE was
proved to be the best choice, and the product was obtained in
86% yield (Table 1, entry 5). Further optimization was
performed with various photocatalysts like TPPT (2,4,6-
triphenylpyrylium tetrafluoroborate), eosin Y, rhodamine 6G,
rose bengal, and Ru(bpy)3Cl2·6H2O (Table 1, entries 10−14).
However, they were less effective than Acr+-MesClO4.
Moreover, no formation of product was observed in the
absence of any photocatalyst as well as under dark conditions
and an argon atmosphere (Table 1, entries 15−17). Finally,
the optimal reaction conditions were attained using 3 mol % of
Acr+-MesClO4 in 1,2-DCE under ambient air and blue LED
irradiation at room temperature for 24 h (Table 1, entry 5).
With the optimized protocol for amination reaction, the
scope of this methodology was investigated, and the results are
To acquire the generality of the current reaction, a variety of
amines were scrutinized as shown in Scheme 3.
Different secondary amines like piperidine, 2,6-dimethyl-
morpholine, and thiomorpholine underwent the amination
smoothly to afford the desired coupling products in moderate
to good yields (3bb−3gd). In addition, a variety of primary
amines gave the anticipated product in good yields (3be−3aj).
However, some other amines, such as aniline, dibenzylamine,
and diphenylamine, failed to produce the desired products
under these optimized conditions.
Similarly, a series of 3-sulfoximino-2H-indazole derivatives
were obtained by the reaction between different substituted
2H-indazoles and sulfoximine (Scheme 4). Interestingly −CF3-
and NO2-substituted indazoles were also compatible with the
present protocol in producing the products in good yields (3pk
and 3qk).
The present protocol was successfully applied to the
coupling of 2H-indazoles with other aromatic heterocycles
including pyrazole, imidazole, benzimidazole, and triazole
derivatives (Scheme 5). In all the cases, it afforded the desired
product in excellent yields (3bl−3bp). Pleasingly, free
aminated product was also obtained under the present reaction
B
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Letter
a b
,
a b
,
Scheme 3. Substrate Scope with Variation of Amines
Scheme 5. Substrate Scope of Heteroaromatic Amines
a
Reaction conditions: 0.2 mmol of 1, 0.6 mmol of 2 in the presence of
3 mol % of Acr+-MesClO4 in 2 mL of 1,2-DCE at room temperature
under blue LED. Isolated yields. NH4 CO2NH2 is used as the
b
c
+
−
amine source.
Scheme 6. Control Experiments
a
Reaction conditions: 0.2 mmol of 1, 0.6 mmol of 2 in the presence of
3 mol % of Acr+-MesClO4 in 2 mL of 1,2-DCE at room temperature
under blue LED. Isolated yields. Reaction time 28 h.
b
c
a
Scheme 4. Scope of 2H-Indazoles with Sulfoximine
a
Reaction conditions: 0.2 mmol of 1, 0.6 mmol of 2k in the presence
of 3 mol % of Acr+-MesClO4 in 2 mL of 1,2-DCE at room
temperature under a blue LED.
(DABCO)20 which suggests that singlet oxygen is not
necessary for this cross-coupling reaction (Scheme 6, eq D).
The redox potentials of 1b, 2a, 2f, 2k, and Acr+-MesClO4
were evaluated by cyclic voltammetry (see SI), and
conditions using ammonium carbamate as the amine source
(3bq and 3mq).
To find out more about the reaction mechanism, a few
control experiments were carried out (Scheme 6). The yield of
the reaction was decreased in the presence of radical
scavengers like 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO), 2,6-di-tert-butyl-4-methyl phenol (BHT), and
2,3-dichloro-5,6-dicyano-1,p-benzoquinone (DDQ) (Scheme
6, eq A). However, 2-(p-tolyl)-2H-indazole (1b) reacted well
with BHT (4) to produce the radical adduct 2,6-di-tert-butyl-4-
((2-(p-tolyl)-2H-indazol-3-yl)methyl)phenol (5) in 54% yield
(Scheme 6, eq B).
These observations indicate that the radical process might
be involved in this reaction. In addition, when benzoquinone
(BQ), a superoxide quencher,19 was employed in the reaction,
only a trace amount of product was achieved (Scheme 6, eq
C). The present reaction was not inhibited by the addition of a
singlet oxygen quencher like 1,4-diazabicyclo[2.2.2]octane
+
E1/2(PC */PC•) was also calculated (see SI). The fluorescence
quenching experiment of the photocatalyst in the presence of
various quenchers was also performed. Based upon the above
experimental outcome and literature reports,9 a plausible
mechanistic proposal is described in Scheme 7. A single
electron transfer (SET) from 2H-indazole to the excited state
of Acr+-MesClO4 (Acr+*) provided the radical cation
intermediate (A) and photocatalyst radical Acr• (for details
see the SI). Although amines (2a, 2f, and 2k) hold similar
oxidation potentials to those of the indazole (1b), the
formation of an amine cation radical could also be possible.9
However, a fluorescence quenching study shows that indazole
has an almost double S−V quenching constant value compared
to amines, and thereby indazole participates in the SET process
with the photocatalyst (see SI). The photoredox cycle is
C
https://dx.doi.org/10.1021/acs.orglett.0c01973
Org. Lett. XXXX, XXX, XXX−XXX

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pubs.acs.org/OrgLett
Letter
Asim Kumar Ghosh − Department of Chemistry, Visva-Bharati
(A Central University), Santiniketan 731235, India
Koushik Majhi − Integrated Science Education & Research
Centre, Visva-Bharati (A Central University), Santiniketan
731235, India
Scheme 7. Plausible Mechanistic Pathway
Sadhanendu Samanta − Department of Chemistry, Visva-
Bharati (A Central University), Santiniketan 731235, India;
orcid.org/0000-0003-2215-9189
Golam Kibriya − Department of Chemistry, Visva-Bharati (A
Central University), Santiniketan 731235, India
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01973
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
A.H. acknowledges the financial support from CSIR, New
Delhi (Grant no. 02(0307)/17/EMR-II). S.N. and A.K.G.
thank CSIR for their fellowship.
•−
completed by O2 through superoxide radical anion (O2
)
formation. Consequently, addition of amine (2) to the 2-(p-
toly)-2H-indazole radical cation (A) affords intermediate B.
Then, O2•− abstracts a proton from B to produce C and HO2 .
•
REFERENCES
Here we could not rule out the possibility of radical-chain
propagation as we were unable to perform the quantum yield
calculation in our system. Therefore, it is plausible that transfer
■
(1) (a) Candeias, N. R.; Branco, L. C.; Gois, P. M. P.; Afonso, C. A.
M.; Trindade, A. F. Chem. Rev. 2009, 109, 2703−2802. (b) Amino
Group Chemistry, From Synthesis to the Life Sciences; Ricci, A., Ed.;
Wiley-VCH: Weinheim, 2007. (c) Hili, R.; Yudin, A. K. Nat. Chem.
Biol. 2006, 2, 284−287.
(2) (a) Brasche, G.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008, 47,
1932−1934. (b) Hartwig, J. F. Acc. Chem. Res. 2008, 41, 1534−1544.
(c) Hatakeyama, T.; Yoshimoto, Y.; Ghorai, S. K.; Nakamura, M. Org.
Lett. 2010, 12, 1516−1519.
(3) (a) Zard, S. Z. Chem. Soc. Rev. 2008, 37, 1603−1618. (b) Chen,
J.-R.; Hu, X.-Q.; Lu, L.-Q.; Xiao, W.-J. Chem. Soc. Rev. 2016, 45,
2044−2056. (c) Xiong, T.; Zhang, Q. Chem. Soc. Rev. 2016, 45,
3069−3087.
(4) (a) Kawano, T.; Hirano, K.; Satoh, T.; Miura, M. J. Am. Chem.
Soc. 2010, 132, 6900−6901. (b) Yoo, E. J.; Ma, S.; Mei, T.-S.; Chan,
K. S. L.; Yu, J.-Q. J. Am. Chem. Soc. 2011, 133, 7652−7655. (c) Allen,
L. J.; Cabrera, P. J.; Lee, M.; Sanford, M. S. J. Am. Chem. Soc. 2014,
•
of an electron from 2H-indazole (1b) to HO2 initiates the
radical chain process.15g Finally, HO2 abstracts a hydrogen
•
from intermediate C to afford the coupling product 3 together
with H2O2. The detection of H2O2 is performed by a starch−
iodine experiment (see SI).
In conclusion, we have established an efficient organo-
photoredox-catalyzed strategy for the direct C−H amination of
2H-indazoles using a series of primary and secondary aliphatic
amines, azoles, and sulfoximines under ambient air in high
yields. Broad functional group tolerance, scalability, metal- and
oxidant-free reaction conditions, and step- and atom-
economical routes associated with this C−N bond formation
imply its great potential for widespread applications in organic
synthesis and pharmaceutical research. As far as we know, this
is the first report for the synthesis of 3-amino-substituted 2H-
indazoles. We believe this visible-light-induced metal- and
oxidant-free C−H amination strategy makes this reaction more
suitable for further synthetic applications in both academic
institutes and industries.
́
136, 5607−5610. (d) Foo, K.; Sella, E.; Thome, I.; Eastgate, M. D.;
Baran, P. S. J. Am. Chem. Soc. 2014, 136, 5279−5282. (e) Matsubara,
T.; Asako, S.; Ilies, L.; Nakamura, E. J. Am. Chem. Soc. 2014, 136,
646−649.
(5) (a) Minisci, F. Synthesis 1973, 1973, 1−24. (b) Chow, Y. L.;
Danen, W. C.; Nelsen, S. F.; Rosenblatt, D. H. Chem. Rev. 1978, 78,
243−274. (c) Bock, H.; Kompa, K.-L. Angew. Chem., Int. Ed. Engl.
1965, 4, 783.
ASSOCIATED CONTENT
* Supporting Information
■
(6) (a) Louillat, M. L.; Patureau, F. W. Chem. Soc. Rev. 2014, 43,
901−910. (b) Monguchi, D.; Fujiwara, T.; Furukawa, H.; Mori, A.
Org. Lett. 2009, 11, 1607−1610. (c) Shrestha, P.; Mukherjee, P.; Tan,
Y.; Litman, Z. C.; Hartwig, J. F. J. Am. Chem. Soc. 2013, 135, 8480−
8483. (d) Wei, W.; Wang, L.; Bao, P.; Shao, Y.; Yue, H.; Yang, D.;
Yang, X.; Zhao, X.; Wang, H. Org. Lett. 2018, 20, 7125−7130.
(7) (a) Park, Y.; Kim, Y.; Chang, S. Chem. Rev. 2017, 117, 9247−
9301. (b) Wang, Q.; Schreiber, S. L. Org. Lett. 2009, 11, 5178−5180.
(c) Gephart, R. T.; Warren, T. H. Organometallics 2012, 31, 7728−
7752. (d) Sharma, U.; Kancherla, R.; Naveen, T.; Agasti, S.; Maiti, D.
Angew. Chem., Int. Ed. 2014, 53, 11895−11899. (e) Rit, R. K.;
Shankar, M.; Sahoo, A. K. Org. Biomol. Chem. 2017, 15, 1282−1293.
(f) Trowbridge, A.; Walton, S. M.; Gaunt, M. J. Chem. Rev. 2020, 120,
2613−2692.
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01973.
Experimental procedures and spectral data (PDF)
AUTHOR INFORMATION
Corresponding Author
■
Alakananda Hajra − Department of Chemistry, Visva-Bharati
(A Central University), Santiniketan 731235, India;
orcid.org/0000-0001-6141-0343;
Email: alakananda.hajra@visva-bharati.ac.in
(8) (a) Kantak, A. A.; Potavathri, S.; Barham, R. A.; Romano, K. M.;
DeBoef, B. J. Am. Chem. Soc. 2011, 133, 19960−19965. (b) Kim, H.
J.; Kim, J.; Cho, S. H.; Chang, S. J. Am. Chem. Soc. 2011, 133, 16382−
16385. (c) Manna, S.; Serebrennikova, P. O.; Utepova, I. A.;
Authors
Sukanya Neogi − Department of Chemistry, Visva-Bharati (A
Central University), Santiniketan 731235, India
D
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Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Antonchick, A. P.; Chupakhin, O. N. Org. Lett. 2015, 17, 4588−4591.
(d) Muniz, K. Acc. Chem. Res. 2018, 51, 1507−1519.
̃
(9) (a) Romero, N. A.; Margrey, K. A.; Tay, N. E.; Nicewicz, D. A.
Science 2015, 349, 1326−1330. (b) Margrey, K. A.; Levens, A.;
Nicewicz, D. A. Angew. Chem., Int. Ed. 2017, 56, 15644−15648.
(c) Tay, N. E. S.; Nicewicz, D. A. J. Am. Chem. Soc. 2017, 139,
16100−16104.
(10) (a) Niu, L.; Yi, H.; Wang, S.; Liu, T.; Liu, J.; Lei, A. Nat.
̈
Commun. 2017, 8, 14226. (b) Wimmer, A.; Konig, B. Adv. Synth.
Catal. 2018, 360, 3277−3285. (c) Ham, W. S.; Hillenbrand, J.; Jacq,
J.; Genicot, C.; Ritter, T. Angew. Chem., Int. Ed. 2019, 58, 532−536.
(d) Ruffoni, A.; Julia, F.; Svejstrup, T. D.; McMillan, A. J.; Douglas, J.
J.; Leonori, D. Nat. Chem. 2019, 11, 426−433.
(11) (a) Runti, C.; Baiocchi, L. Int. J. Tissue React. 1985, 7, 175−
186. (b) Qian, S.; Cao, J.; Yan, Y.; Sun, M.; Zhu, H.; Hu, Y.; He, Q.;
Yang, B. Mol. Cell. Biochem. 2010, 345, 13−21. (c) Han, W.; Pelletier,
J. C.; Hodge, C. N. Bioorg. Med. Chem. Lett. 1998, 8, 3615−3620.
(d) De Lena, M.; Lorusso, V.; Latorre, A.; Fanizza, G.; Gargano, G.;
Caporusso, L.; Guida, M.; Catino, A.; Crucitta, E.; Sambiasi, D.;
Mazzei, A. Eur. J. Cancer 2001, 37, 364−368.
(12) (a) Shen, H.; Gou, S.; Shen, J.; Zhu, Y.; Zhang, Y.; Chen, X.
Bioorg. Med. Chem. Lett. 2010, 20, 2115−2118. (b) Jia, Y.; Zhang, J.;
Feng, J.; Xu, F.; Pan, H.; Xu, W. Chem. Biol. Drug Des. 2014, 83, 306−
316.
(13) Cheng, Y.; Li, G.; Liu, Y.; Shi, Y.; Gao, G.; Wu, D.; Lan, J.; You,
J. J. Am. Chem. Soc. 2016, 138, 4730−4738.
(14) Dudakova, A.; Spiess, B.; Tangwattanachuleeporn, M.; Sasse,
C.; Buchheidt, D.; Weig, M.; Groß, U.; Bader, O. Clin. Microbiol. Rev.
2017, 30, 1065−1091.
(15) (a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
2013, 113, 5322−5363. (b) Narayanam, J. M. R.; Stephenson, C. R. J.
Chem. Soc. Rev. 2011, 40, 102−113. (c) Chatterjee, T.; Iqbal, N.; You,
Y.; Cho, E. J. Acc. Chem. Res. 2016, 49, 2284−2294. (d) Zhou, Q.-Q.;
Zou, Y.-Q.; Lu, L.-Q.; Xiao, W.-J. Angew. Chem., Int. Ed. 2019, 58,
1586−1604. (e) Jiang, H.; Studer, A. CCS Chem. 2019, 1, 38−49.
(f) Ding, W.; Ho, C. C.; Yoshikai, N. Org. Lett. 2019, 21, 1202−1206.
(g) Cismesia, M. A.; Yoon, T. P. Chem. Sci. 2015, 6, 5426−5434.
́
(16) (a) Joshi-Pangu, A.; Levesque, F.; Roth, H. G.; Oliver, S. F.;
Campeau, L.-C.; Nicewicz, D. A.; DiRocco, D. A. J. Org. Chem. 2016,
81, 7244−7249. (b) Fukuzumi, S.; Ohkubo, K. Chem. Sci. 2013, 4,
561−574. (c) Phelan, J. P.; Lang, S. B.; Compton, J. S.; Kelly, C. B.;
Dykstra, R.; Gutierrez, O.; Molander, G. A. J. Am. Chem. Soc. 2018,
̈
140, 8037−8047. (d) Ramirez, N. P.; Konig, B.; Gonzalez-Gomez.
Org. Lett. 2019, 21, 1368−1373.
(17) (a) Naas, M.; El Kazzouli, S.; Essassi, E. M.; Bousmina, M.;
Guillaumet, G. Org. Lett. 2015, 17, 4320−4323. (b) Murugan, A.;
Babu, V. N.; Polu, A.; Sabarinathan, N.; Bakthadoss, M.; Sharada, D.
S. J. Org. Chem. 2019, 84, 7796−7803. (c) Bogonda, G.; Kim, H. Y.;
Oh, K. Org. Lett. 2018, 20, 2711−2715. (d) Basu, K.; Poirier, M.;
Ruck, R. T. Org. Lett. 2016, 18, 3218−3221. (e) Guo, C.; Li, B.; Liu,
H.; Zhang, X.; Zhang, X.; Fan, X. Org. Lett. 2019, 21, 7189−7193.
(18) (a) Mitra, S.; Ghosh, M.; Mishra, S.; Hajra, A. J. Org. Chem.
2015, 80, 8275−8281. (b) Kibriya, G.; Mondal, S.; Hajra, A. Org. Lett.
2018, 20, 7740−7743. (c) Singsardar, M.; Mondal, S.; Laru, S.; Hajra,
A. Org. Lett. 2019, 21, 5606−5510.
(19) Guerrero-Corella, A.; Martinez-Gualda, A. M.; Ahmadi, F.;
́
Ming, E.; Fraile, A.; Aleman, J. Chem. Commun. 2017, 53, 10463−
10466.
(20) Keshari, T.; Yadav, V. K.; Srivastava, V. P.; Yadav, L. D. S.
Green Chem. 2014, 16, 3986−3992.
E
https://dx.doi.org/10.1021/acs.orglett.0c01973
Org. Lett. XXXX, XXX, XXX−XXX