Iodine/Manganese Dual Catalysis for Oxidative Dehydrogenation Coupling of Amines with Thiols

Article abstract of DOI:10.1021/acs.orglett.9b02545

A novel dual catalytic system of iodine and manganese is used for the first time for oxidative dehydrogenation coupling of amines with thiols during aerobic oxidation. Sulfenamides are synthesized via this approach with moderate to high efficiencies. The mechanistic studies indicate that activated MnO₂ is an electron transfer bridge for assisting iodine in completing the catalytic cycle.

Full text of DOI:10.1021/acs.orglett.9b02545

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Iodine/Manganese Dual Catalysis for Oxidative Dehydrogenation
Coupling of Amines with Thiols
Shengping Liu,† Zaojuan Qi,‡ Zhang Zhang,*,† and Bo Qian*,‡
†Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical
Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
‡State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, Lanzhou 730000, P. R. China
S
* Supporting Information
ABSTRACT: A novel dual catalytic system of iodine and manganese is used for
the first time for oxidative dehydrogenation coupling of amines with thiols during
aerobic oxidation. Sulfenamides are synthesized via this approach with moderate
to high efficiencies. The mechanistic studies indicate that activated MnO2 is an
electron transfer bridge for assisting iodine in completing the catalytic cycle.
have been documented. For instance, sulfenamides can be
constructed by the reaction of amines with disulfides,3 sulfenyl
chlorides,2i,4 sulfenyl thiocyanates,5 thiolsulfonates,6 N-
(phenylthiol)phthalimides,7 or thiols;8 synthesized by the
cross-coupling of N-chloroamines9 or N-chlorosuccinimides10
with metal thiolates; or formed by the reaction of lithium
dialkylamides with disulfides.11 Among them, oxidative
dehydrogenation coupling of amines with thiols is the most
intriguing strategy for the formation of N−S bonds under an
aerobic atomosphere due to the atom and step economy.
Copper-catalyzed oxidative coupling reactions of amines with
thiols for forming sulfenamides as the only catalytic example
have been reported.8b However, a systematic and profound
investigation of a simple, inexpensive, ligand-free, and efficient
catalytic system for accessing sulfenamides via the dehydrogen-
ation coupling of amines with thiols has not been explored.
Herein, we describe an iodine/manganese dual catalytic system
for this transformation during aerobic oxidation, generating
sulfenamides with moderate to high yields (Scheme 1b).
A large number of X−S (X = C, N, O, S, or P) bond
formation reactions have been developed through metal,
photoredox, small molecule, or iodine catalysis.12,13 Iodine is
one of the economical and green catalysts that has been
increasingly applied in the construction of X−S bonds.12c As a
single catalyst, iodine could be regenerated by a terminal
oxidant such as TBHP, H2O2, K2S2O8, or molecular oxygen.14
Despite the fact that oxygen is the most ideal oxidant, a higher
temperature is usually required in the transformations.15 To
overcome this kinetically unfavorable effect, Iida and
colleagues reported a subtle strategy with regard to the
catalytic couple of iodine and flavin-catalyzed sulfenylation of
indoles with thiols using oxygen as the oxidant.16 Flavin was
used as an electron transfer bridge between iodine and oxygen
to form C−S bonds. However, pre-preparation and the high
ulfenamides are recognized as important compounds and
Sare broadly applied in pharmaceuticals, agrochemicals, and
industrial utilizations.1 In particular, the sulfenamides, which
possess the structure of arylpiperazine or piperidine, exhibit
high antihypertensive or diuretic activities (Scheme 1a).1c
Sulfenamides also serve as crucial reagents in several organic
transformations, such as oxidation, amination, and sulfuration.2
Considering the significance of sulfenamide derivatives, a
variety of classic methods for the synthesis of sulfenamides
Scheme 1. Sulfenamides for Drugs and a Strategy for the
Synthesis of Sulfenamides
Received: July 21, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b02545
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
cost of flavin limited organic transformations. Therefore, a
commercially available and cheaper catalyst is desired. Actually,
KMnO4 is an inexpensive inorganic compound and is often
used as a strong oxidant rather than a catalyst because of its
highest oxidation state. Even though KMnO4 itself cannot be
an electron transfer bridge, it can be heated to liberate
activated MnO2, which has an intermediate oxidation state for
single-electron transfer (SET). Thus, we wonder whether a
catalytic amount of KMnO4 could cooperate with iodine to
realize the oxidative dehydrogenation coupling of amines with
thiols under mild reaction conditions (Table 1).
With the optimized reaction conditions in hand, the
substrate scope of thiols was investigated as shown in Table
2. Aryl thiophenol with various substituents on the phenyl ring
a
Table 2. Substrate Scope of Thiol
a
Table 1. Optimization of Reaction Conditions
b
entry
catalyst (mol %)
yield (%)
1
2
3
4
5
6
7
8
9
I2 (10)/KMnO4 (10)
I2 (10)
KMnO4 (10)
80
trace
trace
−
a
−
Reaction conditions: morpholine 1a (0.5 mmol, 1 equiv), 2 (0.5
c
mmol, 1 equiv), I2 (10 mol %), KMnO4 (10 mol %), DMF (2.0 mL),
80 °C, 12 h, isolated yield. For 24 h. 1a (1.0 mmol, 2 equiv).
I2 (10)/KMnO4 (10)
I2 (10)/KMnO4 (10)
I2 (10)/KMnO4 (10)
I2 (10)/KMnO4 (10)
I2 (10)/KMnO4 (10)
70
b
c
d
78
e
75
f
43
was compatible with the N−S bond formation reaction,
generating the corresponding products in good to exellent
yields. Electron-donating groups such as methyl, tert-butyl,
methoxy, and methylthio substituents at the ortho, meta, or
para position of the aryl ring were tolerented in the reaction,
affording products 3ab−3ag in 65−74% yields. Electron-
withdrawing groups were also used. Halogen compounds, such
as fluoro-, chloro-, and bromo-subsituted aryl thiophenols,
smoothly provided the desired products 3ah−3an in 66−85%
yields. The aryl thiophenol with an ester group could be
employed in the reaction, yielding product 3ao in 62% yield. In
addition, 1-naphthyl-, 2-naphthyl-, and 2-thienyl-substituted
products 3ap−3ar, respectively, could be obtained in 53−86%
yields. In addition to aryl and heteroaryl groups, alkyl-
substituted thiols were also suitable for the transformation.
Phenylmethanethiol and adamantane-1-thiol underwent de-
hydrogenation coupling to afford sulfenamides 3as and 3at in
66% and 53% yields, respectively.
g
75
a
Reaction conditions: 1a (0.5 mmol, 1 equiv), 2a (0.5 mmol, 1
equiv), catalyst (10 mol %), DMF (2.0 mL), 80 °C, 12 h, oxygen
b
c
d
e
f
balloon. Isolated yields. At 60 °C. At 100 °C. At 120 °C. For 6 h.
g
Under an air atmosphere.
On the basis of the pioneering works about iodine- or
manganese-catalyzed reactions,14−17 we hypothesize that thiol
2 is oxidized by oxidants18 in the reaction system, affording
disulfide 5 that then reacts with I2 to produce R−S−I via SET.
R−S−I subsequently reacts with amine 1 to give the
corresponding product 3 and HI via SET.2i,4,13u,16a HI is
oxidized by MnO2, leading to regeneration of I2. MnO2 is
formed in situ through the heating of KMnO4, producing
Mn(III) that is then oxidized by O2 and 2 to give MnO2
(Scheme 1b).
To verify our hypothesis for the synthesis of sulfenamides,
morpholine 1a and 4-methylbenzenethiol 2a were employed as
the model substrates to optimize the reaction conditions (see
the Supporting Information for details). Initially, numerous
combinations of catalysts were examined in DMF at 80 °C for
12 h with an oxygen balloon (Table S1). Surprisingly, the
catalytic system of I2 and KMnO4 could efficiently catalyze the
oxidative dehydrogenation coupling reaction to provide the
corresponding product 3aa in a ≤80% yield (entry 1). A trace
of sulfenamide 3aa was observed in the presence of I2 or
KMnO4 and not detected in the absence of a catalyst (entries
2−4). Furthermore, diverse solvents were screened for the
reaction of 1a with 2a, affording 3aa in 8−73% yields (Table
S2). Polar aprotic solvents, especially DMF, presented better
effects according to the solvent screening. In addition,
changing the temperature and time led to a decrease in the
yield of 3aa (entries 5−8). The transformation could also be
carried out under an air atmosphere, yielding 3aa in 75% yield
(entry 9).
After the generality of thiols had been examined, a variety of
amines 1 were applied to the oxidative coupling reaction with
4-methylbenzenethiol 2a (Table 3). Thiomorpholine 1b was
treated with 2a to provide the corresponding product 3ba in
60% yield. tert-Butoxycarbonyl (Boc)-protected piperazines 1c
and 1d were successfully converted to sulfenamides 3ca and
3da in 65% and 77% yields, respectively. Analogously,
benzyloxycarbonyl (Cbz)-substituted piperazine 1e also
reacted well to give product 3ea in 73% yield. Other
piperazines having bis(aryl)methyl substituents did not affect
the reaction and were successfully tested, giving products 3fa
and 3ga in 40% and 51% yields, respectively. The
dehydrogeantion coupling of 4-substitued piperidine com-
pounds with 2a was carried out, affording the desired products
in good yields (70% and 75% yields for 3ha and 3ia,
respectively). Although 9H-carbazole decreased the yield of 3ja
(30%), it still showed that aryl amine was also compatible with
the catalytic system for forming N−S bonds. Unexpectedly,
B
DOI: 10.1021/acs.orglett.9b02545
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 3. Substrate Scope of Amine
Scheme 2. Experiments for Mechanistic Studies
a
Reaction conditions: amine 1 (0.5 mmol, 1 equiv), 2a (0.5 mmol, 1
equiv), I2 (10 mol %), KMnO4 (10 mol %), DMF (2.0 mL), 80 °C, 12
b
c
h, isolated yield. 1 (1.0 mmol, 2 equiv). For 24 h.
when using primary amines 1k and 1l as the coupling partner
of 4-methylbenzenethiol 2a, sulfinamide derivatives were
generated in moderate to good yields (70% and 57% yields
for 4ka and 4la, respectively). The primary amines were
convered to sulfinamides rather than sulfenamides, which can
presumably be attributed to the reactivity of primary amines
being higher than that of secondary amines.
To investigate the reaction mechanism for the iodine/
manganese-catalyzed oxidative dehydrogenative coupling, a
series of reactions were performed (see the Supporting
Information for details). Initially, stoichiometric (2,2,6,6-
tetramethylpiperidin-1-yl)oxy (TEMPO) was added to the
treatment of 1a with 2a under the standard reaction
conditions, giving a trace of 3aa (Scheme 2a). The result
revealed that the radical species might be involved in the
reaction. When the transformation was carried out for only 10
min, a trace of 3aa was observed and a 90% yield of disulfide 5
was isolated, suggesting that the generation of 5 from 2a was
rapid (Scheme 2b). Disulfide 5 was reacted with 1a and 2a was
reacted with hydrazine (6), giving product 3aa in 84% and 0%
yields, separately (reactions c and d, respectively, of Scheme
2). When the reaction of 1a with 2a was performed under a N2
atmosphere, 3aa could not be observed and a 31% yield of 5
was isolated (Scheme 2e). The discoveries indicated that
disulfide 5 was a crucial intermediate, hydrazine 6 was not an
intermediate, and oxygen was a key terminal oxidant for the
reaction. Sequentially, two coupling transformations of 1a with
5 were independently performed in the presence of the
different oxidants and catalysts under a N2 atmosphere
(Scheme 2f). Sulfenamide 3aa was obtained in 63% yield
when using I2 as the oxidant, and no product was detected with
an equivalent amount of KMnO4. Combined with the result of
entry 4 in Table 1, the data further confirmed our assumption
that both iodine and manganese were indispensable for
achieving the catalytic cycle and molecular oxygen was the
terminal oxidant. In addition, a facile reaction apparatus was
set up to explore the active manganese species (Scheme 2g).
KMnO4 was heated in DMF, and oxygen bubbles could be
observed in a beaker of water, implying that activated MnO2
might be produced. After the bubbling of oxygen had ceased,
10 mol % I2, 1a, and 2a were added to the reaction tube with a
manganese catalyst under an air atmosphere. Sulfenamide 3aa
and disulfide 5 were independently obtained in 48% and 25%
yields, respectively, after 12 h. Furthermore, freshly prepared
MnO2 was introduced into the reaction mixture, giving 3aa in
70% yield (Scheme 2h). These two reactions confirmed that
MnO2 was an active species in the catalytic cycle. An
exhaustive study of the reaction mechanism is underway.
Additionally, this iodine/manganese dual catalysis gave a
straightforward approach to sulfenamide IV, which possessed
antihypertensive activity (Scheme 3). IV could be readily
prepared in 64% yield by the oxidative dehydrogenation
coupling reaction of piperazine 1f with thiophenol 3u (see the
Supporting Information for details).
In conclusion, a dual catalytic system of iodine/manganese-
catalyzed oxidative dehygenative coupling of amines with thiols
under mild reaction conditions has been established, producing
various sulfenamides in moderate to high yields. The reaction
Scheme 3. Synthesis of Antihypertensive Activity Derivative
IV
C
DOI: 10.1021/acs.orglett.9b02545
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Org. Chem. 2010, 2010, 2670. (c) Correa, A.; Tellitu, I.; Dominguez,
E.; SanMartin, R. Org. Lett. 2006, 8, 4811.
(9) Carr, E. L.; Smith, G. E. P., JR.; Alliger, G. J. Org. Chem. 1949,
14, 921.
(10) Harpp, D. N.; Back, T. G. Tetrahedron Lett. 1971, 12, 4953.
(11) Ikehira, H.; Tanimoto, S. Synthesis 1983, 1983, 716.
(12) For selected reviews of the catalytic construction of X−S bonds,
see: (a) Wang, M.; Jiang, X. Top. Curr. Chem. 2018, 376, 14.
(b) Glass, R. S. Top. Curr. Chem. 2018, 376, 22. (c) Lee, C.-F.; Basha,
R. S.; Badsara, S. S. Top. Curr. Chem. (Z) 2018, 376, 25. (d) Chauhan,
mechanism research suggested that single-electron transfer
might be involved in this transformation, and both iodine and
manganese are indispensable for accomplishing the catalytic
cycle. This protocol also provided an economic and efficient
methodology for synthesizing potential drugs that contained
the sulfenamide building blocks. Further exploitation of this
process for pharmaceutical preparation or industrial applica-
tion is occurring through this approach in our group.
́
̀
P.; Mahajan, S.; Enders, D. Chem. Rev. 2014, 114, 8807. (e) Denes, F.;
Pichowicz, M.; Povie, G.; Renaud, P. Chem. Rev. 2014, 114, 2587.
(13) For selected references on the catalytic formation of the X−S
bond, see: (a) Ni, J.; Mao, X.; Zhang, A. Adv. Synth. Catal. 2019, 361,
2004. (b) Keipour, H.; Jalba, A.; Tanbouza, N.; Carreras, V.; Ollevier,
T. Org. Biomol. Chem. 2019, 17, 3098. (c) Zhou, C.; Tan, Z.; Jiang,
H.; Zhang, M. Green Chem. 2018, 20, 1992. (d) Lauder, K.; Toscani,
A.; Qi, Y.; Lim, J.; Charnock, S. J.; Korah, K.; Castagnolo, D. Angew.
Chem., Int. Ed. 2018, 57, 5803. (e) Maddox, S. M.; Dawson, G. A.;
Rochester, N. C.; Ayonon, A. B.; Moore, C. E.; Rheingold, A. L.;
Gustafson, J. L. ACS Catal. 2018, 8, 5443. (f) Chen, Y.; Murray, P. R.
D.; Davies, A. T.; Willis, M. C. J. Am. Chem. Soc. 2018, 140, 8781.
(g) Liu, T.; Li, Y.; Lai, L.; Cheng, J.; Sun, J.; Wu, J. Org. Lett. 2018,
20, 3605. (h) Nalbandian, C. J.; Brown, Z. E.; Alvarez, E.; Gustafson,
J. L. Org. Lett. 2018, 20, 3211. (i) Velasco, N.; Virumbrales, C.; Sanz,
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b02545.
■
S
Experimental procedures, characterization data, and
NMR spectra of products (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: zhangz@nwnu.edu.cn.
*E-mail: boqian@licp.cas.cn.
ORCID
́
́
R.; Suarez-Pantiga, S.; Fernandez-Rodríguez, M. A. Org. Lett. 2018,
20, 2848. (j) Song, S.; Zhang, Y.; Yeerlan, A.; Zhu, B.; Liu, J.; Jiao, N.
Angew. Chem., Int. Ed. 2017, 56, 2487. (k) Jiang, M.; Li, H.; Yang, H.;
Fu, H. Angew. Chem., Int. Ed. 2017, 56, 874. (l) Shyam, P. K.; Son, S.;
Jang, H.-Y. Eur. J. Org. Chem. 2017, 2017, 5025. (m) Lin, Y.-F.; Wang,
C.; Hu, B.-L.; Qian, P.-C.; Zhang, X.-G. Synlett 2017, 28, 707.
(n) Hirschbeck, V.; Gehrtz, P. H.; Fleischer, I. J. Am. Chem. Soc. 2016,
138, 16794. (o) Zhu, Y.; Chen, T.; Li, S.; Shimada, S.; Han, L.-B. J.
Am. Chem. Soc. 2016, 138, 5825. (p) Oderinde, M. S.; Frenette, M.;
Robbins, D. W.; Aquila, B.; Johannes, J. W. J. Am. Chem. Soc. 2016,
138, 1760. (q) Jouffroy, M.; Kelly, C. B.; Molander, G. A. Org. Lett.
2016, 18, 876. (r) Sakagami, K.; Jin, X.; Suzuki, K.; Yamaguchi, K.;
Mizuno, N. Chem. Lett. 2016, 45, 173. (s) Long, W.; Qiu, W.; Li, C.;
Song, L.; Bai, G.; Zhang, G.; He, H. RSC Adv. 2016, 6, 40945. (t) Lee,
C.; Wang, X.; Jang, H.-Y. Org. Lett. 2015, 17, 1130. (u) Yang, F.-L.;
Tian, S.-K. Angew. Chem., Int. Ed. 2013, 52, 4929. (v) Liu, H.; Jiang,
X. Chem. - Asian J. 2013, 8, 2546. (w) Tanaka, K.; Ajiki, K. Org. Lett.
2005, 7, 1537.
(14) (a) Chen, J.; Jiang, Y.; Yu, J.-T.; Cheng, J. J. Org. Chem. 2016,
81, 271. (b) Parumala, S. K. R.; Peddinti, R. K. Green Chem. 2015, 17,
4068. (c) Hiebel, M.-A.; Berteina-Raboin, S. Green Chem. 2015, 17,
937. (d) Wang, J.; Huang, X.; Ni, Z.; Wang, S.; Wu, J.; Pan, Y. Green
Chem. 2015, 17, 314. (e) Yuan, J.; Liu, C.; Lei, A. Org. Chem. Front.
2015, 2, 677. (f) Ge, W.; Wei, Y. Green Chem. 2012, 14, 2066.
(15) (a) Li, G.; Xie, H.; Chen, J.; Guo, Y.; Deng, G.-J. Green Chem.
2017, 19, 4043. (b) Wang, H.-H.; Shi, T.; Gao, W.-W.; Wang, Y.-Q.;
Li, J.-F.; Jiang, Y.; Hou, Y. S.; Chen, C.; Peng, X.; Wang, Z. Chem. -
Asian J. 2017, 12, 2675. (c) Wan, J.-P.; Zhou, Y.; Liu, Y.; Sheng, S.
Green Chem. 2016, 18, 402.
Bo Qian: 0000-0002-0177-7343
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the Chinese Academy of
Sciences, “Light of West China” Program.
REFERENCES
■
(1) For selected examples of the application of sulfenamides, see:
Craine, L.; Raban, M. Chem. Rev. 1989, 89, 689 and references therein
. References: (a) O’Driscoll, M.; Greenhalgh, K.; Young, A.; Turos,
E.; Dickey, S.; Lim, D. V. Bioorg. Med. Chem. 2008, 16, 7832.
(b) Guarino, V. R.; Karunaratne, V.; Stella, V. J. Bioorg. Med. Chem.
Lett. 2007, 17, 4910. (c) Klioze, S. S.; Allen, R. C.; Wilker, J. C.;
Woodward, D. L. J. Med. Chem. 1980, 23, 677.
(2) (a) For selected examples of the transformation of sulfenamides,
see: Spitz, C.; Lohier, J.-F.; Reboul, V.; Metzner, P. Org. Lett. 2009,
11, 2776. (b) Kuniyasu, H.; Kato, T.; Asano, S.; Ye, J.-H.; Ohmori, T.;
Morita, M.; Hiraike, H.; Fujiwara, S.-i.; Terao, J.; Kurosawa, H.;
Kambe, N. Tetrahedron Lett. 2006, 47, 1141. (c) Davis, F. A. J. Org.
Chem. 2006, 71, 8993. (d) Kondo, T.; Baba, A.; Nishi, Y.; Mitsudo, T.
Tetrahedron Lett. 2004, 45, 1469. (e) Matsuo, J.-i.; Iida, D.;
Yamanaka, H.; Mukaiyama, T. Tetrahedron 2003, 59, 6739.
(f) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2002, 4, 4309.
(g) Matsuo, J.-i.; Iida, D.; Tatani, K.; Mukaiyama, T. Bull. Chem. Soc.
Jpn. 2002, 75, 223. (h) Clennan, N. E. E. L.; Zhang, H. J. Am. Chem.
Soc. 1994, 116, 809. (i) Heimer, N. E.; Field, L. J. Org. Chem. 1970,
35, 3012.
(16) (a) Ohkado, R.; Ishikawa, T.; Iida, H. Green Chem. 2018, 20,
984. (b) Ishikawa, T.; Kimura, M.; Kumoi, T.; Iida, H. ACS Catal.
2017, 7, 4986.
(17) For selected references on the Mn-catalyzed reaction, see:
(a) Cahiez, G.; Moyeux, A.; Buendia, J.; Duplais, C. J. Am. Chem. Soc.
2007, 129, 13788. (b) Huang, X.; Zhuang, T.; Kates, P. A.; Gao, H.;
Chen, X.; Groves, J. T. J. Am. Chem. Soc. 2017, 139, 15407.
(18) For selected references on KMnO4- or MnO2-mediated
disulfide formation, see: (a) Shaabani, A.; Mirzaei, P.; Lee, D.G.
Catal. Lett. 2004, 97, 119. (b) Hajipour, A.; Mallakpour, S.; Adibi, H.
Sulfur Lett. 2002, 25, 155. (c) Noureldin, N. A.; Caldwell, M.;
Hendry, J.; Lee, D. G. Synthesis 1998, 1998, 1587.
(3) (a) Taniguchi, N. Synlett 2007, 2007, 1917. (b) Jin, C. K.;
Moon, J.-K.; Lee, W. S.; Nam, K. S. Synlett 2003, 1967.
(4) Billman, J. H.; Garrison, J.; Anderson, R.; Wolnak, B. J. Am.
Chem. Soc. 1941, 63, 1920.
(5) Major, R. T.; Peterson, L. H. J. Am. Chem. Soc. 1956, 78, 6181.
(6) (a) Taniguchi, N. Tetrahedron 2017, 73, 2030. (b) Dunbar, J. E.;
Rogers, J. H. J. Org. Chem. 1966, 31, 2842.
(7) Shimizu, M.; Fukazawa, H.; Shimada, S.; Abe, Y. Tetrahedron
2006, 62, 2175.
(8) (a) Zhu, M.; Wei, W.; Yang, D.; Cui, H.; Wang, L.; Meng, G.;
Wang, H. Org. Biomol. Chem. 2017, 15, 4789. (b) Taniguchi, N. Eur. J.
D
DOI: 10.1021/acs.orglett.9b02545
Org. Lett. XXXX, XXX, XXX−XXX