Highly Carbon-Selective Monofluoromethylation of β-Ketoesters with Fluoromethyl Iodide

Article abstract of DOI:10.1021/acs.orglett.9b02175

A highly carbon-selective monofluoromethylation of a broad range of β-ketoesters with fluoromethyl iodide under mild conditions is described. The uses of lithium tert-butoxide as the base and diglyme as the solvent made great contributions to the high C/O regioselectivity.

Full text of DOI:10.1021/acs.orglett.9b02175

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Highly Carbon-Selective Monofluoromethylation of β‑Ketoesters
with Fluoromethyl Iodide
Tianqi Ding, Lvqi Jiang,* Jie Yang, Yimin Xu, Guixiang Wang, and Wenbin Yi*
School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China
S
* Supporting Information
ABSTRACT: A highly carbon-selective monofluoromethylation of
a broad range of β-ketoesters with fluoromethyl iodide under mild
conditions is described. The uses of lithium tert-butoxide as the
base and diglyme as the solvent made great contributions to the
high C/O regioselectivity.
ver the past 20 years, fluorine-containing compounds
have attracted increasing attention in pharmaceutical
methyl-S-phenylsulfoximiniun hexafluorophosphate 1i, was
able to react with a variety of 1,3-dicarbonyl compounds.
But only O-selective monofluoromethylation was observed
(Scheme 1a).13 Shortly after, Shen and coworkers developed
O
and agrochemical fields.1 Nowadays, the strategic incorpo-
ration of a fluorine atom or a fluoroalkyl group (such as CF3,
CF2H, and CH2F) in different stages of drug development has
become routine practice in drug discovery.2 In this context,
monofluoromethyl compounds are particularly valuable
because the CH2F functionality can mimic CH3 and CH2OH
groups, which are often encountered in biologically active
molecules.3 But methods for the direct introduction of a
monofluoromethyl group are far less developed in contrast.4
Direct monofluoromethylation has been reported by using
fluoromethanol5 and its derivative fluoromethyl triflate6 or
fluoromethyl halides (ClCH2F,7 BrCH2F,8 or ICH2F9) (1a−e,
Figure 1). Recently, more shelf-stable yet highly reactive
monofluoromethylating reagents (1f−k, Figure 1) have been
developed.10−15
Scheme 1. Regioselective Electrophilic
Monofluoromethylation of β-Ketoesters
another two electrophilic monofluoromethylating reagents 1k,
and both 2-aryl- and 2-alkyl-substituted malonates can react
with monofluoromethyl(4-nitro-phenyl)sulfonium bis(carbo-
methoxy)methylide to generate the corresponding C-selective
monofluoromethylated malonates (Scheme 1b).15 However,
the direct introduction of CH2F to the Csp3 center of general
β-ketoesters remains challenging. Herein we report the first
example of the highly carbon-selective monofluoromethylation
of β-ketoesters with fluoromethyl iodide under mild conditions
(Scheme 1c).
Figure 1. Direct monofluoromethylating reagents.
The control of carbon/oxygen (C/O) regioselectivity in the
alkylation of enolates is one of the oldest research areas in
organic chemistry.16 The keto−enol tautomerism of substrates,
alkylating agents, and reaction conditions, in particular, the
base and solvents, play important roles in the C/O regioisomer
ratio.17 Although the control of C/O regioselectivity in the
difluoromethylation of 1,3-dicarbonyl compounds has been
widely researched in recent years,18 the development of the
control of C/O regioselectivity in the monofluoromethylation
of 1,3-dicarbonyl compounds has been far less. In 2011,
Shibata and coworkers discovered that an electrophilic
monofluoromethylating reagent, N,N-dimethyl-S-monofluoro-
Initially, we chose the reaction of β-ketoester methyl 1-oxo-
1,2,3,4-tetrahydronaphthalene-2-carboxylate 2a with fluoro-
Received: June 24, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b02175
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
methyl iodide (reagent 1e) as a model reaction to optimize the
reaction conditions. To the best of our knowledge, the base
and solvent play the most important roles of the C/O-
alkylation ratio. After screening plenty of inorganic bases such
as different barium salts, sodium salts, and potassium salts in
DMF, we found that the reactions occurred smoothly to give
the monofluoromethylated products (3a + 4a) in good yields,
but the C/O ratio was not satisfactory (Table 1, entries 1−7).
The screening of other monofluoromethylating reagents 1c,
1d, and 1k did not give better results (Table 1, entries 24−26).
Furthermore, other reaction parameters such as time, temper-
ature, and concentration were also screened. (For more details,
see Table S1.) After screening the equivalent of ICH2F, the
equivalent of tBuOLi, the reaction temperature, the reaction
time, and the reaction concentration, the combination of β-
ketoesters 2/ICH2F (2.5 equiv)/tBuOLi (2.0 equiv) in
diglyme (0.1 M) at room temperature for 2 h was selected
as the optimized reaction condition.
a
Table 1. Optimization of the Reaction Conditions
With the optimized reaction conditions in hand, the scope of
the monofluoromethylation of β-ketoesters 2 was explored
(Scheme 2). A wide range of both tetralone carboxylates and
Scheme 2. Scope of C-Selective Monofluoromethylation of
β-Ketoesters 2
b
c
entry reagent
base
solvent
yield (%)
C/O ratio
a
1
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1e
1c
1d
1k
Cs2CO3
CsF
CsOH·H2O
NaOH
NaHCO3
KOH
K2CO3
DBU
DIPEA
Et3N
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
toluene
DCM
dioxane
NMP
DMA
DME
THF
diglyme
MeCN
diglyme
diglyme
diglyme
91
57
77
71
trace
73
69
NR
NR
NR
88
<5
<5
86
trace
trace
20
67
80
8:92
12:88
9:91
2
3
4
5
6
7
8
9
37:63
29:71
15:85
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
LiOH
69:31
76:24
Li2CO3
LiOAc
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
tBuOLi
45:55
56:44
52:48
81:19
75:25
90:10
68:32
80:20
85:15
52
27
87
48
64
70
<10
a
Reaction conditions: 2a (0.2 mmol), reagent 1 (0.5 mmol), base (0.4
b
mmol) in solvent (2 mL) at room temperature for 2 h. Yields (3a +
c
4a) were determined by GC. Ratio of 3a/4a was determined by 19F
NMR spectroscopy with fluorobenzene as the internal standard.
a
Reaction conditions: 2 (0.2 mmol), reagent 1e (0.5 mmol), tBuOLi
(0.4 mmol) in diglyme (2 mL) at room temperature for 2 h. Isolated
yields. The C/O ratio was determined by 19F NMR spectroscopy with
When an organic base such as DBU, DIPEA, or Et3N was used,
no corresponding monofluoromethylated products were
observed (Table 1, entries 8−10). Considering that lithium
salts made great contributions to the highly C-selective
difluoromethylation of β-ketoesters,18d,e we then screened
lithium salts as the base. To our delight, when a lithium salt
LiOH was used, the C/O ratio was significantly improved to
69:31 (Table 1, entry 11). We then further investigated other
lithium salts; the formation of monofluoromethylated products
(3a + 4a) was observed in <5% yield when Li2CO3 or LiOAc
was used (Table 1, entries 12 and 13), but a slightly better
result was observed when tBuOLi was used (Table 1, entry
14). Next, we studied the effect of the solvents on the yield and
the regioselectivity of the reaction (Table 1, entries 15−23). It
was found that diglyme gave the reaction satisfactory results in
terms of both yield and regioselectivity (Table 1, entry 22).
b
c
fluorobenzene as the internal standard. Gram-scale synthesis. DMF
d
was used as solvent. Cs2CO3 was used as base and DMF was used as
solvent.
indanone carboxylates reacted with fluoromethyl iodide to
afford the corresponding Csp3-CH2F products 3a−t bearing a
quaternary carbon center in good yield with high C/O
regioselectivies. Tetralone carboxylates 2a without a sub-
stituent afforded the corresponding product 3a in 75% isolated
yield with good C/O selectivity (90:10). Tetralone carbox-
ylates with a methyl or methoxy group on the benzene ring
provided the desired products 3b−d with slightly improved
yields and regioselectivities, whereas 2e with a bromine atom
on the benzene ring provided the product 3e with slightly
decreased yield. The ethyl tetralone carboxylates 2f and the
B
DOI: 10.1021/acs.orglett.9b02175
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
allyl tetralone carboxylates 2g were also adapted to this
reaction system, affording desired products 3f,g in good yield
and with good regioselectivities. Moreover, indanone carbox-
ylates 2h−t, including electron-donating-group-substituted
methyl indanone carboxylates 2i−k, electron-withdrawing-
group-substituted substrates 2l−n, and alkyl, allyl, benzyl,
and adamantyl indanone carboxylates 2o−t, afforded the
corresponding Csp3-CH2F products 3h−t in high yield (69−
86%) with high regioselectivities (C/O 90:10 to 98:2).
Additionally, a decrease in yield (61%) and regioselectivity
(71:29) was observed for the β-ketoester 2u with a seven-
membered ring. The heterocyclo-ketoesters 2v and 2w were
also tolerated, providing 3v in 72% yield with 88:12 C/O
regioselectivity and 3w in 69% yield with 90:10 C/O
regioselectivity. The current process was scalable, as demon-
strated by the gram-scale synthesis of 3a (69% isolated yield)
and 3h (78% isolated yield). The less reactive acyclic aryl β-
ketoesters 2x and 2y were not compatible, affording the
corresponding C-selective monofluoromethylated products 3x
and 3y in <10% yield. When changing the solvent from
diglyme to DMF, 3y was obtained in 31% yield with
unsatisfactory C/O regioselectivity. Further applications of
fluoromethyl iodide in the C-monofluoromethylation of
malonates were also evaluated. 3z and 3aa were obtained in
high yield with >99:1 C/O regioselectivities when using
Cs2CO3 as the base and DMF as the solvent.
that of In−O for the electrophilic attack of the oxygen atom.
The corresponding monofluoromethylated product 3a is
energetically lower by 24.0 kcal/mol than 4a, leading to the
ratio of C/O regioselectivity of 90:10.
Further synthetic applications of the C−CH2F products
were investigated. As is shown in Scheme 3, compound 5 was
Scheme 3. Synthetic Applications of C−CH2F Products
obtained via Et3SiH/TFA reduction in 74% yield from 3h, and
compound 6 was obtained via LiAlH4 reduction in 79% yield
from 3i. In addition, with the product 3r in hand, a Pd-
catalyzed Tsuji decarboxylative asymmetric allylic alkylation
(DAAA)20 was also surveyed, but no desired product 7 was
obtained (Scheme 3c; for more details, see Table S2).
Therefore, the synthesis of chiral monofluoromethylated
compounds remains challenging.
In conclusion, we have developed the first protocol for
highly carbon-selective monofluoromethylation of β-ketoesters
with fluoromethyl iodide under mild conditions. A broad scope
of β-ketoesters were converted into the corresponding C-
selective CH2F-products in good yield with high regioselectiv-
ities. The effect of the lithium ion had a great influence on the
results. On the basis of the construction of chiral carbon, the
development of the asymmetric monofluoromethylation is
expected to make progress.
Mechanistically, the carbon-selective monofluoro-methyla-
tion of β-ketoester usually proceeds via a direct electrophilic
substitution pathway. To gain more support for the high C/O
regioselectivity, we studied the reaction of β-ketoester with
fluoromethyl iodide by density functional theory calculations.19
As shown in Figure 2, the relative free energy of the
intermediate structure In−C for the electrophilic attack of
the carbon atom is energetically lower by 11.8 kcal/mol than
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.9b02175.
1
Experimental procedures, characterization data, and H
NMR, 13C NMR, and 19F NMR for products (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: lvqi.jiang@njust.edu.cn (L.J.).
*E-mail: yiwb@njust.edu.cn (W.Y.).
ORCID
Wenbin Yi: 0000-0003-4606-7668
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Natural Science
Foundation of China (21776138, 21476116), the Fundamental
Research Funds for the Central Universities (30916011102,
Figure 2. Energy profile (ΔG in kcal/mol) computed at the M06-2X/
6-311G* level of theory for the formation of C- and O-
monofluoromethylated products
C
DOI: 10.1021/acs.orglett.9b02175
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(11) Fujiwara, Y.; Dixon, J. A.; O’Hara, F.; Funder, E. D.; Dixon, D.
D.; Rodriguez, R. A.; Baxter, R. D.; Herle, B.; Sach, N.; Collins, M. R.;
Ishihara, Y.; Baran, P. S. Nature 2012, 492, 95.
(12) Prakash, G. K. S.; Ledneczki, I.; Chacko, S.; Olah, G. A. Org.
Lett. 2008, 10, 557.
(13) Nomura, Y.; Tokunaga, E.; Shibata, N. Angew. Chem., Int. Ed.
2011, 50, 1885.
30918011314), the Natural Science Foundation of Jiangsu
(BK20180476), the Qing Lan and Six Talent Peaks in Jiangsu
Province, the Priority Academic Program Development of
Jiangsu Higher Education Institutions, and the Center for
Advanced Materials and Technology in Nanjing University of
Science and Technology for financial support.
(14) Shen, X.; Zhou, M.; Ni, C.; Zhang, W.; Hu, J. Chem. Sci. 2014,
5, 117.
REFERENCES
■
(15) Liu, Y.; Lu, L.; Shen, Q. Angew. Chem., Int. Ed. 2017, 56, 9930.
(16) (a) Eames, J. Acid−Base Properties of Enols and Enolates. In
Chemistry of Metal Enolates, Part 1; Zabicky, J., Ed.; Wiley-VCH,
2009; pp 441−460. (b) Reutov, O. A.; Beletskaya, I. P.; Kurts, A. L.
Ambident Anions; Michael, J. P., Ed.; Plenum: New York, 1983.
(c) House, H. O.; Czuba, L. J.; Gall, M.; Olmstead, H. D. J. Org.
Chem. 1969, 34, 2324. (d) Brown, C. A. J. Org. Chem. 1974, 39, 3913.
(e) Stork, G.; Hudrlik, P. F. J. Am. Chem. Soc. 1968, 90, 4464.
(17) (a) Ho, T.-S. Chem. Rev. 1975, 75, 1. (b) Damoun, S.; Van de
Woude, G.; Choho, K.; Geerlings, P. J. Phys. Chem. A 1999, 103, 7861
and references therein. .
(1) (a) Bohm, H. J.; Banner, D.; Bendels, S.; Kansy, M.; Kuhn, B.;
Muller, K.; Obst-Sander, U.; Stahl, M. ChemBioChem 2004, 5, 637.
(b) Sani, M.; Volonterio, A.; Zanda, M. ChemMedChem 2007, 2,
1693. (c) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem.
Soc. Rev. 2008, 37, 320. (d) Fah, C.; Mathys, R.; Hardegger, L. A.;
Meyer, S.; Bur, D.; Diederich, F. Eur. J. Org. Chem. 2010, 2010, 4617.
(2) (a) Wong, D. T.; Perry, K. W.; Bymaster, F. P. Nat. Rev. Drug
Discovery 2005, 4, 764. (b) Kirk, K. L. Org. Process Res. Dev. 2008, 12,
305. (c) Wang, J.; Sanchez-Rosello, M.; Acena, J.; del Pozo, C.;
Sorochinsky, A. E.; Fustero, S.; Soloshonok, V. A.; Liu, H. Chem. Rev.
2014, 114, 2432.
(18) Selected examples: (a) Liu, G.; Wang, X.; Lu, X.; Xu, X.;
Tokunaga, E.; Shibata, N. ChemistryOpen 2012, 1, 227. (b) Yang, Y.;
Lu, X.; Liu, G.; Tokunaga, E.; Tsuzuki, S.; Shibata, N. ChemistryOpen
2012, 1, 221. (c) Pegot, B.; Urban, C.; Bourne, A.; Le, T. N.; Bouvet,
S.; Marrot, J.; Diter, P.; Magnier, E. Eur. J. Org. Chem. 2015, 2015,
3069. (d) Wang, J.; Tokunaga, E.; Shibata, N. Chem. Commun. 2018,
54, 8881. (e) Zhu, J.; Zheng, H.; Xue, X.; Xiao, Y.; Liu, Y.; Shen, Q.
Chin. J. Chem. 2018, 36, 1069. (f) Lu, S.; Li, X.; Qin, W.; Liu, J.;
Huang, Y.; Wong, H. N. C.; Liu, G. Org. Lett. 2018, 20, 6925.
(19) All calculations were performed with: Frisch, M. J.; Trucks, G.
W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji,
H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.;
Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision D.01; Gaussian, Inc.: Wallingford, CT, 2013. For more
details, see the SI
(3) (a) Kollonitsch, J.; Patchett, A. A.; Marburg, S.; Maycock, A. L.;
Perkins, L. M.; Doldouras, G. A.; Duggan, D. E.; Aster, S. D. Nature
1978, 274, 906. (b) Mckeage, K.; Keam, S. J. Drugs 2009, 69, 1799.
(c) Rojas, R. A.; Paluga, I.; Goldfrad, C. H.; Duggan, M. T.; Barnes,
N. J. Asthma 2007, 44, 437.
(4) A few examples: (a) Li, Y.; Hu, J. Angew. Chem., Int. Ed. 2005,
44, 5882. (b) Fukuzumi, T.; Shibata, N.; Sugiura, M.; Yasui, H.;
Nakamura, S.; Toru, T. Angew. Chem., Int. Ed. 2006, 45, 4973.
(c) Prakash, G. K. S.; Chacko, S.; Alconcel, S.; Stewart, T.; Mathew,
T.; Olah, G. A. Angew. Chem., Int. Ed. 2007, 46, 4933. (d) Su, Y.;
Feng, G.; Wang, Z.; Lan, Q.; Wang, X. Angew. Chem., Int. Ed. 2015,
54, 6003.
(5) (a) Olah, G. A.; Pavlath, A. Acta Chim. Acad. Sci. Hung. 1953, 3,
203. (b) Olah, G. A.; Pavlath, A. Acta Chim. Acad. Sci. Hung. 1953, 3,
425.
(6) Iwata, R.; Pascali, C.; Bogni, A.; Furumoto, S.; Terasaki, K.;
Yanai, K. Appl. Radiat. Isot. 2002, 57, 347.
(7) (a) Rheude, U.; Sundermeyer, W. Chem. Ber. 1985, 118, 2208.
(b) Grozinger, K. G.; Kriwacki, R. W.; Leonard, S. F.; Pitner, T. P. J.
Org. Chem. 1993, 58, 709. (c) Gerus, I. I.; Kolomeitsev, A. A.;
Kolycheva, M. I.; Kukhar, V. P. J. Fluorine Chem. 2000, 105, 31.
(d) Gao, M.; Miller, M. A.; DeGrado, T. R.; Mock, B. H.; Lopshire, J.
C.; Rosenberger, J. G.; Dusa, C.; Das, M. K.; Groh, W. J.; Zipes, D. P.
Bioorg. Med. Chem. 2007, 15, 1289−1297. (e) Zhang, W.; Zhu, L. G.;
Hu, J. Tetrahedron 2007, 63, 10569.
(8) (a) Lesuisse, D.; Gourvest, J. F.; Hartmann, C.; Tric, B.;
Benslimane, O.; Philibert, D.; Vevert, J. P. J. Med. Chem. 1992, 35,
1588. (b) Kanai, T.; Kai, Y.; Sato, N.; Naito, T.; Kamiya, T.;
Nakamura, T.; Ogura, K. Bull. Chem. Soc. Jpn. 1993, 66, 2335.
(c) Hamill, T. G.; McCauley, J. A.; Burns, H. D. J. Labelled Compd.
Radiopharm. 2005, 48, 1. (d) Donohue, S. R.; Halldin, C.; Pike, V. W.
Bioorg. Med. Chem. 2006, 14, 3712. (e) Chin, F. T.; Morse, C. L.;
Shetty, H. U.; Pike, V. W. J. Labelled Compd. Radiopharm. 2006, 49,
17. (f) An, L.; Xiao, Y.; Min, Q.; Zhang, X. Angew. Chem., Int. Ed.
2015, 54, 9079.
(20) For selected reviews on the DAAA, see: (a) Mohr, J. T.; Stoltz,
B. M. Chem. - Asian J. 2007, 2, 1476. (b) Weaver, J. D.; Recio, A., III;
Grenning, A. J.; Tunge, J. A. Chem. Rev. 2011, 111, 1846. (c) Trost, B.
M. Tetrahedron 2015, 71, 5708. For selected examples of asymmetric
synthesis of α-allyl-α-fluoroalkyl-ketones, see: (d) Shibata, N.; Suzuki,
S.; Furukawa, T.; Kawai, H.; Tokunaga, E.; Yuan, Z.; Cahard, D. Adv.
Synth. Catal. 2011, 353, 2037. (e) Kondo, H.; Maeno, M.; Hirano, K.;
Shibata, N. Chem. Commun. 2018, 54, 5522. (f) Kondo, H.; Maeno,
M.; Sasaki, K.; Guo, M.; Hashimoto, M.; Shiro, M.; Shibata, N. Org.
Lett. 2018, 20, 7044.
(9) (a) Zheng, L.; Berridge, M. S. Appl. Radiat. Isot. 2000, 52, 55.
(b) Zhang, M.; Maeda, J.; Furutsuka, K.; Yoshida, Y.; Ogawa, M.;
Suhara, T.; Suzuki, K. Bioorg. Med. Chem. Lett. 2003, 13, 201.
(c) Hamill, T. G.; Burns, H. D. J. Labelled Compd. Radiopharm. 2004,
47, 99. (d) Zhang, M.; Maeda, J.; Ito, T.; Okauchi, T.; Ogawa, M.;
Noguchi, J.; Suhara, T.; Halldin, C.; Suzuki, K. Bioorg. Med. Chem.
2005, 13, 1811. (e) Zhang, M.; Ogawa, M.; Furutsuka, K.; Yoshida,
Y.; Suzuki, K. J. Fluorine Chem. 2004, 125, 1879. (f) Doi, H.; Ban, I.;
Nonoyama, A.; Sumi, K.; Kuang, C.; Hosoya, T.; Tsukada, H.; Suzuki,
M. Chem. - Eur. J. 2009, 15, 4165. (g) Hu, J.; Gao, B.; Li, L.; Ni, C.;
Hu, J. Org. Lett. 2015, 17, 3086.
(10) He, Z.; Tan, P.; Ni, C.; Hu, J. Org. Lett. 2015, 17, 1838.
D
DOI: 10.1021/acs.orglett.9b02175
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