Silver-Catalyzed Sequential Cascade Reaction of Isocyanides with 1-(2-Ethynyl-phenyl)-prop-2-yn-1-ol: Access to Benzo[b]fluorenes and Benzofuran-Pyrroles

Article abstract of DOI:10.1002/adsc.201801344

A silver-catalyzed cycloaromatization of 1-(2-ethynyl-phenyl)-prop-2-yn-1-ol with isocyanides efficiently provides benzo[b]fluorene and benzofuran-pyrrole derivatives through a modular cascade reaction that includes a nucleophilic attack on the diyne substrate. A C?C cross-coupling/oxygen transportation/Diels-Alder/hydrogen shift/isomerization cascade mechanistic pathway is proposed. (Figure presented.).

Full text of DOI:10.1002/adsc.201801344

Title: Silver-Catalyzed Sequential Cascade Reaction of Isocyanides
with 1-(2-Ethynyl-phenyl)-prop-2-yn-1-ol: Access to
Benzo[b]fluorenes and Benzofuran-Pyrroles
Authors: Jian-Quan Liu, Chen Xinyi, Shen Xuanyu, Wang Yihan,
Xiang-Shan Wang, and Xihe Bi
This manuscript has been accepted after peer review and appears as an
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201801344
Link to VoR: http://dx.doi.org/10.1002/adsc.201801344

10.1002/adsc.201801344
Advanced Synthesis & Catalysis
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Silver-Catalyzed Sequential Cascade Reaction of Isocyanides
with 1-(2-Ethynyl-phenyl)-prop-2-yn-1-ol: Access to
Benzo[b]fluorenes and Benzofuran-Pyrroles
Jian-Quan Liu,a Xinyi Chen,a Xuanyu Shen,a Yihan Wang,b Xiang-Shan Wang*a and
Xihe Bi*b,c
a
School of Chemistry and Materials Science, Jiangsu Key Laboratory of Green Synthesis for Functional Materials
Jiangsu Normal University, Xuzhou, Jiangsu 221116, China. Email: xswang1974@yahoo.com
Jilin Province Key Laboratory of Organic Functional Molecular Design & Synthesis, Department of Chemistry,
b
Northeast Normal University, Changchun 130024, China. Email: bixh507@nenu.edu.cn
State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China.
c
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract: A silver-catalyzed cycloaromatization of 1-(2-
ethynyl-phenyl)-prop-2-yn-1-ol with isocyanides efficiently
provides
benzo[b]fluorene
and
benzofuran-pyrrole
derivatives through a modular cascade reaction that
includes a nucleophilic attack on the diyne substrate. A C–
C
cross-coupling/oxygen
transportation/Diels-
Alder/hydrogen shift/isomerization cascade mechanistic
pathway is proposed.
Keywords: Silver; Cascade Reaction; Isocyanides;
Benzo[b]fluorenes; Benzofuran-Pyrroles
Benzo[b]fluorenes are commonly found in numerous
synthetic applications and as valuable intermediates in
organic chemistry.[1-3] In recent years, significant
progress has been achieved in transition-metal
catalysis for the synthesis of these compounds.[4,5]
Among the published procedures, the Myers-Saito
and Schmittel-type (C2-C6) cyclizations of aryl-
substituted enyne-allenes are powerful strategies for
the synthesis of benzo[b]fluorenes, with the
generation of an allene fragment as key intermediates
(Figure 1a and 1b).[6-8] Owing to the limitations in the
generation of allenic substrates, only a few substituted
benzo[b]fluorenes could be obtained from the multi-
step process. As a result, the developments of new
methodologies for the synthesis of benzo[b]fluorenes
are still highly desired.
1-(2-Ethynyl-phenyl)-prop-2-yn-1-ols are readily
available versatile building blocks whose synthetic
applications have been widely explored to build
naphthalenes.[9,10] A direct cycloaromatization of
these diynols in the presence of an electrophile or a
nucleophile could be the ideal route to
benzo[b]fluorenes. To date, only two comparable
examples are known whereby such combination with
the addition of a transition metal can generate
complex carbocyclic ring systems in a cascade
fashion.[11] In 2000 Saá and co-workers reported the
pioneering work on the thermal intramolecular [4 + 2]
cycloaromatization of 1-(2-ethynyl-phenyl)-prop-2-
yn-1-ol to benzo[b]fluorene scaffolds.[11a] More
recently, the Chen group reported on the first silver-
catalyzed tandem electrophilic cascade cyclization of
1-(2-ethynyl-phenyl)-prop-2-yn-1-ol with NXS (X =
Br or I), which selectively afforded halo-substituted
benzo[a]fluorenes (Figure 1c).[11b] Herein, we wish to
1
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10.1002/adsc.201801344
Advanced Synthesis & Catalysis
14
15
16
17
AgF
AgF
AgF
AgF
DBU
DABCO
PPh3
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
82
67
28
34
report an unprecedented chemoselective silver-
catalyzed aromatization reaction of 1-(2-ethynyl-
phenyl)-prop-2-yn-1-ol with isocyanides, a novel
approach to benzo[b]fluorenes and 2,4-disubstituted
benzofuran-pyrrole (Figure 1d). To the best of our
knowledge, this is the first report on the
cycloaromatization of 1-(2-ethynyl-phenyl)-prop-2-
yn-1-ol with nucleophiles that undergoes a sequential
cascade reaction.
1,10-phen
a All reactions were carried out with 0.5 mmol 1a, 1 mmol 2a, 0.05 mmol
catalyst, and 0.15 mmol additive, in 2.0 mL of the indicated solvent, at
b
80 °C under N2 atmosphere for 12 h; yields of isolated products.
Decomposition of substrate, 3a not detected by 1H-NMR.
With the optimized reaction conditions in hand, a
series of experiments were performed to investigate
the scope of this transformation (Scheme 1). A range
of 1-(2-ethynyl-phenyl)-prop-2-yn-1-ol 1 with various
aryl substituents R1 reacted with ethyl isocyanoacetate
2a to productively deliver the cycloaromatization
products 3. Both electron-donating and electron-
withdrawing R1 groups were well tolerated by the
reaction with 2a, giving the desired products (3b-3j)
in moderate to good yields. The substituent groups R
on the aromatic ring that attached to the propargylic
side chain were also compatible with the
cycloaromatization; the corresponding products (3k
and 3l) were afforded in good yield. The reaction of
fused aromatic 1m with 2a also afforded the expected
product 3m in 62% yield. Interestingly, when 1n was
used as a substrate to react with 2a, a single
regioisomer 3n was produced in 79% yield, with the
other isomeric product 3n' not being detected.
Mulliken charge analysis of the possible allene
intermediate is shown in Supporting Information, the
more negative charge of methoxy ortho position,
which is more feasible to undergo an intramolecular
Diels-Alder reaction, is in good agreement with the
experiment that a single regioisomer 3n was produced.
Under the same conditions, a naphthyl-derivatized
substrate uneventfully generated product 3o in 71%
yield.
At the beginning of our investigation, we strived to
optimize the reaction of 1-(2-ethynyl-phenyl)-prop-2-
yn-1-ol 1a with ethyl isocyanoacetate 2a in the
presence of a variety of salts, solvents, and additives
(Table 1). Benzo[b]fluorene product 3a could thus be
obtained in a 45% isolated yield when the reaction
was performed with 10 mol% of Ag2CO3 in N,N-
o
dimethylformamide (DMF) for 12 h at 80 C, (entry
1). Upon screening various silver salts, we observed
that both AgOAc and AgF were efficient catalysts,
while Ag3PO4 and AgNO3 were unreactive under the
same conditions (entries 2-5). Other metal salts
(AuCl(PPh3)2, Pd(OAc)2, CuI) employed as catalysts
were also ineffective at giving product 3a (entries 6–
8). Subsequently, the effect of solvent was also
investigated (entries 9-13), with 1,4-dioxane proving
as the most suitable; 1,2-dichloroethane (DCE) and
toluene also enabled the formation of 3a in acceptable
yield, whereas ethanol only allowed the formation of
trace amount of the product. Encouraged by these
findings, we tested the impact of additives such as
bases[12] and ligands[13] (entries 14-17), to improve the
efficiency of this reaction. Gratifyingly, the addition
of
a
substochiometric
amount
of
1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) increased the
yield of the desired product 3a to 82% (entry 14).
Conversely, no reaction was observed in the absence
of catalyst (entry 13). Therefore, the reaction
conditions listed in entry 14 were considered as
optimized.
Table 1. Optimization of the Reaction Conditions.a
Scheme 1. The scope of 1-(2-ethynyl-phenyl)-prop-2-yn-
1-ol.
entry
catalyst
Ag2CO3
additive
solvent
Yields (%)
1
--
--
--
--
--
--
--
--
--
--
--
--
--
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DCE
45
2
AgOAc
AgF
41
3
49
4
Ag3PO4
AgNO3
AuCl(PPh3)2
Pd(OAc)2
CuI
0[b]
0[b]
0[b]
0[b]
trace
47
5
6
7
8
9
AgF
10
11
12
13
AgF
Toluene
51
AgF
EtOH
trace
58
AgF
1,4-dioxane
1,4-dioxane
--
0
2
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10.1002/adsc.201801344
Advanced Synthesis & Catalysis
Scheme 3. Synthesis of benzofuran-pyrrole.
The scope for the reaction under the optimized
conditions with respect to isocyanides was then
investigated (Scheme 2). A range of active methylene
isocyanides (2b-2f) reacted with 1a similarly to ethyl
isocyanoacetate, delivering the expected products (4a-
4e) in moderate to high yields. The structure of the
product 4a was unequivocally confirmed by X-ray
single crystal diffraction analysis.[14] In contrast, no
reaction was observed between electron-enriched 4-
methoxyphenyl isocyanide and alkyl isocynides, such
as tert-butyl and cyclohexyl isocyanides, under the
standard reaction conditions..
A series of control experiments were conducted to
investigate the reaction mechanism (Scheme 4). We
found that when quenched the reaction mixture of 1a
and 2f, 5a and 2a in half of standard reaction time, 4e',
F, G, were obtained in acceptable yields, respectively
(Scheme 4a and 4c). In addition, the expected product
4e could be formed from 4e' in 83% yield (Scheme
4b). This result suggests that allenyl amides could be
the key intermediate in the synthesis of
benzo[b]fluorenes. Meanwhile, F and G could also
produce the corresponding product 6a (Scheme 4d
and 4e). There is no doubt that F and G are the crucial
intermediates for the synthesis of benzofuran-pyrroles.
Scheme 2. The scope of isocyanides.
Scheme 4. Mechanistic investigations.
Encouraged by these findings, the reactivity of
substrates with the hydroxyl group at the 2-alkynyl-3-
propargyl phenol of the aryl ring was further
investigated. However, the reaction of phenol 5 with
active methylene isocyanides 2a-2c under the
optimized conditions afforded novel products
featuring a 2,4-disubstituted benzofuran-pyrrole (6a-
6c) in good yields (Scheme 3), instead of
benzofluorene. The structure of the product 6a was
unambiguously confirmed by X-ray single crystal
diffraction analysis.[14] This unexpected outcome can
be rationalized in light of recent reports by the
Likhar’s group and by us on the [3+2] cycloaddition
reaction of isocyanides with alkynes, also to give 2,4-
disubstituted pyrroles.[15]
Based on experiments and related precedents, [15,16]
a plausible reaction mechanism for the synthesis of
benzo[b]fluorene and benzofuran-pyrrole is proposed
(Scheme 5). In the case of benzo[b]fluorene synthesis,
the reaction of 1 with the catalyst gives the silver
3
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10.1002/adsc.201801344
Advanced Synthesis & Catalysis
bromobenzaldehyde was consumed as indicated by TLC about 8 h.
The resulting mixture was concentrated and the residue was taken
up in DCM. The organic layer was washed with brine, dried over
MgSO4 and concentrated. Purification of the crude product by
column chromatography (silica gel; petroleum ether: ethyl acetate
= 20:1-5:1) afforded the substituted 2-ethynylbenzaldehyde.
Then, a solution of substituted 2-ethynylbenzaldehyde (5
acetylide intermediate A, which is converted into the
acetylenic imido complex B by 1,1-insertion with the
isocyanide 2a.[16d] The 2,3-allenamide C that is
formed by intramolecular rearrangement of B. The
presence of DBU could probably not only accelerate
the generation of acetylene silver and allenyl amide,
but also stabilize the formed Ag intermediate.[17] Then, mmol) in THF (10 mL) in Schlenk tube was added
ethynylmagnesium bromide (1.2 equiv) at 0 C and then stirred at
room temperature under nitrogen until the full conversion of
substituted 2-ethynylbenzaldehyde monitored by thin-layer
chromatography about 6 h. After treatment with a saturated
aqueous solution of NH4Cl and extractions with Et2O, the
combined organic layers were washed with brine, dried over
MgSO4 and concentrated under reduced pressure. Purification of
the crude product by column chromatography (silica gel;
petroleum ether: ethyl acetate = 8: 1) afforded the substituted 1-
(2-ethynylphenyl)prop-2-yn-1-ol 1.
Typical synthetic procedure (with 3a as an example): A mixture
of 1a (131 mg, 0.5 mmol), DBU (22 uL, 0.15 mmol) and AgF (6
mg, 0.05 mmol) in 1,4-dioxane (2.0 mL) stired at 80 C then add
2a (110 uL, 1 mmol) under the nitrogen atmosphere, until the
substrate 1a was consumed as indicated by TLC about 12 h. The
resulting mixture was concentrated and the residue was taken up
in DCM. The organic layer was washed with brine, dried over
MgSO4 and concentrated. Purification of the crude product by
column chromatography (silica gel; petroleum ether: ethyl acetate
= 5: 1) afforded 3a in 82% yield as a white solid, m.p. 173-174 C;
1H-NMR (400 MHz, CDCl3) δ 8.11 (s, 1H), 7.85 (d, J = 7.2 Hz,
1H), 7.81 (d, J = 9.2 Hz, 1H), 7.54-7.52 (m, 2H), 7.40 (t, J = 7.6
Hz, 1H), 7.33 (t, J = 7.6 Hz, 1H), 7.16 (dd, J = 9.2 Hz and 2.4 Hz,
1H), 6.53 (t, J = 6.0 Hz, 1H), 4.36 (d, J = 5.6 Hz, 2H), 4.29 (q, J =
7.2 Hz, 2H), 4.11 (s, 2H), 3.94 (s, 3H), 1.35 (t, J = 7.2 Hz, 3H);
13C-NMR (CDCl3, 100 MHz) δ 169.8, 169.4, 158.2, 142.9, 140.5,
140.1, 137.9, 130.6, 129.9, 128.8, 128.6, 127.4, 127.0, 125.2,
120.1, 119.6, 118.6, 103.5, 61.7, 55.5, 41.5, 36.0, 14.2; HRMS
(ESI-TOF) m/z calculated for C23H22NO4 [M+H]+ : 376.1543
found: 376.1550.
C undergoes an intramolecular Diels-Alder reaction
to form the strained cyclic allene D, which isomerizes
by intramolecular hydrogen shift to give the final
product 3a.[18] For benzofuran-pyrrole, the
coordinating effect of the hydroxyl and alkynyl
groups enables the formation of the silver complex
E.[19] 5-Endo-dig cyclization of complex is occurred
on E, generating the benzofuran F. The terminal
alkyne in F undergoes a [3+2] cycloaddition with the
isocyanide reactant, producing the intermediate
G.[16,20] The oxidation of alcohol to carbonyl group
gives the final product 6a.[15a]
Scheme 5. Plausible Mechanism.
In summary, we have developed a novel silver- Typical synthetic procedure (with 6a as an example): A mixture
of 5 (139 mg, 0.5 mmol), DBU (22 uL, 0.15 mmol) and AgF (6
mg, 0.05 mmol) in 1,4-dioxane (2.0 mL) stired at 80 C then add
2 (113 mg, 1 mmol) under the air condition, until the substrate 5
was consumed as indicated by TLC about 12 h. The resulting
catalyzed sequential cascade cyclization reaction of
isocyanides with 1-(2-ethynyl-phenyl)-prop-2-yn-1-
ols, which afforded either benzo[b]fluorenes or
benzofuran-pyrrole in good to excellent yield,
mixture was concentrated and the residue was taken up in DCM.
depending on the presence of a hydroxyl group on the
aryl group of the substrate. The unprecedented
reaction between nucleophiles and 1-(2-ethynyl-
phenyl)-prop-2-yn-1-ol has also been described.
Mechanistic pathways were proposed for the
formation of these alternate products. Considering the
relevance of benzo[b]fluorenes and benzofuran-
pyrrole as potentially useful building blocks, this
practical and novel methodology can find potential
applications in the future.
The organic layer was washed with brine, dried over MgSO4 and
concentrated. Purification of the crude product by column
chromatography (silica gel; petroleum ether: ethyl acetate = 1: 2)
afforded 6a in 85% yield as a yellow solid, m.p. 224-226 C; 1H-
NMR (400 MHz, CDCl3) δ 9.88 (s, 1H), 7.83 (d, J = 8.8 Hz, 2H),
7.68 (t, J = 8.0 Hz, 2H), 7.59-7.57 (m, 1H), 7.42 (s, 1H), 7.38 (s,
1H), 7.31 (t, J = 8.0 Hz, 1H), 6.98 (d, J = 8.8 Hz, 2H), 4.36 (d, J =
7.2 Hz, 2H), 3.86 (s, 3H), 1.38 (t, J = 7.2 Hz, 3H); 13C-NMR
(CDCl3, 100 MHz) δ 189.9, 161.0, 160.3, 157.9, 155.2, 130.9,
129.5, 128.1, 126.7, 126.6, 124.9, 124.1, 122.8, 122.7, 116.4,
114.4, 114.3, 100.3, 61.0, 55.4, 14.3; HRMS (ESI-TOF) m/z
calculated for C23H20NO5 [M+H]+ : 390.1336 found: 390.1349.
Experimental Section
Acknowledgements
Typical synthetic procedure for 1:[21] To a solution of
substituted 2-bromobenzaldehyde (5 mmol) in Et3N (10 mL) in
Schlenk tube was added Pd(PPh3)2Cl2 (2 mol%, 70.2 mg) and CuI
(5 mol%, 47.6 mg), and stirred at room temperature for 10 min
under nitrogen. Then, substituted acetylene (1.2 equiv) was added
and the solution was stirred at 80 C until the substrate 2-
This work was financially supported by NSFC of China (No.
21702078, 21871043), NSF of Jiangsu Province (No.
BK20170231), Natural Science Foundation of Jiangsu Higher
Education Institution (17KJA150003), the open project of Jilin
Province Key Laboratory of Organic Functional Molecular
4
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10.1002/adsc.201801344
Advanced Synthesis & Catalysis
Design & Synthesis (130028830), the Priority Academic Program
Development of Jiangsu Higher Education Institution, and TAPP.
2012, 51, 6493; d) Y. Chen, L. Wang, Y. Liu, Y. Li, Chem.
Eur. J. 2011, 17, 12582.
[9] a) Z. Chen, X. Jia, C. Ye, G. Qiu, J. Wu, Chem. Asian. J. 2014,
9, 126; b) Y. Feng, C. Chen, Y. Liu, Angew. Chem. 2012, 124,
6285; Angew. Chem. Int. Ed. 2012, 51, 6181; c) C. Chen, G.
Li, Y. Liu, Adv. Synth. Catal. 2011, 353, 392.
References
[1] a) B. Nicolas, L. Fabien, T. Jana, S. Ninette, H. Frank, M. K.
Manfred, M. Marcel, Chem. Mater. 2011, 23, 2237; b) F. Liu,
L.-H. Xie, C. Tang, J. Liang, Q.-Q. Chen, B. Peng, W. Wei, Y.
Cao, W. Huang, Org. Lett. 2009, 11, 3850; c) S. J. Gould, C.
R. Melville, M. C. Cone, J. Chen, J. R. Carnery, J. Org. Chem.
1997, 62, 320.
[10] a) T. Lauterbach, S. Arndt, M. Rudolph, F. Rominger, A. S.
K. Hashmi, Adv. Synth. Catal. 2013, 355, 1755; b) J. Liana, R.
Liu, Chem. Commun. 2007, 13, 1337.
[11] a) Z. Chen, M. Zeng, J. Yuan, Q. Yang, Y. Peng, Org. Lett.
2012, 14, 3588; b) Guez. D. Rodrí, A. Navarro, L. Castedo, D.
Domínguez, C. Saá, Org. Lett. 2000, 2, 1497.
[2] a) J. Lee, J. Park, Org. Lett. 2015, 17, 3960; b) E. Katja, H.
Marijana, P. Ivo, C. Irena, J. Ivana, P. Krešimir, K. Marijeta,
K. Z. Grace, J. Med. Chem. 2009, 52, 2482; b) K. S. Feldman,
K. J. Eastman, J. Am. Chem. Soc. 2006, 128, 12562.
[12] a) G. Fang, X. Cong, G. Zanoni, Q. Liu, X. Bi, Adv. Synth.
Catal. 2017, 359, 1422; b) G. Fang, X. Bi, Chem. Soc. Rev.
2015, 44, 8124.
[3] a) K. Wang, Y.-H. Wang, H. Yang, N. G. Akhmedov, J. L.
Petersen, Org. Lett. 2009, 11, 2527; b) D. Kim, J. L. Petersen,
K. Wang, Org. Lett. 2006, 8, 2313; c) L. Francesco, F. Angelo,
R. Angela, A. Rosaria, P. Anja, W. H. Rolf, C. Angelo, J.
Med. Chem. 2004, 47, 6792.
[13] a) R. K. Gadi, K. Ravi, R. Manda, S. R. Maddi, Chem.
Commun. 2018, 54, 759; b) K. Keiichi, S. Yuta, S. Kohei, S.
Kodai, Y. Tohru, Angew. Chem. 2012, 129, 11752; Angew.
Chem. Int. Ed. 2017, 56, 11594.
[4] a) J. Xuan, S. Armido, Chem. Soc. Rev. 2017, 46, 4329; b) A.
Enrique, S. Roberto, A. Manuel, G. G. Patricia, Chem. Rev.
2016, 116, 8256.
[14] CCDC 4a (1861505), 6a (1861506) contains the
supplementary crystallographic data for this paper.
[15] a) R. Zhang, Z.-Y. Gu, S.-Y. Wang, S.-J. Ji, Org. Lett. 2018,
20, 5510; b) D. K. Tiwari, J. Pogula, B. Sridhar, D. K. Tiwari,
P. R. Likhar, Chem. Commun. 2015, 51, 13646; c) X. Meng, P.
Liao, J. Liu, X. Bi, Chem. Commun. 2014, 50, 11837.
[5] a) M. Mou, B. Rengarajan, Adv. Synth. Catal. 2018, 360, 1453;
b) H. Zhu, Z. Chen, Org. Lett. 2016, 18, 488; c) Y.-N. Wu, T.
Xu, R. Fu, N.-N. Wang, W.-J. Hao, S.-L. Wang, G. Li, S.-J.
Tu, B. Jiang, Chem. Commun. 2016, 52, 11943; d) A.
Sikkandarkani, S. Kannupal, J. Org. Chem. 2016, 81, 122; e)
P. Kamalkishore, P. G. Gabriel, H. Trevor, H. Audrey, P. Hoa,
B. Tanmay, H. Kenneth, V. A. Igor, J. Am. Chem. Soc. 2015,
137, 1165; f) P. K. Reinhard, H. Filip, M. Jiří, C. Ivana, K.
Martin, Chem. Eur. J. 2015, 21, 13577; g) A.-H. Zhou, F. Pan,
C. Zhu, L.-W. Ye, Chem. Eur. J. 2015, 21, 10278. h) G. G.
Patricia, A. R. Muhammad, M. S. Ana, A. F. Manuel, S.
Roberto, Org. Lett. 2012, 14, 4778.
[16] a) J.-Q. Liu, X. Shen, Y. Wang, X.-S, Wang, X. Bi, Org. Lett.
2018, 20, 6930; b) Z. Liu, H. Ji, W. Gao, G. Zhu, L. Tong, F.
Lei, B. Tang, Chem. Commun. 2017, 53, 6259; c) Y. Wang, R.
K. Kumar, X. Bi, Tetrahedron Lett. 2016, 57, 5730; d) J. Liu,
Z. Liu, N. Wu, P. Liao, X. Bi, Chem. Eur. J. 2014, 20, 2154.
[17] A series of bases were screened and the details were shown
in supporting information. The results showed that DBU or
DABCO probably coordinates with silver and, therefore,
stabilizes the Ag intermediate, so that they are more efficient
than inorganic bases. This effect could also be found in: R.
Yuan, B. Wei, G. Fu, J. Org. Chem. 2017, 82, 3639.
[6] a) M. Schmittel, A. A. Mahajan, G. Bucher, J. W. Bats, J. Org.
Chem. 2007, 72, 2166; b) M. Schmittel, M. Maywald, Chem.
Commun. 2001, 155; c) M. Schmittel, J. P. Steffen, M.
Maywald, B. Engels, H. Helten, P. Musch, J. Chem. Soc.
Perkin Trans. 2001, 2, 1331; d) M. Schmittel, M. Keller, S.
Kiau, M. Strittmatter, Chem. Eur. J. 1997, 3, 807; e) M.
Schmittel, S. Kiau, Liebigs Ann. 1997, 733; f) M. Schmittel,
M. Strittmatter, K. Vollmann, S. Kiau, Tetrahedron Lett. 1996,
37, 999; g) M. Schmittel, M. Strittmatter, S. Kiau, Angew.
Chem. 1996, 108, 1952; Angew. Chem. Int. Ed. 1996, 35,
1843.
[18] D. Rodríguez, A. Navarro-Vázquez, L. Castedo, D.
Domínguez, C. Saá, J. Org. Chem. 2003, 68, 1938.
[19] a) J. Liu, Z. Liu, P. Liao, L. Zhang, T. Tu, X. Bi, Angew.
Chem. 2015, 127, 10764; Angew. Chem. Int. Ed. 2015, 54,
10618; b) S. Tong, Q. Wang, M.-X. Wang, J. Zhu, Angew.
Chem. 2015, 127, 1309; Angew. Chem. Int. Ed. 2015, 54,
1293.
[20] a) J. Liu, Z. Fang, Q. Zhang, Q. Liu, X. Bi, Angew. Chem.
2013, 125, 7091; Angew. Chem. Int. Ed. 2013, 52, 6953; b) M.
Gao, C. He, H. Chen, R. Bai, B. Cheng, A. Lei, Angew. Chem.
2013, 125, 7096; Angew. Chem. Int. Ed. 2013, 52, 6958.
[7] a) N. Sun, X. Xie, G. Wang, H. Chen, Y. Liu, Adv. Synth.
Catal. 2017, 359, 1394; b) H. Trevor, P. G. Gabriel, J. C.
Ronald, V. A. Igor, J. Org. Chem. 2016, 81, 6007; c) E.
Rettenmeier, M. M. Hansmann, A. Ahrens, K. Rbenacker,
Saboo, T. Massholder, J. Meier, C. Rudolph, M. F. Rominger,
A. S. K. Hashmi, Chem. Eur. J. 2015, 21, 14401; d) R. Shen,
L. Chen, X. Huang, Adv. Synth. Catal. 2009, 351, 2833.
[21] F. Zhang, Z. Qin, L. Kong, Y. Zhao, Y. Liu, Y. Li, Org. Lett.
2016, 18, 5150.
[8] a) Y. Yamamoto, K. Nishimura, S. Mori, M. Shibuya, Angew.
Chem. 2017, 129, 5586; Angew. Chem. Int. Ed. 2017, 56,
5494; b) Z. Zhou, D. Jin, L. Li, Y. He, P. Zhou, X. Yan, X.
Liu, Y. Liang, Org. Lett. 2014, 16, 5616; c) Y. Chen, M. Chen,
Y. Liu, Angew. Chem. 2012, 124, 6599; Angew. Chem. Int. Ed.
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10.1002/adsc.201801344
Advanced Synthesis & Catalysis
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6
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