Synthesis of Multifunctionalized 2-Carbonylpyrrole by Rhodium-Catalyzed Transannulation of 1-Sulfonyl-1,2,3-triazole with β-Diketone

Article abstract of DOI:10.1021/acs.orglett.6b03179

A facile rhodium-catalyzed transannulation of 1-sulfonyl-1,2,3-triazoles with β-diketones was realized, and a series of multisubstituted 2-carbonylpyrroles were synthesized efficiently (up to 94% yield). The protocol features several advantages, such as readily available materials, mild reaction conditions, a concise operating procedure, a broad reaction scope, and excellent regioselectivity when benzoylacetone derivatives were used.

Full text of DOI:10.1021/acs.orglett.6b03179

Letter
pubs.acs.org/OrgLett
Synthesis of Multifunctionalized 2‑Carbonylpyrrole by Rhodium-
Catalyzed Transannulation of 1‑Sulfonyl-1,2,3-triazole with
β‑Diketone
Wanli Cheng, Yanhua Tang, Ze-Feng Xu,* and Chuan-Ying Li*
Department of Chemistry, Zhejiang Sci-Tech University, Xiasha West Higher Education District, Hangzhou, 310018, China
S
* Supporting Information
ABSTRACT: A facile rhodium-catalyzed transannulation of 1-
sulfonyl-1,2,3-triazoles with β-diketones was realized, and a series
of multisubstituted 2-carbonylpyrroles were synthesized efficiently
(up to 94% yield). The protocol features several advantages, such
as readily available materials, mild reaction conditions, a concise
operating procedure, a broad reaction scope, and excellent
regioselectivity when benzoylacetone derivatives were used.
Scheme 1. Proposal of the Transannulation
s one of the most valuble heterocycles, pyrrole is the key
Asubunit in a huge number of natural and unnatural
compounds, which are widespread in pharmacology and
material science.1 Among these compounds, multisubstituted
2-carbonylpyrrole is a very useful fragment in many drug
molecules and liquid crystal materials.2,3a,b For instance,
ketorolac and tolmetin are both a nonsteroidal anti-
inflammatory drug (NSAID) used as an analgesic. The
ionophore X-14547 A also shows antibacterial, antitumor, and
antihypertensive properties (Figure 1).
Figure 1. Multisubstituted 2-carbonylpyrrole-derived drugs.
Accordingly, many efficient methodologies for the synthesis
of multifunctionalized pyrroles were developed.1d,3 However,
synthetic methods to directly access multisubstituted 2-
carbonylpyrrole4,5 using easily available starting materials
under mild reaction conditions are still worth being developed
and should be practically useful in the synthesis of such pyrrole
derivatives.
In 2008, Gevorgyan and Fokin reported that readily available
1-sulfonyl 1,2,3-triazoles 1 could undergo a Dimorth-type
equilibrium to generate an α-diazo imine 2, and in the presence
of a rhodium catalyst, α-imino rhodium carbene 3 could be
produced, which underwent formal 3 + 2 cycloaddition with
nitriles to give birth to imidazoles (Scheme 1A).6 The Dimorth-
type equilibrium simplified the experimental procedure greatly,
and moreover, due to the 1,3-dipole feature of the α-imino
carbene, plenty of unsaturated compounds could be involved in
the transannulation reaction with this triazole to form many
nitrogen-containing heterocycles. As a result, an efficient
shortcut for the synthesis of nitrogen-containing heterocycles
was discovered and large numbers of methodologies based on
such an in situ α-imino intermediate were developed.7−9
Among these reported transformations, the synthesis of
pyrroles via an α-imino carbenoid was one of the main fields.8
Received: October 24, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b03179
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Recently, the Lee group,8m Anbarasan group,8n Tang
group,8o and our group8p reported that the in situ generated
α-imino rhodium carbene 3 could be trapped by enol ether 4
leading to the generation of pyrrole skeleton 5 or 5′ in high
yield (Scheme 1B). Notably, in all four previous reports, to
establish sufficient nucleophilic activity, the carbonyl group has
never been used as a substituent for the alkenyl moiety. It is
well-known that β-diketone undergoes an equilibrium with its
enol form, and we envisioned that if a much easier available
enol, such as 6, rather than enol ether 4, was employed to trap
the triazole-derived α-imino rhodium carbene 3, pyrrole
skeleton 5′ with a carbonyl at the C-3 position may be
produced (R3 = carbonyl). To our surprise, the reaction of 1a
and 6a produced pyrrole 7a with a carbonyl at the C-2 position
in 58% yield (Scheme 1C). Considering the utility of the
product, the easy availability of the starting material, and the
facility of Rh-catalyzed transformation of 1-sulfonyl-1,2,3-
triazole, we attempted the reaction and report the achievement
herein.
in our investigation. The yields ranged from 60% to 68% when
the reaction was carried out in DCM, toluene, and chloroform
separately (entries 6−8), which were much less efficient
compared to the reaction in DCE. A lower or higher reaction
temperature (50 °C or reflux) gave only a moderate yield (54%
or 58% respectively, entries 9, 10). Additionally, if the reaction
time was reduced to 5 h, the yield decreased to 54% (entry 11).
It is worth noting that triazole 1a was recovered in 95% yield
without a catalyst (entry 12), suggesting the crucial role of
Rh2(piv)4. Accordingly, the optimized reaction conditions were
established as indicated in entry 1.
Initially, we attempted the transformation using 4-phenyl-1-
tosyl-1H-1,2,3-triazole (1a),10 and commercially available
acetoacetone (6a) as model substrates. Gratifyingly, in a N2
atmosphere, when 1a (1.5 equiv) and 6a (1.0 equiv) reacted in
the presence of a catalytic amount of Rh2(piv)4 (5 mol %) in
distilled DCE at 70 °C for 14 h, pyrrole 7a was generated in
excellent yield (94%, Table 1, entry 1). The structure of 7a was
With the optimized conditions in hand, the scope of the
reaction was evaluated. As revealed in Scheme 2, various
a
Table 1. Optimization of Reaction Conditions
Scheme 2. Triazole Scope of the Reaction
b
entry
catalyst
solvent
DCE
temp/°C
time/h
yield/%
1
Rh2(piv)4
Rh2(esp)2
Rh2(oct)4
Rh2(OAc)4
Rh2(tfa)4
Rh2(piv)4
Rh2(piv)4
Rh2(piv)4
Rh2(piv)4
Rh2(piv)4
Rh2(piv)4
−
70
14
14
14
14
16
14
14
14
12
14
5
94
23
31
2
DCE
70
3
DCE
70
c
4
DCE
70
trace
c
5
DCE
70
−
6
DCM
toluene
chloroform
DCE
reflux
70
68
62
60
54
58
54
7
8
reflux
50
9
10
11
12
DCE
reflux
70
DCE
d
DCE
70
12
−
a
General reaction conditions: 1a (0.3 mmol), 6a (0.2 mmol),
rhodium(II) catalyst (0.01 mmol), solvent (2.0 mL), N2 atmosphere.
Isolated yield. 1a was decomposed. Without [Rh] catalyst, 1a
b
c
d
recovered in 95% yield. Ts = tosyl, piv = pivalate, esp = α,α,α′,α′-
tetramethyl-1,3-benzenedipropionate, oct = octanoate, OAc = acetate,
tfa = trifluoroacetate, DCE = 1,2-dichloroethane, DCM = dichloro-
methane.
triazoles were tested to react with 6a in this transannulation. In
general, different substituents on the sulfonyl group in triazole
1 influenced the yields greatly (Scheme 2A). For arylsulfonyl-
substituted triazoles, the corresponding pyrroles were obtained
conveniently in good to excellent yields (7a−c, 71−94%,
Scheme 2A). However, only a moderate yield (7d, 55%) was
achieved when the naphthalen-2-ylsulfonyl-substituted triazole
was utilized. As for aliphatic sulfonyls, the methyl- and
propylsulfonyl-substituted triazoles gave rise to the products
in yields of 84% and 69% separately (7e and 7f).
confirmed from the crystal structure of 8a, which was obtained
after tosyl was removed in 7a (see below, eq 1). Encouraged by
this promising result, further screening of the reaction
conditions was carried out. Unfortunately, other rhodium
catalysts could not improve the yield at all. For example, when
Rh2(esp)2 or Rh2(oct)4 was utilized as catalyst, the yield of 7a
was only 23% or 31% respectively (entries 2 and 3); 1a
decomposed when Rh2(OAc)4 or Rh2(tfa)4 was used (entries 4
and 5). As for solvent, DCE proved to be the most suitable one
Different substituents on the 4-poisition of triazoles also had
a great impact on the yield of the corresponding products
B
DOI: 10.1021/acs.orglett.6b03179
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(Scheme 2B). For 4-aryl substituted triazoles, the substrates
bearing electron-donating groups at the p-position of the
phenyl group produced the desired pyrroles (7g−i, 64−83%)
in higher yields than the ones with electron-withdrawing groups
(7j−l, 52−55%); o-MeOC6H4 substituted triazole 1m gave
product 7m in 81% yield because of the same electronic effect
compared to its p-MeOC6H4 substituted isomer; when m-
MeOC6H4 substituted triazole 1n was utilized, the yield of 7n
was decreased to 68%, which was coincident with electron-rich
cases (7h and 7i) and still higher than those electron-poor cases
(7j−l). However, when a highly electron-rich group was
introduced into the triazole, taking 3,4,5-trimethoxyphenyl
substituted triazole 1o as an example, the yield of 7o was
decreased to 65%. Additionally, the 2-naphthyl substituted
triazole worked well in this reaction and the corresponding
product 7p was generated in 73% yield. Notably, a biheteroaryl
ketone is a very important motif found in medicinal
molecules.11 When 4-(thiophen-3-yl) substituted triazole 1q
was employed, 4-(thiophen-3-yl)-1H-pyrrole 7q could be
generated concisely under our mild reaction conditions in
42% yield.
Scheme 4. Proposed Mechanism
in 91% yield. This excluded path b preliminarily. When
benzoylacetones were used, excellent regioselectivity was
observed. This may be because, under the standard reaction
conditions, the substrate, taking 6r (1-phenylbutane-1,3-dione)
as example, more likely exists as an enol form of (Z)-3-hydroxy-
1-phenylbut-2-en-1-one instead of the other one, that is, (Z)-4-
hydroxy-4-phenylbut-3-en-2-one. Thus, the regioselective prod-
uct 3-phenyl pyrrole 7r, rather than the 5-phenyl pyrrole
isomer, was obtained.14
We then investigated the scope of the β-diketone derivatives
6 (Scheme 3). Excellent regioselectivity was observed when
Scheme 3. β-Diketone Scope of the Reaction
In summary, a facile rhodium catalyzed transannulation of 1-
sulfonyl-1,2,3-triazole with β-diketone was achieved, demon-
strating once again the potential of such a triazole in organic
synthesis. This transformation tolerated common functional
groups well, and high chemoselectivity ensured pyrroles as the
main products rather than other products. Excellent regiose-
lectivity was also observed when benzoylacetone derivatives
were used. More importantly, carbonyl substituted enol was
used for the first time to trap α-imino carbene, offering much
more flexibility in pyrrole synthesis.
benzoylacetones were involved in this reaction. Only the 3-aryl-
5-methyl substituted pyrroles 7r−t were generated in moderate
to good yields (7r, 85%; 7s, 72%; 7t, 57%), and no
corresponding 3-methyl-5-aryl pyrroles were detected. The
structures of 7r−t were inferred by comparison of the NMR
data of 8r in the literature,12 and 8r was obtained by removing
the tosyl group in 7r (see below, eq 2). Compared to 6a,
heptane-3,5-dione performed less efficiently (7u, 52%).
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.6b03179.
In addition, when 3-n-hexyl-1,2,3-triazole 1′ was used in this
reaction, no desired pyrrole was obtained and only hydrolysis
product 9′ was isolated in 38% yield (eq 3).
The proposed mechanism of this rhodium-catalyzed trans-
annulation is displayed in Scheme 4.8m,n α-Imino diazo
compound 2a was formed by the Dimorth-type rearrangement
of triazole 1a, and α-imino rhodium carbene 3a was generated
subsequently in the presence of a rhodium catalyst, which then
was attacked by the nucleophilic enol 6a and produced
zwitterionic intermediate 10a. Subsequent addition−elimina-
tion reactions finished the catalytic cycle and produced
compound 12a through 11a, an aldol reaction of 12a resulted
in the formation of 13a, and then aromatization of 13a by
dehydration gave pyrrole 7a (path a). Alternatively, since
hydrolysis product 9 was isolated as a byproduct in some cases,
path b was proposed as another possible reaction pathway. In
path b, 9a was generated from the hydrolysis of 3a, and then
condensation of 9a and 6a could produce 12a, which would
furnish 7a finally.13 However, when 9a was introduced into the
reaction, taking the place of 1a under the standard reaction
conditions, no desired 7a was generated and 9a was recovered
Experimental procedures, characterization data, and
NMR spectra for new compounds (PDF)
Crystal data of 8a (CIF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: xuzefeng@zstu.edu.cn.
*E-mail: licy@zstu.edu.cn.
ORCID
Chuan-Ying Li: 0000-0001-9400-6830
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was generously supported by the National Natural
Science Foundation of China (21372204), the Program for
■
C
DOI: 10.1021/acs.orglett.6b03179
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Funakoshi, Y.; Tanaka, T.; Murakami, M. Org. Lett. 2014, 16, 2760.
(e) Chen, K.; Zhu, Z.-Z.; Zhang, Y.-S.; Tang, X.-Y.; Shi, M. Angew.
Chem., Int. Ed. 2014, 53, 6645. (f) Schultz, E. E.; Lindsay, V. N. G.;
Sarpong, R. Angew. Chem., Int. Ed. 2014, 53, 9904. (g) Yang, Y.; Zhou,
M.-B.; Ouyang, X.-H.; Pi, R.; Song, R.-J.; Li, J.-H. Angew. Chem., Int.
Ed. 2015, 54, 6595. (h) Miura, T.; Funakoshi, Y.; Fujimoto, Y.;
Nakahashi, J.; Murakami, M. Org. Lett. 2015, 17, 2454. (i) Lee, D. J.;
Yoo, E. J. Org. Lett. 2015, 17, 1830. (j) Xu, H.-D.; Jia, Z.-H.; Xu, K.;
Zhou, H.; Shen, M.-H. Org. Lett. 2015, 17, 66. (k) Ryu, Y.; Baek, Y.;
Lee, P. H. J. Org. Chem. 2015, 80, 2376. (l) Lindsay, V. N. G.; Viart, H.
M.-F.; Sarpong, R. J. Am. Chem. Soc. 2015, 137, 8368. (m) Miura, T.;
Nakamuro, T.; Liang, C. J.; Murakami, M. J. Am. Chem. Soc. 2014, 136,
15905. For related publications of our group, see ref 8p and: (n) Ran,
R.-Q.; Xiu, S.-D.; Li, C.-Y. Org. Lett. 2014, 16, 6394. (o) Zhang, W.-B.;
Xiu, S.-D.; Li, C.-Y. Org. Chem. Front. 2015, 2, 47. (p) He, J.; Man, Z.;
Shi, Y.; Li, C.-Y. J. Org. Chem. 2015, 80, 4816. (q) Shi, Y.; Yu, X.; Li,
C.-Y. Eur. J. Org. Chem. 2015, 2015, 6429. (r) He, J.; Shi, Y.; Cheng,
W.; Man, Z.; Yang, D.; Li, C.-Y. Angew. Chem., Int. Ed. 2016, 55, 4557.
(10) For synthesis of 1-sulfonyl-1,2,3-triazoles, see: (a) Yoo, E. J.;
Ahlquist, M.; Kim, S. H.; Bae, I.; Fokin, V. V.; Sharpless, K. B.; Chang,
S. Angew. Chem., Int. Ed. 2007, 46, 1730. (b) Raushel, J.; Fokin, V. V.
Org. Lett. 2010, 12, 4952. (c) Liu, Y.; Wang, X.; Xu, J.; Zhang, Q.;
Zhao, Y.; Hu, Y. Tetrahedron 2011, 67, 6294.
(11) (a) Chen, C.; Reamer, R. A.; Chilenski, J. R.; McWilliams, C. J.
Org. Lett. 2003, 5, 5039. (b) Ruck, R. T.; Huffman, M. A.; Stewart, G.
W.; Cleator, E.; Kandur, W. A.; Kim, M. M.; Zhao, D. Org. Process Res.
Dev. 2012, 16, 1329. (c) Schmidt, F.; Stemmler, R. T.; Rudolph, J.;
Bolm, C. Chem. Soc. Rev. 2006, 35, 454.
(12) (a) Alberola, A.; Andres, J. M.; Gonzalez, A.; Pedrosa, R.;
Vicente, M. Heterocycles 1989, 29, 1973. (b) Kharchenko, V. G.;
Chalaya, S. N.; Litvinov, O. V. Chem. Heterocycl. Compd. 1985, 21, 291.
(13) Miura, T.; Biyajima, T.; Fujii, T.; Murakami, M. J. Am. Chem.
Soc. 2012, 134, 194.
Innovative Research Team of Zhejiang Sci-Tech University
(13060052-Y), and Zhejiang Sci-Tech University 521 project.
REFERENCES
■
(1) (a) Fukuda, T.; Ishibashi, F.; Iwao, M. Heterocycles 2011, 83, 491.
(b) Kashman, Y.; Koren-Goldshlager, G.; Garcia-Gravalos, M. D.;
Schleyer, M. Tetrahedron Lett. 1999, 40, 997. (c) Forte, B.; Malgesini,
B.; Piutti, C.; Quartieri, F.; Scolaro, A.; Papeo, G. Mar. Drugs 2009, 7,
705. (d) Clive, D. L. J.; Cheng, P. Tetrahedron 2013, 69, 5067.
(e) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891.
(2) (a) Forget, P.; Bentin, C.; Machiels, J.-P.; Berliere, M.; Coulie, P.
G.; De Kock, M.; Buggy, D. J. Br. J. Anaesth. 2014, 113, i82.
(b) Eisenach, J. C.; Curry, R.; Tong, C.; Houle, T. T.; Yaksh, T. L.
Anesthesiology 2010, 112, 1216. (c) Amadio, P., Jr; Cummings, D. M.;
Jallad, N. J. Clin. Pharmacol. 1985, 25, 100. (d) Edwards, M. P.; Ley, S.
V.; Lister, S. G.; Palmer, B. D. J. Chem. Soc., Chem. Commun. 1983,
630.
(3) (a) Estev
2010, 39, 4402. (b) Estev
́
ez, V.; Villacampa, M.; Menen
́
dez, J. C. Chem. Soc. Rev.
dez, J. C.
́
ez, V.; Villacampa, M.; Menen
́
Chem. Soc. Rev. 2014, 43, 4633. (c) Ferreira, V. F.; de Souza, M. C. B.
V.; Cunha, A. C.; Pereira, L. O. R.; Ferreira, M. L. G. Org. Prep. Proced.
Int. 2001, 33, 411. (d) Joshi, S. D.; More, U. A.; Kulkarni, V. H.;
Aminabhavi, T. M. Curr. Org. Chem. 2013, 17, 2279. (e) Gulevich, A.
V.; Dudnik, A. S.; Chernyak, N.; Gevorgyan, V. Chem. Rev. 2013, 113,
3084.
(4) For selected examples on the synthesis of 2-carbonyl substituted
pyrrole derivatives, see: (a) Muchowski, J. M.; Solas, D. R. J. Org.
Chem. 1984, 49, 203. (b) Boger, D. L.; Coleman, R. S.; Panek, J. S.;
Yohannes, D. J. Org. Chem. 1984, 49, 4405. (c) Galenko, E. E.;
Galenko, A. V.; Khlebnikov, A. F.; Novikov, M. S. RSC Adv. 2015, 5,
18172. (d) Pusch, S.; Kowalczyk, D.; Opatz, T. J. Org. Chem. 2016, 81,
4170.
(5) For multicomponent synthesis examples, see ref 3a, b.
(6) Horneff, T.; Chuprakov, S.; Chernyak, N.; Gevorgyan, V.; Fokin,
V. V. J. Am. Chem. Soc. 2008, 130, 14972.
(14) (a) Varun, B. V.; Gadde, K.; Prabhu, K. R. Org. Lett. 2015, 17,
2944. (b) Lord, R. M.; Hebden, A. J.; Pask, C. M.; Henderson, I. R.;
Allison, S. J.; Shepherd, S. L.; Phillips, R. M.; McGowan, P. C. J. Med.
Chem. 2015, 58, 4940.
(7) For reviews, see: (a) Chattopadhyay, B.; Gevorgyan, V. Angew.
Chem., Int. Ed. 2012, 51, 862. (b) Gulevich, A. V.; Gevorgyan, V.
Angew. Chem., Int. Ed. 2013, 52, 1371. (c) Davies, H. M. L.; Alford, J.
S. Chem. Soc. Rev. 2014, 43, 5151. (d) Anbarasan, P.; Yadagiri, D.;
Rajasekar, S. Synthesis 2014, 46, 3004. (e) Jiang, Y.; Sun, R.; Tang, X.-
Y.; Shi, M. Chem.Eur. J. 2016, 22, DOI: 10.1002/chem.201601703.
(8) For synthesis of pyrrole via α-imino carbene, see: (a) Miura, T.;
Yamauchi, M.; Murakami, M. Chem. Commun. 2009, 1470.
(b) Chattopadhyay, B.; Gevorgyan, V. Org. Lett. 2011, 13, 3746.
(c) Schultz, E. E.; Sarpong, R. J. Am. Chem. Soc. 2013, 135, 4696.
(d) Parr, B. T.; Green, S. A.; Davies, H. M. L. J. Am. Chem. Soc. 2013,
135, 4716. (e) Spangler, J. E.; Davies, H. M. L. J. Am. Chem. Soc. 2013,
135, 6802. (f) Miura, T.; Tanaka, T.; Hiraga, K.; Stewart, S. G.;
Murakami, M. J. Am. Chem. Soc. 2013, 135, 13652. (g) Alford, J. S.;
Spangler, J. E.; Davies, H. M. L. J. Am. Chem. Soc. 2013, 135, 11712.
(h) Miura, T.; Hiraga, K.; Biyajima, T.; Nakamuro, T.; Murakami, M.
Org. Lett. 2013, 15, 3298. (i) Shi, Y.; Gevorgyan, V. Org. Lett. 2013, 15,
5394. (j) Miura, T.; Funakoshi, Y.; Murakami, M. J. Am. Chem. Soc.
2014, 136, 2272. (k) Kwok, S. W.; Zhang, L.; Grimster, N. P.; Fokin,
V. V. Angew. Chem., Int. Ed. 2014, 53, 3452. (l) Shang, H.; Wang, Y.;
Tian, Y.; Feng, J.; Tang, Y. Angew. Chem., Int. Ed. 2014, 53, 5662.
(m) Kim, C.-E.; Park, S.; Eom, D.; Seo, B.; Lee, P. H. Org. Lett. 2014,
16, 1900. (n) Rajasekar, S.; Anbarasan, P. J. Org. Chem. 2014, 79, 8428.
(o) Feng, J.; Wang, Y.; Li, Q.; Jiang, R.; Tang, Y. Tetrahedron Lett.
2014, 55, 6455. (p) Ran, R.-Q.; He, J.; Xiu, S.-D.; Wang, K.-B.; Li, C.-
Y. Org. Lett. 2014, 16, 3704. (q) Tian, Y.; Wang, Y.; Shang, H.; Xu, X.;
Tang, Y. Org. Biomol. Chem. 2015, 13, 612. (r) Lei, X.-Q.; Li, L.-B.; He,
Y.-P.; Tang, Y.-F. Org. Lett. 2015, 17, 5224. (s) Ding, H.; Hong, S.;
Zhang, N. Tetrahedron Lett. 2015, 56, 507.
(9) For selected examples of synthesis of nitrogen-heterocycles based
on α-imino carbene, see: (a) Chuprakov, S.; Kwok, S. W.; Fokin, V. V.
J. Am. Chem. Soc. 2013, 135, 4652. (b) Zibinsky, M.; Fokin, V. V.
Angew. Chem., Int. Ed. 2013, 52, 1507. (c) Jung, D. J.; Jeon, H. J.; Kim,
J. H.; Kim, Y.; Lee, S. Org. Lett. 2014, 16, 2208. (d) Miura, T.;
D
DOI: 10.1021/acs.orglett.6b03179
Org. Lett. XXXX, XXX, XXX−XXX