Visible-Light-Mediated Decarboxylative Tandem Carbocyclization of Acrylamide-Attached Alkylidenecyclopropanes: Access to Polycyclic Benzazepine Derivatives

Article abstract of DOI:10.1021/acs.orglett.0c01856

A visible-light-mediated decarboxylative tandem carbocyclization of acrylamide-tethered alkylidenecyclopropanes with phenyliodine(III) diacetate and various aliphatic acids has been reported in this paper. An alkyl radical in situ generated from phenyliodine(III) dicarboxylates upon visible-light irradiation catalyzed by fac-Ir(ppy)3 adds to the less hindered central carbon of alkylidenecyclopropane to initiate the tandem annulation, generating tetracyclic benzazepine derivatives in moderate to good yields with broad substrate scope under mild conditions.

Full text of DOI:10.1021/acs.orglett.0c01856

pubs.acs.org/OrgLett
Letter
Visible-Light-Mediated Decarboxylative Tandem Carbocyclization of
Acrylamide-Attached Alkylidenecyclopropanes: Access to Polycyclic
Benzazepine Derivatives
Xiao-Yu Zhang, Chao Ning, Yong-Jie Long, Yin Wei, and Min Shi*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01856
Read Online
ACCESS
Metrics & More
Article Recommendations
*
sı Supporting Information
ABSTRACT: A visible-light-mediated decarboxylative tandem
carbocyclization of acrylamide-tethered alkylidenecyclopropanes
with phenyliodine(III) diacetate and various aliphatic acids has
been reported in this paper. An alkyl radical in situ generated from
phenyliodine(III) dicarboxylates upon visible-light irradiation
catalyzed by fac-Ir(ppy) adds to the less hindered central carbon
3
of alkylidenecyclopropane to initiate the tandem annulation,
generating tetracyclic benzazepine derivatives in moderate to
good yields with broad substrate scope under mild conditions.
he azepine skeleton is one of the most ubiquitous
Therefore, many efforts have been devoted to explore general
and facile protocols for the rapid construction of this kind of
pivotal benzazepine motifs in the field of organic synthesis and
medicinal chemistry owing to their indispensable applications.
Carboxylic acids, as promising fine chemical feedstock, can
be applied to rapidly expand libraries of complex small
T
heterocycles in a variety of biologically active and
1
medicinally valuable compounds. As its structural units,
polyheterocyclic benzazepine motifs built on the azepine
backbone exhibit significant biological and pharmaceutical
2
activities (Figure 1). For example, compound A, in which the
3
molecule. Among all of their applications, the decarboxylative
reduction of carboxylic acids is a general synthetic trans-
4
formation. However, the decarboxylative functionalization of
carboxylic acids with easily accessible phenyliodine(III)
5
,6
diacetate (DIB) has been rarely reported so far. Liu’s
group employed the organocatalyst to achieve arylalkylation of
t
activated alkenes through decarboxylation of PhI(O C Bu) ,
2
2
5
c
affording a variety of oxindoles in good yields (Scheme 1a).
Later on, Zhu and co-workers reported a visible-light-
promoted decarboxylative tandem reaction of N-methyl-N-
phenylmethacrylamides with phenyliodine(III) dicarboxylates
in the presence of fac-Ir(ppy) to provide 3,3-disubstituted
3
oxindoles as products in one step in good yields (Scheme
5d
1
b).
During recent years, photoredox catalysis induced by visible
Figure 1. Representative nature products containing benzazepine
motifs.
light has experienced significant advances due to its special
advantages compared with traditional photochemistry such as
ease of handling, application safety, natural abundance, and
benzazepine fused with indoline, is an anticancer agent.
7
mild conditions. Thus far, our group has been focusing on the
Compound B can be used as a γ-secretase inhibitor in the
exploration of visible-light induced photoredox catalytic
2d
therapy of Alzheimer’s disease. As a metabolite of estrogen,
compound C is demonstrated as an inhibitor for the
proliferation of various cell types and also can be employed
Received: June 2, 2020
2e
as an antiangiogenic and antitumor agent. Hexahydrodiben-
zazepinone derivative D, exhibiting BK channel opening
activities, has potential therapeutic applications in different
pathophysiological conditions such as coronary artery spasm,
2f
hypertension, progressive deafness, and urinary incontinence.
©
XXXX American Chemical Society
https://dx.doi.org/10.1021/acs.orglett.0c01856
A
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Scheme 1. Decarboxylative Tandem Cyclization Using
Phenyliodine(III) Diacetate (DIB) or Its Derivatives
Table 1. Optimization of the Reaction Conditions for
Visible-Light-Mediated Decarboxylative Tandem
Carbocyclization Reaction of 1a
a
b
entry
PS
solvent
time (h)
yield (%)
1
2
3
4
5
6
7
8
9
Ru(bpy) (PF )
DMF
DMF
DMF
DMF
DCM
THF
24
24
24
24
24
24
24
24
24
24
24
12
24
24
28
44
36
86
62
59
70
66
45
42
54
45
ND
ND
3
6
2
Ru(bpz) (PF )
3
6
2
Ir(ppy) (dtbbpy)PF6
2
c
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
fac-Ir(ppy)3
DMA
PhCl
PhCH3
MeCN
DMF
DMF
DMF
DMF
10
11
12
13
14
d
e
f
reactions of alkylidenecyclopropanes (ACPs), a highly strained
but readily accessible molecule, for the rapid synthesis of
complicated molecules. Herein, we demonstrate a novel
visible-light-mediated decarboxylative tandem carbocyclization
using acrylamide-attached alkylidenecyclopropanes with vari-
ous in situ generated phenyliodine(III) dicarboxylates for the
formation of functionalized seven-membered azepine poly-
cyclic structures (Scheme 1c, this work).
a
8
The reaction was run under the following conditions: a solution of
a (0.1 mmol), DIB 2a (0.2 mmol, 2.0 equiv), and photosensitizer
0.002 mmol) in dry solvent (0.5 mL) was stirred at room
1
(
b
temperature under nitrogen atmosphere. Yields were determined
1
by H NMR spectroscopic using CH Br as an internal standard.
2
2
c
d
Isolated yield of 3a after purification by a flash chromatography. 1.0
e
equiv of DIB 2a. Reaction was conducted in the absence of light.
f
To commence our working hypothesis, N-(2-
Reaction was conducted in the absence of PS.
(
cyclopropylidene(phenyl)methyl)phenyl)-N-methylmethacry-
lamide 1a and phenyliodine(III) diacetate (DIB) 2a (2.0
equiv) were utilized as the model substrates to examine the
reaction outcome and subsequently to optimize the reaction
conditions, and the results are shown in Table 1. Initially, an
array of photosensitizers was screened using DMF as solvent
upon irradiation with a 15 W blue LED for 24 h (Table 1,
entries 1−4). To our delight, fac-Ir(ppy) was proven as the
3
best photosensitizer, and the expected tetracyclic benzazepine
product 3a was indeed formed and could be obtained in the
yield of 86% (Table 1, entry 4). Using this photocatalyst, we
further screened the common solvents and found that the use
of other solvents, such as DCM, THF, DMA, PhCl, PhMe, and
MeCN, afforded 3a in moderate yields ranging from 42% to
Figure 2. ORTEP drawings of 3a.
7
0% and identified DMF as the most suitable solvent for this
reaction (Table 1, entries 5−10). Using 1.0 equiv of 2a or
shortening the reaction time to 12 h resulted in a decreased
yield of 3a to 54% and 45%, respectively (Table 1, entries 11
and 12). Moreover, the control experiments revealed that no
reaction occurred when the visible light or catalyst fac-Ir(ppy)3
was not employed (Table 1, entries 13 and 14). The X-ray
diffraction pattern of 3a, whose structure had been
unambiguously determined is shown in Figure 2. The related
CIF data of 3a are indicated in the Supporting Information.
Having established the optimized reaction conditions, we
subsequently investigated the generality of this tandem
reaction. The results are shown in Scheme 2. Under the
optimal conditions, most substrates underwent the reactions
smoothly, generating the products 3b−3m in good yields.
Employing substrates 1b and 1c bearing different N-protecting
accessed in 92% and 90% yield, respectively. Then the
electronic effect of the substrate was examined by changing
1
the substituent R at the para position on the benzene ring.
When electron-withdrawing substituents were present on the
benzene ring (1d−1g), the desired products 3d−3g were
provided in 78−85% yields. For substrate 1h with an electron-
donating substituent on the benzene ring, the corresponding
product 3h was obtained in 87% yield, suggesting that the
1
electronic property of R did not have a significant influence on
the product yield. For substrate 1i having a meta-substituted
methoxy group on the benzene ring, the corresponding
product 3i was obtained in 82% yield as a single regioisomer.
However, the reaction of the ortho-substituted substrate 1j
failed to afford the product 3j, presumably due to steric effects.
By introducing a substituent at another benzene ring, for
2
groups R , the yields of desired products 3b and 3c were
B
https://dx.doi.org/10.1021/acs.orglett.0c01856
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Scheme 2. Substrate scope of acrylamide-tethered
alkylidenecyclopropanes 1
Scheme 4. Substrate Scope of Acrylamide-Tethered
a,b
a,
b
Alkylidenecyclopropanes 1
a
Unless otherwise specified, all reactions were conducted using 1 (0.2
mmol), 2a (0.4 mmol, 2.0 equiv), and fac-Ir(ppy) (2 mol %) in DMF
3
(
1.0 mL) at room temperature under nitrogen atmosphere for 24 h.
Isolated yields. The desired product was obtained in trace amounts.
b
c
3
example, when R was a chlorine atom, the desired product 3k
was acquired in 73% yield. Furthermore, substrate 1l having
two substituted benzene rings underwent this reaction,
delivering the product 3l in 75% yield. Using substrate 1m,
in which the methyl group was substituted by a phenyl group,
the reaction also proceeded smoothly to give the product 3m
in 79% yield. To further examine the generality of this
protocol, we utilized substrates 1n and 1o, in which the
aromatic moiety was substituted by a methyl or n-butyl group.
However, only complex mixtures were obtained under the
standard conditions (Scheme 3).
a
Scheme 3. Reactions of Substrates 1n or 1o with 2a
Unless otherwise specified, all reactions were conducted using 1a
0.2 mmol), 2′ (4.0 equiv), PhI(OAc) (2.0 equiv), and fac-Ir(ppy)
(
(
2
3
2 mol %) in DMF (1.0 mL) at room temperature under nitrogen
b
c
atmosphere for 24 h. Isolated yields. The desired product was
d
obtained in a complex mixture. The desired product was obtained in
trace amounts.
targeted product 3z in 72% yield. However, the use of 3,3,3-
trifluoropropionic acid resulted in a complex mixture, probably
due to the influence of the electronic effect. For 3-cyclohexene-
1-carboxylic acid, the reaction afforded the desired product 3aa
in trace amounts under the optimized reaction conditions.
Gratifying, in the case of tertiary carboxylic acids, the reactions
proceeded smoothly to deliver the desired products 3ab and
3ac in 70% and 67% yields, respectively. The reaction also
tolerated naturally occurring carboxylic acids such as oleic acid,
delivering the desired product 3ad in 75% yield.
To demonstrate its synthetic usefulness, a scale-up experi-
ment was carried out with 0.61 g (2.0 mmol) of 1a and 4-
pentynoic acid 2s′ (0.785 g, 8.0 mmol), affording the
corresponding product 3u in 70% yield (497.7 mg) under
the standard conditions, testifying this reaction’s scalability
(Scheme 5). Furthermore, oxidation of 3u with DDQ
furnished the aromatization product 4a in 98% yield. The
copper-catalyzed click reaction of 3u with tosyl azide afforded
the corresponding [3 + 2] cycloaddition product 4b in 95%
We next focused on examination of the compatibility of the
reaction employing a variety of phenyliodine(III) dicarbox-
ylates 2, and the results are shown in Scheme 4. The ligand
metathesis of carboxylic acids 2′ and DIB (2a) could easily
take place, resulting in the formation of phenyliodine(III)
dicarboxylates 2, which could be used for this reaction without
further purification. As shown in Scheme 4, valeric acid,
9
caproic acid found in milk fat, and heptanoic acid were
compatible in this reaction, generating the products 3p, 3q,
and 3r in the range of 75−79% yields. Moreover, by employing
β-monosubstituted carboxylic acid, 3s could be accessed in
7
7% yield. Notably, primary aliphatic carboxylic acids bearing
alkenyl, alkynyl, phenyl, chloro, and cyclopentyl groups were
suitable for this reaction, furnishing the corresponding
products 3t−3x in good yields ranging from 72% to 83%.
The reaction of 1a with secondary carboxylic acid provided the
C
https://dx.doi.org/10.1021/acs.orglett.0c01856
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Scheme 5. Scale-up Experiment and Synthetic Usefulness
cationic intermediate VI could be also formed by a SET of
radical intermediate V with PhI(OAc) . Finally, the desired
2
product 3a was produced upon deprotonation of VI with
−
OAc.
In conclusion, we presented a practical and useful protocol
for the synthesis of polycyclic benzazepine derivatives by the
use of visible-light photoredox catalysis through fast coupling
of readily accessible alkylidenecyclopropanes with a series of
commercially available aliphatic carboxylic acids in the
presence of phenyliodine(III) diacetate. This decarboxylative
tandem carbocyclization reaction proceeded effectively
through a radical addition initiated cyclopropane ring-opening
and cyclization to give the polycyclic products in high yields
with broad substrate scope and good functional group
tolerance. Moreover, this reaction could be conducted in a
gram scale, and the products could be further functionalized to
deliver interesting compounds. Efforts are underway to further
understand the scope and limitations for this tandem reaction.
In addition, the applications of this protocol to biologically
interesting compounds are being studied in our lab.
a
1
a (2.0 mmol), 4-pentynoic acid 2s′ (8.0 mmol, 4.0 equiv),
PhI(OAc) (4.0 mmol, 2.0 equiv), fac-Ir(ppy) (2 mol %), DMF (10
mL), rt, N , 24 h, 15 W Blue LED. DDQ, THF, rt, overnight. TsN ,
2
3
b
c
2
3
d
i
CuTc, PhMe, rt, 8 h. Pd(PPh ) Cl , CuI, Pr NH, THF, 40 °C, 8 h.
3
2
2
2
e
Lindlar catalyst, MeOH, rt, H2.
yield, indicating the potential utility of the resulting alkyne in
the medicinal chemistry. Finally, Sonogashira cross-coupling of
ASSOCIATED CONTENT
sı Supporting Information
■
*
3
u with 2-iodothiophene also proceeded smoothly, giving
product 4c in 98% yield, which could be further partially
hydrogenated by Lindlar catalyst, affording product 4d in 98%
yield as an E/Z = 1:5 isomeric mixture.
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01856.
Experimental procedures and characterization data for
all compounds (PDF)
On the basis of previously reported literature and our own
5
d
examinations, a plausible mechanism is shown in Scheme 6.
Accession Codes
Scheme 6. Plausible Mechanism for the Formation of 3a
CCDC 1937021 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
■
Min Shi − Key Laboratory for Advanced Materials and Institute
of Fine Chemicals, School of Chemistry & Molecular
Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China; State Key
Laboratory of Organometallic Chemistry, Center for Excellence
in Molecular Synthesis, University of Chinese Academy of
Sciences, Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, Shanghai 200032, People’s Republic of
China; orcid.org/0000-0003-0016-5211; Phone: (+86)-
2
1-6416-6128; Email: mshi@mail.sioc.ac.cn
Authors
Initially, the excited-state *Ir(ppy)3 upon irradiation of
Ir(ppy) with visible light went through a single-electron
Xiao-Yu Zhang − Key Laboratory for Advanced Materials and
3
IV
transfer (SET) with PhI(OAc) , generating Ir (ppy) and the
radical intermediate I,
Institute of Fine Chemicals, School of Chemistry & Molecular
Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China
2
3
5b,10
which interacted with the carbonyl
group in 1a to give an oxygen-coordinated iodine radical
species II. When CO and PhI were released, a methyl radical
Chao Ning − Key Laboratory for Advanced Materials and
Institute of Fine Chemicals, School of Chemistry & Molecular
Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China
Yong-Jie Long − Key Laboratory for Advanced Materials and
Institute of Fine Chemicals, School of Chemistry & Molecular
Engineering, East China University of Science and Technology,
Shanghai 200237, People’s Republic of China
2
was generated. The methyl radical added to 1a to give radical
intermediate III, which subsequently added to the less
hindered carbon center of alkylidenecyclopropane to generate
a radical intermediate IV. The ring-opening step took place to
furnish a cyclohexadienyl radical intermediate V, which
IV
underwent another SET with Ir (ppy)3 to provide the
corresponding cationic intermediate VI. Alternatively, the
D
https://dx.doi.org/10.1021/acs.orglett.0c01856
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Yin Wei − State Key Laboratory of Organometallic Chemistry,
Center for Excellence in Molecular Synthesis, University of
Chinese Academy of Sciences, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032,
People’s Republic of China
1326. (g) Shaw, M. H.; Twilton, J.; MacMillan, D. W. J. Org. Chem.
2
016, 81, 6898. (h) Chen, J. R.; Hu, X. Q.; Lu, L. Q.; Xiao, W. J. Acc.
Chem. Res. 2016, 49, 1911. (i) Arora, A.; Weaver, J. D. Acc. Chem. Res.
2
016, 49, 2273. (j) Romero, N. A.; Nicewicz, D. A. Chem. Rev. 2016,
116, 10075. (k) Teders, M.; Henkel, C.; Anhauser, L.; Strieth-
Kalthoff, F.; Gomez-Suarez, A.; Kleinmans, R.; Kahnt, A.;
Rentmeister, A.; Guldi, D.; Glorius, F. Nat. Chem. 2018, 10, 981.
(l) Strieth-Kalthoff, F.; James, M. J.; Teders, M.; Pitzer, L.; Glorius, F.
Chem. Soc. Rev. 2018, 47, 7190. (m) Huang, X.; Meggers, E. Acc.
Chem. Res. 2019, 52, 833. (n) Fan, X.; Lei, T.; Chen, B.; Tung, C. H.;
Wu, L. Z. Org. Lett. 2019, 21, 4153.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01856
Notes
The authors declare no competing financial interest.
(8) (a) Yuan, Y. C.; Liu, H. L.; Hu, X. B.; Wei, Y.; Shi, M. Chem. -
Eur. J. 2016, 22, 13059. (b) Chen, M.; Wei, Y.; Shi, M. Org. Chem.
Front. 2020, 7, 374. (c) Liu, J.; Li, L.; Yu, L.; Tang, L.; Chen, Q.; Shi,
M. Adv. Synth. Catal. 2018, 360, 2959.
ACKNOWLEDGMENTS
■
We appreciate the Strategic Priority Research Program of the
Chinese Academy of Sciences (Grant No. XDB20000000), the
National Natural Science Foundation of China (Grant Nos.
1421091, 21372250, 21121062, 21302203, 21772037,
1772226, 21861132014 and 91956115), and the Fundamen-
(
(
9) Wilde, M. J.; Rowland, S. Anal. Chem. 2015, 87, 8457.
10) Minisci, F.; Vismara, E.; Fontana, F.; Claudia Nogueira
Barbosa, M. Tetrahedron Lett. 1989, 30, 4569.
2
2
tal Research Funds for the Central Universities (Grant No.
2
22201717003) for the financial support.
REFERENCES
■
(
1) The Chemistry of Heterocyclic Compounds; Weissberger, A.,
Taylor, E. C., Eds.; Wiley-Interscience: New York, 1984; Vol. 43.
(
2) (a) Murphy, M. B.; Murray, C.; Shorten, G. D. N. Engl. J. Med.
2001, 345, 1548. (b) Hou, F.; Zhang, X.; Zhang, G.; Xie, D.; Chen,
P.; Zhang, W.; Jiang, J.; Liang, M.; Wang, G.; Liu, Z.; Geng, R. N.
Engl. J. Med. 2006, 354, 131. (c) McGrath, N. A.; Brichacek, M.;
Njardarson, J. T. J. Chem. Educ. 2010, 87, 1348. (d) Velcicky, J.;
Bodendorf, U.; Rigollier, P.; Epple, R.; Beisner, D. R.; Guerini, D.;
Smith, P.; Liu, B.; Feifel, R.; Wipfli, P.; Aichholz, R.; Couttet, P.; Dix,
I.; Widmer, T.; Wen, B.; Brandl, T. J. Med. Chem. 2018, 61, 865.
(
e) Hughes, R. A.; Harris, T.; Altmann, E.; McAllister, D.; Vlahos, R.;
Robertson, A.; Cushman, M.; Wang, Z.; Stewart, A. G. Mol.
Pharmacol. 2002, 61, 1053. (f) Tashima, T.; Toriumi, Y.;
Mochizuki, Y.; Nonomura, T.; Nagaoka, S.; Furukawa, K.; Tsuru,
H.; Adachi-Akahane, S.; Ohwada, T. Bioorg. Med. Chem. 2006, 14,
8
014.
3) (a) Gooßen, L. J.; Deng, G.; Levy, L. M. Science 2006, 313, 662.
b) Gooßen, L. J.; Gooßen, K.; Rodríguez, N.; Blanchot, M.; Linder,
(
(
C.; Zimmermann, B. Pure Appl. Chem. 2008, 80, 1725. (c) Rodriguez,
N.; Goossen, L. J. Chem. Soc. Rev. 2011, 40, 5030. (d) Dzik, W. I.;
Lange, P. P.; Gooßen, L. J. Chem. Sci. 2012, 3, 2671.
(
4) (a) Xu, P.; Abdukader, A.; Hu, K.; Cheng, Y.; Zhu, C. J. Chem.
Commun. 2014, 50, 2308. (b) Chu, L.; Ohta, C.; Zuo, Z.; MacMillan,
D. W. J. Am. Chem. Soc. 2014, 136, 10886. (c) Liu, J.; Liu, Q.; Yi, H.;
Qin, C.; Bai, R.; Qi, X.; Lan, Y.; Lei, A. Angew. Chem., Int. Ed. 2014,
5
3, 502. (d) Noble, A.; McCarver, S. J.; MacMillan, D. W. J. Am.
Chem. Soc. 2015, 137, 624. (e) Ventre, S.; Petronijevic, F. R.;
MacMillan, D. W. J. Am. Chem. Soc. 2015, 137, 5654. (f) Cao, H.;
Jiang, H.; Feng, H.; Kwan, J. M. C.; Liu, X.; Wu, J. J. Am. Chem. Soc.
2
018, 140, 16360. (g) Candish, L.; Pitzer, L.; Gomez-Suarez, A.;
Glorius, F. Chem. - Eur. J. 2016, 22, 4753. (h) Garza-Sanchez, R. A.;
Tlahuext-Aca, A.; Tavakoli, G.; Glorius, F. ACS Catal. 2017, 7, 4057.
(
5) (a) Togo, H.; Aoki, M.; Yokoyama, M. Tetrahedron 1993, 49,
8
241. (b) Togo, H.; Katohgi, M. Synlett 2001, 2001, 565. (c) Wu, T.;
Zhang, H.; Liu, G. S. Tetrahedron 2012, 68, 5229. (d) Xie, J.; Xu, P.;
Li, H.; Xue, Q.; Jin, H.; Cheng, Y.; Zhu, C. J. Chem. Commun. 2013,
4
(
9, 5672.
6) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2008, 108, 5299.
(
7) Selected reviews and papers: (a) Narayanam, J. M.; Stephenson,
C. R. Chem. Soc. Rev. 2011, 40, 102. (b) Xuan, J.; Xiao, W. J. Angew.
Chem., Int. Ed. 2012, 51, 6828. (c) Prier, C. K.; Rankic, D. A.;
MacMillan, D. W. Chem. Rev. 2013, 113, 5322. (d) Xuan, J.; Zhang, Z.
G.; Xiao, W. J. Angew. Chem., Int. Ed. 2015, 54, 15632. (e) Beatty, J.
W.; Stephenson, C. R. Acc. Chem. Res. 2015, 48, 1474. (f) Romero, N.
A.; Margrey, K. A.; Tay, N. E.; Nicewicz, D. A. Science 2015, 349,
E
https://dx.doi.org/10.1021/acs.orglett.0c01856
Org. Lett. XXXX, XXX, XXX−XXX