Synthesis of Polysubstituted Pyrroles via Silver-Catalyzed Oxidative Radical Addition of Cyclopropanols to Imines

Article abstract of DOI:10.1021/acs.orglett.0c02735

A silver-catalyzed formal [3 + 2] cycloaddition reaction, with cyclopropanols as a C3 subunit and imines as a two-atom subunit, is developed. The reaction takes place under mild conditions and produces a broad array of polysubstituted pyrroles in medium t

Full text of DOI:10.1021/acs.orglett.0c02735

pubs.acs.org/OrgLett
Letter
Synthesis of Polysubstituted Pyrroles via Silver-Catalyzed Oxidative
Radical Addition of Cyclopropanols to Imines
†
†
Yulu Zhou, Mingchang Wu, Yi Liu, Cungui Cheng, and Gangguo Zhu*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c02735
Read Online
ACCESS
Metrics & More
Article Recommendations
*
sı Supporting Information
ABSTRACT: A silver-catalyzed formal [3 + 2] cycloaddition reaction, with
cyclopropanols as a C3 subunit and imines as a two-atom subunit, is
developed. The reaction takes place under mild conditions and produces a
broad array of polysubstituted pyrroles in medium to high yields. It represents
the first example of oxidative radical addition to imines, thus offering a new
choice for the direct C−H functionalization of imines.
adical addition reactions have become a very important
synthetic tool in organic synthesis, since they can
radical addition (ORA) to CN bonds remains a significant
challenge in organic chemistry.
R
Recently, the ORA to aldehyde-derived N,N-dialkylhydra-
zones has been successfully developed, providing an efficient
access to the direct C−H functionalization of hydrazones
assemble carbon−carbon and carbon−heteroatom bonds
under mild and nonbasic conditions that may be compatible
1
with various functional groups. With the fast development of
4
−8
(
Scheme 1b).
In this reaction manifold, the electron-
this field, the continuous expansion of the scope of radical
acceptors is in high demand. So far, CC bonds are the most
common radical acceptors. In contrast, CN bonds have been
much less utilized as acceptors for radical addition. Traditional
methods focus on the reductive radical addition to CN
bonds, in which an aminyl radical is generated, followed by
hydrogen atom abstraction (HAT) from the solvent or other
hydrogen atom sources to give α-branched amines as final
donating dialkylamine groups (NR ) can activate the carbon
2
atom of azomethine (CHN) toward electrophilic sub-
stitution. Therefore, the intermolecular addition is limited to
5
6
electrophilic radicals, such as fluoroalkyl, nitrogen, phos-
phine, and α-carbonyl alkyl ones.
of three-electron π-bonding interactions
7
8a,b
Moreover, the presence
5d,e
may stabilize the
aminyl radical intermediate and facilitate the subsequent single
electron transfer (SET) oxidation. Despite this important
progress, this strategy only works for aldehyde-derived
hydrazones, while the more common and readily available
imines, an important class of building blocks for the assembly
of synthetically attractive nitrogen-containing compounds, are
still unable to undergo the ORA reaction.
2
,3
products (Scheme 1a). Due to the high electronegativity of
the nitrogen atom, the oxidation of an aminyl radical is more
difficult than its reduction, and consequently, the oxidative
Scheme 1. Background and Summary of This Work
We have recently developed a new methodology for the
synthesis of cyclic or acyclic ketones via the ORA to
9
aldehydes. Inspired by this work, we would like to explore
the ORA reaction of imines. In view of the electrophilic
properties of iminyl CN bonds, we envisioned that
nucleophilic carbon radicals might serve as a good coupling
10
11
partner. Previous reports, including our work, indicated
that nucleophilic carbon-centered radicals could be efficiently
generated via the radical ring-opening of cyclopropanols.
Herein, we report a novel Ag-catalyzed formal [3 + 2]
cycloaddition reaction using cyclopropanols as a C3 subunit
Received: August 16, 2020
©
XXXX American Chemical Society
https://dx.doi.org/10.1021/acs.orglett.0c02735
A
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
a
and imines as a two-atom subunit, in which a wide range of
polysubstituted pyrroles can be efficiently synthesized from
readily attained starting materials under mild conditions
Scheme 2. Scope with Respect to the Imines
(
Scheme 1c). The reaction constitutes the first example of
ORA to imines, thus providing a new strategy for the radical
transformation of imines.
To verify the feasibility, the 4-cyanobenzaldehyde-derived
imine 1a and cyclopropanol 2a were chosen as the model
substrates for screening the reaction parameters. Initially, the
reaction was evaluated at 50 °C with 10 mol % of AgNO as
3
the catalyst, 3 equiv of Na S O as the oxidant, and dimethyl
2
2
8
sulfoxide (DMSO) as the solvent. To our delight, the 1,2,5-
trisubstituted pyrrole 3aa was isolated in 71% yield (Table 1,
a
Table 1. Optimization of Reaction Conditions
b
entry
[M]
oxidant
solvent
yield (%)
1
2
3
4
5
6
7
8
9
AgNO3
AgOAc
Na S O
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
MeCN
NMP
DMSO
DMSO
71
65
32
43
77
40
81 (76)
trace
22
2
2
8
8
8
8
8
Na S O
2
2
Ag CO3
Na S O
2 2
2
AgBF4
Na S O
2 2
AgO CCF3
Na S O
2 2
2
AgO CCF3
K S O
2 2 8
2
c
AgO CCF3
(NH ) S O
2
4
2
2
8
8
8
8
8
8
AgO CCF3
(NH ) S O
2
4 2 2
AgO CCF3
(NH ) S O
2
4 2 2
1
1
1
0
1
2
AgO CCF3
(NH ) S O
trace
49
15
2
4 2 2
d
AgO CCF3
(NH ) S O
2
4 2 2
none
(NH ) S O
4
2 2
a
Reaction conditions: 1a (0.25 mmol), 2a (0.5 mmol), [M] (10 mol
b
%
), oxidant (0.75 mmol), solvent (6 mL), 50 °C, 10 h. Isolated yield.
c
d
Yield on a 1.0 mmol scale. 0.5 mmol of (NH ) S O was used.
4
2
2
8
entry 1). A couple of silver catalysts were then screened under
the selected conditions (entries 2−5). When AgO CCF was
2
3
employed as the catalyst, the yield was increased to 77% (entry
5
). Afterward, the effect of oxidants was examined, which
showed (NH ) S O to be the most suitable choice, delivering
4
2
2
8
3
aa in 81% yield (entry 7). Running the reaction in other
solvents, such as N,N-dimethylformamide (DMF), acetonitrile
MeCN), and N-methylpyrrolidinone (NMP), led to reduced
(
efficiencies (entries 8−10). The control experiment demon-
strated that AgO CCF is crucial for this Ag-catalyzed formal
2
3
[
3 + 2] cycloaddition reaction (entry 12).
After determining the optimized reaction conditions, the
scope of this reaction was explored in the context of various
imines using 2a as the coupling partner (Scheme 2). The 4-
and 2-methyl benzenamine-derived imines 1b and 1c afforded
the expected pyrroles 3ba and 3ca in comparable yields,
2
suggesting that the steric hindrance of the R group has little
impact on the reaction. N-Arylimines bearing Me, F, Cl, Br, I,
OMe, and CF were all competent substrates, furnishing the
3
corresponding 1,2,5-trisubstituted pyrroles in moderate to high
yields (3ba−3ia). 4-Methoxyaniline-derived imine 1h afforded
the anticipated product 3ha in 83% yield, while 4-
trifluoromethylaniline-derived imine 1i delivered the corre-
sponding pyrrole 3ia in 37% yield. These results indicated that
substitution of the nitrogen atom of imines with an electron-
deficient benzene ring is unfavorable for the reaction.
a
Reaction conditions: 1 (0.25 mmol), 2a (0.5 mmol), AgO CCF (10
2
3
mol %), (NH ) S O (0.75 mmol), DMSO (6 mL), 50 °C, 10 h.
Yields of isolated products are given. AgNO3 (10 mol %) and
Na S O (0.75 mmol) were used.
4
2
2
8
b
2
2
8
B
https://dx.doi.org/10.1021/acs.orglett.0c02735
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
In addition to N-aryl imines, we also examined the reaction
of N-alkyl imines. The coupling of N-n-Bu imine 1j with 2a
occurred as well, albeit in a low yield (3ja). In contrast, this
reaction could not be extended to the N-sulfonyl imine 1k.
Modulation of the aryl ring of R1 group with various
substituents was feasible. Both the electron-donating (1l)
and electron-withdrawing groups (1r−1t) were well tolerated
under the reaction conditions, and relatively higher yields were
observed for the latter cases (3ra−3ta). Additionally, imines
with heteroaryl groups like pyridine underwent the reaction
uneventfully to produce the desired pyrrole in high yield
To make this method more practical, a one-pot, three-
component reaction of 4, 5, and 2a was conducted, which
successfully delivered the expected product 3aa in a reasonable
yield (not optimized) (Scheme 4). As such, the method
Scheme 4. Three-Component Reaction
1
2
(3ua). The imine 1v (R = n-Bu, R = 4-tol), derived from an
presented here represents an operationally simple, mild, and
efficient process for the assembly of pyrroles, which are
important heteroaromatic compounds and versatile structural
motifs found in natural products, functional material,
aliphatic aldehyde, failed to provide the expected product
under the conditions.
Subsequently, we focused on investigation of the effects of
the cyclopropanol structure. As shown in Scheme 3, the
12
pharmaceuticals, and agrochemicals.
Some experiments were conducted to probe the reaction
mechanism of this Ag-catalyzed ORA of cyclopropanols to
imines (Scheme 5). The formation of 3aa was completely
a
Scheme 3. Scope with Respect to the Cyclopropanols
Scheme 5. Mechanistic Studies
suppressed by adding 2 equiv of 2,2,6,6-tetramethylpiperidi-
nooxy (TEMPO) to the standard reaction conditions (Scheme
a
Reaction conditions: 1a (0.25 mmol), 2 (0.5 mmol), AgO CCF (10
2
3
5
a). The addition of 1,1-diphenylethylene also shut down the
reaction and produced the alkenyl product 6a in 21% yield
Scheme 5b). These results indicated that the radical ring-
mol %), (NH ) S O (0.75 mmol), DMSO (6 mL), 50 °C, 10 h.
Yields of isolated products are given.
4
2
2
8
(
opening of cyclopropanols was feasible under the reaction
conditions. The competitive reaction between 1a and 1l
afforded a 4.7:1 mixture 3aa and 3la in 51% yield (Scheme 5c),
suggesting that the electron-deficient aldehyde-derived imines
are better radical acceptors. A 1:1 mixture of 1e and 1h was
subjected to the reaction conditions. After being stirred at 50
°C for 4 h, a 4.1:1 mixture of 3ha and 3ea was obtained
(Scheme 5d), which demonstrated that electron-rich amine-
derived imines are better coupling partners.
reaction of both 1-aryl- and 1-alkyl-substituted cyclopropanols
proceeded smoothly to form the desired 1,2,5-trisubstituted
pyrroles in reasonable yields (3ab−3ag). 2-Substituted cyclo-
propanols such as 2h and 2i were also amenable to this
reaction, which produced the 1,2,3,5-tetrasubstituted pyrroles
3
ah and 3ai in 67% and 62% yield, respectively, thus providing
an attractive method for the direct synthesis of polysubstituted
pyrroles from readily attained starting materials. It should be
noted that halogen atoms, such as bromine and chlorine, were
well tolerated for this [3 + 2] cycloaddition process, which may
offer a useful handle for further elaboration of the pyrrole
products.
5d,e
On the basis of the above results and previous reports,
a
possible reaction mechanism is depicted in Scheme 6 using
substrates 1a and 2a. Initially, the oxidation of cyclopropanol
2
8
−
2a by AgSO , generated from Ag(I) and S O , produces a
4
2
C
https://dx.doi.org/10.1021/acs.orglett.0c02735
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Scheme 6. Proposed Mechanism
Authors
Yulu Zhou − Key Laboratory of the Ministry of Education for
Advanced Catalysis Materials, Department of Chemistry,
Zhejiang Normal University, Jinhua 321004, P.R. China
Mingchang Wu − Key Laboratory of the Ministry of Education
for Advanced Catalysis Materials, Department of Chemistry,
Zhejiang Normal University, Jinhua 321004, P.R. China
Yi Liu − Key Laboratory of the Ministry of Education for
Advanced Catalysis Materials, Department of Chemistry,
Zhejiang Normal University, Jinhua 321004, P.R. China
Cungui Cheng − Key Laboratory of the Ministry of Education
for Advanced Catalysis Materials, Department of Chemistry,
Zhejiang Normal University, Jinhua 321004, P.R. China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c02735
Author Contributions
†
Y.Z. and M.W. contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
1
1
■
cycloalkanoxyl radical A. The ring-opening of A followed by
the intermolecular radical addition to 1a affords an aminyl
radical C. SET oxidation of C by sulfate radical (SO4• ) and a
subsequent deprotonation (path a) or a concerted proton-
coupled electron transfer (PCET, path b) between C and
This work was supported by the Natural Science Foundation
of Zhejiang Province (LZ20B020001) and the National
Natural Science Foundation of China (21672191).
−
REFERENCES
•‑
■
SO4 may produce the ketone-imine intermediate E, which
undergoes the intramolecular addition of nitrogen atom to
carbonyl group followed by release of H O to generate the
(
1) For selected reviews, see: (a) Ryu, I.; Sonoda, N.; Curran, D. P.
Chem. Rev. 1996, 96, 177. (b) Renaud, P.; Gerster, M. Angew. Chem.,
Int. Ed. 1998, 37, 2562. (c) Sibi, M. P.; Manyem, S.; Zimmerman, J.
Chem. Rev. 2003, 103, 3263.
2) For selected reviews, see: (a) Friestad, G. K. Tetrahedron 2001,
57, 5461. (b) Miyabe, H.; Ueda, M.; Naito, T. Synlett 2004, 1140.
(c) Miyabe, H. Synlett 2012, 23, 1709.
(3) For selected examples, see: (a) Friestad, G. K.; Qin, J. J. Am.
Chem. Soc. 2000, 122, 8329. (b) Friestad, G. K.; Shen, Y.; Ruggles, E.
Angew. Chem., Int. Ed. 2003, 42, 5061. (c) Cullen, S. T. J.; Friestad, G.
K. Org. Lett. 2019, 21, 8290. (d) Torrente, S.; Alonso, R. Org. Lett.
001, 3, 1985. (e) Miyabe, H.; Ueda, M.; Nishimura, A.; Naito, T.
Org. Lett. 2002, 4, 131. (f) Rono, L. J.; Yayla, H. G.; Wang, D. Y.;
Armstrong, M. F.; Knowles, R. R. J. Am. Chem. Soc. 2013, 135, 17735.
g) Hager, D.; MacMillan, D. W. C. J. Am. Chem. Soc. 2014, 136,
6986. (h) Vo, C.-V. T.; Luescher, M. U.; Bode, J. W. Nat. Chem.
2014, 6, 310. (i) Hsieh, S.-Y.; Bode, J. W. Org. Lett. 2016, 18, 2098.
(j) Fujii, S.; Konishi, T.; Matsumoto, Y.; Yamaoka, Y.; Takasu, K.;
Yamada, K.-i. J. Org. Chem. 2014, 79, 8128. (k) Patel, N. R.; Kelly, C.
B.; Siegenfeld, A. P.; Molander, G. A. ACS Catal. 2017, 7, 1766.
2
13
pyrrole 3aa as the final product. Although the isolation of
intermediate E was unsuccessful under the reaction conditions,
its intermediacy could be confirmed by the HRMS analysis.
The p−π conjugating effect between the phenyl group and
aminyl radical C or aminyl cation D may facilitate the
transformation.
In conclusion, a novel method for the direct synthesis of
polysubstituted pyrroles has been established via a Ag-
catalyzed formal [3 + 2] cycloaddition reaction, featuring the
use of cyclopropanols as a C3 subunit and imines as a two-
atom subunit. The pyrrole motif is constructed from two
readily available components in a convergent fashion, thus
offering a highly efficient and attractive approach to access
polysubstituted pyrroles. This reaction constitutes the first
example of the ORA to simple imines, which provides a new
approach for the direct C−H functionalization of imines.
(
2
(
1
(
l) Nam, T. K.; Jang, D. O. J. Org. Chem. 2018, 83, 7373. (m) Li, Y.;
Zhou, K.; Wen, Z.; Cao, S.; Shen, X.; Lei, M.; Gong, L. J. Am. Chem.
Soc. 2018, 140, 15850. (n) Han, B.; Li, Y.; Yu, Y.; Gong, L. Nat.
Commun. 2019, 10, 1. (o) Sakamoto, R.; Tomomi Yoshii; Takada, H.;
Maruoka, K. Org. Lett. 2018, 20, 2080. (p) Bissonnette, N. B.; Ellis, J.
M.; Hamann, L. G.; Romanov-Michailidis, F. Chem. Sci. 2019, 10,
ASSOCIATED CONTENT
sı Supporting Information
■
*
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c02735.
9
2
2
591. (q) Supranovich, V. I.; Levin, V. V.; Dilman, A. D. Org. Lett.
019, 21, 4271. (r) Jia, J.; Lefebvre, Q.; Rueping, M. Org. Chem. Front.
020, 7, 602.
Detailed experimental procedures; characterization data
for the products 3 and 6 (PDF)
(
4) For selected reviews,see: (a) Xu, P.; Li, W.; Xie, J.; Zhu, C. Acc.
AUTHOR INFORMATION
Corresponding Author
Chem. Res. 2018, 51, 484. (b) Xu, X.; Zhang, J.; Xia, H.; Wu, J. Org.
Biomol. Chem. 2018, 16, 1227. (c) Prieto, A.; Bouyssi, D.; Monteiro,
N. Eur. J. Org. Chem. 2018, 2018, 2378.
■
Gangguo Zhu − Key Laboratory of the Ministry of Education for
Advanced Catalysis Materials, Department of Chemistry,
Zhejiang Normal University, Jinhua 321004, P.R. China;
orcid.org/0000-0003-4384-824X; Email: gangguo@
zjnu.cn
(
5) (a) Pair, E.; Monteiro, N.; Bouyssi, D.; Baudoin, O. Angew.
Chem., Int. Ed. 2013, 52, 5346. (b) Prieto, A.; Melot, R.; Bouyssi, D.;
Monteiro, N. Angew. Chem., Int. Ed. 2016, 55, 1885. (c) Prieto, A.;
Melot, R.; Bouyssi, D.; Monteiro, N. ACS Catal. 2016, 6, 1093.
(d) Xu, P.; Wang, G.; Zhu, Y.; Li, W.; Cheng, Y.; Li, S.; Zhu, C.
D
https://dx.doi.org/10.1021/acs.orglett.0c02735
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Angew. Chem., Int. Ed. 2016, 55, 2939. (e) Xie, J.; Zhang, T.; Chen, F.;
Mehrkens, N.; Rominger, F.; Rudolph, M.; Hashmi, A. S. K. Angew.
Chem., Int. Ed. 2016, 55, 2934. (f) Xie, J.; Li, J.; Wurm, T.; Weingand,
V.; Sung, H.-L.; Rominger, F.; Rudolph, M.; Hashmi, A. S. K. Org.
Chem. Front. 2016, 3, 841. (g) Ke, M.; Song, Q. J. Org. Chem. 2016,
8
1, 3654. (h) Janhsen, B.; Studer, A. J. Org. Chem. 2017, 82, 11703.
i) Xu, X.; Liu, F. Org. Chem. Front. 2017, 4, 2306.
6) (a) Zhang, M.; Duan, Y.; Li, W.; Xu, P.; Cheng, J.; Yu, S.; Zhu,
(
(
C. Org. Lett. 2016, 18, 5356. (b) Wu, Z.; Xu, P.; Zhou, N.; Duan, Y.;
Zhang, M.; Zhu, C. Chem. Commun. 2017, 53, 1045. (c) Zhu, X.; He,
Z.; Li, Q.; Wang, X. RSC Adv. 2017, 7, 25171.
(
(
7) Xu, P.; Wu, Z.; Zhou, N.; Zhu, C. Org. Lett. 2016, 18, 1143.
8) (a) Cheng, J.; Xu, P.; Li, W.; Cheng, Y.; Zhu, C. Chem. Commun.
2
016, 52, 11901. (b) Fan, X.; Lei, T.; Zhou, C.; Meng, Q.; Chen, B.;
Tung, C.; Wu, L. J. Org. Chem. 2016, 81, 7127. (c) Zhou, N.; Liu, J.;
Yan, Z.; Wu, Z.; Zhang, H.; Li, W.; Zhu, C. Chem. Commun. 2017, 53,
2
(
036.
9) (a) Che, C.; Huang, Q.; Zheng, H.; Zhu, G. Chem. Sci. 2016, 7,
134. (b) Zhang, Y.; Guo, D.; Ye, S.; Liu, Z.; Zhu, G. Org. Lett. 2017,
4
1
2
9, 1302. (c) Lu, D.; Wan, Y.; Kong, L.; Zhu, G. Org. Lett. 2017, 19,
929. (d) Liu, Z.; Bai, Y.; Zhang, J.; Yu, Y.; Tan, Z.; Zhu, G. Chem.
Commun. 2017, 53, 6440. (e) Chen, Y.; Shu, C.; Luo, F.; Xiao, X.;
Zhu, G. Chem. Commun. 2018, 54, 5373. For a review, see: (f) Kong,
L.; Zhou, Y.; Luo, F.; Zhu, G. Youji Huaxue 2018, 38, 2858.
(
10) For selected reports on radical transformation of cyclo-
propanols, see: (a) Ilangovan, A.; Saravanakumar, S.; Malayappasamy,
S. Org. Lett. 2013, 15, 4968. (b) Zhao, H.; Fan, X.; Yu, J.; Zhu, C. J.
Am. Chem. Soc. 2015, 137, 3490. (c) Fan, X.; Zhao, H.; Yu, J.; Bao, X.;
Zhu, C. Org. Chem. Front. 2016, 3, 227. (d) Bloom, S.; Bume, D. D.;
Pitts, C. R.; Lectka, T. Chem. - Eur. J. 2015, 21, 8060. (e) Kananovich,
D. G.; Konik, Y. A.; Zubrytski, D. M.; Jarving, I.; Lopp, M. Chem.
̈
Commun. 2015, 51, 8349. (f) Li, Y.; Ye, Z.; Bellman, T. M.; Chi, T.;
Dai, M. Org. Lett. 2015, 17, 2186. (g) Wang, S.; Guo, L.-N.; Wang,
H.; Duan, X.-H. Org. Lett. 2015, 17, 4798. (h) Jia, K.; Zhang, F.;
Huang, H.; Chen, Y. J. Am. Chem. Soc. 2016, 138, 1514. (i) Wang, C.-
Y.; Song, R.-J.; Xie, Y.-X.; Li, J.-H. Synthesis 2016, 48, 223.
(
j) Nikolaev, A.; Legault, C. Y.; Zhang, M.; Orellana, A. Org. Lett.
018, 20, 796. (k) Wozniak, Ł.; Magagnano, G.; Melchiorre, P.
2
́
Angew. Chem., Int. Ed. 2018, 57, 1068. (l) Liu, Q.; Xie, G.; Wang, Q.;
Mo, Z.; Li, C.; Ding, S.; Wang, X. Tetrahedron 2019, 75, 130490.
(
m) Cheng, B.-Q.; Zhang, S.-X.; Cui, Y.-Y.; Chu, X.-Q.; Rao, W.; Xu,
H.; Han, G.-Z.; Shen, Z.-L. Org. Lett. 2020, 22, 5456. (n) Wu, L.;
Wang, L.; Chen, P.; Guo, Y.-L.; Liu, G. Adv. Synth. Catal. 2020, 362,
2
(
2
(
189.
11) Che, C.; Qian, Z.; Wu, M.; Zhao, Y.; Zhu, G. J. Org. Chem.
018, 83, 5665.
12) For selected reviews, see: (a) Estev
Menendez, J. C. Chem. Soc. Rev. 2014, 43, 4633. (b) Bhardwaj, V.;
Gumber, D.; Abbot, V.; Dhiman, S.; Sharma, P. RSC Adv. 2015, 5,
5233. (c) Gholap, S. S. Eur. J. Med. Chem. 2016, 110, 13.
13) Yasuda, M.; Shibata, Y.; Baba, A.; Matsuda, H.; Sonoda, N. J.
Org. Chem. 1994, 59, 4386.
́
ez, V.; Villacampa, M.;
́
1
(
E
https://dx.doi.org/10.1021/acs.orglett.0c02735
Org. Lett. XXXX, XXX, XXX−XXX