A Copper-Catalyzed Reductive Defluorination of β-Trifluoromethylated Enones via Oxidative Homocoupling of Grignard Reagents

Article abstract of DOI:10.1021/acs.orglett.8b00379

An efficient copper-catalyzed reductive defluorination of β-trifluoromethylated enones via an oxidative homocoupling of Grignard reagents is reported. The reaction proceeded smoothly with a wide range of substrates, including the ones bearing aromatic heterocycles, such as furyl and thienyl ring systems in high yields (80-92%, except one example) under mild conditions. This provides a practical method for synthesis of gem-difluoroolefin ketones. It is also worth noting that this homocoupling process of Grignard reagents using β-trifluoromethylated enones as oxidizing reagents is effective for both the Csp²-Csp² and Csp³-Csp³ bond formations, including for substrates whose β-hydride elimination of the corresponding transition metal alkyl complex is particularly facile, affording coupling products with high yields (83-95%), simultaneously.

Full text of DOI:10.1021/acs.orglett.8b00379

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
A Copper-Catalyzed Reductive Defluorination of
β‑Trifluoromethylated Enones via Oxidative Homocoupling of
Grignard Reagents
Xiaoting Wu,† Fang Xie,*,† Ilya D. Gridnev,‡ and Wanbin Zhang*,†
†Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Chemistry and Chemical Engineering, Shanghai Jiao
Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
‡Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
S
* Supporting Information
ABSTRACT: An efficient copper-catalyzed reductive defluori-
nation of β-trifluoromethylated enones via an oxidative
homocoupling of Grignard reagents is reported. The reaction
proceeded smoothly with a wide range of substrates, including
the ones bearing aromatic heterocycles, such as furyl and thienyl
ring systems in high yields (80−92%, except one example)
under mild conditions. This provides a practical method for
synthesis of gem-difluoroolefin ketones. It is also worth noting
that this homocoupling process of Grignard reagents using β-trifluoromethylated enones as “oxidizing reagents” is effective for
both the Csp2−Csp2 and Csp3−Csp3 bond formations, including for substrates whose β-hydride elimination of the
corresponding transition metal alkyl complex is particularly facile, affording coupling products with high yields (83−95%),
simultaneously.
Scheme 1. Cleavage of C−F Bond in the Trifluoromethyl
Group Attached to a π Electron System under
Electroreductive Conditions
gem-Difluoroalkenes are versatile building blocks in organic
synthesis, in which the gem-difluorovinyl group can be
transformed into various functionalities.1 Therefore, gem-
difluoroalkene compounds have attracted significant interest
and have become very important synthetic targets in academia
and industry.1c,2 2-Trifluoromethyl-1-alkenes are reactive
compounds, and their selective defluorination is a promising
method for the preparation of difluoro compounds due to the
availability of trifluoromethylated compounds.1c,2k−m Further-
more, in recent decades, the addition of nucleophiles to α-
trifluoromethyl alkenes and subsequent β-fluoride elimination
via an SN2′ reaction has been extensively explored, allowing for
rapid access to gem-difluoroalkenes.2k,3
For SN2′ reactions of organic fluorides, metaphorically, an
electron can be regarded as the smallest nucleophile. In general,
it is not easy to cleave a C−F bond due to its strong bond
energy. However, a C−F bond of the trifluoromethyl group
that is attached to a π system can be readily cleaved under
electroreductive conditions, since electron acceptance into the
π-system and subsequent extrusion of a fluoride ion contribute
greatly to the driving force of the reaction. However, to date,
only a few reductive-type defluorinations for the preparation of
gem-difluorovinyl groups have been reported, and they mostly
consist of electrochemical reductions,4 the use of reductive
metal magnesium,5 and photocatalytic conditions2m,6 (Scheme
1, previous work). As is well-known, oxidative homocoupling
reactions of organometallic reagents occur with an oxidant; the
oxidant can be regarded as an electron acceptor. Inspired by the
mechanism of oxidative coupling reactions of organometallic
reagents,7 we envisioned that an oxidative coupling reaction
may provide a convenient electron source and that compounds
bearing a CF3 group attached to a π-system may accept
electrons and thus act as an “oxidizing reagent”. This strategy
provides a convenient electron source, which results in a
reductive-type reaction of the trifluoromethyl group bonded to
a π-electron system. gem-Difluoroalkenes are thus obtained
Received: February 2, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00379
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
accompanied by an oxidative homocoupling reaction of
organometallic reagents (Scheme 1, our strategy).
used as a ligand of Cu(I)TC, and the yields of 2a and 3a (88%
and 89%, respectively) increased (entry 3). Following screening
of the copper salts and the amount of catalyst (entries 4−8), 1.0
mol % of Cu(I)TC was found to give the best result. The yields
of 2a and 3a were further improved to 91% and 93%,
respectively, and only a small quantity of 1,2-addition product
(2a:4 = 91:9) was observed (entry 7).
gem-Difluoroolefin ketones are versatile synthons for many
fluorinated compounds and possess unique reactivity toward
intramolecular SNV reactions.8 However, only two method-
ologies have been developed for their preparation: one required
precious metal iridium as the catalyst via a photocatalytic
decarboxylative/defluorinative reaction,6a and another required
harsh reaction conditions and utilized hazardous and expensive
reagents.9 On the other hand, homocoupling reactions of
Grignard reagents allow for easy and efficient access to
symmetrical compounds, and homocoupling reactions of aryl
and alkenyl Grignard reagents have been extensively ex-
plored;10 however, the oxidative homocoupling of alkyl
Grignard reagents,11,12 especially those bearing β-hydrogens,12
remains a challenge due to the difficulty of alkyl−alkyl
couplings using transition metal catalysts. As part of our
project on the Cu-catalyzed functionalization of enones,13
herein, we report a highly efficient synthesis of gem-
difluoroolefin ketones via a copper-catalyzed reductive
defluorination. Simultaneously, symmetrical biaryls, alkenes,
and alkanes can be obtained effectively via oxidative
homocoupling of Grignard reagents. In particular, this coupling
process is also effective for Csp3−Csp3 bond formations
(Scheme 1, this work).
With the optimized reaction conditions (Table 1, entry 7) in
hand, the scope of substrates 1 was then examined (Table 2).
a
Table 2. Substrates Scope of β-Trifluoromethylated Enones
We began our study using β-trifluoromethylated enone 1a as
a model substrate (Table 1), which can be readily obtained in
a
Table 1. Optimization of the Reaction Conditions
c
yield (%)
b
entry
ligand
CuX (mol %)
2a:4
2a
3a
b
b
b
1
2
3
4
5
6
7
8
−
−
−
4:96
trace
66
trace
65
Cu(I)TC (2.5)
Cu(I)TC (2.5)
Cu(I)I (2.5)
69:31
90:10
83:17
75:25
77:23
91:9
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
88
89
81
81
Cu(II)(OAc)2 (2.5)
Cu(II)Br2 (2.5)
Cu(I)TC (1.0)
Cu(I)TC (0.1)
73
77
74
76
91
93
81:19
80
82
a
The reaction of 1a (0.20 mmol) with PhMgBr (2.5 equiv) was
performed in DCM (2.0 mL) at room temperature for 3 h in the
presence of the complex in situ from CuX (n mol %) and PPh3 (2n
b
c
1
mol %). Determined by H NMR spectroscopy. Yield of products
a
The reaction of 1a−x (0.50 mmol) with PhMgBr (2.5 equiv) was
isolated after chromatography.
performed in DCM (5.0 mL) at room temperature for 3 h in the
presence of the complex formed in situ from Cu(I)TC (0.005 mmol,
1.0 mol %) and PPh3 (0.01 mmol, 2.0 mol %). Yield of products
(2a−x) and product 3a isolated after chromatography.
b
high yield by the reaction of commercially available trifluoro-
acetophenone and a Wittig reagent.14 A blank experiment using
1a with PhMgBr in the absence of a copper salt provided 1,2-
addition product 4 as the major product (entry 1). Under our
assumption above (Scheme 1), the reaction was carried out by
employing PhMgBr and Cu(I)TC (copper(I)-thiophene-2-
carboxylate) in the presence of 1a in DCM and at room
temperature over 3 h. To our delight, the gem-difluoroolefins
ketone 2a and biphenyl 3a products were obtained in yields of
66% and 65%, respectively, accompanied by a minor 1,2-
addition product 4 (2a:4 = 69:31) (entry 2). Next, PPh3 was
The reaction proceeded smoothly with a wide range of
substrates. The influence of the R1 group in substrates 1 was
first investigated. When R1 was an alkyl group, such as Et or Cy,
the desired products (2b−c) were afforded in moderate to
good yields (66% and 81%, respectively). When R1 was either a
phenyl or substituted phenyl group, good to high yields (80−
92%) of the corresponding gem-difluoroolefins ketones (2a,
B
DOI: 10.1021/acs.orglett.8b00379
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Organic Letters
Letter
2d−q) were obtained, irrespective of the electronic properties
or substitution pattern on the aromatic ring. In addition, the
reaction scope was expanded to include substrates bearing
aromatic heterocycles, such as furyl and thienyl ring systems.
The desired products (2r−s) were obtained with excellent
yields (91% and 92%, respectively). With R2 being a substituted
phenyl group bearing electron-rich or electron-poor substitu-
ents, the reactions proceeded well to afford the corresponding
gem-difluoroolefins ketones (2t−w) in high yields (85−91%).
Finally, β-CF3-α,β,γ,δ-dienone (1x) was also employed as a
substrate in this reaction, giving the corresponding product
(4E)-2x in 89% yield.
Additionally, it is also worth noting that the oxidative
homocoupling product 3a of PhMgBr provided similarly high
yields using this Cu-catalyzed reductive-type reaction of
trifluoromethyl groups bonded to a π-electron system. This
suggests that the Cu-catalyzed system could also be of use for
the oxidative homocoupling of Grignard reagents using 1 as an
“oxidizing reagent”, a reaction which has not been previously
reported. Subsequently, the scope of Grignard reagents in the
reaction with 1a was investigated (Table 3). First, various
smoothly, with the coupling also being highly stereoselective.
Of particular note is that the Csp3−Csp3 homocoupling
products (3l−3o) were obtained in good yields (83−92%)
including those from reactions with PhCH(CH3)MgBr,
Ph(CH2)2MgBr, and Ph(CH2)3MgBr (3m, 83%; 3n, 92%;
3o, 91%). These three substrates are especially challenging
since β-hydride elimination of the corresponding transition
metal alkyl complex is particularly facile. Notably, the
homocoupling product of PhCH(CH3)MgBr is only meso-2,3-
diphenylbutane (3m) with none of the D,L-2,3-diphenylbutane
being observed.
We next turned our attention to the reaction mechanism.
According to a blank experiment (Table 1, entry 1), the major
product was 1,2-addition product 4, with only trace amounts of
2a and 3a being observed in the absence of the copper salt
under the optimized reaction conditions (Table 1, entry 7),
which indicated that this reaction required a copper catalyst.
Furthermore, when 2.0 equiv of TEMPO were used as a radical
scavenger in this reaction system (see Supporting Information),
2a and 3a were isolated in yields of 90% and 92%, respectively,
yields that are identical to those obtained in the absence of
TEMPO. This result suggests that the reaction does not
proceed through a radical process. On the basis of the
experimental results and previous reports,4,7 a possible catalytic
pathway for the reaction of 1a with PhMgBr has been proposed
(Scheme 2). The reaction process may begin with an
a
Table 3. Substrates Scope of Grignard Reagents
Scheme 2. Proposed Reaction Mechanism
organocopper reagent PhCu(I), which formed via trans-
metalation of PhMgBr and Cu(I)TC. Treatment with another
equivalent of PhMgBr results in the formation of a copper
monoanionic salt A.7a,b Subsequent oxidative homocoupling
with 1a acting as an oxidant, electron acceptance into the π-
system of 1a, and extrusion of a fluoride ion afford biphenyl 3a
and the copper species B. The copper species B is readily
transmetalated with another equivalent of PhMgBr to provide
the magnesium species C, which is hydrolyzed to form the
target product 2a. The organocopper reagent PhCu(I) is
regenerated to complete the catalytic cycle.
To further demonstrate the utility of our methodology for
the synthesis of gem-difluoroolefin ketones, a gram-scale
reaction was conducted, and gem-difluoroolefin ketone 2a and
biphenyl 3a were obtained in 88% and 89% yields, respectively
(Scheme 3a). In addition, MeMgBr and EtMgBr were used in
place of PhMgBr, and 2a was obtained easily in high yields
(92% and 90%, respectively), accompanied by the formation of
a
The reaction of 1a (0.50 mmol) with RMgBr (2.5 equiv) was
performed in DCM (5.0 mL) at room temperature for 3 h in the
presence of the complex in situ from Cu(I)TC (0.005 mmol, 1.0 mol
%) and PPh3 (0.01 mmol, 2.0 mol %). Yield of products (3a−o) and
product 2a isolated after chromatography.
b
substituted aryl magnesium reagents were coupled in high
yields (90−95%). Functional groups, such as alkyl (3b), alkoxy
(3c, 3f−h), fluorine (3d), and trifluoromethyl (3e), were all
well tolerated, irrespective of the substitution pattern on the
aromatic ring. 1- or 2-Naphthylmagnesium reagents were also
amenable to this reaction and afforded their corresponding
binaphthyls 3i and 3j with high yields (94% and 95%,
respectively). A phenyl substituted alkenyl Grignard reagent
also afforded its corresponding conjugated diene (3k)
C
DOI: 10.1021/acs.orglett.8b00379
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Organic Letters
Letter
Scheme 3. Gram-Scale Reactions of 1a
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00379.
Experimental procedures and characterization data for all
reactions and products, including 1H, 13C, and 19F NMR
spectra (PDF)
ethane or butane, which are readily expelled as gas from the
reaction mixture (Scheme 3b).
To test the versatility of gem-difluoroolefin ketones obtained
via the aforementioned sequence, we performed several
transformations on γ,γ-difluoroallylic ketone 2a (Scheme 4).
AUTHOR INFORMATION
Corresponding Authors
■
*xiefang@sjtu.edu.cn.
*wanbin@sjtu.edu.cn.
ORCID
Scheme 4. Conversions of γ,γ-Difluoroallylic Ketone 2a
Wanbin Zhang: 0000-0002-4788-4195
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the NSFC (Nos. 21572129 and 21620102003) and
Shanghai Municipal Education Commission (No. 2017-
01070002E00030).
REFERENCES
■
(1) For selected reviews, see: (a) O’Hagan, D. Chem. Soc. Rev. 2008,
37, 308. (b) Landelle, G.; Bergeron, M.; Turcotte-Savard, M.-O.;
Paquin, J.-F. Chem. Soc. Rev. 2011, 40, 2867. (c) Zhang, X.; Cao, S.
Tetrahedron Lett. 2017, 58, 375. For selected papers, see: (d) Ichikawa,
J. J. Fluorine Chem. 2000, 105, 257. (e) Unzner, T. A.; Magauer, T.
Tetrahedron Lett. 2015, 56, 877. (f) Hu, J.; Han, X.; Yuan, Y.; Shi, Z.
Angew. Chem., Int. Ed. 2017, 56, 13342. (g) Sakaguchi, H.; Uetake, Y.;
Ohashi, M.; Niwa, T.; Ogoshi, S.; Hosoya, T. J. Am. Chem. Soc. 2017,
139, 12855. (h) Zhu, C.; Song, S.; Zhou, L.; Wang, D.-X.; Feng, C.;
Loh, T.-P. Chem. Commun. 2017, 53, 9482. (i) Tang, H.-J.; Lin, L.-Z.;
Feng, C.; Loh, T.-P. Angew. Chem., Int. Ed. 2017, 56, 9872. (j) Lu, X.;
Wang, Y.; Zhang, B.; Pi, J.-J.; Wang, X.-X.; Gong, T.-J.; Xiao, B.; Fu, Y.
J. Am. Chem. Soc. 2017, 139, 12632.
(2) For selected reviews, see: (a) Brahms, D. L. S.; Dailey, W. P.
Chem. Rev. 1996, 96, 1585. (b) Burton, D. J.; Yang, Z.-Y.; Qiu, W.
Chem. Rev. 1996, 96, 1641. (c) Tozer, M. J.; Herpin, T. F. Tetrahedron
1996, 52, 8619. (d) Amii, H.; Uneyama, K. Chem. Rev. 2009, 109,
2119. (e) Chelucci, G. Chem. Rev. 2012, 112, 1344. (f) Decostanzi, M.;
Campagne, J. M.; Leclerc, E. Org. Biomol. Chem. 2015, 13, 7351. For
selected recent papers, see: (g) Aikawa, K.; Toya, W.; Nakamura, Y.;
Mikami, K. Org. Lett. 2015, 17, 4996. (h) Gao, B.; Zhao, Y.; Hu, J.; Hu,
J. Org. Chem. Front. 2015, 2, 163. (i) Hu, M.; Ni, C.; Li, L.; Han, Y.;
Hu, J. J. Am. Chem. Soc. 2015, 137, 14496. (j) Zhang, Z.; Yu, W.; Wu,
C.; Wang, C.; Zhang, Y.; Wang, J. Angew. Chem., Int. Ed. 2016, 55, 273.
(k) Huang, Y.; Hayashi, T. J. Am. Chem. Soc. 2016, 138, 12340.
(l) Fuchibe, K.; Hatta, H.; Oh, K.; Oki, R.; Ichikawa, J. Angew. Chem.,
Int. Ed. 2017, 56, 5890. (m) Lang, S. B.; Wiles, R. J.; Kelly, C. B.;
Molander, G. A. Angew. Chem., Int. Ed. 2017, 56, 15073. (n) Takayama,
R.; Yamada, A.; Fuchibe, K.; Ichikawa, J. Org. Lett. 2017, 19, 5050.
(3) (a) Fuchikami, T.; Shibata, Y.; Suzuki, Y. Tetrahedron Lett. 1986,
27, 3173. (b) Miura, T.; Ito, Y.; Murakami, M. Chem. Lett. 2008, 37,
1006. (c) Fuchibe, K.; Takahashi, M.; Ichikawa, J. Angew. Chem., Int.
Ed. 2012, 51, 12059. (d) Hirotaki, K.; Hanamoto, T. Org. Lett. 2013,
15, 1226. (e) Ichitsuka, T.; Fujita, T.; Arita, T.; Ichikawa, J. Angew.
Chem., Int. Ed. 2014, 53, 7564. (f) Liu, Y.; Zhou, Y.; Zhao, Y.; Qu, J.
Org. Lett. 2017, 19, 946.
The product 2a can be readily converted to the corresponding
γ,γ-difluoro allylic alcohol 5 in a yield of 99% by addition of
PhMgBr. Fortunately, 5 can be readily converted to 2-
fluorinated dihydrofuran 6 in a yield of 95% via an
intramolecular SNV reaction, thus averting tedious syntheses
of fluorine-containing five-membered heterocycles, which
usually require harsh reaction conditions.2d,8,15 In addition,
the corresponding gem-difluorodiene 7 was obtained in 99%
yield via a dehydration reaction of 5. Interestingly, hydro-
genation of compound 2a with H2 in the presence of a Pd/C
catalyst and in different solvents allowed for the selective
formation of the hydrogenated products in high yields (8, 99%;
9, 99%). In addition, 2a can also be converted to
tetrasubstituted 2H-pyrrole 10 in a yield of 92% by reaction
with benzyl amine in the presence of a ZnCl2 catalyst.
In conclusion, we have developed an efficient synthesis of
gem-difluoroolefin ketones via a copper-catalyzed reductive
defluorination, accompanying an oxidative homocoupling of
Grignard reagents for the synthesis of symmetrical alkanes or
biaryls. This reaction can be performed under mild conditions
providing high yields for the two desired products, simulta-
neously. In particular, this coupling process is effective for
Csp3−Csp3 bond formation, including for substrates whose β-
hydride elimination of the corresponding transition metal alkyl
complex is particularly facile.
(4) (a) Uneyama, K.; Kato, T. Tetrahedron Lett. 1998, 39, 587.
(b) Uneyama, K.; Maeda, K.; Kato, T.; Katagiri, T. Tetrahedron Lett.
1998, 39, 3741. (c) Uneyama, K.; Mizutani, G.; Maeda, K.; Kato, T. J.
Org. Chem. 1999, 64, 6717.
D
DOI: 10.1021/acs.orglett.8b00379
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(5) (a) Tius, M. A.; Busch-Petersen, J.; Marris, A. R. Chem. Commun.
1997, 1867. (b) Amii, H.; Kobayashi, T.; Hatamoto, Y.; Uneyama, K.
Chem. Commun. 1999, 1323. (c) Amii, H.; Kobayashi, T.; Terasawa,
H.; Uneyama, K. Org. Lett. 2001, 3, 3103. (d) Uneyama, K.; Amii, H. J.
Fluorine Chem. 2002, 114, 127. (e) Carnell, A. J.; Hale, I.; Denis, S.;
Wanders, R. J. A.; Isaacs, W. B.; Wilson, B. A.; Ferdinandusse, S. J.
Med. Chem. 2007, 50, 2700.
(6) (a) Xiao, T.; Li, L.; Zhou, L. J. Org. Chem. 2016, 81, 7908.
(b) Tian, H.; Shimakoshi, H.; Imamura, K.; Shiota, Y.; Yoshizawa, K.;
Hisaeda, Y. Chem. Commun. 2017, 53, 9478.
(7) (a) Whitesides, G. M.; San Filippo, J., Jr.; Casey, C. P.; Panek, E.
J. J. Am. Chem. Soc. 1967, 89, 5302. (b) Kauffmann, T. Angew. Chem.,
Int. Ed. Engl. 1974, 13, 291. (c) Dubbaka, S. R.; Kienle, M.; Mayr, H.;
Knochel, P. Angew. Chem., Int. Ed. 2007, 46, 9093.
(8) (a) Ichikawa, J.; Fujita, T.; Sakoda, K.; Ikeda, M.; Hattori, M.
Synlett 2012, 24, 57. (b) Ichikawa, J.; Fujita, T.; Ikeda, M.; Hattori, M.;
Sakoda, K. Synthesis 2014, 46, 1493.
(9) Cao, C.-R.; Ou, S.; Jiang, M.; Liu, J.-T. Tetrahedron Lett. 2017, 58,
482.
(10) For selected reviews, see: (a) Shi, W.; Liu, C.; Lei, A. Chem. Soc.
Rev. 2011, 40, 2761. (b) Cahiez, G.; Moyeux, A.; Cossy, J. Adv. Synth.
Catal. 2015, 357, 1983. (c) Knochel, P.; Cahiez, G.; Kuzmina, O.;
Steib, A.; Moyeux, A. Synthesis 2015, 47, 1696. (d) Li-Yuan Bao, R.;
Zhao, R.; Shi, L. Chem. Commun. 2015, 51, 6884.
(11) For a review, see: (a) Iwasaki, T.; Kambe, N. Coupling
Reactions between sp3-Carbon Centers. Comprehensive Organic
Synthesis, 2nd ed.; Elsevier Ltd.: Japan, 2014. For selected papers,
see: (b) Nishiyama, T.; Seshita, T.; Shodai, H.; Aoki, K.; Kameyama,
H.; Komura, K. Chem. Lett. 1996, 25, 549. (c) Lei, A.; Zhang, X. Org.
Lett. 2002, 4, 2285. (d) Nagano, T.; Hayashi, T. Chem. Lett. 2005, 34,
1152. (e) Kiefer, G.; Jeanbourquin, L.; Severin, K. Angew. Chem., Int.
Ed. 2013, 52, 6302. (f) Zeng, B.-B.; Ren, J.; Hua, S.-K.; Hu, Q.-P.
Synthesis 2013, 45, 518. (g) Tang, J.; Tang, Y.; Yang, J.; Zhang, Y. Youji
Huaxue 2013, 33, 1010. (h) Zhu, Y.; Xiong, T.; Han, W.; Shi, Y. Org.
Lett. 2014, 16, 6144.
(12) (a) Cahiez, G.; Moyeux, A.; Buendia, J.; Duplais, C. J. Am. Chem.
Soc. 2007, 129, 13788. (b) Moglie, Y.; Mascaro, E.; Nador, F.; Vitale,
C.; Radivoy, G. Synth. Commun. 2008, 38, 3861. (c) Zhou, Z.; Xue, W.
J. Organomet. Chem. 2009, 694, 599. (d) Korenaga, T.; Nitatori, K.;
Muraoka, H.; Ogawa, S.; Shimada, K. Org. Lett. 2015, 17, 5500. (e) Li,
X.; Li, D.; Li, Y.; Chang, H.; Gao, W.; Wei, W. RSC Adv. 2016, 6,
86998.
(13) (a) Zhang, H.; Fang, F.; Xie, F.; Yu, H.; Yang, G.; Zhang, W.
Tetrahedron Lett. 2010, 51, 3119. (b) Fang, F.; Zhang, H.; Xie, F.;
Yang, G.; Zhang, W. Tetrahedron 2010, 66, 3593. (c) Yang, B.; Xie, F.;
Yu, H.; Shen, K.; Ma, Z.; Zhang, W. Tetrahedron 2011, 67, 6197.
(d) Yu, H.; Xie, F.; Ma, Z.; Liu, Y.; Zhang, W. Org. Biomol. Chem.
2012, 10, 5137. (e) Yu, H.; Xie, F.; Ma, Z.; Liu, Y.; Zhang, W. Adv.
Synth. Catal. 2012, 354, 1941. (f) Ma, Z.; Xie, F.; Yu, H.; Zhang, Y.;
Wu, X.; Zhang, W. Chem. Commun. 2013, 49, 5292. (g) Wu, X.; Xie,
F.; Ling, Z.; Tang, L.; Zhang, W. Adv. Synth. Catal. 2016, 358, 2510.
(14) Matoba, K.; Kawai, H.; Furukawa, T.; Kusuda, A.; Tokunaga, E.;
Nakamura, S.; Shiro, M.; Shibata, N. Angew. Chem., Int. Ed. 2010, 49,
5762.
(15) Coe, P. L.; Burdon, J.; Haslock, I. B. J. Fluorine Chem. 2000, 102,
43.
E
DOI: 10.1021/acs.orglett.8b00379
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